Fauna - Microplastics interactions: Empirical insights from benthos community exposure to marine plastic waste.

Microplastic deposition in soft marine sediments raises concerns on their role in sediment habitats and unknown effects on resident macrobenthic communities. To assess the reciprocal influence that MPs and macrobenthos might have on each other, we performed a mesocosm experiment with ambient concentrations of environmental Polyethylene (PE) and a non-manipulated, natural macrobenthic community from the Belgian part of the North Sea (BPNS). Our results show that PE fragments increase mortality of abundant bivalves (specifically Abra alba) after 30 days of exposure but not for the most abundant polychaete Owenia fusiformis, possibly due to its predominant suspension feeding behavior. Fast burial of surface MPs exposes deep-dwelling burrowers to the pollutant, however reducing the amount of MPs interacting with (sub) surface living fauna. We conclude that macrobenthos promotes the sequestration of deposited MPs, counteracting resuspension, and can have cascading effects on biodiversity due to their effect on abundant and functionally important species.

Organic matter processing in a [simulated] offshore wind farm ecosystem in current and future climate and aquaculture scenarios.

The rapid development of blue economy and human use of offshore space triggered the concept of co-location of marine activities and is causing diverse local pressures on the environment. These pressures add to, and interact with, global challenges such as ocean acidification and warming. This study investigates the combined pressures of climate change and the planned co-location of offshore wind farm (OWF) and aquaculture zones on the carbon flow through epifaunal communities inhabiting wind turbines in the North Sea. A 13C-labelled phytoplankton pulse-chase experiment was performed in mesocosms (4 m3) holding undisturbed hard-substrate (HS) communities, natural sediment with infauna, and mobile invertebrate predators. Carbon assimilation was quantified under current and predicted future-climate conditions (+3 °C and -0.3 pH units), as well as a future-climate co-use scenario with blue mussel (Mytilus edulis) aquaculture. Climate change induced an increase in macrofaunal carbon assimilation as well as an organic enrichment of underlying sediments. Dynamic (non-)trophic links between M. edulis and other HS epifauna resulted in shifts among the species contributing most to the phytoplankton-derived carbon flow across climate scenarios. Increased inter- and intraspecific resource competition in the presence of M. edulis aquaculture prevented a large increase in the total assimilation of phytoplankton by HS fauna. Lower individual carbon assimilation rates by both mussels and other epifauna suggest that if filter capacity by HS epifauna would approach renewal by advection/mixing, M. edulis individuals would likely grow to a smaller-than-desired commercial size. In the same scenario, benthic organic carbon mineralisation was significantly boosted due to increased organic matter deposition by the aquaculture set-up. Combining these results with in situ OWF abundance data confirmed M. edulis as the most impactful OWF AHS species in terms of (total) carbon assimilation as well as the described stress responses due to climate change and the addition of bivalve aquaculture.

Climate change effects on the ecophysiology and ecological functioning of an offshore wind farm artificial hard substrate community.

In the effort towards a decarbonised future, the local effects of a proliferating offshore wind farm (OWF) industry add to and interact with the global effects of marine climate change. This study aimed to quantify potential ecophysiological effects of ocean warming and acidification and to estimate and compare the cumulative clearance potential of suspended food items by OWF epifauna under current and future climate conditions. To this end, this study combined ecophysiological responses to ocean warming and acidification of three dominant colonising species on OWF artificial hard substrates (the blue mussel Mytilus edulis, the tube-building amphipod Jassa herdmani and the plumose anemone Metridium senile). In general, mortality, respiration rate and clearance rate increased during 3- to 6-week experimental exposures across all three species, except for M. senile, who exhibited a lower clearance rate in the warmed treatments (+3 °C) and an insensitivity to lowered pH (-0.3 pH units) in terms of survival and respiration rate. Ocean warming and acidification affected growth antagonistically, with elevated temperature being beneficial for M. edulis and lowered pH being beneficial for M. senile. The seawater volume potentially cleared from suspended food particles by this AHS colonising community increased significantly, extending the affected distance around an OWF foundation by 9.2% in a future climate scenario. By using an experimental multi-stressor approach, this study thus demonstrates how ecophysiology underpins functional responses to climate change in these environments, highlighting for the first time the integrated, cascading potential effects of OWFs and climate change on the marine ecosystem.

Interactive effects of vegetation and sediment properties on erosion of salt marshes in the Northern Adriatic Sea.

We investigated how lateral erosion control, measured by novel photogrammetry techniques, is modified by the presence of Spartina spp. vegetation, sediment grain size, and the nutrient status of salt marshes across 230 km of the Italian Northern Adriatic coastline. Spartina spp. vegetation reduced erosion across our study sites. The effect was more pronounced in sandy soils, where erosion was reduced by 80% compared to 17% in silty soils. Erosion resistance was also enhanced by Spartina spp. root biomass. In the absence of vegetation, erosion resistance was enhanced by silt content, with mean erosion 72% lower in silty vs. sandy soils. We found no relevant relationships with nutrient status, likely due to overall high nutrient concentrations and low C:N ratios across all sites. Our results contribute to quantifying coastal protection ecosystem services provided by salt marshes in both sandy and silty sediments.

Physiological responses to ocean acidification and warming synergistically reduce condition of the common cockle Cerastoderma edule.

The combined effect of ocean acidification and warming on the common cockle Cerastoderma edule was investigated in a fully crossed laboratory experiment. Survival of the examined adult organisms remained high and was not affected by elevated temperature (+3 °C) or lowered pH (-0.3 units). However, the morphometric condition index of the cockles incubated under high pCO2 conditions (i.e. combined warming and acidification) was significantly reduced after six weeks of incubation. Respiration rates increased significantly under low pH, with highest rates measured under combined warm and low pH conditions. Calcification decreased significantly under low pH while clearance rates increased significantly under warm conditions and were generally lower in low pH treatments. The observed physiological responses suggest that the reduced food intake under hypercapnia is insufficient to support the higher energy requirements to compensate for the higher costs for basal maintenance and growth in future high pCO2 waters.

Long-term divergent tidal flat benthic community recovery following hypoxia-induced mortality.

Macrobenthos recovery after hypoxia-induced mass mortality was assessed in an estuarine tidal mudflat during 3 years. During the first 2 years, a Pearson-Rosenberg type of community recovery took place along with the improving bottom water oxygen conditions. After 3 months, spionid polychaetes became superabundant (i.e. opportunistic peak), followed rapidly by a steep decline (i.e. ecotone point). Subsequently, a moderate increase in species richness and a steep increase in biomass, related to the growth of long-lived species occurred (i.e. transition region). Afterwards, however, the recovering community diverged again from the ambient, undisturbed, sediments due to enhanced recruitment success of long-lived species presumably resulting from the lowered interference from bioturbation during early recovery stages in the disturbed plots. Hence, despite early community recovery may be more or less deterministic, lagged divergent community reassembling may occur at the longer-term, thereby contributing to benthos patchiness in areas which are frequently subjected to disturbances.