Direct versus indirect methods of quantifying herbivore grazing impact on a coral reef

Two methods were used to assess the grazing impact of roving herbivorous fishes across a coral reef depth gradient within Pioneer Bay, Orpheus Island, Great Barrier Reef. The first technique employed was a method traditionally used to quantify herbivory on coral reefs via the (indirect) inference of herbivore impact from biomass estimates and reported feeding rates. The second method (one of a range of direct approaches) used remote underwater video cameras to film the daily feeding activity of roving herbivores in the absence of divers. Both techniques recorded similar patterns and relative levels of herbivore biomass across five reef zones at the study site. Indirect estimates of the grazing impact across the reef depth gradient of the three predominant species of herbivore broadly coincided with levels quantified directly by remote underwater video, indicating that, to a large extent, presence does correspond to function. However, the video data suggested that, for individual species in particular reef zones, the absolute level of impact may be less than that inferred from presence. In the case of the parrotfish Scarus rivulatus, the video recordings suggested that, at the reef crest, an average of 52% (±18 SE) of each m2 area of reef would be grazed each month, compared with an area of 109% (±41 SE) suggested by inferring grazing activity from presence alone. Potential biases associated with remote video recorders may explain some of the discrepancy between values. Overall, the results suggest that, for some fish groups, the indirect method of inferring function from presence can provide a good indication of relative levels of herbivore impact across a coral reef.

[1]  G. Edgar,et al.  Biases associated with the use of underwater visual census techniques to quantify the density and size-structure of fish populations , 2004 .

[2]  K. Clements,et al.  The trophic status of herbivorous fishes on coral reefs , 2002 .

[3]  M. Hixon,et al.  Succession and Herbivory: Effects of Differential Fish Grazing on Hawaiian Coral‐Reef Algae , 1996 .

[4]  R. Thresher,et al.  Comparative analysis of visual census techniques for highly mobile, reef-associated piscivores (Carangidae) , 1986, Environmental Biology of Fishes.

[5]  D. Bellwood,et al.  Phase Shifts, Herbivory, and the Resilience of Coral Reefs to Climate Change , 2007, Current Biology.

[6]  R. Babcock,et al.  A baited underwater video system for the determination of relative density of carnivorous reef fish , 2000 .

[7]  D. Bellwood,et al.  Confronting the coral reef crisis , 2004, Nature.

[8]  R. Sluka,et al.  Evaluating the use of roving diver and transect surveys to assess the coral reef fish assemblage off southeastern Hispaniola , 2002, Coral Reefs.

[9]  G. De’ath,et al.  Comparison of baited remote underwater video stations (BRUVS) and prawn (shrimp) trawls for assessments of fish biodiversity in inter-reefal areas of the Great Barrier Reef Marine Park , 2004 .

[10]  D. Bellwood,et al.  Locomotion in labrid fishes: implications for habitat use and cross-shelf biogeography on the Great Barrier Reef , 2001, Coral Reefs.

[11]  J. Bell,et al.  Estimating length frequency distributions of large reef fish underwater , 1985, Coral Reefs.

[12]  J. H. Bruggemann,et al.  Bioerosion and sediment ingestion by the Caribbean parrotfish Scarus vetula and Sparisoma viride: Implications of fish size, feeding mode and habitat use , 1996 .

[13]  Anthony W. D. Larkum,et al.  An experimental analysis of factors controlling the standing crop of the epilithic algal community on a coral reef , 1983 .

[14]  D. Bellwood,et al.  Cross-shelf variation in the role of parrotfishes on the Great Barrier Reef , 2008, Coral Reefs.

[15]  Euan S. Harvey,et al.  A comparison of the precision and accuracy of estimates of reef-fish lengths determined visually by divers with estimates produced by a stereo-video system. , 2001 .

[16]  D. Bellwood,et al.  New paradigms for supporting the resilience of marine ecosystems. , 2005, Trends in ecology & evolution.

[17]  N. Polunin,et al.  Algal food supply and grazer demand in a very productive coral-reef zone , 1992 .

[18]  E. Harvey,et al.  A comparison of temperate reef fish assemblages recorded by three underwater stereo-video techniques , 2005 .

