The Effect of Environmental Factors on the Distribution of the Amphipod Pectenogammarus Planicrurus, with Particular Reference to Grain Size

The distribution of Pectenogammarus planicrurus Reid around the British coast appears to be restricted to a few scattered areas. As far as is known it has only been recorded in three localities.

The first of those is the ‘type locality’, described by Reid (1940), at Saltdean, Sussex. Here the upper region of the shore consists mainly of flint pebbles, the middle shore mainly of sand with patches of flint and chalk pebbles and the lower shore of boulders of chalk on a solid chalk base. Reid found it plentiful under stones near high water mark.

In a brief survey of the south coast beaches, from Brighton, Sussex, to Deal, Kent, in the summer of 1965, P. planicrurus was found in large numbers on the chalk and flint beaches associated with the coastal outcropping of the chalks of the North and South Downs. By far the largest populations were found at Seaford, Sussex, where, unlike Saltdean, the pebbles and gravel extend down to low water and P. planicrurus was not restricted to the upper part of the beach as it was at Saltdean. It appears that the ‘type locality’ described by Reid (1940) does not give a true picture of the vertical range of distribution of the species.

The second locality is at Port Erin, Isle of Man, where Jones (1948) observed P. planicrurus ‘under stones’ between H.W.N. and L.W.N. at Spaldrick on the north side of Port Erin Bay. Jones did not find this species in sufficient numbers to formulate a general idea of its habitat.