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Sidney J. Holt (1926–2019) was more than a founding father of quantitative fisheries science, and the man who "helped save the great whales." His accomplishments, over a career spanning seven decades, run deeper: he was a champion of reductionism (i.e. able to identify the factors essential for management) and a systemic thinker who inspired scientists to think critically about marine conservation and management. This article draws on first-hand experiences with Sidney over the last 15 years, when he regularly collaborated with scholars of the ICES Working Group on the History of Fish and Fisheries and the Oceans Past Initiative. Four main themes emerged from our reflections on Sidney's life and legacy, which constitute ongoing scientific challenges: (1) the suitability of maximum sustainable yield as a target reference point for fisheries management; (2) the future of marine mammal conservation; (3) successful implementation of ecosystem-based marine management; and (4) the value of historical perspectives for conservation and management. We consider Sidney's work across these themes, in which he readily collaborated, focused on evidence-based solutions, and, where evidence was lacking, he advocated for the "precautionary principle." We posit there is much that we, and future generations of scientists, can learn from his example. [ABSTRACT FROM AUTHOR]

The concept of "blue growth," which aims to promote the growth of ocean economies while holistically managing marine socioecological systems, is emerging within national and international marine policy. The concept is often promoted as being novel; however, we show that historical analogies exist that can provide insights for contemporary planning and implementation of blue growth. Using a case‐study approach based on expert knowledge, we identified 20 historical fisheries or aquaculture examples from 13 countries, spanning the last 40–800 years, that we contend embody blue growth concepts. This is the first time, to our knowledge, that blue growth has been investigated across such broad spatial and temporal scales. The past societies managed to balance exploitation with equitable access, ecological integrity and/or economic growth for varying periods of time. Four main trajectories existed that led to the success or failure of blue growth. Success was linked to equitable rather than open access, innovation and management that was responsive, holistic and based on scientific knowledge and monitoring. The inability to achieve or maintain blue growth resulted from failures to address limits to industry growth and/or anticipate the impacts of adverse extrinsic events and drivers (e.g. changes in international markets, war), the prioritization of short‐term gains over long‐term sustainability, and loss of supporting systems. Fourteen cross‐cutting lessons and 10 recommendations were derived that can improve understanding and implementation of blue growth. Despite the contemporary literature broadly supporting our findings, these recommendations are not adequately addressed by agendas seeking to realize blue growth. [ABSTRACT FROM AUTHOR]

Abstract During the Toarcian oceanic anoxic event (OAE) considerable environmental changes occurred that were associated with global warming, perturbations to the C-cycle and ocean deoxygenation which resulted in a mass extinction of marine fauna. Recovery of the biota after the event was protracted and has to date undergone limited study. However, understanding the patterns and processes of recovery are critical to anticipating ecosystem responses to the environmental changes predicted for the near future. Results showed that increases in benthic diversity, and the re-establishment of the Toarcian infauna was gradual and followed the changing redox conditions. Pioneering infauna, such as Dacryomya ovum that dominated the seafloor after the event in the Cleveland Basin, Yorkshire, UK, can modify the physico-chemical environment and thus facilitate ecological succession after disturbance. The length of D. ovum increased >8 mm throughout the bifrons Zone and these body-size changes were linked with total organic carbon (TOC) content suggesting a link to primary productivity, although only at intermediate levels of deoxygenation. Major changes in the phytoplankton, and so food supply, seem to have driven changes in bivalve body size, across trophic guilds, both during and after the event in Yorkshire, and on the mid to lower shelf in Spain and France, respectively. Primary productivity collapse seems then to have been a major driver of biotic change throughout the Toarcian event, as it was during the Permian–Triassic, Triassic/Jurassic and Cretaceous/Tertiary mass extinctions. Further investigation of both the palaeontological and geochemical changes that occurred within early successional Toarcian infaunal communities are required to more fully understand the pattern of recovery after the OAE. Highlights • The recovery was slow benthic diversity and infauna increased gradually. • Pioneering infauna such as D. ovum performed important roles in benthic succession. • D. ovum size varied with TOC, and so food supply, when deoxygenation was moderate. • Bivalve size was linked to food supply both during and after the OAE. • Primary productivity collapse was widespread during the Toarcian OAE. [ABSTRACT FROM AUTHOR]

