Bottom-drifting algal/mussel spat associations along a sandy coastal region in northern New Zealand.

摘要

The spatial and temporal variability in density and distribution of mussel larvae and spat associated with bottom-drifting algae was investigated at Ninety Mile Beach, northern New Zealand, between October 1998 and April 2000. Analyses of plankton tows conducted at in-shore and off-shore sites around the southern end of Ninety Mile Beach revealed highest mussel larval densities during spawning peaks in July 1999. Higher densities generally were found in-shore versus off-shore, and in southern versus northern sites. Dredging of the sandy bottom at the same sites indicated that drift algae occur in greater quantities in-shore at the southern end of the beach, compared to off-shore and northern sites. The clumps of mostly filamentous red algae almost exclusively contain spat of Perna canaliculus. Dredged algal samples also showed that smaller mussels (<1 mm) are more abundant during the spawning peak in July, whereas larger mussels (>1 mm) are more common at the end of the spawning period in January. In addition, spatial and temporal patterns of algal and spat composition and arrival to the beach were investigated from beach-cast algal samples. Mussel densities in beach-cast algal samples were highest between July and September and lowest between January and May, in agreement with local spawning and larval availability patterns. A distinct, consecutive shift of mussel size-class dominance throughout the year was observed in the beach-cast material, with the density of smallest mussels peaking in August and largest mussels peaking in January. Analyses of six large algal rafts that were dispersed northward by the predominant along-shore current revealed a marked and consistent pattern of both increasing mussel size and algal branching in the northern direction, along the trajectory of the rafts. The dynamic patterns of mussel larval/juvenile dispersal and transport observed in this study provide a framework to develop future sustainable management and conservation strategies for natural mussel and algal populations, upon which the commercial mussel industry in New Zealand currently depends.