We are often taught about the relationships between organisms as a one-lane, one-way street: the grass is eaten by the rabbit, which is eaten by the snake, which is eaten by the hawk. In reality, this food chain model drastically oversimplifies the complex web of interactions between species. Healthy ecosystems contain numerous species that can fill the same role. Instead of the rabbits only being eaten by a snake, for example, they might be eaten by a snake or a fox or a hawk. This built-in redundancy in ecological roles makes ecosystems more resilient to change. 

New research published in Science suggests that marine ecosystems may not have enough redundancy in their food webs to combat the cocktail of changes they could see in the near future.  

Researchers set up large-scale ecological experiments called “mesocosms” to test how ecosystems responded to ocean acidification, ocean warming, and a combination of both acidification and warming. While ocean acidification alone had little effect on the overall ecosystem health, scenarios testing ocean warming and the combined effects of acidification and warming both altered the food web, negatively impacting the ecosystem’s ability to function normally.

In addition to climate change-induced shifts in ocean environments, like ocean acidification and ocean warming, marine ecosystems face stressors like overfishing, habitat destruction, and pollution. While some species will tolerate changes and replace less resilient species, a shift in the fundamental balance of ecosystem functions could throw off the delicate balance of the ecosystem. Much like Skittles will not adequately replace apples in a nutritious diet, some species do not make suitable substitutions for others in an ecosystem. Without a healthy level of diversity, marine ecosystems may be ill-equipped to handle the inevitable changes to their environment.