Primary Invertebrate Reef Grazers on Little Cayman Tara Bonebrake and Leah Brandt

Introduction Transition of coral dominance to macroalgal dominance (Edmonds, 2001) Increase in algal takes up space that could be utilized for coral colonization (Lessios, 2005) Importance of identifying vertebrate and invertebrate herbivore grazers  Urchins consume different types of macroalgae (Solandt, 2001)

Our study Focus on Diadema and Echinometra as grazers Compare north and south reefs of Little Cayman Aquarium experiment to observe urchin food preference

Hypotheses Diadema is the invertebrate grazer Urchins will graze on brown and green algae Biomass of algae will be low when frequency of grazers is high There will be a difference in urchin population and algal biomass between the north and south sites

Methodology- Field Ten sites around Little Cayman  Five north, five south  Snorkel back reef habitats and dive on reef crests 30m x 2m transects  Five transects each snorkel  Three transects each dive Counted Diadema and Echinometra Collected algae on two transects at 10,20,30m intervals from a 625 cm 2 quadrat

Methodology- Lab Rinse, weigh, and identify algae samples Calculate biomass of algae and each species Two aquariums with two specimens each Seven rocks each with different species of algae tied to it Weigh rocks and specimens

Results Diadema is not the most prevalent grazer Dominance of urchins on the south side Supports hypothesis that there is a significant difference between urchin and algal populations from the north and south sides Table 1: Amount of urchins and algae around Little Cayman NorthSouth Diadema7108 Echinometra13144 Biomass of Algae (g/m^2)

Results Prevalence of urchins at south sites No trend between increasing algal biomass and frequency of urchins Does not support hypothesis that there is a relationship between low algal biomass and high frequency of urchin Figure 1

Results Halimeda species is most abundant on both sides of Little Cayman North has greater occurrence of red algae South has greater occurrence of brown and green

Algae Algae/Lobophora%20variegata%20WAK%20(1).JPG

Discussion Contradiction between literature and experiment of food preference of urchins  Urchins are non-specific in the algae they eat (Solandt, 2001)  Experiment did not support same results Could urchins not prefer the red algae found on the north side? Due to the differences in urchin and algal populations, there could be factors affecting leeward and windward sides of the island

Observations Urchins were not found on macroalgae on the reefs  Turf algae-covered rocks Urchins spent most time near the surface of the water  Did not graze much on rocks, except when we placed them there

Recommendations Change tank set up for aquarium experiment Incorporate forereef and intertidal environments for urchin surveys to compare habitat

References Peter J. Edmunds and Robert C. Carpenter, "Recovery of Diadema antillarum reduces macroalgal cover and increases abundance of juvenile corals on a Caribbean reef" PNAS, , pages Rebecca J. Fox and Don R. Bellwood, "Direct vs. indirect methods of quantifying herbivore grazing impact on a coral reef" Marine Biology, , pages Nancy Knowlton, "Sea urchin recovery from mass mortality: New hope for Caribbean coral reefs?" PNAS, , pages P.S. Lobel and J.C Ogden, "Foraging by the herbivorous parrot fish: Sparissoma radians" Marine Biology, , pages Jean-Luc Solandt and Andrew C. Campbell, "Macroalgal feeding characteristics of the urchin Diadema antillarium at Discover Bay, Jamaica" Caribbean Journal of Science, 2001, 37 (3-4) pages I.D. Williams and N.V.C. Polunin, "Large scale associations between macroalgal cover and grazer biomass on mid-depth reefs in the Caribbean" Coral Reefs, 2001, 19 pages H. A. Lessios "Diadema antillarium in Panama twenty years following mass mortality" Coral Reefs, 2005, 24 pages H.A. Lessios, M.J. Garrido, and B.D. Kessing, "Demographic history of Diadema Antillarium, a keystone herbivore in Caribbean Reefs", Proceeding of the Royal Society of London, pages 1-7