A new way of classify the various ocean environments sheds new light on how marine biomes are defined and changed by nature and humans.
Recently published in Global Ecology and Biogeography, research by Alli Cramer, University of California Santa Cruz, and Washington State University Professor Stephen Katz revealed a new approach that classifies biomes based on their potential to support life and stability of the seabed.
Cramer and Katz reviewed more than 130 studies to weigh variables such as light, depth, and nutrients in seven biomes incorporating dozens of environments, including coral reefs, seagrass beds, ocean ice, and deep abyssal plains.
By analyzing the data inductively, rather than starting from an initial hypothesis, they found that the biomes were more clearly ordered byr two strong variables: gross primary production, a measure of energy in the food web; and the mobility of the substrate, or the movement and composition of the ocean floor.
“This means that energy flow and mobility are common organizing forces in a wide variety of marine ecosystems,” Cramer said. “Despite their differences, coral reefs and deep-sea deserts respond to the same processes“.
While terrestrial biomes have long been defined by climate, marine biomes have eluded clear categorization.
“The oceans are a big black box”Katz said. “Scientists have traditionally viewed depth, temperature and light as important. But we found that they don’t capture all communities. The energy economy of the sea works differently than sunlight.”
As a doctoral student, Cramer set out to develop a more efficient way to classify marine biomes. After analyzing many variables, “Actually, only two ended up revealing the big pattern”, Katz said.
Gross primary production measures the energy that flows through a marine community, either powered by sunlight, the ‘brown food web’ recycled from the depths or chemicals flowing from hydrothermal vents. Coral reefs, sea ice, and mangroves have high primary production, while deep, muddy abyssal plains are low-productivity marine deserts.
The other strong variable, substrate mobility, classified biomes according to the nature of their bottom layer: what they are made of and how much they move and waves and currents churn. A sandy bottom that is mostly stable defines a different biome than the one in constant motion.
“These two axes are important forces in determining ecosystems in the ocean and driving their formation,” Katz said. “One of the novelties of this classification system is that it is simple, so simple that nobody bothered,” he added. “When we told our colleagues about this, they were surprised that no one had tried it before“.
The new method could help scientists, fisheries managers and conservationists rethink the richness and diversity of ocean biomes, as well as the value of high productivity regions that are affected by humans.
“Previous work has analyzed the marine environment ecosystem by ecosystem”Cramer said. “By combining data from many ecosystems, we find the common thread that ties them together. This allows us to see the ocean in new ways and highlights some key places where our actions can alter the function of the ecosystem.”
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