Observations on byssus systems in the spat of Cerastoderma glaucum and C. edule

ABSTRACT-Under laboratory conditions swimming behavior of larvae of the infaunal bivalve Sinonovacula constricta was dominated by a vertically oriented helical spiral with intermittent sinking, enabling larvae to regulate their vertical position in the water column. Instantaneous swimming velocities ranged between 0.4 and 0.7 mm S-' for veliger and veliconcha larvae; these values were directly comparable to those recorded for other marine bivalve larvae. Swimming activity d u e to ciliary beating in the velum represented a negligible fraction of total energy expenditure. Postlarval drifting was first observed on Day 9 after larval metamorphosis and settlement and continued for about 1 mo. A major mechanism underlying postlarval drifting was the secretion of a single byssus thread which was at least 50 times longer than the body size. Calculations Indicated that the viscous drag of the elongated thread was about 6.7 times greater than the viscous drag of the body, thus providing a hydrodynamic basis for postlarvae to remain suspended in the water column. Environmental factors that increased postlarval drifting included lowered temperature, starvation and decreased light ~llumination. There were at least 3 peaks of postlarval drifting, especially on Day 26 after the larval settlement, these data were consistent with direct field observations. Combination of both physical (e.g. tidal current transport) and biological (e.g. byssus thread) processes are critical in determining the secondary pelagic drifting of S. constricta postlarvae.

Section: Methodssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Larval swimming and postlarval drifting behavior in the infaunal bivalve Sinonovacula constricta

Wang¹,

Xu²

1997

“…The byssus system of cockle Cerastoderma edule spat has only recently been studied (Yankson 1986). Nevertheless, Baggermann suggested as early as 1953 that juveniles of this species have a prolonged pelagic dispersal phase.…”

Section: Seasonal Abundance Of Drifting Molluscsmentioning

confidence: 99%

“…This is particularly true for some mollusc species, which are known to build an assisting device for drifting in the water column. In marine bivalves, thin mucus threads many times the length of the animal increase the hydrodynamic drag on the organisms and enable them to be lifted and transported in the water column by currents (Sigurdsson et al 1976, Yankson 1986, Beukema & d e Vlas 1989. In larger specimens buoyancy may b e enhanced by an extreme protrusion and swelling of the foot (Sorlin 1988).…”

Section: Introductionmentioning

confidence: 99%

Migratory rhythms of drifting juvenile molluscs in tidal waters of the Wadden Sea

Armonies¹

1992

After initial spatfall, some species of bivalves and juvenile mud snails may re-enter the water column and thus undergo secondary dispersal. Uslng continuous plankton net records of the number of drifting organisms over a period of 4 mo in summer 1991, rhythms of migratory activity were analysed on a tidal flat area near the Island of Sylt, eastern North Sea. All abundant species showed a clear diurnal pattern. The mud snail Hydrobia ulvae was more abundant in the water column during daytime than in the dark, while the reverse was true for the bivalves observed. In addition, cockles Cerastoderrna edule and razor clams Ensis directus displayed a semilunar rhythm of drifting activity, and in clams Macoma balthlca there was a 10 d periodicity not closely linked to lunar phases. In most species, the quantitative effect of these longer periodicit~es was stronger than that of the diurnal component The pattern of migratory activity, resulting from these diurnal and lunar rhythms together with a seasonal component, was distorted by weather conditions in a species-specific way. As a consequence, records of drifting young molluscs may be severely biased unless these rhythms of migratory activity are taken into account.

“…Transport during secondary dispersal of the much bigger postlarvae (spat of a few mm length) is facilitated by a long thread that increases viscous drag, thus enabling the young bivalves to be carried along on relatively weak currents (Sigurdsson et al 1976, Lane et al 1985, Yankson 1986). Such threads appear to be a common feature in marine molluscs (Sigurdsson e t al.…”

Section: Introductionmentioning

confidence: 99%

Tidal-current transport of thread-drifting postlarval juveniles of the bivalve Macoma balthica from the Wadden Sea to the North Sea

Beukema¹,

Vlas²

1989

172

130

Laboratory experiments were carried out on thread-bearing spat of the tellinid bivalve Macoma balthica, and in the field high numbers of these juveniles (of up to 1 cm shell length) were caught in winter in plankton nets suspended in tidal streams of the Wadden Sea (The Netherlands). These data are used to explain the distribution and dynamics of a population of the species in the North Sea off the West-Frisian island Terschelling. Evidence is presented that nearly all M. balthica arrive in this area in winter by secondary settlement after tidal current transport, facilitated by long hyaline threads. M. balthica were numerous only close to a tidal inlet connecting the area with the Wadden Sea. Further away (more than 10 to 15 km), young M. balthica arrived in low numbers only and were smaller. All or nearly all M. balthica in the North Sea will have originated from massive primary settlement of just-metamorphosed larvae more than half a year previously (in spring and summer) on high tidal flats in the Wadden Sea. Some functional aspects of dispersal by secondary settlement are discussed