Octopus As Predators of Haliotis Laevigata on an Abalone Sea Ranch of South-Western Australia

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Octopus as predators of Haliotis laevigata on an abalone sea ranch of south-western Australia

Submitted by

Claire Greenwell

This Thesis is presented for the degree of Bachelor of Science Honours

School of Veterinary and Life Sciences, Murdoch University, 2017

Declaration

I declare that this Thesis is my own account of my research and contains as its main content work, which has not previously been submitted for a degree at any tertiary education institution.

Claire Nicole Greenwell

ii Acknowledgements

Firstly I would like to thank Brad Adams, and the team at Ocean Grown Abalone. Without your generous support this project would not have been possible. I consider myself privileged to have had the opportunity to undertake this research in such a unique ecosystem. To Mark Wall, thank you for all your efforts, from collecting octopus samples, the explanation of processes, and taking us out diving. Your enthusiasm, hard work, and positive attitude is inspiring. Thanks also to Steve Chase and the dive team for your efforts and making us feel welcome on the ranch. I wish you all the best for the future and look forward to watching the operation grow.

To my supervisors, Neil Loneragan, James Tweedley, and Ryan Admiraal thank you for your friendship, support and encouragement. I have much admiration and respect for you all. Ryan, thank you for your perseverance and help in tackling the data analysis. Despite some pretty nightmarish coding, you have a way of making stats fun. I am extremely grateful for your help. James, thank you for answering my countless questions, and for the many hints and insights along the way. It has been great working alongside you with your passion, enthusiasm and brilliant ideas. And to Neil, I would like to express my deepest gratitude. Thank you for your kindness, for lending an ear, and your words of wisdom. For keeping me on track, and expressing the importance of work-life balance. You are an inspirational leader; the inclusiveness and encouragement that you show towards your students and peers is extraordinary. I am fortunate to have you as a mentor, and as a friend.

Thank you to Sarah Poulton, Jake Daviot, Jason Crisp, Theo Campbell, and Thea Linke for making my days in the lab light hearted. To Brian Poh, thanks for your encouragement, help with dissections, and handy hints along the way. Thank you to my many helpers in the laboratory, specifically Brett Newmarch, Amber Bennett, Stefan Brown, and Jenny Browne for your help in the processing of stable isotope samples. Removing epiphytes is lacklustre work, but you each did it with a smile. Thanks to Sian Glazier for guiding me through the isotope methods. Also to Mike van Keulen for your

iii photography skills, and the use of your personal and microscope cameras, and also to John Huisman for assisting in the identification of algal species. Special thanks goes to the State Agriculture and Biotechnology Centre for granting access to their ball mill, and to Chris Florides for providing training on operational procedures.

To all my family and friends, thank you for your love and support. To Wendy Newmarch, thank you for taking the time to proof read my work. A special mention to Alex Thornton – sharing the journey and bouncing ideas off each other has forged a special friendship, and I thank you for that. I’d like to give a special thanks to my partner Brett, not only for your efforts in the lab, but also for your tremendous support throughout my Honours journey. It hasn’t been easy, but you made the difficult times much lighter, so thank you.

Finally, I’d like to thank the Banksia Association for their generous Banksia Honours Scholarship, and the School of Veterinary and Life Sciences for providing financial support for the stable isotope analyses.

iv Abstract

Octopuses play key ecological roles within coastal marine environments around the world. Their short-lived, rapid-growing lifecycle commands high feeding rates, which has the potential to impose strong top-down controls on the benthic communities where they are found. This Thesis investigated two major questions on the predatory role of octopuses on an abalone sea ranch in south-western Australia: (i) does the distribution of octopus on the sea ranch affect the mortality of Greenlip Abalone, Haliotis laevigata (Chapter 2), and (ii) what is the diet and nutrient assimilation (δ13C and δ15N) of Octopus cf. tetricus in this ecosystem (Chapter 3).

Data were collected by commercial divers over a 27-month period on octopus abundance and the number of empty abalone shells at ~fortnightly to monthly intervals, and the number of abalone surviving on artificial abalone habitats (“Abitats”) every six months. These data were used to examine whether the number of empty shells, and the counts of surviving abalone were related to the presence of octopus. Negative binomial generalised linear models showed that the presence of octopus had a significant impact on the number of empty abalone shells collected and estimated that the shell counts are 78% higher when O. cf. tetricus is present when adjusting for location (“Line”) and Season. The Abitats provide an ideal habitat for octopuses, offering shelter and an abundant food supply. The relationship between octopus and shell counts was also influenced by the spatial position of the Abitats (Line) and Season, which may be linked to environmental variability and the time at which abalone are seeded. The results from time series (AR1) models for the relationship between octopus presence and abalone survival were not significant, contradicting those from the negative binomial models. This result is likely an artefact of the random sampling design for counting abalone to estimate survival and uncertainty in the number of abalone seeded onto each Abitat. A subsample of 110 shells collected by the divers was examined for evidence of octopus predation. Twenty shells (18%) had a small, slightly ovoid hole with a bevelled edge, consistent with the holes made by octopuses. These results confirm that octopuses are a major source of mortality on the sea ranch, supporting the results of the negative binomial models.

v Gastric tract and stable isotope analyses were undertaken to determine the dietary composition of different sizes of O. cf. tetricus, and its significance as a predator of H. laevigata on the abalone sea ranch. The crops and stomachs of 44 individuals were examined to assess whether diet differed between these digestive organs, or with increasing body size (< 300 g, 300 to 999 g, ≥ 1,000 g). A much higher proportion of material could be identified in the crops (%Volume, %V = 96%) than in the stomachs (26%). Molluscs contributed the largest %V in the crops (~31%) followed by crustaceans (33%), with unidentified material only contributing ~4%. In contrast, 74% of stomach contents were not identifiable, with molluscs comprising the majority of identifiable material (~19%), followed by crustaceans (~6%). The dietary composition of O. cf. tetricus did not change with increased body size (from 58.5 to 1596.1 g), paralleling the findings of stable isotope analysis. However, only four octopus > 1,000 g were available for analysis.

The nitrogen (δ15N) and carbon (δ13C) isotope signatures of octopus, fish, abalone, and benthic primary producers were examined to understand the assimilation of nitrogen and carbon by O. cf. tetricus, and the trophic position of this species within the Flinders Bay sea ranch food web. Examination of δ15N values revealed that O. cf. tetricus (8.08 ± 0.19) occupies a mid-trophic level, slightly below teleosts (10.10 ± 0.22) and loliginid squids (9.47 ± 0.27). The δ13C signature of O. cf. tetricus (-23.63 ± 0.42) was similar to three benthic teleosts, Coris auricularis and Opthalmolepis lineolatus, and Upeneichthys vlamingii, highlighting the overlap in use of benthic food resources by several consumers in this system. While gastric tract analyses suggest that O. cf. tetricus is an important predator of H. laevigata, stable isotope analyses show a less obvious trend. This is indicated by the enrichment of δ13C by ~4‰ between abalone and octopus. The results from this Thesis provide information on the predatory role of O. cf. tetricus, their significance as predators of H. laevigata, and their trophic positioning within this coastal marine system.

vi Table of Contents

Acknowledgements ...... iii Abstract ...... v

Chapter 1. General introduction ...... 1 1.1. Octopus cf. tetricus ...... 1 1.2. Fisheries enhancement and application of artificial reefs ...... 3 1.3. Study aims ...... 5

Chapter 2. Distribution of octopus and mortality of Haliotis laevigata on an abalone sea ranch in south-western Australia ...... 7 2.0. Abstract ...... 7 2.1. Introduction ...... 8 2.2. Methods ...... 12 2.2.1. Study site ...... 12 2.2.2. Lease configuration ...... 13 2.2.3. Culture and seeding of Abitats ...... 15 2.2.4. Monitoring abalone and predators ...... 16 Predator surveys ...... 16 Abalone surveys ...... 18 2.2.5. Data exploration and statistical analyses ...... 18 Relationship between octopus presence and empty abalone shells ...... 19 Relationship between octopus presence and abalone survival ...... 23 2.3. Results ...... 24 2.3.1. Patterns of octopus distribution and empty abalone shells ...... 24 2.3.2. Relationship between octopus presence and empty abalone shells ...... 29 2.3.3. Relationship between octopus presence and abalone survival ...... 31 2.4. Discussion ...... 32 2.4.1. Patterns of octopus distribution and empty abalone shells ...... 33 2.4.2. Relationship between octopus presence and empty abalone shells ...... 35 2.4.3. Relationship between octopus presence and abalone survival ...... 37

vii Chapter 3. The diet and nutrient assimilation (δ13C and δ15N) of Octopus cf. tetricus on an abalone sea ranch of south-western Australia ...... 39 3.0. Abstract ...... 39 3.1. Introduction ...... 40 3.2. Materials and methods ...... 44 3.2.1. Collection of Octopus cf. tetricus ...... 44 3.2.2. Quantification of Octopus cf. tetricus diet ...... 44 3.2.3. Stable isotope preparation ...... 47 3.2.4. Analyses of dietary data ...... 49 Comparison of diet between gastric organs ...... 49 Size related differences in diet ...... 51 Stable isotope composition of prey and primary producers ...... 52 3.3. Results ...... 52 3.3.1. Comparison of diet between gastric organs ...... 52 3.3.2. Size related differences in diet ...... 56 3.3.3. Stable isotope composition of prey and primary producers ...... 58 3.4. Discussion ...... 61 3.4.1. Comparison of diet between gastric organs ...... 62 3.4.2. Size related differences in diet ...... 63 3.4.3. Stable isotope composition of prey and primary producers ...... 66

Chapter 4. General conclusions and recommendations ...... 70 4.1. Conclusions ...... 70 4.2. Future research and monitoring ...... 73 4.2.1. Monitoring abalone survival ...... 73 4.2.2. Dietary studies ...... 73 4.2.3. Stable isotopes ...... 74 4.3. Implications ...... 74

References ...... 77

Appendix 1. Cephalopods and their role as predators and trophic intermediaries in the food webs of coastal marine systems ...... 88

viii Chapter 1. General introduction

This Thesis focuses on investigating the predation by octopus on Greenlip Abalone, Haliotis laevigata, on a sea ranch in Flinders Bay, south-western Australia (Fig. 2.1). It builds on an extensive literature review (Appendix 1) that evaluates the role of cephalopods as predators in coastal systems, to examine octopus as predators in the Flinders Bay system. This general introduction provides the overall framework for the Thesis, leading into the research aims and key findings of the literature review.

Functioning as mesopredators in the global oceans, coleoid cephalopods (i.e., cephalopods lacking an external shell) provide an important link between apex predators and lower trophic levels, with the ability to influence the structure and function of marine systems (Anderson 2000; Yick et al. 2012; Tanner et al. 2017). Advanced behavioural, morphological, and physiological traits such as a short life- history strategy, voracious feeding regimes, and a well-developed brain that facilitates rapid learning, has enabled the coleoid cephalopods to thrive within the marine environment (Hanlon and Messenger 1996; Boyle and Rodhouse 2005; Rodhouse et al. 2014). Their ability to modify their foraging behaviour in response to novel feeding opportunities, the use of spatial memory, and active modification of habitats (by octopuses) has enabled these molluscs to adapt readily to anthropogenic-driven changes within coastal systems (Mather 1991; Rigby and Sakurai 2005; Finn et al. 2009). For example, heavy fishing pressure of their teleost competitors, the utilisation of artificial habitats, and ocean warming are having a positive influence on cephalopod abundance

(Polovina and Sakai 1989; André et al. 2010; Coll et al. 2013; Doubleday et al. 2016).

1.1. Octopus cf. tetricus Octopus cf. tetricus is a relatively short-lived (≤ 18 months), medium sized (< 4 kg) coastal octopus species endemic to south-western Australia (Amor et al. 2014; Caputi et al. 2015; Hart et al. 2016). This species inhabits rocky reefs, seagrass beds and sandy substrata at depths of up to 70 m, extending from Shark Bay in the north, to the South Australian border (Fig. 1.1; Norman 2003; Amor et al. 2014; Hart et al. 2016). Until

1 recently it was believed that Octopus tetricus formed a single biological stock that extended from the east coast to the west coast of Australia (Caputi et al. 2015). However, phylogenetic analysis has since confirmed that the west coast species is distinct from O. tetricus on the east coast and does not overlap in its distribution (Amor et al. 2014; Caputi et al. 2015). Therefore, O. cf. tetricus on the west coast of Australia is denoted with a cf. until the species is able to be reclassified (Caputi et al. 2015).

Figure 1.1. Known distribution of Octopus cf. tetricus on the west coast, and Octopus tetricus on the east coast of Australia. Adapted from Amor et al. (2014).

The lifecycle of O. cf. tetricus is characterised by a planktonic paralarval phase (i.e., they are merobenthic), rapid juvenile growth, early maturity (~270 days for males or 950 g, and ~380 days or 1800 g for females) and post-spawning mortality (i.e., semelparity, Joll 1976; Leporati et al. 2015, see also Appendix 1, Fig. A1.1). Females lay a single clutch of eggs containing ≤ 150,000 eggs and tend to them for ~30 days before the eggs hatch in large pulses over several days (Joll 1976; Leporati et al. 2015). Females are able to mate prior to reaching sexual maturity and store sperm for up to 16 weeks, while males mate with multiple immature and mature females until they reach senescence; increasing the probability of reproductive success (Joll 1976; Leporati et al. 2015).

2 Octopus cf. tetricus is the most important commercially fished octopus species in Western Australia (Hart et al. 2013b; Caputi et al. 2015). It is targeted in the Developmental Octopus Fishery (Shark Bay to South Australian border), Cockburn Sound (Line and Pot) Managed Fishery, and is landed as incidental by-catch in significant quantities in the West Coast Rock Lobster Fishery (Shark Bay to Cape Leeuwin; Hart et al. 2013b; Caputi et al. 2015).

1.2. Fisheries enhancement and application of artificial reefs Aquaculture-based fisheries enhancement technologies are extensively utilised as fisheries management tools around the world. Their primary goal is to improve harvests and food security by rebuilding depleted stocks, increasing recruitment and productivity, and supporting natural systems (Munro and Bell 1997; Bell et al. 2008; Taylor et al. 2017). An estimated two-thirds of the world’s coastal fisheries are exploited, overexploited, or in decline, and the global population continues to expand (Botsford 1997; Leber et al. 2004; Worm et al. 2009; Ye et al. 2013) Aquaculture-based enhancement, and the use of habitat enhancement structures that help to replenish depleted stocks are critical to addressing productivity and easing the pressure on wild fish populations (Leber et al. 2004; Taylor et al. 2017). Fisheries enhancement goes beyond simply “good” harvest management, adopting practical solutions that help to overcome ecological limitations in natural systems (Taylor et al. 2017). This includes the use of artificial habitats to increase habitat availability for target species, and the culture of hatchery-reared individuals to increase recruitment and improve stocking densities (Munro and Bell 1997; Taylor et al. 2017; Broadley et al. 2017).

The release of cultured juveniles as a management intervention for improving fisheries can be defined in three broad categories; stock-enhancement, restocking and sea ranching, each with a distinct set of management objectives (Bell et al. 2008; Loneragan et al. 2013; Taylor et al. 2017). Unlike restocking and stock enhancement, animals released as part of sea ranching operations are not expected to contribute to spawning biomass, with the simple aim of increasing yield by harvesting individuals at

3 a larger size through “put, grow, and take” operations (Bell et al. 2008; Loneragan et al. 2013). However, the effectiveness of fisheries enhancement is dependent on the ability of an ecosystem to support additional cultured individuals (i.e., resource availability and the carrying capacity of the population), which may be limiting, particularly in the absence of suitable habitat (James et al. 2007; Loneragan et al. 2013). In such instances, artificial habitats can play an important role in supporting increased productivity (Bohnsack 1989; Briones-Fourzàn and Lozano-Álvarez 2001; Leitão 2013; Wu et al. 2016).

Artificial reefs are defined as natural or manufactured objects purposefully submerged in aquatic systems with the aim of modifying biological, physical, or socio- economic processes (Seaman 2000; Seaman 2008). They are common coastal features; used globally to restore ecosystems and to increase the biomass of commercially and recreationally important stocks (Leitão 2013; Cresson et al. 2014a; Mazzei and Biber 2015; Wu et al. 2016). With their often complex design, artificial reefs provide an important substratum and enable the settlement of a diverse array of marine flora and fauna which, in turn, provide an abundant food source for higher trophic level consumers (Leitão 2013; Cresson et al. 2014b). Purposely designed structures used to support species-specific culture have been effectively implemented in a number of sea ranching operations (e.g., the sea cucumber Apostichopus japonicus and Haliotis spp.), achieving the dual aim of fisheries enhancement and habitat improvement (James et al. 2007; Melville-Smith et al. 2013; Zhang et al. 2015; Xu et al. 2017).

Years of research and development have culminated in Australia’s first commercial abalone (H. laevigata) sea ranch, operated by Ocean Grown Abalone (OGA, www.oceangrownabalone.com.au). Established in the shallow coastal waters of Flinders Bay on the south-west coast of Australia, the operation successfully combines aquaculture-based enhancement with species-specific artificial reefs.

Despite significant advances in global fisheries enhancement and artificial reef design technology, predation pressure remains a significant threat to the survival of

4 released juveniles (Støttrup et al. 2008; Hines et al. 2008; Bell et al. 2008; Poh et al. 2017). Octopus cf. tetricus has been identified as a potentially important predator of H. laevigata (Hart et al. 2013a; Melville-Smith et al. 2013). Numerous incidences of predation by octopus have been observed in stock enhancement trials and sea ranching operations in south-western Australia (Hart et al. 2013a; Melville-Smith et al. 2013), which could have significant negative impacts for the survival of released individuals.

1.3. Study aims The primary objective of this study is to assess the predatory impact of O. cf. tetricus on H. laevigata within the commercial sea ranch operated by OGA in Flinders Bay, Western Australia. This has been achieved by investigating:

(i) the spatial and temporal pattern of distribution and abundance of O. cf. tetricus and H. laevigata across the sea ranch (Chapter 2) to evaluate whether the presence of octopus is correlated with abalone mortality; (ii) the diet of O. cf. tetricus to understand how the dietary composition of this predator changes according to the analysis of digestive organ (i.e., crops vs stomachs), with increasing body size, and whether H. laevigata forms an important component of the diet (Chapter 3); and (iii) the assimilation of nutrients within the food web of Flinders Bay to determine the source of carbon assimilated by O. cf. tetricus and its position in the food web, using stable isotope analysis (Chapter 3).

The knowledge gained from these studies will provide a greater understanding of the role of octopus in structuring coastal systems, particularly in Western Australia, and their significance as predators of abalone in a rapidly growing sea ranching operation. The understanding and directions for my Honours research were developed through the extensive literature review (comprising 134 references) in Appendix 1, which synthesised knowledge on the role of coleoid cephalopods as predators and trophic intermediaries in the food webs of coastal marine systems. This review included a meta- analysis of the diets of 24 coastal coleoid cephalopod species from the Loliginidae,

5 Octopodidae, Sepiidae, and Sepiolidae and highlighted distinct dietary patterns among these families. These differences were related to variation in lifestyle between the groups (i.e., benthic vs pelagic) and in general found a rapid shift in diet with ontogeny, whereby a broader range of prey types, including mobile fish, and other cephalopods were ingested by larger individuals (Appendix 1).

6 Chapter 2. Distribution of octopus and mortality of Haliotis laevigata on an abalone sea ranch in south-western Australia

2.0. Abstract

This study examined the distribution and abundance of octopus across an abalone, Haliotis laevigata, sea ranching site situated in Flinders Bay, Western Australia to understand how octopus may be impacting the production of abalone. Octopuses are important predators among benthic communities, and the artificial habitats used for the production of H. laevigata provide an ideal habitat for these predators, offering shelter and an abundant food supply. The study used data collected during “predator” surveys by commercial divers. A total of 64 predator surveys were conducted over a 27-month period at ~fortnightly to monthly intervals, resulting in the removal of 654 octopuses and collection of 17,666 empty abalone shells from 5,308 artificial abalone habitats (“Abitats”). Octopuses were widely distributed across the sites, with some locations (“Lines”) observing a greater number of octopuses, which may be associated with the number of Abitats within a Line. The abundance of empty abalone shells was higher in some areas, which may be explained by a combination of factors including environmental variability and the spatial arrangement of Abitats. A subsample of 110 shells was examined for evidence of octopus predation; 18% of these had a small, slightly ovoid hole with a bevelled edge, consistent with the boreholes made by octopus. A negative binomial generalised linear model was used to assess the relationship between the presence of octopus and empty abalone shell counts, and indicated that octopus presence is associated with an estimated 78% increase in the number of empty abalone shells per Abitat per day, adjusting for Line and Season. A time series model was used to assess the relationship between the presence of octopus and abalone survival (number of abalone on Abitats), but did not find a significant relationship. These contradictory findings are quite possibly an artefact of the sampling method for counting abalone, and uncertainty in the numbers of juvenile abalone seeded onto the Abitats. They highlight the importance of undertaking repeated measures on the same Abitats over time to better account for the variability that naturally exists between Abitats to measure survival with greater precision.

7 2.1. Introduction

The global production of wild abalone, Haliotidae has been in decline since the 1960s, stimulating significant investment in fisheries enhancement techniques (i.e., sea ranching and restocking) in most abalone-producing countries of the world (e.g., Australia, Japan, Mexico, South Africa, and USA, Prince 2004). Increased demand for seafood and anthropogenic stressors, particularly overfishing, climate change, and habitat degradation have had significant negative ecological impacts on coastal marine systems in recent times (Bell et al. 2008; Pearce et al. 2011; Taylor et al. 2017). Thus, novel enhancement and farming techniques, including the use of artificial reefs that provide suitable habitat to increase productivity, are fundamental to ensuring the longevity of food security (Molony et al. 2003; Zhang et al. 2015; Wu et al. 2016; Taylor et al. 2017). For example, artificial oyster-shell reefs have been successfully implemented in China, enhancing production of the highly sought after sea cucumber Apostichopus japonicus (Zhang et al. 2015); and advances in the collection, culture, and management of the scallop Patinopecten yessoensis in Japan have seen the reinvigoration of the collapsed fishery (Uki 2006).

However, enhancement efforts of coastal fisheries are not always successful (e.g., Grimes 1998; Brown and Day 2002; Bell et al. 2005, 2008). While a series of experimental trials have successfully demonstrated the proof of concept, efforts to increase abalone production using artificial habitats have been limited (Schiel 1993; James et al. 2007; Roberts et al. 2007; De Waal et al. 2013; Hart et al. 2013c). This is due to ecological constraints including a lack of suitable habitat and strong density- dependent processes in the larval phase (Shepherd et al. 2001; De Waal and Cook 2001; Bell et al. 2008; Hart et al. 2013c). As Hart et al. (2013c) point out; enhancements are unlikely to be successful when animals are released at sizes at which density- dependence processes are influential. Thus a good grounding of species biology, ecology, and the factors influencing the carrying capacity of a population (i.e., recruitment and mortality) are critical if fisheries enhancement is to be effective (Shepherd et al. 2001; Hart et al. 2013c).

8 In addition to density-dependent effects, high mortality of transplanted or cultured juveniles (i.e., seeds) presents a significant challenge and has the potential to impede the economic viability of fisheries enhancement projects (McCormick et al. 1994; Shepherd et al. 2001; James et al. 2007; De Waal et al. 2013; Hart et al. 2013c). Newly released seeds can have poor behavioural responses towards predators since culture conditions lack the stimuli and environmental cues required for the development of instinctive survival patterns that are essential for survival in the wild (Bell 1999; James et al. 2007; Daniels and Watanabe 2010). Laboratory experiments on cultured and wild Red Abalone, Haliotis rufescens, on artificial reefs show that wild individuals moved swiftly into concealed positions and suffered significantly lower predation rates by crabs, sea stars, and lobsters than cultured individuals, which initially tended to be relatively inert in their response to predators (Schiel and Welden 1987). However, as abalone acclimatised to the artificial reefs, their behavioural response to predators improved, resulting in lower predation rates compared with abalone released soon after being taken from the hatchery (Schiel and Welden 1987).

Crabs and fish, including wrasses, have been identified as predators of juvenile abalone < 2 years old (Schiel and Welden 1987; Shepherd 1998; Shepherd and Clarkson 2001; James et al. 2007). In a long-term study of the Blue-throated Wrasse, Notolabrus tetricus, at West Island in South Australia, abalone mortality was positively correlated with wrasse density, with larger wrasses typically preying on larger abalone (Shepherd and Turner 1985; Shepherd 1998; Shepherd and Clarkson 2001). Predation on abalone may be amplified when juvenile densities are increased through the addition of cultured juveniles to the environment due to opportunism by fishes. However, other studies by Shepherd et al. (2001) and Hart et al. (2013a) did not identify an increase in predation following releases of cultured abalone, suggesting that trends might be site specific.

