Most Antarctic bivalves are small and protect their young by holding fertilized eggs or larvae in their mantle cavities for varying periods. Nourishment for these early growth stages is provided by yolk reserves rather than by planktotrophy. The anomalously large Antarctic scallop, Adamussium colbecki, has unprotected planktotrophic larvae that are spawned during the austral spring. Successful recruitment of these larvae, in populations which are most abundant in oligotrophic habitats, may be associated with episodic pulses of organic material. Reasons why planktotrophy persists in A. colbecki are suggested by a comparison with another large Antarctic bivalve, Laternula elliptica. The latter has protected lecithotrophic larvae that are released at the beginning of the austral winter. This comparison suggests that unprotected larval development persists in A. colbecki because of unusual anatomical and ecological adaptations among the adults of the Adamussium lineage that have been evolving in the Southern Ocean since the early Oligocene.

Only one living specimen of Adamussium colbecki was found amongst the shells of this species collected in the Lazarev and Weddell Seas, and those of the limpet Nacella cf. concinna from three locations in the southern Weddell Sea. In order to explain this peculiarity four hypotheses are discussed. The possibility that the shells belong to living deep-water populations is in contradiction to the high number of trawl samples taken in the area and the abundance of empty shell material. 14C dates show the shells are recent, thus excluding the possibility that the shells belong to autochthonous fossil populations exposed on the seafloor. Lateral transport of living specimens or shells over long distances by marine currents or by ice is unlikely due to their state of preservation and the water circulation pattern. The most likely explanation is that the shells are allochthonous, transported only over short distances by marine currents from adjacent areas underneath floating ice shelves where both species have living populations.

Swimming activity of the Antarctic scallop at a temperature of c. −1.4°C was analysed using in situ video recordings obtained from a remotely operated vehicle (ROV) in Terra Nova Bay, Ross Sea. Data are presented on swimming trajectories, distance travelled and velocity during a swimming bout, adduction frequency, shell gape angle, and the angular opening and closing velocities of shell. This scallop is an effective swimmer although swimming bouts in response to the ROV were generally short, consisting of 2–5 adduction cycles in the take-off phase followed by 1–4 (exceptionally 14) adductions during level swimming. The maximum velocity during each adduction cycle ranged from 19.4–43.1 cm s−1 and the mean velocity during a swimming bout from 12.0–23.5 cm s−1. Each adduction cycle consists of opening, closing and glide phases of approximately equal duration. Adduction frequency during swimming averaged 1.5 adductions s−1.

Meiofaunal community structure in coastal sediments of Terra Nova Bay (Ross Sea) was related to quantity and biochemical composition of sedimentary organic matter. The sediments were generally characterized by large amounts of chloropigments and labile compounds (dominated by proteins), indicating high inputs of primary organic matter. Meiofaunal densities were very high and comparable to those from the most productive areas worldwide. Sediments with high densities of the scallop had low meiofaunal densities especially in the top 2 cm, suggesting that scallop clapping contributed to meiofauna resuspension. However, it is not possible to exclude the probability that meiofauna are part of the scallop beds apparently have an important role in structuring meiofaunal communities with nematodes dominant where Adamussium colbecki is absent, and gastrotrichs dominant (44–51%) in A. colbecki beds, reaching the highest density reported so far.