Increasing Sea Temperatures Research Articles

Predicting future thermal habitat suitability of competing native and invasive fish species: from metabolic scope to oceanographic modelling

Global increase in sea temperatures has been suggested to facilitate the incoming and spread of tropical invaders. The increasing success of these species may be related to their higher physiological performance compared with indigenous ones. Here, we determined the effect of temperature on the aerobic metabolic scope (MS) of two herbivorous fish species that occupy a similar ecological niche in the Mediterranean Sea: the native salema (Sarpa salpa) and the invasive marbled spinefoot (Siganus rivulatus). Our results demonstrate a large difference in the optimal temperature for aerobic scope between the salema (21.8°C) and the marbled spinefoot (29.1°C), highlighting the importance of temperature in determining the energy availability and, potentially, the distribution patterns of the two species. A modelling approach based on a present-day projection and a future scenario for oceanographic conditions was used to make predictions about the thermal habitat suitability (THS, an index based on the relationship between MS and temperature) of the two species, both at the basin level (the whole Mediterranean Sea) and at the regional level (the Sicilian Channel, a key area for the inflow of invasive species from the Eastern to the Western Mediterranean Sea). For the present-day projection, our basin-scale model shows higher THS of the marbled spinefoot than the salema in the Eastern compared with the Western Mediterranean Sea. However, by 2050, the THS of the marbled spinefoot is predicted to increase throughout the whole Mediterranean Sea, causing its westward expansion. Nevertheless, the regional-scale model suggests that the future thermal conditions of Western Sicily will remain relatively unsuitable for the invasive species and could act as a barrier for its spread westward. We suggest that metabolic scope can be used as a tool to evaluate the potential invasiveness of alien species and the resilience to global warming of native species.

High recruitment associated with increased sea temperatures towards the southern range edge of a Western Australian endemic reef fish Choerodon rubescens (family Labridae)

Choerodon rubescens is a subtropical wrasse endemic to Western Australia which has recently recruited in high abundance into lagoonal habitats at the southern end of its distribution. Abundance, size structure and habitat associations of juvenile C. rubescens were assessed during summer and autumn 2013 (January–May) via underwater visual census across available shallow water habitats towards the southern range edge of their distribution (32°S, 115°E). High abundances of juveniles (up to 14 fish/40 m2) were found in areas where they were previously absent or in low abundance. Lagoonal habitats presented abundances three to eight times higher than seagrass beds or rocky reef, indicating preference of C. rubescens for mixed lagoonal habitats as settlement grounds. Such habitats contain open sandy areas with small rocks and rubble that are important feeding grounds for juveniles. Based on the size structure of populations encountered, recruitment was estimated to occur during summer 2011–12 and 2012–13. This coincides with water temperatures 1 to 2 °C higher than long-term averages in the region, making conditions more favourable for recruits to survive in greater numbers. We conclude that the high abundance of C. rubescens recruits towards the southern end of their distribution together with trends of increasing water temperature and the availability of suitable settlement habitat to the south of their present range, indicate a capacity for the species to shift its distribution southwards. Monitoring of future recruitment events will be crucial to determining range expansion capacity and guiding management efforts for this endemic and important fisheries species.

Are regional fisheries’ catches changing with climate?