In a sea ranching trial in Port Philip Bay, Victoria, the portunid Rough Rock

Crab, Nectocarcinus integrifrons, was observed foraging around “seeding modules” (i.e., a series of large clean abalone shells strung together and used as a substratum for

9 seeds to attach) within 10 minutes of being placed onto the artificial reefs (James et al. 2007). Numerous crabs were also seen sheltering inside the seeding modules within a few days (James et al. 2007) and thus there is a high potential for increased juvenile abalone mortality, particularly within the first few hours of seeding (McCormick et al. 1994).

The addition of cultured seeds may also intensify predation by mobile predators such as octopuses and rays, responding to increased prey abundance (Hinesa et al. 1997; Shepherd 1998; Shepherd et al. 2001; Anderson 2001; Gende and Sigler 2006). Octopuses are common predators in sub-tidal communities, targeting a range of prey types including abalone, a preferred food item of octopus (Ambrose 1982; 1983). The possession of a range of specialised morphological adaptations, i.e., prehensile arms with strong suckers, a chitinous beak, tongue-like radula, and salivary papilla bearing tiny teeth (see Appendix A1.3) make the octopuses formidable predators, and their rapid growth rates stimulate voracious feeding regimes which have the potential to impose strong top-down controls within these coastal environments (Rodhouse and Nigmatullin 1996; Boyle and Rodhouse 2005).

The stingrays Dasyatis brevicaudata and Myliobatis australis, and stingaree Trygonoptera mucosa have also been identified as important predators of the Greenlip Abalone, Haliotis laevigata, through visual observations of their behaviour and the distinctive scrape markings on abalone shells caused by their blunt teeth (see James 2005). These predators are common in habitats containing high densities of abalone, particularly in the period after seeding, which may be facilitated by high hunting success, thus attracting more rays to the vicinity (Shepherd 1990; Shepherd et al. 2001; James 2005).

The survival of cultured and transplanted juvenile abalone depends on individual size and substrate type (Inoue 1976, cited in McCormick et al. 1994; James et al. 2007). The relationship between survival and juvenile shell length is described by a logistic curve with the survival of Giant Abalone, Haliotis gigantea, increasing from 10 to 70%,

10 as individuals grow from 10 to 30 mm in size (Inoue 1976, cited in McCormick et al. 1994; Hamasaki and Kitada 2008). Thus, the release of larger juveniles (> 30 mm shell width [SW]) can increase survival rates (McCormick et al. 1994; Hamasaki and Kitada 2008). Similarly, the selection of structurally more complex natural habitats with numerous rocky crevices or artificial reefs that incorporate crevices to protect juveniles from predators has a positive influence on their survival (Shepherd and Turner 1985; McCormick et al. 1994; Dixon et al. 2006; James et al. 2007).

Abalone sea ranching in Flinders Bay, Western Australia by Ocean Grown Abalone (OGA) provides an example of world-class fisheries enhancement, combining low environmental impact aquaculture-based enhancement of wild caught H. laevigata and species-specific artificial reefs to increase abalone production. Established on a commercial scale less than three years ago, the operation has been very successful, producing ~40 t of abalone in 2017 with projections to increase production to 100 t by 2018 and to 200 t by 2020 (B. Adams, OGA, 2017 pers comm.). However, a sea ranching trial that concluded in early January 2013 at the same location, found that predation by O. cf. tetricus on abalone is a potential threat to the survival of seeded abalone (Melville-Smith et al. 2013). Ocean Grown Abalone record the presence of octopuses and the number of abalone shells on their whole lease in Flinders Bay at intervals of two to four weeks, and count and measure a sub-sample of abalone across the lease every six months. Electronic records on the counts of octopus, abalone shells, and abalone survival are available from January 2015. These data provide information for examining the relationship between the presence of octopus and abalone mortality.

In this study, data on the abundance and distribution of octopus (mainly O. cf. tetricus), empty abalone shells, and counts of abalone on the Abitats were examined to evaluate:

(i) the distribution and abundance of octopus across the three areas of Abitats in the lease area for the sea ranching operation by OGA;

11 (ii) the distribution and abundance of empty abalone shells collected across the three areas to test whether the number of empty shells is related to the presence of octopus; and

(iii) whether the presence of octopus is related to higher abalone mortality, based on abalone survival counts.

This commercial-scale abalone sea ranching operation provides a unique opportunity to observe how octopus may be impacting the production of abalone in south-western Australia.

2.2. Methods 2.2.1. Study site Ocean Grown Abalone holds three 40 ha sites within their lease in Flinders Bay, Augusta, on the south-west corner of Western Australia (~34°37 S, 115°19 E) where the sea ranching of H. laevigata takes place (Fig. 2.1). The sites range from ~15 to 19 m in depth, and the natural habitat consists of a sandy substratum interspersed with irregular seagrass patches of mixed composition of Amphibolis antarctica, Amphibolis griffithii and Halophila ovalis (Melville-Smith et al. 2013; pers. obs 2017.). Sites are referred to as the Outer (most southern), Middle, and Inner Leases. The inner boundary of the Outer site is located 3.69 km from the nearest land, while the Middle and Inner Lease boundaries are 2.46 and 1.43 km from the nearest land (i.e., Cape Leeuwin). The Inner Lease is situated ~0.20 km from the eastern boundary of the Middle Lease, and the Outer Lease is situated ~1 km south-westerly of the Middle Lease (Fig. 2.1). The southern part of Flinders Bay is characterised by fringing reefs colonised by macroalgae, particularly Ecklonia spp., and natural reefs are situated to the east and west of the lease sites (Melville-Smith et al. 2013).

Figure 2.1. Satellite image (Landsat 2016) showing the Lease (Inner, Middle and Outer) locations of the Greenlip Abalone (Haliotis laevigata) sea ranching sites in Flinders Bay, Western Australia. Inset denotes the location of Flinders Bay in Australia.

2.2.2. Lease configuration A total of 5,308 Abitats were deployed on the seabed by divers to form a series of artificial reef structures. Abitats were deployed in a hierarchy of scales: six to eight Abitats make up a ‘Reef’, twelve to fourteen Reefs make up a ‘Bay’, and one to thirteen Bays make up a ‘Line’ (Table 2.1). Nine Lines are situated on the Outer Lease, three on the Middle Lease, and two on the Inner Lease (Fig. 2.2, Table 2.1). The Abitats were designed to maximise the surface area and growth potential for H. laevigata, and each has a surface area of 10 m2 (B. Adams, OGA, 2015 pers. comm.). The artificial reefs run perpendicular to the prevailing south-westerly swells and are situated adjacent to naturally occurring seagrass beds (B. Adams, OGA, 2015 pers. comm.). This design provides a barrier to drifting algal wrack and thus maximises food availability for the abalone (B. Adams, OGA, 2015 pers. comm.). Haliotis laevigata feed on drift algae, predominantly epiphytic red algae attached to drifting seagrass and macroalgae (Melville-Smith et al. 2013).

13 The Outer Lease was established over the period mid-2014 to early 2015, followed by the Middle and Inner Leases in mid-2015 and late-2015 respectively. Once the Abitats were positioned on the seafloor, they were left for a minimum conditioning period of two weeks before any abalone was seeded.

Table 2.1. Number of Abitats, Reefs and Bays on each Line and Lease at the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia. Bold shows the total for each of the three Lease sites. Each reef has six to ten Abitats. Lease and Line No. Bays No. Reefs No. Abitats Outer (1) 33 429 2712 O1 11 135 810 O2 3 34 196 O3 2 26 103 O4 4 53 320 O5 3 48 259 O6 1 11 79 O7 5 70 380 O8 2 23 380 O9 2 29 185 Middle (2) 21 236 1580 M1 3 42 267 M2 5 35 290 M3 13 159 1023 Inner (3) 12 152 1016 I1 3 131 879 I2 10 21 137 Total 66 817 5308

Figure 2.2. Configuration of Lines within each of the three Leases at the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia. Note, Lines are not to scale.

2.2.3. Culture and seeding of Abitats Wild, locally sourced broodstock are collected during October and November and cultured in the commercial 888 Abalone production facility in Bremer Bay (B. Adams, OGA, 2015 pers. comm.) according to standard H. laevigata aquaculture protocols (Daume and Ryan 2004; Daume et al. 2004; Duame 2006). Over a period of ~18 months, hatchery-reared juveniles are grown to ~40 mm, the optimal size to be seeded onto the Abitats (B. Adams, OGA, 2015 pers. comm.). At this size, H. laevigata readily adapt to a natural macroalgal diet, are less cryptic than smaller abalone, and are better equipped to withstand assaults from teleost and invertebrate predators, having developed a muscular foot of sufficient size to clamp tightly to the surface of the Abitat (B. Adams, OGA, 2015 pers. comm.). Prior to release, juvenile abalone are held in quarantine for two weeks and samples are sent to the Fish Health Unit, Department of

15 Primary Industries and Regional Development to ensure they are free of pathogens and diseases (B. Adams, OGA, 2015 pers. comm.).

The juvenile seed stock is transferred into custom-built release units, each holding ~200 abalone, and then transported to Augusta in oxygenated tanks where they are loaded onto commercial dive vessels (Fig. 2.3a, b). The release units are lowered into the water column inside an aluminium cage (44 release units per cage) by a man- operated loader crane, and divers individually position the release units onto the Abitats (two units per Abitat), which are left to settle overnight (Fig 2.3c, d) (B. Adams, OGA, 2015 pers. comm.). The following day the lids of the release units are removed, and over a period of three to four weeks the juvenile H. laevigata crawl out and colonise the Abitats (B. Adams, OGA, 2015 pers. comm.). Approximately 50,000 H. laevigata are seeded onto the Abitats over a period of four hours on any one stocking day.

The initial seeding of Abitats was carried out in the order that Lines were deployed, with ~400 individuals being seeded onto each Abitat at the first deployment (D1), followed by a reseeding of ~120 H. laevigata individuals onto each Abitat 12 months after the initial seeding (R1).

2.2.4. Monitoring abalone and predators Predator surveys Haliotis laevigata are typically grown on the Abitats for a period of three years until they reach approximately 130 to 140 mm shell width (~5 years old). During this time, surface-supplied commercial divers inspect the Abitats on a weekly basis to observe the general health of the abalone and to remove excessive growths of macroalgae, soft corals and ascidians from the Abitats to increase the surface areas available to abalone. Every 2 to 4 weeks, octopuses and other predators such as bailer shells (Melo spp.) are removed from the area around the Abitats. Divers have constant voice communication with the vessel and the vessel crew records their observations in real time directly onto the OGA database.

(a) (b)

Figure 2.3. Images of abalone seeding operations by Ocean Grown Abalone (OGA) including: (a) abalone seeding unit stocked with juvenile Haliotis laevigata, (b) oxygenated abalone transfer bins which hold the stocked abalone release units whilst being transferred from the production facility in Bremer Bay to Augusta, (c) abalone release units being lowered into the water column in an aluminium cage via crane, and (d) an abalone release unit being positioned onto the artificial abalone habitat (“Abitat”). Images courtesy of OGA.

Surveys of predators are conducted across the three leases, usually on a single day. Due to time constraints, not all Bays or Lines can be surveyed and during periods of harvest or reseeding predator surveys may not be conducted. Any octopuses sighted around the Abitats are counted and removed with the number of octopuses recorded at the Bay level (~33 to 148 Abitats, Table 2.1). Indices of food availability for H. laevigata are recorded at the same time. The availability of algal wrack is subjectively scored on a food index ranging from one to five, with five indicating a high abundance of algal wrack. Any empty abalone shells observed around the Abitats are also collected and recorded with the total number of shells recorded per Bay. The

17 frequency of surveys was lower in winter months and also lower in 2017 than in other years because of logistic constraints (i.e., prevailing poor weather and sea conditions, and other sea ranching duties). A total of 64 predator surveys were conducted between 20 January 2015 and 16 March 2017, during which time 654 octopuses were removed and 17,666 abalone shells were collected.

Abalone surveys Commercial divers monitor the growth and survival of H. laevigata twice annually at intervals of approximately six months. The numbers of stocked abalone on five to ten randomly selected Abitats in each Bay are counted. The stocked number of abalone is then subtracted from the assumed number of abalone seeded onto the Abitats (400) to establish abalone survival. Note that the same Abitats are not surveyed each time. The average survival per Bay is then extrapolated according to the number of Bays on a Line in order to determine an estimate of abalone survival per Line.

2.2.5. Data exploration and statistical analyses Data exploration was carried out using the R statistical software package (R Core Team 2011), and the “ggplot2” (Wickham 2009) and “lubridate” (Garrett and Wickham 2011) add-on packages to provide insights into potential trends and to identify the limitations of the data, following the protocols described in Zuur et al. (2010). In order to elucidate any trends in the distribution and abundance of octopus, the mean numbers of octopus collected per survey per Line, and the mean numbers of octopus collected per survey per Line, adjusted for the number of Abitats (number of octopus 1000-1 Abitats), were calculated and plotted as bubble plots.

Empty abalone shells collected by divers during predator surveys between April and July 2017 were measured to the nearest mm, grouped into 10 mm length classes and plotted in a length frequency histogram. Descriptive statistics were then used to determine the size distribution of these shells. Shells were inspected for any evidence of predation, and any shells with conspicuous holes were examined in more detail. Shells

18 with holes were divided into four areas according to the position of the drill site following Kojima (1992) and based on the underlying anatomy of abalone. The frequency of holes in each area was counted. The four shell areas were:

• I: covers the digestive and respiratory organs, pericardial sac and heart; • II: covers part of the mantle; • III: covers the gonad, gut, and liver; and • IV: covers the adductor muscle that attaches to the shell (Kojima 1992; Morash and Alter 2016). An exact multinomial test was employed to test whether the holes had a non-random distribution over the four areas.

All inferential statistical analyses were performed using the R statistical software package (R Core Team, 2017) and the “MASS” (Venables and Ripley 2002), “pscl” (Zeileis et al. 2008), and “Xnomial” (Fox 2003) add-on packages.

Relationship between octopus presence and empty abalone shells A series of count regression models were developed to test whether the presence of octopus (i.e., “Octopus” > 0) results in a greater number of empty abalone shells (“Shells”) being collected around the artificial reefs, compared with areas in which octopus are absent (Table 2.2). Given that > 1 octopus accounted for only 8% of the total number of observations, and very few counts of > 2 octopuses (2%) were found, the presence of octopus (i.e., counts > 0) was selected as the independent variable.

Diagnostic plots were used to assess the suitability of linear regression models for fitting the data. These showed major violations in the assumptions of linearity, normality, and homoscedasticity. A Poisson log-linear generalised linear model was also deemed inappropriate due to overdispersion, an artefact of the Poisson distribution estimating one parameter for both the mean and the variance (Table 2.2). A negative binomial generalised linear model was ultimately used, as it is appropriate for count data and provides estimates of the mean for the parameter as well as a dispersion

19 parameter (Gardner et al. 1995, Table 2.2). A histogram of the frequency of empty shell counts showed significant variability (Fig. 2.4). Shell counts ranged from 0 to over 100 with a modal count of 3-6 shells, a mean count of 9.9 and a median of 6 (i.e., the count frequency distribution was heavily right skewed, Fig. 2.4), which is expected for count data (see Gardner et al. 1995). However, the high proportion of zero counts is greater than usual, with the proportion of zeros exceeding that predicted by standard models for a set of observed characteristics (Baetschmann and Winkelmann 2013). Thus a zero- inflated negative binomial generalised linear model was also considered (Table 2.2).

Table 2.2. Count models considered for assessing the relationship between the presence of octopus (“Octopus” > 0) and empty abalone shell (“Shells”) counts.

Model Summary Linear Untransformed and log transformed data did not satisfy the (Raw data, ln(x)) assumptions of linear regression. Generalised linear model Data overdispersed, therefore model deemed inappropriate. (Poisson) Most suitable model as indicated by Bayesian information Generalised linear model criterion (BIC) and Akaike information criterion (AIC) (Negative binomial) estimates. Generalised linear model Less suitable than the negative binomial model, as (Zero-inflated negative binomial) indicated by BIC and AIC estimates.

Figure 2.4. Frequency distribution of empty abalone shells collected during predator surveys at the Greenlip Abalone, Haliotis laevigata sea ranching site in Flinders Bay, Western Australia between 20 January 2015 and 16 March 2017. The collection of > 150 shells were treated as outliers and removed for graphical and statistical purposes. Total shell counts = 1,663, � = 9.93, number of surveys = 64.

20 To control for other variables that might be related to the number of empty shells collected, Line and Season were included in the model. Likelihood ratio tests were used for model comparison. A model-building approach was taken, adding one covariate at each step to determine the most parsimonious model to explain the fit of the data. The same approach was used to test for interaction effects, and if present, to determine the extent of that interaction relative to the main effects. None of the interaction effects were significant, thus a model consisting strictly of main effects was selected. Line was considered an important predictor, to account for potential spatial variability across the Leases, while Season was incorporated to account for natural intra-annual variation.

Analyses were carried out both with and without potential outliers to assess their impact. Five extreme observations were noted (i.e., where > 150 shells were collected from a single Bay on any day) and considered as outliers. Models showed that the inclusion of these potential outliers led to a stronger estimated relationship between the presence of octopus and empty abalone shells, and therefore the more conservative model excluding outliers is presented.

A Vuong test was used to assess which of the two models (i.e., a negative binomial model or a zero-inflated negative binomial model) best fit the data (Table 2.2). No significant difference was identified when comparing tests based on raw data. However, BIC (i.e., Bayesian information criterion) and AIC (i.e., Akaike information criterion) estimates indicated that the negative binomial model was significantly better than the zero-inflated negative binomial model. For this reason, and to reduce model complexity, a negative binomial model was employed.

The final negative binomial model, with a log link function, was used to model the number of Shells collected as a function of the covariates [Equation (1)]. Fixed covariates include Octopus > 0 (categorical with two levels), Line (categorical with 14 levels) and Season (categorical with four levels – Summer: December to February, Autumn: March to May, Winter: June to August and Spring: September to November,

21 Table 2.3). The offset terms “Time Since Last Survey × Number of Abitats” were included in the model to account for differences in exposure, as the number of shells collected could be related to the time that has elapsed since the previous survey due to the accumulation or loss of shells. The number of Abitats could be important since octopus commonly display anti-social, intraspecific avoidance behaviour, with competition for shelter sites resulting in incidents of conflict and cannibalism (Mather and O’Dor 1991; Hanlon and Messenger 1996; Caputi et al. 2015). Thus, a greater number of Abitats could potentially support a greater number of octopuses. As Time Since Last Survey and the number of Abitats are both measured without error, they are more appropriately included as offsets rather than as additional covariates.

To accurately interpret the regression coefficients and to account for differences in exposure, as specified by the offset term, a back-transformation of logged counts was carried out, and incident rate ratios calculated. Consequently, the incident rate represents the number of empty abalone shells collected per Abitat per day (Table 2.3).

The full model can be written more explicitly as:

Yi ~ negative binomial (µi, k)

log(µi) = �0 + �1X1i + �2X2(2)i + �3X2(3)i + �4X2(4)i + �5X2(5)i +�6X2(6)i +

� 7X2(7)i + � 8X2(8)i + � 9X2(9)i + � 10X2(10)i + � 11X2(11)i + � 12X2(12)i +

�13X2(13)i + �14X2(14)i + �15X3(2)i + �16X3(3)i + �17X3(4)i + log(Ti) + �i (1) where µ denotes the mean response of the observation, k denotes the negative binomial dispersion parameter, Yi denotes the number of Shells, X1 denotes Octopus > 0, X2 denotes the Line (2 = “O2”, 3 = “O3”, 4 = “O4”, 5 = “O5”, 6 = “O6”, 7 = “O7”, 8 =

“O8”, 9 = “O9”, 10 = “M1”, 11 = “M2”, 12 = “M3”, 13 = “I1”, 14 = “I2”), X3 denotes the Season (2 = “Spring”, 3 = “Summer 2015”, 4 = “Winter”), log(Ti) denotes the offset

(i.e., the number of Abitats × Time Since Last Survey) and �i represents the error associated with omitted or non-observable exogenous variables (Liu et al. 2005).

22 Results from the negative binomial model were then used to provide an estimate of the total number of abalone shells associated with the presence of octopus for the 27- month period in which 17,666 shells were collected. This estimate was then converted to a percentage, representing the proportion of shells associated with octopus presence.

Relationship between octopus presence and abalone survival Potential patterns in abalone survival counts over time were investigated using box plots of the counts of abalone on Abitats. As survival counts were conducted over multiple consecutive days (≤ 10), the survey dates for a given period were aggregated into four periods: March and September of 2015, and the same months of 2016 (i.e., 4 survival counts).

To assess the relationship between average abalone survival (“Survival Count”) and the presence of octopus (“Octopus > 0”), an autoregressive (AR1) linear model (i.e., a time series model where abalone survival counts are dependent on the preceding survival count) was considered [Equation (2)]. The model included the average number of abalone counted during survival surveys for abalone seeded at the first deployment (D1), prior to harvesting for a given Bay. Average survival counts were chosen in favour of absolute survival counts due to the variability in abalone survival counts between Abitats.

A new variable “Time” was created, representing the number of days from the first survival count. The first survival count for a given Bay was recorded as time point 0, and successive counts refer to the number of days since time 0. All octopuses recorded within each Bay up to the first survival count (0 days), and then between successive abalone counts, were aggregated to account for the total number of octopuses present during a given time period. Survival counts from January 2017 were not included in these analyses as, after this time, data were recorded at the Reef level (i.e., an aggregation of Abitats) instead of per Abitat.

23 Potential outliers (i.e., where abalone survival counts for a given Bay had declined by a mean of > 150 abalone between successive surveys) were modeled separately to assess the potential impact of those observations. Diagnostic plots used to assess the suitability of simple linear models indicated major violations in the assumptions of linearity, normality, and homoscedasticity. Data transformations did not resolve these issues but the removal of extreme observations greatly improved the model suitability. Thus the model presented excludes outliers. These extreme observations are likely due to natural mortality of abalone in response to unfavorable environmental conditions such as poor current flows and low food availability, as opposed to octopus predation.

The full model can be written as:

Yi = �0 + �1X1i + �2X2i + �3X3i + �i (2)

where Yi denotes the number of Shells, X1 denotes Octopus > 0, X2 denotes the Previous

Average Shell Count, X3 indicates Time (number of days) since the first survey count,

2 2 and �i ~ N (0, � ) is the error term for some constant measure of variability � .

2.3. Results 2.3.1. Patterns of octopus distribution and empty abalone shells Overall, the total number of octopuses collected was greatest on the Outer Lease (422 = 65% of all octopus), which also had the greatest number of Abitats (2,712, Table 2.1), followed by the Middle (154 octopus) and Inner Leases (78 octopus). Octopuses were found across the Lines in each of the three Leases, with the greatest mean number of octopuses sampled on Line O1 (0.47 octopus per survey), and lowest on O8 (0.13, Fig. 2.5). When adjusted to a standard number of Abitats per Line (i.e., octopus 1000-1 Abitats), the adjusted mean number of octopus was greatest at O6 (4.11), followed by I2 (3.04), and the lowest adjusted mean was recorded on O8 (0.33, Fig 2.6).

Figure 2.5. Bubble plot showing the mean number of octopus collected on each Line at the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia, during predator surveys conducted between 20 January 2015 and 16 March 2017. Note, Lease configurement not to scale.

Figure 2.6. Bubble plot showing the standardised mean number of octopus (i.e., the number of octopus per Abitat × 1000) collected on each Line at the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia during predator surveys conducted between 20 January 2015 and 16 March 2017. Total number of octopus collected = 654. Note, Lease configurement not to scale.

A total of 17,666 shells were collected between January 2015 and March 2016: 9,598 from the Outer Lease, 3,976 from the Middle and 4,092 from the Inner Lease. These shells represent 0.3% of all cultured abalone seeded onto the Abitats. The average number of shells collected per survey was highest on the Inner Lease (21.1), compared with the Middle (6.3) and Outer (3.5) Leases. The average shell counts per Line were highest on Lines I1 and I2, with 22.16 and 18.25 shells respectively (Fig. 2.7). When adjusting for the number of Abitats per Line (shells 50-1 Abitats), shell counts were greatest on Lines I2 and O6, with 6.66 and 3.66 shells respectively. The lowest adjusted mean shell count occurred on Line O1 with 0.49 shells (Fig. 2.8).

