You are browsing the archive for 2013 October.

Profile photo of Gillian

by Gillian

Creative design in an extreme clime for a limited time, the Antarctic Ice fish

October 25, 2013 in Uncategorized

 

Fig 1, A member of the family Channichthydiea, commonly known as the Antarctic Ice fish.

(Fig 1, Chaenocephalus aceratus, a member of the family Channichthydiea, commonly known as the Antarctic Ice fish,

http://afg.scarmarbin.be/system/images/44/gallery/chionodraco-hamatus-3-jpg.jpg?1290183825

Introduction

Chaenocephalus aceratus is a fish with clear blood. It belongs to a family of sixteen known members of the Channichthydiea (common, Antarctic Icefish), sub order Nototheioidei. The Channichthydiea are peculiar possessing a gene mutation that stopped the production of haemoglobin – normal in the oxygen/blood transport system for the vast majority of organisms. This gene mutation and a variety of environmental factors are thought to be responsible for the interesting physiological development of the Channichthydiea as a whole and Chaenocephalus aceratus in particular, as will be discussed later (Portner, 2006), (Holland, 2006). There have been recent concerns over global temperature rise and the impact such an event would have on the human race, (Intergovernmental Panel on Climate Change, 2013). A variety of indicators is useful to monitor climate. Chaenocephalus aceratus has an unusual physiology, very sensitive to temperature changes in the region of +/- 2.5 degrees centigrade. Slight temperature changes in the Antarctic might have great impact on the rest of the worlds’ climate. Chaenocephalus aceratus stress experiments to temperature (Wilson, 2002), (Bilyk, 2011) suggest that this organism is a tool to be used for monitoring temperature deviance in Antarctic waters.

Chaenocephalus aceratus Overview

Chaenocephalus aceratus was discovered by Ditlef Rustad, a zoologist researching near Bouvet Island, Antarctica in 1928 (Jabr, 2012). Immediately noticeable was that this fish had major differences from other known Antarctic fish. The fish had no swim bladder, the skin was scale-less, tissues were translucent, gills white and, most notable, the fish exhibited colourless blood. It is now known that a gene mutation occurred to suppress the haemoglobin – making function within the now known family Channichthydiea. This lack of pigmented protein throughout the tissue layers allows light to pass though virtually uninhibited giving a glassy look and apt common name – the ice fish- as can be seen in Fig.1 & Fig.3. Living without haemoglobin as an oxygen transporter will be discussed later. Much work has since been carried out on Chaenocephalus aceratus to discover how such an organism was able to evolve and thrive in the now exacting and hostile marine Antarctic climate.

Icefish resting

Fig 2, Chaenocephalus aceratus

http://www.bbc.co.uk/nature/blueplanet/factfiles/fish/picpops/blackfin_icefish_dougallen_bas.shtml

 

Environmental Overview

The Antarctic environment has changed significantly over the last +/- 40 million years (Eastman, 2005) as the continental land mass moved toward the South Pole. The fossil record emerging from Antarctica supports the theory that the earlier environment was much warmer supporting a bio-diverse rich population of organisms. The majority of species present were poor at adapting quickly to the cooling continent. Changes in climate and ocean currents had a marked effect on Antarctica culminating in the formation of both an ice sheet over Antarctica and of the formation of opposing circumventing currents around Antarctica known as the coastal Polar Current (anticlockwise) and Antarctic Circumpolar Current (clockwise) (Denny, 2008), see Map1. below, (Team, 1993)

 4_oceancirc

 Map 1. Showing the two polar currents encasing the Antarctic continent, Polar Current moving anti clockwise, Circumpolar Current, clockwise. (http://ferrebeekeeper.files.wordpress.com/2012/06/7829088.jpg)

