VIII.—Structure and Biology of the Larva and Spat of Venerupis pullastra (Montagu)

Four phases of metamorphosis in the eastern oyster Crassostrea virginica were characterized: 'settlers' have attached to the substrate but retain larval characteristics; metamorphosis and degeneration of the velum has begun in 'prodlssoconch postlarvae'; in 'dissoconch postlarvae' shell growth beyond the prodissoconch has begun but the foot persists; and 'juveniles' have lost all larval organs and metamorphosis 1s complete. These phases were used in exarmning the metamorphic process dunng and following continuous and short-term exposures to hypoxia (1.5 mg 0, I-', 20% of air saturation) and microxia (<0.07 mg O2 1-l, < 1 % of air saturation) We observed no abnormal development in the oysters, but development was delayed following 3 d exposures to hypoxia, and 2 and 3 d exposures to microxia. Under continuous exposure to microxia, oysters did not develop to the dlssoconch postlarva or juvenile phases Approximately 50% of the control oysters died within the 2 wk penod following settlement I\?ortality was virtually confined to the settler and prodissoconch postlarva phases. Short-term exposures to hypoxia ( l to 3 d) and microxia (1 d ) had little effect on the median mortality time or final total mortality, compared to controls. Microxic treatments longer than 1 d did affect mortality and oysters continuously exposed to rnicroxia had a median mortality tune of 87 h. Short-term exposures to low oxygen did not have permanent effects on post-settlement growth rates. Oysters exposed to microxic treatments, however, appeared to have slower growth rates dunng the exposure penod. We conclude that low oxygen conditions, In particular those that are microxic and last longer than 24 h, have detrimental effects on the development, growth, and mortality of postsettlement oysters.

Section: Discussionsupporting

confidence: 91%

Description of metamorphic phases in the oyster Crassostrea virginica and effects of hypoxia on metamorphosis

Baker¹,

Mann²

1994

“…These authors' viewpoint is supported by similar comments with respect to the larvae of barnacles (Bousfield 1955), fish (Fortier & Leggett 1983), brachyuran crabs (see contributions in Kennedy 1982;Sulkin 1984) and even dinoflagellates (Tyler & Seliger 1978. Quayle (1952) examined vertical distribution of Venerupis pullastra (Montagu) larvae in Scottish coastal waters and concluded that they perform active die1 migrations, being near the surface at night and at certain tidal phases, and nearer the bottom in the daytime. By contrast Korringa (1952) suggests that larvae are predominantly passive drifters.…”

Section: Yes Yesmentioning

confidence: 82%

Distribution of bivalve larvae at a frontal system in the James River, Virginia

Mann¹

1988

The James River is the southernmost of the major subestuaries of the Chesapeake Bay, USA. A frontal system develops on the early flood tide in the Hampton Roads region of the lower James. This system, together with a cyclonic gyre in Hampton Roads, is in part responsible for partial retention of downstream-flowing water in the estuary and it's injection into deeper, upstream-flowing water. The role of the frontal system in retention of bivalve larvae in the James was investigated In a 2-part study: a field exammation of larval distr~bution versus depth along a transect across the front in relation to salinity and temperature of the converging and diverging water masses, and a laboratory examination of the ability of oyster Crassostrea virginica larvae to swim in and through salinity gradients comparable to or greater than those encountered near the frontal system. Field studies indicate that larvae are passively transported through the frontal system and plunge to depth as the more saline water in which they are entrained encounters less saline water The deeper, more saline water flows upstream as it leaves the frontal system. Laboratory studies demonstrate that both straight hinge stage (mean length = 7 5~) and umbo stage (mean length = 157.5 to 159.7 pm) larvae actively swim through a salinity discontinuity of 3 %D when exposed in a column of 22 960 water overlayed by 19 9b. water (extreme values charactenstic of bottom and surface water at the frontal system). Further, their mean rates of vertical movement (0.37 to 1.02 mms-') illustrate the ability of larvae to move through the depth of the water column in the James in less than one tidal cycle. Pediveliger stage oyster larvae (mean length 317.2 pm), by contrast, restricted swimming to small but frequent excursions above the bottom in the laboratory apparatus and did not swim through the salinity interface. Following passive transport through the frontal system in the lower James straight hinge and umbo stage larvae may employ active depth regulation to redistribute throughout the water column; however, pediveliger stage larvae probably remain near the sediment-water interface.

“…In a 10 m mesocosm, sea scallop larvae moved from a mean depth of 6.9 m during the day to 3.7 m at night (Silva & O'Dor 1988), and Pecten maximus larvae also occur shallower at night in experimental water columns (Kaartvedt et al 1987). Field studies of other species of bivalve larvae (Quayle 1952(Quayle , 1959 and total bivalve larvae (Harding et al 1986, Scrope-Howe & Jones 1986) have also found this pattern.…”

Section: Discussionmentioning

confidence: 93%

“…Active migration of late stage oyster larvae in relation to tidal circulation within some estuaries has been reported (Nelson & Perkins 1931, Carriker 1951, Kunkle 1958, although there are other interpretations of these data which do not involve larval behavior (Korringa 1952, de Wolf 1973, Andrews 1983. Diel vertical migration of some coastal bivalve larvae (Quayle 1952, 1959, Verwey 1966, Harding et al 1986, and offshore bivalve larvae (Scrope-Howe & Jones 1986) is suggested by the occurrence of the larvae in shallower depths at night.…”

Section: Introductionmentioning

confidence: 99%

Diel vertical migration of sea scallop larvae Placopecten magellanicus in a shallow embayment

Tremblay¹,

Sinclair²

1990

Vertical distribution of sea scallop larvae was studied while anchored for 50 h at a shallow location (< 25 m) off Grand Manan Island in the outer Bay of Fundy. Changes in the depth-averaged concentration of larvae (no. m-3) were unrelated to changes in the centre of mass (ZCM) of larvae, and appear to reflect the movement of a patch (or patches) 01 larvae back and forth past the anchor station. A small-amplitude diel vertical migration, comparable to observations under controlled conditions, was indicated by changes in the ZCM. During the day the ZCM ranged from 5.2 to 11.5 m, while at night the ZCM was shallower and less variable (4.1 to 6.8 m). The concentration of all size groups was greatly reduced within 1 to 8 m of the bottom, and evidence for vertical stratification by size was lacking. Sea scallop larvae appear to be unable to form aggregations below a critical level of water column stratification.