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1985; Morgan, 1997). These observations support the fact that the acute P. elegans
recruitment phases on Drum Sands were seasonal events rather than responses to non-
seasonally related events.
The timing and duration of recruitment phases have been shown to vary for different
P. elegans populations. The adult population studied by Gudmundsson (1985) at
Cullercoats, North Sea coast of England, were 100% sexually mature during
December and eggs were laid into egg capsules from December to March with
hatching occurring from February to April. A second population studied at the nearby
Blyth Estuary showed a similar reproductive timing, although lagging 1 month behind
the Cullercoats population (Gudmundsson, 1985). Rasmussen (1973) studied P.
elegans populations at Horsen's Fjord and Isefjord. The former population reached
sexual maturity during September, egg-laying occurred between September and March
with larval hatching from November to April. At Isefjord, a shorter reproductive
season was reported with egg-laying not taking place until January and eventuating in
April with larvae hatching between February and May. Muus (1967) found that the
female P. elegans population in the brackish Kysing Fjord had eggs/larvae in their
tubes during only April and May, while Hempel (1957) found that a North Sea
population off the German coast had a more prolonged spawning season, from
February to September.
The differences observed between Kysing Fjord (Muus, 1967) and North Sea
populations (Hempel, 1957) were suggested to have been due to differences in salinity
between the two locations (Muus, 1967). This is supported by the more-or-less
continual recruitment at Drum Sands where the salinity is typically marine with only a
small freshwater input from the River Almond. Additionally, from her observations,
Anger (1984) suggested that reproduction may occur throughout the year in the Baltic
and North Seas, with spring and autumn being the most likely seasons in which
production of offspring mainly takes place. Brey (1991) suggested that a mild winter
led to a prolonged recruitment phase and Muus (1967) stated that higher densities of
P. elegans in the Kysing Fjord occurred as a result of the mild winters of 1956/57.
Therefore, it appears that temperature and salinities are the two main factors
determining the periods of larval recruitment for P. elegans.
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