The evolutionary instincts of both animal and plant species drive their geographical migration when climatic and environmental conditions shift. Changes in marine conditions affect a wide range of species, from plankton to whales. So the adaptation of these species to the new environmental conditions creates a North Atlantic ecosystem drift. 

As ecosystems migrate, the species living there also migrate. But the most visible population shifts are in commercially valuable species like mackerel and capelin. When these species migrate, fishermen’s livelihoods disappear, and politicians hear about it. 

Abundant fish in the waters around Iceland propelled the country’s growth and financial wealth. But in 2018-19, Iceland’s capelin fishery was closed for the winter fishing season. The cause of the closure was warm water. The closure of Iceland’s second most important export fishery created economic distress and political headaches.

Why leave?

 Warmer water in the seas around Iceland caused the capelin to migrate farther north, thus abandoning their traditional feeding grounds. But this is not just a case of the fish being finicky. There are both biological and ecological reasons why certain fish species migrate.

Migration is one of the primary mechanisms for short-term species adaptation to changing environmental conditions. Huge bird populations migrate annually. If conditions get too harsh for a species in one environment, then they migrate to a better place. 

The ability to migrate is dependent on many factors. If migration occurs on land, then geographic barriers come under consideration. If a species requires a specific food source, then either the food source must migrate, or that the same food source must be present at the new location. 

This food-web dependency leads to the concept of ecosystem migration or ecosystem drift. When fundamental climatic conditions change, then entire ecosystems migrate to follow optimal climatic conditions. If the plankton at the base of the food web move northward, then the fish that depend on them follow.

But fish also have a metabolic dependency on temperature. Warm water holds less oxygen than cold water. So, fish evolve for survival in specific water temperatures. When the water temperatures warm and oxygen levels drop, then the new conditions place stress on the fish’s metabolic needs. Fish swim to live and need water flowing over their gills to acquire oxygen. For the fish, less oxygen in the water means more energy expended in swimming. This loss of energy efficiency affects the entire species and the amount of food they require. Thus it alters the ecosystem creating winners and losers.

Plankton fossils tell a story

In a study area to the south of Iceland, researchers acquired a set of sea-bottom cores. So, each core recorded the sedimentation history at a single location.  The oldest sediments are at the bottom of the core and the youngest sediments at the top. Each layer of sediments contains the fossil remains of microscopic plankton; thus, scientists documented changes in the plankton populations over time. This information is relevant since the species of plankton present at any given time in history is a reflection of prevailing water temperatures.  

This research demonstrated that the plankton species present today are different than those at the start of the industrial revolution. Shifts in North Atlantic circulation patterns have caused the ocean waters to warm.  Since plankton are at the base of the food web, the data suggest that climate change is driving the North Atlantic ecosystem drift. Whole marine ecosystems are migrating northward in response to warming oceans. This type of poleward migration in the North Atlantic has similarities to documented changes in Pacific ecosystems.

Political fallout

North Atlantic ecosystem drift has also affected mackerel fisheries. Migration of the Atlantic mackerel fishery into Icelandic waters created a nasty dispute where Britain accused Iceland of stealing its fish. The mackerel fishery is co-managed by the European Union, Great Britain, Norway, and the Faroes Islands. This management structure is essential since it determines the allocation of annual mackerel quota for each country. Without allocated quota, over-fishing and subsequent collapse of the fishery is a real possibility.

This dispute moved from a management conflict to a trade war when no agreement materialized. The politics of a single fishery migrating is one of the reasons Iceland decided not to join the European Union. Today Iceland sets its own mackerel quota, which it raised by 30 percent in 2019.

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ArcheanWeb:

Species adaptation to climate change (Source: ArcheanWeb) – https://archeanweb.com/2020/03/31/species-adaptation-to-climate-change/ Also:

Heat affects the ocean’s food chain (Source: ArcheanWeb) – https://archeanweb.com/2020/01/30/heat-affects-the-oceans-food-chain/ Also:

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Sources:

Research Shows That Changes in Ocean Circulation Has Caused a Shift in Ocean Ecosystems Not Seen for 10,000 Years (By Peter T. Spooner; The National Interest) – https://nationalinterest.org/blog/buzz/research-shows-changes-ocean-circulation-has-caused-shift-ocean-ecosystems-not-seen-10000

Warming Waters, Moving Fish: How Climte Change is Reshpaing Iceland (By Kendra Pierre-Louis, The New York Times) – https://www.nytimes.com/2019/11/29/climate/climate-change-ocean-fish-iceland.html

Feature Image: Mackerel at a market (Modified) – By Vincent van Zeijst – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=39517943