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Marine Ecology & Stock Assessment

Recruitment and Response to Damage of an Alaskan Gorgonian Coral

Calcigorgia spiculifera colony
Figure 5.  A Calcigorgia spiculifera colony inside a settlement ring.  Photo by Erika Ammann.

Benthic habitats in deep-water environments experience low levels of natural disturbance and recover slower than shallow-water habitats. Deep-water corals are particularly sensitive to disturbance from fishing gear, in part because they are long-lived, grow slowly, and are believed to have low rates of reproduction.

Limited data describes recruitment and recovery of deep-water corals. This information is critical to understanding long-term effects of anthropogenic disturbances, such as commercial fishing, on the population dynamics of benthic habitat.

In 2009, ABL scientists initiated a multi-year study to examine recruitment and recovery of the gorgonian coral Calcigorgia spiculifera. This species is broadly distributed in the Gulf of Alaska and along the Aleutian Islands and was chosen because it is found within diver depth. C. spiculifera as well as many other gorgonian corals is found in areas and depths that coincide with trawl and longline fisheries and can be damaged by these fisheries.

The body plan of C. spiculifera is similar to many other gorgonian corals commonly found throughout the North Pacific Ocean. Therefore, sensitivity to disturbance, rate of recovery, and recruitment of C. spiculifera is likely to be similar to other coral species; thus, results from this research could be applied broadly.

Recovery rate and recruitment data are necessary for modeling habitat impacts and forecasting recovery and will ultimately guide fisheries managers in making decisions regarding benthic habitat conservation measures. In this study, recruitment is being investigated by observing settlement of coral planulae onto rings equipped with natural stone tiles; coral recovery is being examined by observing the response of colonies to damage treatments.

The study site Kelp Bay in Southeast Alaska has hundreds of C. spiculifera colonies concentrated at depths easily accessible to scuba divers. Field operations in Kelp Bay began in August 2009 when a team of four divers located and tagged 48 C. spiculifera colonies. Of that total, nine colonies were fitted with settlement rings equipped with removable tiles (Fig. 5). The remaining 39 tagged colonies were ascribed to three damage treatment groups and a control group.

The damage treatments were designed to mimic actual damage that can occur from a passing trawl. These treatments were performed in situ and included deflection, gorgonin excision, and branch severance. Video of each colony was recorded before and after the treatments were performed to establish baseline coral characteristics and to identify immediate treatment effects.

In June 2010, the dive team returned to the study site and collected a subsample of the stone tiles. The tiles were preserved in solution and will be inspected in the laboratory for adhesion of coral recruits. Damaged and control colonies were videoed once again so that comparisons can be made to pretreatment images. Subsequent site visits in September 2010 and beyond will allow additional tile collections and will detail the long-term effects of disturbance.

By Pat Malecha

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