Species do not live in isolation; they live in very tangled, complicated, interconnected webs. So studying them individually is of limited use, as is studying cells grown in a sterile petri dish. These lab studies can provide suggestive and promising results, but these results aren’t always applicable to how the cells behave in the context of an organism, let alone as part of a species in an ecosystem.
The increased carbon dioxide that humanity has been relentlessly pumping into the air since the dawn of the industrial revolution is acidifying the oceans. Studies conducted to determine what this ocean acidification will do to fish mainly have the direct effect of increased CO. rated2 levels on the growth and physiology of the fish, but they did not take into account any effects of ocean acidification on food webs as a whole.
Scandinavian marine biologists have attempted to rectify this situation by studying the effects of ocean acidification in 10 mesocosms — fiberglass tanks strewn with rocks, sediment, plankton and other microorganisms — they’ve set up off Sweden’s west coast. Five were controls; the other five received increased CO2, set to mimic levels that the Intergovernmental Panel on Climate Change estimates could occur by the end of this century. Those estimates are about 760 atm (short for micro atmospheres) pCO2compared to the current 380 atm pCO2). Being Scandinavians, these researchers investigated the survival of…herring.
While the phytoplankton in the mesocosms were in bloom, the researchers added herring eggs to all 10 fertilized in mid-April 2013. Significantly more herring larvae survived in the five with the increased CO2 levels than in controls, especially during the critical first feeding period just after the eggs hatch. This was a surprise, as the high CO2 levels had negative effects on herring larvae in laboratory studies.
The scientists concluded — and then demonstrated — that herring’s survivability differs based on food availability. It was already known that increased CO2 in the ocean stimulates some species of phytoplankton. This abundance of phytoplankton provides an abundance of zooplankton – small crustaceans that eat the phytoplankton. This seems to carry over to the herring larvae that eat these crustaceans.
A similar effect, where the plus of more food is the minus of more CO. overcomes2 (and more acidic), was also seen for mussels in the western Baltic.
The authors conclude: “Despite the positive emergence for the herring larvae under high CO2 circumstances, the findings of this study should not be extrapolated to imply a bright future for fish recruitment in an acidifying ocean.” Part of the problem is that there were no predators of herring larvae in any of the testing environments — although less artificial than labs, these mesocosms are still being designed and controlled.
We should also keep in mind that herring is only one species. Other species — cod and silverfish, corals, larger phytoplankton — are not expected to fare as well in a more acidic ocean, and biodiversity as a whole will almost certainly decline. Like the authors of a similar study just done in the Great Barrier Reef, these scientists argue that the primary utility of these studies at the community level is to help us prepare for and mitigate the dramatic effects that climate change will have. all life forms share the oceans.
Natural Ecology and Evolution2018. DOI: 10.1038/s41559-018-0514-6 (About DOIs).