Reporting: Rick Stuart-Smith, Jemina Stuart-Smith, Antonia Cooper, Graham Edgar, May 2009.

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Summary

This report outlines results of subtidal ecological surveys undertaken in the Cod Grounds Commonwealth Marine Reserve (CGCMR) and nearby reference sites off the central coast of New South Wales in May 2009.

The CGCMR was established in May 2007 with the primary aim of protecting critical habitat of the endangered grey nurse shark (Carcharias taurus).

It encompasses an area of 3.1 square kilometres, within a 1000 metre radius of the Cod Grounds pinnacles, which lie approximately 7 km offshore from Laurieton.

Twenty-four transects were surveyed at 11 sites between the 12th and 17th May 2009 by a team of skilled volunteer divers as part of the Reef Life Survey (RLS) program (www.reeflifesurvey.com), using standard RLS underwater visual census protocols.

Surveys were based around 50 m transects, with species-level abundance and size data recorded for all fishes, abundance data for large mobile macroinvertebrates, and percentage cover data for sessile biota within a standard area.

The fish fauna of the reserve and nearby reference sites was generally similar in composition to inshore reefs of the area, but with a very high overall biomass. Few rare species were sighted.

An average of 15.7 fish species was recorded per 50 m transect, with mado (Atypichthys strigatus), silver sweep (Scorpis lineolata) and one-spot pullers (Chromis hypsilepis) the most abundant.

Average fish biomass (over all sites) was 272.4 kg per 500 m2, and higher carnivores and planktivores were the dominant trophic groups. Four grey nurse sharks were recorded on transects, and a further 18 counted at the base of the main pinnacles (site 8CG).

The mobile macroinvertebrate fauna was dominated by echinoderms and molluscs, with the spiny sea urchin (Centrostephanus rodgersii), orange feather star (Cenolia trichoptera), eastern slate-pencil urchin (Phyllacanthus parvispinus) and the mollusc Astralium tentoriformis most important by abundance and frequency of occurrence.

Very clear depth related patterns were evident in the macroinvertebrate fauna, largely related to which urchin species was dominant. Centrostephanus rodgersii dominated transects between 25 and 28 m, P. parvispinus dominated transects between 29 and 32 m and Prionocidaris callista were most abundant on transects deeper than 32 m.

The sessile community was characterised by either a high cover of crustose coralline algae or a diverse sessile invertebrate assemblage and a general lack of large macroalgae.

Distinct differences were also noticed in the sessile community between transects at different depths. Baseline Biodiversity Survey, Cod Grounds NSW Transects less than 29 m had very low sessile invertebrate cover and low taxonomic richness, whilst transects deeper than 29 m had relatively lower cover of crustose coralline algae and higher richness and cover of sponges, ascidians and corals.

The CGCMR encompasses an area of high conservation value, not only due to the presence of a significant grey nurse shark aggregation site, but also because it is a productive area that supports a large biomass of fishes, including many exploited species.

Illegal fishing is considered to be the greatest threat to these communities at present.

It is recommended that continued monitoring of the area be undertaken, with the addition of more external reference sites so that changes in the communities within the reserve can be compared with similar unprotected reefs nearby.