A total of 110 empty H. laevigata shells were measured, and they ranged from 33 to 100 mm in shell length (SL) and had a mean SL of 55.9 mm (± 1SE = 1.2 mm) (median SL = 54.0 mm). The modal length class was 50-59 mm, representing 35% of all shells collected (Fig. 2.9a). Twenty shells (18%) had bevelled boreholes that were characteristic of the holes made by octopuses (Fig. 2.10a, see Arnold and Arnold 1969; Nixon and Elaine 1988; Kojima 1992). The boreholes were slightly ovoid at the top, narrowing into a smaller aperture towards the inner surface of the shell (Fig. 2.10b).

Only one hole was found on each of the 20 shells with a borehole. Shells with holes spanned the entire length range of all shells examined (33 to 100 mm), but their mean SL of 62.0 ± 3.6 mm was slightly longer than for shells without a hole (54.6 ± 0.8 mm, N = 90). A total of 70% of shells with a drill hole were within the length range of 60 to 89 mm (Fig. 2.9b). The majority of the holes were concentrated in areas IV (40%) and I (35%), with 8 and 7 holes respectively, and 10% and 15% in each of areas II and III (Fig. 2.10b). An exact multinomial test showed that the frequency of holes did not differ significantly among the four regions (P = 0.18).

Figure 2.7. Bubble plot showing the mean number of shells collected on each Line at the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia during predator surveys conducted between 20 January 2015 and 16 March 2017. Number of shells collected = 17,666, 64 surveys completed. Note, Lease configurement not to scale.

Figure 2.8. Bubble plot showing the standardised mean number of shells (i.e., number of shells per Abitat × 50) collected on each Line at the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia during predator surveys conducted between 20 January 2015 and 16 March 2017. Number of shells collected = 17,666, 64 surveys completed. Note, Lease configurement not to scale.

(a) (b)

Figure 2.9. Shell length frequency distribution of (a) empty Haliotis laevigata shells collected from the Greenlip Abalone sea ranching site in Flinders Bay, Western Australia during predator surveys between 20 January 2015 and 16 March 2017, Total number of shells = 110, and (b) H. laevigata shells with boreholes, collected between April and July 2017, Number of shells with holes = 20.

(a) (b)

Figure 2.10. Haliotis laevigata shells (a) with a bevelled borehole, characteristic of those made by octopus, and (b) location of the boreholes recorded on 20 shells. Shells collected from the Greenlip Abalone sea ranching site in Flinders Bay, Western Australia between April and July 2017. Note, no scale bar is shown on (b), and dots representing the location of boreholes are not in proportion to the size of the aperture. Shells with an borehole range from 33 to 100 mm in length.

2.3.2. Relationship between octopus presence and empty abalone shells Negative binomial regression models suggest that the presence of octopus leads to a 78% (95% confidence limit [CL] = 49 - 126%;) increase in the number of empty shells collected per Abitat per day relative to the absence of octopus, when adjusting for the variables Line and Season (P < 0.001, Table 2.3). Line was also found to be an important covariate associated with the number of empty shells collected. On the outer Lease, the number of shells on Lines O7 and O2 were significantly higher (P < 0.001) than the reference group (O1) with 113% (CL = 61 - 183%) and 87% (CL = 35 - 163%) more shells per Abitat per day, respectively, adjusting for Octopus > 0 and Season (Table 2.3). The number of shells collected on the Lines M1, M2, M3, O4, and O5 were significantly lower than the reference group when adjusting for Octopus > 0 and Season (P < 0.001, Table 2.3). Autumn had significantly higher shell counts compared with Spring and Summer with 46% (CL = 16 – 84%) and 55% (CL = 25 – 92%) more shells per Abitat per day respectively when adjusting for Octopus > 0 and Line (P < 0.001, Table 2.3).

Based on a 78% increase in shell counts, the number of empty abalone shells associated with the presence of octopus is 7,741 for the 27-month period in which shells were collected. This represents 44% of all empty shells collected.

29 Table 2.3. Summary of the results for the negative binomial model to investigate variation in the number of abalone shells and presence of octopus. Number of Abalone Shells on Octopus > 0, Line, and Season, with the number of Abitats multiplied by the time since last survey as an offset in the model. Variable refers to terms included in the model; Estimate refers to the count for the coefficient; Incidence Rate refers to the exponentiated values of the regression coefficients; Std. Error = asymptotic standard errors of the regression coefficients; p-value = significance; Confidence Interval = 95% confidence interval of the exponentiated regression coefficients. Bold = P < 0.05; * indicates the reference level for each of the factors.

Confidence Interval Incidence Std. Variable Estimate z-value P-value 2.5% 97.5% Rate Error (Intercept) -6.972 0.001 0.099 -70.736 < 0.001 0.001 0.001 Octopus > 0 0.576 1.778 0.086 6.687 < 0.001 1.493 2.126 Line (* O1) O2 0.623 1.865 0.165 3.765 < 0.001 1.347 2.626 O3 -0.120 0.819 0.204 -0.979 0.328 0.550 1.257 O4 -1.658 0.190 0.306 -5.413 < 0.001 0.106 0.371 O5 -0.558 0.572 0.165 -3.385 < 0.001 0.412 0.808 O6 -0.377 0.686 0.264 -1.429 0.153 0.411 1.213 O7 0.754 2.127 0.134 5.635 < 0.001 1.611 2.832 08 -0.234 0.791 0.416 -0.564 0.573 0.366 2.053 O9 -0.459 0.632 0.248 -1.853 0.064 0.394 1.068 M1 -0.919 0.399 0.201 -4.556 < 0.001 0.269 0.610 M2 -2.096 0.123 0.353 -5.945 < 0.001 0.064 0.266 M3 -0.699 0.497 0.120 -5.828 < 0.001 0.388 0.638 I1 -0.046 0.954 0.151 -0.307 0.759 0.709 1.302 I2 0.266 1.305 0.274 0.974 0.329 0.782 2.346 Season (*Autumn) 2015 Spring -0.380 0.684 0.109 -3.494 < 0.001 0.543 0.861 2015 Summer -0.439 0.645 0.103 -4.263 < 0.001 0.522 0.796 2015 Winter 0.210 1.235 0.120 1.757 0.079 0.966 1.584

Null deviance: 2153.9 on 1596 degrees of freedom Residual deviance: 1888.6 on 1579 degrees of freedom Number of Fisher Scoring iterations: 1 Theta: 0.438

30 2.3.3. Relationship between octopus presence and abalone survival The average H. laevigata survival counts varied greatly among Bays, particularly during the March 2016 and September 2016 survey periods (Fig. 2.11). A number of outliers were observed, where average counts were as low as 40 individuals (Fig. 2.11). Despite significant overlap in the average counts between each of the periods, there is a clear declining trend, with the mean survival count decreasing from 310 in March 2015 to 294 in September (5.2% decline), 261 in March 2016 and 236 in September (Fig. 2.11). Assuming an average starting count of 400, this represents an average of 59% survival over two years from September 2014 to September 2016. The greatest average decline in numbers was recorded on the first count (23%) compared with subsequent 6 monthly survivals of 88.8 to 94.8%. The median average survival count was slightly higher than the mean in each period and was 318 abalone at 6 months (79.5% survival), 296 at 12 months, 273 at 18 months and 254 after two years (63.5% survival over 2 years, Fig. 2.11).

Figure 2.11 Boxplots of six monthly average survival counts of Haliotis laevigata, surveyed by divers at the Greenlip Abalone sea ranching site in Flinders Bay, Western Australia. Survival counts consider abalone seeded at the first deployment (D1), prior to harvesting of a given Bay. N = 126 counts. Individual points represent outliers in the data (i.e., observations that fall 1.5 times below the lower interquartile range).

31 Autoregressive time series models (AR1) showed that the relationship between the presence of octopus and abalone survival was not significant (P = 0.09, Table 2.4). Successive abalone survival counts were significant in the model (P < 0.001), with average survival increasing by 1.15 abalone compared with the previous average count, when adjusting for Octopus > 0 and Time (Table 2.4).

Table 2.4. Summary of autoregressive AR(1) model output for the relationship between the Count of abalone shells remaining on Abitats and the presence of octopus. Average Count of abalone survival on Octopus > 0, Time, and Previous Average Count. Variable refers to terms included within the model; Estimate refers to the count for the coefficient; Std. Error refers to the standard errors asymptotic standard errors of the regression coefficients; p-value refers to the significance of the model parameter; Confidence Interval refers to the 95% confidence level of the regression coefficients. Bold face indicates a significance level of P < 0.05.

Confidence Interval Std. Variable Estimate z-value P-value 2.50% 97.50% Error (Intercept) -92.10 33.075 -2.785 0.007 -158.359 -25.845 Previous Average Count 1.145 0.10 11.552 < 0.001 0.946 1.344 Octopus > 0 23.194 13.352 1.737 0.088 -3.552 49.94 Time -0.049 0.058 -0.865 0.391 -0.165 0.066

Residual standard error: 32.11 on 56 degrees of freedom Adjusted R-squared: 0.751

2.4. Discussion

This study examined the relationship between octopus and abalone mortality to evaluate the significance of octopus as predators of H. laevigata on a sea ranch of south-western Australia. The data used for these analyses came from counts of octopus and empty abalone shells (~2 to 4 weekly intervals) and counts of surviving abalone on Abitats, recorded by commercial divers as part of the Ocean Grown Abalone monitoring program for abalone and octopus. Direct evidence of predation was identified from the occurrence of distinctive drill holes in a sub-sample of 110 empty H. laevigata shells of H. laevigata, and the significance of predation was shown in negative binomial models.

32 2.4.1. Patterns of octopus distribution and empty abalone shells Despite octopus abundance being highest on the Outer Lease, the number of surveys and the number of Abitats was also higher in this area. The mean number of octopus sampled was broadly similar among Lines. However, when adjusting for the number of Abitats, there were notable differences identified among Lines. This may be a result of observer bias, with fewer octopuses sighted on Lines comprising a greater number of Abitats. For example, on the Inner Lease, the adjusted mean number of octopus was 6.6 times higher on Line I1 (137 Abitats) compared with I2 (879 Abitats). Lines O6 and O9 run perpendicular to one another, however octopus were 2.9 times higher on O6 (79 Abitats) compared with O9 (185 Abitats). In addition, the spatial layout of Abitats within a Line may be a contributing factor. Octopuses have sophisticated sensory organs used to detect predators, and a complex camouflage system allowing them to remain inconspicuous (see Appendix 1, A1.4.1, A1.4.2). Therefore, they have the potential to be overlooked by divers.

Environmental variability and the spatial layout of the Abitats likely contribute to lower shell counts on some Lines. Typically, larger numbers of empty shells were found on Lines comprising fewer Abitats. For example, on the Outer Lease shell counts were greatest on the Line O6, which comprises the fewest number of Abitats (79), and lowest on Line O1, which comprises the largest number of Abitats (810). On the Inner Lease, shell counts were 5.3 times higher on Line I2 (137 Abitats) than on Line I1 (879 Abitats). Where divers are required to cover a larger distance, less time can be spent at any one Bay, which may result in lower shell recovery. In areas of high current flows, there may be a greater propensity for shells to be buried or dispersed away from the Abitats, which could be amplified during storm events leading to lower shell counts (Hines and Pearse 1982). The dispersal of shells, even just a few metres away from the Abitats may reduce the number of shells that are collected, as divers are likely to be focused on the area directly surrounding the Abitats.

Among the sample of empty shells examined, 18% had drill holes which were characteristic of the holes made by octopus (Pilson and Taylor 1961; Kojima 1992). The

33 holes had a distinctive bevel around the aperture and were slightly ovoid; features that readily distinguish octopus predation from other sources (Pilson and Taylor 1961; Kojima 1992). Drilling by octopuses has been documented for several other coastal species (e.g., Octopus bimaculatis, Pilson and Taylor 1981; Ambrose 1983; Tegner and Butler 1985; and Octopus vulgaris, Ambrose 1983; Kojima 1992; Smith 2003), however this appears to be the first account for Octopus cf. tetricus, the most commonly encountered octopus species in Flinders Bay. The percentage of shells with boreholes contrasts with the findings of Ambrose (1983), Kojima (1992), and Smith (2003), who identified that < 10% (3.4 to 7.7%) of Haliotis sp. shells had been drilled by octopus. These findings demonstrate that O. cf. tetricus will resort to drilling a tightly attached abalone when they are unable to simply pull abalone off of the substratum (McQuaid 1994; Smith 2003). The presence of drill holes in the shells of H. laevigata suggest that O. cf. tetricus produce cephalotoxins that are capable of paralysing their prey when injected (Ghiretti 1959; Nixon 1984).

The presence of drill holes suggests that at least one-fifth of all abalone mortality on the sea ranch is attributable to octopus predation. This percentage likely represents the minimum mortality of H. laevigata by octopus but confirms that octopuses are a major source of mortality. Octopus may be able to pull small abalone directly off the reef without the need to bore into the shell, or alternatively, they may target abalone in a “feeding” position. When H. laevigata feed, they elevate their shell, the forepart of the foot, and extend their tentacles to catch drifting algae (Shepherd

1973). Whilst in this position, H. laevigata may be more vulnerable to predation, as their typical stronghold on the reef substratum is reduced.

Predation by octopus is likely to be related to the size of the octopus, with larger individuals targeting larger abalone. Size-related octopus predation has been documented in South Africa, where O. vulgaris predates on the mussel Perna perna and larger octopuses targeted larger prey, gaining a higher energy return per attack than on smaller prey (McQuaid 1994). While the distribution of borehole locations was not

34 significantly different from a random distribution (which may be related to small sample sizes), holes in the shells of H. laevigata were concentrated over the adductor attachment, the heart and the pericardial sac (Kojima 1992; Morash and Alter 2016). The injection of cephalotoxin into these regions is perhaps the most efficient location to target, as it is close to the muscle responsible for holding the abalone on the substratum. Octopus have excellent cognitive abilities, with the ability to learn from past experiences (Anderson et al. 2008b). Therefore the areal distribution of boreholes is likely to be the result of a learnt behaviour, with octopus targeting the areas which succumb to cephalotoxin most rapidly (Wodinsky 1969; Anderson et al. 2008b).

2.4.2. Relationship between octopus presence and abalone shells The presence of octopus was associated with a greater number of empty abalone shells (adjusted for the number of Abitats and time since the previous survey) than when octopuses were absent. The artificial abalone habitats used for the production of H. laevigata in Flinders Bay likely provide octopus with two important resources: the abalone on the Abitats provide a concentrated potential food source, and the Abitats provide shelter for octopus. The rapid growth rates of octopus command voracious feeding regimes, and thus their predatory impact on benthic communities can be significant (Boyle and Rodhouse 2005; Eddy et al. 2017). While octopuses adapt rapidly to new environments (Rigby and Sakurai 2005) they are vulnerable to predation from teleosts, particularly at smaller sizes (Aronson 1991; Mather and O’Dor 1991). Thus, the selection of ‘homes’ is driven by a need to avoid predators in areas that provide adequate resources (i.e., food, or sites for the brooding of eggs, Aronson 1991; Mather 1991; Mather 1994; Anderson 1997). Octopuses are commonly observed among the Abitats, sheltering inside established dens surrounded by empty abalone shells, and feeding on ranched H. laevigata (M. Wall, OGA, 2017 pers. comm.).

Despite the association between the presence of octopus and the number of empty shells collected, the recovery of shells in other studies is discernibly low (i.e., 3 to 10% of all seeded abalone (McCormick et al. 1994; McShane and Naylor 1997;

35 Dixon et al. 2006; Goodsell et al. 2006). Empty shells have the potential to be buried, swept away by currents, or crushed by crabs so that shells cannot be distinguished from the substratum (Hines and Pearse 1982; Schiel and Welden 1987; McCormick et al. 1994; Catchpole et al. 2001; Dixon et al. 2006; James et al. 2007). Laboratory studies demonstrate that the loss of shells due to crabs and lobsters can be as high as 71% (Schiel and Welden 1987). Consequently, shell counts are likely to provide unreliable estimates of mortality, and the impact of octopuses, based on empty abalone shells may be underestimated (Tegner and Butler 1985; McCormick et al. 1994; Dixon et al. 2006). However, a dedicated study investigating shell recovery rates would be required to understand whether shell counts provide a reliable index of total abalone mortality within the Flinders Bay system. While estimates are only likely to provide the minimum mortality of H. laevigata, the collection of shells can be useful in elucidating the cause of death (Schiel and Welden 1987; McCormick et al. 1994; James 2005; Dixon et al. 2006).

The results from the negative binomial models estimated that 44% of all empty abalone shells observed were associated with the presence of octopus. This estimate is 26% higher than the proportion of shells found with octopus drill holes, calculated from a sub-sample of 110 empty abalone shells. The higher proportion of shells associated with octopus presence estimated by the model suggests that octopus can remove abalone from the Abitats by direct force. Based on shell recovery rates of 3% and 10% (McCormick et al. 1994; McShane and Naylor 1997; Dixon et al. 2006; Goodsell et al.

2006), the number of empty abalone shell associated with the presence of octopus could range from 77,410 to 258,033 shells for the 27-month period over which shells were collected

The high spatial variability in shell counts observed among Lines (compared with the reference level) may be associated with natural environmental variability across the Lease or associated with the number of Abitats, as previously discussed. The significantly lower number of shells collected during spring and summer compared with

36 autumn may be related to environmental variability or to the numbers of abalone seeded within a particular season. For example, roughly ten times fewer H. laevigata were seeded during summer compared with autumn, and, consequently, predation rates and the number of empty shells collected are also likely to be lower. Cultured juveniles are highly vulnerable to predation immediately after seeding, due to poor behavioural responses towards predators (Schiel and Welden 1987; McCormick et al. 1994). Cultured abalone are typically sluggish in their response to predators and take longer to firmly attach to the reef substratum compared with wild individuals (Schiel and Welden 1987). This behaviour is likely a reflection of their juvenile history, typified by an absence of predators (Schiel and Welden 1987). The acclimatisation to the wild can take several days, and consequently, newly released individuals are likely to be naïve to predation (Schiel and Welden 1987). Additionally, abalone experience high levels of stress during the transplantation process, which stimulates mucus secretions that are highly attractive to predators (Tegner and Butler 1989). Consequently, predator abundance and abalone mortality may increase immediately following seeding (Shepherd 1990; McCormick et al. 1994; James et al. 2007). Furthermore, elevated stress levels following transplantation may reduce fitness, leaving weakened abalone susceptible to scavengers (Tegner and Butler 1989). Evidence for elevated mortality in the post-release period was identified from abalone survival counts, whereby survival was lowest at the first six monthly survival count compared with subsequent counts.

2.4.3. Relationship between octopus presence and abalone survival The relationship between the presence of octopus and abalone survival counts was not significant, contrasting the findings found for the presence of octopus and empty abalone shell counts. In addition, the relationship between the presence of octopus and abalone survival was contrary to what would be expected, given that octopuses are voracious predators and appear to be preying upon abalone. These findings are likely to be an artefact of random sampling design (where random Abitats are sampled at each time point but without a unique identifier to indicate whether the same Abitat has been resampled at multiple time points), and significant variation in the number of abalone

37 seeded on individual Abitats. When abalone are seeded, two seeding modules are placed onto each Abitat, with each module estimated to contain ~200 individuals. However, the actual number of abalone has the potential to vary significantly from this estimate, since abalone are not individually counted during the packing process. Rather, the packing of seeding modules is based on weight. Due to natural variation in growth, the size and weight of abalone differ considerably among individuals, and thus the total number of abalone per module is likely to vary greatly, and as a consequence, the “number” seeded per Abitat (“400”) is an approximation only. In addition, survival counts are based on randomly selected Abitats within a Bay, and the Abitats counted on subsequent surveys may differ from those counted previously. Thus, changes in abalone survival based on this counting methodology, cannot be estimated with precision over time. Quantification of the number of abalone seeded on each Abitat and repeated counts on the same Abitats over time, would allow changes in survival to be better understood. Given the significant variability between abalone survival counts, and the counterintuitive relationship between the presence of octopus and abalone survival, estimates from the model cannot be considered reliable.

38 Chapter 3. The diet and nutrient assimilation (δ13C and δ15N) of Octopus cf. tetricus on an abalone sea ranch in south-western Australia 3.0. Abstract

This study used gastric tract (crop and stomach) and stable isotope analyses to evaluate the dietary composition of the commercially important Octopus cf. tetricus, and its significance as a predator of Greenlip Abalone, Haliotis laevigata, on artificial abalone habitats (“Abitats”) in Western Australia. The contents of the crop and stomach from 44 octopuses, ranging from 58.5 to 1596.1 g (mantle length = 52 to 152 mm) were compared with understand the dietary composition that could be determined from examining each organ. A total of 13 taxa were identified in the crop contents and 10 in the stomach. Within the stomach contents, 74% of the total percentage volume (%V) of material was unidentifiable, with molluscs comprising the majority of identified items (total %V = 19%: ~6% octopus, 2% abalone and 2% bivalves). In contrast, < 4% of material in the crop contents was unidentifiable; providing a much higher taxonomic resolution of dietary items than stomachs. Among the crop contents, molluscs contributed the largest %V (~31% abalone, ~13% non-cephalopod molluscs, ~6% octopus and ~4% bivalves), followed by crustaceans (33%). Dietary composition based on crops did not differ significantly among three size classes of octopus (< 300 g, 300- 999 g, ≥ 1,000 g), paralleling the findings of stable isotope analysis. Examination of the nitrogen stable isotope (δ15N) of octopus, fish, abalone and macrophytes revealed that O. cf. tetricus occupies a mid trophic level position, slightly below teleosts and loliginid squids. The carbon stable isotope (δ13C) signature of O. cf. tetricus was similar to the teleosts Coris auricularis, Opthalmolepis lineolatus and Upeneichthys vlamingii, which may be explained by an overlap in the use of food resources among these benthic consumers. Gastric tract analyses suggest that O. cf. tetricus is an important predator of H. laevigata. This trend was less obvious from stable isotope analysis, due to the relative enrichment of δ13C in O. cf. tetricus compared with H. laevigata. These findings may be explained by the contribution of other prey items to the diet of octopus, such as crustaceans and other cephalopods (as identified by gastric tract analysis).

39 3.1. Introduction

Octopuses play important ecological roles within coastal marine environments around the world, both as predators and prey of a diverse range of species (for detail, see Appendix 1). Due to rapid growth rates which stimulate voracious feeding regimes, and the ability to adapt rapidly to their surroundings, octopuses can impose significant predatory impacts; controlling the trophic structure and functioning of the communities in which they live (Nixon 1987; Rodhouse and Nigmatullin 1996; Boyle and Rodhouse 2005; André et al. 2010).

Octopus cf. tetricus is a coastal merobenthic species (i.e., they possess a planktonic larval phase), endemic to the waters of south-western Australia (Caputi et al. 2015; Hart et al. 2016). The limited dietary information available for this species indicates that O. cf. tetricus predates on Western Rock Lobster, Panulirus cygnus, caught in lobster traps/pots (Hart et al. 2016), and its diet is likely to comprise predominantly crustaceans and molluscs, like the diets of other coastal octopuses (Joll 1977; Mangold 1983; Villanueva 1993; Smith 2003; Villegas et al. 2014).

The dietary composition of octopuses is influenced by ontogeny, and as a consequence, size (Ambrose 1984; Ambrose 1986; Villanueva 1993; Smith 2003; Boyle and Rodhouse 2005; Regueira et al. 2017). As octopuses increase in body size, the breadth of their diet typically increases; reflecting an increase in arm length relative to mantle size, and growth of the brachial crown that allows them to capture larger, more mobile benthic organisms (Villanueva et al. 1995; Rodhouse and Nigmatullin 1996; Smith 2003; Boyle and Rodhouse 2005). For example, a study of the Musky Octopus Eledone moschata in the Adriatic Sea (Croatia), found that teleosts and cephalopods became increasingly important in the diet as body size increased, while the relative contribution of crustaceans declined (Šifner and Vrgoč 2009).

Foraging behaviour and habitat type are also important factors influencing the dietary composition of octopuses (Ambrose 1984; Hewitt et al. 2008). Past foraging success can drive the modification of prey selection (Ambrose 1984; Mather and O’Dor

40 1991; Anderson 1997; Smith 2003; Gasalla et al. 2010), while the strong affinity of some prey taxa towards a particular set of environmental and biological characteristics affects the functional composition of a community, and therefore prey availability (Ambrose 1984; Hewitt et al. 2008).