The cooling marine environment allowed for greater oxygen solubility in sea water resulting in oxygen rich waters (Denny, 2008), (Holland, 2006). Water cooling deterred or killed off much of the historic marine biodiversity of the Antarctic continent. The opposing Antarctic current system effectively trapped in the adapting organisms. Thus limited, trapped, adapting marine species were left to acclimatise in the increasingly colder and oxygen rich environment. The threat of predation decreased as historic predators unable to adapt to the new conditions were naturally removed from the locale. (N.C. Peacock, pers. comm.) Ecosystem niches in the benthic layer and water column historically held by temperate favouring marine organisms had been vacated and had become available for occupation by local inhabitants such as the Nototheioidei with Chaenocephalus aceratus eventually taking posts on the sea floor (Figure 4, below) (Eastman, 2005).

 

Physiological coping mechanisms for Chaenocephalus aceratus

Chaenocephalus aceratus has developed strategies for survival in Antarctic waters. These include maximizing oxygen uptake (albeit as a response to lacking haemoglobin) and developing Antifreeze proteins (AFP), as an insurance against freezing to death in icy waters.

Haemoglobin deficient

The colourless, haemoglobin free blood of the Chaenocephalus aceratus (see Fig 3, below and test tube to the right) arose due to a gene mutation thought to have occurred between 10-12 million years ago (mya) (Sidell, 2006).

F1_large

Fig 3,  Test tubes containing blood drawn from two related Antarctic fish, the one on the right from an Ice fish.

Photo by Kristin O’Brien.

http://jeb.biologists.org/content/209/10/1791/F1.large.jpg)

 Oxygen is therefore not bound to blood proteins, as with haemoglobin in other Nototheioidei, but moved as a solute. Noticeable in the anatomy of the modern Chaenocephalus aceratus is an enlarged heart, more than four times greater in size than the heart of a comparable Nototheioidei cousin. The capillary system is similarly bigger to cope with blood transport at approximately four times greater flow. (Sidell, 2006). The lack of blood proteins makes the blood less viscous and therefore less prone to sluggishness in the cold. The high partial pressure of dissolved oxygen in the surrounding water plus the scale-free skin of Chaenocephalus aceratus, also allows for oxygen transfer through the fish skin. It is suggested that the resulting blood/oxygen transport system evolved because of unfavourable gene mutation rather than a response to the environmental situation (Sidell, 2006).

 

Ice

‘Antarctic fish inhabiting the southern reaches of the Ross Sea experience an almost constant mean annual temperature of -1.86’C’ (Wilson, 2002). If temperature is seen to be constant then there is a potential motivator for evolving out the unnecessary mechanisms used to regulate (previously) fluctuating body temperatures. Differing studies indicates that Antarctic fish and Antarctic Nototheioidei in particular have extremely low tolerances to heat increase (Wilson, 2002), (Bilyk, 2011). A suggestion is that Antarctic fish including Chaenocephalus aceratus have evolved their temperature regulation mechanisms to become redundant.

Sea Water freezes at around -2’C. The potential of ice-crystals forming, puncturing cell walls, piercing flesh and resulting in death is very real for marine fauna. However Antarctic fish possess antifreeze proteins (AFP) which seem to inhibit the growth of ice crystals and actually bind the ice into its fatty layer (Fletcher, et al., 2001). So whilst tolerance for heat rise is not currently an effecting factor for the Chaenocephalus aceratus of Antarctica the ice rich waters seems to have promoted evolution of antifreeze proteins (AFP) to keep the fish ice cold but not frozen.

Conclusion

Chaenocephalus aceratus of the family Channichthydiea have evolved and become successful in a climate too cold-hostile for other fauna to bear by investing in antifreeze proteins [(AFP), fats] with which to insulate itself. In addition the Antarctic Ice fish compensated against the loss of genetic function (that historically supported the superior transport of oxygen to body tissues) by physically growing its blood transport system.

