Short-term effects of bottom trawling on a 'hard-bottom' (pebble, cobble, and boulder) seafloor were studied on the outer continental shelf in the eastern Gulf of Alaska. Eight sites were trawled in August 1996; then, from a research submersible we videotaped each trawl path and a nearby reference transect to obtain quantitative data. Boulders were displaced, and large epifaunal invertebrates were removed or damaged by a single trawl pass. These structural components of habitat were the dominant features on the seafloor. There was a significant decrease in density, and an increase in damage, to sponges and anthozoans in trawled versus reference transects. Changes in density, or damage to most motile invertebrates were not detected. Delayed mortality, of apparently undamaged invertebrates, may have resulted in greater impact than we detected. Alternatively, over time, some invertebrates may have recovered from any damage previously suffered. A subsequent survey at these sites will address these questions.

A unique feature of the benthic habitat in the Aleutian Islands is the presence of a highly diverse and abundant coral and sponge community. These communities likely provide important habitat for a variety of fish and invertebrate species. Summaries of historical data and recent direct observations with a submersible indicate that the Aleutian Islands may harbour the highest diversity and abundance of coldwater corals in the world. There are 69 documented taxa (species and subspecies) of coral in the Aleutians of which 25 are endemic. Within the Aleutian Islands, there is an increase in diversity of corals west of about longitude 169°W. This shift in diversity is consistent with the hypothesis of an ecological boundary in the vicinity of Samalga Pass. Given the endemism and high diversity and abundance of corals in the Aleutians, there is evidence that this region is the evolutionary centre of origin for some taxa of coldwater corals.

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