Together with the influence of abiotic environmental factors,
mollusks sustain the influence of species in communities. The most close
to them are epibenthic organisms, which inhabit the outer shell surface,
and endolithic organisms that bore shell, with which mollusks enter in
certain relationships. The main interactions that determine the functioning
of the community are trophic and topical relationships between the
component species. The ecology of communities of marine benthic
commercial scallop Patinopecten (=Mizuhopecten) yessoensis with its
dominant endobionts (polychaetes) and epibionts (barnacles) were
investigated. In this study, we performed the fatty acid analysis of the
animals and their potential food materials available in the environment
with the aim of determining the main food sources and the trophic
relationships between the species. Scallop morphometric parameters at
different abundance of epi- and endobionts were compared.
Also, an influence of abiotic environmental factors on these
relationships was determined. It was determined that the main mollusk’s
endobionts are polychaetes; among them the dominant species is
Polydora brevipalpa. It was revealed the existence of competition for
food between elements of community was proved. A decrease in the
internal volume of scallop with an increase in the degree of shell
occupation by polychaete suggested the reduction in the filtering
capability of scallop. Linear regressions for the degree of polychaete
occupation on the scallop weight and shell height revealed negative
relations between them. Polychaete can directly affect the host through
their boreholes. Scallop expends energy for shell regeneration to prevent
the polychaete penetration into its interior cavity. It was revealed, that
dominant epizoobionts of the scallops in natural populations are barnacles
Hesperibalanus hesperius and Balanus rostratus. The differences in the
fatty acid profiles of barnacles and their host scallop suggest that no
trophic competition exists between species.
However, high value of epizoobionts on the upper valve embarrasses
a dehiscing of shell that worsens water filtration and feeding of scallop.
Scallop growth rates decreases under barnacle mass > 30-50 g. Barnacles
lived in the studied community were found to have advantages in
comparison with individuals inhabited stones. It was shown that changes
in abiotic environmental factors result in flourish of some species and
depression of another species of community, and character of the
relationships changes. Data obtained revealed that a mud content of >
25% in bottom sediment negatively affects the scallop. Comparison of
scallop parameters showed that, in spite of the best food potential at the
muddy site, scallops grew significantly slower at the muddy site than at
the sandy site. Most probably, low oxygen concentration in the nearbottom
water and high resuspension of inorganic fine grained particles
enriched with inedible dead organic matter are the main reasons of the
reduction in growth of scallop inhabiting the muddy site. The valves of
scallops collected from sand substratum had significantly more H.
hesperius barnacles than scallops sampled from muddy sand. The degree
of shell bioerosion of the scallop by polychaete worms significantly
higher on the muddy sand than on the sand. With a high degree of
polychaete infestation, the relationships in the commensal association of
scallop and polychaete acquired some features of parasitism. Thus,
changes in the abiotic conditions of environment influence on the
mollusks not only directly, and also by means of the animals that are in
association with the mollusk.