Endangered Species Research (2005) 1:1-9
Population ecology of the fan mussel, Pinna nobilis, in a
Department of Zoology-Marine Biology, School of Biology, University of Athens, Panepistimioupolis, 15784 Athens, Greece
A substantial population of the endangered
Mediterranean bivalve Pinna
exists in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). The
population density of P.
was estimated in the lake with line transect sampling. Individuals of the
youngest age class (small) had peak densities in the 1-3 m bathymetric zone and
their densities were higher in poorly sorted sediments. Older (large)
individuals (belonging to all age classes except the first one) had peak
densities in the 11-13 m bathymetric zone. No P.
found deeper than 22 m. The absence of large individuals in shallow waters may
partly be explained by illegal fishing. There are several hypotheses proposed to
explain the lack of small individuals in deeper areas, but no definite
explanation is offered. In Lake Vouliagmeni, P. nobilis densities
were high, although marine seagrass was completely absent. Thus, P. nobilis does not actually require seagrass meadows, as
stated by many authors, and it may exist in large numbers in bare soft-sediment
areas as well. P. nobilis had fast growth, mostly during its first 3 years of life, and may
live beyond 15 years. By recording the
exact location of each P. nobilis individual
within 800 m2 transects, as a pair of coordinates, the exact spatial
distribution was defined and aggregation indices were calculated. P.
nobilis had an aggregated
dispersion, but no evidence for preferential settlement near adults or
previously-settled individuals was found. The aggregated dispersion of P.
nobilis probably relates to the patchiness of the local environment. The
size of P. nobilis population in Lake Vouliagmeni was estimated to be
8501 ± 4395 (mean ± 1 sd) individuals,
of which 4355 ± 3460 belonged to the first age class and 4146 ± 1405 belonged
to all other age classes.
Key Words: Pinna nobilis, population ecology, Vouliagmeni, marine lake, distance sampling, spatial distribution, growth, endangered species, SCUBA