Climate change affects ocean conditions, which will in turn impact marine organisms and ecosystems, with consequences for fisheries. The Iberian Peninsula has faced an increase in both air and sea surface temperature, and rainfall has decreased in intensity and frequency in Portugal. As Portugal is the third highest per capita consumer of fish in the world and its coast is located in a biogeographic transition zone, between temperate and subtropical waters, the study of the effects of climate change on Portuguese fisheries is of the utmost importance. The present work focused on Setúbal, an important fishing port in central Portugal. Landings Per Unit of Effort (LPUE) time series (1927–2012) of the most important species were analysed and their relationships with sea surface temperature (SST), rainfall and the winter North Atlantic Oscillation (NAO) index were investigated. Mean annual SST has increased 0.9°C from 1926 to 2012. The main target species in 2012 were the same as in 1927. However, their landings have changed and have responded to changes in environmental variables, particularly SST. LPUE of the European sardine has shown a decreasing trend and was negatively correlated with SST and NAO, whereas the LPUE of the Atlantic chub mackerel has been increasing since 2000. The LPUE of the common cuttlefish has kept more or less stable through the studied time series, but it was correlated with SST. The LPUE of soles has increased with time and SST. The LPUE of the common octopus was correlated with SST and NAO and has presented higher values since 1975. Further increases in sea temperature in the future will pose challenges for fisheries in Setúbal. Purse-seine fisheries may try to compensate the expected losses in sardine landings by targeting the chub mackerel. Although landings of the most important species in multi-gear fisheries seem to have been favoured by increases in temperature, further studies on the tolerance of each particular species to increases in temperature are needed. As a recent increase in the relative importance of subtropical species in Portuguese fisheries has already been previously detected, climate change may also bring new fishing opportunities for this region.

THE IMPORTANCE OF TEMPERATURE IN FARMED SALMON GROWTH: REGIONAL GROWTH FUNCTIONS FOR NORWEGIAN FARMED SALMON

A reliable growth function is a vital part of deriving the optimal harvesting strategy and production plan for any aquaculture operation. The range of environmental and biological conditions along the Norwegian coast suggests that the growth of farmed salmon will differ from one region to another. We estimate an aggregated regional growth function for three different regions in Norway using monthly data from 2005 to 2011. There is currently some variation for the grow-out period, and Atlantic salmon is raised between 16–24 months to reach weights of 2–8 kg. These results indicate that an increase in sea temperature positively affects the growth in the regions of Northern and Central Norway, while an increase in sea temperatures negatively affect the growth in the Southern region.

Back to the future: The history of acroporid corals at the Flower Garden Banks, Gulf of Mexico, USA

Fossil elkhorn corals, Acropora palmata, were discovered at the Flower Garden Banks (FGB) on the shelf-margin off the Texas coast in 2006. Radiocarbon dating revealed an A. palmata-dominated community aged 10,157–6838 cal BP. The Acropora reefs correspond in time to an interval of warmer-than-present sea-surface temperatures (SSTs) during the Holocene thermal maximum (HTM). The subsequent demise of A. palmata in the middle Holocene was a consequence of the inability of the shallowest reef facies to keep pace with rising sea level following complete submergence of the banks, possibly coupled with decreasing SSTs following the HTM. In 2007, the first fossil staghorn corals, Acropora cervicornis, were discovered at the FGB. Based on radiocar­ bon dating of these corals to 1027–211 cal BP, it appears that populations of A. cervicornis flourished in deeper waters (~25–32 m depth) on the edges of the banks until the peak of the Little Ice Age (LIA) when they died, pre­ sumably from cold-water exposure. The recent return of A. palmata to reefs of the FGB associated with increasing sea temperatures appears to be both an echo of the past and a harbinger of the future. © 2013 Published by Elsevier B.V.

Increase in parasite burden and associated pathology in harbour porpoises (Phocoena phocoena) in West Greenland

