International Journal of Marine Science, 2016, Vol.6, No.21, 1-20
15
suggesting dissimilar tolerances to the stressors inherent to each zone. We selected these species as a proxy to
identify site and species dependent factors that may contribute to the continued trend of decreased coral cover at
offshore compared to inshore reefs.
Figure 11. Quantum yield of photochemical energy conversion of
M. cavernosa
and
P. astreoides
inhabiting an offshore reef (Acer24)
or an inshore reef (Birthday) within the Florida Keys Reef Tract. The yields of all corals of the two species within 1 m of 90m
transects (n=3) were obtained for a given sampling event. Points represent means and error bars indicate 95% confidence intervals.
Reciprocal transplantation of
M. cavernosa
and
P. astreoides
between Birthday Reef (inshore site) and Acer 24
(offshore site), revealed that fragments of both species transplanted to the inshore site, displayed significantly
lower brightness in images than conspecifics and ramets transplanted to the offshore site, regardless of their
collection site (Figure 11). We interpret this result to signify decreased levels of stress or photoacclimation at
inshore reefs resulting in greater symbiont concentrations within the host or increased pigment concentration
within the algal symbionts (
Symbiodinium
spp.
commonly referred to as zooxanthellae). Although increases in
symbiont density can also occur when inorganic nitrogen concentrations increase (Muscatine et al., 1989;
Marubini and Davies, 1996), our study of the abiotic differences between the inshore and offshore zone did not
yield a significant difference in inorganic nitrogen forms between zones. A sister study examining the symbiont
diversity within the corals of this study determined that symbiont diversity was greater for corals collected from
the offshore reef but this diversity was not affected by where a fragment was transplanted to (Hauff et al., 2016).
Instead, inshore sites displayed increased seawater temperatures and a wider range of turbidities. Further, the two
CREMP sites nearest to our transplant sites, Western Washerwoman (inshore) and Looe Key (offshore), displayed
significantly different turbidities during the winter (µ= 3.1 NTU and µ= 0.26 NTU respectively) and summer
following analysis of the WQMP dataset (µ = 0.8218 NTU and µ = 0.480 NTU respectively). From this
information differences in brightness of transplanted coral colonies may be a function of the effects of turbidity
and temperature. Temperature and turbidity have been identified as mediators of growth for
Orbicella annularis
populations near Key Largo, FL (Hudson, 1981).
