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 grazerUrchins will graze on brown and green

algaeBiomass of algae will be low when

frequency of grazers is highThere 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 cm2 quadrat

Methodology- Lab

Rinse, weigh, and identify algae samplesCalculate biomass of algae and each

speciesTwo aquariums with two specimens eachSeven rocks each with different species of

algae tied to itWeigh 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

North South

Diadema 7 108

Echinometra 13 144

Biomass of Algae (g/m^2)

10818 6265

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 urchinPrevalence of Grazers on North and South Sites

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Biomass (g/m^2)

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zers

North Sites

South Sites

Figure 1

ResultsPercent Algae by Type for South and North Sites

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South vs. North

Blue-Green

Red

Green

Brown

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

Invertebrates vs. Biomass of Brown Algae

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Biomass (g/m^2)

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Diadema N

Echinometra N

Diadema S

Echinometra S

Algae

http://www.liveaquaria.com/images/categories/product/p-80740-halimeda.jpg

http://i95.photobucket.com/albums/l140/JFK_Jr/BrownalgaePhaeophytaDictyotasp.jpg

http://www.wetwebmedia.com/Algae%20and%20Plt%20Pix/Brown%20Algae/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, 2001 98, pages 5067-5071

Rebecca J. Fox and Don R. Bellwood, "Direct vs. indirect methods of quantifying herbivore grazing impact on a coral reef" Marine Biology, 2008 154, pages 325-334

Nancy Knowlton, "Sea urchin recovery from mass mortality: New hope for Caribbean coral reefs?" PNAS, 2001 98, pages 4822-4824

P.S. Lobel and J.C Ogden, "Foraging by the herbivorous parrot fish: Sparissoma radians" Marine Biology, 1981 64, pages 173-183

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 227-238

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 358-366

H. A. Lessios "Diadema antillarium in Panama twenty years following mass mortality" Coral Reefs, 2005, 24 pages 125-127

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, 2001 268 pages 1-7