11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 10: Ecological Processes on Today's Reef Ecosystems
10-21
The Roles Of Nutrients And Herbivory in Controlling Micro-And Macrobioerosion
Patterns in Eastern African Reefs
Marina CARREIRO-SILVA* 1,2 , Timothy MCCLANAHAN 3 , Victor KENNEDY 1 ,
Joseph MIHURSKY 1 , Marjorie REAKA 4
1 Chesapeake Biological Laboratory, Center for Environmental Science, University of
Maryland, Solomons, MD, 2 Departamento de Oceanografia e Pescas, Universidade dos
Açores, Horta, Portugal, 3 Wildlife Conservation Society, Bronx, NY, 4 Department of
Biology, University of Maryland, College Park, MD
The roles of nutrients and sea urchin and fish herbivory in controlling patterns and rates
of internal bioerosion by micro- and macroborers were studied on nine reefs along the
East African coast. Bioerosion rates by microborers (algae, bacteria, and fungi) were
measured at three to six months intervals using herbivore-exclusion cages and
experimental substratum made of Lambis chiragra mollusk shells. Bierosion rates by
macroborers (mainly worms, bivalves and sponges) were measured on branching Porites
killed during the 1998 bleaching event, four and six years after their death. Hypotheses
tested were that (1) rates of micro- and macrobioerosion would be correlated with the
spatial variation in nutrient availability; (2) grazing by herbivorous fish and sea urchins
would reduce measurable microbioerosion and macrobioerosion rates. In contrast to
result of experimental studies in Glovers reef, Belize, no clear relationship was found
between nutrient levels and microbioerosion and all reefs experienced high colonization
and bioerosion rates by microbial endoliths. Instead, microborers’ density of colonization
and bioerosion rates were negatively correlated with current speed and cover of
encrusting coralline algae. In contrast, macrobioerosion rates were positively correlated
with chlorophyll a concentrations in reef waters. Microbierosion rates were more
influenced by grazing fish whereas macrobioerosion rates were more influenced by seaurchin
biomass. A complex mix of physical, chemical and ecological processes interact in
determining rates of bioerosion. Macroborers, which are predominantly suspension and
filter feeders, are more influenced by particulate organic material and plankton in the
water column. Microborers may be stimulated by inorganic nutrients, but coralline algae
may inhibit colonization of microborers by reducing light availability.
10-22
Vegetarians Are Shallow: Declining Herbivore Pressure With Depth
Eran BROKOVICH* 1,2 , Shai EINBINDER 2,3 , Inbal AYALON 4 , Nitzan SEGEV 4 ,
Yonathan SHAKED 4 , Amatzia GENIN 3,4 , Moshe KIFLAWI 5,6 , Salit KARK 1
1 The Biodiversity Research Group, Department of Evolution, Systematics and Ecology,
The Hebrew University of Jerusalem, Jerusalem, Israel, 2 Marine Twilight-Zone Research
& Exploration (MTRX), The Interuniversity Institute for Marine Sciences at Eilat (IUI),
Eilat, Israel, 3 Department of Evolution, Systematics and Ecology, The Hebrew University
of Jerusalem, Jerusalem, Israel, 4 The Israel National Monitoring Program, The
Interuniversity Institute for Marine Sciences at Eilat (IUI), Eilat, Israel, 5 Department of
Life Sciences, Ben-Gurion University, Beer-Sheva, Israel, 6 The Interuniversity Institute
for Marine Sciences at Eilat (IUI), Eilat, Israel
Coral reef herbivore fishes play an important role in mediating competition between fast
growing benthic algae and relatively slow-growing corals. Herbivore abundance and
composition may be affected by primary production levels which will decline with
decreasing light levels along the depth gradient. Herbivory studies, even those related to
depth gradients, have traditionally concentrated on shallow coral reefs. Hence, the
importance of herbivory in deep coral reefs (> 30 m) remains largely unexplored. This
study aims to examine herbivore assemblage-structure and potential pressure on turf and
macro-algae down to a depth of 65 meters. The study combines visual census of fish
assemblages; field measurements of turf algae growth rate; and in-situ evaluations of
herbivore pressure using caged vs. exposed settlement plates and bioassays. The number
of herbivore species dropped threefold between 5 m and 65 m; along with a decrease in
their abundance and algal growth rate. At 65 m most individuals sampled where large
roaming Scarids. The rate of macro-algae consumption was 2.25 gr dry algae/hour at one
meter depth and dropped rapidly (as a function of the natural log of depth) to almost zero
at 65 m. This pattern correlated with fish abundance and biomass. The percent of turf
algae consumed increased from 30% in one meter to 60% in 10 m then declined to near
zero in 50 m. The lower herbivory pressure in the deep reef suggests that the role of
fishes in maintaining suitable algal-free substrate for coral recruitment is less significant
than in shallow reefs. Whether or not algae can out-compete corals at these depths due to
eutrophication and whether herbivorous fish can mitigate an increase in algal growth
remains to be examined.
