Idotea

Abstract: The population dynamics and bteeding biology of Idotea baltica, I. chelipes and I. granulosa wete studied in the littoral belts of two northern Baltic rocky shore habitats. Population sizes are largest in the aurumn, after occupation of the Fucus belt by a new Idotea generation from the belt of filamentous algae. Two periods of dectease in the population density, one in late autumn and another after the breeding period in the following summer were observed. Adult males are eliminated from populations before females. Most individuals in each species breed simultaneously in eatly summer. Brood numbers are related to female size, but great marsupial mortality occurs during incubation. Idotea juveniles grow exp.nentially in late summer, but during winter the growth is delayed. Another period of intensive growth occurs in spring before breeding. I. baltica is the dominant species in both habitats examined. I. chelipes and I. granulosa were found not to coexist. The roles of different factors affecting...

Abstract: Feeding rates and microhabitat preferences of Idotea baltica, I. chelipes and I. granulose were investigated experimentally to elucidate their role in the local declines of Fucus vesiculosus in northern Baltic littoral communities. The mean ingestion rates (mg Fucus AFDW per 10 mg Idotea AFDW per day) varied from 1.1 to 1.6 in males and from 2.6 to 3.5 in females, the average daily consumption per individual being 2.1 mg Fucus AFDW in I. Baltica females, 1.6 mg in I. granulose and 0.7 mg in I. chelipes females. The feeding rates were significantly affected by the quality of fucoid tissues, the palatability of which increases with the algal age. The old eroding Fucus thalli also are most attractive microhabitats for I. baltica and I. chelipes compared to apical segments and thalli with epiphyte load. These results suggest that normally young Fucus plants escape harmful grazing in the presence of more attractive adult algae with a capacity for renewal and compensatory growth. If the demographic str...

Abstract: Descriptions of the ecology of Idotea are often generalized, and there appears to be no comprehensive work on the habits of individual species. The present account of the ecology of Idotea in the Isle of Man, together with a discussion of relevant literature, includes extended observations on the commoner species, and illustrates that each species has a fairly characteristic range of habitat. Collections were made on various types of rocky shore, and in some localities quantitative sampling was attempted with the aid of a wire frame enclosing an area of 0.1 m2. Rock pools were examined, as were regions of the shore subject to the influence of freshwater streams. Surf plankton was collected by dragging a D-net along the edge of the sea on various sandy beaches, and the faunas of surface drift weed and buoys were sampled from a small boat. Dredgings were made off the south coast of the Isle of Man in depths down to about 10 fathoms. Both a naturalist's dredge and a D-net were used, the latter serving mainly to skim accumulations of algae, with accompanying Idotea, from a sandy bottom. Seven species of Idotea were found in the Isle of Man-I. emarginata (Fabricius), I. neglecta G. O. Sars, I. baltica (Pallas), I. linearis (Pennant), I. granulosa Rathke, I. pelagica Leach and I. viridis (Slabber). Collinge (1917) records two other species from Britain: I. metallica Bosc. and I. sarsi Collinge. The first of these does not seem to be a British resident, the few specimens which have been recorded being chiefly found amongst Lepas on floating wood (Tattersall 1911), whilst the second, I. sarsi, is synonymous with I. baltica. I have examined the type specimens of I. sarsi in the British Museum, and they cannot be distinguished from I. baltica (Naylor 1955 c).