Knowledge about parasitism in harbour porpoises and their health status around Greenland is scarce. This study provides knowledge about the poorly studied cetacean in its rapidly changing environment. Parasites and pathological findings in 20 harbour porpoises (Phocoena phocoena) hunted in waters around West Greenland are presented. Carcasses were dissected, and parasitological, histological and bacteriological investigations were carried out. Protozoa (Sarcocystis sp.), Nematoda (Halocercus invaginatus, Stenurus minor, Anisakis simplex sensu lato (s.l.), Crassicauda sp.), Trematoda (Campula oblonga) and Cestoda (Phyllobothrium delphini, Monorygma grimaldii) were found. Parasitic infection of the peribullar cavity and lung with pseudaliid nematodes was found in most animals. Sixty per cent of the porpoises were infected with stomach worms, and trematodes were present in liver and pancreas of 90 and 30 % of the porpoises, respectively. Crassicauda sp. was isolated from perimuscular fascia in 45 % of the animals. This is the first record of tetraphyllidean merocercoids in harbour porpoises. M. grimaldii and P. delphini were found in blubber layer of 15 % and abdominal cavity of 50 % of the porpoises. Bronchopneumonia, gastritis, cholangitis, pancreatitis and panniculitis were almost exclusively associated with parasitic infection and usually mild. Compared with a previous study of Greenlandic porpoises from 1995, a significant increase in severity of parasitic infections and the emergence of new parasite species were observed, most likely associated with changes in diet, influenced by increasing sea temperatures and receding ice cover.

Sequencing‐based gene network analysis provides a core set of gene resource for understanding thermal adaptation in Zhikong scallop Chlamys farreri

Marine organisms are commonly exposed to variable environmental conditions, and many of them are under threat from increased sea temperatures caused by global climate change. Generating transcriptomic resources under different stress conditions are crucial for understanding molecular mechanisms underlying thermal adaptation. In this study, we conducted transcriptome-wide gene expression profiling of the scallop Chlamys farreri challenged by acute and chronic heat stress. Of the 13953 unique tags, more than 850 were significantly differentially expressed at each time point after acute heat stress, which was more than the number of tags differentially expressed (320-350) under chronic heat stress. To obtain a systemic view of gene expression alterations during thermal stress, a weighted gene coexpression network was constructed. Six modules were identified as acute heat stress-responsive modules. Among them, four modules involved in apoptosis regulation, mRNA binding, mitochondrial envelope formation and oxidation reduction were downregulated. The remaining two modules were upregulated. One was enriched with chaperone and the other with microsatellite sequences, whose coexpression may originate from a transcription factor binding site. These results indicated that C.farreri triggered several cellular processes to acclimate to elevated temperature. No modules responded to chronic heat stress, suggesting that the scallops might have acclimated to elevated temperature within 3days. This study represents the first sequencing-based gene network analysis in a nonmodel aquatic species and provides valuable gene resources for the study of thermal adaptation, which should assist in the development of heat-tolerant scallop lines for aquaculture.

Seasonal increase in sea temperature triggers pancreas disease outbreaks in Norwegian salmon farms

Pancreas disease (PD) is a viral disease causing negative impacts on economy of salmon farms and fish welfare. Its transmission route is horizontal, and water transport by ocean currents is an important factor for transmission. In this study, the effect of temperature changes on PD dynamics in the field has been analysed for the first time. To identify the potential time of exposure to the virus causing PD, a hydrodynamic current model was used. A cohort of salmon was assumed to be infected the month it was exposed to virus from other infective cohorts by estimated water contact. The number of months from exposure to outbreak defined the incubation period, which was used in this investigation to explore the relationship between temperature changes and PD dynamics. The time of outbreak was identified by peak in mortality based on monthly records from active sites. Survival analysis demonstrated that cohorts exposed to virus at decreasing sea temperature had a significantly longer incubation period than cohorts infected when the sea temperature was increasing. Hydrodynamic models can provide information on the risk of being exposed to pathogens from neighbouring farms. With the knowledge of temperature-dependent outbreak probability, the farmers can emphasize prophylactic management, avoid stressful operations until the sea temperature is decreasing and consider removal of cohorts at risk, if possible.

Decline in Kelp in West Europe and Climate.

