Hypoxia is a mounting problem affecting the world’s coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O2/liter to designate waters as hypoxic is below the empirical sublethal and lethal O2 thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated. benthic community oxygen coastal ecosystems eutrophication impacts D issolved oxygen in coastal waters has changed drastically over the past decades, arguably more so than any other ecologically important variable (1, 2), leading to the widespread occurrence of hypoxia. An assessment of the literature shows that the number of coastal sites where hypoxia has been reported has increased with an exponential growth rate of 5.54% year 1 over time [Fig. 1 and supporting information (SI) Table S1]. Although this growth rate can be partially attributed to an increased observational effort, increasing the number of costal ecosystems monitored and the likelihood of detecting hypoxia therein, this growth also reflects an increase in the prevalence of hypoxia in different types of coastal ecosystems. Multiple reports from careful monitoring time series provide evidence for an unambiguous increase in the number of hypoxic zones and their extension, severity, and duration (3–6). This growth is expected to continue because the prevalence of hypoxia is forecast to increase further owing to the combined effects of eutrophication, leading to the excessive production of organic matter that increases the oxygen demand of coastal ecosystems (7), and the increase in temperature caused by climate change, which enhances the respiratory oxygen demand of the organisms (8), reduces oxygen solubility (9), and reduces the ventilation of coastal waters by affecting stratification patterns (10).

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Thresholds of hypoxia for marine biodiversity.

Despite uncertainty in all levels of analysis, recent and long-term changes in our climate point to the distinct possibility that greenhouse gas emissions have altered mean annual temperatures, precipitation and weather patterns. Modeling efforts that use doubled atmospheric CO2 scenarios predict a 1–7°C mean global temperature increase, regional changes in precipitation patterns and storm tracks, and the possibility of “surprises” or sudden irreversible regime shifts. The general effects of climate change on freshwater systems will likely be increased water temperatures, decreased dissolved oxygen levels, and the increased toxicity of pollutants. In lotic systems, altered hydrologic regimes and increased groundwater temperatures could affect the quality of fish habitat. In lentic systems, eutrophication may be exacerbated or offset, and stratification will likely become more pronounced and stronger. This could alter food webs and change habitat availability and quality. Fish physiology is inextricably linked to temperature, and fish have evolved to cope with specific hydrologic regimes and habitat niches. Therefore, their physiology and life histories will be affected by alterations induced by climate change. Fish communities may change as range shifts will likely occur on a species level, not a community level; this will add novel biotic pressures to aquatic communities. Genetic change is also possible and is the only biological option for fish that are unable to migrate or acclimate. Endemic species, species in fragmented habitats, or those in east–west oriented systems will be less able to follow changing thermal isolines over time. Artisanal, commercial, and recreational fisheries worldwide depend upon freshwater fishes. Impacted fisheries may make it difficult for developing countries to meet their food demand, and developed countries may experience economic losses. As it strengthens over time, global climate change will become a more powerful stressor for fish living in natural or artificial systems. Furthermore, human response to climate change (e.g., increased water diversion) will exacerbate its already-detrimental effects. Model predictions indicate that global climate change will continue even if greenhouse gas emissions decrease or cease. Therefore, proactive management strategies such as removing other stressors from natural systems will be necessary to sustain our freshwater fisheries.

/pdf/potential-impacts-of-global-climate-change-on-freshwater-4agnfth259.pdf

Potential impacts of global climate change on freshwater fisheries

Abstract The American Fisheries Society (AFS) herein provides a list of all native freshwater mussels (families Margaritiferidae and Unionidae) in the United States and Canada. This report also provides state and provincial distributions; a comprehensive review of the conservation status of all taxa; and references on biology, conservation, and distribution of freshwater mussels. The list includes 297 native freshwater mussels, of which 213 taxa (71.7%) are considered endangered, threatened, or of special concern. Twenty-one taxa (7.1%) are listed as endangered but possibly extinct, 77 (20.6%) as endangered but extant, 43 (14.5%) as threatened, 72 (24.2%) as of special concern, 14 (4.7%) as undetermined, and only 70 (23.6%) as currently stable. The primary reasons for the decline of freshwater mussels are habitat destruction from dams, channel modification, siltation, and the introduction of nonindigenous mollusks. The high numbers of imperiled freshwater mussels in the United States and Canada, which har...

