The avocado of the ocean

The avocado of the ocean

Top image: Calanus hyperboreus (top), Calanus glacialis and Calanus finmarchicus (bottom). The “bubble” in the middle of the animals is the lipid sack, which is why these species are so popular among predators. Photo: Janne Søreide/UNIS. 

Calanus glacialis (Arctic feed) is a copepod species considered to be a key element in the Arctic ecosystem. It contains up to 80 % fat, but that’s not why we compare it to the avocado. Both the copepod and the avocado might be regarded as biological anachronisms; adapted to an environment that no longer exists.

6 July 2012
Text: Jørgen Berge, Professor at UNIS and University of Tromsø and Geir Wing Gabrielsen, Professor at Norwegian Polar Institute and UNIS

Calanus glacialis (Arctic feed) is a copepod species considered to be a key element in the Arctic ecosystem and very common here in Isfjorden. It is known to be an important food source for fish, sea birds and marine mammals, as it contains, compared to its body size, very large amounts of fat.

To build up energy reserves for the long polar night, the Arctic feed graze on the intense spring bloom during the few weeks in spring and summer, and it bioaccumulates energy in the form of storage lipids. Combined with behavioral traits that make them aggregate in the water column, the Arctic feed thus become an energy source large enough to support even the big bowhead whale that used to be abundant in our waters up until the 1800s.

However, the bowhead whale and other whales were hunted to near extinction, and today it is mainly polar cod and sea birds, especially the Little Auk (Alle alle), which mainly feed on the copepod. To a certain degree the Little Auk has replaced the whales in this ecosystem.

Grønfjorden Svalbard

In the period 1600-1800 whaling was intense in Svalbard. Annually up to 3000 whales were killed. This photo is taken in Grønfjorden. Photo: Unknown.

Why the copepod is an avocado… of sorts
What was the interplay between Calanus glacialis, whales and seabirds back in the 1600’s when whaling was the main activity in Svalbard? Calculations show that the whales before and during the whaling period ate as much as four million tons of Calanus glacialis every year, and that just in the Svalbard waters!

In a recently published scientific article the Calanus glacialis was compared to avocados.

The avocado has a large stone which is adapted to pass through the digestive system of a mammal in order to germinate. However, the large mammals that used to feed on avocados have been extinct for about ten thousand years.

Luckily for the avocado, we humans are fond of this fruit. We have become the avocado’s main dispersal mechanism through agricultural activity. Evolutionary speaking though, the avocado is what we call an anachronism: a biological organism that today lives in an environment which it is not biologically adapted to.

Is this also the case with the Calanus glacialis? Can we really understand the biology of a species that relatively recently was adapted to an environment dominated by whales?
The amount of Little Auks has most probably increased dramatically after the near-extinction of whales in Svalbard waters, and has in a sense taken over as the main predator of the copepod. However, there are big differences in when, where, how and how much the birds consume when compared to the whales’ feeding habits. This means that the Calanus glacialis now lives in a very different environment compared to a few hundred years ago. Their adaption is not controlled by today’s environment, but yesterday’s.

Little Auks

The avacado hunters, Little Auks (Alle alle) in Bjørndalen, Svalbard. These days the chicks are born and in the next 2-3 weeks the Little Auks will fly back and forth between the nest and the ocean to find Arctic feed for the young. Every audult will bring up to 1200 individual Calanus glacialis for the chicks up to five times a day. Photo: Geir Wing Gabrielsen / UNIS.

Poorer chick production
Studies performed along the west coast of Svalbard show that the Little Auk works very hard in order to find its preferred food, the arctic feed. The changes in the ocean temperature over the last few years have resulted in an increasing amount of red feed (Calanus finmarchius), a southern closely related but less energy rich species compared to the arctic feed, being consumed by the Little Auk. The birds must then fly longer distances to reach the fat-rich Calanus glacialis, which means longer absences from the nest, which again results in poorer survival rates for the Little Auks chicks.

Today, the Little Auk is the ultimate avocado hunter. We know they need sufficient amounts of the Calanus glacialis to successfully produce viable offspring. What we do not know much about is how this copepod responds to a warmer climate and how their response affects the ecosystem. Recently we have seen a larger amount of herring in the Svalbard fjords.

Herring feeds mainly on Calanus glacialis and Calanus finmarchius. As of now we do not know how the increased presence of herring affects the ecosystem and whether the Little Auk has gotten a permanent competitor for the food.

The “Kiwi-syndrome”
However, we do know that biological systems are not static. Frequently we hear about Arctic ecosystems that have a vulnerable balance and are threatened by human influence. In reality such a balance rarely exists.

As an example we can look at the Kiwi bird in New Zealand, which is close to extinction. For millions of years this bird lived with no natural enemies and gradually lost the ability to fly. However, when New Zealand was discovered by humans in 1642, they brought with them predatory mammals such as rats and cats. This changed the Kiwi’s natural environment, and the Kiwis were significantly reduced in numbers by the new predators. Today, the Kiwi is close to extinction basically because it is adapted to an environment without predators. We assume, much in the same way, that all animals and plants are perfectly adapted to a stable and unchangeable environment, as the kiwi once was. We call this the “Kiwi-syndrome”.

In constant change
The truth is that environments and habitats are in constant change. The dispersal of species changes according to often small changes in the climate. The oceans around Svalbard are constantly affected by southerly currents which supply a continuous and natural import of southern organisms. For many species this represents challenges for survival and effective breeding. Therefore, one cannot speak of a balance in an ecosystem. A planned reference area for Eastern Svalbard is therefore not worth much unless one constantly monitors the area and study the changes that happens continuously.

After the whales disappeared from the Svalbard coast line, the amount of Little Auks increased substantially. Now the bird species faces some environmental changes that might result in a reduction. Much in the same way the Calanus glacialis has survived different regimes of predators; from whales to polar cod and the Little Auk, and now also perhaps herring.

These days a master- and PhD course, AB-322, is running at UNIS. The Little Auk is one of the focal points in this course, which also entails a process which is invaluable for all life in Svalbard: the transportation of nutrients and energy from the ocean through the sea birds.

The Arctic has undergone huge changes since the last Ice Age, which peaked some 18 000 years ago, and we observe big ongoing changes today. Most species survive such changes, which makes it difficult to pinpoint exactly what “their” environment is. The environment often changes more rapidly than species change through evolution.

But what we do know is that right now scientists and students are out observing the Little Auk and try to find out where and how it finds food. At the same time, there are millions of mothers and fathers out in the fjords of Svalbard, on a desperate hunt for the “avocado” of the ocean!

Jørgen Berge, Geir Wing Gabrielsen

The authors, Jørgen Berge (left) and Geir Wing Gabrielsen – with avocados – in Bjørndalen outside Longyearbyen, where UNIS staff and students conduct fieldwork. Photo: Hugh Ellis.





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