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Triple threat processes and/or other forcings can lead to changes in the ocean happening fast and abruptly. These changes, referred to as “tipping points”, are critical thresholds in a marine system that, when exceeded, can lead to a significant change in the state of the system, which often can be irreversible. This leaflet has been prepared mainly (but not only) for high school pupils with the financial support of Norges forskningsråd (Research Council of Norway) (309382).

Between September 2016 and August 2017, we conducted year-long reciprocal transplantation experiments using the cold-water coral Desmophyllum dianthus along natural oceanographic horizontal and vertical gradients (vertically: 20 m to 300 m depth and horizontally: head to mouth of fjord) in Comau Fjord to study its acclimatisation potential to changing environmental conditions. Seasonal calcification, respiration and tissue biomass of native and novel (cross-transplanted) corals were determined at six shallow (A-F, 20 m) and one deep station (Ed, 300 m) during autral summer (January), autumn (May) and winter (August). Temperature was measured continuously at each of the coral stations using TidbiT temperature loggers, and CTD casts and discrete water samples were taken once per season. In addition, temperature and salinity were measured continuously with a CTD at another station (X).

Temperature dependent cell respiration and energy expenditure for protein synthesis were determined in primary hepatocytes of different fish species of the South Atlantic: the circumpolar-distributed Antarctic eelpout Pachycara brachycephalum (sampling location: 62°19′S; 58°33′W) and, of two notothenioids the sub-Antarctic Lepidonotothen squamifrons (sampling location: 53°24′S; 42°40′W) and the high-Antarctic icefish Chionodraco hamatus (sampling location: 70°19′S; 10°22′W). We used intermittent-flow respirometry and closed system respirometry to analyse cellular response to acute warming.

Mesozooplankton samples were collected with the Multinet midi (Hydrobios, Kiel) and Bongo nets during the POLARSTERN cruise PS78 (ARK-XXVI/1) on a transect across Fram Strait. The samples were analyzed with imaged-based ZooScan analysis (Gorsky et al. 2010) and microscopic counts to compare the taxonomic resolution and abundance of both methods as described in Cornils et al. (2022). The data collection includes abundance, biovolume, biomass and length measurements derived from the image-based analysis with ZooScan as well as abundances based on microscopic counts. To compare biomass estimates from image parameters direct measurements of prosome length and individual dry mass of Calanus spp. are also provided. The data analysis is described in Cornils et al. (2022).The R scripts deposited at GitHub (Cornils 2022) allow the transformation of the EcoTaxa image dataset https://ecotaxa.obs-vlfr.fr/prj/2771 to abundance, biovolume and dry mass of the zooplankton organisms.

The Daily Egg Production Method (DEPM) to estimate the Anchovy Spawning Stock Biomass (SSB) in the Gulf of Cádiz (ICES, Subdivision 9a South) is conducted by Spain (Centro Nacional Instituto Español de Oceanografía, CSIC) every three years, since 2005. BOCADEVA 0720 is the sixth survey of the historical DEPM series for anchovy in the Gulf of Cádiz and was delivered on board R/V Ramón Margalef (CNIEO) from the 9th to the 17th of July 2020. The surveyed area extended from Strait of Gibraltar to Cape San Vicente (Spanish and Portuguese waters in the Gulf of Cadiz). Plankton samples, along a grid of 21 transects perpendicular to the coast were obtained for the spawning area delimitation and density estimation of the daily egg production. The survey objectives also included the characterization of the oceanographic and meteorological conditions in the study area. The samples to estimate adult parameters (sex ratio, female mean weight, batch fecundity and spawning fraction) were obtained in the acoustic survey “ECOCADIZ 2020-07”, carried out during the same period. This working document provides a d escription of the survey, laboratory analysis and estimation procedures used to obtain the Gulf of Cadiz Anchovy SSB by DEPM for 2020 in the South-Atlantic Iberian Stock.

The dataset contains carbon (C) and nitrogen (N) stable isotope compositions analysed in the muscle tissue and energy density values and concentrations of 19 elements analysed in whole bodies of 15 meso- to bathypelagic species sampled in the twilight zone (deep pelagic area) of the Bay of Biscay, North-East Atlantic. The species included 4 crustacean species (Pasiphaea sivado, Sergia robusta, Systellaspis debilis, Ephyrina figueirai) and 11 fish species (Xenodermichthys copei, Searsia koefoedi, Myctophum punctatum, Notoscopelus kroeyeri, Lampanyctus crocodilus, Argyropelecus olfersii, Arctozenus risso, Stomias boa, Serrivomer beanii, Chauliodus sloani, Aphanopus carbo). The elements included 6 major constitutive elements (macro-minerals) and 13 trace elements among which 9 essential (micro-nutrients) and 4 non-essential elements (undesirables, with no know biological function). Specimens were collected during a single fishery in a canyon of the slope of the Bay of Biscay in October 2017, during the EVHOE fishery survey (“Evaluation Halieutique de l'Ouest de l'Europe”; https://doi.org/10.17600/17002300) conducted each autumn by the “Institut Français de Recherche pour l'Exploitation de la Mer” (Ifremer) on R/V Thalassa. A total of 266 individuals belonging to the 15 species were collected at night using a 25 m vertical opening pelagic trawl in the deep scattering layer (ca. 800 m depth in the water column; 1330 m bottom depth). All organisms were collected during one haul of 60 min, at a speed of approximately 4 knots (geographical coordinates at the beginning of the turn/end of the fishing: 45.103°N, -3.543° W).

