Presentation given at Reef Conservation UK 2008.

1. Patch size dependent grazing and algal succession on a Caribbean coral reef Stoyle, G.W. & Box, S.J. 2008 Utila Centre for Marine Ecology Bay Islands Honduras

3. Herbivorous fishes critical to ecosystem function

4. Grazing reinforces resistance and resilience

6. Patch size may be an important factor in benthic community processes

7. Few studies have considered such processes at discrete scales

8. Few studies regarding successional processes

10. Monitor changes in density & grazing intensity following treatment

11. Correlate any changes with patch size

12. Model likelihood fish will bite as patch size increases

14. Correlate macroalgal regrowth (if any) with herbivore decline

16. Grid design: 6m2 divided into nine 2m2 cells

17. Observations: Bi-weekly, 3 months pre-treatment, 3 months post-treatment, 4mins/cell

18. Regular photographic census: CPCe analysis

19. Treatment spatial scale (4 size classes, 4 replicates): 25cm2, 50cm2, 100cm2, 200cm2

20. Macroalgal cover reduced from 76.76% to 12.50% Grid Layout Treatment Patches (grey areas) Mean % Pre-Treatment Benthic Cover

21. Results: Herbivore Density Post-treatment mean total density between grids did not significantly alter for each species Mean abundance pre (1) and post (2) treatment in grids A&B Post-treatment mean total density between size classes did significantly alter for some species Mean abundance of 5 dominant herbivores between size classes following treatment (Combined grids)

22. Results: Feeding Post-treatment mean total fish biting per species significantly altered* *Bite counts were restricted to whether fish bit or not, due to limited observers (binomial data) 1-way ANOVA results showing difference in total bites per species before and after treatment in grids A&B

23. Results: Size Dependence Pre-Treatment Post-Treatment No. fish biting at least once Survey Data represents all species, all cells and both grids combined adjusted per unit area (2m2) Control

24. Results: Size Dependence Pre-Treatment Post-Treatment No. fish biting at least once Survey Data represents all species, all cells and both grids combined adjusted per unit area (2m2) 25cm2

25. Results: Size Dependence Pre-Treatment Post-Treatment No. fish biting at least once Survey Data represents all species, all cells and both grids combined adjusted per unit area (2m2) 50cm2

26. Results: Size Dependence Pre-Treatment Post-Treatment No. fish biting at least once Survey Data represents all species, all cells and both grids combined adjusted per unit area (2m2) 100cm2

27. Results: Size Dependence Pre-Treatment Post-Treatment No. fish biting at least once Survey Data represents all species, all cells and both grids combined adjusted per unit area (2m2) 200cm2

28. Logistic Regression Model Multiple comparisons showed highly significant differences in number of fish taking at least one bite between smallest and largest size classes Binary logistic regression uses Yes/No data to predict a probability of success (p), in this case the likelihood a fish will bite, from a predictor variable (x) in this case the size of cleared patch: pis the probability of a fish biting at least once, b0, b1 are the coefficientsfor the predictor variablex (size class of cleared patch) and e is the natural logarithm Dunn’s multiple comparisons showing differences in total number of fish biting at least once between each size class

29. BLR Model Outputs with GLM Likelihood of fish biting at least once – data represents most significant differences between smallest and largest treatment areas

30. Algal Succession: Pre-treatment Total Macroalgae 76.76%

31. Algal Succession – 1 week Total Macroalgae 12.50%

32. Algal Succession: 4 weeks Total Macroalgae 15.57%

33. Algal Succession: 8 weeks Total Macroalgae 26.62%

34. Algal Succession: 12 weeks Total Macroalgae 56.03%

36. Herbivore regime between cells did alter following treatment (increase)

37. Increases were positively correlated with larger treatment areas for some species

38. Likelihood of fish biting was positively correlated with larger treatment areas

39. Herbivory density and feeding intensity declined as macroalgal density increasedSECONDARY

40. Current herbivore regime not sufficient to maintain low algal assemblage

41. Less parrotfish & smaller parrotfish....WHY?

42. BUT sufficient herbivory could maintain free space in optimal size patches

44. UCME staff & interns for field assistance

45. Kevin Kohler (NCRI) for developing CPCe

46. Parrotfish of Utila