CO2 currently accumulating in the atmosphere permeates into ocean surface layers, where it may impact on marine animals in addition to effects caused by global warming. At the same time, several countries are developing scenarios for the disposal of anthropogenic CO2 in the worlds' oceans, especially the deep sea. Elevated CO2 partial pressures (hypercapnia) will affect the physiology of water breathing animals, a phenomenon also considered in recent discussions of a role for CO2 in mass extinction events in earth history. Our current knowledge of CO2 effects ranges from effects of hypercapnia on acid-base regulation, calcification and growth to influences on respiration, energy turnover and mode of metabolism. The present paper attempts to evaluate critical processes and the thresholds beyond which these effects may become detrimental. CO2 elicits acidosis not only in the water, but also in tissues and body fluids. Despite compensatory accumulation of bicarbonate, acid-base parameters (pH, bicarbonate and CO2 levels) and ion levels reach new steady-state values, with specific, long-term effects on metabolic functions. Even though such processes may not be detrimental, they are expected to affect long-term growth and reproduction and may thus be harmful at population and species levels. Sensitivity is maximal in ommastrephid squid, which are characterized by a high metabolic rate and extremely pH-sensitive blood oxygen transport. Acute sensitivity is interpreted to be less in fish with intracellular blood pigments and higher capacities to compensate for CO2 induced acid-base disturbances than invertebrates. Virtually nothing is known about the degree to which deep-sea fishes are affected by short or long term hypercapnia. Sensitivity to CO2 is hypothesized to be related to the organizational level of an animal, its energy requirements and mode of life. Long-term effects expected at population and species levels are in line with recent considerations of a detrimental role of CO2 during mass extinctions in the earth's history. Future research is needed in this area to evaluate critical effects of the various CO2 disposal scenarios.

/pdf/biological-impact-of-elevated-ocean-co2-concentrations-3pqkmtp446.pdf

Biological Impact of Elevated Ocean CO2 Concentrations: Lessons from Animal Physiology and Earth History

In Lake Nabugabo, Uganda, a satellite of Lake Victoria, f50% of the indigenous fishes disappeared from the open waters subsequent to the establishment of the introduced predatory Nile perch, Lates niloticus. This pattern is similar to the faunal loss experienced in the much larger Lake Victoria. Several of these species persisted in wetland refugia (e.g. ecotonal wetlands, swamp lagoons); however, deep swamp refugia (habitats lying well within the dense interior of fringing wetlands), are available only to a subset of the basin fauna with extreme tolerance to hypoxia. Although airbreathers are common in deep swamp refugia; we also documented a surprisingly high richness and abundance of nonair-breathing fishes. We describe several mechanisms that may facilitate survival in deep swamp refugia including high hemoglobin concentration, high hematocrit, large gill surface area and a low critical oxygen tension (P ). In addition, c swamp-dwelling fishes showed lower PO thresholds for onset of aquatic surface respiration than the lake-dwelling 2 fishes. This suggests higher tolerance to hypoxia in the swamp fishes because they are able to withstand a lower oxygen tension before approaching the surface. We suggest that physiological refugia may be important in modulating the impact of Nile perch and indigenous fishes in the Lake Nabugabo region; this highlights the need to evaluate relative tolerance of introduced predators and indigenous prey to environmental stressors. 2002 Elsevier Science Inc. All rights reserved.

Physiological refugia: swamps, hypoxia tolerance and maintenance of fish diversity in the Lake Victoria region.

