Inter- and intra- species variation in secondary metabolites from Caribbean octocorals of the genus Pseudopterogorgia

Abstract

Trends of the past century suggest that coral bleaching events may become more frequent and severe as the climate continues to warm, exposing coral reefs to an increasingly hostile environment. The combination of higher than average temperatures (as small as 1°C–2°C) and intense light can lead to mass coral bleaching events, which result in apoptosis and/or the expulsion of the zooxanthellae from the host tissue. The decline of coral reefs is significant, because coral reefs maintain high levels of biodiversity, provide habitats for coastal fisheries, protect shorelines from erosion, and may contain potential pharmacological compounds. A striking difference between Caribbean octocorals and other zooxanthellate cnidarians is their seemingly greater resistance of bleaching. While there have been numerous reports of scleractinian coral bleaching throughout the world’s tropical oceans, there have been far fewer observations of bleaching among octocorals. If the increasing incidence of bleaching events continues, the relative insensitivity of most gorgonians to high temperatures may have important consequences for Caribbean reefs.

This research attempts to examine whether secondary metabolites from the genus Pseudopterogorgia act as antioxidants and thus mediate thermal and UV induced oxidative stress and thereby protect the coral-algal symbiosis. Chemical diversity in soft corals may have an adaptive value in mediating ecological interactions in reef environments. Extracts from Pseudopterogorgia sps have differing antioxidant potentials as seen using the FRAP assay. Diterpenes isolated from P elisabethae exhibit antioxidant potential in FRAP and pseudopterosins scavenge superoxide radicals generated in mouse neuronal cells deprived of NGF and prevent apoptosis. Most significantly, pseudopterosins (and especially the aglycone) reduce the loss of quantum photosynthetic yield in zooxanthellae exposed to excess heat and light, and reduced significantly the oxidation of the probe DCFH in the zooxanthellae/ micro-plate based assay.