Global warming during the Early Jurassic, and associated widespread ocean deoxygenation, was comparable in scale with the changes projected for the next century. This study quantifies the impact of severe global environmental change on the biological traits of marine communities that define the ecological roles and functions they deliver. We document centennial-millennial variability in the biological trait composition of Early Jurassic (Toarcian) seafloor communities and examine how this changed during the event using biological traits analysis. Environmental changes preceding the global oceanic anoxic event (OAE) produced an ecological shift leading to stressed benthic palaeocommunities with reduced resilience to the subsequent OAE. Changes in traits and ecological succession coincided with major environmental changes; and were of similar nature and magnitude to those in severely deoxygenated benthic communities today despite the very different timescales. Changes in community composition were linked to local redox conditions whereas changes in populations of opportunists were driven by primary productivity. Throughout most of the OAE substitutions by tolerant taxa conserved the trait composition and hence functioning, but periods of severe deoxygenation caused benthic defaunation that would have resulted in functional collapse. Following the OAE recovery was slow probably because the global nature of the event restricted opportunities for recruitment from outside the basin. Our findings suggest that future systems undergoing deoxygenation may initially show functional resilience, but severe global deoxygenation will impact traits and ecosystem functioning and, by limiting the species pool, will slow recovery rates. [ABSTRACT FROM AUTHOR]

Predicting the ability of the biosphere to continue to deliver ecosystem services in the face of biodiversity loss and environmental change is a major challenge. The results of short-term and small-scale experimental studies are both equivocal and difficult to extrapolate from. In this study we use data on benthic palaeocommunities covering 4,000,000 years (in the Late Jurassic when temperate coastal seas in NW Europe experienced fluctuations in oxygenation). The biological traits associated with each species in the palaeocommunities were combined to index the delivery of ecological functions. Five ecosystem functions were examined: food for large mobile predators, biogenic habitat provision, nutrient recycling/regeneration, inorganic carbon sequestration and food-web dynamics. In modern systems these ecological functions underpin ecosystem services that are important for human well-being. Our results show that the supply of food for higher predators was remarkably constant during the 4,000,000 years, suggesting that redundancy amongst species in the assemblage drives the biodiversity-ecosystem function ( BEF) relationship. By contrast, the provision of biogenic habitat varied with the occurrence of a relatively few taxa, a pattern consistent with a rivet type model of BEF. For nutrient regeneration, carbon sequestration and food-web dynamics the patterns were complex and suggestive of an idiosyncratic model of BEF. To our knowledge this is the first study to quantify ecological functioning through deep time and demonstrates the utility of this approach to understanding long-term patterns of BEF in both ancient and contemporary marine ecosystems. The delivery of all five ecological functions studied became increasingly variable as the regional climate became drier, thus modifying the supply of terrigenous nutrient inputs. [ABSTRACT FROM AUTHOR]

Severe paleoclimatic change during the Toarcian (Early Jurassic) oceanic anoxic event (OAE) was characterized by a negative ä13C excursion, increased weathering, higher seawater temperatures, oceanic deoxygenation, and mass extinction. We present abundance and size data (n » 36,000) for the two dominant epifaunal bivalve species from the Toarcian OAE, Yorkshire, UK. We statistically correlate the biotic data with geochemical proxies for environmental change and show that our results are comparable with changes in present-day ecosystems affected by hypoxia. Bositra radiata dominated during declining oxygen levels immediately before the Toarcian OAE sensu stricto, and shell size doubled when δ13Corg was decreasing, indicating a connection with primary productivity. Small Pseudomytiloides dubius dominated during the Toarcian OAE and varied sharply in abundance, indicating that it was highly opportunistic. P. dubius shell size is strongly related to Mo concentration, [Mo]; this indicates a relationship between size and N2-fixing primary productivity via [Mo] limitation. A secondary factor contributing to small shell size was lower oxygen levels. After the Toarcian OAE diversity increased, P. dubius was less abundant and shell size doubled, indicating that bivalve populations were less limited by resources and conditions were more favorable. Size frequency distributions show that both Toarcian species had short life spans, rapid generation times, high recruitment, and high juvenile mortality. The opportunist Mulinia lateralis is a present-day analog for P. dubius. This research provides a case study for the long-term impacts of deoxygenation upon marine ecosystems, including that being observed today. [ABSTRACT FROM AUTHOR]

