11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 5: Functional Biology of Corals and Coral Symbiosis: Molecular Biology, Cell Biology and Physiology
5.95
Defenses Against Oxidative Stress in Zooxanthellate Symbioses
David TAPLEY* 1
1 Biology, Salem State College, Salem, MA
Photosynthesis by zooxanthellae within cnidarian symbioses produces hyperbaric oxygen
tensions within the animal hosts. As a result, the host organisms experience elevated
exposure to reactive oxygen species (ROS), including superoxide, hydrogen peroxide,
and the hydroxyl radical. The primary defenses against ROS in most metazoans include
the enzymes superoxide dismutase (SOD) and catalase (CAT) as well as several lowmolecular-weight
organic molecules such as ascorbate, glutathione, and urate. Unlike
most metazoans, including other cnidarians, sea anemones in the genus Aiptasia do not
regulate activities of SOD and CAT in response to artificially elevated oxygen tensions or
light intensities. In fact, SOD activity is remarkably low in this genus. Instead, the
primary defenses against ROS in these symbioses appear to be saturating concentrations
of uric acid, a potent scavenger of hydroxyl radicals, and constitutively elevated activities
of CAT. Furthermore, CAT activity is inversely correlated with acclimation irradiance,
indicating that direct photoinactivation of catalase in zooxanthellate symbioses occurs.
Given that defenses against ROS in other cnidarian zooxanthellate symbioses follow
different patterns, including more robust enzymatic defenses, studies of such defenses
among coral reef cnidarians need to consider the exact pattern of defenses for the species
under consideration.
5.96
Nutrient Transfer in A Multi-Level Mutualism: Contributions Of Anemonefish To
Host Anemone And Zooxanthella Nutrition
Modi ROOPIN 1 , Nanette CHADWICK* 1
1 Biological Sciences, Auburn University, Auburn, AL
Many coral reef symbioses consist of multiple partners, but most of the empirical and
theoretical work on symbioses has been limited to 2-way systems. This limitation extends
to cnidarian-zooxanthella symbioses, in which most research has ignored the nutritional
impacts of additional partners, such as obligate fish or mobile invertebrate residents. We
used the anemone-fish-zooxanthella symbiosis as a model system to assess the potential
contribution of large ectosymbionts to the nutritional budget of cnidarian hosts and their
zooxanthellae. Under both laboratory and field conditions, anemonefish excreted large
quantities of ammonia, mostly during the daytime after consumption of zooplankton.
Host anemones rapidly absorbed most of the ammonia excreted by the fish, and did so
almost exclusively during the daytime, suggesting that this process is driven by
zooxanthella photosynthesis. In controlled laboratory experiments, the ammonia waste
products of resident anemonefish allowed the maintenance of high zooxanthella levels in
host sea anemones, and significantly retarded the catabolism of host tissue reserves.
These results provide a physiological mechanism to explain our field observations that
host anemones with few or no fish shrank over several years, while those with large
resident fish grew substantially. In the Red Sea, localized concentrations of ammonia
near sea anemones with resident fish were significantly higher than those in the
surrounding oligotrophic waters. We conclude that zooplanktivorous fishes and
crustaceans that form symbioses with cnidarians serve as an important link between open
water and benthic ecosystems, by importing particulate nutrients from the plankton and
releasing them in dissolved form near benthic hosts. These multi-level symbioses connect
associates in a complex web of interactions that buffer adverse impacts of environmental
variation, thereby enhancing reef diversity and productivity.
5.97
The Photobiology of Symbiodinium Indicates Populational Differences in Hyposaline
Tolerance in Siderastrea radians from Florida Bay, Florida, USA
Kathryn M. CHARTRAND* 1 , Michael J. DURAKO 1
1
Department of Biology and Marine Biology, University of North Carolina Wilmington,
Wilmington, NC
Studies of coral populations along gradients in physical-environmental conditions may provide
insights as to how future climate patterns may affect coral symbioses. In this mesocosm study,
Siderastrea radians, collected from five distinct basins in Florida Bay along a northeast-tosouthwest
salinity gradient, was used to assess effects of chronic hyposalinity on the
photophysiology of Symbiodinium as an indicator of holobiont stress. Colonies from each basin
were assigned four salinity treatments (30, 20, 15, and 10) and salinities reduced 2 d-1 from
ambient (30) to simulate a natural salinity drop. Maximum and effective quantum yields were
measured using PAM-fluorometry at dawn and noon, respectively. There was generally no
decrease in yields for 20 and 15 treatment colonies versus controls (i.e. 30) up to five days posttarget
salinity. This indicates a greater ability to withstand reduced salinity for relatively
extended periods of time in S. radians compared to other reef species. When salinity of 10 was
reached, colonies showed significant reduction in maximum yields versus those at 20 and 30,
indicating a critical threshold for hypo-saline tolerance. At salinity of 10, colony yields from the
most salinity-variable northeast Blackwater Sound (BLK) versus the most marine southwest
Twin Key basin (TWN) were significantly different, suggesting a populational shift in salinity
tolerance linked to historical basin salinity ranges. Subcladal ID of Symbiodinium for each basin
population was completed using PCR-DGGE analysis of the ITS2 region. TWN colonies
possessed a distinct symbiont type versus those in BLK, further correlating with differences in
photobiology measured during hyposalinity experiments. These findings suggest that long-term
differences in basins salinities lead to differential responses in the holobiont, which are related
to a shift in symbiont photophysiology and colony symbiont association.
5.98
Cladal Diversity in Zooxanthellae Harbored By Sponges Of The Clionaidae: A Case Study
Involving Cliona Varians.
Malcolm HILL* 1 , April HILL 1 , Ericka POPPELL 1 , Blake RAMSBY 1
1 Biology, University of Richmond, Richmond, VA
Among the Porifera, zooxanthellae are primarily restricted to a single family (Clionaidae),
which includes major bioeroders on tropical reefs. Zooxanthellae have been found to benefit
their host sponges by elevating growth rates through photosynthetic activities. Early work also
demonstrated that at least one species of zooxanthellate-sponge was capable of switching
partners when exposed to stressful conditions. Despite this early work, very little is known
about the types of zooxanthellae harbored by these sponges. To address this deficit in our
understanding, we examined the zooxanthellar diversity present in different species of clionaid
sponges from the Florida Keys. Attention was focused on three morphotypes of Cliona varians
that occur in disparate habitats. Our findings indicate that the level of specificity between host
and symbiont varies among sponge species. Some species appear to harbor a single type of
zooxanthellae (e.g., Cliona caribbea, Cervicornia cuspidifera) while others (e.g., Cliona varians)
harbor multiple clades. Data will also be presented relating zooxanthellar densities, chlorophyll
concentrations, and phophotochemical efficiencies to the cladal diversity uncovered among
sponge species. Our data will be placed in the context of current hypotheses proposed to explain
the nature of associations that involve multiple partners. These data may also provide important
insights into the relative stability of sponge-zooxanthellar symbioses on tropical coral reefs.
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