Merging trait-based ecology and regime shift theory to anticipate community responses to warming.

Anthropogenic warming is altering species abundance, distribution, physiology, and more. How changes observed at the species level alter emergent community properties is an active and urgent area of research. Trait-based ecology and regime shift theory provide complementary ways to understand climate change impacts on communities, but these two bodies of work are only rarely integrated. Lack of integration handicaps our ability to understand community responses to warming, at a time when such understanding is critical. Therefore, we advocate for merging trait-based ecology with regime shift theory. We propose a general set of principles to guide this merger and apply these principles to research on marine communities in the rapidly warming North Atlantic. In our example, combining trait distribution and regime shift analyses at the community level yields greater insight than either alone. Looking forward, we identify a clear need for expanding quantitative approaches to collecting and merging trait-based and resilience metrics in order to advance our understanding of climate-driven community change.

Climate variability hypothesis is partially supported in thermal limits of juvenile Northwest Atlantic coastal fishes.

As ocean warming continues to impact marine species globally, there is a need to understand the mechanisms underlying shifts in abundance and distribution. There is growing evidence that upper and lower temperature tolerances rather than mean preferences explain range shifts, but the full thermal niche is unknown for many marine species and observational data are often ill-suited to estimate the upper and lower thermal tolerances. We quantified critical thermal maximum (CTmax ) and critical thermal minimum (CTmin ) using standard methods to quantify temperature limits and thermal ranges of 14 economically and ecologically important juvenile fish species on the US Atlantic coast. We then tested the climate variability hypothesis (CVH), which states that higher-latitude species should have a wider temperature tolerance due to higher climatic variability closer to the poles. Our findings generally support the CVH in the juvenile fishes that we evaluated. However, low-latitude species were not uniformly stenothermal. Rather, species with median occurrences across a wide range of latitudes had wide temperature tolerances, but only the tropical species we tested had more narrow ranges. These findings suggest that quantifying temperature tolerances may be used to predict which low-latitude species are most likely to shift in response to warming water and those that may be more sensitive to climate change in this region.

Energetic consequences of resource use diversity in a marine carnivore.

Understanding how intraspecific variation in the use of prey resources impacts energy metabolism has strong implications for predicting long-term fitness and is critical for predicting population-to-community level responses to environmental change. Here, we examine the energetic consequences of variable prey resource use in a widely distributed marine carnivore, juvenile sand tiger sharks (Carcharias taurus). We used carbon and nitrogen isotope analysis to identify three primary prey resource pools-demersal omnivores, pelagic forage, and benthic detritivores and estimated the proportional assimilation of each resource using Bayesian mixing models. We then quantified how the utilization of these resource pools impacted the concentrations of six plasma lipids and how this varied by ontogeny. Sharks exhibited variable reliance on two of three predominant prey resource pools: demersal omnivores and pelagic forage. Resource use variation was a strong predictor of energetic condition, whereby individuals more reliant upon pelagic forage exhibited higher blood plasma concentrations of very low-density lipoproteins, cholesterol, and triglycerides. These findings underscore how intraspecific variation in resource use may impact the energy metabolism of animals, and more broadly, that natural and anthropogenically driven fluctuations in prey resources could have longer term energetic consequences.

Poleward bound: adapting to climate-driven species redistribution.

One of the most pronounced effects of climate change on the world's oceans is the (generally) poleward movement of species and fishery stocks in response to increasing water temperatures. In some regions, such redistributions are already causing dramatic shifts in marine socioecological systems, profoundly altering ecosystem structure and function, challenging domestic and international fisheries, and impacting on human communities. Such effects are expected to become increasingly widespread as waters continue to warm and species ranges continue to shift. Actions taken over the coming decade (2021-2030) can help us adapt to species redistributions and minimise negative impacts on ecosystems and human communities, achieving a more sustainable future in the face of ecosystem change. We describe key drivers related to climate-driven species redistributions that are likely to have a high impact and influence on whether a sustainable future is achievable by 2030. We posit two different futures-a 'business as usual' future and a technically achievable and more sustainable future, aligned with the Sustainable Development Goals. We then identify concrete actions that provide a pathway towards the more sustainable 2030 and that acknowledge and include Indigenous perspectives. Achieving this sustainable future will depend on improved monitoring and detection, and on adaptive, cooperative management to proactively respond to the challenge of species redistribution. We synthesise examples of such actions as the basis of a strategic approach to tackle this global-scale challenge for the benefit of humanity and ecosystems. Supplementary Information: The online version contains supplementary material available at 10.1007/s11160-021-09641-3.

Population level differences in overwintering survivorship of blue crabs (Callinectes sapidus): A caution on extrapolating climate sensitivities along latitudinal gradients.

