Full description This study was nested in sub-project 3.2.2 “Ecosystem impacts of human usage and the effectiveness of zoning for the biodiversity conservation” in Node 3.2. The focus of this study was on trophic effects in the NMP. Due to the importance of herbivores in coral-reef systems, this study focused on characterising and quantifying the process of herbivory in the NMP with a particular emphasis on the removal of adult macroalgae.
We used a range of approaches to gain an understanding of spatial and species-related patterns in herbivory in five distinct studies. Using underwater video cameras and Sargassum myriocystum assays, 23 different fish species were observed consuming macroalgae, but seven species (Naso unicornis, Kyphosus sp., K. vaigiensis, Siganus doliatus, Scarus ghobban, S. schlegeli and initial-phase Scarus sp.) together accounted for 95% of the observed bites across five regions. Of these species, three were identified as the most important in consuming macroalgae: N. unicornis, Kyphosus sp. and K. vaigiensis. These results were supported by stable isotope analyses that incorporate nutrients from food sources over far longer periods than those examined using the assay approach.
The attached final report provides details on the 5 studies conducted related to herbivory:
1. Spatial patterns in herbivory on a coral reef are influenced by structural complexity but not by algal traits.
2. Herbivore diversity on coral reefs: a transcontinental comparison.
3. Variation in macroalgal herbivory by fishes across a western-continental coral-reef system.
4. Variability in the food sources of herbivorous invertebrates and fishes in a coral-reef system: a stable isotope approach.
5. The role of herbivory on the spatial distribution of recruiting and established algal communities in coral versus algal dominated habitats.
For detailed methodology refer to attached final report:
* Chapter 2 : Spatial patterns in herbivory on a coral reef are influenced by structural complexity but not by algal traits (conducted mostly in Mandu sanctuary zone and one experiments in Maud sanctuary zone). Tethered (Sargassum myriocystum) experiments, censuses of herbivorous fish assemblages, transects of algal cover and biomass, coral cover and structural complexity, algal transplant experiments, experimental tests of palatability of algae (L. variegata) from high and low herbivory habitats (April 2008 - Mandu sanctuary zone) were conducted.
* Chapter 3 : Herbivore diversity on coral reefs: a transcontinental comparison (conducted between December 2008 and February 2009 in the Keppel Islands Group (23 degrees 109S, 151 degrees 009E) on the Great Barrier Reef and on Ningaloo Reef (22 degrees 07S, 113 degrees 52E). Within each region, we selected three representative reefs (hereafter referred to as locations) that were all situated within sanctuary zones, to minimise the potential effect of extractive activities. The three Keppel Island locations were Olive Point (23° 09S 150° 55E), Middle Island (23° 10S, 150° 55E) and Halfway Island (23° 11S 150° 58E). The three Ningaloo locations were Mangrove Bay (21°58S, 113° 54E), Mandu (22°05S, 113° 52E), and Osprey (22°14S, 113° 52E). Within each location, two sites were haphazardly selected about 100 m apart. Macroalgal assays and video analysis were conducted.)
*Chapter 4 - Rates of Sargassum consumption and identity of herbivores vary across hundreds of kilometres along a continental fringing coral reef (conducted during April and May 2009 on Ningaloo Reef in five sanctuary zones. Within each region, three reef-flat sites were randomly selected at 2-3 m depths and spaced approximately 300 m apart [see thumbnail]. Macroalgal tethers and video analysis were used along with underwater visual censuses (UVC) were carried out on snorkel.
* Chapter 5 - Variability in the food sources of herbivorous invertebrates and fishes in a coral-reef system: a stable isotope approach (All sampling was undertaken at depths between 1 and 6 m in each habitat/region (Bundegi, Mandu, Maud) over two months (July - September 2008) to minimise temporal variations in isotopic signatures.
Within each region/habitat, 3-5 replicate samples of benthic primary producers and herbivorous invertebrates were haphazardly collected by hand by divers over distances of metres to 100s of metres. Samples of Epilythic Algal Matrix (EAM) were obtained by collecting boulders and pieces of dead coral and gently brushing off all loose sediment and detritus particles with a soft brush. These aqueous EAM samples were filtered through a 125 μm sieve and allowed to settle for 1-2 hours before excess water was decanted. In each region/habitat, 3-5 individuals of two gastropod species and one echinoderm species were collected by hand, and14 nominally herbivorous fish species were collected by spear fishing. Since Kyphosidae species were often difficult to distinguish, they have been pooled for this study. Muscle tissue was taken from the foot of gastropods, the Aristotle’s lantern of sea urchins, and the dorsal body of fish. Samples were then frozen immediately after collection and processing and stored at -20°C until laboratory analysis. Prior to analysis, macrophytes were rinsed with seawater, and cleaned of epiphytes where necessary.
Sampling resulted in three species of invertebrates and 14 species of nominally herbivorous fishes, including 8 species designated as scrapers and six as browsers. Stable isotope analysis was conducted on smaples
* Chapter 6 - The role of herbivory on the spatial distribution of recruiting and established algal communities in coral versus algal dominated habitats (The study from August 2008 until May 2009 in the Mandu sanctuary zone. Fish abundance and biomass were characterised for each site in three seasons: spring (November 2008), summer (February 2009) and autumn (May 2009). A diver swam a 25 m transect at a constant speed (ca 8 minutes per transect) and counted the abundance and size class (to 5 cm) of individual nominally herbivorous fish along 2.5 m on both sides of the transect line. Four replicate transects were conducted at each site at each time period, and each transect was separated by at least 10 m.
Macroalgal biomass was measured by clearing three 0.25 m2 haphazardly placed quadrats of all macroalgae (thalli larger than 2 cm) at each site-habitat combination. Macroalgal biomass was sampled in the same three seasons described above for the fish assemblages.
To assess the influence of large herbivorous fish on algal recruitment in habitats dominated by either macroalgae or coral, herbivore exclusion cages were installed at the two sites in the lagoon and reef flat. The cages were triangular in shape, and measured 50 x 50 x 50 cm.
Recruitment tiles were installed in the plots in August 2008 and collected in February 2009. The tiles measured 10 x 10 cm and were made from PVC.
Authors: David Abecasis, David Bellwood, Scott Bennett, Chris Doropoulos, Glenn Hyndes, Peter Micheal, Mathew Vanderklift, Adriana Verges. Acknowledgements: We are grateful to the team of staff and volunteers for their tireless support in the field and/or laboratory: A. Bostock, E. Crochelet, R. Czarnik, F. Dalaine, J. Eyres, M. Haywood, K. Inostroza, P. Kiss, R. Larsen, A. Lemmon, I. McLeod, P. Michael, N. Millar, T. Minutoli, V. Mocellin, A. Richards, J. Santana, D. Thomson, F. Vitelli and co-authors. We thank J. Tanner for the stable isotope analyses, and J. Ortiz for statistical advice and thoughtful discussions on aspects of the study. We also thank the co-authors of the chapters within this report for their discussions and other contributions: D. Abecasis, D. Bellwood, S. Bennett and P. Michael. Additional funding through ECU and D. Bellwood at James Cook University allowed the cross continental comparison in Chapter 3. Insightful comments and discussions were provided throughout the study by R. Babcock. The Department of the Environment and Conservation of Western Australia provided a permit to the authors during 2008 -2009 to perform this study within the Sanctuary Zones of the Ningaloo Marine Park (Permit Number CE002084) and to collect flora samples (Permit Number SF006457). The study was funded mainly by the Western Australia Marine Science Institution under the Ningaloo Research Program.