The effects of the red tide producing dinoflagellate, Karenia brevis, and associated brevetoxins on viability and sublethal stress responses in scleractinian coral: a potential regional stressor to coral reefs

Abstract

Coral cover is in decline on a global scale, with increased mortality events being attributed to a number of global and regional stressors. While the impacts of global stressors (e.g. sea surface temperature rise, ocean acidification) are well documented, there is growing interest in identifying and understanding the impacts of regional stressors. The reason for this change in focus is that regional stressors can often work in combination, sometimes synergistically, with global stressors and that stressors on a regional scale tend to be more easily mitigated by management practices. One regional stressor that impacts a myriad of marine organisms in the southeastern United States is the annual red tide blooms produced by the dinoflagellate, Karenia brevis. Their impacts, along with the lipid soluble polyether neurotoxins they produce, termed brevetoxins, are well studied in economically important organisms, such as bivalves. However, little is known of their impacts on organisms that possess ecological importance, such as species of scleractinian coral. To address this gap in knowledge, a multifaceted study is discussed herein, which evaluated the effects of ecologically relevant concentrations of K. brevis and associated brevetoxins on different coral life history stages and coral species. The second chapter addresses the impacts of red tide on larval behavior, settlement and survival of the coral species Porites astreoides, as well as impacts of photochemical efficiency and oxidative stress within different coral species (P. astreoides larvae, P. astreoides adults, Acropora cervicornis, Cladocora arbuscula, and Phyllangia americana). The third chapter confers the use of broad-scale proteomic analysis to identify the cellular response of the non-model coral species, P. astreoides, following exposure to red tide. Coral larvae actively avoided both medium and high bloom conditions of K. brevis and brevetoxins, while percent larval settlement and survival were impacted following exposure to high bloom concentrations of K. brevis. Photochemical efficiency of in hospite Symbiodinium was reduced following exposure to both K. brevis and brevetoxin in P. astreoides larvae, as well as exposure to K. brevis in P. astreoides adults, while being unimpacted in A. cervicornis. Compared to controls, high bloom conditions resulted in an increase in biomarkers of lipid peroxidation in C. arbuscula. This was also seen in P. astreoides larvae at 24 hours; however, this difference was indistinguishable following 48 hours. Surprisingly, no other biomarker of oxidative stress analyzed were impacted. Broad-scale proteomic analysis of P. astreoides following exposure to red tide conditions revealed variable changes in proteome expression depending on if the corals were exposed to K. brevis or brevetoxins. Exposure to brevetoxins resulted in differential expression of proteins related to DNA organization, chromatin formation and transcription expression; while exposure to K. brevis resulted in differential expression of proteins related to redox homeostasis, protein folding, energy metabolism, and production of reactive oxygen species. The results of this study demonstrate the potential for annual red tide blooms to act as a regional stressor on coral species. They highlight the ability of red tide conditions to negatively impact coral at multiple life history stages and that the extent of these effects may be species specific. They also provide further incite of coral’s response to red tide exposure at the cellular level