SPATIAL VARIABILITY IN THE POPULATION-STRUCTURE OF THE SHORE CRAB CARCINUS-MAENAS (CRUSTACEA, BRACHYURA) IN A SHALLOW-WATER, WEAKLY TIDAL FJORD

The spatial variability in population structure of the shore crab Carc inus maenas was studied in a shallow-water fjord in the island of Fyn, Denmark. The fjord comprises an enclosed area which is geomorphologic ally divided into a shallow cove (mean depth 2 m), known as Kertinge N or, and a deeper narrow area, closer to the open sea, known as Kertemi nde Fjord. Tidal range is small (ca 20 cm). Sex-ratio favoured males a t most of the sites sampled with the exception of the inland slope bet ween the shallow Kertinge Nor and the deeper Kerteminde Fjord, which a pparently was a spawning site. Crab densities were much higher in Kert eminde Fjord than in the shallower Kertinge Nor. Ventral carapace colo ur varied between green and orange-red, with the proportion of the gre en morphotype increasing with increasing distance from the open sea. A nalysis of the population size structure identified 3 differentiated a reas for both male and female crabs. Sites closer to the mouth of the fjord were characterized by a numerical dominance of small crabs, wher eas crabs in Kertinge Nor were clearly of a much larger size. Sites in Kerteminde Fjord were characterized by a wider range of sizes. Some c rabs in Kerteminde Fjord carried epibionts on the carapace, but those were absent in crabs from Kertinge Nor; moreover, a few crabs in Kerti nge Nor carried Mytilus edulis byssus threads indicating that epibiont s had fallen from the carapaces. Thus, population structure characteri stics, such as colour morphotype proportions, size structure and occur rence of epibionts, are in accordance with the occurrence of a high de gree of environmental variability in the area decreasing towards the m outh of the fjord and the open sea.