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: We modelled the larval phenology of the invasive crab Hemigrapsus sanguineus along the Atlantic coast of North America and North Europe. The phenology was computed from laboratory data on survival and duration of larval development, temperature and abundance of larvae in the field.

Description: The ingestion of microplastics has been shown for a great variety of marine organisms. However, benthic marine mesoherbivores such as the common periwinkle Littorina littorea have been largely disregarded in studies about the effects of microplastics on the marine biota, probably because the pathway for microplastics to this functional group of organisms was not obvious. In laboratory experiments we showed that the seaweed Fucus vesiculosus retains suspended microplastics on its surface. The numbers of microplastics that adhered to the algae correlated with the concentrations of suspended particles in the water. In choice feeding assays L. littorea did not distinguish between algae with adherent microplastics and clean algae without microplastics, indicating that the snails do not recognize solid nonfood particles in the submillimeter size range as deleterious. In periwinkles that were feeding on contaminated algae, microplastics were found in the stomach and in the gut. However, no microplastics were found in the midgut gland, which is the principle digestive organ of gastropods. Microplastics in the fecal pellets of the periwinkles indicate that the particles do not accumulate rapidly inside the animals but are mostly released with the feces. Our results provide the first evidence that seaweeds may represent an efficient pathway for microplastics from the water to marine benthic herbivores.

Description: Pelagic Sargassum and floating marine debris were collected in the Sargasso Sea (subtropical NW Atlantic) during the cruise MSM41 of the German research vessel Maria S. Merian in April 2015. Flotsam items were collected 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. All mobile epifaunal organisms were carefully washed down from the flotsam items with freshwater and retrieved in a sieve with a mesh size of 250 µm. The species were identified and the individuals counted. Each Sargassum thallus was inspected under a stereo microscope to identify the attached sessile epifaunal species. Sessile species were not quantified. The marine debris items or sub-samples thereof (in case of large bulky items) were preserved in buffered formalin-seawater solution. The sessile epifauna on the debris items was analyzed after the cruise in the laboratories of the Alfred Wegener Institute in Bremerhaven, Germany. Each Sargassum clump was blotted on tissue paper to remove adherent seawater and weighed. The sizes of the debris items were measured to calculate the surface area.

Description: This is a laboratory experiment, carried out in Helgoland to explore how responses to the time scale and magnitude of fluctuations in environmental variables depend on the choice of time reference frame. The experiment consisted of exposing larvae of an intertidal invertebrate, Hemigrapsus sanguineus to different initial feeding periods (in days; food = freshly hatched Artemia sp Nauplii provided ad libitum), followed by a period without food. An ovigerous female of H. sanguineus was collected by hand in the intertidal of Helgoland (SW beach: “Kringel”; coordinates: 54.177323°N, 7.885273°E) during low tide on the 15th October 2020. It was kept until larval hatching in an aquarium (vol = 2 L with a shelter) at salinity = 32 ppt, temperature = 18°C, photoperiod 12:12, permanent oxygenation and fed every second day (from frozen shrimp); water was changed every day. Experiments started on date 31st October 2020 (day 0 of the feeding period). The feeding protocol was carried out with groups of freshly hatched zoea I larvae (3 replicates of 10 larvae each) at 4 temperatures (15, 17, 19, 21°C). Larvae were reared at salinity = 32 ppt. The response variables were developmental time (in days) and the number of larvae reaching the second zoeal stage. Additional columns provide calculations of the average duration of development depending on temperature and the proportion of feeding time given as a proportion of the full developmental time.

Description: Increases in atmospheric carbon dioxide (CO2) change ocean chemistry, as dissolved CO2 leads to a reduction in the seawater pH. Many marine taxa have been shown to be affected by ocean acidification; however, information on marine fungi is lacking. We analyzed the effect of pH on mycoplankton communities. The pH of microcosms was adjusted to a value mimicking the predicted ocean acidification in the near future. Fungal communities were analyzed using a double-marker gene approach, allowing a more detailed analysis of their response using 454 pyrosequencing. Mycoplankton communities in microcosms with in situ and adjusted water pH values differed significantly in terms of structure and diversity. The differences were mainly abundance shifts among the dominant taxa, rather than the exclusion of fungal groups. A sensitivity to lower pH values was reported for several groups across the fungal kingdom and was not phylogenetically conserved. Some of the fungal species that dominated the communities of microcosms with a lower pH were known pathogenic fungi. With the increasing awareness of the significant role fungi play in marine systems, including performing a diverse range of symbiotic activities, our results highlight the importance of including fungi in further research projects studying and modeling biotic responses to the predicted ocean acidification.

Description: Pelagic Sargassum and floating marine debris were collected during cruise MSM41 of the German research vessel Maria S. Merian in April 2015 in the Sargasso Sea, western subtropical North Atlantic. In total 39 debris samples and 42 Sargassum samples were taken and characterized. The associated biota was analyzed. Mobile species were counted, sessile organisms were recorded as present/absent. A visual ship-based survey was conducted to quantify pelagic Sargassum and floating marine debris in the Sargasso Sea. Biomass and surface area of Sargassum was measured from thalli beached at Sisal Beach, Yucatan peninsula, Mexico to establish the biomass:surface area ratio for the two species Sargassum fluitans and Sargassum natans.

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.

Description: To establish the surface area : biomass relationship of pelagic Sargassum spp., individual thalli of beach-cast Sargassum fluitans and Sargassum natans were collected at Sisal Beach, Yucatan peninsula, Mexico in November 2016. 22 thalli each of both species were collected. Additionally, three thalli of an additional species were collected. This species could not be clearly identified and the thalli were not further considered for analysis. Each thalli was blotted with tissue paper to remove adherent seawater and weighed on the beach using a spring balance. Subsequently, the single parts of the thalli (blades, pneumatocysts, stipes) were separated from each other, spread in a tray and photographed together with a ruler as a size reference and a label. The two dimensional projection area of each thallus part was determined using an image analysis software from which the surface area of each three dimensional structure was calculated to obtain the total surface area of the thallus.

Description: During cruise MSM41 of the German research vessel Maria S. Merian in April 2015 a visual ship based survey was conducted on the composition and density of natural and anthropogenic flotsam in the Sargasso Sea (subtropical NW Atlantic). On transits between the regular stations of the cruise, flotsam was quantified on transects of 10 m width and lengths of 9.1 - 25.5 km. Start and end coordinates were determined from a handheld GPS. This dataset summarizes the metadata of this survey, including the time, coordinates of start and end point of the transects, as well as distance and area covered. Additionally, results are presented as densities of floating marine debris and pelagic Sargassum given in total numbers per transect and standardized to items km-2. The speed of the vessel was recorded from the handheld GPS for 2-7 times per transect in irregular intervals to estimate the average vessel speed during the observations.