A small step for krill, a giant leap for spineless invertebrates
Probably made famous by the deep-thinking and entertaining Will and Bill from Happy Feet Two, krill are small shrimp-like crustaceans that play a big role in our ecosystems. Euphausids, or krill, comprise a group of about 85 species worldwide, and though there are many species in southern Africa it is unfortunately not common to see krill swarms off Plettenberg Bay. Adult krill can range in size from 1 to 8 cm, but do not let their small size fool you! Krill have a critical ecological role as a particularly important link in the marine food web between primary producers and hundreds of marine species including birds, fish (many of which are commercially important), and whales (including even the largest of whales, the blue whale). Krill feed on phytoplankton which are microscopic single-celled plants, and then krill, in turn, are fed on by a multitude of species. Krill biomass worldwide is thought to surpass 300 million tons. However, it is not only marine species that eat krill, krill has been harvested by humans for consumption purposes and for other purposes including for aquaculture, aquarium food, bait in sport fishing, and in the pharmaceutical industry as krill oil. Unfortunately, over the past years there are concerns that the number of krill has decreased, and this coupled with human harvesting resulting in further decreases can have very concerning effects on the marine food web. Effects can include algal blooms of phytoplankton not consumed by krill, reductions in the number of a variety of baleen whales and fish (many of which have commercial value) as their krill prey has decreased, and then a decrease in the number of other commercial fish stocks through trophic cascading.
Written by: Minke Witteveen
For further reading:
- Branch, G.M., Griffiths, C.L., Branch, M.L. and Beckley, L.E. 2010. Two Oceans: A guide to the marine life of southern Africa. Pp. 102. Random House Struik Publishers, Cape Town.
- Everson, I. 2000. Krill: Biology, Ecology, and Fisheries. Pp. v-vii. Blackwell Science Ltd, Oxford.
- National Geographic. 2016. Krill: Euphausiacea. Accessed: 2016-08-27. URL: http://animals.nationalgeographic.com/animals/invertebrates/krill/