Kelp ecosystems form widespread underwater forests playing a major role in structuring the biodiversity at a regional scale. Some seaweeds such as Laminaria digitata are also economically important, being exploited for their alginate and iodine content. Although some studies have shown that kelp ecosystems are regressing and that multiple causes are likely to be at the origin of the disappearance of certain populations, the extent to which global climate change may play a role remains speculative. Here we show that many populations of L. digitata along European coasts are on the verge of local extinction due to a climate-caused increase in sea temperature. By modeling the spatial distribution of the seaweed, we evaluate the possible implications of global climate change for the geographical patterns of the species using temperature data from the Coupled Model Intercomparison Project phase 5 (CMIP5). Projections of the future range of L. digitata throughout the 21st century show large shifts in the suitable habitat of the kelp and a northward retreat of the southern limit of its current geographic distribution from France to Danish coasts and the southern regions of the United Kingdom. However, these projections depend on the intensity of warming. A medium to high warming is expected to lead to the extirpation of the species as early as the first half of the 21st century and there is high confidence that regional extinction will spread northwards by the end of this century. These changes are likely to cause the decline of species whose life cycle is closely dependent upon L. digitata and lead to the establishment of new ecosystems with lower ecological and economic values.

Seasonality and site fidelity of the zebra shark, Stegostoma fasciatum, in southeast Queensland, Australia

Site fidelity and migratory movements of vertebrate animals occur at many spatial and temporal scales. Larger migratory movements tend to occur in species that live in seasonal environments in which food supplies vary markedly, while species found in thermally stable environments are more site-attached. In the marine environment, seasonal migrations are often associated with predictable temporary aggregations that have largely been targeted for exploitation. We employed passive acoustic telemetry to investigate inter- and intraseasonal site fidelity of zebra sharks to an aggregation site in southeast Queensland, Australia, close to the southern latitudinal extent of this species' range. We tracked 10 zebra sharks over two aggregation seasons (21 months). We applied a generalized linear mixed-effects model to investigate the presence/absence of these zebra sharks with respect to several environmental variables. We found that different environmental factors were associated with site fidelity of zebra sharks at different temporal levels and that these may be indicative of the mechanisms driving the movements. Seasonal patterns may be driven by endogenous systems, and cues such as photoperiod and water temperature are likely to be important. Intraseasonal patterns are more likely to be indicative of direct behavioural responses to changes in environmental conditions such as increased wave heights, as well as foraging bouts away from a core refuge. Understanding the relative contributions of these environmental parameters, as well as biological factors, will be important for making predictions of site fidelity and movements of migratory marine vertebrates under differing future scenarios such as increases in sea temperature.

Thermal dependence of cardiac function in Arctic fish: implications of a warming world

With the Arctic experiencing one of the greatest and most rapid increases in sea temperatures in modern time, predicting how Arctic marine organisms will respond to elevated temperatures has become crucial for conservation biology. Here, we examined the thermal sensitivity of cardiorespiratory performance for three closely related species of sculpins that inhabit the Arctic waters, two of which, Gymnocanthus tricuspis and Myoxocephalus scorpioides, have adapted to a restricted range within the Arctic, whereas the third species, Myoxocephalus scorpius, has a wider distribution. We tested the hypothesis that the fish restricted to Arctic cold waters would show reduced cardiorespiratory scope in response to an increase in temperature, as compared with the more eurythermal M. scorpius. As expected from their biogeography, M. scorpioides and G. tricuspis maximised cardiorespiratory performance at temperatures between 1 and 4°C, whereas M. scorpius maximised performance over a wider range of temperatures (1-10°C). Furthermore, factorial scope for cardiac output collapsed at elevated temperature for the two high-latitude species, negatively impacting their ability to support aerobically driven metabolic processes. Consequently, these results concurred with our hypothesis, suggesting that the sculpin species restricted to the Arctic are likely to be negatively impacted by increases in ocean temperatures.

