Seamount coral reefs of Tasmania:
Community structure, impacts of trawling,
and conservation

Tony Koslow, Ph.D.
CSIRO Marine Research, Hobart, Tasmania, Australia, and Pacific Fisheries Environmental Laboratory,
Pacific Grove, California

Wednesday, September 22, 1999
3:00 p.m.—Pacific Forum

A field of ~70 small seamounts, with peaks at 660 to 1,700 m depth, is found on the continental slope south of Tasmania. The shallower seamounts (peaks <1000 m depth) are fished for orange roughy. In 1995, a Marine Protected Area (MPA) was proposed for a group of 12 deeper seamounts (peaks >1150 m) to protect the hitherto undescribed benthic fauna. In 1998, CSIRO conducted a survey to assess the diversity and depth distribution of the seamount benthic fauna, the impact of the trawling, and the conservation value of the proposed MPA.

The invertebrate fauna on unfished, relatively shallow seamounts (peaks <1400 m depth) was dense, diverse, and dominated by suspension feeders—in particular, a reef-forming colonial hard coral—as well as a variety of hard and soft corals, hydroids, sponges, and suspension-feeding ophiuroids and sea-stars. Two hundred sixty-two species of invertebrates and 37 species of fish were enumerated from the 11-day cruise, compared with 598 species of invertebrates reported from seamounts worldwide since the Challenger Expedition of 1872-76 (Wilson and Kaufmann 1987). Twenty four—43% of the invertebrate species were new to science, and between 16 and 33% appeared to be restricted to the seamount environment. Many apparently have restricted distributions and differ from species found on seamounts around New Zealand.

A photographic survey showed that trawl operations effectively removed the reef aggregate from heavily fished seamounts. The average benthic biomass of dredge samples from unfished seamounts was 106% greater than from heavily fished seamounts, and the number of species per sample was 46% greater.

Most species had a broad-depth distribution, and those restricted to the shallowest or deepest depths tended to co-occur on the continental slope. The fauna unique to the region’s seamounts appears to be adequately represented within the MPA, which is now permanently established.

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