Marine biology over the next 100 years

This page is part of the topic Biological responses to 21st climate climate change

Just north of the Antarctic Polar Front, the surface water temperature rises abruptly by about 3°C. The Front acts as a barrier for Gene flow - the movement of genetic information among populations within a species - in both directions, causing Antarctic evolutionary processes to occur in some degree of isolation. The number of established terrestrial alien species is much lower (and marine alien species very much lower) south of the Front, although there is evidence that some species exchange occurs in both directions (see Barnes et al., 2006).

Currently, benthic fish and cephalopods may have major barriers to dispersal, e.g. deep-water areas between continental shelves. The continental shelf areas and seamounts are typically separated by very deep (>4000 m) water. Such depths probably constitute insuperable barriers for the adults even in the larger fish species, but pelagic larvae may or may not be able to cross, depending on such factors as length of larval life, distance to be crossed, current direction and the existence of possible oceanographic barriers. The importance of the latter in influencing larval dispersal is becoming increasingly apparent, and indeed in a study of pelagic dispersal in the Antarctic Allcock et al. (1997) conclude that a previously suspected oceanographic barrier between Shag Rocks and South Georgia prevents transport between the two areas for the larvae of the octopus Pareledone turqueti.

The major unknown in the population genetics of Antarctic pelagic organisms is the extent to which they cross between water masses. It is unlikely that planktonic animals like salps, ctenophores and krill can cover significant (horizontal) distances under their own power; thus, to a large extent, they only move with the current systems. However, they may have considerable control of their own buoyancy and consequently can regulate the depths at which they float. With this capability they could possibly select currents at different depths to carry them in some “preferred” direction. The main water mass of the Southern Ocean rotates in clockwise direction around the Antarctic continent, but at a speed that would take perhaps several years for a complete circumnavigation. Nevertheless, this is the strongest and largest ocean current system in the world with a mean velocity of around 10-20 cm/sec between frontal jets and double that in the jets. These considerations would suggest that planktonic species are likely to have a high degree of genetic mixing over an extended time scale. Gene flow exerts a major influence on the rate and pattern of evolution. Spatial patterns of gene flow will play a central role in defining population structure in many polar species. Additional data are needed to understand the extent to which oceanography, coupled with the biology of individual species, may affect the genetic isolation of organisms here.

There is oceanographic evidence of separation of various component parts of the Southern Ocean. For example, the Weddell-Scotia Confluence seems to separate water to the west of the Scotia Arc from that immediately to the east, whilst other bodies of water show rotational movements (gyres) of long duration (e.g. perhaps a year or more in the Weddell Sea), which may lead to planktonic species being retained, and thus genetically isolated, within these bodies of water. Recent work on krill demonstrated a significant genetic break between the South Georgia and Weddell populations, underscoring the potential importance of oceanographic barriers to gene flow. Additional data are needed to understand the extent to which the oceanography of the Southern Ocean, coupled with the biology of individual species, may affect the genetic isolation of planktonic organisms. Palaeontologists are beginning to piece together a long history of temperate, cool temperate and cold climate marine biotas that have evolved in a mid- to high-latitude setting. Palaeobiological data will be used to assess the age of Antarctic habitats and species, and palaeontological information and data on modern forms will be used to compare diversity gradients in the fossil record and the living biota in the southern and northern polar regions. For many decades there was thought to be a fairly simple relationship between diversity and latitude, basically declining from the tropics to the poles. On land this is broadly true, with some notable divergences and exceptions. In the sea though it seems much more complicated, and very different in the north and south polar regions. Along the coast of North America there is evidence for a decline in molluscan, bryozoan and some other faunas towards the Arctic. A different pattern has emerged in the Southern Hemisphere, where what little information we have suggests a lack of uniformity to large-scale patterns in species richness. In the deep sea (the dominant area of the Southern Ocean) there is no obvious spatial trend at all (e.g. Brandt et al., 2007). On the continental slope there is simply not enough information to discern any trends. On the continental shelf the pattern is very taxon-dependent. For example in decapod crustaceans and hermatypic corals there is a strong latitudinal gradient, but there is a similarly strong longitudinal gradient (e.g. Stehli and Wells, 1971). In other taxa, e.g. pycnogonids, polychaetes and bryozoans, the Antarctic shelf is richer than average by area (e.g. Barnes and Griffiths, 2008; Munilla and Soler-Membrives, 2008). Gastropod molluscs are richer in Antarctica than at any southern latitude in the Atlantic, but poorer than at any latitude in the Indian Ocean (Linse et al., 2006). The problem is made more complex by the fact that the Southern Ocean is very poorly studied in many places (e.g. for the 40 degrees of longitude (length of the Mediterranean) of the Amundsen Sea), and rates of species description are low. In the 1970s it was suggested that whole fauna marine richness would be highest in the tropics and decline to lowest levels around Antarctica, but the only area where this notion has been tested, the South Orkney Islands, is richer that any southern hemisphere Atlantic or East Pacific archipelago (Barnes et al., 2008). The one area where a latitudinal cline is evident on the shelf is in the shallows, due to ice scour.

As well as understanding biodiversity and distribution, we are now starting to understand many aspects of the ecology, physiology, trophic and population dynamics of polar species. It is from this knowledge and understanding that concern about the future impacts of climate change (principally ice loss, warming and acidification) has rapidly emerged.

Pages in this topic

1. The impact of global climate change in polar marine environments
2. Pathways of research in cold-adapted organisms and climate change
3. Near-shore marine disturbances over the next 100 years
4. Prospects for marine invasions by non-indigenous species
5. Marine picoplankton response to climate change
6. Biological response of birds and mammals