Foraging Habitats and Interspecies Interactions of the Striped Red Goatfish, Mullus Surmuletus

Foraging habitats and interspecies interactions of the striped red goatfish, Mullus surmuletus Jessica R. Hanaway-Moore and Gabrielle R. Keeler University of California, Santa Cruz Department of Ecology and Evolution Corsica Field Quarter, Fall 2012 Keywords goatfish, habitat specialization, foraging behavior, interspecies interactions, community ecology Abstract With this study, we aimed to determine whether M. surmuletus exhibit specific foraging habitats and to describe the relationship between M. surmuletus and other fish species. We used bite rate as a proxy to determine costs and benefits. We found that M. surmuletus is a habitat specialist and exhibits ontogenetic shifts in habitat utilization. Additionally, M. surmuletus acts as a nuclear species in foraging associations and positively affects the feeding rate of follower fishes. We also identified a relationship between follower species composition and foraging habitat. Introduction The striped red goatfish, Mullus surmuletus, are benthic carnivores distributed along the eastern Atlantic and throughout the Mediterranean Sea. Adults can be found in depths greater than 400m, while juveniles tend to reside in shallower waters (Machias et al. 1998). In the Mediterranean Sea, M. surmuletus is a commercially important food fish and has been subjected to intense exploitation, mostly via trawling, with young fish being subjected to the greatest fishing pressure. (Tserpes et al. 2002). Studies have found ontogenetic diet shifts of trawled goatfish populations (Kolasinski et al. 2009; Chérif et al. 2011; Bautista-Vega et al. 2008; Labropoulou & Eleftheriou 1997; Labropoulou et al. 1997), but they have not looked specifically at those living in shallow water, nor have they looked at foraging behavior. Likewise, few studies have examined habitat utilization of goatfish and none have studied M. surmuletus. Understanding juvenile habitat selection and usage is critical for designing effective management strategies because healthy juvenile populations are important for maintaining adult goatfish populations. Recognizing community interactions is also fundamental to the persistence and stability of natural populations. The linkage between species is the foundation of community infrastructure and can be a vital component in the rise or fall of populations. Other species of goatfish are known to participate in what are called nuclear-follower foraging associations (Sazima et al. 2007). Nuclear fish form the core of a foraging association, while follower fish accompany these fish during foraging or while travelling between foraging habitats. Past studies on nuclear-follower foraging describe the composition of these associations (Sazima et al. 2007; Lukoschek & McCormick 2002), but do not investigate possible benefits of associating. Such relationships are difficult to quantify and ours is the first study to use feeding rate as a proxy for overall benefit of nuclear-follower foraging associations. Using observational data, we addressed the following questions: (1) How does M. surmuletus interact with their foraging habitat? (2) What is the relationship between M. surmuletus and their follower fish? (3) Is there a correlation between follower fish and M. surmuletus foraging habitat? Methods Data Collection We observed the feeding habit and relationship of Mullus surmuletus with other Mediterranean fishes in different substrate types along the northwestern coast of Corsica, France at Station de Recherche Océanographiques et sous-marines (STARESO). This area is characterized by large, continuous Posidonia oceanica meadows as well as patches of sandy and rocky bottoms. The study site did not exceed 12 m depth and the mean water temperature was 21°C. We collected observations in daylight hours during October 2012 when ocean conditions were calm with minimal swell and wave action. To assess foraging habitat use, we took uniform point contact (UPC) data in sites where we observed M. surmuletus foraging during preliminary observations. We completed twenty 30x2m transects at depths ranging from 4 to 8 m with headings running near parallel to the adjacent shoreline. We assigned the habitat to six substrate categories: (1) Turf algae: foliose green algae, brown algae or erect coralline algae covering boulders and bedrock, (2) Posidonia oceanica: dominant seagrass species found in large meadows or small patches, (3) Sand: sediment less than 1 cm, (4) Cobble: sediment between 1 to 10 cm, not covered by any turf algae, (5) Dead P. oceanica: sites covered by thick layers of necrotic seagrass, (6) Other: any other substrate type, including encrusting algae, sessile invertebrates, and bare rocks larger than 10 cm. To assess the foraging habits of M. surmuletus, we