Abstract: The global deposition of organic rich-mudrocks, a mass extinction, and marked geochemical changes in the sedimentary rocks and fossils deposited during the early Toarcian indicates a period of extreme environmental change and an oceanic anoxic event. This study investigates at a high-resolution the environmental and biotic changes that occurred during the event in a shallow-marine area using rocks deposited on the East Midlands Shelf, UK. We present a new graphic log, geochemical data (δ13Corg, total organic carbon, CaCO3, total sulphur and total nitrogen), and benthic macroinvertebrate ranges from North Quarry, Holwell, Leicestershire, UK. Comparison of the ammonite ranges between the Cleveland Basin (Yorkshire) and East Midland Shelf successions in the UK shows that there is a hiatus on the shelf across the Dactylioceras semicelatum–Cleviceras exaratum Subzone boundary. The new high-resolution geochemical data show that an ~−5‰ δ13Corg excursion occurs similar to other lower Toarcian sections in the world, δ13Corg shifts ‘A’ to ‘C’ are missing in the hiatus, but that δ13Corg shift ‘D’ is present. Similar to the Cleveland Basin, the C. exaratum Subzone of the East Midlands Shelf succession is dominated by three epifaunal bivalve species, but their ranges differ significantly between the successions. An increase in the faunal diversity occurs within the upper C. exaratum Subzone at Holwell and other UK sections. The biotic data indicate that conditions on the East Midlands Shelf were more hospitable than in the Cleveland Basin. The bivalve populations on the shelf may have provided a source of new recruits for the basins. [Copyright &y& Elsevier]

A growing volume of evidence shows that the broad-scale biogeographic redistribution of species is occurring in response to increasing global temperatures. The present study documents poleward movements of up to eight species of nominally 'tropical' macroinvertebrates (molluscs, polychaetes, crustaceans and foraminifera) from intertidal mudflats on the south east coast of Australia. The speed of movement was comparable with that for Australian marine fauna generally, but was particularly fast for worms and molluscs (~70–300 km decade−1) and may be facilitated by the southward flowing East Australia Current. Further, two temperate taxa appear to have extended their ranges northwards. Changes in species biogeographic ranges raises questions surrounding the response of ecological processes within the altered and novel species combinations, including processes that underpin valuable ecosystem services. Using biological traits analysis to investigate how the observed species range changes might have impacted mudflat ecosystem functioning, and to predict the possible impacts of further poleward movements of tropical taxa. Our models suggest the changes to date, and those likely to occur in the near future, are within the envelope whereby ecological functioning is maintained by functional compensation and redundancy within the mudflat assemblage. However, in the most extreme scenario the replacement of temperate by tropical taxa resulted in major changes in ecological functioning with potential impacts on nutrient cycling and C-cycling, undermining the potential of these mudflats to continue to deliver critical ecosystem services. The widespread nature of biogeographic range shifts and the value of coastal systems should add further weight to calls for global action to mitigate global temperature change. Image 1 • Up to 8 tropical invertebrate species moved 145 km poleward over 20–60 years. • Rates of movement were very fast for worms and molluscs (70–300 km decade−1). • Altered species composition to date has not impacted mudflat ecological functioning. • Future shifts may compromise nutrient cycling, c-cycling and biogenic habitat. • Functioning was conserved followed by a threshold after 10–50% of species were lost. [ABSTRACT FROM AUTHOR]

Extreme global warming and environmental changes associated with the Toarcian (Lower Jurassic) Oceanic Anoxic Event (T-OAE, ~183 Mya) profoundly impacted marine organisms and terrestrial plants. Despite the exceptionally elevated abundances of fossil insects from strata of this age, only assemblages from Germany and Luxembourg have been studied in detail. Here, we focus on the insect assemblage found in strata recording the T-OAE at Alderton Hill, Gloucestershire, UK, where <15% of specimens have previously been described. We located all known fossil insects (n = 370) from Alderton Hill, and used these to create the first comprehensive taxonomic and taphonomic analysis of the entire assemblage. We show that a diverse palaeoentomofaunal assemblage is preserved, comprising 12 orders, 21 families, 23 genera and 21 species. Fossil disarticulation is consistent with insect decay studies. The number of orders is comparable with present-day assemblages from similar latitudes (30°–40°N), including the Azores, and suggests that the palaeoentomofauna reflects a life assemblage. At Alderton, Hemiptera, Coleoptera and Orthoptera are the commonest (56.1%) orders. The high abundance of Hemiptera (22.1%) and Orthoptera (13.4%) indicates well-vegetated islands, while floral changes related to the T-OAE may be responsible for hemipteran diversification. Predatory insects are relatively abundant (~10% of the total assemblage) and we hypothesise that the co-occurrence of fish and insects within the T-OAE represents a jubilee-like event. The marginally higher proportion of sclerotised taxa compared to present-day insect assemblages possibly indicates adaptation to environmental conditions or taphonomic bias. The coeval palaeoentomofauna from Strawberry Bank, Somerset is less diverse (9 orders, 12 families, 6 genera, 3 species) and is taphonomically biased. The Alderton Hill palaeoentomofauna is interpreted to be the best-preserved and most representative insect assemblage from Toarcian strata in the UK. This study provides an essential first step towards understanding the likely influence of the T-OAE on insects. [ABSTRACT FROM AUTHOR]