There is ongoing concern, in some quarters, regarding global temperature rises and the repercussions for the worlds’ ecosystems (Intergovernmental Panel on Climate Change, 2013). Chaenocephalus aceratus is uniquely placed to give early warning with regard to changes in the Antarctic micro climate it currently inhabits. A shift in global climate patterns is likely to have an effect on the currents surrounding the Antarctic continent disturbing the natural closed ecosystem defences, the nutrient dispersal, the stability of water temperature and the potential release of oxygen into less oxygenated waters or the atmosphere. Warmer waters may well encourage more temperate dwellers towards the Antarctic. Any fast rise in temperature above 4’C will be likely to kill the family Channichthydiea. If heat doesn’t bring about their demise then the rise in temperature may well cause super oxidation and death of fish tissues (Ansaldo, et al., 2000). Predation from outside visitors or competition by visitors for food may negatively impact on the fish. De-oxygenation of the Antarctic waters may leave Chaenocephalus aceratus and its family Channichthydiea literally gasping for breath (Portner, et al, 2006). However the author believes any reliable study worth commenting on needs conducting over a geological time period to fully appreciate the capacity of this family to evolve in response to its changing environment.

Chaenocephalus-aceratus

Fig 4, Chaenocephalus aceratus on the sea bed

http://en.es-static.us/upl/2012/01/icefish4.jpg

References

Ansaldo, M., Luquet, C.,   Evelson, P. et al., e., 2000. Antioxidant levels from different Antarctic fish caught around South Georgia Island and Shag Rocks. POLAR BIOLOGY   Volume: 23 Issue: 3, pp: 160-165.

Bilyk,Kevin T., A. L. D., 2011. Heat Tolerance and its plasticity in Antarctic fishes. Elsevier, Comparative Biochemistry and Physiology, Part A, Volume Part A, pp. 382-390.

Denny, M., 2008. How the Ocean Works. Princeton: Princeton University Press.

Eastman, J. T., 2005. The Nature of the diversity of Antarctic Fishes. Polar Biology, Volume 28, pp. 93-107.

Fletcher, G., Hew, C. & Davies, P., 2001. Antifreeze proteins of teleost fishes. Annual Review of Physiology, pp. 359-390.

Holland, H. D., 2006. The Oxygenation of the atmosphere and  oceans. Philosophical Transactions of the Royal Society Biological Sciences, pp. 903 – 915.

Intergovernmental Panel on Climate Change, 2013. http://www.ipcc.ch/report/ar5/wg1/#.UmmtYX5waP8.   [Online]
Available at:http://www.ipcc.ch/report/ar5/wg1/#.UmmtYX5waP8

 

Jabr, F., 2012. How the Antarctic Icefish Lost Its Red   Blood Cells But Survived Anyway. [Online]
Available at: http://blogs.scientificamerican.com/brainwaves/2012/08/03/how-the-antarctic-icefish-lost-its-red-blood-cells-but-survived-anyway/

 

 

 

Portner, Hans O.,  et al, 2006. Climate – dependent evolution of Antarctic ectotherms. An integrative analysis. Elsevier, Deep Sea   Research II, Volume 53, pp. 1071-1104.

Sidell, Bruce D., K. M. O., 2006. When bad things happen to   good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes. The Journal of Experimental Biology.

Team, m. f. t. O. U. C., 1993. http://www.eng.warwick.ac.uk/staff/gpk/Teaching-undergrad/es427/rice.glacier.edu-oceans/GLACIER%20Oceans-%20–%20Antsurfwater.htm.   [Online]
Available at: http://www.eng.warwick.ac.uk/staff/gpk/Teaching-undergrad/es427/rice.glacier.edu-oceans/GLACIER%20Oceans-%20–%20Antsurfwater.htm

Wilson, et al., 2002. Turning up the heat on subzero fish: Thermal dependence of sustained swimming in an Antarctic notothenioid. Journal of Thermal Biology, pp. 381-386.

