Top image: The Lumpfish (Eumicrotremus spinosus) has quite a particular diet. (Photo: UNIS).
Around the coast of Svalbard we find many exciting animals in the sea. Few are as strange as the two fish you will meet here. Perhaps they are facing an uncertain future?
28 September 2017
Text: Jørgen Berge, Professor at UiT – The Arctic University of Norway, UNIS and NTNU
Throughout the history of the earth we have seen a number of mass extinctions of species. Only a few of the species that once lived on earth are alive today. Many extinctions, such as those of the dinosaurs 65 million years ago, are explained by major global disasters as a collision with a meteorite. But very few species have ever been eradicated as a direct consequence of such a disaster. For this to be the case, the disaster should occur largely across the whole range of the species at the same time. What, on the other hand, causes species to die out are the subsequent climate or environmental changes that come after a major meteorite impact or massive volcanic eruption. And those species that seem to deal with such changes the worst, they are the species we often define as specialists. A specialist in this context is a species that is either adapted to a very specific area of living, hunting a particular prey or having completely special and defined “requirements” for its environment. Generalists, on the other hand, are often able to utilize the opportunities available, or eat the food that is at all times readily available. Evolution works in the moment and does not benefit anyone who is not able to utilize their environment optimally here and now. In this way, speciation (the process by which biological populations evolve to become distinct species) tend to be more and more specialized, and in the long term, they also provide a basis for mass extinctions in major disasters or abrupt climate changes.
There are many educated “truths” in the marine environment of the arctic about predators that should be dependent on a particular prey; sea angels (Clione limacina) are said to eat exclusively sea butterflies (Limacina helicina), the comb jelly Beroe cucumis eats exclusively a particular Arctic comb jelly (Mertensia ovum), the little auks are totally addicted to the copepod Calanus finmarchicus, to name a few. As a biologist, I think that such unique relationships are never real and that reality is always more complex. Nevertheless, it is possible to say that some of these are actually specialists, despite the fact that, for example, sea angels actually prove to have both Calanus finmarchicus and larvae from molluscs on the menu, as well as sea butterflies. Although they are able to eat several different types of prey, they often have a strong preference for one of them. They have evolved into more specialists than generalists.
Quite peculiar diet
In the fjords around Svalbard we find two fish species which can safely be said to be quite so peculiar in their diet; lumpfish (Eumicrotremus spinosus) and Atlantic poacher (Leptagonus decagonus). Both are quite small fish species, and both appear to be adapted to typical Arctic waters. The weirdest of them is probably the lumpfish, a small, round fish with almost unimaginably poor swimming abilities. Amazingly, it seems to have specialized in eating one of the fastest swimmers in the ocean – the amphipod Themisto libellula. It, of course, also eats other prey, but surveys show that the vast majority of individuals mainly eat Themisto libellula when available. While the amphipod lives in the free water masses and performs daily migrations up and down in the water column, the lumpfish is generally quiet and waits for its food. The amphipod follows the sunlight and migrates to the upper water layers at night and down to the depths during the day. While other animal plankton usually stay a little away from the bottom as they seek shelter in the deep darkness, it is observed that the Themisto libellula is sitting on the bottom. Here the lumpfish is waiting. It is, as I said, a distinctly bad swimmer, and it looks like it has found itself a niche where the combination of patience and the migration of the prey down to the bottom is its main weapon.
The other peculiar species, the Atlantic poacher, may not be as particular in the diet as the lumpfish, but it still exhibits an impressive degree of specialization. The studies I have done with students on UNIS course around Svalbard show that almost 90% of all individuals had eaten one very special kind of copepod; Bradyidius similis. This is a species that is a small (3-4mm) free-flowing copepod that rarely dominates in the plankton community. Other studies have given a more flexible picture of its diet, but it seems that the Atlantic poacher is a species that knows what it will eat!
The purpose of this article is not to say that lumpfish and the Atlantic poacher are two species that will be extinct. But there is still reason to contemplate on what the future can bring to the fauna around Svalbard. Perhaps we will see that species such as lumpfish and the Atlantic poacher will face a more uncertain future. It is probably especially critical for the lumpfish, as it seems to be so dependent on the Themisto libellula. This amphipod is a species that seems to migrate northwards as the sea climate around Svalbard gets warmer and new southern species come in, and in recent years it has become less and less dominant in the fjords on the west coast of Svalbard.
So while more well-known and often economically important species such as the snow crab, mackerel, cod and mussels migrate further north and become part of the ecosystem of Svalbard, it is probably also likely that we will lose some species at the same time, either locally from the fauna of Svalbard, or completely because some species actually cease to exist. Hopefully, it will not happen with these two peculiars, although there is every reason to be a little worried about the lumpfish. Unfortunately!