Part Two
ANTARCTICA – ECOLOGY
This lecture practically took me back to the good ol’ college days. I was endlessly fascinated by biology, studying the entire curriculum (and then some) completely on my own, given how much I loved the subject. Then I got into medicine and had no more time for anything else, meaning this lecture was exactly the refresher I needed.
James – a renowned biologist – started off by explaining the definition of ecology – the study of the interrelationships between organisms and their environment, both biotic and abiotic. Individuals come together to form populations, populations interact to form communities, and multiple communities together form ecosystems. He then went on to discuss trophic levels, starting from primary producers such as photosynthetic algae and moving all the way up to quaternary consumers. Roughly 10% of the energy available at one trophic level is transferred to the next, with the rest being lost to metabolic processes. As such, large numbers of primary producers are required to sustain organisms at the top of the pyramid.
In the Southern Ocean, phytoplankton act as the keystone primary producers, particularly around the Antarctic Convergence where upwelling brings nutrient-rich water to the surface. Productivity here is highly seasonal, with explosive phytoplankton blooms occurring during the summer months when light is abundant, and near-total shutdown during the dark winter. Entire food webs are built around these brief but intense periods of abundance, making timing just as important as quantity. Krill sit at the centre of this system, forming the crucial link between plankton and larger animals.
Sea ice, James explained, is not just frozen water but a vital habitat in its own right. Algae grow on its underside, providing food for krill larvae during the winter months when phytoplankton in open water is scarce. If winter sea ice forms late or melts early, krill recruitment suffers, sending shockwaves up the food chain that affect fish, penguins, seals, seabirds, and whales alike.
After this, James explained the various types of biological interactions that take place in the Southern Ocean:
Commensalism: An interaction between two species in which one benefits while the other is neither helped nor harmed. For example, around South Georgia, snailfish have suckers on their bellies that allow them to attach to crabs. The crab provides transport and access to leftover food, while remaining largely unaffected.
Mutualism: An interaction that benefits both species. While relatively rare in Antarctic ecosystems, one example involves algae and sea urchins. Sea anemones typically prey on sea urchins, but urchins can shelter among kelp for protection. The kelp becomes tangled in the urchins’ spines, and when an anemone attempts to capture the urchin, it often ends up grabbing only the kelp instead – allowing the algae to remain submerged but not so deep as to be unable to photosynthesise. Another example is the relationship between phytoplankton, krill, and seabirds. When krill feed on phytoplankton, they release dimethylsulfide, which rises into the air and attracts seabirds. The birds then eat the krill and conveniently deposit nutrient-rich waste back into the system. Circle of life and all that.
Predation: An interaction in which one species hunts and consumes another. Unfortunately, krill doesn’t fare too well in this fight.
Parasitism: An interaction in which one species lives on or inside another, causing it harm. A classic example is seabird ticks that live on penguins, which can even be fatal if present in large enough numbers.
Competition: An interaction in which two species are negatively affected due to limited resources. This can be interspecific, as in fur seals and elephant seals competing for territory, or intraspecific, such as male fur seals fighting other male fur seals for access to the same female.
We then moved on to ecological factors that influence organisms in Antarctica. One of the most important points James made was that Antarctic ecosystems have very little redundancy. There are relatively few species performing each ecological role, meaning that if one key species declines, there are often no substitutes to fill the gap. This makes the entire system highly specialised but also dangerously fragile. These key ecological factors include:
-
-
-
Biomagnification: The accumulation of harmful chemicals in the tissues of organisms at higher levels of the food chain. In the Southern Ocean, phytoplankton absorb pollutants from air and water, which are then passed on to zooplankton, krill, fish, and eventually top predators such as whales. Many of these pollutants originate far from Antarctica, reinforcing the fact that this supposedly pristine environment is still deeply connected to the rest of the planet.
-
Invasion: Invasive species in Antarctic waters include king crabs, which are now encroaching onto the Antarctic Peninsula. These are crush-type predators that were historically absent from the benthic marine ecosystem. As a result, many native molluscs have thin shells and are poorly adapted to defend themselves. If king crabs continue to expand their range, these native populations are likely to decline dramatically.
-
Climate change: Beyond its effects on sea-ice algae and krill populations, melting ice directly impacts species that depend on it for hunting or breeding, such as leopard seals. Antarctic species are highly specialised for stable, cold conditions, with narrow tolerance ranges and slow life histories. Many grow slowly, reproduce late, and live long lives, making rapid environmental change especially difficult to adapt to. As such, even small shifts in temperature or ice cover can have outsized ecological consequences.
-
-
James ended by pointing out that top predators such as penguins, seals, and seabirds act as sentinel species. Changes in their breeding success, foraging behaviour, or population size often signal deeper disruptions within the ecosystem, long before those changes are obvious elsewhere. In Antarctica, when something goes wrong, it tends to ripple through the system fast.
Tags :