How does rising atmospheric CO2 affect marine organisms?

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Sea Fan Adaptive Responses to Pathogen- and Heat-Induced Stress
Reference
Mydlarz, L.D., Holthouse, S.F., Peters, E.C. and Harvell, C.D. 2008. Cellular responses in sea fan corals: Granular amoebocytes react to pathogen and climate stressors. PLoS ONE 3: 10.1371/journal.pone.0001811.

Background
The authors write that "tropical corals are under unprecedented stress from pathogens and climate change." Whether this statement is correct in an absolute sense matters but little, since the two types of stress are acting against a backdrop of numerous localized anthropogenic-induced stresses that have grown ever stronger and more pervasive with the passing of time, making earth's corals ever more susceptible to the debilitating effects of pathogenic and climatic stress. Consequently, it is important to learn what resources corals may possess that could help them cope with possible future global warming and various diseases that may accompany and/or be facilitated by rising temperatures.

What was done
Working in both the laboratory and the field, i.e. at sea, Mydlarz et al. documented the responses of Caribbean sea fan corals (Anthozoa, Alcyonacea; Gorgoniidae) and their cell-based immune defenses (granular acidophilic amoebocytes, which are known to be involved in wound repair and histocompatibility) to both (1) naturally occurring infections and (2) experimental inoculations with the fungal pathogen Aspergillus sydowii, as well as to (3) experimentally-induced increases in water temperature under laboratory conditions and (4) warming associated with the 2005 Caribbean Bleaching Event, which they describe as a "once-in-hundred-year climate event."

What was learned
The four researchers report that "an increase of amoebocytes was observed in sea fan corals naturally temperature stressed during the 2005 Caribbean-wide bleaching event, as well as experimentally temperature stressed sea fans in the lab," and that "with both naturally occurring infections and experimental inoculations with the fungal pathogen Aspergillus sydowii, an inflammatory response, characterized by a massive increase of amoebocytes, was evident near infections." In addition, they note that "the sea fan has been shown to produce lipid-based anti-fungal metabolites which can halt growth of A. sydowii in culture (Kim et al., 2000)," and they say that Ward et al. (2007) observed "higher anti-fungal activity of sea fans during experimental heat stress and detected a dramatic (176%) increase in potency of anti-fungal metabolites extracted from the sea fans kept at 31.5C (2.5C above summer ambient) and exposed to fungus, relative to controls."

What it means
According to Mydlarz et al., "taken together, these studies suggest an unexpected degree of resilience under adverse environmental conditions." Indeed, they say "it is clear from the data presented in this paper that the sea fan aggressively combats infection in the gorgonian-Aspergillus pathosystem and exhibits the capability for resilience against multiple challenges," not the least of which, we might add, would be further global warming (if the planet ever starts to warm again after its hiatus of the past decade or so).

References
Kim, K., Harvell, C.D., Kim, P.D., Smith, G.W. and Merkel, S.M. 2000. Fungal disease resistance of sea fan corals (Gorgonia spp.). Marine Biology 136: 259-267.

Ward, J.R., Kim, K. and Harvell, C.D. 2007. Temperature drives coral disease resistance and pathogen virulence. Marine Ecology Progress Series 329: 115-121.

Reviewed 26 May 2010