/pdf/conservation-status-of-the-freshwater-mussels-of-the-united-30ebv3vga8.pdf

Conservation status of the freshwater mussels of the United States and Canada

The American Fisheries Society (AFS) herein provides a list of all native freshwater mussels (families Margaritiferidae and Unionidae) in the United States and Canada. This report also provides state and provincial distributions; a comprehensive review of the conservation status of all taxa; and references on biology, conservation, and distribution of freshwater mussels. The list includes 297 native freshwater mussels, of which 213 taxa (71.7%) are considered endangered, threatened, or of special concern. Twenty-one taxa (7.1%) are listed as endangered but possibly extinct, 77 (20.6%) as endangered but extant, 43 (14.5%) as threatened, 72 (24.2%) as of special concern, 14 (4.7%) as undetermined, and only 70 (23.6%) as currently stable. The primary reasons for the decline of freshwater mussels are habitat destruction from dams, channel modification, siltation, and the introduction of nonindigenous mollusks. The high numbers of imperiled freshwater mussels in the United States and Canada, which har...

Conservation Status of Freshwater Mussels of the United States and Canada

The potent analgesic effects of cannabis-like drugs and the presence of CB1-type cannabinoid receptors in pain-processing areas of the brain and spinal cord, indicate that endogenous cannabinoids such as anandamide may contribute to the control of pain transmission within the central nervous system (CNS). Here we show that anandamide attenuates the pain behaviour produced by chemical damage to cutaneous tissue by interacting with CB1-like cannabinoid receptors located outside the CNS. Palmitylethanolamide (PEA), which is released together with anandamide from a common phospholipid precursor, exerts a similar effect by activating peripheral CB2-like receptors. When administered together, the two compounds act synergistically, reducing pain responses 100-fold more potently than does each compound alone. Gas-chromatography/mass-spectrometry measurements indicate that the levels of anandamide and PEA in the skin are enough to cause a tonic activation of local cannabinoid receptors. In agreement with this possibility, the CB1 antagonist SR141716A and the CB2 antagonist SR144528 prolong and enhance the pain behaviour produced by tissue damage. These results indicate that peripheral CB1-like and CB2-like receptors participate in the intrinsic control of pain initiation and that locally generated anandamide and PEA may mediate this effect.

Control of pain initiation by endogenous cannabinoids

Invasive species have been characterized as tolerant of environmental extremes. This hypothesis was evaluated for invasive aquatic species in North America, particularly Asian clams, Corbicula flum...

Evolutionary and physiological adaptations of aquatic invasive animals: r selection versus resistance

12 – Ecology of an Invasive Pest Bivalve, Corbicula

Following acclimation to 5°, 15° or 25°C for 14 days, samples of 30 Dreissena polymorpha (zebra mussels) and Corbicula fluminea (Asian clams) were held in either aerated (control) or extremely hypoxic N2 gassed water (PO2 , 3% of full air saturation). Mortality was negligible in all aerated controls. Mean hypoxia tolerance in D. polymorpha ranged from 3‐4 days at 25°C to 38‐42 days at 5°C. Hypoxia tolerance time of zebra mussels increased significantly with declining test temperature (P , 0.001) and increasing acclimation temperature (P , 0.001). Larger zebra mussels were more tolerant than smaller individuals. Asian clams were 2‐7 times more tolerant of hypoxia than zebra mussels, surviving a mean of 11.8 and 35.1 days at 25°C and 15°C, respectively, and without mortality for 84 days at 5°C, and were not influenced by temperature acclimation. At 25°C, larger specimens of Asian clams were less tolerant of hypoxia than smaller individuals. Both species are amongst the least hypoxia tolerant freshwater bivalve molluscs, reflecting their prevalence in well-oxygenated shallow water habitats. Prolonged exposure to extreme hypoxia may provide an efficacious control strategy, particularly for D. polymorpha.

