International Journal of Marine Science, 2016, Vol.6, No.21, 1-20
17
been noted outside of the Florida Keys (Edmunds and Elahi, 2007). Following dramatic decreases in the
abundance of
O. annularis
(formerly
Montastraea annularis
) at a reef near St. John Island in the United States
Virgin Islands, the mean size of corals continued to decrease over a five-year period, from 1999-2003, despite the
stabilization of percent coral cover (Edmunds and Elahi, 2007). The authors projected that this species of coral
would become locally extinct if the level of stressors remained unchanged over the next 30-50 years. Corals at
offshore reefs of the FKNMS appear to be experiencing this trend now.
Figure 12. Brightness time series of reciprocally transplanted
M. cavernosa
and
P. astreoides
from September 2011-April 2013. The
monthly brightness value of each individual coral within the transplant study is presented. Points identify the site a coral was
transplanted to (Circle = Acer 24, Triangle = Birthday). Loess regression lines have been fitted to each subset of corals also based
upon the site a coral was transplanted to (Line = Acer 24, Dash = Birthday). Confidence intervals (95%) have been place around each
line. The four graphs are separated along the y-axis by collection site and along the x-axis by species.
5 Conclusion
Offshore bank reefs harbor relict communities of scleractinian corals and these communities do not show signs of
rebounding. Although the stressors associated with this zone appear lower than those associated with more
successful inshore patch reefs our results indicate that corals inhabiting offshore shallow reefs are experiencing
more significant levels of stress compared to conspecifics from inshore patch reefs. This result may not be
reflected in the acuteness of stress but rather the absence of a phase to recover from seasonal stressors. In support
of this claim we provide several tracts of evidence. First, the brightness of corals (an indication of symbiont
density) transplanted to an offshore site became progressively lighter over a two-year period regardless of the site
of collection while corals transplanted to an inshore site displayed seasonality in brightness. Second, the linear
relationship between seawater temperature and brightness was significant for corals transplanted to inshore sites
but this relationship did not exist for corals transplanted to an offshore site. Third, the mean colony size of the two
species used for transplantation as well as a common generalist, were smaller at offshore sites. Finally, we
identified a factor, turbidity that provides an explanation supporting the potential for chronic stress to occur at
offshore sites. We propose that decreased turbidity results in increased irradiance at offshore sites resulting in