Following prey capture, the flesh of crustaceans and molluscs is delicately removed from the exoskeleton or shell with the use of the beak, suckers and radula (Boyle and Rodhouse 2005). Larger prey are more easily gleaned than small prey (Boucher-Rodoni and Mangold 2009). A cocktail of digestive compounds are released from the posterior salivary gland, which help to break down the prey prior to ingestion (Nixon 1984; Grisley and Boyle 1987; Grisley and Boyle 1990). The partly digested prey enters the oesophagus, which feeds into the crop diverticulum that briefly stores the food (Boyle and Rodhouse 2005; Boucher-Rodoni and Mangold 2009). Digestive enzymes supplied by the digestive gland further break down the prey, which then passes to the stomach in instalments (Boucher-Rodoni and Mangold 2009). Rapid digestion results in little, often unrecognisable food in the stomach, with material beyond the stomach being visually unidentifiable (Grisley and Boyle 1990; Boyle and Rodhouse 2005; Regueira et al. 2017). When only a small amount of prey is consumed (< 1% of the total octopus weight), prey can be digested with the first release of enzymes (Boucher-Rodoni and Mangold 2009).

Dietary studies of octopuses are commonly undertaken by examining prey items found in the gastric tract (i.e., the crop and stomach) and analysing middens (i.e., counting the prey remains discarded around an octopus’ den, Nixon 1987; Villanueva 1993; Mather and Nixon 1995; Smith 2003). Gastric tracts typically contain a broader range of prey taxa and a higher occurrence of soft bodied organisms than those found in middens (Boyle and Rodhouse 2005; Jackson et al. 2007; Villegas et al. 2014). This is despite the fact that prey remains are highly fragmented due to their mastication by the octopus’ beak, the selective rejection of hard parts during consumption, and rapid digestion. Conversely, hard-shelled prey (i.e., gastropods and bivalves), are typically

41 over-represented in midden counts as water currents and benthic scavengers (e.g., brachyurans) rapidly remove the remains of lightweight prey such as crustaceans, polychaetes and teleosts (Ambrose and Nelson 1983; Smith 2003).

In addition to these analyses of gastric tract and midden contents, biochemical techniques such as stable isotope analysis have been used increasingly in cephalopod research of their trophic ecology. These chemical tracers facilitate an understanding of the long-term assimilation of nutrients into tissues; helping disentangle trophic relationships and overcoming some of the inherent bias of gastric tract analyses, including the ‘last meal’ bias (Jackson et al. 2007; Layman et al. 2012). Since stable isotopes summarise long-term dietary intake and do not identify individual items in the diet, their use in dietary studies is most valuable when combined with gastric tract analysis. This allows the breadth of diet to be evaluated whilst enabling the longer term assimilation of carbon and nitrogen to be quantified (Jackson et al. 2007; Layman et al. 2012; Phillips et al. 2014).

Limited information is known about the trophic position of octopuses in south- western Australia (Caputi et al. 2015), and the trophic functioning of artificial reefs is a relatively new area of research (Cresson et al. 2014a). Recent research suggests that artificial reefs can enhance primary productivity and, as a consequence, support secondary production and increase yields in small-scale fisheries (Cresson et al. 2014a; Wu et al. 2016). Given the increasing importance of cephalopods in the marine environment (Doubleday et al. 2016) and their innate ability to adapt to new surroundings (Mather 1994; Rigby and Sakurai 2005; Finn et al. 2009), improving our understanding of the trophic relationships of octopus within the food web is fundamental to assessing their ecological role in marine communities (Livingston 2003; Navarro et al. 2013).

Artificial reefs are typically deployed to enhance the production of small-scale coastal fisheries worldwide (Cresson et al. 2014a; Taylor et al. 2017). Throughout Asia, this is combined with aquaculture-based enhancement (i.e., the release of cultured

42 individuals in the marine environment), to enhance the yields of commercially valuable stocks such as the sea cucumber Apostichopus japonicus, Haliotis sp., and bivalve shellfish including the Manila Clam, Venerupis philippinarum (Goodsell et al. 2006; James et al. 2007; Becker et al. 2008; Melville-Smith et al. 2013; Zhang et al. 2015; Taylor et al. 2017). In recent times, species-specific artificial reefs have been used to support the sea ranching of cultured Haliotis laevigata in south-western Australia (see Chapter 2, Figure 2.2). However, high stocking densities may increase the abundance of opportunistic predators such as fishes, crabs, and octopuses responding to an increase in prey abundance, which could have negative impacts for the survival of released H. laevigata (McCormick et al. 1994; Shepherd and Clarkson 2001; James et al. 2007; Melville-Smith et al. 2013; Hart et al. 2013a). In a three-year abalone sea ranching trial in Flinders Bay, O. cf. tetricus was identified as a potentially important predator of H. laevigata, with numerous incidences of predation observed during the study period (Melville-Smith et al. 2013).

The aims of this study were to examine the contents of the gastric tract, and the assimilation of carbon and nitrogen by O. cf. tetricus collected from artificial reefs in Flinders Bay, Western Australia (used to grow cultured H. laevigata, see Chapter 2.2) to determine:

(i) whether the dietary composition of O. cf. tetricus differs between the crops and stomachs and, if so, which organ provides the best dietary information;

(ii) whether the dietary composition of O. cf. tetricus changes with increasing body size;

(iii) whether O. cf. tetricus consumes H. laevigata, and if so, what proportion of the diet it represents; and

(iv) the assimilation of nutrients (C and N) by O. cf. tetricus and H. laevigata within the marine food web of Flinders Bay to understand the long-term dietary trends of O. cf. tetricus and where this species fits within the food web, using stable isotope analysis.

43 3.2. Materials and methods 3.2.1. Collection of Octopus cf. tetricus Individuals of O. cf. tetricus were caught by commercial abalone divers from the Ocean Grown Abalone (OGA) lease sites, situated in Flinders Bay, Western Australia (see Chapter 2.2). Samples were collected by hand during daylight hours between March and August 2017 at depths of ~20 m. Samples were frozen within 7 h after capture, i.e., as soon as possible with the constraints of commercial operations on the abalone lease (see Chapter 2.2).

3.2.2. Quantification of Octopus cf. tetricus diet After defrosting, the total weight (g), total length (mm), and mantle length (mm) of each O. cf. tetricus was measured and its gastric tract removed. The crop was separated from the rest of the tract and its fullness was estimated visually on a scale of 1 to 10, with 10 being the equivalent of 100% full. Any material found in the oesophagus, before it entered the crop was grouped with the crop contents. All contents from the stomach were removed and examined separately. Contents that could not be identified from the crop and stomach were rinsed through a 500 �m sieve to remove silt and excess liquid that would hinder the identification of the remaining contents (e.g., Smith 2003; Regueira et al. 2017). The material was then sorted under a dissecting microscope and identified to the lowest taxonomic level possible, based mainly on the examination of hard parts, namely the radula and odontophore of abalone; and crustacean exoskeletons, legs and chelipeds. Cephalopod flesh was recognised by its distinctive texture, the characteristic chromatophores on the skin’s surface and the presence of black ink in the gastric tract, while bivalves could be recognised by their characteristic feeding structures (i.e., the ctenidium, Fig. 3.1). Where no identifiable features were present to discriminate between abalone and bivalves, the material was assigned as ‘non- cephalopod mollusc’.

The volumetric contributions of each prey item found within the crop and the stomach of O. cf. tetricus was estimated by eye and expressed as percentage by volume

44 (%V). Prey in an advanced state of digestion, or so highly masticated that it could not be identified was labelled ‘unidentified’ (Table 3.2).

Octopus were assigned to three weight classes; i.e., < 300 g, 300-999 g, and ≥ 1000 g, in an attempt to measure size related changes in dietary composition (following Smith 2003). The size class categories were selected to evaluate the diets of juvenile, sub-adult and mature or large individuals. Since males and females mature at different weights, ~950 and ~1,800 g respectively (Leporati et al. 2015), a lower limit of 1,000 g was set as a baseline to account for differences between sexes.

45 (a) Odontophore of Haliotis laevigata (b) Radula of Haliotis laevigata

(e) Octopus tissues (f) Rinsed octopus tissue

Figure 3.1. Dietary items found in the crops and stomachs of Octopus cf. tetricus: (a) odontophore of Haliotis laevigata; (b) radula of H. laevigata; (c) contents of crop including brachyurans and H. laevigata, as evidenced by chelipeds and odontophore; (d) stomach contents showing the advanced state of digestion compared with the crop; (e) cephalopod tissue found in the crop before rinsing; and (f) cephalopod tissue found in the crop after rinsing. Numbers in images denote the octopus sample number, and the contents (c) and (d) are from the same animal.

46 3.2.3. Stable isotope preparation A range of consumer and primary producer species that were visually abundant around the artificial reefs, were collected by hand or hand spear by SCUBA divers at depths of ~19 m during May 2017 and frozen (Table 3.1).

Each fish was thawed, identified to species and the total length (mm) measured. A portion of the dorsal muscle tissue was removed for stable isotope analysis and the skin removed using a scalpel, dissection scissors, and forceps. The total weight and shell length of each H. laevigata was measured, and a section of the muscular foot was removed (following Guest et al. 2008). A segment of the mantle tissue of O. cf. tetricus was extracted, and the thin outer layer of tissue containing the chromatophore organs was removed.

Algae and seagrass were identified to at least family level, rinsed with deionised water to remove salts, and then epiphytes were removed using a razor blade to minimise the influence of epiphytes on the isotopic ratios. Tissue was selected haphazardly from the lower, midline and tip of each algal frond (following Guest et al. 2008).

Each consumer tissue sample was placed in a pre-cleaned open glass vial, while algae samples were dried in clean aluminum foil trays and oven dried at 60 °C for up to 72 h. Dried samples were then broken down manually into small pieces using a mortar and pestle and placed into 2.0 mL Eppendorf tubes. Standard measures of 0.5 mL for consumer tissue and 1.0 mL for primary producer tissue were placed into each tube with a 5 mm ball bearing. A Qiagen TissueLyser II (ball mill), operated at 27 shakes per second, was used to grind each of the tissue samples into fine powders.

Samples were sent to the West Australian Biogeochemistry Centre at the University of Western Australia and analyzed on a Delta V Plus continuous flow isotope-ratio mass spectrometer. The isotope ratios of nitrogen 15N/14N and carbon 13C/12C were calculated and presented as a delta (δ) value, representing the relative per mil (‰) difference between the sample and the recognized international standard (Pee Dee belemnite carbonate and atmospheric nitrogen for δ13C and δ15N, respectively).

Table 3.1. The number of primary producer and consumer samples collected and analysed for stable isotopes of δ13C and δ15N from the Greenlip Abalone (Haliotis laevigata) sea ranching site in Flinders Bay, Western Australia in May 2017. The total numbers of samples of major groupings are shown in parentheses. * refers to location (Line) from which abalone were sampled (see Chapter 2.2.2).

Taxa Number of samples

Primary producers (18) Seagrass (3) Amphibolis antarctica 3 Macroalgae (15) Rhodophyta (9) Graciliara sp. 3 Plocamium mertensii 3 Spyridia sp. 3 Phaeophyceae (6) Sargassum sp. 3 Sargassum sp. 3 Consumers (61) Abalone (24) Haliotis laevigata 1 Year O1* 4 Haliotis laevigata 1 Year O5* 4 Haliotis laevigata 2 Years O1* 4 Haliotis laevigata 2 Years O5* 4 Haliotis laevigata 3 Years O1* 4 Haliotis laevigata (Seeds 0+) 4 Cephalopods (14) Loliginidae sp. 2 Octopus (12) O. cf. tetricus (< 300 g) 4 O. cf. tetricus (300 – 999 g) 4 O. cf. tetricus (≥ 1,000 g) 4 Teleosts (20) Coris auricularis 4 Chrysophrys auratus 4 Neatypus obliquus 4 Pseudocaranx georgianus 2 Opthalmolepis lineolatus 4 Upeneichthys vlamingii 2 Tunicata sp. (3)

48 3.2.4. Analyses of dietary data Multivariate analyses were carried out using the PRIMER v7 multivariate statistical package (Clarke et al. 2014a) and the Permutational Multivariate Analysis of Variance (PERMANOVA)+ add-on module (Anderson et al. 2008a) to evaluate how the dietary composition of O. cf. tetricus varied among body size classes (i.e., weight class) and between gastric organs (i.e., crop vs. stomach). The null hypothesis of no significant difference in dietary composition between a priori groups was rejected when a significance level (P) was ≤ 0.05.

Comparison of diet between gastric organs In order to elucidate any broad trends in dietary composition between gastric organs (accounting for potential changes with increasing body size), the mean volumetric percentage contributions of each of the 13 dietary categories found in the crops and stomachs of O. cf. tetricus in each weight class (Table 3.2) were calculated and plotted as stacked bar graphs.

Preliminary analyses were employed to determine whether the dietary composition of O. cf. tetricus differed according to the Gastric Organ (2 levels; Crop and Stomachs), taking into account any potential confounding effect of Weight Class (3 levels; < 300, 300-999 and > 1,000 g). This analysis included unidentified material, unlike traditional multivariate analysis of diet, where unidentified material is eliminated as a dietary category (e.g., Platell and Potter 2001; Platell et al. 2010; French et al. 2012; Coulson et al. 2015). The rationale for this was to place focus on what was unknown about the diet, and to make comparisons between the gastric organs.

As the gastric tracts of individual octopus may contain only a small number of dietary categories, two octopuses collected at the same time from the same location may differ markedly in their dietary composition. This can mask subtle but ‘real’ trends in diet. To reduce this potential effect, samples for each weight class for each dietary organ were randomly sorted into groups of between three and five, depending on the

49 total number of octopus in the samples (Platell and Potter 2001; Lek et al. 2011; Coulson et al. 2015).

The dietary categories ‘Octopus cf. tetricus’ and ‘unidentified cephalopods’ were grouped for this and subsequent multivariate analyses, as the latter category comprised only a very small proportion of the diet. Algae and shell grit/sediment were removed from the analysis, since the ingestion of these items is likely to be an unintentional consequence of prey capture (Boyle and Rodhouse 2005). The data for the remaining dietary categories were then standardised (i.e., re-converted to percentage contribution). The percentage volumetric contribution of the different dietary categories in each group of replicates were averaged and square-root transformed to down-weight abundant items and remove any tendency for the main dietary constituents to be excessively dominant (see Lek et al. 2011). These averaged and transformed data were then used to construct a Bray–Curtis resemblance matrix, which was in turn, subjected to PERMANOVA (Anderson et al. 2008a). A two-way crossed PERMANOVA was used to elucidate whether there was a significant interaction between the Gastric Organ and Weight Class, and if so, to determine the extent of that interaction relative to the main effects.

Two-way Analyses of Similarities (ANOSIM; Clarke and Green 1988) were used to test which factors, if any, were significant. In this and subsequent ANOSIM tests, both R-statistics and their associated significance level (P) are cited. The magnitude of the R-statistic ranges from ~0 to 1, with 0 indicating that the average similarity among and within groups does not differ, and 1 indicating that all samples within each group are more similar to each other than to any of the samples from other groups (Clarke et al. 2014a). A non-metric Multidimensional Scaling (nMDS) ordination plot was constructed from the same Bray-Curtis resemblance matrix used above, to provide a visual representation of the similarity among groups of samples.

A shade plot (i.e., a visual representation of a frequency matrix, Clarke et al. 2014b), was constructed to elucidate the dietary categories responsible for any

50 differences in the dietary composition of O. cf. tetricus based on samples of crops and stomachs. On this plot, white space for a dietary category demonstrates that the category was never recorded, while the depth of shading from grey to black is linearly proportional to the square-root transformed percentage volumetric contribution of that category. To improve clarity, dietary categories that contributed < 10% of the overall volume of any group of samples (i.e., barnacles, and isopods) were excluded from the shade plot. The dietary categories (y-axis) are ordered to optimise the seriation statistic ρ, by non-parametrically correlating their resemblances to the distance structure of a linear sequence (Clarke et al. 2014a). The order of the samples (x-axis) was seriated independently of the dietary categories, but employing a constrained seriation by Gastric Organ. Thus, crop samples were kept together and separate from those of stomachs and vice versa, but samples within each gastric organ were ordered to maximise ρ (Clarke et al. 2014a; Coulson et al. 2015).

Size related differences in diet Having determined which gastric organ of O. cf. tetricus provided the best representation of dietary composition, the data from that organ was used to determine the presence and strength of any weight related changes in dietary composition (i.e., crops and/or stomachs). For these analyses the %V contribution of the unidentified material was removed, the data were then re-standardised and samples were pooled into groups of three to four samples from the same weight class, where possible, and averaged.

These pre-treated data were then square root transformed and used to create a Bray–Curtis resemblance matrix, which was subjected to one-way ANOSIM to determine whether dietary composition differed among weight classes. This same matrix was used to construct an nMDS ordination plot, which provided a visual representation of the similarity of samples. A shade plot was used to determine the basis for any differences in diet among weight classes and the trends in dietary categories responsible for those differences.

Stable isotope composition of prey and primary producers Mean values (± 1 SE) of δ15N and δ13C were calculated for each taxonomic group of consumers and primary producers collected. Prior to undertaking analyses, Shapiro- Wilk tests showed that the stable isotope data were not normally distributed. Therefore, a non-parametric Kruskal-Wallis test was used to determine whether the δ13C and δ15N signatures differed significantly among O. cf. tetricus and other consumers, and between primary producers. When significant differences were detected, a post-hoc Dunn’s multiple comparisons test was performed to determine which a priori groups differed from each other. The Dunn’s test is appropriate for groups with unequal numbers of observations (Zar 2010). These inferential statistical analyses were performed using the R statistical software package (R Core Team 2017) and the “FSA” (Ogle 2017) add-on package.

To calculate the number of trophic levels present within the system, the mean δ15N value for all primary producers was calculated and assigned the trophic level of one (following Linke 2011; Como et al. 2017). The mean δ15N value for abalone was calculated and assigned the trophic level of two, and higher sequential trophic levels were estimated by adding the δ15N fractionation between trophic levels, assumed to be 3.4‰ (Vander Zanden and Rasmussen 2001).

3.3. Results 3.3.1. Comparison of diet between gastric organs Of the 44 O. cf. tetricus sampled, 34 contained food in either the crop and/or the stomach. Prey items found in the gastric tract were allocated to one of 13 dietary categories (Table 3.2). All 13 dietary categories were found in the crops, compared with 10 in the stomachs. Of the stomach contents, 74% of all material was unidentifiable, compared with only 4% in the crops (Table 3.2, Fig. 3.2). For crops alone, molluscs made the largest contribution by volume percentage (%V), comprising 54% of the diet of O. cf. tetricus (Table 3.2, Fig. 3.2). One third (~31%) of the molluscs was attributed to abalone, ~13% to non-cephalopod molluscs, ~6% to octopus and ~4% bivalves

52 (Table 3.2, Fig. 3.2). Crustaceans (~33%) were the second largest dietary category by %V, of which ~8% were brachyurans (comprising at least three species; Table 3.2). For stomachs alone, molluscs comprised the majority (73%) of the identifiable contents (19% of the total stomach contents), of which ~6% was octopus, 2% abalone and 2% bivalves (Table 3.2). A total of ~6% of the diet in the stomach comprised crustaceans (Table 3.2). Barnacles, brachyurans and isopods were absent from the stomach contents (Table 3.2, Fig. 3.2).

Table 3.2. Mean volumetric contribution (%V) of the major dietary components found in the crops and stomachs of Octopus cf. tetricus, collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017. * = dietary items excluded from the multivariate analysis of crop and stomach dietary composition.

Dietary Category Crops Stomachs Molluscs (total) 53.90 19.16 Abalone 31.10 2.21 Bivalve 3.59 2.21 Non-cephalopod mollusc 13.24 8.31 Cephalopod 5.97 6.44 Octopus cf. tetricus 5.68 5.85 Unidentified cephalopod 0.29 0.59 Crustaceans (total) 33.49 5.96 Amphipod 0.03 0.29 Barnacle 0.03 0.00 Brachyuran 7.97 0.00 Isopod 0.29 0.00 Unidentified crustacean 25.16 5.66 *Algae 3.15 0.06 *Shell fragment/Sediment 5.43 0.56 *Unidentified Material 4.04 74.26 Samples examined (N) 44 44 Samples with prey (N, %) 34, 77.3% 34, 77.3%

Two-way PERMANOVA detected a significant difference in the dietary composition of O. cf. tetricus between Gastric Organ (crops vs stomach), but not among

Weight Classes, and the Gastric Organ × Weight Class interaction was not significant (Table 3.3). A two-way ANOSIM demonstrated that the contents of the crops and

53 stomachs differed significantly and that the magnitude of those differences was moderate (R = 0.53, P < 0.001). This is clearly evident on the nMDS ordination plot, with the points representing the crops (to the left of the nMDS) typically very well separated from those of the stomachs (to the right of Fig. 3.3).

Crops Stomachs 15 15 4 14 16 4 Unidentified material 100% Shell fragment/sediment Algae 80% Un-identified crustacean Isopod 60% Brachyuran Barnacle 40% Amphipod Cephalopod Volumetric Contribution 20% Non cephalopod mollusc Bivalve

0% Abalone

Weight Class (g)

Figure 3.2. Stacked bar graphs showing the mean percentage volumetric contributions of the various dietary categories to sequential weight classes (g) in the crops and stomachs of Octopus cf. tetricus collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017. Number of crops and stomachs examined are shown above the stacked bar graphs for each weight class. N = 34

Table 3.3. Degrees of freedom (df), mean squares (MS), pseudo-F ratios, and significance levels (P) for PERMANOVA test, employing a Bray-Curtis similarity matrix derived from the mean percentage volumetric contributions of the eight main dietary categories to the crops and stomachs of Octopus cf. tetricus collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017. Bold face denotes significant difference.

Factor df MS %MS Pseudo-F P Gastric Organ 1 21560 83.33 12.78 0.001 Weight Class 2 2404.10 9.29 1.98 0.089 Gastric Organ × Weight Class 2 695.55 2.69 0.57 0.732 Residual 18 1212.70 4.69

Figure 3.3. nMDS ordination plot, constructed from a Bray–Curtis similarity matrix of the volumetric contributions of the eight main dietary categories from the Crops and Stomachs of Octopus cf. tetricus, collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017.

The shade plot indicates that the differences between crops and stomachs were due to the large volumetric contributions of unidentified material in the stomachs, while abalone and brachyurans had a greater contribution in the crops than stomachs (Fig. 3.2 and 3.4). The contribution of crustaceans was also higher in the crops than stomachs (Fig. 3.4). Crustaceans occurred in all but one group of crops, while abalone were present in all but two of the 12 groups. Unidentified material was present in every group of stomachs, with three samples containing only unidentified material (Fig. 3.4).

Figure 3.4. Shade plot showing the mean square-root transformed percentage volumetric contributions of eight main dietary categories found in the crops and stomachs of Octopus cf. tetricus collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017. White represents an absence of prey, and grey to black represents the increasing contribution of a dietary category to the total diet.

This analysis demonstrates that the examination of different gastric organs can lead to dramatically different results in the dietary compositions of O. cf. tetricus. Size related changes in the diet of O. cf. tetricus was therefore undertaken using only the data obtained from crops, as this was considered to provide a more-reliable indicator of dietary composition.

3.3.2. Size related differences in diet One-way ANOSIM demonstrated that the dietary composition of O. cf. tetricus did not differ between weight classes (R = 0.05, P = 0.31), which is evident from the nMDS plot, with the interspersion of points representing each of the three weight classes (Fig. 3.5). Points from the smallest size class are towards the centre-right of the nMDS plot, with those for the largest octopus above and below them.

Figure 3.5. nMDS ordination plot, constructed from a Bray–Curtis similarity matrix that employed the volumetric contributions of the nine main dietary categories to the crops of sequential weight classes (p < 300, p 300–999, r ≥ 1,000 g) of Octopus cf. tetricus collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017.

The shade plot demonstrates that abalone and crustaceans, including brachyurans are abundant and frequently consumed components of the diet of O. cf. tetricus regardless of body size (Fig. 3.6, see also Fig. 3.2). Other molluscs such as cephalopods and bivalves, and small crustaceans including amphipods and isopods, vary in their relative contributions between weight classes, but the presence of these dietary categories is less consistent among groups of samples and they contribute less to the overall diet (Fig. 3.6).

Figure 3.6. Shade plot showing the mean square-root transformed percentage volumetric contributions of each of the nine main dietary categories found in the crops and stomachs of Octopus cf. tetricus in sequential weight classes (p < 300, p 300–999, r ≥ 1,000 g) collected from the Greenlip Abalone, Haliotis laevigata, sea ranching site in Flinders Bay, Western Australia between March and July 2017. White represents an absence of prey, and grey to black represents the increasing contribution of a dietary category to the total diet.