Effects of temperature and temperature acclimation on survival of zebra mussels (Dreissena polymorpha) and Asian clams (Corbicula fluminea) under extreme hypoxia

North American (NA) freshwater bivalve molluscs (class Bivalvia) fall in the subclasses Paleoheterodonta (Superfamily Unionoidea) and Heterodonta (Superfamilies Corbiculoidea and Dreissenoidea). They have enlarged gills with elongated, ciliated filaments for suspension feeding on plankton, algae, bacteria, and microdetritus. The mantle tissue underlying and secreting the shell forms a pair of lateral, dorsally connected lobes. Mantle and shell are both single entities. During development, the right and left mantle lobes extend ventrally from the dorsal visceral mass to enfold the body. Each lobe secrets a calcareous shell valve which remains connected by a mid-dorsal isthmus. Like all molluscs, the shell valves consist of outer proteinaceous and inner crystalline calcium carbonate elements. The lateral mantle lobes secrete shell material marked by a high proportion of crystalline calcium carbonate making them thick, strong and inflexible, while the mantle isthmus secretes primarily protein, forming a dorsal elastic hinge ligament uniting the calcareous valves. The hinge ligament is external in all freshwater bivalves. Its elasticity opens the valves while the anterior and posterior shell adductor muscles run between the valves and close them in opposition to the hinge ligament which opens them on adductor muscle relaxation. The key presented in this chapter, as well as many of the major keys to freshwater bivalves, relies on the integrated use of important anatomical structures and shell characters to identify unionoidean bivalves. This key is artificial, and it is divided into four sections corresponding to geographical provinces to facilitate identification.

11 – mollusca: bivalvia

All larger intertidal animals are alternately aerial and aquatic in habit. The majority of littoral molluscs (surprisingly including bivalves as well as gastropods) are adapted for respiration both as air-breathers and by aquatic ventilation of ctenidia or other â€œ?�gillâ€ structures. Temperature relations of aquatic respiration in one of the most common littoral snails, Littorina littorea have been extensively investigated ( Newell, 1969, 1973 ; Newell and Pye, 1970a, b, 1971a, b ; Pye and Newell, 1973 ; Newell and Roy, 1973) , and the occurrence of some degree of regulation in â€œ?�standard metabolismâ€ has been established for that species (Newell and Pye, 1970b ; Pye and Newell, 1973). Comparative studies on congeneric and other related intertidal snails are less extensive ( Sandison, 1966, 1967; Toulmond, 1967a, b). The present report deals with teniperature-induced shifts in oxygen uptake rates for the aquatic respiration of six (and the aerial respiration of four) species of littoral and sublittoral snails. Parallel studies (McMahon and Russell-Hunter, 1974, 1977) on responses to low oxygen stress revealed considerable interspecific differences, but these were less related to vertical zonation on seashores than to microenvironmental factors and to the physiological adaptations of each individual species. With interspecific (and even with infra specific) differences in temperature relations, we are soniewhat more directly con cerned with degrees of aerial exposure and hence with the principal patterns of their distributional ecology including intertidal vertical zonation. Using oxygen electrodes, respiration rates in sea water over a range of natural temperatures were deterniined for Acmaea testudinalis, Mitrella lunata, Lacuna vincta, Littorina obtusata, L. littorea, and L. saxatilis. Corresponding aerial respiration rates were determined for Acmaea and for the three Littorina spp. Early results in these investigations were reported in two preliminary abstracts (McMahon and Russell-Hunter, 1973; Russell-Hunter and McMahon, 1974).

Robert F. McMahon

Papers

Evolutionary and physiological adaptations of aquatic invasive animals: r selection versus resistance

12 – Ecology of an Invasive Pest Bivalve, Corbicula

Effects of temperature and temperature acclimation on survival of zebra mussels (Dreissena polymorpha) and Asian clams (Corbicula fluminea) under extreme hypoxia

11 – mollusca: bivalvia

Temperature relations of aerial and aquatic respiration in six littoral snails in relation to their vertical zonation