Winter mortality can strongly affect the population dynamics of blue crabs (Callinectes sapidus) near poleward range limits. We simulated winter in the lab to test the effects of temperature, salinity, and estuary of origin on blue crab winter mortality over three years using a broad range of crab sizes from both Great South Bay and Chesapeake Bay. We fit accelerated failure time models to our data and to data from prior blue crab winter mortality experiments, illustrating that, in a widely distributed, commercially valuable marine decapod, temperature, salinity, size, estuary of origin, and winter duration were important predictors of winter mortality. Furthermore, our results suggest that extrapolation of a Chesapeake Bay based survivorship model to crabs from New York estuaries yielded poor fits. As such, the severity and duration of winter can impact northern blue crab populations differently along latitudinal gradients. In the context of climate change, future warming could possibility confer a benefit to crab populations near the range edge that are currently limited by temperature-induced winter mortality by shifting their range edge poleward, but care must be taken in generalizing from models that are developed based on populations from one part of the range to populations near the edges, especially for species that occupy large geographical areas.

Overwintering survivorship and growth of young-of-the-year black sea bass Centropristis striata.

Overwintering conditions have long been known to affect fish survival and year-class strength as well as determine the poleward range limit of many temperate fishes. Despite this known importance, mechanisms controlling overwintering mortality are poorly understood and the tolerance of marine fishes to the combined effects of winter temperature, salinity, and size is rarely quantified. In recent years, higher abundances of the temperate Serranid, black sea bass Centropristis striata, have been observed at latitudes further north than their traditional range suggesting that warming water temperatures, particularly during winter, may be facilitating the establishment of a population at more northern latitudes. To examine overwintering survival of C. striata, the combined effects of temperature, salinity and body mass were quantified in laboratory experiments. We identified 6°C as the lower incipient lethal temperature for C. striata, below which fish cease feeding, lose weight rapidly and die within 32 days. A short cold exposure experiment indicated that temperatures below 5°C resulted in mortality events that continued even as the temperature increased slowly to 10°C, indicating that even short cold snaps can impact survival and recruitment in this species. Importantly, fish in lower salinity lived significantly longer than fish at higher salinity at both 3°C and 5°C, suggesting that osmoregulatory stress plays a role in overwintering mortality in this species. Size was not a critical factor in determining overwintering survival of young-of-the-year (YOY) C. striata. Overwintering survival of YOY C. striata can be effectively predicted as a function of temperature and salinity and their interaction with an accelerated failure model to project future range limits. Identifying temperature thresholds may be a tractable way to incorporate environmental factors into population models and stock assessment models in fishes.

Response to Comments on "Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery".

Palmer et al and Swain et al suggest that our "extra mortality" time series is spurious. In response, we show that including temperature-dependent mortality improves abundance estimates and that warming waters reduce growth rates in Gulf of Maine cod. Far from being spurious, temperature effects on this stock are clear, and continuing to ignore them puts the stock in jeopardy.

Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery.

Several studies have documented fish populations changing in response to long-term warming. Over the past decade, sea surface temperatures in the Gulf of Maine increased faster than 99% of the global ocean. The warming, which was related to a northward shift in the Gulf Stream and to changes in the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation, led to reduced recruitment and increased mortality in the region's Atlantic cod (Gadus morhua) stock. Failure to recognize the impact of warming on cod contributed to overfishing. Recovery of this fishery depends on sound management, but the size of the stock depends on future temperature conditions. The experience in the Gulf of Maine highlights the need to incorporate environmental factors into resource management.

Silver hake tracks changes in Northwest Atlantic circulation.

Recent studies documenting shifts in spatial distribution of many organisms in response to a warming climate highlight the need to understand the mechanisms underlying species distribution at large spatial scales. Here we present one noteworthy example of remote oceanographic processes governing the spatial distribution of adult silver hake, Merluccius bilinearis, a commercially important fish in the Northeast US shelf region. Changes in spatial distribution of silver hake over the last 40 years are highly correlated with the position of the Gulf Stream. These changes in distribution are in direct response to local changes in bottom temperature on the continental shelf that are responding to the same large scale circulation change affecting the Gulf Stream path, namely changes in the Atlantic meridional overturning circulation (AMOC). If the AMOC weakens, as is suggested by global climate models, silver hake distribution will remain in a poleward position, the extent to which could be forecast at both decadal and multidecadal scales.

The effect of maternal exposure to contaminated sediment on the growth and condition of larval Fundulus heteroclitus.

We employed a factorial laboratory experiment to determine the single and combined effect of maternal and larval exposure to contaminated sediment from Elizabeth River, Virginia, a site contaminated with high concentrations of multiple pollutants. Females were exposed to either reference or contaminated sediment and the larvae from both groups of mothers were in turn transferred to either reference or contaminated sediment. We found a strong maternal influence on yolk area, length and RNA:DNA ratio at hatch. Further, the maternal exposure significantly influenced growth rate and RNA:DNA ratios of larvae 14 days after hatch and was a more important factor in determining these endpoints than larval exposure. We found that after 14 days larvae were larger and had higher survivorship when the maternal and larval exposures were the same. There also was no statistical difference with respect to growth and condition between larvae that had hatched from exposed mothers and remained in contaminated water and larvae that had hatched from reference mothers and were placed in either reference or contaminated sediment. However, larvae that hatched from exposed mothers and then were switched to reference sediment had significantly lower growth, lower RNA:DNA ratios, and were smaller despite being large at hatch size, indicating that there are fitness trade-offs in exchange for apparent resistance to contaminants which are provided by the mother. Maternal effects add complexity to ecotoxicological research and should be incorporated into studies to predict population level responses more realistically.