Is the lagoonal mudsnail Hydrobia neglectarare because of competitively-induced reproductive depression and, if so, what are the implications for its conservation?

✍ Scribed by R.S.K Barnes; Silvia Maria Gandolfi

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 105 KB
• Volume: 8
• Category: Article
• ISSN: 1052-7613
• DOI: 10.1002/(sici)1099-0755(1998110)8:6<737::aid-aqc312>3.0.co;2-m

✦ Synopsis

1. Females of the rare lagoonal mudsnail Hydrobia neglecta respond to increasing population density by a lowered output of eggs. The effect is even more marked when the widespread and abundant congener H. ul6ae comprises part of a joint population. Thus, increasing the density by 50% from 18000 H. neglecta per square metre decreases egg production by 30%, but when H. ul6ae comprises 33% of the higher mudsnail density the decrease is 63%.

2. Mortality of both male and female H. neglecta is also greater in the presence of H. ul6ae than in its absence, whilst mortality of H. ul6ae in mixed populations is minor.

3. Since an allopatric female H. neglecta produces only 11 -14 eggs during her expected reproductive lifetime, such a reduction of fecundity in the presence of moderate numbers of H. ul6ae could prove disastrous for populations of H. neglecta closed to intraspecific immigration but open to invasion by H. ul6ae. Such is the position in several areas, including the semi-isolated, landlocked lagoons that are the habitat of H. neglecta outside the Baltic Sea.

4. This probably partly explains why H. ul6ae and H. neglecta are rarely sympatric in such lagoons, and why H. neglecta is only common in Britain where H. ul6ae is absent from the adjacent intertidal zone and unable to be washed into lagoons by overtopping. This has important repercussions on attempts to conserve this rare hydrobiid, and probably on other rare and legally-protected lagoonal species.