Littorina littorea, a species of both ecological and economical value that belongs to the genus Littorina, is one of the most thoroughly studied of all marine gastropod genera (Reid, 1996). Although the species is of marine origin, it is able to survive brackish conditions as well, as is the case in the western Scheldt estuary were L. littorea is found far inland, upstream along a salinity/pollution gradient.Two experiments were conducted on this species. In the first experiment we translocated periwinkles from a relatively clean (i.e. Westkapelle) to an intermediately (i.e. Ellewoutsdijk) and a polluted (i.e. Hansweert) site and determined the effect of translocation on the energy reserves (glycogen, lipids and proteins) of the species (i.e. after four weeks of translocation). In a second experiment we assessed the energy reserves of resident periwinkles from relatively clean, intermediately and polluted sites over time (i.e. 16/03/05, 23/03/05, 30/03/05, 13/04/05 and 11/05/05). During both experiments we recorded, in addition to the energy reserves, sex related abnormalities (i.e. TBT related female intersex; male penis shedding) and/or parasitism and we determined the shell height and width of the periwinkles as well.A morphological polymorphism was detected, whereby periwinkles from Ellewoutsdijk were significantly bigger and taller compared to their conspecifics from Westkapelle and Hansweert. This polymorphism is tentatively explained in terms of nutrients and organic matter availability. Parasite infection was evident at all three sites. No sex related infestation preference was found, except at Hansweert, where more males were infected than females. Similar to parasitism, female intersex and sterility has been found at all three sampling sites. The highest intersex incidence (ISI=0.2) and sterility (4%) could be detected at Ellewoutsdijk. Nonetheless, sterility incidence did not differ significantly among the three sites. Finally, since penis shedding was only detected in 4 males, we did not consider it further in this study.Translocation (experiment 1) revealed a clear effect on the energy reserves in the translocated specimens which could be explained in terms of adaptation or acclimation related phenomena. Indeed, glycogen and protein levels of specimens that were translocated from Westkapelle to Ellewoutsdijk and Hansweert were significantly lower compared to the glycogen and protein levels of resident Ellewoutsdijk and Hansweert specimens, despite the latter did not differ significantly from the glycogen and protein levels of the resident Westkapelle specimens. Although not significant, similar trends were observed for the lipid content. Only lipid levels revealed a sex related effect whereby females contained more lipids than males, irrespective from the site which was considered.The temporal energy reserve levels (experiment 2) revealed a consistent pattern as well. Initially all energy sources increased, which can be explained by an expected post-winter recovery and a pre-spawning preparation period. However, on 13/04/05, four weeks after the first energy reserve measurements were taken, protein and glycogen levels dropped dramatically at all sites, after which they increased again on 11/05/05. This sharp decrease and subsequent energy reserve increase can be explained by the spawning of L. littorea during April and its post-spawning recovery period respectively. |
