Decoupled Seasonal Stress as an Indication of Chronic Stress in Montastraea cavernosa and Porites astreoides Inhabiting the Florida Reef Tract
International Journal of Marine Science
Although mass mortality from disease and climate anomalies are largely to blame for rapid losses in coral cover along the Florida reef tract, the failure of extant populations to recolonize the offshore zone is puzzling given improvements to water quality and narrower range in seawater temperature compared to the inshore patch reef zone. Using existing data from the Coral Reef Environmental Monitoring Program (CREMP) and from an inshore and offshore site established to compliment this dataset
... ment this dataset we identified significantly increased abundance and diversity of scleractinian coral from inshore to offshore across the Florida reef tract. Applying exploratory statistical methods we identified two abundant species, Montastraea cavernosa and Porites astreoides, inhabiting both zones to varying degrees. Following reciprocal transplantation of conspecifics between a representative offshore and inshore reef (6 m depth), we monitored monthly coral colony brightness (a measurement related to endosymbiotic dinoflagellate density) over a two-year period to examine symbiont loss, a common stress response in scleractinian corals. Although species-specific stress patterns were not identified, zone-specific variation was evident. Trigonometric regression of stress level by month revealed a significant relationship supporting an annual stress and recovery period at the inshore patch reef zone. Contrary to this result, conspecifics transplanted to the offshore zone did not display recovery resulting in a continued chronically bleached state over the two-year period. Our results implicate alleviation or decreased stress at inshore sites and the importance of extending greater protection to reefs within this zone. Relative abundances of corals inhabiting offshore bank reefs and inshore patch reefs, spanning a 16-year period, were obtained from CREMP (http://ocean.floridamarine.org/FKNMS_WQPP/pages/cremp.html). This dataset has been applied to the detection of potential causal factor for regional differences in benthic communities coupled with the WQMP (http://ocean.floridamarine.org/FKNMS_WQPP/pages/wqmp.html) (Maliao et al., 2008) . This previous work indicated that the CREMP monitoring strategy correlates well with the results of other sampling efforts including the Atlantic and Gulf Rapid Assessment protocol (AGRRA; http://www.agrra.org/). The CREMP and WQMP datasets (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) were used to establish the extent of variability in coral communities and local environment between the inshore and offshore zones and sites associated within each zone. Of the available reefs within the two datasets we selected reefs within the lower and middle keys for three reasons. Firstly, throughout the lower and middle keys regions there are a number of offshore bank reefs as well as patch reef formations that spatially parallel one another (Figure 1) . Secondly, for the past three years we have monitored an inshore patch reef and an offshore bank reef at the heart of this distribution, Birthday and Acer 24 reefs respectively ( Figure 1 ). Thirdly, this region has been characterized by decreasing gradients of nutrients, turbidity and temperature from the inshore to offshore zones. Differences in these factors among sites and between the inshore and offshore zones (i.e. nutrients, turbidity, and temperature) may provide a foundation to understand the evident variation in coral cover. Acer 24 reef (offshore) and Birthday reef (inshore) along 30 m transects is presented in Figure 5 . Scleractinian coral cover was significantly greater at Birthday Reef (ANOVA: p < 3.83e-07), while the benthic community at Acer 24 contained significantly greater gorgonian coral cover (ANOVA: p < 2.01e-08), supporting our observations from the inshore vs. offshore analyses. Gorgonian cover also displayed seasonality at Acer 24 reef, with a greater percent cover observed during winter sampling (ANOVA: p < 0.003). This pattern was not evident at Birthday reef. Macro algal and turf algal cover was not significantly different between the Birthday reef and Acer 24, and accounted for greater than 30% of all reef cover. Increased macro algal cover was observed during winter months, but this difference was not significant compared to summer.