[19]  R. Millar,et al.  Detection of spatial variability in relative density of fishes: comparison of visual census, angling, and baited underwater video , 2000 .

[20]  D. Bellwood.  Direct estimate of bioerosion by two parrotfish species, Chlorurus gibbus and C. sordidus, on the Great Barrier Reef, Australia , 1995 .

[21]  M. Shortis,et al.  Improving the statistical power of length estimates of reef fish: a comparison of estimates determined visually by divers with estimates produced by a stereo-video system. , 2001 .

[22]  K. Clements,et al.  The trophic status of herbivorous fishes on coral reefs , 2002 .

[23]  D. J. Creasey,et al.  Reactions of fish to sound generated by divers' open-circuit underwater breathing apparatus , 1974 .

[24]  Daniel R. Brumbaugh,et al.  Fishing, Trophic Cascades, and the Process of Grazing on Coral Reefs , 2006, Science.

[25]  David R. Bellwood,et al.  Sleeping Functional Group Drives Coral-Reef Recovery , 2006, Current Biology.

[26]  M. Kulbicki,et al.  A general approach to length-weight relationships for New Caledonian lagoon fishes , 2005 .

[27]  Gary A. Kendrick,et al.  A comparison of underwater visual distance estimates made by scuba divers and a stereo-video system: implications for underwater visual census of reef fish abundance , 2004 .

[28]  T. P. Neufeld,et al.  Direct Induction of Autophagy by Atg1 Inhibits Cell Growth and Induces Apoptotic Cell Death , 2007, Current Biology.

[29]  N. Polunin,et al.  Large-scale associations between macroalgal cover and grazer biomass on mid-depth reefs in the Caribbean , 2001, Coral Reefs.

[30]  Marc Soria,et al.  Visual censuses of tropical fish aggregations on artificial reefs: slate versus video recording techniques , 2005 .

[31]  M. Kulbicki.  How the acquired behaviour of commercial reef fishes may influence the results obtained from visual censuses , 1998 .

[32]  D. Bellwood,et al.  Quantifying herbivory across a coral reef depth gradient , 2007 .

[33]  G. Davis,et al.  Population estimates of four kelp forest fishes and an evulation of three in situ assessment techniques , 1989 .

[34]  P. Sale,et al.  Correction for bias in visual transect censuses of coral reef fishes , 1983, Coral Reefs.

[35]  Fj Scott,et al.  EFFECTS OF GRAZING ON SPECIES COMPOSITION OF THE EPILITHIC ALGAL COMMUNITY ON CORAL REEFS OF THE CENTRAL GREAT-BARRIER-REEF , 1987 .

[36]  B. Mapstone,et al.  Observer effects and training in underwater visual surveys of reef fishes , 1997 .

[37]  Bellwood.  Carbonate transport and within-reef patterns of bioerosion and sediment release by parrotfishes (family Scaridae) on the Great Barrier Reef , 1995 .

[38]  N. Polunin,et al.  Partitioning among grazers of food resources within damselfish territories on a coral reef , 1989 .

[39]  J. Bruggemann,et al.  Foraging by the stoplight parrotfish Sparisoma viride. I.: Food selection in different, socially determined habitats , 1994 .

[40]  M. Hay.  Herbivory, Algal Distribution, and the Maintenance of Between-Habitat Diversity on a Tropical Fringing Reef , 1981, The American Naturalist.

[41]  J. Travis.  A Method for the Statistical Analysis of Time-Energy Budgets , 1982 .

[42]  P. A. Stickels,et al.  Interaction between nutrients and herbivory in controlling algal communities and coral condition on Glover's Reef, Belize , 2003 .

[43]  G. Russ,et al.  Grazer biomass correlates more strongly with production than with biomass of algal turfs on a coral reef , 2003, Coral Reefs.

[44]  T. Hughes.  Catastrophes, Phase Shifts, and Large-Scale Degradation of a Caribbean Coral Reef , 1994, Science.

[45]  D. Klumpp,et al.  TEMPORAL AND SPATIAL PATTERNS IN PRIMARY PRODUCTION OF A CORAL-REEF EPILITHIC ALGAL COMMUNITY , 1989 .

[46]  M. Smith.  Effects of observer swimming speed on sample counts of temperate rocky reef fish assemblages , 1988 .