The distribution of intertidal macrofauna on the coasts of iceland in relation to temperature

Abstract

Abstract Records of intertidal macrofauna, mostly collected since 1974, were analysed by the use of a 10×10 km plotting system. Data have been obtained on 208 such squares of the total of378 straddling the intertidal, or 55.0 %. Adequate data were available on 103 species. Nine of 37 obligate intertidal species (24 %) appear to reach distributional limits towards cooler seas going clockwise around Iceland from the south coast. The presence of warm springs in the intertidal extends the range of one species far beyond the main limits. There is no example of obligate intertidal species reaching distributional limits towards warmer seas within Iceland, emphasizing the non-arctic character of the intertidal fauna Of66 species occurring both in the intertidal and subtidal, II (17 %) reach distributional limits towards cooler seas in the intertidal and appear not to penetrate further subtidally, while one species (I %) may show the reverse pattern oflimits towards warmer seas. However, some 34 intertidal-subtidal species (51 %) show a more restricted distribution in the intertidal than in the subtidal, the restriction being to the warmer coastal regions in all but one instance. Low and variable air temperatures probably become critical to these species on colder coasts. Distributional limits in the intertidal, both of obligate intertidal species and of those also found in the subtidal, tended to concentrate in regions ofthe coasts with relatively abrupt temperature changes, while there were also instances oflimits along stretches of coasts with uniform temperatures.