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 (<5 cm S-') and a high-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.

Spatial variability in sexual and asexual reproduction of the fissiparous seastar Coscinasterias muricata: the role of food and fluctuating temperature

“…Anthony & Svane (1995) showed that substratum instability caused by moving mussels in a current-swept habitat significantly increased pedal laceration (fragmentation and clonal proliferation) in a subtidal population of the sea anemone Metridium senile. Larger forms of M. senile, with apparently higher clonal diversity, attached to rock walls in deeper sheltered localities compared with shallow current-swept mussel beds of Mytilus edulis (Anthony & Svane 1994). These observations parallel our own on C. muricata, and further emphasise habitat instability as an important factor in clonal proliferation of invertebrates.…”

Acontia and mesentery nematocysts of the sea anemone <i>Metridium senile</i> (Linnaeus, 1761) (Cnidaria: Anthozoa)

“…M. senile grew on hard substrates and appeared in two size-groups and several colour morphs (Anthony and Svane, 1994). Small red-brown individuals (pedal disc diameter (PDD)<20 mm) form mass aggregations in surface water down to 2 m. Small to large, reddish to white individuals (PDD up to 45 mm) grew solitary or in small presumed clones from the surface down to ca.…”

“…The nudibranch Aeolidia papillosa (Linnaeus, 1767) is the chief predator of the Swedish M. senile population (Wahl, 1985;Anthony and Svane, 1994). Acontia are long, thread-like structures filled with nematocysts.…”

Effects of substratum instability on locomotion and pedal laceration in Metridium senile (Anthozoa:Actiniaria)

“…Kaplan 1984), and in shallow (2 to 8 m deep) channels at Strommarna on the Swedish west coast, large subtidal beds of M. edulis are nearly 100% covered by populations of M. senile. Small body size (<2 cm pedal disc diameter, PDD) and high rates of pedal disc laceration (the mode of asexual reproduction in M. senile ;Bucklin 1987) are characteristic features of these populations of sea anemones (Anthony & Svane 1994). Larger forms of M. senile are found abundantly in sheltered and deeper localities attached directly to the rock wall and undergo pedal laceration at lower rates (see Anthony & Svane 1994).…”

“…Pedal laceration, and hence clonal growth, in Metridium senile may be stimulated by high current velocities, and differential size-frequency distributions between habitats are generally assumed to result from the effect of different current regimes, and/or genetically determined differences in rate of laceration among clones (Shick 1991, Anthony & Svane 1994. However, pedal disc laceration may also be a consequence of pedal disc locomotion in M. senile, and escape-recolonization events in pace with the dynamics within mussel patches are therefore likely to be imporlant features contributing to both individual (polyp) and clonal size of M. senile inhabiting mussel beds.…”