Niche differentiation between two littoral prawns in Gullmar Fjord, Sweden: Palaemon adspersus and P. squilla

Palaemon squilla (L.) at the Swedish west coast occurred on bottoms covered with Zostera marina L., on bare sand bottoms, in moving water and in rock pools, while P. adspersus Rathke was found on Zostera covered bottoms only. During summer 1978 the increase in length of P. adspersus was 2.2 times greater than that of P. squilla , the former species also attaining a larger maximal size. Laboratory studies showed a wide tolerance in both species to combinations of temperature and salinity. P. squilla tolerated higher temperatures than P. adspersus. The locomotory activity of P. squilla was more than twice that of P. adspersus and concentrated to the dark period. Stomach analyses revealed no interspecific differences in food selection. P. squilla appears to be an opportunistic species able to survive in many different habitats, with a higher dispersal ability, smaller size and larger tolerance to extreme values of abiotic parameters, while P. adspersus is a K‐strategist with a high competitive ability, a larger proportion of availably energy devoted to growth, and with larger body size and lower mobility. Although these differences enable the two species to coexist in certain habitats, their habitat segregation still appears to be of primary importance to reduce competition between them.