Indicator Properties of Baltic Zooplankton for Classification of Environmental Status within Marine Strategy Framework Directive

Abstract

The European Marine Strategy Framework Directive requires the EU Member States to estimate the level of anthropogenic impacts on their marine systems using 11 Descriptors. Assessing food web response to altered habitats is addressed by Descriptor 4 and its indicators, which are being developed for regional seas. However, the development of simple foodweb indicators able to assess the health of ecologically diverse, spatially variable and complex interactions is challenging. Zooplankton is a key element in marine foodwebs and thus comprise an important part of overall ecosystem health. Here, we review work on zooplankton indicator development using long-term data sets across the Baltic Sea and report the main findings. A suite of zooplankton community metrics were evaluated as putative ecological indicators that track community state in relation to Good Environmental Status (GES) criteria with regard to eutrophication and fish feeding conditions in the Baltic Sea. On the basis of an operational definition of GES, we propose mean body mass of zooplankton in the community in combination with zooplankton stock measured as either abundance or biomass to be applicable as an integrated indicator that could be used within the Descriptor 4 in the Baltic Sea. These metrics performed best in predicting zooplankton being in-GES when considering all datasets evaluated. However, some other metrics, such as copepod biomass, the contribution of copepods to the total zooplankton biomass or biomass-based Cladocera: Copepoda ratio, were equally reliable or even superior in certain basin-specific assessments. Our evaluation suggests that in several basins of the Baltic Sea, zooplankton communities currently appear to be out-of-GES, being comprised by smaller zooplankters and having lower total abundance or biomass compared to the communities during the reference conditions; however, the changes in the taxonomic structure underlying these trends vary widely across the sea basins due to the estuarine character of the Baltic Sea.

Mercury-methylating bacteria are associated with copepods: A proof-of-principle survey in the Baltic Sea

“…The strong decrease in Hg inputs to the Baltic Sea during the last decades has not resulted in a consistent decrease in fish Hg levels across the sea [17,46]. During this time, significant and basin-specific changes occurred in zooplankton communities [47] in concert with alterations in climate, nutrient inputs and terrestrial runoff [17,44]. It is plausible that synchronous shifts in the methylation capacity of zooplankton, at both the individual microbiome and community levels, have taken place contributing to the MeHg dynamics in the food web.…”

Linking consumer physiological status to food-web structure and prey food value in the Baltic Sea

“…dk). Time series on zooplankton biomass (including copepods, cladocerans and rotifers) were integrated from national and international stations in coast and open sea (Gorokhova et al 2016;Fig. 1).…”

“…1, Supplementary Table S1). We calculated the average summer biomass (mg m 3 ) and mean zooplankter size (lm ind -1 ) as described in Gorokhova et al (2016). Zooplankton mean body size was used as a metric to represent the prey food value for zooplanktivores (herring and sprat).…”

Price vs. Value of Marine Monitoring

“…Compared to the present temporal resolution of the Finnish national zooplankton monitoring (sampling twice a year), a monitoring scheme fully covering the population dynamics of zooplankton would require considerably increased resources. However, the status assessment uses one zooplankton indicator (mean size versus total stock) and the twice a year sampling during the productive season fulfills the data requirements for this indicator (Gorokhova et al, 2016). Optimizing the sampling program needs to be considered carefully taking into account what the requirements for the indicator are and what would be gained by adding spatial or temporal coverage.…”