primary invertebrate reef grazers on little cayman tara bonebrake and leah brandt
TRANSCRIPT
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
0
20
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140
0 500 1000 1500 2000 2500
Biomass (g/m^2)
Nu
mb
er o
f Gra
zers
North Sites
South Sites
Figure 1
ResultsPercent Algae by Type for South and North Sites
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 2
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
0
10
20
30
40
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80
0 200 400 600 800 1000 1200 1400
Biomass (g/m^2)
Freq
uenc
y
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