The first insights on habitat and phylogenetic origin of a newly found population of Solen marginatus are provided in the mid-North Atlantic Azores archipelago, in the bay of Praia da Vitória, Terceira Island. Distribution is confined to the northern portion and most sheltered part of the bay down to 14.2 m depth. Densities with an average of 12.69 individuals/m2 were found at 8.4 m depth, using 4 × 20 sqm visual transects. Sizes of shell length between 10 and 12 cm comprised 60% of collected specimens (n = 118), ranging between 8.79 and 15.4 cm and averaging 11.28 cm. Considering shell length, the high densities and dispersion area, a settlement period above 20 years is estimated. Greater genetic affinity was found in the Ria de Aveiro (North of Portugal) and the Asturias populations (North of Spain). The source origin remains undetermined, with intentional or non-intentional anthropogenic introduction, as well as natural dispersion remaining possible, although more unlikely. Due to the commercial value of this species, a new clam fishery is likely to develop in the area, requiring further studies and immediate conservation measures.

The population biology of the stout razor clam Tagelus plebeius is poorly understood, despite the species' current wide distribution, and the potential use of its Holocene shell deposits to infer past environmental and ecological conditions. This study investigates distribution and growth pattern of T. plebeius in the south-western Atlantic Mar Chiquita Coastal lagoon (37°32′S 57°19′W), Argentina. The population includes the oldest individuals (up to 27 years) reported so far with shell length up to 77.9 mm. A von Bertalanffy model with L∞ = 67.60 mm (95% CI = 64.55; 70.64), k = 0.181 year−1 (CI = 0.142; 0.218), and t0 = −0.77 (CI = −1.46; −0.08) best described their individual growth for the whole population. The higher density, growth rate k, t0 and maximum age and lower L∞ were in the low intertidal rather than in the medium intertidal, but there were no differences in density and age between medium and high intertidal. Given the results and the current knowledge on the effects of different factors influencing this species, we conclude that the distribution pattern and shell growth observed in our study reflect a response to metabolic necessities in combination with a strong influence of biological interactions.

The aim of this study was to characterize new microsatellite loci in the razor clam Ensis arcuatus (Bivalvia: Pharidae) and examine the temporal genetic variability of a natural bed in Cies Islands (Galicia, north-western Spain) exploited by apnoea divers and affected by the ‘Prestige’ oil tanker spill in November 2002. In this work, we characterized four polymorphic microsatellites using an alternative approach that relies on the amplification and sequencing of ISSR markers. Observed heterozygosities ranged from 0.1053–0.6800 and number of alleles from 4–19. Linkage equilibrium was observed in all loci and two of them showed significant deviations from Hardy–Weinberg equilibrium. Estimators of FST between samples were low (<0.05) and not different from zero with a confidence level of 5%. We did not detect a clear decreasing tendency in genetic diversity although we found a significant change in allelic frequencies among samples (P = 0.0024) after the ‘Prestige’ oil spill. We propose that both phenomena could be related to a high variance in genetic success and/or a movement of adults or larvae from different source populations.