Seasonal and spatial dynamics of meroplankton in a sub-Arctic fjord With additional focus on larvae of the invasive red king crab

Abstract

Many benthic marine organisms produce pelagic larvae, meroplankton, which spend from hours to months in the pelagic. During this time, they form an important part of the pelagic community. Few studies have focused on the year round dynamics of meroplankton, thus many aspects of meroplankton dynamics remains unknown at high-latitudes. In the 1960s the red king crab was intentionally introduced into Russian waters and now serves as an important resource for Norway and Russia while at the same time posing a threat to the ecosystem. Currently there is no knowledge on when and where larvae are released in Norwegian waters. The objectives of this thesis were to increase our understanding on the seasonal and spatial dynamics of meroplankton at high-latitudes, identify environmental variables responsible for spawning and the potential role of meroplankton in the pelagic. The temporal and spatial dynamics of red king crab larvae was also investigated. Sampling monthly to bi-monthly over a 1.5-years in Porsangerfjord, Norway, showed that meroplankton abundance and assemblage separate into different seasonal communities. The highest abundance and greatest number of taxa occurs in spring and summer, correlating with increased chlorophyll a and temperature. Numerically, meroplankton contributed highly to the mesozooplankton community these seasons, suggesting that they are an important component of the pelagic food web. In spring, different meroplankton assemblages were found along the fjord and correlated with temperature and chlorophyll a. This provides evidence that larval release by benthic invertebrates is coupled with variations in these environmental variables. In a warming ocean this coupling could cause a shift in reproductive phenology and a range expansion of benthic organisms. Larvae of the red king crab were continually released over a period of six months and the greatest densities of larvae was found at protected stations. Having a prolonged larval release is advantageous for this invasive species as it ensures some larvae coincides with favorable conditions. These findings coupled with a wide tolerance to environments as larvae and adults means that they have the potential to continue their expansion in Norway and north into Svalbard waters.