3.3.3. Stable isotope composition of prey and primary producers The mean δ15N values for O. cf. tetricus ranged from 7.92 ± 0.30 (≥ 1,000 g) to 8.27 ± 0.36‰ (300-999 g, Table 3.4, Fig. 3.6). The mean δ15N values for abalone (3.77 ± 0.09 to 3.99 ± 0.01‰) sampled from different locations and of different ages were from 3.93 to 4.93‰ lower than those for octopus, with the lowest δ15N recorded for the newly seeded H. laevigata (3.34 ± 0.06‰, Table 3.4, Fig. 3.7). The δ15N values for the teleosts ranged from 9.02 ± 0.14 (Upeneichthys vlamingii) to 11.54 ± 0.54‰ (Chrysophrys auratus), while loliginid squids were 9.49 ± 0.27‰ (Table 3.4, Fig. 3.7). Considerable differences were also identified between primary producers, with the mean δ15N values ranging from 1.80 ± 0.18 (the seagrass Amphibolis antarctica) to 3.76 ± 0.05‰ (the red alga Plocamium mertensii, Table 3.4, Fig 4.7).

58 The δ15N values did not differ significantly among size classes of O. cf. tetricus

2 (Kruskal-Wallis, X2 = 0.35, P = 0.84, Table 3.4). However, significant differences were

2 found between O. cf. tetricus and other consumer groups (Kruskal-Wallis, X3 = 48.93,

P < 0.001), including teleosts (10.10 ± 0.22‰, Dunn’s Test, Z11, 19 = -2.72, P = 0.03) and abalone (3.77 ± 0.05‰, Z11, 23 = -3.08, P < 0.01, Table 3.4).

Table 3.4. Stable nitrogen (δ15N) and carbon (δ13C) values and for primary producers and consumers collected from the Greenlip Abalone (Haliotis laevigata) sea ranching site in Flinders Bay, Western Australia in May 2017, and prepared for stable isotope analysis. N = sample size. The total numbers of samples of major groupings are shown in parentheses. * refers to location (Line) from which abalone were sampled (see Chapter 2.2.2) δ15N ‰ δ13C ‰

Taxon N Mean SE Mean SE Primary producers (85) 2.90 0.17 -28.08 1.49 Seagrass (3) 1.80 0.18 -17.85 0.14 Amphibolis antarctica 3 1.80 0.18 -17.85 0.14 Macroalgae (15) 3.12 0.15 -30.13 1.20 Rhodophyta (9) 3.09 0.23 -32.71 1.46 Graciliara sp. 3 2.25 0.19 -26.92 0.44 Plocamium mertensii 3 3.76 0.05 -36.02 0.24 Spyridia sp. 3 3.28 0.05 -35.19 0.20 Phaeophyceae (6) 3.15 0.15 -26.26 0.19 Sargassum sp. 3 3.44 0.02 -26.50 0.20 Sargassum sp. 3 2.87 0.19 -26.01 0.28 Consumers Abalone (24) 3.77 0.05 -27.41 0.26 Haliotis laevigata Y1 O1* 4 3.77 0.09 -27.55 0.15 Haliotis laevigata Y1 O5* 4 3.99 0.01 -28.27 0.15 Haliotis laevigata Y2 O1* 4 3.90 0.08 -27.69 0.45 Haliotis laevigata Y2 O5* 4 3.80 0.03 -28.43 0.23 Haliotis laevigata Y3 O1* 4 3.83 0.09 -27.55 0.43 Haliotis laevigata (0+ Seeds) 4 3.34 0.06 -25.00 0.08 Cephalopods (14) 8.28 0.22 -23.37 0.34 Loliginidae sp. 2 9.49 0.27 -21.82 0.20 Octopus (12) 8.08 0.19 -23.63 0.42 O. cf. tetricus (< 300 g) 4 8.05 0.43 -23.86 0.76 O. cf. tetricus (300 – 999 g) 4 8.27 0.36 -24.03 0.49 O. cf. tetricus (≥ 1,000 g) 4 7.92 0.30 -23.00 0.51 Teleosts (14) 10.10 0.22 -23.23 0.47 Coris auricularis 4 9.66 0.02 -23.00 0.10 Chrysophrys auratus 4 11.54 0.54 -21.53 0.44 Neatypus obliquus 4 10.20 0.08 -27.05 0.14 Pseudocaranx georgianus 2 10.41 0.02 -21.34 0.26 Opthalmolepis lineolatus 4 9.37 0.20 -22.56 0.06 Upeneichthys vlamingii 2 9.02 0.14 -22.71 0.30 Tunicata sp. (3) 4.48 0.42 -22.41 0.28

59 15 2 The δ N values differed significantly between the teleosts (X5 = 17.47, P <

0.05): C. auratus and Opthalmolepis lineolatus (Z3,3 = -3.17, P = 0.02), and C. auratus and Pseudocaranx georgianus (Z3,3 = 0.64, P = 0.02, Table 3.4). Significant differences

15 2 in δ N were also identified among the primary producers (X2 = 6.49, P = 0.04): between Phaeophyceae (3.15 ± 0.15‰) and A. antarctica (Z2,2 = 2.25, P = 0.05), and

Rhodophyta (3.09 ± 0.23‰) and A. antarctica; (Z2,2 = 2.44, P = 0.04, Table 3.4).

Considering the baseline values for δ15N and a fractionation of 3.4‰ for trophic levels above herbivores (i.e., abalone, Vander Zanden and Rasmussen 2001), the food web spanned ~4 trophic levels between primary producers and teleosts (Fig. 3.7). Octopus cf. tetricus occupied a mid trophic level of <3.5, while teleosts and loliginid squid occupied a trophic level of ≥ 3.5. H. laevigata occupied the trophic level of two, just above the primary producers (Fig. 3.7).

14 Legend

Seagrass 12 Rhodophyta Phaeophyceae C. auratus TL 4 Abalone P. georgianus 10 Tunicata N. obliquus C. auricularis Loliginidae sp. Cephalopods O. lineolatus U. vlamingii Teleosts 8 O. cf. tetricus TL 3

N (‰ ) 6 δ15 Tunicata sp. 4 P. mertensii H. laevigata TL 2 Spyridia sp. Sargassum sp. H. laevigata (seeds) TL 1

2 Graciliara sp. A. antartica

0 -40 -35 -30 -25 -20 -15 δ13C (‰)

Figure 3.7. Mean (± 1 SE) carbon and nitrogen isotope values of abalone Haliotis laevigata; primary producers Amphibolis antarctica, Gracilliara sp., Sargassum sp.; cephalopods Loliginidae sp., and Octopus cf. tetricus; and teleosts Coris auricularis, Neatypus obliquus, Opthalmolepis lineolatus, Chrysophrys auratus, Pseudocaranx georgianus, and Upeneichthys vlamingii. Samples collected from the Greenlip Abalone, H. laevigata, sea ranching site in Flinders Bay, Western Australia during May 2017. TL denotes trophic level, with the trophic baseline (TL 1) derived from the mean δ15N primary producer value.

60 The mean δ13C values of O. cf. tetricus size classes varied by only ~1‰ ranging from -23.00 ± 0.51 (≥ 1,000 g) to -24.03 ± 0.49‰ (300-999 g, Table 3.4). The δ13C value of H. laevigata seeds (-25.00 ± 0.08‰) was slightly more enriched than older age classes, which ranged from -27.55 ± 0.15‰ to -28.43 ± 0.23‰ (Table 3.4, Fig. 3.7). Among the teleosts, Neatypus obliquus had the lowest δ13C signature of -27.05 ± 0.14‰, while C. auratus had the highest at -21.53 ± 0.44‰ (Table 3.4, Fig. 3.7). Among the primary producers, the red alga P. mertensii was the most depleted in δ 13C (-36.02 ± 0.24‰), and the seagrass A. antarctica was most enriched (-17.85 ± 0.14‰, Table 3.4, Fig. 3.7).

The δ13C values of O. cf. tetricus did not differ significantly among size classes

2 13 (X2 =1.5, P = 0.47). However, the δ C signature of O. cf. tetricus differed significantly

2 from potential other consumer groups (X3 = 36.7, P < 0.001). A subsequent multiple comparisons test revealed that the only significant difference was between O. cf. tetricus (-23.63 ± 0.42‰) and abalone (-27.41 ± 0.26‰, Z11,23 = -3.73; P < 0.001).

13 2 Significant differences in δ C were also identified among the teleosts (X5 = 17.5, P <

0.01): between N. obliquus and C. auratus (Z3,3 = -3.56, P < 0.01), and N. obliquus and

13 P. georgianus (Z3,3 = -3.03, P = 0.35, Table 3.4). The δ C values differed significantly

2 among the primary producers (X2 = 12.26, P < 0.01): between the Rhodophyta (-32.71

± 1.46‰) and the seagrass A. antarctica (Z2,2 = -3.25, P < 0.01), and Rhodophyta and

Phaeophyceae (-26.26 ± 0.19‰, Z2,2 = 2.27, P = 0.05, Table 3.4).

3.4. Discussion

This study used gastric organ content (crops and stomachs) and stable isotope analyses to evaluate the feeding of O. cf. tetricus, and its significance as a predator of H. laevigata on artificial abalone habitats in a sea ranch of south-western Australia. It also provides the first comparative assessment of using different dietary organs for evaluating the diet of octopuses, identifying significant differences in the relative contributions of taxon between crops and stomachs. Multivariate statistical analyses were employed to understand how the dietary composition of O. cf. tetricus changes

61 with increasing body size. However, no difference in diet was identified. The isotopes δ15N and δ13C were examined to understand the long-term dietary trends of O. cf. tetricus and the trophic level occupied by this species in the food web.

3.4.1. Comparison of diet between gastric organs The dietary composition of O. cf. tetricus differed greatly between the crop and stomach. Much greater taxonomic resolution was found in the crop contents than the stomachs, which in terms of volume were dominated by highly digested, unidentifiable material. Abalone made the greatest %V contribution to the crops, but was negligible in the stomachs. Consequently, the contribution of abalone to the diet of O. cf. tetricus would be greatly underestimated if combining dietary information on crops and stomachs, or using stomachs alone. This highlights the difficulties of gastric tract analysis in assessing dietary composition among octopuses.

As part of the ingestion process of octopuses, prey is masticated by the beak, and hard parts may be selectively excluded (Boyle and Rodhouse 2005; Boucher- Rodoni and Mangold 2009). Food moves through the oesophagus and is briefly stored in the highly distendible crop, before passing to the stomach where the bulk of digestion takes place (Boucher-Rodoni and Mangold 2009, Appendix 1). The rapid digestion process means that prey identification from the stomach contents can be difficult, with the potential for soft-bodied organisms to be under-represented due to their shorter gut retention time than robust hard parts, such as the exoskeletons of crustaceans (Breiby and Jobling 1985; Pierce et al. 1994; Boyle and Rodhouse 2005; Regueira et al. 2017). Consequently, crop contents provide a better representation of the diet as prey, while in a masticated form, is typically less digested compared with stomach contents, and the bias towards hard-shelled prey is less. In a study of the Flying Squid Todarodes sagittatus (which lack a crop) in the Norwegian Sea, > 50% of individuals contained prey in the stomach that was in an advanced state of digestion (i.e., of a pulp-like consistency, Breiby and Jobling 1985). This precluded the complete identification of

62 prey, particularly where hard structures were absent, and consequently soft bodied prey were likely to be underestimated (Breiby and Jobling 1985).

3.4.2. Size related differences in diet No significant ontogenetic changes were found in the dietary composition of O. cf. tetricus. This is atypical for octopus as crustaceans are frequently consumed by juveniles, but as they increase in body size, teleosts and other cephalopods become more important (Nixon 1987; Villanueva 1993; Smith 2003; Villegas et al. 2014). In addition to abalone, in this study O. cf. tetricus consumed mainly crustaceans including brachyurans, and bivalves. The non-significant difference between size classes in the present study was also reflected in the stable isotope analysis. This may be an artefact of few large individuals (>1,000 g) being available for study and no octopus ≥ 2,000 g being sampled. The lack of ontogenetic differences may also be due to a low diversity of prey in the sea ranching lease of Flinders Bay, or the high abundance of H. laevigata available to O. cf. tetricus.

However, the absence of these larger individuals could be related to the regular removal of octopuses from the ranch, preventing growth to the upper size limits for this species (Leporati et al. 2015). Alternatively, the absence of very large individuals may be associated with an offshore migration of mature individuals (Leporati et al. 2015). On the west coast of Australia, it is believed that mature O. cf. tetricus females migrate offshore to rocky-reefs, which provide a suitable substratum to lay and brood their eggs, and are followed by males in search of mates (Anderson 1997; Leporati et al. 2015).

The diversity of prey found in the crops (13 prey categories) was lower than that of other gastric tract analysis studies (Cortez et al. 1995; Grubert et al. 1999; Šifner and Vrgoč 2009), however sample sizes were also much smaller in the current study, particularly for octopus ≥ 1,000 g (total N = 44, Nlarge = 4). For example, in a study of the Maori Octopus, Octopus maorum (N = 137), on the eastern shelf of Australia, 14 taxon were identified, of which 10 were identified to species level (Grubert et al. 1999), and in a study of the Gould Octopus, Octopus mimus (N = 947), in the Pacific Ocean

63 (Chile), 25 different prey items from five taxonomic groups were identified (Cortez et al. 1995) over 7 and 12 months respectively.

While the breadth of diet may increase with a larger number of samples, the low diversity in the diet of O. cf. tetricus may be due to three other main factors. Firstly, the ability to effectively discriminate between unique molluscan and crustacean species due to mastication and the gleaning of prey items is likely to be a contributing factor (Boyle and Rodhouse 2005). In the study of O. mimus, mollusc shells were collected from around octopus middens during sampling, which aided in the identification of prey when occasional shell fragments were located in the gastric tract (Cortez et al. 1995). A similar approach could be implemented and extended to include a survey of benthic invertebrates to assist in future identification of potential prey items. While at least three species of brachyurans were present in the diet of O. cf. tetricus, prey fragments were either too small or too fragmented to accurately identify species. In addition, non- cephalopod molluscan tissue was commonly encountered, but could not be identified due to the absence of distinguishing morphological features, such as an odontophore, radula or ctenidia. Complementary DNA-based approaches could be applied to aid in the identification of digested prey items, with the potential to provide a more comprehensive understanding of diet (Braley et al. 2010; Pompanon et al. 2012).

Midden counts could also be used to complement gastric tract analysis, helping to reveal additional prey sources and a more complete picture of the diet of O. cf. tetricus (see Smith 2003). While midden counts are biased towards hard-shelled prey such as bivalves and gastropods (Ambrose 1984; Smith 2003), such analyses would assist in determining dietary breadth. For example, a four-year study of prey remains in the middens of the California Two Spot Octopus, Octopus bimaculatus, in the North Pacific Ocean (California) resulted in 55 different species being identified (Ambrose 1984). While the vast majority of prey identified were gastropods and bivalves (~78%), crustaceans, teleosts, and other cephalopods were also found (Ambrose 1984).

64 The second reason for the low diversity of the crop contents of O. cf. tetricus may be a function of the readily available food sources associated with the sea ranching Abitats in Flinders Bay. Haliotis laevigata are likely to attract other animals, which are also potential prey of octopus, including crabs (Carter et al. 1985; James et al. 2007); a preferred prey of octopuses (Ambrose 1984; Ambrose 1986; García García and Valverde 2006). Consequently, O. cf. tetricus feeding on abalone and crabs around the Abitats expend relatively little energy in obtaining their nutritional needs, as they do not need to move far from their dens to find suitable prey. Octopuses have been identified as time saving foragers, spending much of their time within their dens (Mather and O’Dor 1991; Scheel et al. 2016). Thus, the occupation of these artificial habitats appears to be well suited to the time minimising foraging strategy of O. cf. tetricus.

Thirdly, the low diversity in the diet of O. cf. tetricus may be an artefact of the husbandry practices carried out as part of the sea ranching operations. Abitats are routinely scraped clean to remove the growth of algae and sessile invertebrates to increase the surface area available to abalone (see Chapter 2, 2.2.4). Due to the considerable distance of the Abitats from the source of colonists (i.e., natural reefs in Flinders Bay), and the relatively short timeframe between Abitat cleaning, the diversity of sessile invertebrates growing on the Abitats is likely to be comparatively lower than what may be expected if successional processes were left to equilibrate (Svane and Petersen 2001).

Shade plots highlight the importance of molluscs and crustaceans to the diet of

O. cf. tetricus, concurrent with the findings for other coastal octopuses (Ambrose and Nelson 1983; Ambrose 1984; Ambrose 1986; Nixon 1987; Smith 2003; Scheel et al. 2016). However, the relative contribution of various prey items differs considerably between species (see Appendix 1, A1.7.1), which likely represents a compromise between prey availability and prey preferences (Ambrose 1984). For example, while crustaceans are a preferred prey source of O. bimaculatus in California, their abundance

65 is relatively low in the local environment, and thus gastropods are consumed most frequently (Ambrose 1984).

The contribution of abalone to the diet of O. cf. tetricus is greater than that observed in the gastric tract of other species (Grubert et al. 1999; Smith 2003; Villegas et al. 2014), which is likely to be the result of O. cf. tetricus exploiting the readily available abalone on the Abitats in Flinders Bay. Octopuses adapt readily to novel feeding opportunities (Rigby and Sakurai 2005), and since H. laevigata are very abundant on the Abitats, it is no surprise that the majority of the diet is attributable to abalone. Ambrose (1984) noted a similar finding for O. bimaculatus situated within close proximity to mussel beds, with these individuals feeding almost exclusively on mussels. Although, O. cf. tetricus is likely to consume crustaceans whenever the opportunity arises due to their high energetic returns and low handling time (from capture to ingestion, Ambrose 1984, McQuaid 1994).

Crustaceans are an important prey for cephalopods due to their low lipid content (1.08 g per 100 g; García García and Valverde 2006; United States Department of Agriculture 2016a). Unlike other active marine predators, which use lipids for their long-term energy stores, cephalopods utilise amino acids as their principal energy source, which supports rapid growth rates (Lee 1995; Boyle and Rodhouse 2005). As a result, lipid digestibility is low in cephalopods (O’Dor et al. 1984; Lee 1995) and high lipid diets reduce their growth rates (García García and Aguado Giménez 2002). Abalone is lower in lipids than crustaceans (0.76 g per 100 g) and has a high caloric content (United States Department of Agriculture 2016b). Thus, the combination of crustaceans and abalone, and their associated macronutrient composition may be sufficient to meet the nutritional needs of O. cf. tetricus. Based on crop content analysis, O. cf. tetricus appears to be an important predator of H. laevigata.

3.4.3. Stable isotope composition of prey and primary producers The δ15N signatures of O. cf. tetricus were similar between size classes, reflecting the similar dietary composition between the groups (Table 3.4). The δ15N signature of O. cf.

66 tetricus is lower than that of O. maorum (12.6‰) on the south-eastern Australian continental shelf, but similar to the Southern Keeled Octopus, Octopus Berrima, at the same location (9.0‰, Davenport and Bax 2002). Dietary studies have shown that O. maorum consumes large volumes of cephalopods and fishes (Grubert et al. 1999), which explains the higher δ15N signature in this species. However, no dietary information is available for O. berrima. The lower δ15N value of O. cf. tetricus is likely explained by the high consumption of H. laevigata and potentially crustaceans, but also the low volumes of teleosts consumed.

The δ15N values of O. cf. tetricus were enriched by more than one trophic level compared with H. laevigata, but depleted compared with the teleosts and loliginid squids, highlighting distinct differences in diet among the groups (Cherel et al. 2011). The low δ15N signature of H. laevigata highlights its role as a primary consumer, and its exclusive macroalgal diet (Guest et al. 2008). Generally, the δ15N signature increased with fish size, with the highest values for the largest individuals caught (C. auratus), which may be explained by the ability of larger fish to capture larger prey from a wider range of sources (Davenport and Bax 2002). The δ15N value of Pink Snapper, C. auratus, was consistent with the values attained for this species on the southeast Australian continental shelf (11.3‰; Davenport and Bax 2002). The diet of C. auratus in south-western Australia comprises echinoderms, teleosts, crustaceans and molluscs, including cephalopods (French et al. 2012). The trophic shift for vertebrate consumers is higher than herbivores or those that feed on invertebrates alone (McCutchan et al.

2003). Thus, the consumption of teleosts by C. auratus likely explains the enrichment of δ15N compared with O. cf. tetricus and other teleosts. The δ15N value for Maori Wrasse, O. lineolata, in the current study (9.4‰) was lower than that identified by Davenport and Bax (13.1‰, 2002). Such differences may be indicative of local variation in dietary composition, driven by intraspecific competition and resource availability (Anseeuw et al. 2010; Lek et al. 2011).

67 The δ15N values indicate that the food web of Flinders Bay spanned ~4 trophic levels, with O. cf. tetricus occupying a mid-trophic position, slightly below the teleosts and loliginid squids. The δ15N signatures of O. cf. tetricus and loliginid squid parallel Lozano-Montes et al. (2011) who found that the trophic level for cephalopods (octopus and squid) on the west coast of Australia range from 3.1 to 3.6. The enrichment of δ15N by more than 3.4‰ between H. laevigata and O. cf. tetricus indicates that octopuses are assimilating δ15N from other dietary sources in addition to abalone, and they are feeding on consumers at trophic levels 2 and 3. This enrichment likely reflects the consumption of other prey taxon such as cephalopods and crustaceans, as indicated by complimentary crop content analyses. It is likely that crustaceans and echinoderms are at the intermediate trophic level, although echinoderms are present in low numbers around the Abitats (M. Wall, Ocean Grown Abalone, 2017 pers. comm.). In a study by Lepoint et al. (2000), these taxon occupied a mid trophic position between fishes and non- cephalopod molluscs, with a similar position expected for the Flinders Bay sea ranch ecosystem. The relatively low enrichment of δ15N between abalone and primary producers is consistent with Guest et al. (2008), with herbivores exhibiting significantly lower fractionation compared with high trophic level carnivores (Vander Zanden and Rasmussen 2001; McCutchan et al. 2003).

Evidence from δ13C isotopes of consumers and the crop contents of O. cf. tetricus suggests that carbon in the Flinders Bay system is derived largely from benthic sources. Octopus cf. tetricus had similar δ13C values among size classes reflecting the similarity of diet, as confirmed by gut content analysis. Based on a δ13C fractionation of ~1‰ between trophic levels (Layman et al. 2012; Cresson et al. 2014b), the enrichment of ~4‰ between H. laevigata and O. cf. tetricus suggests that an intermediary food web constituent, such as crustaceans, is likely to be an important component of the diet. Bayesian mixing models such as Stable Isotope Analysis in R could be utilised to identify the relative contributions of the various nutrients assimilated by O. cf. tetricus (Parnell et al. 2010, see Chapter 4.2).

68 Haliotis laevigata seeds were slightly more enriched than abalone seeded > 1 year earlier, which may be explained by differences in food availability. Under culture conditions, seeds are reared on diatom plates for ~9 months and are then weaned onto commercially formulated feeds (Melville-Smith et al. 2013). After being seeded onto the Abitats, abalone switch to a natural macroalgal diet. In a feeding study of Disk Abalone, Haliotis discus discus, off northern Japan a decrease in δ13C was associated with a shift in diet from diatoms to juvenile Phaeophyceae and/or small Rhodophyta, while an increase in δ13C represented a shift in diet to adult Phaeophyceae (Won et al. 2010).

The δ13C values of H. laevigata were intermediate between the Rhodophyta and Phaeophyceae values, suggesting a mixed diet. While the δ13C signatures of Sargassum and Gracilliara are similar to that of H. laevigata, the slight depletion of δ13C in H. laevigata suggests that other macroalgal species are also important components of the diet. At least 57 species of macroalgae were identified on the Abitats over a six- month period from July 2015 to February 2016 (Melville-Smith 2016). Diversity was highly seasonal, with species richness and abundance notably higher in the winter months (Melville-Smith 2016). Therefore, the diet of H. laevigata is likely to change seasonally, which may have important implications for the interpretation of δ13C sources if the longer-term assimilation of nutrients is not considered (see Chapter 4.2).

