Ecology on a rapidly changing planet
Ecological news often focuses on how climate change affects species survival. Admittedly an important topic, but is this a case of “not seeing the forest for the trees?” Species are under threat, and the causes are varied. Some are hunted to extinction, but others succumb to disease — like the Golden Toad. Still, others are under stress because their ecosystems are changing. While we often think of ecosystems as permanent, this is far from the truth. Ecosystems migrate and drift as the climate changes, and entire ecosystems can come under threat.
An ecosystem context for climate change is why scientific research puts such an emphasis on tracking the health of individual species. The rise or fall of species populations reflects the health of an ecosystem. Species extinction is one of the parameters used by scientists to understand changes within specific ecosystems. The rate at which species loss occurs, either locally or globally, indicates environmental stress.
One reason climate change alarms ecological researchers is because species loss in the Anthropocene is abnormally high. Historically, species have disappeared at a rate of about 0.01 percent every 100 years. While scientists struggle with exact extinction rates, they generally believe today’s rate is hundreds of times greater than the background level.
Evolution versus adaptation
The good news is, life is tenacious and resilient. During its four-billion-year journey, life survived multiple global climate disasters because of its ability to adapt. When mass extinctions wiped out up to 95 percent of the earth’s species, evolution kicked in, and new species evolved. The rise of mammals started about 65 million years ago when an asteroid struck at the ancient location of the Mexican Yucatán Peninsula. This asteroid strike initiated the Cretaceous K-T extinction event, which ended the age of the dinosaurs and heralded in the rise of mammals — including Homo sapiens.
But adaptation through evolution occurs on a longer timescale than short-term species adaptation. When environmental change is extremely rapid most species have only three options: adapt, migrate, or perish. Huge bird populations migrate annually. If conditions get too harsh for a species in one environment, they may migrate to a better place. But seasonal migration is cyclical, and migrating from a changing ecosystem is more of a one-way ticket.
Food-web dependency leads to the concept of ecosystem migration. When fundamental environmental conditions change on the scale of decades, then entire ecosystems can slowly migrate to follow optimal climatic conditions. However, this type of adaptation is affected by the presence or absence of geographical barriers. Thus, oceans are a prime location for observing ecosystem drift in the absence of geographical barriers.
Ocean barriers are usually more environmental than physical. Temperature stratification, salinity differences, and nutrient supply are all examples of marine environmental barriers. Recent research reported in Current Biology, documents links between populations of marine species and atmospheric/oceanic warming.
The study involved 304 prominent marine species ranging from phytoplankton to fish and marine mammals. The work demonstrates a poleward drift of these species over the past century. Accordingly, population abundance decreased at the equatorward end of the species’ geographical range and rose at the range’s poleward end.
The study focused on species populations and not complete ecosystems. Still, the researchers note: “the temporal population-abundance response of species to warming at any position in their range may not exclusively depend on their thermal physiology but also the responses of the species with which they interact.” The interaction of multiple species within a defined geographical range is the heart of an ecosystem.
The North Atlantic provides a vivid example of human disruption when marine ecosystems migrate. Population shifts in commercially valuable species like mackerel and capelin have economic ramifications. When these species migrate, fishermen’s livelihoods disappear, and politicians hear about it.
Abundant fish in the waters around Iceland have 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. This closure of Iceland’s second most important export fishery created economic distress and political headaches.
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.
When fundamental environmental conditions change, entire ecosystems migrate, following optimal climatic conditions. If plankton at the base of the food web move northward, the fish feeding 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, the new conditions stress 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 south of Iceland, researchers acquired a set of sea-bottom cores — with each core recording 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 sediment layer contains the fossil remains of microscopic plankton, letting scientists document changes in the plankton populations over time. This information is relevant since the species of plankton present at any given point in time is a reflection of prevailing water temperatures.
This research demonstrated that today’s plankton species are different from 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 climate change is driving this North Atlantic ecosystem drift. Whole marine ecosystems are migrating northward in response to warming oceans.
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 an 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 reason Iceland decided not to join the European Union. Today Iceland sets its own mackerel quota, which it raised by 30 percent in 2019. The knock-on effects of migrating ecosystems stretch from the open oceans into the heart of our world economies.
Terrestrial ecosystems migrate also. But geographical barriers and the species composition of these ecosystems make migration a much slower process than seen in the open oceans — providing food for thought and a sequel story.
Extinction Over Time (Source: Smithsonian)
As the ocean warms, marine species relocate toward the poles (Source: Cell Press; Science Daily)
Climate Change Drives Poleward Increases and Equatorward Declines in Marine Species. (By Reuben A. Hastings, Louise A. Rutterford, Jennifer J. Freer, Rupert A. Collins, Stephen D. Simpson, Martin J. Genner; Current Biology)
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)
Warming Waters, Moving Fish: How Climate Change is Reshaping Iceland(By Kendra Pierre-Louis, The New York Times)
Feature Image: Swirling fish schools (By: Phil Manker) (Modified) – https://commons.wikimedia.org/wiki/File:Swirling_fish_schools.jpg – This file is licensed under the Creative Commons Attribution 2.0 Generic license. – https://creativecommons.org/licenses/by/2.0/deed.en