1 Ecology, Evolution and Life History.- Ecology of Notothenioid Fish in the Weddell Sea (With 8 Figures).- Morphological Adaptations and Mode of Life in High Antarctic Fish (With 6 Figures).- The Biological and Demographic Peculiarities of the Icefish Champsocephalus gunnari Lonnberg, 1905 from the Kerguelen Plateau (With 8 Figures).- Is the Growth of Polar Fish Limited by Temperature? (With 6 Figures).- Review of the Early Life History of Antarctic Notothenioid Fish (With 1 Figure).- Age Determination in Antarctic Fish (With 4 Figures).- Microstructural Analysis of Growth Patterns in the Early Life History of Antarctic Fishes (With 7 Figures).- The Fossil and Modern Fish Faunas of Antarctica: Evolution and Diversity (With 3 Figures).- The Contribution of the BIOMASS Program to Antarctic Marine Ecosystem Research (With 3 Figures).- 2 Physiology, Biochemistry and Molecular Biology.- The Sensory Biology of Notothenioid Fish (With 9 Figures).- Viscosity of Body Fluids from Antarctic Notothenioid Fish (With 9 Figures).- Low Temperature Limits Burst Swimming Performance in Antarctic Fish (With 6 Figures).- Respiratory and Cardiovascular Adaptations in Hemoglobin-Free Fish: Resolved and Unresolved Problems (With 2 Figures).- Structural and Mechanical Characteristics of the Heart of the Icefish Chionodraco hamatus (Lonnberg) (With 10 Figures).- Physiological Roles of High Lipid Content in Tissues of Antarctic Fish Species (With 5 Figures).- Biochemical Mechanisms of Cold Adaptation and Stenothermality in Antarctic Fish (With 10 Figures).- Polymerization of Microtubule Proteins from Antarctic Fish (With 6 Figures).- The Biochemistry of Oxygen Transport in Red-Blooded Antarctic Fish (With 2 Figures).

Biology of Antarctic Fish

Most fishes of the perciform suborder Notothenioidei are endemic to the subzero marine waters of Antarctica. A number of remarkable physiological attributes allow them to inhabit this extreme environment; for example, the blood of almost all notothenioid species contains antifreeze glycopeptides. To establish a molecular phylogenetic hypothesis for these fishes, DNA sequences from two mitochondrial genes, portions of the 12S and 16S ribosomal genes (928 base pairs [bp]), were determined for 18 species. These belong to 15 genera in five families of the suborder. The DNA data suggest that two of these families are unnatural groups and consequently that the classification and phylogeny of this suborder is in need of revision. In terms of DNA variation, the Bovichtidae are a distantly related sister group to the other families of the suborder that includes the icefishes, the only vertebrates without hemoglobin. The fishes of the suborder (except the Bovichtidae) seem to have speciated rapidly, forming an adaptive radiation in the Antarctic waters. A phylogenetic analysis of published hemoglobin amino acid sequences for other notothenioid fishes supports these results from mtDNA. On the basis of molecular phylogeny, the evolution of antifreeze glycopeptides was studied. The age of the radiation of notothenioid fishes had been estimated to be at least 38 Mya. However, the level of mtDNA variation detected in notothenioid fishes appears to be too low to agree with this date of origin and might instead suggest a younger age (10-15 Mya). Alternatively, the low level of detected mtDNA variation would agree with the traditional old-age estimate if an extremely slow rate of mtDNA evolution is postulated for this group. This slow-rate hypothesis, if true, could be explained by decreased metabolic rates slowing down the tempo of molecular evolution.

/pdf/molecular-evolution-at-subzero-temperatures-mitochondrial-12ou009ds4.pdf

Molecular Evolution at Subzero Temperatures: Mitochondrial and Nuclear Phylogenies of Fishes from Antarctica (Suborder Notothenioidei), and the Evolution of Antifreeze Glycopeptides

Icefish or white-blooded fish are a family of species, unique among vertebrates in that they possess no haemoglobin. With the exception of one species which occurs on the southern Patagonian shelf, icefish live only in the cold-stable and oxygen-rich environment of the Southern Ocean. It is still questionable how old icefish are in evolutionary terms: they may not be older than 6 Ma, i.e. they evolved well after the Southern Ocean started to cool down or they are 15–20 Ma old and started to evolve some time after the formation of the Antarctic Circumpolar Current. Individuals of most icefish species with the exception of species of the genus Champsocephalus have been found down to 700–800 m depth, a few even down to more than 1,500 m. Icefish have been shown to present organ-level adaptations on different levels to compensate for the ‘disadvantages’ of lacking respiratory pigments. These include a low metabolic rate, well perfused gills, increased blood volume, increased cardiac output, cutaneous uptake of oxygen, increased blood flow with low viscosity, enlarged capillaries, large heart, and increased skin vascularity. Biological features, such as reproduction and growth, are not unique and are comparable to other notothenioids living in the same environment. Icefish produce large yolky eggs which have a diameter of more than 4 mm in most species. Consequently, the number of eggs produced is comparatively small and exceeds 10,000–20,000 eggs in only a few cases. With the exception of species of the genus Champsocephalus which mature at an age of 3 to 4 years, icefish do not attain maturity before they are 5–8 years old. Spawning period of most icefish species is autumn-winter. The incubation period spans from 2 to 3 months in the north of the Southern Ocean to more than 6 months close to the continent. Growth in icefish to the extent it is known is fairly rapid. They grow 6–10 cm in length per annum before they reach spawning maturity. Icefish feed primarily on krill and fish. Some icefish species were abundant enough to be exploited by commercial fisheries, primarily in the 1970s and 1980s with Champsocephalus gunnari as the main target species. Most stocks of this species had been overexploited by the beginning of the 1990s, some had further declined due to natural causes. Other species taken as by-catch species in fisheries were Chaenocephalus aceratus, Pseudochaenichthys georgianus, and Chionodraco rastrospinosus. Chaenodraco wilsoni was the only species exploited on a commercial scale in the high-Antarctic.

