Description: Phytoplankton, microzooplankton, copepod and dissolved nutrient data from a mesocosm experiment, which took place in summer 2016. A range of Si:N ratios and two levels of copepod grazing pressure were manipulated on a natural plankton community in Kiel Bay, Southern Baltic Sea, Germany.

Description: Phytoplankton, microzooplankton, copepod and dissolved nutrient data from a mesocosm experiment, which took place in summer 2016. A range of Si:N ratios and two levels of copepod grazing pressure were manipulated on a natural plankton community in Kiel Bay, Southern Baltic Sea, Germany.

Description: Phytoplankton, microzooplankton, copepod and dissolved nutrient data from a mesocosm experiment, which took place in summer 2016. A range of Si:N ratios and two levels of copepod grazing pressure were manipulated on a natural plankton community in Kiel Bay, Southern Baltic Sea, Germany.

Description: Phytoplankton, microzooplankton, copepod and dissolved nutrient data from a mesocosm experiment, which took place in summer 2016. A range of Si:N ratios and two levels of copepod grazing pressure were manipulated on a natural plankton community in Kiel Bay, Southern Baltic Sea, Germany.

Description: Sustainable Development Goal 14 of the United Nations aims to “conserve and sustainably use the oceans, seas and marine resources for sustainable development”. Achieving this goal will require rebuilding the marine life-support systems that deliver the many benefits that society receives from a healthy ocean. Here we document the recovery of marine populations, habitats and ecosystems following past conservation interventions. Recovery rates across studies suggest that substantial recovery of the abundance, structure and function of marine life could be achieved by 2050, if major pressures—including climate change—are mitigated. Rebuilding marine life represents a doable Grand Challenge for humanity, an ethical obligation and a smart economic objective to achieve a sustainable future.

Description: Generalisations on the combined effects of consumers and resources on autotrophs in aquatic food webs largely rely on freshwater studies. In this study, we tested these general concepts with marine benthic microalgae, which are important components of coastal food webs. We manipulated nitrogen availability and herbivore presence in a factorial field experiment in the Western Baltic Sea. Moreover, we investigated how herbivore control varied among 3 sites and 2 seasons and tested for trophic cascades by enhancing demersal fish density at 2 sites. Nitrogen availability and herbivore presence had strong and antagonistic effects on microalgal biomass, species composition and diversity. Herbivores significantly reduced algal biomass, whereas nutrient enrichment led to an increase in biomass. Herbivore effects on microalgal biomass increased with increasing nitrogen availability, indicating a functional response of herbivores to nutrient enrichment. The response of microalgae at the species level suggested a trade-off between nutrient use and grazing resistance which appeared to be linked to algal growth form. Compared to other growth forms, large erect species were most responsive to both nitrogen loading and herbivory. Grazing reduced microalgal diversity at low nutrient supply, but enhanced it at high nutrient supply. Herbivore effects varied considerably among different sites and were stronger in spring than in summer. Manipulations of fish density during summer did not have any effects on microalgal community structure. In conclusion, our results demonstrate that herbivores and nutrients have strong and balancing effects on marine microbenthic community structure.

Description: The combined and interactive effects of climatic and ecological factors are rarely considered in marine communities. We designed a factorial field experiment to analyze (1) the interactive effects of ambient UV radiation and consumers; and (2) the effects of photosynthetically active radiation (PAR 400 to 700 nm), UVA (320 to 400 nm) and UVB (280 to 320 nm) radiation on a marine hard-bottom community in Nova Scotia, NW Atlantic. Species recruitment and succession on ceramic tiles were followed for 5 mo. We found strong negative UV effects on biomass and cover of the early colonizing macroalga Pilayella littoralis, whereas UVB was more harmful than UVA radiation. Consumers, mainly gammarid amphipods, increased P. littoralis biomass when UV was excluded, probably through fertilization. These initially strong and interacting UV and consumer effects on total biomass and cover diminished as species succession progressed. Species diversity was not affected by experimental treatments, but significant shifts in species composition occurred, especially at the recruitment stage. Red algae were most inhibited by UV, whereas sedentary invertebrates and some brown algae tended to increase under UV exposure. Consumers suppressed green and filamentous brown algae, but favored the other groups. Again, these effects diminished during the later stages of succession. We conclude that UV radiation can be a significant structuring force in early successional benthic communities, and that consumers can mediate its effects.

Description: Der Klimawandel wird alle Aspekte des Lebens im Meer beeinflussen, von grundlegenden biologischen Prozessen, wie dem Überleben und Wachstum einzelner Lebewesen, bis zur Verbreitung und Häufigkeit von Arten und der Organisation mariner Nahrungsnetze. Diese Veränderungen beeinflussen die Struktur und Funktion des Ökosystems Meer und damit auch die Fischbestände und Fischereien. Viele Fischer müssen sich anpassen, wo und was sie fischen und wie reichhaltig, groß und wertvoll die gefischten Arten und der Gesamtfang sind. Viele Arten werden ihre Verbreitung polwärts verschieben, in größere Tiefen oder weiter in den offenen Ozean. Einige polare und tropische Arten werden möglicherweise aussterben. All dies wird zu einer Umstrukturierung der Lebensgemeinschaften führen mit schwer vorhersagbaren Folgen. Basierend auf verfügbaren Klimaprojektionen wird erwartet, dass die globale Fischproduktion und Fangmenge zurückgehen wird, allerdings mit großen regionalen Unterschieden, wie der Zunahme in hohen und Abnahme in niedrigen Breiten. Ein Großteil künftiger Veränderungen wird allerdings von der Entwicklung der Fischerei selbst und anderer menschlicher Einflüsse abhängen. Eine Reduzierung des Fischereidrucks sowie nachhaltiges Fischerei- und Ozeanmanagement werden nötig sein, um Fisch und Fischerei in Zukunft zu erhalten. Dabei kann der Schutz der biologischen Vielfalt im Meer als Versicherung in Zeiten des Wandels dienen.

Description: Understanding how changes in limiting nutrient availability affect life in the oceans requires interdisciplinary efforts. Here we illustrate this with an example of silicon, one of the most common elements on land which bioavailable form, silicic acid (Si(OH)4), is a limiting nutrient for silicifying primary producers, such as diatoms. Silicic acid concentrations in the pelagic polar and subpolar North Atlantic have declined by 1-2 μM during spring pre-bloom conditions over the past 25 years. Many coastal areas of the North Atlantic region also face decreased relative availability of silicon due to increased riverine supply of nitrogen and phosphorus and stable or declining loads of silicon. Both declining silicic acid concentrations and declining silicon to nitrogen (Si:N) ratios limit the growth of diatoms, which are major primary producers contributing up to a quarter of global primary production. To assess the effects of declining silicon availability on phytoplankton communities we conducted a mesocosm experiment manipulating Si:N ratios and copepod grazing pressure on phytoplankton communities from the Baltic Sea. Declining Si:N ratio affected not only diatom abundance and relative biomass but also their species composition and overall plankton diversity. Our results illustrate the importance of silicon in structuring community composition at the base of temperate marine food webs. Changes in silicic acid concentrations and Si:N ratios, therefore, may have far-reaching consequences on oceanic primary production and planktonic food webs. The decline in silicon concentrations in polar and subpolar North Atlantic waters is attributed to natural multi-decadal variability but is likely amplified by reduced ocean mixing due to increased water temperatures, illustrating the need of international efforts to curb global climate change. The decline in Si:N ratios in coastal oceans also highlights the need for further reduction of nutrient pollution and improved river basin management. This may require interdisciplinary and international approaches to manage anthropogenic perturbations of the silicon cycle.