In the past year, our research has found that there are more marine species in shallow tropical seas than in colder latitudes and the deep-sea. However, we were surprised to find that previous research had overlooked that the number of species dips at the equator. Then we found that over the past century, this dip has deepened and widened in response to climate warming. In other words, species are being lost at the equator, and some are shifting into formerly cooler seas. Consequently, further declines of marine biodiversity around the equator due to climate change are likely.
In addition, we discovered that the latitudinal diversity of fish was the opposite to that of large mobile invertebrates. That is, fish were relatively less abundant in colder latitudes than species such as crabs, lobsters, starfish, sea urchins, sea cucumbers, snails, and octopus, compared to the tropics. We think this is because fish are superior predators and herbivores in warm waters, but not in colder conditions. Thus, we predict that as fish extend their range into high latitudes as the oceans warm, they will cause a decrease in the diversity of large invertebrates. These increases in fish, and possible decreases in invertebrates, will change food webs, fisheries and ecosystems.
How these findings will affect marine life around Auckland is not yet clear because strong regional differences in the magnitude of ocean warming influence local situations. Some changes may be welcomed, such as more kinds and abundance of species. In contrast, traditionally fished species may decline. Whether these changes will be detectable against the direct and indirect impact of fishing remains to be seen. Unfortunately, there is no systematic monitoring of trends in marine biodiversity in New Zealand that would enable detection and understanding of the causes of ecological change. However, monitoring inside and outside marine reserves will help distinguish the effects of fishing from climate change.
Change can upset local economies and society, but forecasting what will happen, and then detecting early changes, will help Auckland adapt and possibly benefit from the change. For example, it may be necessary to reduce fishing pressure on species declining due to climate change, but allow increased fishing on other species. In order to be prepared and adapt to changing life in the oceans we need to be able to predict how species and ecosystems will respond to the changing environment and detect such changes.
Mark J. Costello is Associate Professor and Chhaya Chaudhary a PhD candidate at the University of Auckland’s Faculty of Science. His research expertise spans biodiversity, ecology, biogeography, conservation and marine reserves, especially in the ocean. Read Mark’s academic biography