Spatial variation in the abundance and condition of the bivalveNuttallia olivaceain relation to environmental factors and sublethal predation

Our aim was to assess the spatial heterogeneity in the abundance and condition of the tellinacean bivalveNuttallia olivaceain estuarine tidal flats, as well as to reveal the relationships between these variables and abiotic and biotic factors. The intensity of sublethal siphon predation by juvenile stone flounderPlatichthys bicoloratuswas considered as a possible factor affecting the bivalve condition. A 2-scale sampling of stations at 200 to 800 m intervals and 2 to 5 plots at 5 to 20 m intervals on a transect line at each station was conducted in the Natori River estuary, Japan. Abundance and somatic condition greatly varied at both scales. Densities varied from 0 to 4902 ind. m–2among stations and from 2480 to 6448 ind. m–2among plots at the station with the highest density. Body mass index varied from 4.0 to 5.0 between stations and from 4.9 to 5.7 between plots at the station with the highest body mass. It was commonly observed thatN. olivaceawas abundant and that body condition was high at sites with low silt-clay contents and low elevations, as revealed by generalized linear models. A negative influence of siphon predation was detected only on somatic condition, but it accounted for only 1.2% of the variation, whereas environmental variables accounted for 30.2%. These results indicate that environmental variables are key factors affecting bivalve abundance and condition, while sublethal predation is only a potential factor affecting bivalve condition.