Warm-water decapods and the trophic amplification of climate in the North Sea

Climatic resilience: Marine heatwaves do not influence the variations of green crab (Carcinus maenas) megalopae supply patterns to a Western Iberian estuary

Extreme climatic events like marine heatwaves (MHWs) are becoming more frequent, intense, and longer lasting all around the world. The consequences of these anomalously warm periods are devastating for marine ecosystems. Still, little is known about these extreme events off the western Iberia coast. Here we analyzed MHW events occurring from 1982 to 2020 on the Aveiro coast, western Iberia coast of Portugal. A total of 79 events were detected for the region, with an average duration of 15.8 days, and a mean intensity of 1.9 °C ± 0.4 °C above the 90th percentile of sea surface temperatures (SST) for the region. The maximum intensity of the events has increased by 0.5 °C over the last decade. The relation between SST, and therefore, MHW events, the North Atlantic Oscillation index (NAO), and the regional Iberian Upwelling Index (UI) was identified. The intense upwelling of the region seems to mitigate the duration of warming conditions, resulting in shorter MHW events. Furthermore, the impacts of SST and MHW events on the supply patterns of Carcinus maenas megalopae were examined, utilizing daily data from 2002, 2006-2009, 2012, and 2013, collected at the entrance of Ria de Aveiro. Cross-correlations were employed to assess the effect of SST on megalopae supply, while ordinary least square cumulative sums were used to identify variations over time. The influence of SST on supply was noticed with a 5-to-11-day lag, but this relation changed over the years. Contrary to our hypothesis, we found no evidence supporting a diminishment in megalopae supply due to MHW events. These elusive findings, coupled with the apparent lack of influence of these extreme events, highlight the relatively weak intensity and brief duration of the MHW events in the region, coupled with the high thermal tolerance of these species.

A century of coping with environmental and ecological changes via compensatory biomineralization in mussels

Accurate biological models are critical to predict biotic responses to climate change and human-caused disturbances. Current understanding of organismal responses to change stems from studies over relatively short timescales. However, most projections lack long-term observations incorporating the potential for transgenerational phenotypic plasticity and genetic adaption, the keys to resistance. Here, we describe unexpected temporal compensatory responses in biomineralization as a mechanism for resistance to altered environmental conditions and predation impacts in a calcifying foundation species. We evaluated exceptional archival specimens of the blue mussel Mytilus edulis collected regularly between 1904 and 2016 along 15 km of Belgian coastline, along with records of key environmental descriptors and predators. Contrary to global-scale predictions, shell production increased over the last century, highlighting a protective capacity of mussels for qualitative and quantitative trade-offs in biomineralization as compensatory responses to altered environments. We also demonstrated the role of changes in predator communities in stimulating unanticipated biological trends that run contrary to experimental predictive models under future climate scenarios. Analysis of archival records has a key role for anticipating emergent impacts of climate change.

Synchrony is more than its top-down and climatic parts: interacting Moran effects on phytoplankton in British seas

Large-scale spatial synchrony is ubiquitous in ecology. We examined 56 years of data representing chlorophyll density in 26 areas in British seas monitored by the Continuous Plankton Recorder survey. We used wavelet methods to disaggregate synchronous fluctuations by timescale and determine that drivers of synchrony include both biotic and abiotic variables. We tested these drivers for statistical significance by comparison with spatially synchronous surrogate data. Identification of causes of synchrony is distinct from, and goes beyond, determining drivers of local population dynamics. We generated timescale-specific models, accounting for 61% of long-timescale (> 4yrs) synchrony in a chlorophyll density index, but only 3% of observed short-timescale (< 4yrs) synchrony. Thus synchrony and its causes are timescale-specific. The dominant source of long-timescale chlorophyll synchrony was closely related to sea surface temperature, through a climatic Moran effect, though likely via complex oceanographic mechanisms. The top-down action of Calanus finmarchicus predation enhances this environmental synchronising mechanism and interacts with it non-additively to produce more long-timescale synchrony than top-down and climatic drivers would produce independently. Our principal result is therefore a demonstration of interaction effects between Moran drivers of synchrony, a new mechanism for synchrony that may influence many ecosystems at large spatial scales.