Antarctic icefishes (Channichthyidae) : a unique family of fishes. A review, Part I

The blood of seven Antarctic nototheniid species and representatives from three other families contained low haemoglobin concentrations compared with non-polar marine teleosts. Haematocrit values were slightly lower than values from other teleosts, while haemoglobin and erythrocyte counts were substantially reduced by comparison. Interspecific variation in haemoglobin concentration seemed to be a function of activity level. Mean corpuscular haemoglobin concentration of all Antarctic species was strikingly low by comparison with species from lower latitudes and was not correlated with the habits of the species. Haemoglobin componentry was compared using celluslose-acetate electrophoresis and, unlike many temperate species, only one major haemoprotein was isolated from each benthic species, but four components were evident in the pelagic species Trematomus borchgrevinki. The possible functional significance of these findings was discussed in relation to the ecology of each species.

Comparative study of the erythrocytes and haemoglobins in nototheniid fishes from Antarctica

The icefishes (family Channichthyidae) comprise a unique group of teleost fishes endemic to Antarctic and sub-antarctic seas. All members of the family totally lack haemoglobin.



Haematological parameters and viscosity were determined for blood from 11 specimens of two channichthyid species (Chionodraco kathleenae Regan, 1914; Cryodraco antarcticus Dollo, 1900), and 14 specimens of a red-blood Antarctic nototheniid species (Pagothenia bernacchii (Boulenger, 1902)), captured near the Italian research station at Terra Nova Bay, Ross Sea, Antarctica. Channichthyid blood contained only a small number of non-pigmented cells (10 000-40 000 cells μI−1, depending on species) in contrast to nototheniid blood (360 000-450 000 cells μI−1 in unstressed specimens).



Blood viscosity was measured by cone plate viscometry over a range of shear rates (11.3-450s −1), at six temperatures between – 1.8°C and + 15°C. At the ambient Antarctic seawater temperature of – 1.8° C, and at low shear rate (22.5 s−1), the viscosity of channichthyid blood was relatively low (3.99 ± 0.40 cP) compared with blood taken from unstressed P. bernacchii, which was about 25% more viscous (4.91 ± 0.59 cP). The viscosity of channichthyid blood was almost independent of shear rate, approximating an ideal Newtonian fluid, while the viscosity of nototheniid blood was much more dependent upon both shear rate and temperature, increasing sharply at low shear rates and low temperatures.



Viscosity of nototheniid blood varied with haematocrit, which was in turn strongly influenced by stress. Blood samples taken from P. bernacchii under moderate stress induced by handling during acute caudal venepuncture had haematocrit values in the range 15–20% and viscosities of 8-l0cP, while undisturbed specimens sampled through a venous cannula yielded haematocrits of 8–10%. The viscosity of nototheniid plasma did not differ significantly from that of channichthyid whole blood or channichthyid plasma. The higher viscosity of nototheniid blood is attributable to cell content, and in stressed specimens possibly also to adrenergic swelling of erythrocytes.



The absence of erythrocytes in channichthyid blood avoids the great increases in viscosity which are induced in corpusculate blood by sub-zero seawater temperatures.

Thin-blooded Antarctic fishes: a rheological comparison of the haemoglobin-free icefishes Chionodraco kathleenae and Cryodraco antarcticus with a red-blooded nototheniid, Pagothenia bernacchii

J. A. Macdonald

Papers

Comparative study of the erythrocytes and haemoglobins in nototheniid fishes from Antarctica

Thin-blooded Antarctic fishes: a rheological comparison of the haemoglobin-free icefishes Chionodraco kathleenae and Cryodraco antarcticus with a red-blooded nototheniid, Pagothenia bernacchii