ISOTOPIC RECORDS OF GROWTH IN DEEP WATER STYLASTERIDAE CORALS (CNIDARIA: HYDROZOA): ECOLOGICAL AND PALEOCLIMATIC IMPLICATIONS

Deep water coral skeletons represent a potential archive for paleoecological and paleoclimatological reconstruction. Most research has focused on scleractinian and gorgonian taxa, whereas stylasterid hydrocoral skeletal growth is not well understood. Consequently, fundamental issues of proxy development in stylasterids remain unresolved, such as growth rate and increment periodicity. We describe stable carbon and oxygen isotope profiles measured through ontogeny in Stylaster erubescens skeletal aragonite. These corals were collected by submersible from the Charleston Bump, an area of steep relief and intense Gulf Stream current flow in the northwestern region of the Blake Plateau, western North Atlantic. Corals were collected from depths of 400 to 700 meters in an ecosystem that is presently managed for commercial fisheries.

Incremental growth is visibly evident in most, but not all, of the colonies. Isotopic profiles oscillate in a generally sinusoidal fashion, often in tandem with growth banding. It is not yet established whether S. erubescens precipitates its skeleton in oxygen isotopic equilibrium with seawater. A linear relationship between oxygen and carbon isotopes suggests some likelihood of kinetic fractionation effects. However, these isotopic oscillations appear seasonal, thus may be used as a growth rate proxy even in the absence of temperature reconstructions. Using the relationship between these oscillations and incremental banding, mean estimates of coral growth are constructed. Growth rate estimates will be discussed with reference to the corals' utility as a paleo proxy and the impact of commercial fishing on modern coral ecosystems. Presently, exploitation of deepwater fisheries is expanding worldwide and the impact to these habitats varies greatly. While the Charleston Bump fisheries are managed within an ecosystem framework, and coral impact is minimal, others fisheries have extensively damaged deepwater corals.