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Research Technical Report

The Abundance and Distribution of Megafaunal Marine Invertebrates in Relation to Fishing Intensity Off Central California

Graiff, K.W. (December 2008)

M.S. Thesis, Washington State University, 60pp.


Deep-water megafaunal invertebrates such as corals and sponges contribute to biodiversity, create fish habitat, and can indicate long-term environmental conditions. These structurally complex invertebrates are easily damaged by commercial and recreational fishing gear. This impact is of particular concern because the long-term viability of fish populations may be threatened by habitat degradation, specifically the removal and destruction of structure-forming invertebrates. This study examines the abundance and distribution of megafaunal invertebrates on the continental shelf at three sites within the Monterey Bay National Marine Sanctuary, CA. Each site (Portuguese Ledge, Point Sur, and Big Creek) has been subjected to varying levels of fishing effort and gear use. Of particular interest were the effects of fishing to the abundance of megafaunal invertebrates categorized as slow-growing, sessile species and fast-growing, mobile species. The level of fishing disturbance to these two biologically different groups of invertebrates was predicted to vary based on the magnitude, areal extent, and frequency of each bottom-contact fishing gear. Underwater video surveys, conducted in the 1990s using the Delta submersible, were used to describe habitat and quantify invertebrates. A total of 54,439 individual invertebrates from 54 taxa were documented on high-relief rock and soft sediment habitats among the three sites. Overall, there were little to no detected effects on invertebrates due to fishing. Environmental variables are most likely influencing invertebrate abundance and distribution. The documentation of invertebrates at these sites is important because they are within newly established marine protected areas. These historical data will serve as a reference point for future monitoring of the sites in terms of how habitat conditions and invertebrate abundances have benefited from the implementation of new management regulations.

Reviewed: April 11, 2024
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