 

 

4 Comments »

Profile photo of Charlotte

by Charlotte

Coral Reef Degradation

October 24, 2013 in Articles 2013-14

coral reef pic

Figure 1 Diverse Coral on the Great Barrier Reef. Photograph taken by David Doubilet (http://ngm.nationalgeographic.com/2011/05/great-barrier-reef/holland-text) Accessed 19/12/13.

Degradation of coral reefs is becoming a growing problem; coral are part of the Phylum Cnidaria and are a varied group of animals, most of which live in colonies and create a diverse ecosystem in the form of coral reefs. These ecosystems can be found worldwide, mainly 30° North or South of the Equator (Spalding et al., 2001) shown in Figure 2 (http://oceanservice.noaa.gov/education/kits/corals/media/coral05a_480.jpg. Accessed 19/12/13). This is due to the unique symbiotic relationship between coral and zooxanthellae, which is dependent on availability of light, ocean temperature and the alkalinity of the ocean (Gattuso et al., 1999; Kleypas et al., 1999).

Map of coral distribution

Figure 2 The global distribution of Coral Reefs (http://oceanservice.noaa.gov/education/kits/corals/media/coral05a_480.jpg. Accessed 19/12/13)

Coral bleaching 1

Figure 3 Coral bleaching has taken place and the white calcium carbonate skeleton is revealed.. (Photo: A. Bruckner) (Bruckner, 2001)

Coral have a hard calcium carbonate skeleton that protects their tissues, these tissues are inhabited by photosynthetic micro-organisms, zooxanthellae. The coral rely on zooxanthellae which fix carbon and provide them with energy whilst the coral simultaneously provides the zooxanthellae with protection and nutrients (Kaiser et al., 2011).  The calcium carbonate skeleton makes the coral appear structurally strong, however today coral reefs are threatened by a number of physical and human activities. Up to 30% of coral reefs are already severely damaged and it is predicted that by 2030 up to 60% of these will be lost (Wilkinson, 2002).

There are a number of threats that cause stress to coral reefs, these include diseases, overfishing, tourism, storms and other weather processes such as hurricanes. However, the impacts of climate change are a growing threat that will continue into the future and will be a focal point in the investigation of coral reef degradation. Climate change is a process caused by the release of carbon dioxide into the atmosphere; as the atmosphere warms, global ocean temperatures increase. The ocean also acts as a carbon sink, the increasing levels of carbon dioxide cause an increase in ocean acidification. This combined with a rise in global ocean temperatures causes a large amount of stress to the corals, which results in coral bleaching shown in Figure 3 (Bruckner, 2001) and Figure 4 (http://images.nationalgeographic.com/wpf/media-live/photos/000/166/cache/article-acidification_16643_600x450.jpg. Accessed 19/12/13).  A rise in ocean temperature by 1°C can exceed the corals thermal threshold; once their thermal limit is breached the coral quickly expel the zooxanthellae from their tissues due to the environmental stress (Hoegh-Guldberg, 1999). This reveals their calcium carbonate skeleton which make them appear white in colour, as seen in Figures 3 and 4. If the coral is not then inhabited by another algae with a higher tolerance level, it will eventually die due to the absence of nutrients provided by the symbiotic zooxanthellae. With human activity believed to be enhancing climate change through the continuation of increasing CO₂ emissions, the frequency of bleaching events is predicted to increase (Sheppard, 2003). It has been predicted that consequences of ocean warming and ocean acidification will lead to the loss of 95% of eastern Caribbean coral reefs by 2035 (Buddemeier et al., 2011). Therefore the need for conservation of reefs now is extremely important for sustainability in the future.

coral bleaching2

Figure 4 Photograph of Coral Bleaching showing the white calcium carbonate skeleton (Ove Hoegh-Guiderg/AFP/Getty Images) Accessed at: http://images.nationalgeographic.com/wpf/media-live/photos/000/166/cache/article-acidification_16643_600x450.jpg

