Manganese (Mn) is an essential trace metal for all organisms. However, in excess it causes toxic effects but the impact on aquatic environments has so far been highly overlooked. Manganese is ...abundant both in costal and deep sea sediments and becomes bioavailable (Mn2+) during redox conditions. This is an increasing phenomenon due to eutrophication-induced hypoxia and aggravated through the ongoing climate change. Intracellular accumulation of Mn2+ causes oxidative stress and activates evolutionary conserved pathways inducing apoptosis and cell cycle arrest. Here, studies are compiled on how excess of dissolved Mn suppresses the immune system of various aquatic organisms by adversely affecting both renewal of immunocytes and their functionality, such as phagocytosis and activation of pro-phenoloxidase. These impairments decrease the animal's bacteriostatic capacity, indicating higher susceptibility to infections. Increased distribution of pathogens, which is believed to accompany climate change, requires preserved immune sentinel functions and Mn can be crucial for the outcome of host-pathogen interactions.
•Manganese (Mn) is essential for all organisms but toxic at high concentrations.•In the sea Mn becomes bioavailable due to eutrophication and climate change.•Excess of Mn causes oxidative stress and induces cell death pathways.•Thus causing immunosuppression and increased susceptibility for infections.•Such immune defects are crucial for health and survival of aquatic organisms.
The potential for climate-related spread of infectious diseases through marine systems has been highlighted in several reports. With this review we want to draw attention to less recognized ...mechanisms behind vector-borne transmission pathways to humans. We have focused on how the immune systems of edible marine shellfish, the blue mussels and Norway lobsters, are affected by climate related environmental stressors. Future ocean acidification (OA) and warming due to climate change constitute a gradually increasing persistent stress with negative trade-off for many organisms. In addition, the stress of recurrent hypoxia, inducing high levels of bioavailable manganese (Mn) is likely to increase in line with climate change. We summarized that OA, hypoxia and elevated levels of Mn did have an overall negative effect on immunity, in some cases also with synergistic effects. On the other hand, moderate increase in temperature seems to have a stimulating effect on antimicrobial activity and may in a future warming scenario counteract the negative effects. However, rising sea surface temperature and climate events causing high land run-off promote the abundance of naturally occurring pathogenic Vibrio and will in addition, bring enteric pathogens which are circulating in society into coastal waters. Moreover, the observed impairments of the immune defense enhance the persistence and occurrence of pathogens in shellfish. This may increase the risk for direct transmission of pathogens to consumers. It is thus essential that in the wake of climate change, sanitary control of coastal waters and seafood must recognize and adapt to the expected alteration of host-pathogen interactions.
•Stressors induced by climate changes are causing immunosuppressed invertebrates with impaired bacteriostatic capacity.•Climate changes increase distribution and abundance of human pathogens in coastal waters.•Resulting in: Increased risk for pathogen transmission to shellfish consumers Need for more reliable pathogen indicators.
Ocean acidification (OA) can shift the ecological balance between interacting organisms. In this study, we have used a model system to illustrate the interaction between a calcifying host organism, ...the blue mussel Mytilus edulis and a common bivalve bacterial pathogen, Vibrio tubiashii, with organisms being exposed to a level of acidification projected to occur by the end of the 21st century. OA exposures of the mussels were carried out in relative long‐term (4 months) and short‐term (4 days) experiments. We found no effect of OA on the culturability of V. tubiashii, in broth or in seawater. OA inhibited mussel shell growth and impaired crystalline shell structures but did not appear to affect mussel immune parameters (i.e haemocyte counts and phagocytotic capacity). Despite no evident impact on host immunity or growth and virulence of the pathogen, V. tubiashii was clearly more successful in infecting mussels exposed to long‐term OA compared to those maintained under ambient conditions. Moreover, OA exposed V. tubiashii increased their viability when exposed to haemocytes of OA‐treated mussel. Our findings suggest that even though host organisms may have the capacity to cope with periods of OA, these conditions may alter the outcome of host–pathogen interactions, favouring the success of the latter.
•Experimental exposure of sea stars and brittle stars to manganese (∼12mgL−1).•For both species the capacity to turn from dorsal to ventral posture was reduced by ∼50% when exposed to Mn.•The motoric ...disorder was not restored after two weeks of recovery from Mn-exposure.•Manganese accumulated 5 fold in tube feet, organs involved in their turning-over activity, of sea stars and remained high after two weeks of recovery.•Acetylcholinesterase activity increased with increasing levels of Mn in the tube feet.