10-23
The Role of Herbivory in Structuring Benthic Algal Communities on the Great Barrier
Reef
Andrew HOEY* 1 , David BELLWOOD 1
1 ARC Centre of Excellence for Coral Reef Studies and School of Marine and Tropical Biology,
James Cook University, Townsville, Australia
We used a combination of visual census and algal transplants to examine the relationship
between herbivore distribution and relative removal rates of macroalgae. The distribution of
herbivorous fishes and removal rates of Sargassum sp. was quantified on two reefs in each of
three cross-shelf regions on the northern Great Barrier Reef. Sargassum sp. collected from an
inner-shelf reef flat was transplanted to the reef crest and back reef of each reef for a period of
24 hours. The rate of removal of Sargassum was greatest on mid-shelf reefs (57.5 – 79.9%.d-1),
and decreased markedly on both inner- (10.8 – 16.9%.d-1) and outer-shelf reefs (10.1 –
10.4%.d-1). These relative rates of removal were poorly correlated with the abundance and
biomass of macroalgal browsers and all herbivorous fishes, collectively. The biomass of
macroalgal browsers on the outer-shelf reef crest was at least double that of any other habitat
yet the rate of Sargassum removal was the lowest. In contrast, the mid-shelf reef crest displayed
the highest rate of Sargassum removal yet the biomass of macroalgal browsers was an order of
magnitude lower than that of the outer-shelf reef crest. These results highlight the potential
difficulties of modeling ecosystem processes on correlative relationships alone.
10-24
Size-Dependent Variation in The Functional Role Of The Parrotfish Scarus Rivulatus On
The Great Barrier Reef, Australia
Roberta BONALDO* 1 , David BELLWOOD 1
1 Australian Research Council Centre of Excellence for Coral Reef Studies and School of
Marine Biology, James Cook University, Townsville, Australia
Biodiversity loss and fishing-induced changes in the size distributions of fishes can impact
ecosystem function on coral reefs. These changes have led to an urgent need for studies on the
particular roles of species, to underpin effective coral reef management. The present study
focuses on the feeding ecology of six size classes (from 2.5 to 30 cm total length) of Scarus
rivulatus (family Labridae), one of the most abundant parrotfishes on the Great Barrier Reef,
Australia. Individuals in all six size classes strongly selected the epilithic algal matrix for
foraging and rejected other substratum types, including coral, macroalgae and sand. The six size
classes also had similar feeding rates (bites.min-1) and diel feeding patterns, with higher
feeding activity during the afternoon. However, the size of grazing scars by S. rivualtus
differed significantly among the six size classes, with small individuals scraping a greater
substratum area per unit biomass and larger individuals taking greater volume of material per
unit biomass. Thus, biomass can not be not be viewed as a proxy for ecosystem impact;
different sized individuals of S. rivulatus, and probably other parrotfish species, have a
markedly different impact on the benthic community. Selective harvesting of large individuals
will therefore change the functional role of this species. These results emphasize the importance
of considering the size of individuals when evaluating the role of reef species in ecosystem
process. These intraspecific functional differences will be critical when formulating reef
management strategies and evaluating the impact of fishing activity on reef ecosystems.
78