Coral reefs are a valuable ecosystem that need to be preserved. Although they can be found worldwide they only make up <0.1% of the global ocean surface area. However, they are extremely rich in biodiversity with over a quarter of all fish species exploiting them and a much greater density of vertebrate species present than can be found in a rain forest (Kaiser et al., 2011). Furthermore they not only play an integral part to marine organisms but also impact greatly upon humans, providing massive economic benefits. For example the Great Barrier Reef provides tourism revenue of around $700 million each year for Australia (Spurgeon, 1992). They also provide social benefits in less economically developed countries. In such areas subsistence fishing is the main source of diet and income for local inhabitants of coastal regions (Kent, 1998). On a larger scale the fishing industry is reliant on coral reefs in many parts of the world such as Asia, Europe and the US to create a habitat for fish species that can be exploited. Therefore coral reef degradation will not only result in economic loss from decreased tourism but also from the reduction in fishing industries. It will cause social and ecological problems such as a reduction in fish available for people in less developed countries, and a decrease in the biodiversity of coral reefs. A reduction in biodiversity in one of the key ecosystems in the ocean would have adverse effects globally and for future generations thus making the conservation of coral reefs not only a priority, but also a necessity.

References:

Bruckner, A.W. 2001. Coral health and mortalit: Recognizing signs of coral diseases and predators. In: Humann and Deloach (eds.), Reef Coral Identification. Jacksonville, FL: Florida Caribbean Bahamas New World Publications, Inc. pp. 240-271.

Buddemeier, R., Lane, D., Martinich, J. (2011) Modeling regional coral reef responses to global warming and changes in ocean chemistry: Caribbean case study. Climatic Change, 109, 375–397.

Gattuso, J.P., Allemande, D., Frankignoulle, M. (1999) Photosynthesis and calcification at cellular, organismal and community levels in coral reefs. A review of interactions and control by carbonate chemistry. American Zoologist, 39, 160-83.

Hoegh-Guldberg, O. (1999) Climate change, coral bleaching and the future of the world’s coral reefs. Marine and Freshwater Research, 50, 839-66.

Kaiser, M.J., Attrill, M.J., Jennings, S., Thomas, D.N., Barnes, D.K.A., Brierley, A.S., Hiddink, J.G., Kaartokallio, H., Polunin, N.V.C., Raffaelli,  D.G. (2011). Marine Ecology Processes, Systems and Impacts, 305-306.

Kaiser, M.J., Attrill, M.J., Jennings, S., Thomas, D.N., Barnes, D.K.A., Brierley, A.S., Hiddink, J.G., Kaartokallio, H., Polunin, N.V.C., Raffaelli,  D.G. (2011). Marine Ecology Processes, Systems and Impacts, 306.

Kent, G. (1998). Fisheries, food security and the poor. Food Policy. 22: 393-404.

Kleypas, J.A., McManus, J.W., Menez, L.A.B. (1999) Environmental limits to reef development: where do we draw the line? American Zoologist, 39, 146-59.

Sheppard, C.R.C. (2003). Predicted recurrences of mass coral mortality in the Indian Ocean. Nature 425: 294-297.

Spalding, M.D, Ravilious, C., Green, E.P. (2001). World Atlas of Coral Reefs. University of California Press, Berkeley.

Spurgeon, J.P.G. (1992). The economic valuation of coral reefs. Marine Pollution Bulletin 24: 529-36

Wilkinson, C., Ed., Status of Coral Reefs of the World (Australian Institute of Marine Science, Townsville, Australia, 2002)

Websites:

http://ngm.nationalgeographic.com/2011/05/great-barrier-reef/holland-text (Accessed 19/12/13)

http://oceanservice.noaa.gov/education/kits/corals/media/coral05a_480.jpg (Accessed 19/12/13)

http://images.nationalgeographic.com/wpf/media-live/photos/000/166/cache/article-acidification_16643_600x450.jpg (Accessed 19/12/13)

4 Comments »