11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 19: Biogeochemical Cycles in Coral Reef Environments
19-21
Coral Mucus Stable Isotope Composition And Labelling
Malik NAUMANN* 1 , Christoph MAYR 2 , Ulrich STRUCK 3 , Christian WILD 1
1 Coral Reef Ecology Work Group (CORE), GeoBio-Center, Ludwig-Maximilians-
Universität München, München, Germany, 2 GeoBio-Center & Department of Earth and
Environmental Science, Ludwig-Maximilians-Universität München, München, Germany,
3 Museum für Naturkunde, Humboldt Universität zu Berlin, Berlin, Germany
Recent research showed that mucus released by reef corals functions as a carrier of
energy and nutrients to the reef community, thereby importantly contributing to the
conservation and fast recycling of organic matter and nutrients in oligotrophic reef
ecosystems. However, food web processes involved in the uptake, assimilation and
degradation of this material are poorly understood. Staining techniques involving
different dyes proved to be inefficient tools in order to label coral mucus. This study now
aims to elucidate the usefulness of stable isotopes in order to study the fate of coral
mucus. Natural C stable isotope signatures (δ13C) of coral mucus (-25.5 ± 1.0 ‰) were
similar to those of particulate organic matter (POM) suspended in reef waters (-23.6 ± 0.4
‰), whereas N stable isotope signatures (δ15N) of coral mucus (+1.2 ± 0.3 ‰) were
comparably lower than those of POM (+15.9 ± 4.1 ‰). For experimental investigations,
where larger differences in δ13C and δ15N are required, a technique involving label
addition to the coral incubation water was developed. This produced δ13C values of up to
+122 ‰ and δ15N values of up to +2280 ‰ for mucus exuded by hermatypic corals of
the genera Fungia and Acropora, indicating fast transfer of assimilated C and N as
labelled compounds from the endosymbiotic dinoflagellates to the coral host under light
conditions. The usefulness of this technique was demonstrated by laboratory experiments
with labelled coral mucus addition. Another potential advantage of stable isotope
labelling is that such a non-noxious methodology can be used in-situ. This was confirmed
by benthic chamber experiments on coral reef sands revealing fast advective transport of
labelled coral mucus from the water column into the sediment surface layer.
19-22
Biogeochemical Constraints On Ecology Of Coral Reefs
Marlin J ATKINSON* 1
1 Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI
Biogeochemistry is the study of rates of input, production and consumption of
compounds that are involved in biological and geological processes. The fluxes and
chemical kinetics of these compounds often set limits to ecosystem-metabolism and
directly control organism-metabolism. The biogeochemistry of coral reefs is sufficiently
well understood that we can delimit a number of basic rate processes, but we are just
beginning to link biogeochemistry with ecological processes. Basic parameters in
biogeochemistry are light, temperature, concentration (hence water residence time), water
motion, waves, surface roughness or bottom drag, and community structure. The
combinations of these variables often set limits for biomass accumulation, nutrient input,
community metabolism, zonation of metabolism, herbivory, and food chain dynamics.
This talk review will briefly review the concepts and approaches for biogeochemical
constraints for the above ecological processes.
19-23
Diurnal And Seasonal Nutrient Dynamics Associated With A Nuisance Macroalgae Bloom
in The Permeable Coastal Margin Of Kihei, South Maui
Iuri HERZFELD* 1 , Francis J. SANSONE 1 , Celia M. SMITH 2
1 Department of Oceanography, University of Hawaii, Honolulu, HI, 2 Botany Department,
University of Hawaii, Honolulu, HI
Nutrient regimes on coral reefs are dynamic and driven by forces acting on multiple spatial and
temporal scales. We explored nutrient dynamics over time-scales ranging from days to seasons
associated with a coastal fringing reef on the island of Maui, Hawaii. Studies were performed
at Waipuilani Beach Park, Kihei, a site that is experiencing chronic nuisance blooms of the
macroalgae Ulva fasciata and Hypnea musciformis. In an attempt to elucidate the mechanisms
affecting nutrient concentrations in the water column, multiple 48-hour diurnal multi-parameter
surveys of reef water-column and sediment porewater dissolved nutrients (N, P, Si, and Fe) and
carbonate chemistry, water physics (tides, waves, currents), and wind speed were performed in
2005-2007 during both dry and wet seasons. Sampling was conducted over different tidal
phases and amplitudes in order to decouple the effects of light and tides on nutrient supply and
demand. Preliminary results indicate that diurnal nutrient concentrations in the water column
and sediment porewater are affected by changes in the kinetic energy being dissipated by the
system (wave height and near bottom current velocity), indicating an enhanced remineralization
of organic matter. Over seasonal time-scales, nutrient concentrations in the water column are
affected by a combination of fresh groundwater inputs, and recirculated brackish groundwater
that is actively being altered by sediment diagenesis. We conclude that water column nutrient
dynamics at our study site are the result of an intricate interplay between the hydrologic cycle
and the atmospheric and gravitational forces that enhance porefluid flow in this permeable
coastal margin.
19-24
Dual-Carbon Sources Fuel The Deep Reef Community, A Stable Isotope Investigation
Kenneth SULAK* 1 , James BERG 2 , Michael RANDALL 1 , George DENNIS III 3 , Robert
BROOKS 4
1 Florida Integrated Science Center, U.S. Geological Survey, Gainesville, FL, 2 ENSR
International, Westford, MA, 3 Vero Beach Ecological Services Office, U.S. Fish and Wildlife
Service, Vero Beach, FL, 4 ENSR International, St. Petersburg, FL
Surface marine phytoplankton is considered the sole carbon source for the OCS deep reef
community (>60 m), the endpoint of one vertically-intergrated, surface to substrate ecosystem.
Accordingly, community structure on deep reefs may be directly tied to phytoplankton carbon,
channeled via benthic particulate consumers. We tested the hypothesis that phytoplankton
carbon is the sole fuel of the deep-reef community, and an alternative hypothesis that terrestrial
carbon may contribute secondarily. Our objective was to define trophic structure on, off, and
above, northeastern Gulf of Mexico deep reefs via analysis of carbon and nitrogen stable
isotopes. We analyzed 114 entities (carbon sources, sediment, fishes, and invertebrates).
Carbon signatures supported surface phytoplankton as the primary fuel for the deep-reef
community. However, unexpectedly, a second non-terrestrial carbon source was identified as
important to the reef food web. This is the pelagic macroalgae Sargassum and the associated
macroalgal epiphyte Cladophora liniformis. Macroalgal carbon signatures were detected among
23 consumer species. Most notably, macroalgae contributed 45 % of total carbon to the 13C
isotopic spectrum of the particulate-feeding reef-crest gorgonian Nicella. Terrestrial carbon
from coastal rivers was not detected. Nitrogen signatures revealed a 4-step trophic chain from
particulate organic matter through apex macrovores. Eleven trophic guilds fell into four 15Ndefined
trophic levels, and three 13C consumer groups. Trophic enrichment in d15N per
trophic step was 1.67 ‰, in d13C, 2.0 ‰, both departing from the classical 3.0-3.4 ‰, and
1.0% per step, respectively. In contrast to ubiquitous phytoplankton, the secondary macroalgal
carbon source is spatially heterogeneous in surface waters. The spatial distribution of some
key particulate-feeding sessile reef invertebrates may depend on carbon fallout from spatially
discontinuous surface macroalgae, providing novel insight into the spatial heterogeneity of key
colonial reef invertebrates.
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