Marsh, G. Alex

Bleaching of reef corals and other cnidarians symbiotic with zooxanthellae can be attributed to the stress response of the host, algae or both. To determine if zooxanthellae are involved in the bleaching process, I infected a single strain of sea anemone, Aiptasia pallida with zooxanthellae from different hosts. I measured expulsion of the algae from the host during 24-hour incubations at 25, 32 and 34C, as well as photosynthetic rates at these temperatures. Photosynthesis and expulsion of zooxanthellae were inversely and directly proportional to elevated temperatures, respectively. Photosynthesis and expulsion of zooxanthellae isolated from Condylactis gigantea showed the greatest sensitivity to elevated temperature when compared to other zooxanthellae tested. These results suggest that zooxanthellae have a function in the bleaching process and that this function may be related to their photosynthetic response. Thus, the differential tolerance of zooxanthellae to stress could partly explain the spatial variability characteristic of coral-bleaching episodes.

Aerial photo-interpretation, GIS analysis, and groundwater modeling were employed to determine the impact of permitted groundwater withdrawal, primarily for agricultural irrigation, on protected wetland communities within Jonathan Dickinson State Park (JDSP), Martin County Florida. Since 1952, much of the wetland habitat has succeeded to terrestrial pine flatwoods in the southwestern section of the wilderness preserve of JDSP. The drying trend can not be linked to natural hydrologic impact, but strongly correlates to groundwater drawdown calculated using a three-dimensional groundwater computer model.

Differences in relative primary productivity of periphyton were determined for three light regimes: open slough (control), sawgrass canopy, and cattail canopy. The center of Water Conservation Area 2-A, Everglades was chosen as the study site because it is relatively unaffected by nutrient runoff. Periphyton productivity was determined by the light and dark bottle method, and biomass was recorded as ash-free dry weight. Statistically significant correlations were found between periphyton biomass and water temperature and between organic content and water temperature. Mean photosynthetically active radiation reaching the surface of the water under sawgrass and cattail canopy was 45% $\pm$ 3% and 11% $\pm$ 1% respectively. Relative primary productivity of periphyton was lower under cattail canopy than under sawgrass canopy due to increased shading of cattail. This reduction of periphyton biomass and primary productivity can be considered an indirect effect of nutrient enrichment from the Everglades Agricultural Area.

The abundance, biomass, and size class composition of Mnemiopsis mccradyi were monitored weekly from March 1994 to May 1995. Relationships between M. mccradyi abundance and several environmental variables were investigated, including water temperature, salinity, rainfall, density of specific M. mccradyi prey, and abundance of the predatory ctenophore Beroe ovata. The mean abundance from September to May was 14.8 ctenophores/m^3, while the mean from May to September was 0.3 ctenophores/m^3. Temperature observations indicated 26C (Sept-May) as optimal for population abundance, and 29-32C (May-Sept) as a possible upper temperature limit to larval development. Adults ctenophores dominated the population from May to September, while larvae and juveniles increased in number and biomass during the period of highest abundance. These results revealed two distinct seasons of M. mccradyi abundance based on ambient water temperature, and indicated that the dynamics of this population are attuned to the environmental conditions of a southern Florida estuary.

The Boca Raton artificial reef was designed to mitigate for the burial of nearshore rock habitat resulting from beach restoration. Seasonal recruitment and community development of the reef were studied from April 1988 to July 1990. Species diversity within the fish community reached an equilibrium 2-2.5 months following reef placement. Seasonality was recorded for juvenile, intermediate and adult life history stages. Encrusting invertebrates and algae exhibited preferences for vertical and horizontal substrates, respectively, while nonencrusting invertebrates exhibited no preference for surface orientation. No conspicuous seasonal trends were evident for the encrusting or non-encrusting invertebrates, except for Watersipora sp. and Botryllus schlosseri. Equilibrium was not attained by invertebrates or algae, nor was there evidence of true ecological succession beyond the earliest stages. Instead, the reef appeared to be maintained in an early stage of development as a result of frequent physical disturbance.

Benthic faunal repopulation of a newly created borrow pit off Delray
Beach, Florida was monitored from 15 June 1978 to 23 June 1979. For
comparative purposes, a single sampling of an adjacent five year old
borrow pit was conducted concurrently with the final sampling of the
new pit. Repopulation of the new pit was rapid, with 35 species and
1081 inds./m^2 collected at the initial sampling, 21 days postdredging.
Abundance peaked at 1761 inds./m^2 in the third sampling
period (169 days postdredging) and species richness peaked at the
fifth sampling period (325 days post dredging) with 57 species. Polychaete annelids and peracarid crustaceans were the numerically
most important initial colonizers of the new pit, together comprising
91.8% of the fauna. Species diversity (H') and equitability were
lowest during the first sampling period (4.21 and 0.82, respectively)
and, although variable, increased toward the end of the study (5.10
and 0.92, respectively). The disturbed area showed complete recovery
based on several aspects of community structure, although differences
in species composition were still evident between the new and old
pits.

Seasonal settling patterns and community development of the
fouling complex on gelcoat-covered fiber glass plates
(103.22 cm2 ) were observed from September 1976 to September
1977 at three stations in northern Lake Worth, Florida. Percent
coverage for each species was estimated using 60 points
randomly positioned over the plate area. Physico-chemical
conditions at stations 1 and 2 were relatively stable, whereas
station 3 was subjected to wide variations in salinity and,
to a lesser extent, dissolved oxygen. Plates at stations 1
and 2 consistently collected more species than those at
station 3. Peak settling and growth at all stations occurred
in the spring and early summer. Three species settled only
on plates that had been previously colonized. Even though
gelcoat-covered fiber glass was designed to discourage fouling,
it proved to be a satisfactory substrate for a thriving community.