The influence of shell growth rate on striae deposition in the scallop Pecten maximus

The relationship between shell growth rate and striae deposition was investigated in a field study in which groups of juvenile scallops, Pecten maximus, (Pectinidae: Bivalvia) were deployed for monthly periods over a year in the Menai Strait (North Wales). The number of striae deposited per day, inter-striae width (the increment of shell deposited between successive striae) and striae abundance (the number of striae deposited per mm of shell height) all correlated well with measured shell growth rates. During the winter months, when seawater temperatures were minimal (6°C), inter-striae width declined, whilst striae abundance increased, whereas during the summer when seawater temperatures were maximal (18°C), shell growth was rapid with maximum inter-striae width, resulting in a seasonal pattern of narrowly grouped, then widely spaced striae. This seasonal pattern in inter-striae width variation provides an accurate and reliable method for estimating the number of growth cycles and hence the age of P. maximus.

Variations de la croissance de la coquille, et de la structure d'âge du bivalve Macoma balthica (L.) dans une population intertidale de l'estuaire du Saint-Laurent (Québec)

Greater annual shell growth rate and increased mortality are observed in Macoma balthica (L.) with an increase of immersion time in the intertidal zone of the St. Lawrence estuary. There is also a greater annual growth rate in tidal pools, and sediment temperature alone may explain spatial variations in spring and annual growth. Reciprocal transfers of specimens between upper (0.8 m above mean water level) and lower (1.2 m below mean water level) tidal level result in enhanced shell growth for individuals of the upper level transferred to the lower level. There is no corresponding change of shell growth rate for individuals of the lower level. This genotypic difference in short-term physiological responses to environmental changes may be the result of different selective pressures associated with habitat temporal heterogeneity. An opportunistic strategy is associated with the more terrestrial and unpredictable environment (upper tidal level) and a more specialized strategy accompanied by low phenotypic variability is associated with the more marine and stable environment (lower tidal level).

Alterations in Growth and Physiology of Soft-Shell Clams, Mya arenaria, Chronically Oiled with Bunker C from Chedabucto Bay, Nova Scotia, 1970–76

Two populations of soft-shell clam, Mya arenaria, one from a chronically oiled lagoon (since the Arrow oil spill in 1970) and the other from a nonoiled lagoon, were compared as to population structure, growth, and metabolism. The oiled lagoon sediments contained up to 3800 μg/g oil (UV determination), and clams up to 200 μg/g hydrocarbon in their tissues (fluorescence). The oiled population of clams differed from the nonoiled population in lower total numbers with fewer mature adults, a 1–2-yr lag in tissue growth, a lower shell growth rate, and a reduced carbon flux with a lower assimilation rate. Results are interpreted to indicate that the recovery potential of M. arenaria in these oiled sediments is low and that these oiled populations remain under continued stress 6 yr after the Arrow spill. Key words: physiology, petroleum, growth, carbon flow, clams, recruitment