REPRODUCTIVE ADAPTATIONS IN 2 PALAEMON PRAWN SPECIES WITH DIFFERING HABITAT REQUIREMENTS

Reproductive adaptations in 2 littoral prawns, P. adspersus Rathke and P. squilla (L.), were investigated in a non-tidal sympatric site in Sweden. The larger sized P. adspersus, a habitat specialist living in less fluctuating environments than does P. squilla, had a smaller reproductive effort, fewer but larger offspring, fewer clutches per year and reproduced later in life. These findings agree with predictions from r- and K-selection models. Emphasis is put on the necessity of including non-breeding females in the calculations of average expected reproductive effort, as this category is shown to influence results substantially. Differences in reproductive adaptations between P. squilla populations from the non-tidal Swedish site and 2 tidal-affected sites were analyzed. In one tidal-affected site P. squilla inhabited the intertidal Fucus zone; in the other it was displaced from this zone into intertidal rockpools by a 3rd, larger species. In both tidal sites eggs were heavier than in, but reproductive effort equal to, the non-tidal Swedish site. In the rockpool site, eggs were lighter and reproductive effort less than in the Fucus site, indicating adverse effects on reproduction by the habitat displacement.