11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 4: Coral Reef Organisms as Recorders of Local and Global Environmental Change
4-9
Long-Term Caribbean Nutrient Perturbations Recorded by Gorgonian Corals
David BAKER* 1 , Kirby WEBSTER 2 , Eduardos VALAITIS 3 , Kiho KIM 2
1 Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY,
2 Department of Biology, American University, Washington, DC, 3 Department of
Mathematics & Statistics, American University, Washington, DC
Over the last century the Wider Caribbean has experienced dramatic changes from human
activities. Widespread land-use change to agriculture, the concomitant removal of coastal
mangrove forests, and recently accelerated population growth has led to perturbation of
aquatic ecosystems. Of particular concern is increasing amounts of anthropogenic
nutrients, and their effect on coastal marine habitats. Coral reefs are particularly sensitive
to nutrification, and there is an abundance of reports on the deleterious effects of nitrogen
(N) on these systems. However, the paucity of historical nutrient pollution data inhibits
our understanding of the full scope of the problem. Fertilizer and sewage-derived N
represent opposing end-members across the natural range of δ 15 N from near zero to > 20
‰, respectively. The relative proportion of N from these and natural sources dictates the
resulting δ 15 N of any mixture. Thus, in the absence of information about the relative
contributions of fertilizer and sewage derived N, interpretation of δ 15 N values is
problematic. In this study, we use fertilizer use and human population data in a
cointegration model to tease apart their respective contributions to long-term changes in
N inputs to the Wider Caribbean. We analyzed four species of gorgonians collected from
10 regions within the past 155 years as an integrator of N sources. We show that δ 15 N
values of gorgonian corals are positively correlated with population, and negatively
correlated with fertilizer consumption. Trends in gorgonian δ 15 N since 1851 indicate a
minimum inflection value in the 1970’s, after which δ 15 N increases. We conclude that
widespread land-use change to agriculture has historically perturbed N dynamics in
coastal Caribbean environments however, recent population growth has offset fertilizer
isotope signals in corals, and suggests that the interplay between fertilizer and sewage
derived N on coral δ 15 N may lead to underestimation of their respective contributions.
4-10
Identification Of Bleaching Events In Coral Skeletal Records Using High-Resolution
Stable Isotope And Trace Element Records
Abbey CHRYSTAL* 1 , Andrea GROTTOLI 1 , Lisa RODRIGUES 2
1 School of Earth Sciences, The Ohio State University, Columbus, OH, 2 Department of
Geography and the Environment, Villanova University, Villanova, PA
Coral skeletal stable oxygen isotopes (δ18O) reflect changing seawater temperature and
salinity, while stable carbon isotopes (δ13C) reflect metabolic and kinetic fractionation.
These isotopic changes may provide a record of past bleaching events. The effects of
bleaching and subsequent recovery on skeletal isotopes in the mounding coral Porites
lobata were experimentally investigated by inducing bleaching in outdoor tanks via
increased water temperature (30°C). Control fragments from the same parent colonies
were separately maintained at ambient seawater temperature (27°C). After one month all
were returned to the reef for 20 months of recovery. Alizarin red staining was used to
mark specific dates throughout the 21 months. Isotopes were measured by Kiel-SIR-MS
at 0.1 mm increments along the major axis of growth for one bleached and one control
fragment. Skeletal δ18O did not differ between the bleached and control fragments
during the month of elevated temperatures, nor during recovery under natural reef
temperature variations. However, δ13C decreased dramatically relative to the control
several weeks into recovery, recovered to control levels after 4 months, and showed a
negative departure again the following summer. The initial lag in δ13C depletion
suggests that while P. lobata is fairly resistant to initial physiological effects of
bleaching, it continues to be affected by the stress event during the first few weeks of
recovery. Lower δ 13 C values the second summer suggest that the bleached fragment was
more susceptible to thermal-stress from a second moderate warming. Overall, highresolution
skeletal δ 13 C has potential as a proxy for past bleaching events in this species
independent of δ 18 O variability. Skeletal trace element analyses in both bleached and
control fragments are underway and will also be presented.
