The ecology and growth of the netted dogwhelk Nassarius reticulatus (Gastropoda: Nassariidae)
The distribution of Nassarius reticulatus around Anglesey (North Wales, UK) revealed well established populations along the west coast, smaller populations along the north coast and a complete absence of this gastropod from the east and south coast. Nassarius reticulatus is well adapted to varying degrees of wave exposure and prefers fine sand sediments, with <0.5% organic and < 2% silt content. New recruits appear in the population at a size of 7-8.9 mm between February and April one year after hatching. Mortality was higher in an intertidal lagoon than in a subtidal beach in Rhosneigr, especially during summer. Whelks from the intertidal lagoon had a higher L,,, and a lower K value than whelks from the subtidal beach in Rhosneigr. Nassarius reticulatus forms taller and thicker shells when inhabiting sheltered areas, which are more resistant to predation pressure. Growth rate increased with increasing seawater temperature. Smaller individuals allocated more energy to growth, while larger whelks invested more energy in reproduction. Shell growth rate was similar between males, females and imposex-affected females. Limitations in food availability suppressed shell growth and reproductive output. Length frequency analysis overestimated the shell growth of N. reticulatus, due to overlapping older size-classes. Estimation of the age and growth of N. reticulalus from statolith growth rings was a more reliable method than length frequency analysis. The first prominent statolith ring is formed during larval settlement and subsequent rings are formed annually. Spawning of N. reticulatus in the laboratory occurred throughout the year, with a peak during July. Breeding size classes of N. reticulatus have a shell length >_ 21 mm. Nassarius reliculatus produced smaller egg capsules containing smaller eggs, which had a shortened embryonic development and produced smaller larvae during the summer. Hatching occurred successfully over a range of seawater temperatures (8.5-20°C), however, larvae only metamorphosed at temperatures > 16.3°C. Lack of a suitable substrate for settlement reduced the growth rate of the larvae and delayed metamorphosis. Imposex examination in sympatric populations of N. reticulatus and Nucella lapillus indicated that both gastropod species were highly affected by TBT pollution in areas adjacent to commercial ports and small marinas.