The Antarctic silverfish, Pleuragramma antarctica, is an abundant fish species found exclusively in the Southern Ocean surrounding Antarctica. This small, silvery fish plays a significant role in the Antarctic marine ecosystem. Its widespread distribution and high numbers make it a central component of the region’s food web.
Surviving in Icy Waters
The Antarctic silverfish thrives in sub-zero waters, averaging around -1.8 degrees Celsius, thanks to remarkable biological adaptations. A primary adaptation involves the production of antifreeze glycoproteins (AFGPs) in its blood and tissues. These proteins bind to any ice crystals that enter the fish’s body, preventing them from growing and causing cellular damage.
Another adaptation for survival in these cold waters is related to their buoyancy control. Unlike most fish that use a gas-filled swim bladder, Antarctic silverfish utilize specialized lipid sacs. These lipid sacs, containing a high percentage of lipids (30-57% of dry weight in adults), reduce the fish’s density, allowing for neutral buoyancy. This high lipid content, combined with a high water content (around 80%) and reduced bone density, helps the fish maintain its position throughout the water column without expending excessive energy.
A Central Link in the Food Web
Antarctic silverfish occupy a central position within the Southern Ocean’s food web, serving as a conduit for energy transfer from lower to higher trophic levels. Their diet varies with life stage and location. Post-larval silverfish primarily consume copepods, while juveniles feed predominantly on copepods. As they grow, their diet shifts, with adult silverfish consuming a mix of krill, such as Euphausia superba and Euphausia crystallophorias, and even other fish, including their own species or lanternfish.
Their abundance and wide distribution make them a primary food source for many predators. Penguins, including Adélie penguins, rely on them as high-caloric prey. Seals, such as Weddell seals, and marine flying birds also depend on silverfish. Larger marine predators, like baleen whales (e.g., humpbacks) and toothed whales (e.g., orcas), also consume silverfish.
Challenges in a Changing Climate
Antarctic silverfish populations face pressure from climate change, particularly in the warming Western Antarctic Peninsula. Rising ocean temperatures directly impact these fish, as they are adapted to a narrow range of cold temperatures. Studies show that even a 5°C increase in water temperature can be lethal to related Antarctic fish species and can hinder their ability to process food.
Reduced sea ice, a consequence of warming temperatures, poses a threat to silverfish. Sea ice serves as a spawning habitat for eggs and a nursery for newly hatched larvae. A decline in sea ice cover is a habitat loss, potentially disrupting reproductive success and larval development. Long-term studies correlate warming waters, decreased sea ice, and reduced silverfish larvae abundance, suggesting potential local population collapse.