The changing Arctic environment is affecting zooplankton that support its abundant wildlife. We examined how these changes are influencing a key zooplankton species, Calanus finmarchicus, principally found in the North Atlantic but expatriated to the Arctic. Close to the ice-edge in the Fram Strait, we identified areas that, since the 1980s, are increasingly favourable to C. finmarchicus. Field-sampling revealed part of the population there to be capable of amassing enough reserves to overwinter. Early developmental stages were also present in early summer, suggesting successful local recruitment. This extension to suitable C. finmarchicus habitat is most likely facilitated by the long-term retreat of the ice-edge, allowing phytoplankton to bloom earlier and for longer and through higher temperatures increasing copepod developmental rates. The increased capacity for this species to complete its life-cycle and prosper in the Fram Strait can change community structure, with large consequences to regional food-webs.

The land ocean aquatic continuum (LOAC) consists of soils, streams, rivers, groundwater, lakes, wetlands, estuaries, and shelf seas and plays a key role in the global carbon (C) cycle. Inland waters receive ∼5.1 Pg C per year from land, which is ∼55% of global net ecosystem production from terrestrial ecosystems (Drake et al., 2018). This is approximately double the oceanic uptake of anthropogenic CO 2, which slows climate change and drives ocean acidification. Our understanding of what drives the export of C into the LOAC, its fate therein, and hence its export to the open ocean, remains incomplete.

Land-ocean dissolved organic matter (DOM) transport is a significant and changing term in global biogeochemical cycles which is increasing as a result of human perturbation, including land-use change. Knowledge of the behavior and fate of transported DOM is lacking, particularly in the tropics and subtropics where land-use change is occurring rapidly. We used Parallel Factor (PARAFAC) Analysis to investigate how land-use influenced the composition of the DOM pool along a subtropical land-use gradient (from near-pristine broadleaf forest to agri-urban settings) in Belize, Central America. Three humic-like and two protein-like components were identified, each of which was present across land uses and environments. Land-use mapping identified a strong (R 2 = 0.81) negative correlation between broadleaf forest and agri-urban land. All PARAFAC components were positively associated with agriurban land-use classes (cropland, grassland, and/or urban land), indicating that land-use change from forested to agri-urban exerts influence on the composition of the DOM pool. Humic-like DOM exhibited linear accumulation with distance downstream and behaved conservatively in the coastal zone whilst protein-like DOM exhibited nonlinear accumulation within the main river and nonconservative mixing in coastal waters, indicative of differences in reactivity. We used a hydrodynamic model to explore the potential of conservative humics to reach the region's environmentally and economically valuable coral reefs. We find that offshore corals experience short exposures (10 ± 11 days yr −1 ) to large (∼120%) terrigenous DOM increases, whilst nearshore corals experience prolonged exposure (113 ± 24 days yr −1 ) to relatively small (∼30%) terrigenous DOM increases. Plain Language SummaryThe transport of land-derived dissolved organic matter into the oceans plays a substantial and important role in the global carbon and nutrient cycles. Land-use change can alter the type and amount of material being transported, with widespread implications for downstream ecosystems. This is particularly true in the tropics and subtropics where land-use change is occurring most rapidly, and where research into its effects is often lacking. We investigated whether landuse had an effect on the type and amount of land-derived material found in a subtropical river system that is experiencing a rapid conversion from forest to agricultural and urban land-use. We found that streams draining agricultural and urban land contained more land-derived material than those draining forested land, and that a substantial fraction of this material reached the coastal environment. We estimated the frequency with which this land-derived material reached the region's environmentally and economically valuable coral reefs, and suggest that land-use-derived material reaches nearshore corals often and offshore corals rarely. FELGATE ET AL.

Lipid-storing copepods are fundamental to the functioning of marine ecosystems, transferring energy from primary producers to higher trophic levels and sequestering atmospheric carbon (C) in the deep ocean. Quantifying trophic transfer and biogeochemical cycling by copepods requires improved understanding of copepod metabolic rates in both surface waters and during lipid-fueled metabolism over winter. Here we present new biomass turnover rates of C and nitrogen (N) in Calanoides acutus, Calanoides natalis, Calanus glacialis and Calanus hyperboreus alongside published data for Calanus finmarchicus and Calanus pacificus. Turnover rates in metabolically active animals, normalised to 10°C, ranged between 0.007 – 0.105 d-1 and 0.004 – 0.065 d-1 for C and N, respectively. Turnover rates of C were typically faster than those for N, supporting the understanding that non-protein C, e.g. lipid, is catabolised faster than protein. Re-analysis of published data indicates that inactive, overwintering C. finmarchicus turn over wax ester lipids at a rate of 0.0016 d-1. These and other basal rate data will facilitate the mechanistic representation of copepod physiology in global biogeochemical models, thereby reducing uncertainties in our predictions of future ocean ecosystem functioning and C sequestration.

Major changes in North Atlantic zooplankton communities in recent decades have been linked to climate change but the roles of environmental drivers are often complex. High temporal resolution data is required to disentangle the natural seasonal drivers from additional sources of variability in highly heterogeneous marine systems. Here, physical and plankton abundance data spanning 2003–2017 from a weekly long-term monitoring site on the west coast of Scotland were used to investigate the cause of an increasing decline to approximately -80± 5% in annual average total zooplankton abundance from 2011 to 2017. Generalized additive mixed models (GAMMs), with an autoregressive correlation structure, were used to examine seasonal and inter-annual trends in zooplankton abundance and their relationship with environmental variables. Substantial declines were detected across all dominant taxa, with ∼ 30–70% of the declines in abundance explained by a concurrent negative trend in salinity, alongside the seasonal cycle, with the additional significance of food availability found for some taxa. Temperature was found to drive seasonal variation but not the long-term trends in the zooplankton community. The reduction in salinity had the largest effect on several important taxa. Salinity changes could partly be explained by locally higher freshwater run-off driven by precipitation as well as potential links to changes in offshore water masses. The results highlight that changes in salinity, caused by either freshwater input (expected from climate predictions) or fresher offshore water masses, may adversely impact coastal zooplankton communities and the predators that depend on them.