Year-round meroplankton dynamics in high-Arctic Svalbard

Meroplankton is often neglected in Arctic zooplankton studies, so our knowledge about their seasonal dynamics is limited. To investigate the highly dynamic nature of meroplankton, we sampled the zooplankton community in a high-Arctic fjord in West-Spitsbergen bi-weekly from December 2011 to December 2012. Five significantly different seasonal meroplankton assemblages were identified, representing winter, early spring, spring, summer and autumn. Meroplankton persistently dominated the zooplankton community during the productive seasons in both abundance (41-91%) and biomass (54-98%). Cirripedia and Bivalvia larvae occurred in particularly high numbers and dominated during spring and summer respectively. In the remaining seasons, the meroplankton diversity and abundance were comparatively poor, but interestingly Bryozoa larvae were present mainly during winter. Chlorophyll a and day length were identified as the main environmental variables structuring the meroplankton assemblage, followed by hydrography. Timing of the spring bloom determined the onset of the "meroplankton-boost" and from the observed hydrography, local rather than advective processes shaped the meroplankton community. Our investigation suggests that benthic invertebrate larvae play a significant role in the pelagic ecosystems in Arctic coastal regions, tightly linking the pelagic and benthic realms, thus deserving more attention in future studies.