Annual and lunar-cycle-related breeding rhythmicity in the acorn barnacle Tetraclita kuroshioensis Chan, Tsang & Chu, 2007 (Cirripedia: Balanomorpha: Tetraclitidae) in Okinawa, Japan

Abstract

Abstract We investigated the reproduction of the barnacle Tetraclita kuroshioensisChan, Tsang & Chu, 2007 (Cirripedia: Thoracica: Tetraclitidae) at different heights in the intertidal zone in Okinawa, Japan with a focus on gonadal development, the brooding of eggs, and unhatched larvae, as well as the role of environmental factors in breeding rhythmicity. Histological observations collected around each full moon from September 2019 to October 2020 showed various stages of oocyte development in September and October 2019 and from March to September 2020, whereas mature testes were observed from April to October 2020. The breeding season of this species thus lasts for at least seven months under long-day conditions at a water temperature above 21 °C. Barnacles collected from three tidal levels on multiple occasions during April, August, and October 2020 displayed little vertical variation in their stage of ovarian development, but there was a noticeable difference in the percentage of brooding individuals in August and October, as well as an increased prevalence of brooding during the new-moon phase at the upper and middle tidal heights. Our findings indicate that larval release by T. kuroshioensis undergoes seasonal variation, apparently influenced by the cycles of lunar (major factor) and tide (minor factor) in their habitat.