The δ13C values of O. cf. tetricus were similar to the teleosts King Wrasse, C. auricularis, O. lineolatus, and Bluespotted Goatfish, U. vlamingii, indicating an overlap in the primary carbon sources utilised among these species (Davenport and Bax 2002). These teleost species are benthic feeders and utilise similar food resources to O. cf. tetricus, explaining the similar δ13C signatures among consumers (Currie and Sorokin 2010; Lek et al. 2011). For example, a study from south-western Australia found that O. lineolatus fed mainly on large benthic crustaceans and gastropods, while C. auricularis fed mainly on small crustaceans and gastropods (Lek et al. 2011).

69 Chapter 4. General conclusions and recommendations 4.1. Conclusions

The study on the distribution and abundance of octopus, and the mortality of Greenlip Abalone, Haliotis laevigata, based on data collected by commercial divers (Chapter 2), demonstrated that octopuses are broadly distributed across the Ocean Grown Abalone (OGA) sea ranch in Flinders Bay, Western Australia. The presence of octopus had a significant impact on the survival of abalone, with an estimated 78% more empty shells recorded when octopus are present than when absent, adjusting for location (“Line”) and Season. The abundance of octopus was typically greater on Lines that comprised fewer abalone habitats (“Abitats”), which may be related to detection bias and the time divers spend within a Bay searching for octopus and counting shells. Bays with greater numbers of Abitats provide greater areas of shelter for octopus, potentially making their detection more difficult, particularly because of their cryptic adaptations. While the number of empty shells was higher in some locations than others, this may be related to factors other than octopus predation alone. Environmental influences, such as storm events and currents likely play an important role in the dispersal of shells, and the number of Abitats within a Line may result in partially buried or dispersed shells being overlooked due to the time constraints imposed on divers. The abundance of other abalone predators, such as crayfish and crabs, will also contribute to the number of empty shells in an area.

The boreholes found in the sample of H. laevigata shells collected by OGA divers were consistent with those made by other octopus species (e.g., Octopus bimaculatis, Pilson and Taylor 1981; Ambrose 1983; and Octopus vulgaris, Ambrose 1983; Kojima 1992), providing evidence of drilling by Octopus cf. tetricus and the possession of cephalotoxins in this species. Boreholes were found in shells across the entire length range (33 to 110 mm), which indicates that octopus prey on all sizes of abalone. An exact multinomial test showed that the frequency of boreholes did not differ significantly among the four regions, which may be related to small sample sizes (total of 20 shells with holes). However, 75% of holes were concentrated over the

70 adductor muscle, pericardial sac and the heart, organs that are most sensitive to the injection of toxin. The areal distribution of boreholes may be related to a learnt behaviour, whereby octopuses learn the most efficient location to drill over time, with the adductor muscle potentially succumbing to the cephalotoxins of octopus more quickly than other locations (Kojima 1992).

Negative binomial generalised linear models demonstrated that the presence of octopus results in a 78% increase in the number of empty abalone shells collected per Abitat per day after adjusting for Line and Season. There was also a significant association between the number of empty shells and Line, as well as between the number of shells and Season. In contrast, results from time series models used to assess the relationship between the presence of octopus and abalone survival (counts every six months) were not significant, which is counterintuitive to what was expected. This finding may be an artefact of the random sampling design for estimating abalone survival (i.e., counting abalone on random Abitats within a Bay at each time point, rather than taking abalone counts from the same Abitats each time), and uncertainty in the numbers of live abalone seeded onto each Abitat. This highlights the importance of quantifying the number of juvenile abalone being seeded onto unique Abitats, and undertaking repeated measures on the same Abitats over time in order to reduce variability among survival counts and to allow abalone survival to be measured with greater precision.

The study on the diet and nutrient assimilation (δ13C and δ15N) of O. cf. tetricus

(Chapter 3) demonstrates that O. cf. tetricus, like other coastal octopuses, feeds predominantly on molluscs and crustaceans (Nixon 1987; Grubert et al. 1999; Smith 2003). Pronounced differences in diet were found between the contents of the crops and stomachs, with the crops containing a much high proportion of identifiable items than the stomachs, which contained large proportions of highly digested, unidentifiable material. No differences in dietary composition were identified between the weight classes of octopus, paralleling the results of the stable isotope analyses. However, few

71 octopus > 1,000 g were examined and no octopus > 1,600 g. As O. cf. tetricus grows to a maximum size of ~4 kg (Hart et al. 2016), ontogenetic differences may be more pronounced if larger individuals (i.e., > 2,000 g) are sampled and included in dietary analyses.

The relatively low diversity of prey items in the crops and stomachs of O. cf. tetricus is likely due to a combination of factors. Firstly, prey items are highly masticated as part of the ingestion process making identification to species level extremely difficult. A reference collection of benthic epifauna, particularly molluscs and crustaceans, collected from the local environment, may enhance species identification in the future. Secondly, abalone is available in excess and concentrated on the Abitats within the sea ranching lease. The predation on abalone and organisms attracted to the structures, such as brachyurans, provides an opportunity for in-situ foraging by octopus and suits a time minimising foraging strategy. Finally, the routine cleaning of Abitats to remove algae and sessile invertebrates growing on their surface is likely to reduce species diversity, and ultimately, the range of prey available to O. cf. tetricus.

The most important dietary component in the crops of octopus was abalone and to a lesser extent crustaceans. These results clearly show that O. cf. tetricus is exploiting the high abundance of abalone, but also feeds on crustaceans whenever the opportunity arises, likely due to their low handling time from capture to ingestion. In addition, the high amino acid, low lipid macronutrient combination of abalone and crustaceans is likely to adequately satisfy the dietary needs of octopus, whilst supporting rapid growth.

The examination of δ15N and δ13C stable isotopes highlights the importance of incorporating information obtained from gastric contents for explaining trends among consumers and assessing trophic interactions. Observations from gastric tract analyses suggest that O. cf. tetricus is an important predator of H. laevigata. However, this trend was less obvious from stable isotope analyses due to the relative enrichment of δ13C (~4‰) between the two species. These findings are likely due to the contribution of

72 other prey items to the diet of octopus, such as crustaceans and other cephalopods (as identified by gastric tract analysis). The δ15N values of O. cf. tetricus show that the species occupies a mid-trophic level, slightly below the teleosts and loliginid squid, and is more than one trophic level above H. laevigata.

4.2. Future research and monitoring 4.2.1. Monitoring abalone survival Monitoring abalone after seeding would be valuable to the sea ranching operation. Remote underwater video systems could be utilised to understand the behavioural responses of both abalone seeds and predators, including octopus, immediately after the deployment of the abalone seeds in their release units (Fig. 2.3a). A subsequent census of survival by divers shortly after seeding (within two weeks) could allow initial predation rates to be quantified.

The information on abalone survival would be greatly enhanced by quantifying the number of abalone seeded onto the Abitats for future deployments and counting abalone on the same uniquely identified Abitats within each Bay to estimate survival on each Abitat. This will allow patterns of variability in abalone survival to be identified across the ranch and survival estimates to be measured with greater precision.

4.2.2. Dietary studies Future dietary studies of O. cf. tetricus in this area would benefit from collecting larger numbers of octopus, particularly those > 1,000 g and placing them on ice immediately following their capture to slow their digestive processes (Pierce et al. 1994; Boyle and Rodhouse 2005; Boucher-Rodoni and Mangold 2009). This would potentially reduce the proportion of “unidentified” food items in the stomachs.

The collection of additional octopus over a longer period and larger weight range may identify subtle differences in diet between size classes, particularly since the diversity of diets among octopuses appears to be dependent on the timeframe over which information is collected (Nixon 1987; Mather and O’Dor 1991). Furthermore, the

73 collection of samples throughout the year may enable seasonal variation in the diet to be identified. Comparison with diets of octopus from areas outside the lease would allow the relative contribution of abalone to the diet to be evaluated under natural conditions to help evaluate their selection of abalone on the sea ranching release.

4.2.3. Stable isotopes Further sampling of source and consumer pools at temporal scales that reflect the assimilation and turnover rates of nutrients should be carried out to allow seasonal trends in nitrogen and carbon assimilation to be investigated (Post 2002; Layman et al. 2012). The collection of a broader range of prey types for stable isotope analysis, including crustaceans, would also be important to provide a complete depiction of the Flinders Bay food web, and the nutrient assimilation by O. cf. tetricus. Bayesian mixing models such as Stable Isotope Analysis in R, could be incorporated to identify the relative contributions of the various nutrients assimilated by octopus (Parnell et al. 2010). These mixing models provide powerful insights into the relative contribution of sources to consumers and are most effective when combined with gastric tract analyses, allowing the proportional contributions estimated from isotopes to be interpreted (Layman et al. 2012; Phillips et al. 2014). In addition to analyzing other consumers, assessing the δ15N and δ13C isotopes of detritus, particulate organic matter (POM) and epiphyte signatures may provide further insight into nutrient sources utilised by abalone (see e.g., Guest et al. 2008).

4.3. Implications

The results from this Thesis highlight the importance of O. cf. tetricus as a predator of H. laevigata on the sea ranching lease in Flinders Bay, south-western Australia. Firstly, the identification of distinctive boreholes in the shells of abalone provides an insight into the feeding behaviour of octopuses. If octopuses are not able to remove abalone from the Abitats by direct force, they resort to drilling, which accounted for 18% of the sub-sample of shells investigated. This percentage likely represents the minimum predatory impact on H. laevigata, but confirms that octopuses are a major source of

74 mortality. It is possible that smaller abalone, or those in a “feeding” position (Shepherd 1973), can be pulled directly from the Abitats. When H. laevigata feed, they elevate the forepart of their foot and their shell to catch drifting algae (Shepherd 1973). Whilst in this position their stronghold on the reef substratum is reduced, rendering them vulnerable to predation.

Secondly, negative binomial models provide further evidence of the deleterious impacts of octopus to the survival of cultured abalone. The proportion of empty abalone shells associated with the presence of octopus was 44% of all empty shells collected. This figure may be underestimated, as it is likely that shell recovery is lower than the total mortality of abalone. Finally, crop contents suggest that H. laevigata forms a major component of the diet of O. cf. tetricus, highlighting the ability of these opportunistic and cunning predators to adapt to novel feeding opportunities.

No larger octopus (> 1,600 g) were collected during the four months in which octopus were collected by commercial divers. However, the absence of these larger individuals could be related to the removal of octopuses from the ranch, limiting the numbers of larger individuals. Alternatively, the absence of larger individuals may be associated with an offshore migration of mature individuals in search of suitable reefs for the brooding of eggs (Leporati et al. 2015). Consequently, the size classes examined in this study may be representative of the local population of O. cf. tetricus in this ecosystem. Further sampling of octopus within the lease and at locations away from the sea ranch is needed to test this hypothesis.

While this study provides an assessment of the dietary composition of O. cf. tetricus in the Flinders Bay sea ranch ecosystem and the importance of H. laevigata to the diet in this system, these findings cannot be extended to populations inhabiting natural environments. The high stocking densities of abalone on the Abitats is likely to drive the foraging behaviour of O. cf. tetricus and subsequently the composition of its diet. The Abitats also provide potential shelter for octopus, and the combination of abalone abundance and shelter may concentrate octopus within the sea ranching lease.

75 Sampling of O. cf. tetricus from locations beyond the sea ranch would provide information on what constitutes “natural” densities and diet, and to what extent the diet and nutrient assimilation of O. cf. tetricus on the sea ranch differ from other “natural” octopus populations.

The knowledge gained from these studies provides a greater understanding of the significance of O. cf. tetricus as predators of abalone, and the trophic positioning of this important mesopredator within the food web of a rapidly expanding sea ranching operation. This information can be extended to future sites, including the new lease being established in Esperance to improve operational procedures. It also highlights the value of collecting information outside the sea ranch to understand the population size and structure of O. cf. tetricus, their densities, and diets under natural conditions. This will enable a greater understanding of how octopuses have responded to the high densities of abalone on the Abitats and the provision of additional shelter within the OGA lease.

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87 Appendix 1. Cephalopods and their role as predators and trophic intermediaries in the food webs of coastal marine systems A1.0. Abstract

Cephalopods are formidable predators that display complex, flexible behaviours that have allowed them to thrive in the world’s oceans. In recent decades their biomass has increased significantly, which is likely to have considerable ecological implications, particularly in dynamic, shallow water coastal environments. In contrast to the landings from most global finfish fisheries, which are at their limits, those for cephalopods have increased markedly since the 1990s. Their short life history strategy characterised by rapid growth stimulates voracious feeding regimes, and their large global biomass has the potential to impose significant top-down controls on a broad range of commercially and ecologically important species. This review summarises the role of coleoid cephalopods (i.e., the Loliginidae, Octopodidae, Sepiidae, and Sepiolidae), as predators in coastal marine food webs. The morphological and physiological traits and feeding behaviours that contribute to their success as predators are summarised from the existing literature. Equipped with a range of unique morphological features and highly developed sensory organs, cephalopods are well adapted for a predatory lifestyle. Information on the diet composition of coastal coleoid cephalopods was synthesised from published literature. Distinct dietary patterns were found, with crustaceans, teleosts, and molluscs common in the gastric tracts of all members. However, the relative contributions of the various prey taxa varied considerably among individual families, reflecting the position they occupy within the water column. Loliginidae had the most distinct diet, with teleosts, and cephalopods making a greater contribution to their diets than those of the other families. A pronounced shift in diet with ontogeny is a ubiquitous feature across the four families, with increased body size facilitating cannibalism and intraspecific predation. Finally, their role as predators and trophic intermediaries in coastal marine ecosystems is described. Further studies that utilise biochemical tracers are needed to evaluate trophic relationships, long-term dietary trends, and their response to environmental variability. This information will help inform reliable assessments of cephalopods and other fished species, and ensure that cephalopod fisheries are developed in an ecologically sustainable way.

Table of Contents

Appendix 1. Cephalopods and their role as predators and trophic intermediaries in the food webs of coastal marine systems ...... 88 A1.0. Abstract ...... 88 A1.1. Introduction ...... 90 A1.1.1. Focus of the review ...... 95 A1.2. Biodiversity and zoogeography ...... 95 A1.3. Feeding morphology and physiology ...... 96 A1.3.1. Sensory organs ...... 97 A1.3.2. Chromatophore organs ...... 98 A1.3.3. Feeding apparatus ...... 99 A1.4. Feeding behaviour ...... 100 A1.4.1. Foraging behaviour ...... 100 A1.4.2. Diel feeding activity ...... 101 A1.4.3. Shoaling ...... 102 A1.4.4. Prey selection ...... 103 A1.5. Growth rates and food intake ...... 106 A1.6. Diets ...... 107 A1.6.1. Broad dietary trends ...... 107 A1.6.2. Ontogenetic dietary shifts ...... 110 A1.6.3. Cannibalism ...... 110 A1.6.4. Influence of sampling method on interpretation of diets ...... 111 A1.6.5. Dietary differences among families ...... 114 A1.7. Predation in marine systems ...... 117 A1.7.1. Predation impacts ...... 117 A1.7.2. Trophic relationships ...... 119 A1.8. Conclusions and directions for future research ...... 120 A1.9. References ...... 123

89 A1.1. Introduction

Cephalopods are exclusively marine molluscs distributed widely throughout the world’s oceans (Boyle & Rodhouse, 2007). They are found in practically all habitats from the polar seas to the tropics; in neritic and open oceanic waters from the littoral zone through to abysmal benthic environments up to 5,000 m deep (Amaratunga & Caddy, 1983; Boyle & Rodhouse, 2007). The class Cephalopoda comprises approximately 800 species from two subclasses: the Coleoidea, represented by the Octopoda, Sepiida, Sepiolida, Teuthida, and Vampyromorphida; and the Nautiloidea, represented by the Nautilida; a primitive group distinguished by their distinctive external shell (Boyle and Rodhouse 2005; Rodhouse et al. 2014).

Cephalopods share a number of basic features in their body organisation such as the presence of a radula (i.e., a file-like feeding organ), an internal or external shell, and a central nervous system that is arranged around the oesophagus (Boyle & Rodhouse, 2007). However, the two subclasses have a number of distinct biological characteristics, the most obvious being the complete loss of an external shell among the coleoids (Boyle and Rodhouse 2005). The coleoids are monocyclic, single-season breeders characterised by high growth rates, early maturity, and post-spawning mortality (i.e., they are semelparous, Boyle & Boletzky, 1996; Boyle & Rodhouse, 2005). They have a short life-history strategy characterised by rapid growth, with most medium size coastal species senescencing after one to two years of life (Fig. A1.1). Due to their rapid growth rates, the demands on protein synthesis are high (Lee 1995). Unlike other active marine predators that utilise lipids for their long-term energy stores, cephalopods synthesize amino acids very efficiently, which has facilitated the evolution of rapid growth rates throughout the lifecycle (Lee 1995; Boyle and Rodhouse 2005).

Figure A1.1. Generalised stages in the lifecycle of a benthic octopus, adapted from the descriptions found in Boyle and Rodhouse (2005); Promboon et al. (2011) and Caputi et al. (2015). Images sourced from Carefoot (2017) and Integration and Application Network (2017).

Cephalopods are considered to be the most evolved of all invertebrates, possessing a range of highly-developed chemical, tactile, and visual senses, which facilitate learning and aid in the capture and selection of prey (Lee 1995; Darmaillacq et al. 2004). They are very versatile predators, with the ability to change their prey when their preferred prey is unavailable. Their diet also varies with ontogeny and these two characteristics of cephalopod feeding lead to their occupation of several trophic levels and ecological niches during their lifecycle (Rodhouse et al. 2014).

Predation is a central feature of community organisation, playing a key role in the structure and function of marine systems. Predators have the ability to control prey populations directly by reducing abundance, but also through indirect processes which disrupt competition and succession (Underwood and Fairweather 1989). Seminal works examining the interactions among rocky intertidal invertebrates (Paine 1966; 1974), and sea otters in North Pacific kelp-forest ecosystems (Estes and Duggins 1995) revealed the significance of predation (i.e., “top-down processes”), and introduced the term “keystone species” in recognition of the impact of those species on community structure

91 and function, far beyond their relative biomass in the community. The impacts of predation within marine food webs can vary considerably between communities (Heithaus et al. 2008), dependent on a range of factors including predation intensity, the metabolic needs of the predator, dietary preferences, and prevailing environmental conditions (Ambrose 1984; Williams et al. 2004). For short-lived, opportunistic, high turn-over species such as cephalopods, their predatory impact on prey populations varies greatly; both spatially and over time as their populations fluctuate in biomass (Rodhouse and Nigmatullin 1996; Heithaus et al. 2008).

An example of the potential scale of predation impacts by cephalopods is provided by the Humboldt Squid, Dosidicus gigas, during their migration to the Gulf of California (Ehrhardt 1991; Rodhouse and Nigmatullin 1996). During their migration, their diet shifts from one dominated by myctophids (25%) and crabs (20%) early in the migration in winter (January), to one comprising predominantly sardines (80%) and mackerel (18%) towards the end of the migration in summer (July, Ehrhardt 1991). In 1980 and 1981, D. gigas consumed an estimated 60,000 metric tonnes of Californian Sardines, Sardinops sagax caerule (Ehrhardt 1991), and the increased mortality through heavy predation pressure is thought to have been a factor contributing to greatly reduced commercial sardine landings during this period (Ehrhardt 1991).

Cephalopods are important species within marine food webs, both as predators of invertebrates and fish, and as prey for higher trophic level consumers such as marine mammals, predatory fish and seabirds (Boyle and Rodhouse 2005). Rich in protein, coastal cephalopods have comparable mean calorific values (i.e., 22.7 ± 1.5 kJ/g dry wt) to teleosts (24.7 ± 0.9 kJ/g for demersal fishes and 26.6 ± 0.9 kJ/g for pelagic fishes; Blaber and Bulman 1987), and their soft, unarmored and highly digestible body renders them vulnerable to predation (Boyle and Rodhouse 2005). Recent evidence suggests that their biomass and landings from commercial fisheries are increasing as a result of changing ecological conditions, such as ocean warming, and heavy fishing pressure on predators of cephalopods (Fig. A1.3, André et al. 2010; Coll et al. 2013; Doubleday et

92 al. 2016). Although, overexploitation and unfavourable environmental conditions such as a severe El Niño event in 2015 have resulted in temporal declines of squids in recent times, particularly in the waters around Chile, Peru, Argentina, and U.S.A. (FAO 2016a). Improving our understanding of cephalopod predator-prey interactions is fundamental to assessing their ecological role within the marine environment, and evaluating how ecosystems may respond to environmental perturbations (Livingston 2003; Navarro et al. 2013).

Cephalopods, particularly the squids, are also commercially important, supporting various industrial, local and artisanal fisheries across the globe, with major fisheries occurring around Argentina, China, India, Japan, Peru, New Zealand, and Russia (Fig 2.2; Rodhouse et al. 2014). In recent decades, the economic value of cephalopods has grown significantly. Estimated global landings have increased from 1 million tonnes in the mid 1960s to over 3 million tonnes since 1995, and 4 million tonnes in some years from 2005 to 2014 (Fig. A1.3, FAO 2016). Landings peaked in 2014 at 4.75 million tonnes (Fig. A1.3, FAO 2016). Overall, squids contribute to approximately three-quarters of the total catch, with the remainder of landings comprising cuttlefish and octopus (Fig 2.3). This trend is consistent with traditional teleost fisheries, whose tonnage has also quadrupled since the 1950s (Worm and Branch 2012). Unlike finfish, which are at their global limits of exploitation (Worm and Branch 2012; Bell et al. 2016), cephalopods represent one of the few marine resources with potential for increased sustainable harvest at local levels (Clarke 1996b; Caddy and

Rodhouse 1998; Hunsicker et al. 2010).

Figure A1.2. Global cephalopod landings in 2014. White indicates no catch, and blue (1.5e-21- 4.1e-7 t/km2) to red represents an increase in cephalopod landings (1.2e-2–6.2e+1 t/km2; Pauly et al. 2015).

Figure A1.3. Trends in global landings of cephalopod species groups from 1950 to 2014, nei = not enough information (taken from FAO 2016).

94 A1.1.1. Focus of the review This review focuses on synthesising the current knowledge of coastal cephalopod diets, and the role of cephalopods as predators and trophic intermediaries in coastal marine food webs, as their biology and ecology has been reviewed extensively (Boyle 1990; Rocha et al. 2001; Boyle and Rodhouse 2005). It also focuses exclusively on coastal coleoid species (i.e., the Loliginidae, Octopodidae, Sepiidae, and Sepiolidae) because of their relatively similar biology, and the intensity of anthropogenic impacts, such as fishing, nutrient enrichment, and habitat modification on their populations in coastal systems. As nautiloids are very distinct from coleoids in their biology, life history strategy, and behaviour, they ‘must be considered separately’ (Hanlon and Messenger 1996), and are not examined in this review. Thus, in this review, the term cephalopod refers to the coastal coleoid species only.

The review of coastal cephalopods and their place in food webs considers the following major topics: (i) biodiversity and zoogeography; (ii) feeding morphology and physiology; (iii) feeding behaviour; (iv) growth rates and food intake; (v) diets; and (vi) predation in marine systems, and concludes with a summary of the major findings and directions for future research. The section on cephalopod feeding includes a meta- analysis of the diets of 24 species from the families Loliginidae, Octopodidae, Sepiidae, and, Sepiolidae. This meta-analysis, which is based on 28 studies provides an understanding of how dietary composition differs among families and two main dietary methodologies: the examination of gastric tracts and octopus middens.

A1.2. Biodiversity and zoogeography

Among the ~ 800 species of cephalopod, diversity is greatest in shallow coastal waters and in the deep oceans beyond the mesopelagic zone (Boyle & Rodhouse 2005; Coelho, 1985). In shallow coastal zones, benthic octopuses (Octopodidae) dominate the rocky habitats of temperate and tropical waters, and the Sepiidae (cuttlefish) and Sepiolidae (bobtail squid) are abundant in habitats with soft bottoms where they can burrow or remain inconspicuous near the substratum (Boyle & Rodhouse 2005). The true squids

95 (i.e., the Loliginidae) are mostly pelagic and are commonly found in coastal waters and on continental shelves, but the distribution and depth at which they occur varies widely among its members (Coelho 1985; Clarke 1996b; Boyle and Rodhouse 2005). The Ommastrephidae squids are generally found in the epipelagic and mesopelagic zones of shelf waters (Coelho 1985; Clarke 1996b; Boyle and Rodhouse 2005).

