International Journal of Marine Science, 2016, Vol.6, No.21, 1-20
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While transplantation site affected the brightness of coral fragments, the conditions previously experienced by a
transplanted fragment (i.e. collection site) did not have a significant effect on this observation. It is important to
caution that changes in brightness may be caused by an array of factor in corals in including host pigments,
symbiont loss, symbiont pigments, and the environment. While we controlled for site dependent differences as
best as possible these factors could contribute to the observed variability. Evidence that the differences in abiotic
conditions identified between these two sites were not significant enough to elicit a visible response following
transplantation. This finding is contradictory to studies that have reported significant interactions between the
environmental history experienced by these two species and their response to future stress (Haslun et al., 2011;
Kenkel et al., 2013). For instance, we have shown previously (Haslun et al., 2011) that
M. cavernosa
from the
Flower Garden Banks National Marine Sanctuary (FGBNMS), a well-developed and thermally stable
scleractinian reef ecosystem, are more susceptible to increased thermal stress than conspecifics from the FKNMS,
where increased SWTs are experienced. Similarly,
P. astreoides
has been shown to display experience-dependent
acclamatory responses
via
the expression of genes associated with calcification and metabolism when exposed to
different temperature regimes (Kenkel et al., 2013). Both of the aforementioned studies reported that pronounced
differences in seawater temperature existed between the collection locations. In this study, mean maximum and
mean minimum temperatures for summer and winter respectively, deviated by approximately 1°C between inshore
and offshore zones, which is less than that observed between the FGBNMS and the FKNMS (Haslun et al., 2011)
or the more extreme temperature regimes at near shore sites (< 1 km from shore) of the FKNMS (Kenkel et al.,
2013). It is possible that the dissimilarity in SWT observed between our sites was not acute enough to illicit an
acclamatory effect in the observed brightness of
P. astreoides
and
M. cavernosa
or another stressor that was
unmeasured imparted the perceived responses.
Bleaching (loss of color largely associated with symbionts) of corals during summer seasons is a common
response to increased stress from light and temperature levels (Fitt et al., 2000) and not necessarily detrimental to
the organism. The primary purpose of this response is to limit the host’s cellular stress caused by symbiont
malfunction (Strychar et al., 2004). Coral fragments experiencing the conditions at the inshore site displayed
seasonality in colony brightness, characterized by a summer stress period and a winter compensatory period
(Figure 12). The seasonal pattern was also reflected in the significant relationship identified between temperature
and brightness for these corals. Therefore, seasonal stress levels from temperature remain coupled to bleaching at
Birthday reef and may be critical to the continued success of coral at inshore reefs via local adaptation or
acclimatization to the conditions present. Seasonality in coral fragment brightness was not detected for fragments
transplanted to Acer 24. On the contrary, we observed a significant positive linear trend between brightness and
month, indicating that fragments of both species of coral became progressively lighter over this two-year period.
Therefore, bleaching (the loss of symbionts) and temperature stress can be considered uncoupled for
P. astreoides
and
M. cavernosa
experiencing the conditions at Acer 24. Given the narrower annual temperature range
characteristic of this site, this result is intriguing. From our results we hypothesize that stress resulting from
increased irradiance (i.e. decreased turbidity), characteristic of offshore sites, provides an additional source of
stress increasing the cumulative stress level during summer and winter periods beyond that of corals at inshore
sites. The increased cumulative stress level may decrease a colony’s potential for recovery during the winter
season resulting in a state of chronically mild bleaching (i.e. more pale than conspecifics).
Chronic bleaching (an archetype of chronic distress) can be difficult to observe given its non-lethal nature (Lasker
and Coffroth, 1999). Horizontal linear extension was evident at both transplant sites throughout the course of our
study (pers. obs.), however we were unable to determine whether or not the degree of growth differed between
sites. In order to detect potential differences in fitness associated with chronic distress, we investigated site
dependent community characteristics. Eventual mortality may occur when organisms must allocate resources to
protection and maintenance (Lasker and Coffroth, 1999) rather than fecundity and growth. We observed a
significant difference between the mean colony area of
M. cavernosa
and
P. astreoides
at Birthday reef and Acer
24, as well as another commonly observed species,
S. siderea
(a known generalist). Similar observations have
