11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 19: Biogeochemical Cycles in Coral Reef Environments
19-5
Cyanobacteria Mats in Two Shallow Coral Reef Ecosystems: La Reunion (Sw
Indian Ocan) And Sesoko (Okinawa, Nw Pacific Ocean)
Charpy LOIC* 1 , Casareto BEATRIZ 2 , Langlade MARIE JOSÉ 3 , Suzuki YOSHIMI 4 ,
Palinska KATARZYNA 5 , Golubic STJEPKO 6
1 IRD, Marseille, France, 2 Laboratory of Aquatic Science and Consultan, Tokyo, Japan,
3 IRD, Marseille, France, Metropolitan, 4 Shizuoka University, Shizuoka, Japan,
5 University of Oldenburg, Oldenburg, Germany, 6 Boston University, Boston, MA
Various types of microbial mats are present in Okinawa and La Reunion coral reef
ecosystems. The heterocystous Nodularia and non-heterocystous Leptolyngbya
cyanobacteria were present in the two ecosystems. Many mats contained a mixture of
different morphotypes. Using the acetylene reduction technique, nitrogenase activity was
observed in all the tested mats. The conversion ratio of ethylene to N (C2H2:N2)
calculated from 15N2 method ranged between 1.1 and 5.8. Nitrogen fixation by
Nodularia, Hydrocoleum lyngbyaceum and Hydrocoleum cantharidosmum mats were
particularly high at Sesoko compared with literature data. Nitrogen fixation represented
between 5% (Leptolyngbya ) to 21% (Hydrocoleum cantharidosmum ) of that required
for primary production measured using 13C uptake and C:N ratio.
19-6
Functional Role Of Crustose Coralline Algae in Nutrient Dynamics Of Coral Reef
Ecosystem
Yeong Shyan YUEN* 1 , Seitaro S. YAMAZAKI 1 , Takashi NAKAMURA 1,2 , Hideo
YAMASAKI 1
1 Faculty of Science, University of the Ryukyus, Okinawa, Japan, 2 Amakusa Mar. Biol.
Lab., Kyushu University, Kumamoto, Japan
Coral reefs worldwide, especially those located near the coastline are constantly being
subjected to anthropogenic nutrient input. This anthropogenic nutrient input generally
increases the nitrogenous compound concentrations in seawater. This is in contrast with
the paradigm that coral reefs thrive best in oligotrophic waters. Accordingly, the study of
biogeochemical of nitrogen cycle in reef ecosystems should consider this increasing
eutrophication phenomenon. In addition, crustose coralline algae (CCA), a main reefbuilder,
have been overlooked when it comes to the study of organisms involved in the
major nitrogen cycle processes. CCA is well known for its important role in reefbuilding,
inducer for invertebrates’ larval settlement and metamorphosis as well as
primary producer. In this study, we consider CCA as a combination of the algal
component and its calcium carbonate substratum. Here, we report the NH4 + and NO3 -
uptake activities by CCA and the organisms involved in these activities. Laboratory
experiments on the nutrients uptake involved the incubation of CCA in seawater
containing a spike of nutrient and monitor its depletion. Organisms involved in nutrients
uptake was identified using molecular biological approach. Our results show that
microbial consortium residing in the substratum plays a major role in nitrogen cycle
processes in the CCA system. The substratum covered by CCA would create a low
oxygen concentration environment as well as anoxic environment, which is ideal for the
growth of various microbes. Our finding leads us to conclude that CCA is an important
functional group involved in the nutrient dynamics in coral reef ecosystems.
19-7
Nitrogen Dynamics in Symbiotic Relationships in Corals
Kazuyo SHIROMA* 1 , Yoshimi SUZUKI 1 , Kazuhiro DAIGO 1 , Sylvain AGOSTINI 1 , M.F. M.
FAIROZ 1 , Beatriz E. CASARETO 1,2
1 Shizuoka University, Shizuoka, Japan, 2 Laboratory of Aquatic Science, Tokyo, Japan
Symbiotic systems in corals are found to be complex and diverse today. The components are
not only corals and zooxanthellae but algae and bacteria also have important roles in/on corals.
The systems sustain coral symbiosis with nitrogen cycling in oligotrophic environment.
Empirical data have demonstrated imbalance of nitrogen budget that contributed in the
symbiotic relationships with measurement such as nutrients in seawater and nitrogen isotope in
corals. These studies found that besides external resources, internal resources are used in coral
symbiosis.
Isotope technique enables determination of external resource usage or translocation of nitrogen
from symbionts to corals without facing to nitrogen conservation issues. However, the
calculation used today overestimate uptake rate by coral symbiosis since only uptake but not
excrete rates are considered. If the assimilation of ammonium only contribute 10 % of nitrogen
required by zooxanthellae, nitrogen cycle in corals are underestimated. Here, we propose
possible methods to evaluate internal and external nitrogen cycles found in symbiotic systems
in corals.
By introducing C and N stable isotopes into seawater simultaneously, we found that uptake
ratios fluctuate, possibly caused by variation in internal resource availability to coral symbiosis.
In the future, mathematical model is built to develop as a tool to predict nitrogen dynamics in
coral reefs with environmental data. Construction of mathematical model of the symbiosis
become useful tool to predict fluctuations of symbiotic relationships in corals those are
vulnerable to environmental changes.
19-8
Dissolved Organic Carbon Dynamics and Microbial activity in Tropical and Sub-tropical
Coral Reefs
Fairoz M F M * 1 , Forest ROHWER 2 , Yoshimi SUZUKI 1 , Beatriz CASARETO 3
1 Global Biogeochemistry Lab, Shizuoka University, Japan, Shizuoka, Japan, 2 Biology
Department, San Diego State University, U.S.A., San Diego, CA, 3 Laboratory of Aquatic
Research and Consultants (Pvt) Ltd., Tokyo, Japan, Tokyo, Japan
The marine microbial food web is supported by dissolved organic carbon (DOC). Yet very few
measurements of DOC have been made on coral reefs and the relationship between DOC,
microbial activity, and macro-organisms in reef environment is not well understood. In previous
studies we have shown that additions of labile DOC kill corals. In this study, DOC, nutrients
and coral reef characters were measured on Sri Lankan reefs and compared with similar
measurements from the Caribbean, Line Islands, Bermuda, and Japan. The water chemistry
analysis and reefs surveys were performed using JGOFS and Reef Check protocols,
respectively. On the northern Sri Lanka coral reef, the DOC levels were high with low nutrient
levels. These conditions correlated with higher coral and lower algae cover. DOC levels were
lower and nutrient levels were higher at reefs in southern region, which had low live coral and
higher algae cover. However, this is significant variation in the general trends. We suggest that
the biogeochemical origin and fate of labile fraction of DOC in coral reef will be important to
describe the interactions between microbial activity and coral stress.
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