David W. McKay: Where have all the Musculus discors gone?
As a keen marine mollusc recorder I get great pleasure from finding additional species at sites I regularly visit. I don't always find some of the common species on every visit, largely because if I think they are common I don't always look for them. But for small species I collect samples of the various species of seaweed, soak them in a container of fresh water for a few hours then examine what has fallen to the bottom of the container under the microscope. I am unlikely to miss species.
This year my collecting has been largely confined to the shores near my home and one of the habitats I almost always collect is coralline algae. This year I have not seen a single specimen of Musculus discors (Linnaeus, 1767). This is a species I would expect to find in almost all the samples I collect. Many of the sites I have sampled I visit regularly and the absence of Musculus discors has been a surprise. Other Mytilids, especially Modiolarca tumida (Hanley, 1843) and Modiolula phaseolina (Philippi, 1844), appear to be more common. Have these species become more common because they are occupying the niche formerly held by Musculus discors?
Has anyone else noticed this decline in Musculus discors abundance? I am interested in other members' observations to see if this is a phenomenon local to the Moray Firth or if it is more widespread.
Musculus discors (Linnaeus, 1767), Findochty, Moray, Scotland 16 January 2009
