The ecology and dynamics of the brackish water prawn, Palaemonetes varians (Leach) and its interrelationships with the common goby, Pomatoschistus microps (Kroyer) in artificial coastal lagoons of the Ribble Estuary, Lancashire.
The Brackish Water Prawn Palaemonetes varians (Leach) is common
throughout coastal waters of the UK and Western Europe. Its preferred
habitat is within sheltered waters of lagoons, though it is not a major
constituent of estuarine tidal flux.
Bottle traps were used to assess the seasonal 'activity' and habitat
density of P. varians in artificial coastal lagoons on saltmarshes and claimed
marshland habitats. Additionally, the potential diet resources available to P.
varians were investigated between sites.
The data revealed that relict landward lagoons and saltmarsh borrow
pits were successful breeding areas for P. varians, the latter acting as a major
replenishing resource in the estuary. Differences in breeding period and
growth rate, assessed using maturation, zoeal and enclosure data were found
to be attributed to environmental temperature rather than habitat food
P. varians was found to adapt to varying prey resources showing an
ontogenetic shift in prey size with increasing body size, which was correlated
with chelal grab width. The chelal morphology of P. varians in relation to
feeding behaviour was described using Scanning Electron Microscopy (SEM).
Structural and setal variation accounted for 'passive' and 'active' feeding
behaviour portrayed by P. varians.
Within the sites studied, the Common Goby, Pomatoschistus microps
(Kreyer) was also a cohabitant with P. varians. Bottle trap data demonstrated
that whilst the seasonal activity of P. microps in claimed marsh lagoons was
linked to temperature, within the intertidal borrow pits an autumnal inmigration
pattern was identified. The autumnal peak of P. microps was
shown to have a profound effect on the abundance of P. varians.
Different seasonal and ontogenetic diet trends were established for
P. microps, via gut and morphological analyses and they were used to
investigate the extent to which P. varians was utilised as a prey resource.
Furthermore, comparisons were made between the Grass 'Shrimp', P. pugio
(Holthuis) and MUmmichog, Fundulus heteroclitus L. These species occupy a
comparative habit and are important species in the ecological structuring of
American saltmarsh ecosystems.
Digital video and mesocosms were used as further tools to investigate
the interrelationships and predation of P. varians by P. microps. It is shown
that whilst the predation of P. varians does occur in microcosms, the predation
efficiency of P. microps was limited by tail-flip escape swimming (TFES) of