11th ICRS Abstract book - Nova Southeastern University

10.371
The sea urchins of Zanzibar and their effect on local coral communities
Omri BRONSTEIN* 1 , Yossi LOYA 1
1 Tel Aviv University, Tel Aviv, Israel
Poster Mini-Symposium 10: Ecological Processes on Today's Reef Ecosystems
As part of a GEF/World Bank targeted research on coral bleaching and local ecological
responses, a study aimed at assessing the impact of sea urchin populations on coral
communities around the island of Zanzibar was conducted. Between October 2006 and
November 2007, surveys of urchin populations were performed every 4 months at 6
locations around the island. Data on species assemblage, densities and size frequency
distributions was obtained. Results show dominance of two urchin species, Diadema
setosum and Echinometra sp., in 5 out of 6 stations, with D. setosum dominating the
western side of Zanzibar (56% - 98%) and Echinometra sp. dominating the eastern side
(60% – 97%). Average densities of D. setosom and Echinometra sp. ranged from 0-29.5
and 0-88.4 individuals m-2 respectively. To estimate the daily rate of bioerosion by a
single urchin, experiments were conducted on Echinometra sp. using the ignition-loss
method. Skeletons of the coral Acropora formosa collected from the study sites were used
as the food source. Individual CaCO3 bioerosion rates for Echinometra sp. were used to
assess the dependence of bioerosion rates on urchin population densities. Despite the fact
that individuals from denser populations erode at lower rates (0.012±0.001 g day-1) than
those from less dense populations (0.028±0.002 g day-1), overall bioerosion per area was
significantly greater in areas with denser populations. The data obtained here sheds new
light on our knowledge of urchin populations in protected and unprotected reefs around
Zanzibar and emphasizes the significant role of urchins in bioerosion of the reef. The
dense populations of sea urchins on the coral reefs of Zanzibar and their significant role
in bioerosion stress the need for long term monitoring and in depth research of this group
in the reef.
10.372
Stress Resistance in An Extreme Environment: Lessons Learnt From A Temperate
Symbiotic Sea Anemone
Milena PALKA 1 , Simon DAVY* 1
1 Marine Biology, Victoria University of Wellington, Wellington, New Zealand
Coral bleaching, is of huge global concern. In contrast to tropical corals, which are highly
sensitive to fluctuations in environmental parameters such as temperature, light and
salinity, zooxanthellate invertebrates in temperate waters rarely bleach despite highly
variable conditions. Here we are testing the effects of combined salinity-light stress on
the temperate sea anemone, Anthopleura aureoradiata and measuring photosynthetic
health and symbiosis stability. We are employing pulse amplitude modulated (PAM)
fluorometry, a powerful yet simple and non-invasive tool, for measuring various aspects
of photosynthesis through chlorophyll fluorescence. In the field, the effects of fluctuating
environmental factors on A. aureoradiata are being evaluated using Diving PAM. In the
lab, anemones are being exposed to varying levels of salinity (10-60 ppt) and light (1-420
µmol photons/m2sec) and photosynthetic health is being measured with Imaging PAM.
Because A. aureoradiata resides on shallow mudflats and in rock pools, it is likely to be
exposed to considerable environmental fluctuations. Since it has never been seen to
bleach, we hypothesize that the resistance of A. aureoradiata to changes in salinity is a
function of the robust photophysiology of its zooxanthellae. It is expected that
photophysiological stress, specifically zooxanthellar expulsion and loss of photosynthetic
capacity, will only occur at extreme levels of salinity and light. Remarkably, preliminary
results have shown that algal photosynthetic health was maintained while the anemone
itself clearly suffered from tissue damage. Zooxanthellae exposed to extreme levels of
salinity did not acclimatize to treatments as readily as those exposed to ranges closer to
the norm (Fv/Fm at 0.462 and 0.502 respectively), when held at the highest light levels.
The algae are least affected at the lowest irradiance, and hence light appears to be
exacerbating the impact of salinity. Thus, the data collected to date supports the idea that
these zooxanthellae have a robust photosynthetic stability.
10.373
Dynamic Of The Population Size Frequency Distribution in Two Scleractinian Coral
Species On Heron Reef, Gbr
Juan ORTIZ* 1 , Glen HOLMES 1
1 Centre for Marine Studies, The University of Queensland, St Lucia, Australia
Coral reefs are under constant and increasing stress as a consequence of a variety of factors (e.g.
over-fishing, agricultural runoffs, global warming, ocean acidification). Under these adverse
conditions coral growth and its variability is a key factor for understanding the potential
consequences of these disturbances. In this study we measure growth (two-dimensional growth
and tri-dimensional growth). The annual growth rates over a tree year period of two species of
scleractinian corals (Pocillopora damicornis and Stylophora pistillata) in four different
sections of Heron reef (Great Barrier Reef, Australia) will be presented. Preliminary results for
the first two years of the study show that both species presented considerably high growth rates
(between 34 and 87%). Both populations were skewed towards small colonies in the first year
but the skewness was significantly reduced for the second year. This bias toward bigger
colonies was accompanied by a reduction in the number of colonies despite the fact that the
total combined cover for this two species did not change. This study emphasizes how
significant ecological patterns can be masked when coral cover is used on its own as an
indicator of coral reef status. Our results may help coral reef managers to determine what areas
of the reef are more likely to be affected by disturbances that can either be size specific or
genotype specific.
10.374
Experimental Evaluation Of Post-Settlement Movement in The Coral-Associated Goby
gobiodon Histrio
Marlene WALL 1 , Joerg OTT 1 , Juergen HERLER* 1
1 University of Vienna, Vienna, Austria
Crypto-benthic reef fish play an important role in the functions of coral reef ecosystems.
Worldwide degradation of reef puts habitat specialized fishes at high risk by habitat loss. To
receive a better understanding of the susceptibility of coral-associated fishes to habitat loss,
post-settlement movement was surveyed in Gobiodon histrio. After observing movement
patterns under natural conditions in the northern Red Sea, a combination of manipulative field
and laboratory experiments were conducted. In the field, the homing ability was tested by
displacing individuals in different distances from their home coral. A considerable difference
was observed between minimum and maximum displacement (0.5m = 100%; 4 m = 16.4% of
fishes returned). Aquarium experiments were designed to test for the assumption that Gobiodon
histrio can distinguish its host-coral from a choice of different colonies. In addition, a partner
finding experiment was performed. In both experiments a high fidelity for host corals (75%)
and partners (60%) was observed. The study indicates a high movement rate for single adults.
In contrast, breeding pairs show a high stability in their habitat choice. Social structure of G.
histrio in the northern Red Sea shows similarities to the Western Indo-Pacific but differs in the
proportion of single adults, which is much lower in the latter. The high proportion of single
adults and their high movement rate indicates a limitation of high quality habitats (particular
Acropora species) for breeding. The apparently more generalized behaviour results from
occupation of sub-optimal corals by single adults while moving and searching for breeding
corals and partners. This study shows that G. histrio frequently moves between corals but this
depends on the social status of fishes. Vulnerability of populations to habitat loss increases
highly when particular corals are affected by damage.
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