opportunistically observed individuals within our study area while on SCUBA. To avoid depth bias, we conducted meandering search patterns that encompassed a wide depth range where M. surmuletus could be found. We only took data while swimming away from STARESO (north or south) to avoid repetitive observations of individual M. surmuletus and to avoid observational interference, which may have arisen from disturbances created by data collectors. Likewise, we did not take observations more than once a day for a given heading. When a M. surmuletus was found, we recorded the depth and visually estimated their lengths using marked dive slates as size references. We then observed the foraging strategies of each goatfish for two minutes, taking data on the number of feeding instances and noting the habitat of each feeding instance. A feeding instance began when the barbels were deployed and ended when the goatfish’s snout was lifted from its downward feeding position. We used the number of feeding instances divided by time observed as a proxy for an individual’s bite rate. In addition, we noted any fishes associating with M. surmuletus during these two-minute observations. The fish species were identified and the number present was recorded. We defined an associate species as any fish that came within half a meter of the goatfish during feeding instances. To further investigate the relationship between M. surmuletus and associate fishes, we then conducted a new set of opportunistic surveys focused on the species found most often with the goatfish in the previous search. We observed each associate fish for a maximum of two minutes. During this time, we recorded the amount of time (in seconds) an associate spent alone, time with a M. surmuletus, and time with any other fish species. Again, we used feeding instances over time as a proxy for bite rate of associate fishes. Data Analysis We began our analysis of habitat use by combining our own UPC data with harbor UPC data collected by Tristan McHugh and Kristen Elsmore (2012) to calculate the proportion of available foraging habitats. We considered the number of goatfish bites observed over a given foraging habitat to be representative of the amount of time the goatfish spent over a specific foraging habitat. We compared the available habitat to the observed foraging habitat by conducting a Pearson chi-squared analysis. In order to determine a relationship between goatfish size and foraging habitat, we separated goatfish individuals into two categories, small (<15cm) and large (>15cm), and did a PERMANOVA analysis (in PRIMER). We assessed the question of specific follower species by comparing the proportion of fish species present at the study site to the proportion of follower species we observed with goatfish during feeding instances. We used the available fish data from fish transects done for other similar projects (Bernardi 2010). We compared the available fish species to the actual follower fish species by conducting a Pearson chi-squared analysis. Using linear regression, we tested the hypothesis that the relationship between M. surmuletus and their follower fish was commensal by first comparing goatfish feeding rate and total goatfish associates. To examine differences in feeding rates of follower species when alone and with M. surmuletus, we ran an ANOVA in JMP. We also chose to compare the community composition of follower species with goatfish foraging habitat. The community composition refers to the unique makeup of follower fish that were found with an individual goatfish. We used PERMANOVA analyses (in PRIMER) to determine a correlation between these two factors. We also conducted a RELATE test (in PRIMER) to show the strength of the relationship between follower species composition and foraging site. Results A total of 69 goatfish and 213 follower individuals were observed for a total of 172 hours and 35 minutes. Presence of an observer did not appear to affect the behavior of most study fish. During a few observation sessions, individual Coris julis switched focus from foraging to examining the observer, in which case a new individual was chosen for observation. M. surmuletus size ranged from 5cm to 21.5cm. Goatfish smaller than 15cm were considered small and goatfish greater than or equal to 15cm were considered large. Follower species size was not recorded. Foraging Habitat The two most abundant habitat types surveyed were turf algae (49%) and Posidonia oceanica (15%). All other habitat types accounted for less than 10% each of the remaining habitat. M. surmuletus foraged on turf algae approximately 78% of the time, sand 12%, cobble 6%, and dead Posidonia 4%. We did not observe M. surmuletus foraging in P. oceanica or “other” substrates. Foraging habitat used by M. surmuletus is

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