antarctica is the only continental land mass on earth which has a completely uninterrupted series of currents circulating around it,ultimately influencing the environment ant the ability of organisms to migrate in out of the ocean in addition to this,there amassive sheet of frozen ice that expands and contracts annually as you can see in this animation At its peak in the winter this sea ice occupies an area of 15 million square kilometers, twice the size of australia this seasonal sea ice supports a unique and fascinating ecosystem and it, certainly not a flat expanse of nothingness sea ice provides a complex three-dimensional habitat which is substrate for a diverse array of microoganisms which can grow underneath the ice or even within it,zooplankton and also predators ice breeding crabeater seals,for example,are the most abundant of all seal species in the world remember this clip of diverse sea floor communities from our introductory topicthere are also links between ice and benthic communities like these when big icebergs break off glaciers they can scour the sea floor, at least in shallow areas and can have a big effect on these ecosystems.is the highly seasonal nature of its productivity so the high latitude of antarctica in the southern ocean means that not only is it extremely cold,but it also experiences several months of complete darkness during the winter during these months of darkness,there's no phytoplankton production but in the summer months the region experiences 24 hours of daylight which combined with warmer summer temperatures and the retreat of the seasonal sea ice results in really large blooms of phytoplankton so that for a short time the southern ocean is the most productive ocean on the earth this productivity is the basis of the southern ocean food web,which is geared around exploiting this seasonal but highly abundant food resource the antarctic krill which eats phytoplankton is arguably the most important species in the southem ocean ecosystem these krill from large aggregations called swarms and are sometimes said to be the most abundant organism on earth with a standing stock of an estimated 500 million tons while the veracity of this statement could be debated,it,s clear that krill do play a central role in the southen ocean ecosystem. consume phytoplankton and themselves are food for fish squid see birds seals,and whales while it's commonly described as the last pristine wilderness while it's commonly described as the last pristine wilderness on earth frome an ecological viewpoint,nothing could be further from the truth for the southern ocean after antarctica's discovery in the 1800s,the region was targeted for commercial hunting,firstly taking millions of fur seals and then targeting whales,and many whale species were removed from the southern ocean during that period the removal of fur seals and whales will have had enormous repercussions for the ecosystem the effects of which still need to be considered by scientists and policymakers today humans continue to have an effect on souther ocean ecosystems, and you'll learn about how fishing in the southern ocean is currently managed when we get to Module 4.but fishing isn't the only impact of humans in this region as an increasing number of ships and people visit antarctica and as we see changes to the physical enviroment as a result of climate chang which you'll learn about in module3,antarctic
systems are at an increasing risk from invasion of nonnative species the presence of new species in marine ecosystems can have a dramatic effect,and you'll hear about an example of this in the next topic