The number of cephalopod species varies greatly among genera and families, with over half of the described species being attributed to monotypic genera, and the majority of these occur within a diverse range of families of mainly deep-sea origin including the highly unusual Vampyroteuthidae, Opisthoteuthidae, and Cirroteuthidae which occupy the mesopelagic, bathypelagic, and abyssal waters of the world’s oceans (Boyle and Rodhouse 2005). In contrast, the genera Octopus and Sepia each have over 100 species, while other coastal forms from the Loliginidae and Sepiolidae each contribute a considerable number of species to the class (Voss 1977; Boyle and Rodhouse 2005). The faster, more active coastal cephalopods are thought to have evolved to compete successfully with teleost fishes through the loss of the external shell (Vermeij 1994; Boyle and Rodhouse 2005). This allowed the exploitation of a high- energy lifestyle and invasion of productive coastal regions from the relatively unfavourable deep sea, where the majority of original cephalopod fauna were restricted (Vermeij 1994; Boyle and Rodhouse 2005).

A1.3. Feeding morphology and physiology

Cephalopods possess a range of advanced behavioural, morphological, and physiological traits that contribute to their success as predators within the marine environment (Rocha et al. 2001; Boyle and Rodhouse 2005). They have the largest, most complex nervous system of all invertebrates (Young 1971) including a well- developed brain that features a chemo-tactile memory system. This facilitates rapid learning and cognition, and the development of complex plastic behaviours (Hanlon and Messenger 1996; Rodhouse et al. 2014). Extensive research on octopuses highlights their highly adaptable and intelligent nature. This includes: the active selection of home

96 sites and subsequent modification of habitat; the use of defensive tools such as shells and coconuts for protection against predators; the use of spatial memory and visual landmarks in navigation; and the modification of foraging behaviour when presented with novel feeding opportunities (Mather 1991b; Mather 1994; Rigby and Sakurai 2005; Finn et al. 2009). For example, data from acoustically tagged Giant Pacific Octopus, Octopus doeflini, off the coast of Japan revealed that this normally benthic species undertakes distinct, large vertical movements within the water column (Rigby and Sakurai 2005). Observations by SCUBA divers confirmed that this vertical migration was in response to the presence of a pelagic gillnet, and octopuses were scaling the net and feeding opportunistically on the ensnared fish (Rigby and Sakurai 2005); a highly adaptive behaviour demonstrating clear intelligence.

A1.3.1. Sensory organs Cephalopod sensory organs are very sophisticated, with the ability to detect prey through sight, scent, sound, and distant touch (Budelmann 1996). Despite possessing only a single colour photoreceptor in their retina and therefore being colour blind cephalopods have acute vision (Marshall and Messenger 1996; Hanlon and Messenger 1996). A strong rectilinear arrangement of photoreceptor cells in the retina allows polarised light to be discriminated and subsequently, camouflaged prey to be detected (Shashar et al. 2000; Boyle and Rodhouse 2005). Polarisation sensitivity is utilised during foraging as a means to detect counter shaded camouflage by light-reflecting fish and prey that utilise transparency as a predator avoidance mechanism (Shashar et al. 2000).

Coleoids possess an epidermal line system, analogous to the lateral line in fish that is sensitive to particle motion, giving the sense of distant touch and aiding in the detection of prey (Hanlon and Messenger 1996; Boyle and Rodhouse 2005). The epidermal line is sensitive to water movements as low as 0.06 �m, which is equivalent to a cuttlefish buried in the sand being able to detect a fish of 1 m in body length from 30 m away (Budelmann 1996). In addition, specialised receptor cells on the surface of

97 the suckers enhance chemotactile sensitivity, with up to 10,000 chemoreceptor cells present in any one sucker of an octopus (up to 16 million per individual; Budelmann 1996). Complex balance and orientation organs known as statocysts, which parallel the inner ear of the vertebrates, are situated in the cartilage on either side of the brain (Williamson 1995; Boyle and Rodhouse 2005). These highly advanced organs provide the animal with critical sensory information, which is incorporated into a range of behaviours including locomotion, eye movement control, and body-colour patterning (Williamson 1995) as well as providing the information required for stabilization and the regulation of activities within a three dimensional space (Budelmann 1996).

A1.3.2. Chromatophore organs

Cephalopods “have evolved the most sophisticated system of colour control and pattern formation known” in the animal kingdom (Boyle and Rodhouse 2005). The colouring and patterning of cephalopods result from an arrangement of three layers of pigmented cells called chromatophore organs, an important feature of cephalopod physiology (Hanlon and Messenger 1996; Boyle and Rodhouse 2005; Osorio 2014). The chromatophore organs are used frequently to provide camouflage to avoid predation and ambush unsuspecting prey, and to facilitate communication between conspecifics (Boyle and Rodhouse 2005; Hanlon 2007). Located under the skin at a density of 50 chromatophores per mm2, these organs form part of the neuro-musculature system and consist of intracellular, pigment containing, cytoelastic sacs which are arranged radially within the muscle fibres (Boyle and Rodhouse 2005; Hanlon 2007; Osorio 2014). The pigment sacs become increasingly visible as the chromatophore muscles contract, imparting colour pigment against a patch of the skin’s surface approximately 300 �m across (Boyle and Rodhouse 2005; Osorio 2014). When muscles relax, the pigment sacs retract and the colouration against the skin is reduced, exposing the light coloured tissue below (Boyle and Rodhouse 2005; Osorio 2014). However, the appearance of the skin’s surface is further complicated by differing pigment hues, static reflecting mirror-like iridophores, and matte white leucophores situated beneath the chromatophores that

98 scatter light outwards (Boyle and Rodhouse 2005; Osorio 2014). These features combine to produce the complex patterning, texture, and colouration observed within the group (Boyle and Rodhouse 2005; Osorio 2014). The chromatophore organs are controlled directly by the brain and each muscle is innervated by motor-neurons that convey signals, without synapse, that allow for rapid (0.2 to 2.02 seconds) and complex changes to take place in response to the surrounding environmental conditions (Boyle and Rodhouse 2005; Hanlon 2007). Body patterning is highly complex, and often the intricacy of patterning is associated with habitat complexity, reproductive strategies, predation, and socialisation (Hanlon and Messenger 1996; Boyle and Rodhouse 2005).

A1.3.3. Feeding apparatus Cephalopods are well adapted for a predatory lifestyle, possessing a range of unique apparatus to capture and handle a broad selection of prey (Rodhouse and Nigmatullin 1996). Most notable are the prehensile arms which bear numerous strong suckers that are used for pulling and overcoming large prey, and the extensible tentacles of the Decapodiformes (i.e., cuttlefish and squid), used for seizing prey (Rodhouse and Nigmatullin 1996; Hanlon and Messenger 1996). The arm appendages form the versatile brachial crown, which serves as the functional mouth and aids in the capture, manipulation, and immobilisation of large prey (Boletzky 1983; Rodhouse and Nigmatullin 1996). The suckers, equipped with chemo-sensory receptors, are particularly important among the octopuses who use them for the ‘blind’ detection of prey whilst foraging in crevices and under ledges where potential prey remain unseen

(Hanlon and Messenger 1996).

The buccal mass is a complex structure comprising a chitinous beak and associated musculature used for tearing food into small pieces; a tongue-like radula equipped with rows of small chitinous teeth used for drilling and rasping; and salivary papilla bearing tiny teeth that can be protruded from the mouth (Kojima 1992; Mather and Nixon 1995; Boyle and Rodhouse 2005). Some cephalopods, particularly the octopuses, also possess posterior salivary glands that produce cephalotoxin; a

99 glycoprotein, capable of paralysing prey when injected (Ghiretti 1959; Nixon 1984). The cephalotoxin can also stimulate external digestion in octopuses, aiding in the breakdown of membranes and musculo-skeletal attachments of prey (Nixon 1984). The chemical composition of cephalotoxins varies among species, and the details of their properties and primary structures are not yet fully understood (Ueda et al. 2008).

A1.4. Feeding behaviour A1.4.1. Foraging behaviour Cephalopods utilise a range of hunting strategies whilst pursuing prey, including active searching, ambush, luring, pursuit, stalking, speculative pouncing, and even hunting in disguise whereby individuals mimic seaweed or herbivorous fish (Hanlon and Messenger 1996). Hunting strategies vary considerably among species, although flexibility in the use of hunting forms is a common feature (Boyle & Rodhouse, 2007). The method adopted is dependent on the surrounding environment, physical structure of the substratum, and an individual’s positioning within the water column (Forsythe and Hanlon 1997). For example, benthic coastal octopuses such as the Common Octopus, Octopus vulgaris, and the Brazil Reef Octopus, Octopus insularis, commonly use ambush predation, remaining inconspicuous on the substratum, searching for prey using their acute eyesight, then attack potential prey as they move within striking distance (Leite et al. 2009). However, they also are active searchers commonly adopting tactile foraging behaviours such as (i) “crawl”, where they use their strong suckers to move along the substratum searching for prey using their tactile and chemical senses; (ii) “poke”, where they use their arms and chemo-tactile senses to explore crevices likely to contain prey; and (iii) “web-over” where an octopus extends its arms and web over a small part of the substratum, and then uses its arm tips to explore the enclosed area for prey (Mather 1991a; Leite et al. 2009).

The diversity of feeding strategies that may be used by a cephalapod is demonstrated by the Carribbean Reef Squid, Sepioteuthis sepioidea, which adopts four flexible modes of hunting (Moynihan and Rodaniche 1982; Hanlon and Messenger

100 1996). During the day, small schools of squid typically wait for small fishes to come towards them, and then ambush them one by one with their extendable tentacles (Moynihan and Rodaniche 1982; Hanlon and Messenger 1996). When the squids are dispersed at night, they actively search and stalk their prey, nearing ever closer before striking (Moynihan and Rodaniche 1982; Hanlon and Messenger 1996). They also hunt in disguise at night, using floating seagrasses and seaweed to remain camouflaged, often with a head-down posture and then ambush unsuspecting prey that approach too closely (Moynihan and Rodaniche 1982; Hanlon and Messenger 1996). Sepioteuthis sepioidea also engage in speculative hunting, using their arms to disturb the sediments to flush out small invertebrates and fishes (Moynihan and Rodaniche 1982).

Cephalopods hunt and locate their prey visually, and octopuses are able to target sedentary or slow moving organisms such as mussels and abalone with precision. Sedentary prey may be attacked and captured by pulling or drilling (Mather 1991a). For example, O. vulgaris will commonly attempt to force a mussel open in the first instance, with each pull usually lasting for just a few seconds (McQuaid 1994). However, if pulling is not successful within five or ten minutes, the octopus resorts to drilling a hole in the mollusc’s shell using its salivary papilla (McQuaid 1994; Mather and Nixon 1995). When feeding on large mussels, octopus may give a single cursory pull and immediately resort to drilling, adopting a strategy that minimises the time required to successfully overcome the prey item (McQuaid 1994).

A1.4.2. Diel feeding activity As opportunists, cephalopods show a degree of flexibility in the times they are most active in response to their surrounding environment (Meisel et al. 2003). While some species are characterised as typically either diurnal, nocturnal, or crepuscular feeders, individuals may undertake foraging excursions outside these periods (Mather 1991a; Forsythe and Hanlon 1997). In some cases they are active at different times in different locations. For example, O. vulgaris has a distinct nocturnal pattern of foraging activity in the Mediterranean Sea and in the laboratory (Altman 1967; Kayes 1974; Brown et al.

101 2006). However, O. vulgaris off the coast of Bermuda in the Atlantic Ocean is very active during the day (Mather 1988). This contrast may be due to prey availability, minimising the risks of predation, or a strategy to reduce the potential for interspecific competition. Thus, individual populations of the same species may utilise different ecological cues to maximise their foraging opportunities when prey is most abundant (Mather 1988; Meisel et al. 2003). Resource partitioning has been demonstrated in three co-occurring Hawaiian octopuses, Octopus cyanea (diurnal), Octopus hawaiians (crepuscular), and Octopus ornatus (nocturnal, Houck 1982). Although these species are found within close proximity (~ 30 m) of each other on shallow reef flats, the temporal partitioning of their foraging patterns appears to be an effective mechanism for reducing interspecific interactions (Houck 1982; Meisel et al. 2003). Distinct differences in diel activity, as well as habitat preferences may also result in dietary variation between species (i.e., resource partitioning), since different prey are likely to be active at different times within a 24-hour period (Houck 1982).

A1.4.3. Shoaling The behavioural adaptation of shoaling is commonly observed among the squids and is likely to have evolved as a mechanism for reducing predation whilst increasing an individual’s feeding success (Neill and Cullen 1974; Krause 1994; Boyle and Rodhouse 2005). Although cooperative hunting has not been documented among the cephalopods (Hanlon and Messenger 1996). Shoaling varies greatly over temporal and spatial scales, but can have significant impacts on local prey densities (Boyle and Rodhouse 2005).

Sepioteuthis sepioidea is a particularly interesting example of a shoaling species. They are highly gregarious and form large, closely packed groups that comprise juveniles, sub-adults, and mature adults of both sexes, which congregate near the substrate; a situation that is unique among the cephalopods (Moynihan and Rodaniche 1982; Hanlon and Messenger 1996). When exposed to a potential threat, all members of the group turn to face it, “close ranks and assume stereotyped line and crescent formations” (Moynihan and Rodaniche 1982). With the largest individuals positioned in

102 the wings or at the front of a progressively diminishing diagonal line, they advance toward the threat (Moynihan and Rodaniche 1982). It has been suggested that shoaling could increase observational learning within a population, fostering group traditions, which may be beneficial to short-lived species (Moynihan and Rodaniche 1982; Hanlon and Messenger 1996).

A1.4.4. Prey selection Cephalopods are voracious active predators that hunt exclusively live prey (Boyle & Rodhouse, 2007). They are flexible carnivores, able to exploit a wide range of prey types (Boyle & Rodhouse, 2007; Nixon, 1987). Whilst foraging, an active predator can opt to consume a potential prey item as it is encountered, or disregard it in favour of alternative prey (McQuaid 1994). The response of a predator to a potential prey item depends on past experience with that prey type, the characteristics of the prey (i.e., prey defence mechanisms), the calorific value of the prey, and its own prey preferences (Shettleworth et al. 1993; Darmaillacq et al. 2004).

Optimal foraging theory suggests that a predator should select prey that maximises fitness, with behaviours that optimise net energy intake conferring a selective advantage (Hughes 1980; McQuaid 1994; Krebs 2008). Prey selection should, therefore, be based on a balance between net energy gain and handling time (Hughes 1980; Anderson et al. 2008b). However, due to competition, the risk of predation, or the requirement for specific resources, foraging behaviours may deviate from those considered to be optimal (Hughes 1980). In theory, a predator should only pursue a potential prey if it is unlikely that the predator would be able to secure a prey of higher calorific value in the same time that it takes to capture and ingest the lower value prey item (Hughes 1980). This predicts that high-value prey will be consumed whenever the opportunity arises, with diet composition expanding to include other less valuable prey when high-value prey is scarce, or when specific nutrients are sought (Hughes 1980). Thus, the diet of these actively searching mobile predators likely represents a

103 compromise between prey availability and prey preferences, with the dietary composition for any particular species likely to vary in space and time (Ambrose 1984).

Cephalopods are frequently described as opportunistic or generalist predators due to the broad range of prey items found in their diet, and the differences in the diet of conspecifics between geographical regions (Rodhouse and Nigmatullin 1996; Boyle and Rodhouse 2005). However, some species appear to be much more selective in their feeding than others, providing evidence that cephalopods may actively seek specific prey types and focus on specific prey characteristics (e.g., items of a particular size, Ambrose 1984; Ambrose 1986; Kojima 1992; McQuaid 1994; Anderson et al. 2008). This contrasts with the view of Rodhouse and Nigmatullin (1996), who suggest that few, if any, are selective in their choice of prey.

Binary-choice laboratory experiments reveal that the California Two Spot Octopus, Octopus bimaculatus, has a strong preference for crabs, with individuals ignoring all other prey types until crabs have been depleted (Ambrose 1984). However, in the subtidal habitats surrounding Santa Catalina Island in California, U.S.A., O. bimaculatus feeds mainly on gastropods (> 70%), with crustaceans forming just 5% of the diet since crustaceans are present at very low densities (Ambrose 1984). These findings demonstrate that while octopuses have strong prey preferences, their diet can be limited by prey availability, but they will consume their preferred prey types whenever they are encountered (Ambrose 1984).

Octopus vulgaris in the southern Caribbean exhibit marked prey selectivity, with strong differences detected between individuals (Anderson et al. 2008b). A total of seventy-five prey taxa were identified from 38 octopus dens, however, the remains surrounding individual dens varied significantly, even when dens were separated by a short < 50 m distance (Anderson et al. 2008). For example, the middens adjacent to the den of one individual consisted exclusively of a single species of bivalve, Pinna carnea, while the midden at a den located only 50 m away contained the remains of six taxa: three crustacean, two bivalve, and one gastropod species (Anderson et al. 2008b). These

104 small-scale spatial differences may be the result of learnt behaviours, with octopus targeting the species that succumb to their foraging technique most easily (Anderson et al. 2008b). The fact that octopuses can be ‘specialising generalists’ may enable individuals to capitalise on local prey abundance and maximise energy intake, with foraging efficiency and learning leading to increased specialisation (Anderson et al. 2008b).

Selective predation of abalone and bivalves by octopus based on size provides evidence for the selection of prey that maximises energy intake. Kojima (1992) examined the predation of octopus, mainly O. vulgaris, on the abalone Haliotis discus discus by examining shells for boreholes. Octopus predation increased with shell size from 2.5% of small shells (30-39 mm shell width [SW]) to 44% of large shells (100-109 mm SW), which is likely driven by prey profitability (Kojima 1992). While the direct removal of H. discus discus was unable to be quantified, it is possible that smaller individuals could simply be pulled from the reef by octopus, without the need to bore into the shell. Shells less than 30 mm in length comprised only 16% of the total number of shells. However, since the direct removal of abalone from the substratum is likely to be less energetically costly than drilling, octopus may predate on juvenile abalone when the opportunity arises. Juvenile abalone are cryptic and reside in interstitial reef cavities (Shepherd and Turner 1985; Prince et al. 1988, 2008), yet foraging for prey in crevices using chemotactile exploration (Mather 1991a), which may allow octopuses to detect and prey on smaller abalone.

Experiments on captive held O. vulgaris in South Africa, which feed mainly on the mussel Perna perna, demonstrate a non-random selection of mussels when offered an excess of prey (McQuaid 1994). Large octopus selected larger mussels with higher energetic returns, calculated by dividing the energetic value of the prey, (i.e., mussel flesh dry mass), by the total handling time (i.e., the amount of time required to consume the prey item, McQuaid 1994). Larger mussels have a higher energetic value, however, shell thickness is greater and the diameter of the adductor mussels holding the shell

105 closed is stronger, making larger mussels more energetically costly for smaller octopus to overcome (McQuaid 1994). Therefore, it is not surprising that prey size selection varies among octopuses based on body size, with larger octopuses targeting larger mussels, while smaller individuals prefer smaller mussels (McQuaid 1994).

A1.5. Growth rates and food intake

Cephalopod growth has been modelled as a two-step process, characterised by an initial exponential growth phase whereby the relative instantaneous growth rates remain constant, followed by a logarithmic phase in which growth slows gradually and concludes with sexual maturation, spawning, and death (Forsythe and Van Heukelem 1987; Semmens et al. 2004; Boyle and Rodhouse 2005). Although this two-step growth phase is less evident in the data collected from field studies, probably due to a lack of data on the difficult to sample small juveniles and paralarvae (Forsythe and Van Heukelem 1987; Semmens et al. 2004; Boyle and Rodhouse 2005).

Laboratory studies demonstrate the rapid non-asymptotic rates at which cephalopods grow (i.e., 3-10% of body weight d-1), and the approximately linear relationship that exists between daily food intake and growth when food is provided in excess (Joll 1977; Lee 1995; Semmens et al. 2004). In a laboratory study of the relationship between food intake and growth in Octopus cf. tetricus, one individual gained ~1,350 g in a period of 69 days (19.6 g d-1), increasing in size from ~750 to 2,100 g, while another gained ~800 g in 45 days (17.8 g d-1), increasing from ~500 to

1,300 g (Joll 1977).

Temperature and feeding rates are key factors influencing growth, particularly in the early growth phase, where elevated temperatures promote higher growth rates (Joll 1977; Forsythe 2004). The Forsythe Hypothesis postulates that monthly cohorts that experience gradually warming temperatures grow more rapidly than cohorts that hatch in cooler conditions (Forsythe 2004). This hypothesis, which has received strong endorsement (Jackson et al. 1997; Villanueva 2000; Hatfield et al. 2001; Forsythe et al.

106 2001; Vidal et al. 2002), predicts that elevated temperatures will accelerate cephalopod lifecycles. Therefore anthropogenic climate change is likely to have a positive influence on cephalopod biomass within the global oceans (Forsythe 2004). At least for as long as the optimal thermal range of a species is not exceeded (Doubleday et al. 2008).

A1.6. Diets A1.6.1. Broad dietary trends In order to determine the dietary composition of coastal cephalopods, a meta-analysis of 24 species across 28 studies was conducted encompassing species within the Loliginidae, Octopodidae, Sepiidae and Sepiloidae. To ensure the consistency of taxonomic resolution between families, each prey item was allocated to one of seven main dietary groups, namely bivalves, cephalopods, crustaceans, gastropods, polychaetes, teleosts, and ‘other’ prey, which includes taxonomic categories outside these groups or prey that could not be identified. Dietary composition was expressed as percent number (%N, i.e., the frequency of an individual prey item, expressed as a percentage of all prey items). Note that in a few cases, prey items were grouped into one of the seven main dietary groups when higher taxonomic resolution was presented.

While dietary information is limited to a few common species, such as Loligo forbesi, Loligo vulgaris, Octopus vulgaris, Sepia elegans, and Sepia officinalis, conspicuous trends were identified among families (Table A1.1). Crustaceans, teleosts, and molluscs including other cephalopods typify the diet of these coastal families. However, the relative contributions of the various prey taxa varied considerably among the individual families. For example, crustaceans, teleosts, and shelled molluscs, such as bivalves and gastropods, dominate the diets of benthic octopuses (Table A1.1). Typically, the demersal sepiolids and sepiids consume large amounts of crustaceans and teleosts, while the semi-pelagic loliginid squids tend to consume large proportions of fishes, cephalopods, and crustaceans (Table A1.1).

107 Table A1.1. Percentage contribution (% number of total prey items) of the seven main prey groups in the gastric tracts of species within the Octopodidae, Sepiidae, Sepiloidae, and Loliginidae, and midden counts within the Octopodidae. B = bivalves, CE = cephalopods, crustaceans (CR), gastropods (G), polychaetes (P), teleosts (T), and (O) other prey. N (sample size) refers to the number of gastric tracts examined that contained food, or the number of middens counted. Location = broad geographic region of the study. Lifestyle = position in the water column adults of the species occupy.

