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Seasonal variation and population dynamics of isopods inhabiting intertidal macroalgae
J. Arrontes and R. Anadón

Patterns of seasonal abundance and size-frequency distributions of intertidal isopods were investigated in macroalgal dominated communities (Fucus vesiculosus, Gelidium latifolium and Cystoseira baccata) on two semiexposed shores of North Spain. All species were found to display a seasonal cycle in abundance. In the three dominant species, Dynamene bidentata, D. magnitorata and Cymodoce truncata, fluctuations of density were related to reproductive biology. Macroalgae appeared to be a habitat for juveniles of these species; adults were collected in very small numbers. Ovigerous females were never found. Disappearance from the algae was therefore due to mortality and migration of mature animals towards the reproductive habitat. Dynamene bidentata exhibited a prolonged breeding season, with a fairly continuous release of juveniles. In D. bidentata, differences in size-frequency distributions were found between groups of individuals collected on different algal species. In Gelidium, first stage juveniles formed the bulk of the recruitment. A small number of subadult and adult specimens was collected at any time. Fucus lacked first stage animals during most of the study and recruitment was of stage-3 juveniles. A late recruitment in Fucus is interpreted as an adaptation to avoid the harsher environmental condition in this community. Recruitment in D. magnitorata and C. truncata was restricted to two months (in late spring and summer) and always involved newly released individuals. Differences in synchrony of recruitment between the three dominant species might be due to location of populations within the geographical range of the species, though additional information is needed about the distribution of C. truncata.

Keywords: Intertidal, isopods, macroalgae, population dynamics, seasonality, synchrony in recruitment.
Contents of this volume Sci. Mar. 54(3) : 231-240 Back PDF
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