• Energy Research

Estuaries are among the most valuable aquatic systems by their services to human welfare. However, increasing human activities at the watershed along with the pressure of climate change are fostering the co-occurrence of multiple environmental drivers, and warn of potential negative impacts on estuaries resources. At present, no clear understanding of how coastal ecosystems will respond to the non-stationary effect of multiple drivers. Here we analysed the temporal interaction among multiple environmental drivers and their changing priority on shaping phytoplankton response in the Bahía Blanca Estuary, SW Atlantic Ocean. The interaction among environmental drivers and the number of significant direct and indirect effects on chlorophyll concentration increased over time in concurrence with enhanced anthropogenic stress, changing winter climate and wind patterns. Over the period 1978-1993, proximal variables such as nutrients, water temperature and salinity, showed a dominant effect on chlorophyll, whereas in more recent years (1993-2009) climate signals (SAM and ENSO) boosted indirect effects through its influence on precipitation, wind, water temperature and turbidity. Turbidity emerged as the dominant driver of chlorophyll while in recent years acted synergistically with the concentration of dissolved nitrogen. As a result, chlorophyll concentration showed a significant negative trend and a loss of seasonal peaks reflecting a pronounced reorganisation of the phytoplankton community. We stress the need to account for the changing priority of drivers to understand, and eventually forecast, biological responses under projected scenarios of global anthropogenic change.

The relationship between the ciliate community and the environmental variables in Ushuaia and Golondrina bays (54°79′S 68°22′W and 54°85′S 68°36′W, respectively) in the Beagle Channel, Argentina was investigated. The study was performed in three zones within the bays, previously delimited on the basis of their water quality. The most perturbed sites were located inshore. In order to analyse the contribution of each species to the similarity or dissimilarity between zones, similarity percentages analysis was undertaken using the Bray–Curtis similarity index. The variations in species composition and dominance in the selected zones were examined by the abundance–biomass comparison plot. We also studied the relationship between environmental and ciliates variability. The ciliate community comprised a total of 43 species belonging to 15 genera. Ciliate abundance and biomass varied temporally and spatially. A more diverse community dominated by small and opportunistic species tolerant to environmental changes was found in the most perturbed zone, while in the less stressed zone the community comprised bigger species, probably adapted to more stable environmental conditions. A community comprising species from both zones was found in a transitional area. We conclude that the structure of the community varied closely with environmental conditions.

Rapid climate-driven melting of coastal glaciers may control plankton dynamics in the Western Antarctic Peninsula. It is known that in Potter Cove, 25 de Mayo/King George Island, phytoplankton is tightly coupled to meltwater input. However, no information on zooplankton is available in this regard. The aim of this study was therefore to examine the structure and dynamics of microzooplankton and mesozooplankton in two zones (the inner and outer Potter Cove) differently impacted by glacier melting during two contrasting austral summers (2010 and 2011). Microzooplankton composition differed between the two zones and years analyzed, and its total biomass was observed to be highest far from the glacier influence and during 2010. Mesozooplankton composition and biomass were similar in the two zones and years analyzed. Colder than usual conditions in the summer of 2010 prevented glacier melting, thus favoring the development of an exceptional micro-sized diatom bloom (~190 µg C l−1 and >15 µg l−1 chlorophyll a), which was tightly followed by a maximum in large copepod abundance. After the bloom and in coincidence with intense glacier melting, large diatoms and large copepods were observed to be replaced by nanophytoplankton and microzooplankton (aloricate ciliates and dinoflagellates), respectively. In 2011, low phytoplankton abundance, probably controlled by high tintinnid biomass, was observed as a result of warmer temperatures than 2010 and low-salinity waters. Large copepods appeared to have exerted a high grazing pressure on aloricate ciliates and heterotrophic dinoflagellates in 2011. Our results suggest that whereas the joint effect of water temperature, salinity and phytoplankton availability as well as composition could be of primary relevance in structuring micro- and mesozooplankton community, zooplankton could be of secondary relevance in controlling phytoplankton biomass in Potter Cove during the two summers analyzed.

Climate variability plays a central role in the dynamics of marine pelagic ecosystems shaping the structure and abundance changes of plankton communities, thereby affecting energy pathways and biogeochemical fluxes in the ocean. Here we have investigated complex interactions driven a climate-hydrology-plankton system in the southern East China Sea over the period 2000 to 2012. In particular, we aimed at quantifying the influence of climate phenomena playing out in tropical (El Nino 3.4) and middle-high latitudes (East Asia Winter Monsoon, EAWM, and Pacific Decadal Oscillation, PDO) on pelagic copepods. We found that the EAWM and El Nino 3.4 showed a non-stationary and non-linear relationship with local temperature variability. In the two cases, the strength of the relationship, as indexed by the wavelet coherence analysis, decreased along with the positive phase of the PDO. Likewise, the influence of EAWM and El Nino3.4 on copepods exhibited a non-stationary link that changed along with the PDO state. Indeed, copepods and EAWM were closely related during the positive phase, while the link copepods-El Nino 3.4 was stronger during the negative phase. Our results pointed out cascading effects from climate to plankton driven by the positive phase of the PDO through its effect on temperature conditions, and likely through a larger southward transport of nutrient-rich water masses to northern Taiwan and the Taiwan Strait. We suggest a chain of mechanisms whereby the PDO shapes interannual dynamics of pelagic copepods and highlight that these results have implications for integrative management measures, as pelagic copepods plays a prominent role in food web dynamics and for harvested fish in the East China Sea.

Quantifying biotic feedbacks in response to environmental signals is fundamental to assess ecosystem perturbation. We analyzed the joint effects of eutrophication, derived from sewage pollution, and climate at the base of the pelagic food web in the Bahía Blanca Estuary (SW Atlantic Ocean). A two-year survey of environmental conditions and microplankton communities was conducted in two sites affected by contrasting anthropogenic eutrophication conditions. Under severe eutrophication, we found higher phytoplankton abundance consistently dominated by smaller sized, non siliceous species, while microzooplankton abundance remained lower and nutrient stoichiometry showed conspicuous deviations from the Redfield ratio. Phytoplankton growth in such conditions appeared controlled by phosphorous. In turn, microplankton biomass and phytoplankton size ratio (20μm) displayed a saturation relationship with nutrients in the highly eutrophic area, although mean phytoplankton growth was similar in both eutrophic systems. The strength of links within the estuarine network, quantified through path analysis, showed enhanced relationships under larger anthropogenic eutrophication, which fostered the climate influence on microplankton communities. Our results show conspicuous effects of severe sewage pollution on the ecological stoichiometry, i.e., N and P excess with respect to Si, altering nutrient ratios for microplankton communities. This warns on wide consequences on food web dynamics and ultimately in ecosystem assets of coastal pelagic environments.