The size of the annual bloom in phytoplankton can vary similarly from year to year in different parts of the same oceanic region, a phenomenon called spatial synchrony. The growth of phytoplankton near the ocean surface is the foundation of marine food webs, which include numerous commercially exploited species. And spatial synchrony in phytoplankton abundance time series can have consequences for the total production of marine ecosystems. Therefore we studied the spatial synchrony of fluctuations in green phytoplankton abundance in 26 areas in seas around the British Isles. Variation and synchrony can occur differently on long and short timescales. We used a novel wavelet-based approach to examine long- and short-timescale fluctuations separately, and we thereby show that slow synchronous fluctuations in phytoplankton can be explained by the effects of slow synchronous fluctuations in sea surface temperature and related oceanographic phenomena, and by the effects of synchronous fluctuations in a zooplankton predator. Crucially, these drivers reinforce one another in a super-additive way, the interaction constituting a new mechanism of synchrony. Future changes in the climate or changes in predation are likely to influence phytoplankton synchrony via this mechanism and hence may influence the aggregate productivity of British seas.

Climate change-related regime shifts have altered spatial synchrony of plankton dynamics in the North Sea

During the 1980s, the North Sea plankton community underwent a well-documented ecosystem regime shift, including both spatial changes (northward species range shifts) and temporal changes (increases in the total abundances of warmer water species). This regime shift has been attributed to climate change. Plankton provide a link between climate and higher trophic-level organisms, which can forage on large spatial and temporal scales. It is therefore important to understand not only whether climate change affects purely spatial or temporal aspects of plankton dynamics, but also whether it affects spatiotemporal aspects such as metapopulation synchrony. If plankton synchrony is altered, higher trophic-level feeding patterns may be modified. A second motivation for investigating changes in synchrony is that the possibility of such alterations has been examined for few organisms, in spite of the fact that synchrony is ubiquitous and of major importance in ecology. This study uses correlation coefficients and spectral analysis to investigate whether synchrony changed between the periods 1959-1980 and 1989-2010. Twenty-three plankton taxa, sea surface temperature (SST), and wind speed were examined. Results revealed that synchrony in SST and plankton was altered. Changes were idiosyncratic, and were not explained by changes in abundance. Changes in the synchrony of Calanus helgolandicus and Para-pseudocalanus spp appeared to be driven by changes in SST synchrony. This study is one of few to document alterations of synchrony and climate-change impacts on synchrony. We discuss why climate-change impacts on synchrony may well be more common and consequential than previously recognized.

Biomass changes and trophic amplification of plankton in a warmer ocean

Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3-D coupled physical-biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate-change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis, including European seas (NE Atlantic, Barents Sea, Baltic Sea, Black Sea, Bay of Biscay, Adriatic Sea, Aegean Sea) and the Eastern Boundary Upwelling System (Benguela). Results indicate that globally and in Atlantic Margin and North Sea, increased ocean stratification causes primary production and zooplankton biomass to decrease in response to a warming climate, whilst in the Barents, Baltic and Black Seas, primary production and zooplankton biomass increase. Projected warming characterized by an increase in sea surface temperature of 2.29 ± 0.05 °C leads to a reduction in zooplankton and phytoplankton biomasses of 11% and 6%, respectively. This suggests negative amplification of climate driven modifications of trophic level biomass through bottom-up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. Simulations suggest negative amplification is the dominant response across 47% of the ocean surface and prevails in the tropical oceans; whilst positive trophic amplification prevails in the Arctic and Antarctic oceans. Trophic attenuation is projected in temperate seas. Uncertainties in ocean plankton projections, associated to the use of single global and regional models, imply the need for caution when extending these considerations into higher trophic levels.

North Sea ecosystem change from swimming crabs to seagulls

A recent increase in sea temperature has established a new ecosystem dynamic regime in the North Sea. Climate-induced changes in decapods have played an important role. Here, we reveal a coincident increase in the abundance of swimming crabs and lesser black-backed gull colonies in the North Sea, both in time and in space. Swimming crabs are an important food source for lesser black-backed gulls during the breeding season. Inhabiting the land, but feeding mainly at sea, lesser black-backed gulls provide a link between marine and terrestrial ecosystems, since the bottom-up influence of allochthonous nutrient input from seabirds to coastal soils can structure the terrestrial food web. We, therefore, suggest that climate-driven changes in trophic interactions in the marine food web may also have ensuing ramifications for the coastal ecology of the North Sea.