The production of Macoma balthica (L.) in the Ythan Estuary

Abstract

Macoma balthica (L.) is an important food species for many vertebrate predators on the Ythan Estuary. It occurs throughout much of the estuary and in the intensive study area had a maximum density of about 6000/m 2 after spat settlement. The animals have a marked stratification in their depth distribution. Small animals live chiefly near the surface and larger animals deeper down. Some individuals live for about 6 years but before spat settlement, the population was made up chiefly of 1 + animals (from 87–93% of the total) and after spat settlement was dominated by 0 + animals (from 85–91% of the total). In (1972), growth took place mainly in the spring and early summer but continued until October for the 0 + year group. There was a large seasonal variation in the condition of M. balthica, the dry flesh weight of animals of a given size being two to three times greater in summer than in winter. The spawning season lasted from late February to early April. The biomass of the population was greatest in June even though the density was then lower than in winter. The average production of M. balthica in the intensive study area was 10·07 g dry wt m −2 year −1 (42·8 kcal m −2) and the annual P B ratio 2·07. The mean annual biomass of M. balthica over the whole estuary in (1973) was 2·77 g dry wt m −2 and production therefore equal to 5·73 g dry wt m −2 year −1.