Antarctic krill the penultimate Keystone species
As the title suggests, krill is one of the most important and wide-ranging planktonic organisms within the oceans of the world, with an estimated biomass of 379,000,000 tonnes annually. They belong to the class Malacostraca within the subphylum Crustacea and have chitinous exoskeletons and identifiable as krill species by their visible external gills. Adults range in size from a few centimetres to over fifteen centimetres for one species Thysanopoda spinicaudaon but are average at around 1 to 2 centimetres. Euphausiids feed on phytoplankton and zooplankton packaging and converting them into energy that is passed on through the food chain to higher trophic levels, exploited by fishes, cephalopods (squids and octopus), pinnipeds (seals), and cetaceans (whales and dolphins).
This natural exploitation didn’t go unnoticed by the whalers of old as they searched the seas they did not just look for the blow of the whale but also looking for the telltale sign of a reddish tinge to the surface waters which indicated the presence of massive krill swarms. The motivation for the start of the scientific work on krill and led to the financing of the discovery expedition also known as the British National Antarctic Expedition that ran between 1901 to 1904 funded by the South Georgia whaling industry.
During the 1970s there was an increase in research in krill due to warnings from The Club Of Rome about the ever-growing human population that had ignited the public attention and triggered new interest in krill as a form of protein. This new investment was to take fishing fleets into the southern ocean in search of mainly one species of krill Euphausia superba (The Atlantic krill). As a result of overfishing during the last forty years, with catches peaking in the 1980s due to Soviet and Japanese fishing fleets landing over half a million tonnes a year, the species is now on The International Union for Conservation of Nature (IUCN) red list.
To date, most Krill caught within our oceans are harvested by mostly Norwegian fishing vessels from the southwest Atlantic catches equate to approximately 300,000 tonnes per year. This harvest of krill is mainly used for high-quality aquaculture feed and also used to produce krill oil a supplement as it is high in Omega 3 fatty acids and Phospholipid-derived fatty acids (PLFA), used for human consumption.
Krill are also likely to suffer at the hands of humans in another way as within the last century anthropogenically influenced global warming has increased levels of CO2 within the Oceans making them more acidic. This change can impact krills habitat range while also having effects on the reproductive fecundity and the recruitment success of Atlantic krill. As krill have a direct affinity for sea ice which provides nursery grounds for the larvae, while also providing them with a food supply as they graze the underside of sea ice feeding on algae that form on the ice substrate. Furthermore, the sea ice encourages further algal blooms of phytoplankton as it retreats during the spring. These blooms are fundamental for the adult reproduction during the summer spawning season. Overall with overfishing and climate change the accumulative impact on krill is suggested to be adverse.
Considering all this exploitation, it seems hypocritical that a species that is suffering from anthropogenic influences have the power to some extent increase primary production while also acting as a very efficient biological pump. As they are very messy feeders, they spit out the exoskeletal remains of their food and produce strings of faecal matter that contains a significant amount of carbon and silicate shell from diatoms. This waste is unlike the waste generated by other smaller zooplankton that stays in suspension in the water column recycled for years. Instead, the waist from krill sinks very fast at about 850m per day were it is then sequestered into the sediments lacking away the carbon and efficiently lowering the CO2 levels making ti one of the most significant natural biofeedback mechanisms on the planet and is estimated to be between 342 and 536 million tonnes per year.