2014 MARINE ECOLOGICAL SURVEY OF ELIZABETH AND MIDDLETON REEFS, LORD HOWE COMMONWEALTH MARINE RESERVE Andrew S. Hoey*, Morgan S. Pratchett, Jacob Johansen, and Jessica Hoey FINAL REPORT – June 1st, 2014 Produced for The Department of the Environment *Corresponding author – Dr Andrew Hoey, ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville QLD 4811. E-mail: [email protected], Telephone/ Fax: (07) 47815979 / 47816722 Page 1 In responding to a tender from the Department of Environment, a team of researchers representing the ARC Centre of Excellence for Coral Reef Studies at James Cook University (JCU) completed surveys of the coral reef fauna at Elizabeth and Middleton Reef. The field team comprised Professor Morgan Pratchett, Dr Andrew Hoey, Dr Jacob Johansen and Mrs Jessica Hoey. All the abovementioned researchers contributed to the preparation of this report. © Commonwealth of Australia 2014 This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth. Requests and inquiries concerning reproduction and rights should be addressed to the Commonwealth Copyright Administration, Attorney General’s Department, Robert Garran Offices, National Circuit, Barton ACT 2600 or posted at http://www.ag.gov.au/cca The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Australian Government. This report has been produced for the sole use of the party who requested it. The application or use of this report and of any data or information (including results of experiments, conclusions, and recommendations) contained within it shall be at the sole risk and responsibility of that party. JCU does not provide any warranty or assurance as to the accuracy or suitability of the whole or any part of the report, for any particular purpose or application. Address all correspondence regarding this report to Dr Andrew Hoey. E-mail: [email protected] Page 2 1 Executive Summary Elizabeth and Middleton Reefs are of considerable ecological importance. They are the southernmost open ocean platform reefs in the world, and support a unique mix of tropical and subtropical species, including several endemic species. Due to their isolation they also provide a refuge for the ‘vulnerable’ black cod. The purpose of this study was to undertake rigorous surveys of shallow coral reef habitats at Elizabeth and Middleton Reefs to assess the current condition of these habitats and detect any changes in the period since the last survey, in March 2011. Field-based surveys of habitat structure (percentage cover of hard and soft corals, sponges and algae, topographic complexity), coral replenishment (juvenile corals), coral health (the incidence of coral disease and coral predation), functionally important reef fishes (e.g., surgeonfishes, parrotfishes, drummers), endemic fishes, and invertebrates (holothurians, urchins and the corallivorous crown-of-thorns starfish) were undertaken at Elizabeth and Middleton Reefs from 4th to 9th March, 2014. Two depth zones (shallow reef crest and deep reef slope) were sampled at each of 16 sites, encompassing exposed reef fronts, back reefs and lagoonal habitats. Apex predators, including Galapagos sharks and Black cod, were also sampled at each site, using replicate 250 - 500m transects. Main findings include: • Mean cover of hard (scleractinian) corals (Elizabeth Reef: 29.2%; Middleton Reef: 19.3%) was slightly lower than 2011 levels, notably within lagoonal habitats. • Coral cover at both Elizabeth and Middleton Reefs is lower than has been recorded on the southern Great Barrier Reef and Lord Howe Island, suggesting that coral assemblages are recovering from previous disturbances. The protracted recovery appears to be related to low rates of coral replenishment and coral growth. • The health of existing corals was generally high, with a low incidence of coral bleaching and coral disease, and very low densities of coral predators, such as the crown-of-thorns starfish. Consequently these were not likely to be having a Page 3 major influence on coral assemblages, and seemed unlikely to be the cause of observed reductions in coral cover. • Cover of macroalgae (conspicuous seaweeds >5 mm in height) was generally low (ca. 10%) and displayed limited change to 2011 levels. The exception to this was the back reef on Middleton Reef where macroalgae doubled from 2011 and currently covers over 2/3 of the shallow habitats at these sites. • The density and biomass of functionally important herbivorous fishes, namely parrotfishes, surgeonfishes and drummers, was generally stable between 2011 and 2014. The only exception was a significant reduction in the abundance of juvenile parrotfish within the lagoons, and appears to be related to a reduction of branching corals in these habitats. • Densities of endemic fishes (Amphiprion mccullochi, Chaetodon tricinctus, and Coris bulbifrons) varied greatly among study sites, but were generally greater than or equal to densities recorded in 2011. The densities of C. tricinctus