Common rock oysters Saccostrea cucullata (Bivalvia) were sampled from intertidal volcanic rocks at five sites around Ascension Island (central-east Atlantic) in austral winter 2012–2014. Their left valves were sectioned to reveal annual growth increments. Their periodicity was validated by the presence of specific growth marks in the increment sequence visible in consecutive years of sampling. No significant differences in shell height-weight relationships were revealed between sites. Marginal analysis of the increment width showed that S. cucullata accelerated their growth in cooler winter months and decelerated the growth in warmer summer months. Rock oysters in Ascension Island lived up to 14–16 years with maximum age of 26 years. Young oysters (1–5 years old) had the same growth rates both in shell height and weight in all sites. However, their starting point (size and weight of 1-year-old animals) was different in various sites, with largest animals occurring in the most protected site Northeast Bay with sheltered inlets and smallest animals inhabiting exposed to surf site of Letterbox. Growth in shell height was best described by von Bertalanffy growth function with the largest L∞ in animals inhabiting the windward side and smallest animals occurring in the leeward side of the Island. In summary, S. cucullata around Ascension Island lived longer but had slower growth than those from tropical regions of Southwest Asia probably due to comparatively low productivity observed in the central part of the equatorial tropical Atlantic.

We surveyed 110 Saccostrea oysters sampled from southern Kagoshima Bay and Wakayama Prefecture to monitor the species diversity of marine benthos using morphological features and DNA barcoding. Prior to the survey, we re-identified 55 Saccostrea oysters sampled from the Yaeyama Islands, a hot spot for Saccostrea species in Japan. Analysis of partial nucleotide sequences from the mitochondrial large subunit of ribosomal DNA (LSrDNA) led to the discovery of the Indo-West Pacific rock oyster S. cucullata-F in Kagoshima Bay, and S. cucullata-C and S. cucullata-F in Wakayama Prefecture. This is the first record of the Indo-West Pacific rock oyster in mainland Japan (Hokkaido, Honshu, Shikoku and Kyushu Islands). We postulate that there may have been a northward shift in the distribution patterns of the species due to global warming, these Pacific rock oysters are relic species from the Middle or Late Pleistocene, or the non-indigenous species were introduced by oil tanker or other industrial activities.