Effects of thermal stress on early developmental stages of a gorgonian coral

Ongoing sea temperature increase threatens reefs worldwide. In this study we experimentally examined for the first time the response of the early life stages of a long-lived structural gorgonian, the Mediterranean species Paramuricea clavata (Risso 1826), to the highest summer temperature recorded so far in the study area (25°C; the Medes Islands, Northwestern Mediterranean). This temperature also simulates the end-of-century predicted warming (+3°C) over the temperature maxima recorded during the species' reproductive period. The results showed a severe negative impact of constant thermal stress on the viability of P. clavata embryos and larvae, resulting in reduced survivorship, completely abnormal embryonic development and impaired metamorphosis. The deteriorating effect was rapid for embryos (after 7 h), whereas the impact on larvae became evident after 10 d of stress. Larval modifications started 7 d earlier under elevated temperature conditions, but the appearance of spherical, aberrant shapes prevented an assessment of whether metamorphosis was initiated but abnormal, or deterred altogether. The apparent higher sensitivity of embryos suggests that thermal stress during embryonic develop- ment may be the most critical factor for the viability of P. clavata larvae. In the context of an ongo- ing warming trend, the reduced viability of early life stages would jeopardize the persistence of P. clavata, which relies on successful recruitment for replenishment of its populations. Further research into the effects of thermal stress on the reproduction of structural invertebrate species and the viability of their early life stages will improve our understanding of the long-term conse- quences of environmental global change in marine benthic communities.

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.

Reaching the limit: Constrained behavioural flexibility of juvenile Atlantic cod (Gadus morhua) at current coastal temperatures

The currently rising sea temperatures are expected to affect the structure of aquatic communities. Through increased metabolic rates, activity and feeding motivation, higher temperature can be expected to add to competition and predation risk for many small fish and juveniles. However, behavioural flexibility e.g. individual variation in the expression of behavioural traits may act to buffer the detrimental effects of increased temperature. In the present study we ask how juvenile Atlantic cod respond to food availability and predation risk at the limits of their current natural temperature at the Icelandic coast (3°C–13°C). At 13°C Atlantic cod juveniles responded less to risk, remaining active, dispersed and leaving shelter positions earlier. However, at the same time their feeding attempts reduce significantly and correspondingly to the lower temperature. Therefore, our results suggest that at 13°C Atlantic cod juveniles do not adjust their behaviour to manage the increased feeding motivation while under risk. However, we do find evidence for individual variation in how behaviour is expressed across treatments indicating natural variation that could respond to selection. In conclusion, our results suggest that increased sea temperature could have both immediate negative effects on survival and initiate a selective response in Atlantic cod populations.

Ocean warming alters species abundance patterns and increases species diversity in an African sub‐tropical reef‐fish community

AbstractThe impacts of ocean warming resulting from recent climate change on the abundance patterns of marine species have been well documented in temperate seas of the northern hemisphere, but the impacts of a widening tropical belt are largely unexplored. Using measurements of sea surface temperature and spear‐fishing records for 84 species spanning a 19‐yr period, we examined the effects of ocean warming on a sub‐tropical reef‐fish community on the southeastern coast of Africa. Corresponding with a 0.46°C increase in average sea surface temperature between the time periods 1989–97 and 2002–2007, the ratio of species showing an overall decrease/ no change/increase in abundance was 1 : 3 : 2 among six species at the northern limits of their distribution in the region (temperate species), 1 : 15 : 6 among 22 broadly distributed species, and 1 : 5 : 9 among 15 species at the southern limits of their distribution (tropical species). Also, the relative abundance of temperate species as a whole decreased by 10–13% whereas that of tropical species increased by 9%, and broadly distributed species showed little change. Average species richness and diversity increased 33 and 15% respectively between the two time periods. These results are broadly consistent with a predicted poleward shift in species ranges and a predicted increase in species richness and diversity with increasing sea temperature. Our findings confirm that large‐scale climate change causing a widening of the tropical belt and subsequent ocean warming is having a profound impact on marine species abundance patterns and community composition at a local scale in the sub‐tropics.

