The 18.6-year lunar nodal cycle may affect ecosystems on the Northwest Atlantic continental shelves

As one of the foremost global forcings, tidal circulation exerts a pervasive influence on biological and physical processes occurring in the world's oceans on hourly to decadal time scales. This research identified the 18.6-year periodic variation in the lunar orbital plane within an annually resolved 140-year (1875 to 2015) shell growth master chronology measured from 21 live collected Arctica islandica, a bivalve known to be one of the longest lived non-colonial animals. The potential ecological implications of this result warranted detailed inventory of underlying physical processes. The absence of long-term in situ hydrological data for the bivalve's habitat was circumvented by the use of satellite data and numerical modeling which show that coastal regions of the Northwest Atlantic shelf clearly record diurnal tidal currents influenced by the 18.6-year nodal lunar cycle. The approach described here demonstrates that combining physical and biological data can help to identify subtle ecological processes over long time-scales for accurately disentangling the latter from variation introduced by anthropogenic climate change.