Global climate change & coral recruitment: The interactive effects of temperature and ontogeny on the biology of porites astreoides larvae  (Year 2 of 2) Project Number: SEGM-2003-13B Principle Investigators: Edmunds, P. J. Region(s):  Over the next century it is likely that the effects of global climate change will intensify, and the destructive effects on biomes and biota will become more severe. Coral reefs provide one example of a biome that is severely threatened by global climate change and rising seawater temperatures, as corals already are close to their upper thermal limit, and coral reefs have suffered the effects of anthropogenic attrition for decades. Degraded reefs such as many in the Florida Keys may suffer catastrophic losses from which they will be unable to recover. Despite the research attention that such scenarios have attracted, surprisingly little attention has been paid to coral reproduction and coral larvae that, arguably, offer one of the only viable mechanisms of reef recovery. The goal of this project is to carry out a multidisciplinary analysis of the biology, physiology and genetics of coral larvae in order to understand how global climate change will affect the coral population structure of reefs such as those in the Florida Keys. The second year of this project will build on the Year I (saturation) with a NITROX mission focused on shore-side experiments where experiments can be controlled with more rigor, and reagents inappropriate for saturation diving can be employed. Specifically, Year II will be used to: a) test the effects of and temperature and age on the physiology and gene expression of larvae, and 2) to compare the effects of temperature on the photobiology of adult and larval corals. This research has the goal of testing the effects of elevated temperature on the larvae of tropical reef corals in order to better understand how coral reefs will respond to the increases in sweater temperature caused by global climate change. This topic is of profound importance because it addresses the fundamental processes that contribute to the maintenance of existing coral populations and allow denuded reefs to recover their coral cover. The degraded state of many coral reefs in the Caribbean and Pacific underscores the need to understand the processes that might mitigate the recent losses of coral cover. Moreover, the severe threat posed by rising seawater temperatures (e.g., via bleaching mortality) identifies high temperatures as one of the most important abiotic factor driving the loss of coral reefs. To achieve this goal of this study, we have developed Porites astreoides as a model system that can provide moderate-to-large numbers of brooded larvae for use in manipulative experiments designed to test the effects of temperature on the development, physiology and gene expression on coral larvae. The present research was designed to address three questions: a) Are there differences in the taxonomic composition of the zooxanthella symbionts of coral larvae and the parental colonies that brood them? Because adult corals and their larvae are exposed to different environments (benthic versus pelagic, respectively), potentially with larvae exposed to extreme irradiances and temperatures at the surface of the water, the selective acquisition of different zooxanthellae clades by the larvae could be a powerful mechanism to enhance survival. P. astreoides is known to harbor multiple clades of algae, and thus the potential exists for maternal control of the zooxanthellae types passed to the brooded larvae. b) Do coral larvae and the parental colonies that brood them differ in their response to elevated temperatures? Because coral larvae are exposed to more extreme abiotic conditions than the benthic adults, it is likely that they differ in their response to thermal stress. For example, larvae exposed to thermal extremes close to the air-water interface might acquire resistance through shock proteins and/or changes in their zooxanthellae clades. c) Does the response of coral larvae to elevated temperatures differ with their release date and age? Our earlier work at NURC has shown that coral larvae differ with respect to their age and release date, thereby suggesting that they develop rapidly and potentially have the ability to match their phenotype to contemporaneous conditions. To text this possibility, we proposed to quantify the effect of high temperatures on coral larvae differing in age and release date relative to the new moon (the peak time for release).   The Year I field work for this project took place in June 2002 and was able to exploit a small number of larvae released in the first few days of the project (close to the June new moon). Unfortunately, additional larval were not forthcoming and little progress was made in accomplishing the primary goals of this research (although we tackled an alternative project addressing the effect of “light pressure” on the photophysiology of coral colonies across a depth profile). In 2002 it seemed likely that the poor larval release was a result of inclement weather, with the consequences being aggravated by the late sampling period (most larvae are released from Porites astreoides in April, May and June, and thus the 2002 sampling took towards the end of the larval release period). To avoid the Year I problems in our Year II sampling, we scheduled our second trip a month early to sample the May new moon, and “saturated” the reef with 200 larval traps (we used ˜140 in 2002, and ˜100 in 1999 when we obtained numerous larvae). Despite this effort, we were unable to collect a single coral larva between April 29 and May 6, 2003. We are perplexed by this lack of success and find it amazing that no larvae were obtained with such a broad effort. Unfortunately, we cannot know the reasons for this failure, as work on coral reproduction is fraught with the vagaries of erratic larval release and spatio-temporal variation in reproductive effort. However, in light of: 1) the well known periodicity of larvae release in this species in the upper Florida Keys (McGuire 1998, Edmunds et al. 2001), 2) the well known cycle of gametogenesis that corresponds with our sampling periods (Chornesky and Peters 1987), and 3) the poor-to-non-existent larval release in consecutive years (2002 and 2003), we are considering the possibility of reproductive failure in Porites astreoides. While we need time to digest our findings, currently we are exploring the possibility of a note to Coral Reefs in the context of the implications for the future growth of corals in the Florida Keys. Faced with a lack of larvae from Porites astreoides, we directed some of our effort to two alternative projects. First, we collected samples of Porites astreoides as described in our permit in order to examine the population structure using genetic markers developed in 2002. Second, we used pieces of Porites astreoides collected within the constraints of our permit to address size-class dependent variation in photophysiology and zooxanthellae clades. Preliminary research we completed in Jamaica (January 2003) suggested that small and medium-sized coral colonies have differing photosynthetic performance that might shed light on the causes of elevated mortality in the smallest size class. Using samples from the upper Florida Keys were are testing the effects more rigorously and assaying for differences in zooxanthellae clades. Leg 1    Begin Date: 4/29/2003   End Date: 5/6/2003   Support Vessel/Platform: R/V Wildcard System Ops Days Dives Dive Time (hrs) Depth (m) NITROX SCUBA 8 87 57.9 20

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Updated: May 28, 2004