Harbour porpoises respond to climate change

The effects of climate change on marine ecosystems and in particular on marine top predators are difficult to assess due to, among other things, spatial variability, and lack of clear delineation of marine habitats. The banks of West Greenland are located in a climate sensitive area and are likely to elicit pronounced responses to oceanographic changes in the North Atlantic. The recent increase in sea temperatures on the banks of West Greenland has had cascading effects on sea ice coverage, residency of top predators, and abundance of important prey species like Atlantic cod (Gadus morhua). Here, we report on the response of one of the top predators in West Greenland; the harbour porpoise (Phocoena phocoena). The porpoises depend on locating high densities of prey species with high nutritive value and they have apparently responded to the general warming on the banks of West Greenland by longer residence times, increased consumption of Atlantic cod resulting in improved body condition in the form of larger fat deposits in blubber, compared to the situation during a cold period in the 1990s. This is one of the few examples of a measurable effect of climate change on a marine mammal population.

Novel Ecosystems: Altering Fish Assemblages in Warming Waters

The effects of increasing sea temperatures extend far beyond changes in species' distributions. By altering local fish abundances, temperature changes will have profound effects on the structure, functioning and services of marine ecosystems.

Safeguarding coastal coral communities on the central Great Barrier Reef (Australia) against climate change: realizable local and global actions

The threats of wide-scale coral bleaching and reef demise associated with anthropogenic (global) climate change are widely known. Less well considered is the contributing role of conditions local to the reef, in particular reef water quality, in co- determining the physiological tolerance of corals to increasing sea temperatures and declining pH. Here, the modelled benefit of reduced exposure to dissolved inorganic nitrogen (DIN) in terrestrial runoff, which raises the thermal tolerance of coastal coral communities on the central Great Barrier Reef (Australia), is considered alongside alternative future warming scenarios. The simulations highlight that an 80% reduction in DIN 'buys' an additional ~50-60 years of reef-building capacity for No Mitigation ('business-as-usual') bleaching projections. Moreover, the integrated management benefits provided by: (i) local reductions of ~50% in DIN contained in river loads, and (ii) global stabilisation of atmospheric CO2 below 450 ppm can help ensure the persistence of hard- coral-dominated reefscapes beyond 2100. The simulations reinforce the message that

Biological invasions and climatic warming: implications for south-eastern Aegean ecosystem functioning

The Aegean Sea, due to the complexity and variety of morphological features, bathymetry, hydrological, hydrodynamic features and climatic characteristics, offers a unique opportunity for monitoring the spreading and/or invasion of alien biota. It is known that the establishment of warm/tropical marine alien species is related mainly to the increase in sea temperature. A significant increase in aliens' number along the southern Aegean (Dodecanese) coasts has been documented in the last twenty years, while their arrival has produced evident changes in coastal ecosystem composition and function. Although the study area acts as a crossroad for tropical alien species introduction in the eastern Mediterranean Sea, a direct attempt to link temperature alterations with new alien species arrivals has not been performed. Satellite and in situ derived marine temperature data showed that the study area has gone through a remarkable warming, while the link between global temperatures and regional ones revealed that this warming is not a local phenomenon but part of global climate trends. Examining relationships between new alien species arrivals data since 1929 against global temperatures, it is shown that their introduction rate parallels the significant increase of marine temperatures. The association of alien introductions with marine water warming, as well as potential effects on ecosystem functioning of selected species is discussed.

Infection of North Sea cod, Gadus morhua L., larvae with the parasitic nematode Hysterothylacium aduncum Rudolphi

Investigation of 2197 cod larvae and post-larvae collected in the North Sea revealed high prevalence of infection with a parasitic anisakid nematode identified morphologically and genetically as Hysterothylacium aduncum. Nematodes were third stage larvae and were almost exclusively found in the body cavity and they were never encapsulated. Prevalence increased significantly from 1992 to 2001 concomitantly with increased sea temperature. The possibility that the extent of parasitism is influenced by temperature change is discussed.