In the oceans, naturally occurring manganese (Mn) is released from the sediments during events of hypoxia. While neuro- and immuno-toxic effects of bioavailable manganese are well documented for crustaceans, studies of similar effects of manganese on other marine invertebrates are comparatively few. Here, we developed a new functional test “the repeated turning assay” to investigate if manganese exposure at ∼12mgL−1 affected motoric behaviour of two asteroid echinoderms, the Common sea star, Asterias rubens, and the Black brittle star, Ophiocomina nigra. By measuring of the turning-over capacity, from dorsal to ventral position, after one and two weeks of manganese exposure, we showed that for both species Mn exposure significantly delayed the ability to turn. After a recovery period of two weeks, the capacity of turning-over was not restored to that of unexposed animals neither for A. rubens nor for O. nigra. Further investigation of sea stars showed that Mn accumulated ∼5 fold in the tube feet, organs involved in their turning-over activity, and the high concentration remained after the recovery period. In the tube feet we also recorded an increased activity of acetylcholinesterase (AChE), here used as a proxy for neuromuscular disturbances. The results indicated that Mn induces neuromuscular disturbance in echinoderms which is important news, given that previous studies have concluded that adult echinoderms are relatively tolerant to Mn.
The Norway lobster Nephrops norvegicus lives at low-light depths, in muddy substrata of high organic content where water salinities are high and fluctuations in temperature are moderate. In this ...environment, the lobsters are naturally exposed to a number of potential stressors, many of them as a result of the surficial breakdown of organic material in the sediment. This process (early diagenesis) creates a heterogeneous environment with temporal and spatial fluctuations in a number of compounds such as oxygen, ammonia, metals, and hydrogen sulphide. In addition to this, there are anthropogenically generated stressors, such as human-induced climate change (resulting in elevated temperature and ocean acidification), pollution and fishing. The lobsters are thus exposed to several stressors, which are strongly linked to the habitat in which the animals live. Here, the capacity of Nephrops to deal with these stressors is summarised. Eutrophication-induced hypoxia and subsequent metal remobilisation from the sediment is a well-documented effect found in some wild Nephrops populations. Compared to many other crustacean species, Nephrops is well adapted to tolerate periods of hypoxia, but prolonged or severe hypoxia, beyond their tolerance level, is common in some areas. When the oxygen concentration in the environment decreases, the bioavailability of redox-sensitive metals such as manganese increases. Manganese is an essential metal, which, taken up in excess, has a toxic effect on several internal systems such as chemosensitivity, nerve transmission and immune defence. Since sediment contains high concentrations of metals in comparison to sea water, lobsters may accumulate both essential and non-essential metals. Different metals have different target tissues, though the hepatopancreas, in general, accumulates high concentrations of most metals. The future scenario of increasing anthropogenic influences on Nephrops habitats may have adverse effects on the fitness of the animals.
We compared eelgrass Zostera marina communities in 3 regions in Sweden believed to be affected by eutrophication and overfishing, to determine whether bottom-up or top-down processes control the ...biomass of epiphytic macroalgae and grazers. Nitrogen and carbon isotope signatures were analyzed to explore the food webs and to identify the grazing species feeding on filamentous algae and/or eelgrass. Mixing model (IsoSource version 1.3.1) analysis of the isotope signatures indicated that the amphipods Gammarus locusta and Microdeutopus gryllotalpa fed primarily on filamentous algae and that only 2 small gastropod species consumed eelgrass. Moreover, the grass shrimp Palaemon elegans and P. adspersus were ca. 1 trophic level above amphipods and algae, but according to the mixing model played different trophic roles in the different areas. The highest biomass of filamentous algae was found in the west coast beds housing grazers with the lowest biomass and mean size (predominantly G. locusta and M. gryllotalpa, 0.5 to 3 mm). In contrast, the Baltic Sea beds had low algal biomass, but the grazers (mostly G. locusta and Idotea baltica) had higher biomass and were significantly larger (mean size ca. 10 mm). An overall negative correlation was found between grazer biomass and biomass of filamentous algae. The significantly smaller grazers and absence of isopod grazers on the west coast may be due to substantial consumption by small predatory fish. This supports the suggestions that, in Swedish eelgrass beds, grazers are top-down controlled, and overexploitation of large predators and eutrophication play an important role in the recent increases in algal biomass.
