License to Krill I

Krill are small crustaceans that resemble shrimp and feed of diatoms. They are very abundant in Antarctica, in fact their total global combined weight ranges from 500 to 700 million tonnes (Voytek,1990)! Krill are small creatures as demonstrated by figure 1, which shows their size relative to a paper clip. Despite how small they are, they are essential for life in Antarctica. According to the National Geographic (2014), 'without krill, most of the life forms in the Antarctic would disappear'.

Figure 1. Size of krill relative to a paperclip. Source: The National Geographic (2014)

Why are krill so important?

Krill play an important role in the Antarctic food chain. Krill are at the bottom of the food chain which means that they are important food sources for whales, penguins, seals, fish, copepods and sea birds (Tomaselli, 2012). These animals make up the majority of those found in Antarctica. Because so many animals rely on krill, a change in krill availability may result in starvations among some of these Antarctic animals.

Figure 2 shows which animals feed on krill. Krill are consumed by Emperor penguins, Adélie penguins, crabeater seals, leopard seals, and baleen whales. It’s important to note that the figure does not show all of the animals feeding on krill, only a selection.

Figure 2: Antarctic food chain. Source: Voytek (1990)

Krill population

Given the importance of Antarctic krill in maintaining populations of marine and terrestrial animals, it is desirable to keep krill populations steady. But this not the case. In fact, humans are reducing the levels of krill in Antarctica, both directly and indirectly.

First I’ll explain the direct impacts on krill population. Krill populations are declining due to fishing. The Soviet Union began fishing Antarctic krill in the early 1960s (Aronson et al. 2011). In the 1970s and 1980s, many other countries followed (ibid). Krill are sought after because they are used as fish bait, fish feed in aquaculture and for aquarium trade (ibid). Furthermore, krill can be transformed into krill oil, which is a source of omega-3 and can have beneficial health impacts for us. Krill oil can help protect us against and lower the risk of suffering from health conditions such as rheumatoid arthritis, heart disease, stroke, depression and osteoporosis (University of Maryland Medical Center, 2013; accessed 28 November 2014).

These health benefits incentivise pharmaceutical companies to fish Antarctic krill because there is a market for krill oil products. Below is a video published on YouTube by the pharmaceutical company, BioCeuticals, which catches krill to turn into krill oil. I've posted this video because it gives you a flavour of the use of krill to humans.

What is interesting to note about this video is the way the company justifies its activities. Phrases like “krill is found in great abundance all around the Antarctic continent” and "the estimated biomass of Antarctic krill is twice the biomass of the worldwide human population"  indicates that krill are plentiful anyway so fishing would not create any disastrous ecological impacts. Also, the fact that the company interviewed a WWF Director demonstrates that they care about krill levels in Antarctica and want to engage in fishing in a sustainable manner.

Despite what this company claims about sustainable fishing, Antarctic krill populations have been declining. Figure 3a shows this steady decline. Even though there have been fluctuations since the 1970s, the general trend is a decrease in krill. Figure 3b shows where the krill populations have been declining and to what extent. In figure 3b, the red area indicates where the largest declines have occurred, which has been in the North. This region also happens to be the most accessible for ships because it is close to Argentina, making visits likely. As the video above showed, large ships travel to Antarctica to catch krill and turn them into oil almost immediately (while on the ship).

Figure 3. Krill population decline. 
a) Krill density in Antarctica from 1976 to 2000
b) Krill density across Antarctica
Source: Atkinson et al.(2004)

Indirectly, humans are having an impact on krill populations via climate change. Climate change is causing an increase in sea surface temperatures which is affecting the spawning and nursery areas of krill (Atkinson et al. 2004). According to Hill et al. (2013), sea surface temperatures have been increasing by 0.2^oC every ten years, but this is predicted to increase to warming of between 0.27^oC and 1.08 ^oC by the end of this century. Warmer sea temperatures are causing reduced sea ice extent which is problematic for krill because sea ice forms a large part of krill’s habitat. Atkinson et al. (2004) explains that sea ice also shields krill from predators and fosters sea algae, which are a key food source for krill. Additionally, climate change is exacerbating the destruction of their habitat because winter sea ice duration is reducing due to warmer temperatures and warmer oceans, thus humans are indirectly having a negative impact on krill.

So in this post, hopefully my readers have understood the importance of krill for Antarctic animals that feed on krill and have realised what negative impacts we are having on them, both directly and indirectly. The new scores are negative impacts 4, natural/positive impacts 2. Next week, I will discuss another indirect effect that humans have had on krill population.