Marine life provides income and food for people throughout the world, making it important to understand how climate change might alter the balance of the oceans. In a new PLOS Biology study, Ivan Nagelkerken and colleagues constructed an aquarium system that contained a mini food web typical of a coastal ecosystem in South Australia. Over six months, they monitored how increased temperatures and acidity levels affected the species therein. I interviewed Nagelkerken via email to find out more.
What first drew you to marine ecology?
IN: My father was a marine ecologist, and growing up close to the ocean and seeing him at work when I was young made a great impression on me.
How is climate change thought to affect the oceans?
IN: Climate change can directly affect the behavior, physiology, distribution and life cycle of many marine species. Since species interact with each other through competition, predation and so on, climate change may also indirectly affect other members of the aquatic ecosystem.
What are ecological food webs, and what does a typical marine food web look like?
IN: A food web is an ecological network in which species are linked via predator-prey interactions. A simple marine food web might include primary producers (such as algae), herbivores (for example, snails or turtles), mesopredators (often medium-sized fish that eat invertebrates or smaller fish), and apex or top predators (including sharks and killer whales).
You constructed a “mesocosm” to study the effect of predicted temperature and acidity changes on marine food webs. Could you describe the system you created?
IN: We used 12 large (1,600-liter) fiberglass tanks that were seeded with rocks and sediment collected from the ocean and therefore contained a large natural diversity of species. The tanks were also seeded with live fish and received fresh, unfiltered flow-through seawater to enable spores and larvae to enter the system. Over six months, we maintained the tanks under the ocean temperature and acidity conditions forecast for the year 2100.
One of the mesocosm tanks
What were the effects on your mesocosm of these increased temperature and acidity levels?
IN: Elevated temperature was the most detrimental factor as it reduced the flow of energy from the bottom to the top of the food web. The increased primary productivity at the bottom of the food web was transformed into detritus, instead of acting as an increased food supply for species higher up the food web.
Did anything particularly interest or surprise you?
IN: Surprisingly, we found that ocean acidification was positive for the growth and survival of some species. However, the species that benefited were mainly “weedy” species, which can outcompete more sensitive species and reduce overall biodiversity.
What do you hope your study might lead to?
IN: We hope that our results might contribute to the discussion and implementation around the 2015 Paris climate agreement on reduction of the greenhouse gas emissions leading to global temperature increases. Our study shows that temperature increases in particular could be detrimental to marine food webs. It is also critical to understand if our results can be extrapolated to other marine food webs elsewhere in the world.
Research Article: Ullah H, Nagelkerken I, Goldenberg SU, Fordham DA (2018) Climate change could drive marine food web collapse through altered trophic flows and cyanobacterial proliferation. PLoS Biol 16(1): e2003446. https://doi.org/10.1371/journal.pbio.2003446
Images Credits: Mark Goebel, Flickr; Ivan Nagelkerken; Ivan Nagelkerken