Effects of flow-habitat on body size and reproductive patterns in the sea anemone Metridium senile in the Gullmarsfjord, Sweden

Abstract

In the Gullmarsfjord, on the west coast of Sweden, a variety of morphs of Metridium senile (L.) are found. A small form (pedal disc diameter 0.3 cm) is found in dense clones (90% coverage) in high-flow habitats at 2 to 5 m depth, and larger forms (pedal disc diameter = 2.5 to 3.5 cm) are found abundantly in subtidal low-flow habitats where body size increases with depth. In order to investigate the adaptive significance of body size and laceration in M senile from different current regimes, individuals of a large and small morph were reciprocally transplanted between a low-flow ( 65 cm S-') subtidal habitat, and incidents of pedal laceration were monitored from August 1992 to January 1993. For comparison, 2 experiments (analogous to the field transplants) were carried out in laboratory flumes. The relative importance of sexual reproduction in the 2 habitats was investigated by comparing gonad sizes of mature females. The results of field and laboratory experiments showed that individuals from the high-flow habitat decreased their rate of laceration in low flow, but maintained a higher rate of pedal laceration than the low-flow population irrespective of site of transplantation, suggesting that properties of asexual proliferation possess both habitat-related and intrinsic components. Sexual reproductive allocation was positively correlated with body size and was significantly greater among females from the low-flow population When adjusted for a common body weight, however, differences in gonad sizes were insignificant. Frequent asexual replication of the genet and fertility at a small size (1 g) are argued to be important features in the high-flow habitat which compensate for the reduced reproductive output of individual anemones and eventually maximize clonal fitness.