and C. bulbifrons increased on both reefs from 2011 to 2014, while densities of A. mccullochi increased on Middleton and remained stable on Elizabeth Reef. • Densities of the Galapagos reef shark were extremely high in 2014, and were approximately double those recorded in 2011 and up to 36 times higher than recorded in 2006. All observed were small immature individuals suggesting that the shallow water environments of Elizabeth and Middleton Reefs are an important nursery habitat for this species. • Densities of black cod, listed as vulnerable in NSW waters and under the Environment Protection and Biodiversity Conservation Act 1999, remained relatively unchanged between 2011 and 2014. • Elizabeth and Middleton Reefs appear to support healthy fish assemblages and coral assemblages in a state of recovery. The key threats to these reefs are likely to be i) increasing seawater temperatures, ii) physical damage from severe storms, and iii) outbreaks of crown-of-thorns starfish. The impact of these threats is likely to be magnified, relative to low latitude reefs, by the limited capacity for recovery (slow growth and limited replenishment of corals) following such disturbances. Page 4 2 Recommendations 1. Given the isolation and apparent constraints on population and community resilience of reef corals and associated organisms at Elizabeth and Middleton Reefs, anthropogenic disturbances should be minimized through the maintenance of current protection and regulation. 2. Ongoing and regular (at least every 2-3 years) monitoring is critical to assess effects of historical (outbreaks of Acanthaster planci) and emerging threats (e.g., climate change) to corals, and to monitor population fluctuation in key fish species, such as the Galapagos shark and Black cod. This monitoring is a key requirement for effective long-term management of these unique assemblages. 3. In addition to monitoring the population status of key benthic and fish taxa (i.e., corals, macroalgae, herbivorous fish, apex predators), process-orientated monitoring of growth, mortality, and recruitment of these groups would greatly improve our understanding of the dynamics and resilience of these unique coral reef assemblages. This would however, require increased frequency and duration of survey trips. In particular, there is a clear need to understand the determinants of macroalgal abundance and biomass, and the rates of recruitment, growth and mortality of coral assemblages. 4. The current survey highlighted the benefits of matching previous sampling methods and sites, facilitating rigorous temporal comparisons of fish and benthic communities for the first time. Future sampling should continue to use sampling methods that are compatible (if not identical) with the past two surveys (2011 and 2014) and, as a minimum, continue to survey the same sites to maximise detection of long-term trends. Implementation of comparable sampling methods across all Commonwealth Marine Reserves would also enable meaningful spatial and temporal comparisons. 5. A lack of access to data from previous surveys limited our capacity to evaluate long-term trends at these reefs. To facilitate spatial and temporal comparisons, all data arising from these surveys should be made publicly available in a centralised and accessible database, or within an appropriate existing Page 5 database. At the very minimum, all reports relevant to each of the offshore Commonwealth reserves should be digitised and made publically available by the Department of the Environment. Page 6 Table of Contents 1. Executive Summary 3 2. Recommendations 5 3. Introduction 12 3.1 Elizabeth and Middleton Reefs 14 (Lord Howe Commonwealth Marine Reserve) 3.2 Objectives and scope 17 4. Methods 18 4.1 Habitat structure 18 4.2 Reef fishes 22 4.3 Unitary invertebrates (e.g., sea cucumbers) 23 4.4 Species richness 23 5. Findings 24 5.1 Habitat structure 24 5.1.1 Coral cover 24 5.1.2 Macroalgal cover 26 5.1.3 Temporal changes in coral and macroalgae 26 5.1.4 Topographic complexity 31 5.2 Replenishment and resilience of coral populations 32 5.2.1 Juvenile corals 32 5.1.2 Coral predators 39 5.1.3 Coral condition 40 5.3 Coral reef fishes 43 5.3.1 Roving herbivorous fishes 43 5.3.2 Endemic fishes 53 5.3.3 Apex predators 59 5.3.4 New species records 62 5.4 Unitary invertebrates 63 5.4.1 Sea cucumbers (Holothurians) 63 5.4.2 Sea urchins (Echinoids) 65 6. Conclusions 69 Page 7 6.1 Habitat structure 69 6.2 Reef fishes 73 6.3 Unitary invertebrates 77 7. Acknowledgements 80 8. References 81 Page 8 List of Figures Figure 1: Map showing the location of the study sites. (a) Geographic location of 19 Elizabeth and Middleton reefs off Australia’s east coast. (b) Locations of the nine study sites on Middleton Reef. (c) Location of the seven study sites on Elizabeth Reef. Note that site 6 on Elizabeth Reef was separated into shallow (6s) and deep (6d) due to the lack of shallow and deep habitat in close proximity.