13Knowledge on the seasonal timing and composition of pelagic larvae of many benthic 14 invertebrates, referred to as meroplankton, is limited for high-latitude fjords and coastal areas. 15We investigated the seasonal dynamics of meroplankton in the sub-Arctic Porsangerfjord larvae appeared during spring and summer, forming two peaks in meroplankton abundance. 21The spring peak was dominated by cirripede nauplii, and late summer peak was dominated by

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This study investigates the temporal and spatial patterns of larval stages of the invasive red king crab Paralithodes camtschaticus (RKC) and co-existing native brachyurans and anomurans in a Norwegian fjord. It is one of few field studies describing the larval stage of native and invasive brachyurans and anomurans in the southern Barents Sea. Larvae were collected at 6 to 18 stations at roughly 1 to 2 mo intervals over a 1.5-yr period. To help explain timing in hatch of RKC larvae, the reproductive state of females was determined. The first larval stage of RKC was found in higher abundances in shallow bays, reflecting the spawning migrations of reproducing females. RKC was the first species among anomurans and brachyurans to release their larvae in Norwegian waters, and due to an extended larval release (January−May) their larvae occurred for the longest period of time in the water column. The native boreo-Arctic Pagurus pubescens and Hyas araneus released their larvae early in the year, starting in March. In contrast, larvae of the native boreal Pagurus bernhardus, Hyas coarctatus and Munida sp. were observed later in spring and summer. The combination of protracted hatching, high fecundity and high adult abundance of RKC are likely strong contributing factors to the species' successful establishment in the southern Barents Sea and could favour the dispersal of RKC south along the Norwegian coast and potentially north into Arctic shelf areas.

The spatial patterns in abundance and composition of benthic invertebrate larvae (meroplankton), the correlation between these patterns and environmental variables (temperature, salinity and chl a) and the relative abundance of meroplankton in the mesozooplankton community were investigated in the sub-Arctic Porsangerfjord, Norway (70°N). Zooplankton samples and CTD-profiles were collected at 17 stations along the fjord in April 2013. A total of 32 morphologically different larval types belonging to 8 phyla were identified. Meroplankton were found at all stations, and their community and abundance differed significantly along the fjord. Meroplankton abundance in the inner and outer parts of the fjord was low and was dominated by Gastropoda and Echinodermata. The greatest numbers were recorded in shallow bays and the middle part of the fjord where Cirripedia and Polychaeta were dominant. Meroplankton contributed significantly to the mesozooplankton community in the bays (30 to 90%) and mid-fjord (13 to 48%) areas. These changes in community structure were attributed to spatial gradients in environmental variables such as chl a, salinity and temperature. The different communities suggested a seasonal succession in reproductive events from the fjord mouth toward the head. Considering that spring is an important season for reproduction in pelagic organisms, meroplankton may play a role in the pelagic ecosystem of high-latitude fjords as grazers and prey. Furthermore, the spatial dynamics and reproductive timing of benthic and holoplanktonic organisms are sensitive to local hydrographical features, illustrating their sensitivity to changing environments.