The biology and ecology ofRissoa parva(da Costa) [Gastropoda: Prosobranchia]

Abstract

Populations of the prosobranch gastropod Rissoa parva (da Costa) have been investigated from Wembury, Devon, and a number of localities in south-west England and Wales. The distribution of individuals on the shore at, and subsequent to, settlement has been found to be greatly influenced by the anatomical characteristics of algal substrata, animals being more commonly encountered among the fronds of filamentous algal forms. Only during the summer months were individuals found in any appreciable numbers on the more simple forms such as the Fucus spp.While individuals of R. parva generally avoid areas of excessive sedimentation a positive correlation between increased population density of this species and increased sediment content of the algal substratum has been shown for populations collected from the filamentous red algae Lomentaria articulata Lyngb. and Plumaria elegans Schimtz. A similar, though not so marked, correlation is also found for populations living on Gigartina stellata Batt. On Fucus serratus L. no such correlation was evident.The nature of the algal substraum affects the seasonal variation in population density: on the mat-like growth forms of Corallina officinalis L. and Lomentaria articulata population densities remain fairly high, even increase in some instances, over the winter months, whereas on other algal substrata a sharp decline in density closely follows an August/ September maximum.Recently settled individuals are evident throughout the year, though settlement intensity varies, being highest during August 1972 at Wembury. The post-settlement phase of the life-cycle varies between 3 and 9 months, according to the season, and as many as six generations per annum have been recorded.

Invertebrate communities in holdfasts of the kelp Macrocystis pyrifera from southern Chile

“…This implies that the general pattern of temporal change for animal abundance is determined by a few species whose temporal changes strongly affect Our results, however, document neither juvenile recruitment nor individual growth, at least not for the most frequent and dominant taxa in M. pyn'fera holdfasts. The data on individual size and biomass indicate that M. pyrifera holdfasts do not seem to play an important role as nursery grounds, which has been suggested for holdfasts of M. pyrifera in central California (Andrews, 1945), and in holdfasts of other brown algae elsewhere (Bayne, 1964;Wigham, 1975;Cancino and Santelices, 1981). Thus, the temporal variations we found may be primarily due to the migration behaviour of some of the dominant species.…”

“…A diversity of invertebrates occurs in the holdfasts of M. pyrifera in southern South America (Dayton, 1974;Barrales and Lobban, 1975) but almost any aspect of their biology other than taxonomy is completely unknown. The general roles played by holdfast of algae and O Inter-Research/Printed in F. R. Germany especially by kelp-like Phaeophyta with respect to the fauna which inhabits them include those of mechanical shelter (wave impact), refuge from predators, and nursery grounds (Andrews, 1945;Bayne, 1964;Wigham, 1975;Moore, 1978;Cancino and Santelices, 1981). Such roles have been described mostly for invertebrates occurring in kelp holdfasts which, being relatively compact, maintain a community structure which can sometimes be quantitatively different from that existing outside the holdfasts.…”

Landing on one's foot: small-scale topographic features of habitat and the dispersion of juvenile intertidal gastropods

“…Individuals that happen to land in crevices when they arrive on the shore in a wave are able to survive by this sudden change of size that wedges them into the crevice (Fretter & Manly 1977). There have also been accounts of passive entrapment of newly-arrived juveniles of Rissoa parva in the complex fronds of foliose algae (Wigham 1975). There are several experimental accounts of 'bulldozing' or accidental grazing by adult limpets on small juveniles, leading to negative correlations in their densities (Dayton 1971, Underwood et al 1983, Branch 1984.…”

Comparison of patterns of spatial variation of microgastropods between 2 contrasting intertidal habitats

“…Despite their diverse nature, little is known about the basic ecology of most Australian microgastropods (Beesley et al 1998) and there have been no quantitative descriptions of their spatial or temporal patterns of variability. However, studies on the basic ecology and life histories of European microgastropod species are most abundant, and some have shown the importance of substratum, mortality, recruitment and migration of adults in determining the pattern of spatio-temporal variation (Smith 1973, Wigham 1975, Southgate 1982, Fernández et al 1988.…”