Density surface modelling with line transect sampling as a tool for abundance estimation of marine benthic species: the <Emphasis Type="Italic">Pinna nobilis</Emphasis> example in a marine lake

Density estimation of marine benthic fauna is most often conducted with fishery surveys using dredges or trawls. These estimates are often unreliable due to low and variable efficiency and are inappropriate when dealing with rare or endangered species. In the marine Lake Vouliagmeni, a density surface modelling (DSM) approach using survey data from line transects, integrated with a Geographic Information System (GIS), was used to estimate the population density of the endangered fan mussel Pinna nobilis. This is the first time that such an approach has been applied for a marine benthic species. DSM was beneficial in relation to traditional distance sampling. Apart from providing a more precise total abundance estimate, it related the density of the species to spatial covariates of interest, gave a depiction of the species dispersion in the study area, and provided abundance estimates in any sub-region of the study area. In Lake Vouliagmeni, a marked zonation of P. nobilis distribution was revealed, with the species being restricted in the shallow peripheral zone at depths <22 m. Two density peaks were observed, a major peak at depths between 12 and 13 m and a secondary peak at ∼4 m. A main hotspot of high density was also observed in the northeastern part of the lake. Total abundance of the species was estimated to be 6,770 individuals with a 95% confidence interval of 5,460–8,393 individuals.