Abstract:
Soft sediments are one of the most poorly documented major habitats in the world, despite covering much of the global seafloor. Basic information on the species present, their associations, and relationships with physical factors like sediment type and depth is lacking even for most coastal areas. The primary aim of this thesis was to create the first description of soft sediment communities within the Cape Rodney-Okakari Point (Leigh) Marine Reserve, located in north-eastern New Zealand. The reefs in this reserve have been thoroughly mapped and the subject of hundreds of ecological studies, while the soft sediments have received virtually no attention. The second aim was to investigate whether movement of the spiny lobster Jasus edwardsii from the reserve reefs to soft sediments beyond the reserve boundaries where they are legally harvested, is potentially due to the lobsters utilising dense prey patches there. Organisms larger than 4 mm were sampled from 306 stations inside and outside the reserve using a Smith-McIntyre grab. A sediment sample was also taken for grain size analysis. The faunal samples formed six main clusters that were well defined by their taxonomic composition and dominant sediment type. A total of 154 taxa were recorded, with gastropods being the most diverse class found. Diversity was roughly consistent across the marine reserve, but total abundances were much higher in the coarse sediments on the eastern side of Goat Island than in the fine sediments on the western side. The most abundant taxa were filter-feeding molluscs, presumably exploiting the westward tidal current flowing around Cape Rodney and being deflected offshore by Goat Island. The most abundant single taxon was the bivalve Tawera spissa, which formed a narrow but very dense band at about 22 m depth along most of the eastern side of the reserve. Distribution and abundance patterns of larger individuals (>15 mm) of all species, considered likely prey for lobsters, did not straightforwardly account for lobster movement. This study has now created a baseline for future researchers to make comparisons to and track any changes and patterns that may be seen in the future at Leigh Marine Reserve.