Kelp forests are productive coastal ecosystems that provide a range of ecosystem services. Mapping the distribution and area occupied by kelp forests is a critical step to identify their ecosystem ...functions and services, including their role in the carbon cycle, and to detect changes in their distribution. We compiled quantitative data of the dominant genera
Laminaria
and
Saccharina
across the Nordic region, allowing us to separate kelp forests (areas with dense or moderately dense kelp coverage) from occurrences of single or few individuals. By fitting boosted regression trees to the compiled data, we modelled and predicted the distribution of kelp forests across the Nordic region. Despite the large scale of the analyses, the models captured well the kelps’ environmental affinities and predicted the presence of kelp forests with high accuracy. Dense kelp forests are found along the rocky shores of all the Nordic countries, except in the brackish Baltic Sea, with largest areas in Norway, Greenland and Iceland. The results of this study set the scene for future studies on the importance of kelp forests in the Nordic region, including their contribution to the marine carbon budget.
In the oceans, naturally occurring manganese (Mn) is released from the sediments during events of hypoxia. While neuro- and immuno-toxic effects of bioavailable manganese are well documented for ...crustaceans, studies of similar effects of manganese on other marine invertebrates are comparatively few. Here, we developed a new functional test “the repeated turning assay” to investigate if manganese exposure at ∼12 mg L−1 affected motoric behaviour of two asteroid echinoderms, the Common sea star, Asterias rubens, and the Black brittle star, Ophiocomina nigra. By measuring of the turning-over capacity, from dorsal to ventral position, after one and two weeks of manganese exposure, we showed that for both species Mn exposure significantly delayed the ability to turn. After a recovery period of two weeks, the capacity of turning-over was not restored to that of unexposed animals neither for A. rubens nor for O. nigra. Further investigation of sea stars showed that Mn accumulated ∼5 fold in the tube feet, organs involved in their turning-over activity, and the high concentration remained after the recovery period. In the tube feet we also recorded an increased activity of acetylcholinesterase (AChE), here used as a proxy for neuromuscular disturbances. The results indicated that Mn induces neuromuscular disturbance in echinoderms which is important news, given that previous studies have concluded that adult echinoderms are relatively tolerant to Mn.
Shells of
Arctica islandica
collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak (Swedish West Coast) were used to monitor local climate variations and the influence of human ...activities on the local environment. For this purpose, we analysed the growth, structure and chemical composition of these shells and compared them with shells collected from Kiel Bay, Norway and Iceland. The growth rate of the studied shells registers an NAO periodicity of ca 8 years. However, the observed signal is weak because of other environmental interferences that are either of natural or anthropogenic origin. For example, the oxygen isotope ratios show temperature fluctuation, but also the influx of low salinity water. Higher contents of S, N, Cu, Zn, As, Cd and P in shell portions formed during the last century are related to human activities such as mining and industrial development. Our study indicates that in order to use
Arctica
shells as archives of climate change it is necessary to study the full range of environmental data that is recorded in the shells by using a multi element and isotope approach in combination with different analytical techniques including investigation of growth rates and shell structure.
The interaction between bottom-up and top-down processes in coastal ecosystems has been scarcely studied so far. Temporal changes in trophic interactions of Zostera marina along the Swedish west ...coast are relatively well studied, with the exception of epifaunal communities. Epifauna was used as a model study to explore resource (bottom-up) or predator (top-down) regulated in a vegetated ecosystem. We conducted a 21-year comparative study (1997 and 2018) using epifauna of 19 Zostera marina meadows along the Swedish Skagerrak coast. Large changes were observed in the composition of small (0.2–1 mm) and large (>1 mm) epifauna. In the small-sized epifauna, the nematode Southernia zosterae and harpacticoids showed an increase of 90% and a decrease of 50% of their abundances, respectively. In the large-sized epifauna, the polychaete Platynereis dumerilii and chironomid larvae were absent in 1997 but thrived in 2018 (>2000 ind. m−2). Mesoherbivores (Idoteids and gammarids) were locally very abundant in 1997 but disappeared in 2018. An 83% decline of mytilids settling in Zostera marina leaves was observed. Our results showed that epifauna is predominantly top-down regulated. An integrative framework of the study area is outlined to shed light on the causes and consequences of the environmental shifts reported in Zostera meadows from the northern Skagerrak area throughout the last three decades.
•Epifaunal communities greatly varied from 1997 to 2018.•Epifauna is mainly top-down regulated.•Filamentous algae thrive in the study region.•Several shifts on Zostera marina meadows from the Skagerrak coast
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