Description: Under climate change, increased temperatures combined with food limitation may be critical for species with complex life cycles, if high growth rates characterise the larval development. We studied the effect of increased temperature and food limitation on larval survival and on functional traits (developmental time, body mass, elemental composition, growth) at moulting and metamorphosis in the crab Carcinus maenas collected in the North Sea (Helgoland, Germany). We followed the approach of models of metamorphosis integrating responses of body mass and developmental time to increased temperature and food limitation. We also evaluated if body mass decreased with temperature (according to the temperature-size rule) and if developmental time followed an inverse exponential reduction (expected from some metabolic theories), as both trends are relevant for modelling effects of climate change on fitness and population connectivity. Larvae produced by four females during the reproductive period (i.e. spring-summer 2016) were reared separately from hatching to metamorphosis to the megalopa at two food conditions (ad libitum and low food availability), and at four temperatures covering the range experienced in the field (〈20°C) and those expected from climate change (〉20°C). Survival and developmental rates were obtained by daily monitoring of the experiments. Biomass data (body mass and elemental composition) were obtained by sampling larvae at the zoea IV and megalopa stages and further processed with standard methods (see Torres & Giménez 2020 for details). We propose that integrative studies of traits at metamorphosis could be a basis to develop a mechanistic understanding of how species with complex life cycles will respond to climate change. Such models could eventually include hormonal and metabolic regulation of development as drivers of responses to environmental change.

Description: Clumps of pelagic Sargassum as well as floating marine debris were collected during cruise MSM41 of the German research vessel Maria S. Merian in the Sargasso Sea (subtropical NW Atlantic) in April 2015. Samples were taken with a dip net (mesh size: 1 mm) from the rescue boat of the research vessel at 19 stations distributed in coordination with the other sampling activities of the cruise. Few, mostly larger, debris samples were taken from aboard the research vessel using a dip net with a mesh size of 9 cm. The exact sampling position of each floating item was recorded by a handheld GPS. In total, 42 Sargassum samples and 41 samples of marine debris were collected. On board the vessel, the Sargassum samples were analyzed for their species composition (Sargassum natans, Sargassum fluitans, indeterminable small fragments). Each fraction was weighed (wet weight) after the algae had been blotted on tissue paper to remove adherent seawater. The type of each debris sample was determined and the sizes of the debris samples were measured. Small objects were preserved in buffered seawater-formalin solution for later analysis of the associated biota. Small sub-samples have been taken from samples, which were too large to be preserved in total. Polymer compositions of the plastic debris samples were analyzed by Near Infrared Spectroscopy.