The aim of the study was to investigate the mechanisms allowing pipefish to inhabit low salinity areas of the Baltic Sea. The parental Syngnathus typhle generation for this experiment was caught in seagrass meadows of six sampling sites along the German coastline of the Baltic Sea in spring 2017, i.e. in the Flensburg Fjörd, Falckensteiner Strand, Orth Bay next to Fehmarn, Salzhaff and 2 sample sites around Rügen. Three sampling sites are characterized by relatively high salinity conditions (14 - 17 PSU; high salinity origin; H) and three sampling sites by relatively low salinity conditions (7 - 11 PSU; low salinity origin, L; Table 1). Salzhaff was assigned the category low because salinity drops are common after rainfall accompanied with freshwater discharge due to enclosed morphology of the inlet. Therefore, pipefish in Salzhaff are likely to be exposed to salinity levels below 10 PSU. A minimum of 30 non-pregnant males and 30 females were caught snorkelling with hand nets at each sampling site at depths ranging between 0.5 and 2.5 m. At each sampling site, water temperature and salinity were measured from water collected about 1 m below the surface using a salinometer (WTW Cond 330i). The common garden experiment was conducted at the facilities of the GEOMAR (west shore) in spring 2020.

This data set describes times series of diatom species counts, organic matter measurements including total carbon TC, total organic carbon TOC, nitrogen N, stable carbon isotopes d13C, and mercury Hg concentrations in four short cores (PG2133, PG2139, PG2203, PG2208 from Lake Bolshoe Toko, eastern Siberia. These short core have been dated using 210Pb and 137Cs methods covering the transition zone of the industrialization until 2013 CE. Methods are provided in the associated paper (Biskaborn et al. 2021).

Fish and fishers are affected by the environmental conditions they experience throughout their lives, from daily, annual to decadal time scales. Currently, the oceans are changing fast, as global warming increases the temperature of the water and reduces oxygen levels within it. However, there is still an important knowledge gap about how these shifting conditions influence wild populations of fish, especially in the early life stages of tropical species inhabiting mangrove lagoons or for adult fishes dwelling in the deep ocean. In this dissertation, we use the chronological and chemical properties of otoliths – calcified structures within the inner ear of fish – to investigate how temperature correlates with fish growth, to improve our understanding of their populations, and to develop proxies for hypoxia exposure in deep-sea fishes. Chapter 1 asks how the water temperature inside mangrove lagoons regulates the first year of growth for yellow snappers in the Gulf of California. We found that these animals grow faster in warmer waters until they experience a thermal threshold (~ 32° C) beyond which their growth rate is reduced. Chapter 2 tests the effects of extrinsic (water chemistry and temperature) and intrinsic (growth rate and taxonomy) factors on otolith chemistry. Using distinct species from Galápagos (yellow snapper and sailfin grouper) and the same species (yellow snapper) between Galápagos and the Gulf of California, we observed that extrinsic factors seem to be more important than intrinsic factors as influences on otolith microchemistry. Chapter 3 examines the population structure of yellow snappers in the Gulf of California and Galápagos mangroves by using otolith microchemistry and genetic analyses in tandem. These methodologies were complementary and helped to elucidate a source-sink metapopulation structure for Galápagos snappers, and a self-recruitment scenario for the Gulf snappers, with important implications for the mangrove management at these ecosystems. Chapter 4 explores the use of fish as mobile monitors of hypoxic conditions in Oxygen Minimum Zones (OMZs). Surprisingly, fishes with distinct life-history traits (longevity and thermal history) and from different OMZs (NE Pacific and SE Atlantic), but exposed to comparable low oxygen conditions, exhibited high similarity in their otolith chemistry. These findings may provide a baseline for tracking the ongoing expansion of OMZs. Lastly, Chapter 5 inquires how fishers’ local ecological knowledge (LEK) in the Galápagos Archipelago can help to elucidate the effects of climate variability on fish. We observed that LEK is in line with the scientific literature regarding distributional shifts in marine species and anomalous weather conditions during strong El Niño years.

Previous studies with Baltic Sea phytoplankton combining elevated seawater temperature with CO2 revealed the importance of size trait-based analyses, in particular dividing the plankton in-to edible (> 5 and 100 µm) size classes for mesozoopankton grazers. While the edible phytoplankton responded predominantly negative to warming and the inedible group stayed unaffected or increased, independent from edibility most phyto-plankton groups gained from CO2. Because the ratio between edible and inedible taxa changes profoundly over seasons, we investigated, if community responses can be predicted according to the prevailing composition of edible and inedible groups. We experimentally explored the combined effects of elevated temperatures and CO2 concentrations on a late-summer Baltic Sea community. Total phytoplankton significantly increased in response to elevated CO2 in particu-lar in combination with temperature, driven by a significant gain of the inedible < 5 µm fraction and large filamentous cyanobacteria. Large flagellates disappeared. The edible group was low as usual in summer and decreased with both factors due to enhanced copepod grazing and overall decline of small flagellates. Our results emphasize that the responses of summer communities are complex, but can be predicted by the composition and dominance of size classes and groups.