4-11
Coral Growth Records From Southeast Florida: A History Of Anthropogenic Influence
Kevin P HELMLE* 1 , Richard E DODGE 1 , Peter K SWART 2 , J Harold HUDSON 3
1 National Coral Reef Institute, Nova Southeastern University Oceanographic Center, Dania
Beach, FL, 2 Rosenstiel School of Marine and Atmospheric Science, University of Miami,
Miami, FL, 3 Florida Keys National Marine Sanctuary (ret.), National Oceanic and Atmospheric
Administration, Key Largo, FL
Coral skeletal growth records of extension, density, and calcification from Southeast Florida
reveal a three-decade period of stress spanning ca. 1940 to 1970. The period is characterized by
dramatically decreased annual extension rate and increased skeletal bulk density. No similar
periods of growth departures of this intensity or duration are present in locally collected corals
dating back to 1694. Coral growth from a total of 80 corals exhibits strong correlation with
master chronologies indicating a common growth response to one or a combination of
environmental limiting factors. Near-shore shallow-water corals in Southeast Florida are
affected by a number of stresses including freshwater drainage and coastal runoff. The 30-year
period of high skeletal densities and low extension rates matches with a 30-year period of
increased freshwater discharge, at times, an order of magnitude greater than normal.
Construction of the four major South Florida canal systems diverted waters from Lake
Okeechobee in the 40s, 50s, and 60s to the ocean. Comparison of temporal patterns in coral
extension with environmental variables reveals a positive correlation between extension rate
and salinity (represented by sea water density). The direct cause may be linked to influences
from freshwater discharge such as high turbidity and decreased light penetration, salinity, or
deleterious water quality. Further analysis of skeletal chemistry will help to identify specific
limitations on the growth potential of these corals. Since the early 1970’s, growth rates have
generally increased relative to the historical average; however, the frequency of single-year
stress bands has also risen. Increased growth rates coincide with warmer temperatures and stress
bands likely resulting from partial bleaching when temperature thresholds are exceeded. This
research has applications to better understanding coral stress and recovery with particular regard
to watershed management.
4-12
The Significance Of Geochemical Proxies in Corals, Does Size (Age) Matter?
Tim OURBAK* 1,2 , Kristine DELONG 1 , Thierry CORRÈGE 3 , Bruno MALAIZÉ 3 , Halimeda
KILBOURNE 4,5 , Sandrine CAQUINEAU 2 , David HOLLANDER 6
1 College of Marine Science, St Peterbsurg, FL, 2 Institut de Recherche pour le Developpement,
Bondy, France, 3 UMR 5805 EPOC, Universite Bordeaux 1, Talence cedex, France, 4 Earth
Systems Research Laboratory Physical Sciences Division, NOAA, Boulder, CO, 5 College of
Marine Science, St Peterbsurg, 6 College of Marine Science, St Petersburg, FL
Massive corals contain a myriad of geochemical tracers that have lead to numerous
paleoenvironmental studies (sea surface temperature reconstructions for example). Most of the
time, coring is achieved on a coral head, which is then sampled to produce geochemical
analyses, used as proxies to estimate paleoclimate variability.
The present work deals with the impact of the age (and the size) of the coral head on
geochemical results.
We analyzed three pristine coral heads using a multiproxy approach (Sr/Ca, Mg/Ca, δ 18 O ,
δ 13 C). The first one is a 7m high core from New Caledonia where the modern period (top of the
core) is compared to the settlement period (bottom of the core, when the coral was still at a
juvenile stage).
The geochemical signatures of two coral heads (small vs. large) that have grown in a similar
environment (Vanuatu) are also compared.
Large geochemical differences observed (between juvenile vs. mature and, to a less extent,
between small vs. large coral heads) could not be explained only because of environmental
variability.
We will develop the potential causes of such differences in term of variability of the tracers
(kinetic effects, reproductive patterns etc).
The implications of this work are that paleonvironmental work based on coral archives should
clearly state the length of the core retrieved. For example, if the SST range is well captured by
Sr/Ca ratio, independently of the size/stage of growth of the coral head, applying directly
calibration equation to reconstruct absolute SST bias the result and only relative SST values
should be compared and interpreted.
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