Effects of environmental gradients on the distribution of harpacticoid copepods in an intertidal flat, Portobello Bay, Otago Harbour, New Zealand

Harpacticoid copepods are often one of the most dominant taxa in marine sediments, but there is limited knowledge of the physicochemical sediment characteristics that affect distribution of native New Zealand copepod species. Environmental gradients and abundance of harpacticoid copepods were therefore surveyed in Portobello Bay, an intertidal sand and mud flat in Otago Harbour, New Zealand. Generalised linear mixed models (GLMMs) were used to determine the relationship between physical factors and species abundance as well as to examine interspecies interactions. Six copepod species were present at the study site: Amphiascoides sp., Enhydrosoma sp., Parastenhelia megarostrum, Robertsonia propinqua, and two species of Quinquelaophonte. Distribution of species was found to be significantly correlated to sediment size, organic content, tidal reach, salinity and pH. In addition to these physical factors, species-species interactions also affected copepod abundance. This information is relevant for understanding factors influencing copepod distribution, but also will shape guidelines for use in marine sediment bioassays using harpacticoid copepods.