Family Species B CE CR G P T O N Location Lifestyle Enteroctopus dofleini1 19 77 1.22 2.78 193 Gulf of Alaska Benthic

Octopus bimaculatus2 5.83 6.7 83.5 3.97 North Pacific Benthic

Octopus bimaculatus2 6.7 5.03 73.18 15.09 North Pacific Benthic

Octopus bimaculatus3 62.5 1.3 32.5 0.6 3.1 261 Gulf of California Benthic

4 Octopus cyanea 47 32 17 4 56 South Pacific Benthic

Octopus insularis5 17.53 70 12.47 117 South East Atlantic Benthic

Octopus insularis6 15.8 68.4 13.2 2.6 12 South East Atlantic Benthic

Middens Octopus insularis 83.4 0.2 6.6 9.4 0.4 72 South East Atlantic Benthic

Octopodidae Octopus insularis6 2.4 97.6 16 South East Atlantic Benthic

Octopus vulgaris7 72 19 9 7 Balearic Sea Benthic

Octopus vulgaris8 51 30 19 38 Caribbean Sea Benthic

Octopus vulgaris9 30.63 21.74 47.59 0.04 41 North West Atlantic Benthic

Octopus vulgaris10 12.8 12.1 71.5 3.6 245 South Atlantic Benthic Eledone cirrhosa11 5.98 70.64 0.13 2.09 17.73 3.43 498 North West Atlantic Benthic

Eledone moschata12 0.6 10.8 57.1 2.1 1.3 28 0.1 799 North Adriatic Sea Benthic

Octopus bimaculatus3 5.3 3.6 51.5 19.2 1.5 4.8 14.1 261 Gulf of California Benthic Octopus hubbsorum13 1 3 88 4 2 2 226 North East Pacific Benthic

Octopus magnificus14 2.41 0.81 62.77 2.41 6.6 23.83 1.17 102 South West Atlantic Benthic 15

Octopodidae Octopus maorum 2.68 78.19 18.12 1.01 72 Tasman Sea Benthic Gastric tracts Gastric Octopus mimus16 9.09 67.29 12.62 11 485 South Pacific Benthic

Octopus vulgaris10 51.6 28.6 8.2 8.5 3.1 250 South Atlantic Benthic

Table A1.1 continued Family Species B CE CR G P T O n Location Lifestyle Doryteuthis pealeii17 49.45 27.73 22.82 1383 North West Atlantic Pelagic

Doryteuthis sanpaulensis18 6.4 23.3 36.4 33.9 313 South West Atlantic Pelagic

Loligo forbesi19 7.49 26.4 73.7 1715 Irish, Celtic Seas Pelagic

Loligo forbesi20 6.9 17.35 0.13 75.62 1322 South East Atlantic Pelagic

Loligo forbesi21 0.43 7.54 20.78 3.2 68.04 0.01 360 Northern North Sea Pelagic

Loligo plei22 7.5 36.9 7.5 48.1 264 South West Atlantic Pelagic

Loliginidae Loligo vulgaris 19 7.2 72.7 1.1 280 North East Atlantic Semi-pelagic

Loligo vulgaris23 25.6 19.8 51 3.6 346 North East Atlantic Semi-pelagic

Loligo vulgaris20 18.51 15.22 6.87 59.4 1837 South East Atlantic Semi-pelagic

Loligo vulgaris24 41.91 22.11 7.26 22.77 5.95 284 South East Atlantic Semi-pelagic Sepia elegans25 80 20 72 North West Atlantic Demersal tracts Sepia elegans26 83 0.2 15.1 1.7 366 North West Atlantic Demersal

Sepia elegans27 1.64 80.99 3.31 12.4 1.66 41 Aegean Sea Demersal

Gastric Gastric Sepia officinalis25 1.8 67.5 30.7 150 North West Atlantic Demersal

Sepia officinalis26 0.9 57.1 0.3 39.7 2 623 North West Atlantic Demersal Sepiidae Sepia officinalis28 11.89 12.52 46.43 2.06 1.59 25.52 339 North West Atlantic Demersal

Sepia officinalis27 62.26 5.66 32.08 24 Aegean Sea Demersal

Sepia orbignyana27 6.35 77.78 1.59 14.28 27 Aegean Sea Demersal Rondeletiola minor27 55 15 25 5 14 Aegean Sea Benthic

Rossia macrosoma27 1.92 80.77 1.92 1.92 13.46 0.1 18 Aegean Sea Benthic

Sepietta intermedia27 5 75 15 5 15 Aegean Sea Benthic

Sepietta neglecta27 62.5 18.75 18.75 14 Aegean Sea Benthic 27

Sepiolidae Sepietta oweniana 59.46 6.76 16.22 17.56 25 Aegean Sea Benthic

Sepietta robusta27 7.41 88.89 3.7 14 Aegean Sea Benthic

1Vincent et al. (1998); 2Ambrose (1984); 3Villegas et al. (2014); 4Scheel et al. (2016); 5Leite et al. (2009); 6Leite et al. (2016); 7Ambrose and Nelson (1983); 8Anderson et al. (2008); 9Kuhlmann and McCabe (2014); 10Smith 2003; 11Regueira et al. (2017); 12Šifner and Vrgoč (2009); 13Lopez-Uriarte and Rios-Jara (2009); 14Villanueva (1993); 15Grubert et al. (1999); 16Cortez et al. (1995); 17Hunsicker and Essington (2006); 18Dos Santos and Haimovici (2002); 19Collins (1994); 20Pierce et al. (1994); 21Wangvoralak et al. (2011); 22Gasalla et al. (2010); 23Coelho et al. (1997); 24Sauer and Lipiński (1991); 25Guerra (1985); 26Castro and Guerra (1990); 27Vafidis et al. (2009); 28Alves et al. (2006).

109 A1.6.2. Ontogenetic dietary shifts

Large changes in diet with ontogeny have been well documented among the cephalopods; a reflection of the changes that occur in the brachial crown with growth (Boyle and Rodhouse 2005). While the minimum prey length typically does not change, often the maximum prey size and diversity of prey increases with increasing body size (Smith 2003; Boyle and Rodhouse 2005). As is the case with many marine predators, including their teleost competitors, larger individuals are better equipped to consume a wider range of prey types (Gosline 1996; Consoli et al. 2010).

The potential scale of ontogenetic changes in diet are shown by O. vulgaris in False Bay South Africa, with small individuals (0-300 g) frequently consuming large numbers of small crustaceans (e.g., amphipods and isopods), and moderate numbers of winkles and large crustaceans (e.g., crabs and lobsters; Smith 2003). As individuals increase in size (301-1,000 g), the number of small crustaceans and winkles consumed decreases and the number of larger prey items, such as large crustaceans, abalone, and teleosts increases (Smith 2003). The diet of the largest individuals (>1,000 g) is most diverse, with high numbers of abalone, teleosts, small and large crustaceans, and other octopuses (Smith 2003).

Among the squids, piscivory increases markedly with growth, while the importance of crustaceans and cephalopods appears to be variable, likely due to temporal and spatial differences in prey availability (Table A1.1; Pierce et al. 1994; Coelho et al. 1997; Gasalla et al. 2010).

A1.6.3. Cannibalism

Cannibalism and interspecific predation are a ubiquitous feature among cephalopods (Table A1.1; Ibáñez and Keyl 2010). Cannibalism is most frequent during periods of low food abundance and under high population densities, such as large squid aggregations and when the territories of benthic octopuses are reduced, leading to increased encounters (Aronson 1986; Boyle and Rodhouse 2005; Ibáñez and Keyl

110 2010). The rare phenomena of sexual cannibalism has also been noted for Octopus cyanea (Hanlon and Forsythe 2008). In the majority of interactions, however, differences in intra-cohort body size appears to be an important feature, with incidents of cannibalism typically increasing in larger individuals.

A1.6.4. Influence of sampling method on interpretation of diets Until recently, the primary method used to understand the trophic role and dietary composition of cephalopods was gastric tract analysis and midden counts, for benthic octopuses (e.g., Nixon 1987; Mather 1991a; Smith 2003; Jackson et al. 2007) (Table A1.1). Gastric tract analysis is based mainly on the examination of hard structures, such as bones, otoliths, gill lamellae, polychaete setae, cephalopods lenses and beaks, and crustacean exoskeleton to identify prey to at least order for invertebrates, but often family or species for vertebrates (Nixon 1987; Boyle and Rodhouse 2005; Jackson et al. 2007). Soft tissue components can be under-represented in studies based on gastric tracts due to the metabolism of cephalopods being rapid (Pierce et al. 1994; Smith 2003; Boucher-Rodoni and Mangold 2009). Midden counts are based on the collection of shells and the remains of any prey discarded by octopus around their dens.

In order to determine whether dietary composition varies between sampling methodologies, data was collected from studies utilising gastric tracts and midden counts (Table A1.1). The Octopodidae are the only coleoid family that discards their prey in middens close to their dens, therefore only species belonging to this family were included in this analysis. The selected dietary data from Table A1.1 (i.e., percentage contribution by numbers) were square root transformed and used to construct a Bray- Curtis resemblance matrix. This matrix was, in turn, subjected to one-way Analysis of Similarities (ANOSIM; Clarke and Green, 1998) test to determine whether dietary composition differed significantly between methods. It was also used to produce a non- metric multidimensional scaling plot (nMDS; Clarke, 1993) to provide a visual representation of the similarity among samples, and the dietary items responsible for any differences among a priori groups using shade plots (Clarke et al 2014).

111 One-way ANOSIM demonstrated that the diet composition of the Octopodidae differed significantly between the two methodologies (R = 0.69, P = 0.001). This is shown on the associated nMDS plot, with the points representing diet derived from gastric tracts forming a discrete group on the right hand side of the plot, clearly separated from the midden counts on the left hand side (Fig. A1.4). The points from the midden counts were also more widely dispersed, indicating greater variation in the diet than those from gastric tracts (Fig. A1.4). Hard parts in middens can accumulate over time which may account for the greater variation in items found in midden contents. Gastric tract analysis shows that crustaceans and teleosts are most important to the diets of octopuses, but for midden counts hard-shelled prey such as bivalves and gastropods are most important (Fig. A1.5).

This analysis demonstrates that sampling method can lead to dramatically different results, even within a species, highlighting the limitations of each technique. For example, the gastric tracts of O. vulgaris contained a high percentage by number (%N) of crustaceans (51.6%), teleosts (8.5%) and polychaetes (8.2%) in their gastric tracts, but a lower percentage of shelled molluscs (28.6%, Table A1.1; Smith 2003). In contrast, middens contained a high %N of shelled molluscs (84.3%), and a low %N of crustaceans (12.1%), teleosts, and polychaetes (< 3.6% total, Table A1.1; Smith 2003).

Hard parts of prey such as exoskeletons, bones, and setae have a higher gut retention time than soft tissues, and thus crustaceans, teleosts, and polychaetes are likely to be over-represented in gastric tract analysis (Pierce et al. 1994; Smith 2003). Conversely, midden counts are heavily biased towards shelled molluscs, and against soft-bodied organisms. In dynamic shallow-water environments, lightweight prey discards, such as fish skeletons are readily lost from midden piles, and small, soft- bodied organisms that are consumed whole leave behind no trace, resulting in an over- estimation of the importance of shelled molluscs when the remains from middens are counted (Ambrose and Nelson 1983; Mather 1991a; Smith 2003).

112

Figure A1.4. Non-metric multi-dimensional scaling (nMDS) ordination plot, derived from a Bray–Curtis similarity matrix of the square-root transformed percentage contribution (% number of total prey items) of the seven main prey groups in the gastric tracts (p) and midden piles (q) of octopus species.

Figure A1.5. Shade plot showing the mean square-root transformed percentage contribution (% number of total prey items) in the gastric tracts (p) and midden piles (q) of octopus species. White represents an absence of prey, and grey to black represents the increasing contribution of a dietary category to the total diet. Prey groups (x-axis) are bivalves (B), cephalopods (CE), crustaceans (CR), gastropods (G), polychaetes (P), teleosts (T), and (O) other prey.

While gastric tract analysis typically uncovers a greater range of prey taxon, this approach can result in biases in diet composition, particularly when fragments of large prey are discarded and small prey are consumed whole (Table A1.1; Nixon 1987; Boyle

113 and Rodhouse 2005). Furthermore, prey types with few hard parts such as flatworms, or molluscs where the hard shell has been discarded, may go undetected altogether (Nixon 1987).

Biochemical measures of diet, such as stable isotope analysis and fatty acid trophic markers provide complementary techniques to track the origins and pathways of organic molecules to understand the trophic role of cephalopods within the food web (Graeve et al. 2002; Jackson et al. 2007). When food is digested by a consumer, nutrients and distinct fatty acid ratios are assimilated into the animal’s tissues producing unique isotopic and fatty acid signatures (Petersen and Fry 1987; Graeve et al. 2002; Jackson et al. 2007; Navarro et al. 2013). These signatures provide precise information with respect to trophic positioning (i.e., an organisms position within a food web), and the trophic pathways within a marine ecosystem (Navarro et al. 2013). They are also useful in that they offer spatial and temporal insights into trophic relationships, as well as providing information on long-term dietary habits of cephalopods, helping alleviate the bias associated with rapid digestion and the selective removal of hard parts (Layman et al. 2012; Navarro et al. 2013).

A1.6.5. Dietary differences among families The information from the 24 species representing the four families detailed in Table A1.1 (i.e., members of the Loliginidae, Octopodidae, Sepiidae, and Sepiloidae) was subjected to the same suite of multivariate techniques described above (i.e., nMDS,

ANOSIM, and shade plots).

One-way ANOSIM demonstrated that the dietary composition of species in each of the four families differed significantly (R = 0.49, P = 0.001). Pairwise comparisons between families demonstrated that the dietary compositions of the loliginid squids differed significantly from each of the other families (P = 0.001). This is shown clearly on the nMDS plot where the points for the loliginid squid form a discrete group on the right-hand side of the plot, distinct from the other families on the left-hand side (Fig.

114 A1.6). While less marked with some overlap between the groups, significant (P ≤ 0.04) differences were detected between each of the other families except between the Octopodidae and the Sepiloidae (Fig. A1.6, Table A1.2).

Non-metric MDS Standardise Samples by Total Transform: Square root Resemblance: S17 Bray-Curtis similarity 2D Stress: 0.18 Family Octopodidae Sepiidae Sepiolidae Loliginidae

Figure A1.6. nMDS ordination plot derived from a Bray–Curtis similarity matrix of the square-root transformed percentage contribution (% number of total prey items) of the seven main prey groups in the gastric tracts of species within the Octopodidae (p), Sepiidae (q), Sepiloidae (¢), and Loliginidae (¿).

115 Table A1.2. Pairwise R statistics and significance level (P) values derived from a one-way ANOSIM test on the square-root transformed percentage contribution (% number of total prey items) of the seven main prey groups in the gastric tract of species within the Octopodidae, Sepiidae, Sepiloidae, and Loliginidae. Grey shading indicates no significant difference between families (P = > 0.05).

Groups R statistic P value Octopodidae vs Sepiidae 0.17 0.040 Octopodidae vs Sepiolidae 0.06 0.213 Octopodidae vs Loliginidae 0.83 0.001 Sepiidae vs Sepiolidae 0.23 0.021 Sepiidae vs Loliginidae 0.82 0.001 Sepiolidae vs Loliginidae 0.93 0.001

The shade plot shows that the loliginid squids consume larger proportions of teleosts and cephalopods (mainly other squids), with few bivalves or polychaetes compared with the other families (Fig. A1.7). Crustaceans are the most important dietary component in the octopodids, sepiids and sepiloids, followed by teleosts, while the relative importance of each of the remaining prey categories varies among families.

These differences in diet composition among families are likely to be a reflection of lifestyle (i.e., the position they occupy within the water column), and resource availability. Not surprisingly, benthic octopuses consume large numbers of crustaceans (e.g., brachyurans), teleosts, gastropods, and bivalves as these prey items are typically abundant in benthic environments (Fig. A1.7). Similarly, the low contributions of benthic prey, such as shelled molluscs and polychaetes, and high %N of teleosts, crustaceans (e.g., prawns), and other cephalopods (e.g., other squids) to the diet of the Loliginidae is representative of their semi-pelagic lifestyle (Fig. A1.7). The presence of both demersal and pelagic fishes in the diets of the loliginids indicates, however, that they feed throughout the water column (Pierce et al. 1994; Dos Santos and Haimovici 2002; Gasalla et al. 2010).

116 9 Family 8 Octopodidae 7 CE Sepiidae 6 Sepiolidae Loliginidae 5 4 T 3 2 1 P 0

Figure A1.7. Shade plot showing the mean square-root transformed percentage contribution (% number of total prey items) of the seven main prey groups, bivalves (B), cephalopods (CE), crustaceans (CR), gastropods (G), polychaetes (P), teleosts (T), and (O) ‘other’ prey, in the gastric tract of members of the Octopodidae (p), Sepiidae (q), Sepiloidae (¢), and Loliginidae (¿). White represents an absence of prey, and grey to black represents the increasing contribution of a dietary category to the total diet.

A1.7. Predation in marine systems A1.7.1. Predation impacts Predation is a fundamental ecological process controlling the structure and functioning of all ecosystems on earth. It has a negative impact on prey survival and abundance, and is distinguished from other forms of foraging behaviour by the disfigurement or complete elimination of another animal (Curio 1976). Some predators (i.e., keystone species), play key roles within an ecosystem and are essential for maintaining species richness and community organisation (Underwood and Fairweather 1989; Gasalla et al. 2010). The ability of cephalopods to adapt to their environment and exert a strong influence on marine communities has embedded their description as a keystone species within the literature (Boyle and Rodhouse 2005; Gasalla et al. 2010; Rosa et al. 2012; Pierce and Portela 2014). Rapid growth coupled with high metabolic rates has resulted in flexible yet voracious feeding regimes, and their opportunistic, plastic life-history strategy enables them to respond to environmental fluctuations rapidly, which can have significant impacts on both the higher and lower trophic levels in the food web

117 (Rodhouse and Nigmatullin 1996; Boyle and Rodhouse 2005; André et al. 2010). As a consequence, their predatory impact on prey populations can vary both spatially and temporally (Rodhouse and Nigmatullin 1996), and their large biomass within the global oceans is likely to have a significant impact on the teleost, crustacean, and molluscan prey that form the great majority of their diet (Nixon 1987; Table A1.1).

Despite being referred to as keystone species, few studies have quantified experimentally the scale of cephalopod impacts on the ecological function of coastal systems. Recent ecological modelling has utilised a keystoneness index (sensu Libralato et al. 2006) and this highlights the importance of squid trophic interactions in the Southern Brazil Bight ecosystem (Gasalla et al. 2010). The predatory impact of D. gigas on the Californian sardine S. sagax caerulea, as previously mentioned, provides an illustration of the potential scale a cohort can exert on a prey population; and although a mesopelagic species, it highlights the potential top-down controls that high turnover coastal species pose in these dynamic shallow water environments.

A study of O. vulgaris, commonly found in the intertidal and sub-tidal communities off southern California, showed that when present in high densities, it dramatically reduces the density and diversity of motile invertebrate prey (Ambrose 1986). However an 80% reduction in O. vulgaris density over a five year period resulted in a five-fold increase in prey abundance (Ambrose 1986). Unlike other intertidal communities, where species richness has been positively correlated with predation pressure (e.g., Paine 1966; Peterson et al. 1979), high octopus density appears to have a negative impact on species richness (Ambrose 1986). In this system, the absence of a competitive dominant may explain why predation did not result in increased species richness (Ambrose 1986). Additionally, being a motile invertebrate community may reduce the effectiveness of predation, since organisms are able to actively seek refuge and move to more favourable locations (Ambrose 1986). Several species of crabs, shrimps, and bivalves remained at relatively low densities throughout the duration of the study, which is thought to have been driven by selective predation,

118 leading to a reduction in the abundance of preferred species despite octopus occurring in low numbers (Ambrose 1986).

A1.7.2. Trophic relationships Cephalopods are considered important intermediaries within the marine food web, facilitating a transfer of energy between first and second order consumers, and higher trophic level predators at a range of stages and sizes throughout their lifecycle (Dos Santos and Haimovici 2002; Boyle and Rodhouse 2005). Highly muscular and offering a rich source of protein (> 90% of the live weight), little of the cephalopod body is resistant to digestion, providing a high intrinsic food value for consumers (Semmens et al. 2004; Boyle and Rodhouse 2005). However, the indigestible hard parts, particularly the chitinous beak, provide an important tool for disentangling trophic relationships and understanding their importance within the marine food web (Boyle and Rodhouse 2005). Analysis of the stomach contents of cephalopod predators highlights their global importance within the diets of many vertebrate species (e.g., Clarke 1996a; Cherel and Hobson 2005; Cherel et al. 2009; Staudinger et al. 2013). For example, global seabird, pinniped, and cetacean populations are estimated to consume between 12.5 and 24 million tonnes annually (Staudinger et al. 2013), which is at least twice the biomass of global cephalopod landings (Fig. A1.3). The high volume of paralarvae and juvenile cephalopods (> 55%) in the diet of commercially valuable finfishes such as the Yellowfin Tuna, Thunnus albacares, and Blackfin Tuna, Thunnus atlanticus, provides evidence of the importance of cephalopods as trophic intermediaries, even from a small size (Staudinger et al. 2013). As juveniles, cephalopods form an important food component for many predatory fishes, however, as these molluscs increase in size their relationships with other taxa shift, and the hunters become the hunted.

Cephalopods occupy a range of trophic levels, which differ considerably between species, life-stage, location, and ecosystem type (Livingston 2003; Navarro et al. 2013; Rodhouse et al. 2014). Analysis of trophic relationships highlights the diverse nature of cephalopod feeding regimes and their ability to feed at multiple levels, as

119 evidenced by distinct isotopic nitrogen (�15 N) signatures. It is these distinct �15 N signatures that allow for the relative trophic position of a consumer to be characterised

(Vander Zanden and Rasmussen 1999; Layman et al. 2012). The mean (± 1 s.d.) trophic level of squids determined from synthesized stable isotope data (and adjusted for isotopic variability), in temperate coastal and shelf areas has been estimated at 3.61

± 0.76, slightly higher than those in tropical areas (3.23 ± 0.59; Navarro et al. 2013). These results are broadly similar to that of Lozano-Montes et al. (2011) who found that the mean trophic level of squid and octopus in temperate waters on the west coast of

Western Australia ranged from 3.1 to 3.6 (± 0.50). Navarro et al. (2013) found that the mean trophic level of squid varied considerably among oceans, being greatest in

Antarctica (4.11 ± 0.99), followed by the Arctic (4.01 ± 0.49), Indian Ocean (3.29 ± 0.35), Pacific Ocean (3.46 ± 0.91), and least in the Mediterranean (2.65 ± 0.24).

Body size is an important feature of trophic positioning, with increased size resulting in a progressive increase in �15N; denoting a shift in diet to higher trophic levels with growth (Cherel et al. 2009; Ruiz-Cooley et al. 2010). Similarly, isotopic carbon (�15 C) ratios vary among primary producers, offering insights into the original sources of dietary carbon and enabling variation in habitat use to be identified (Cherel et al. 2009; Ruiz-Cooley et al. 2010). Although this method is commonly used to determine trophic level, the analysis of dietary composition of coastal cephalopods has not been determined using this approach.

A1.8. Conclusions and directions for future research

This review summarises the current knowledge of coastal cephalopod diets and the characteristics of their biology that contribute to their success as predators within global marine ecosystems. Their live fast, die young life history strategy commands voracious feeding routines, which is supported by their ability to adapt to new and novel foraging opportunities. With a range of highly sophisticated sensory and chromatophore organs, coupled with a range of unique morphological accessories, such as prehensile arms with strong suckers, a chitinous beak for tearing food, a tongue-like radula, salivary papilla

120 bearing tiny teeth, and some with cephalotoxins they are well-adapted predators. Flexibility in foraging behaviours and the times an individual is most active enables the cephalopods to strike a balance between energy intake and energy expenditure, consistent with the principles of optimal foraging theory (e.g., Hughes 1980). They show intelligence; a feature that is unique among the invertebrates, with the ability to learn from past experiences; enhancing foraging efficiency and the opportunity for specialisation on high energy content prey.

The methodology adopted in dietary studies was shown to significantly influence the results of these studies. Multivariate analyses of coastal octopuses demonstrated distinct differences between the dietary compositions determined from gastric tract analysis and midden counts, with large volumes of prey taxa with hard parts such as crustaceans and teleosts identified within gastric tracts, while middens are heavily biased towards hard-shelled prey, such as bivalves and gastropods. The meta- analysis of 24 species, representing four families of coastal cephalopods (Octopodidae, Loliginidae, Sepiidae, and Sepiloidae) demonstrated the importance of crustaceans and teleosts to the diet of all families, but also highlighted distinct differences between families with respect to relative prey contributions, particularly for the semi-pelagic Loliginidae. Such differences are likely a consequence of the variation in lifestyle that occurs between the groups. A rapid shift in diet with ontogeny is a ubiquitous feature among the cephalopods. An increase in body size facilitates the capture and ingestion of a wider range of prey types, and the incorporation of larger, more mobile species such as teleosts and other cephalopods, including their conspecifics, i.e., cannibalism.

Cephalopods play key trophic roles within marine systems, supporting the transfer of energy between lower order consumers and higher trophic level predators. They can exert considerable predatory impacts within a community, which is enhanced by their ability to respond rapidly to favourable environmental perturbations such as increased water temperatures that promote growth. They occupy a range of trophic level

121 positions, however, this varies considerably during the course of an individuals life history and the ecosystem type in which they inhabit.

The trophodynamics of cephalopod communities are yet to be fully explored, with most research limited to a few commercially valuable species, particularly pelagic squids, which dominate the cephalopod landings from global fisheries (Rodhouse et al. 2014). Additionally, most of the work on cephalopod diets and trophic analysis is restricted to a few commonly occurring and easily accessible species, with little information known about the long-term dietary trends and nutrient assimilation in coastal systems (Rodhouse et al. 2014). In view of the current unprecedented level of exploitation of cephalopods, further studies that utilise biochemical tracers such as stable isotopes and fatty acids, are needed to evaluate trophic interactions, diet composition, cephalopod lifecycles and their response to environmental variability. This information will help inform reliable assessments of cephalopods and other fished species, and ensure that cephalopod fisheries are developed in an ecologically sustainable way (Boyle and Rodhouse 2005; Jackson et al. 2007; Hunsicker et al. 2010; Rodhouse et al. 2014). It will also provide the basis for developing more realistic marine ecosystem models, and assessing the ecological role of cephalopods in the marine environment.

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