The Changing Ocean and Life’s Capacity to Adapt
Robert Eagle, University of California – Los Angeles
Human emission of carbon dioxide is not just a concern for climate, but has a duel impact upon the oceans with potentially profound effects. Atmospheric warming also propagates into ocean warming; with potential impacts on ocean life as well as oceanic processes that can affect biological processes such as deoxygenation. Additionally, a portion of CO2 emissions dissolve directly into the oceans, causing the ocean to become more acidic and perturbing oceanic carbonate chemistry. This cascade of effects can have potentially significant impacts on a wide variety of marine life, including organisms that form biominerals from calcium carbonate including corals, fish, and phytoplankton.
A major hindrance to our ability to predict these responses in the future comes from the timeframe on which observations can be carried out. Most experiments that are done only characterize very short-term biotic responses, from a few weeks to months. These experiments therefore do not either realistically capture the slow increase in CO2 over time or give organisms the chance to adapt or evolve to future ocean conditions. There is no real reason to suppose that an organism’s response over a period of a few weeks will necessarily reflect its long-term adaptive or evolutionary response to changing conditions over the next 100 years. We must consider three main areas.
Firstly, given sufficient time to acclimatize to conditions, are organisms able to adapt to acidic seawater and warmer oceans? The focus here is on the mobilization of existing capacity in an organism to compensate for changing conditions. Understanding the mechanisms underlying adaptive responses is important, as it will inform us of the likelihood of their being maintained over longer time periods. For example, if a response involved increased energy expenditure to maintain proton gradients across membranes, we could calculate the increased energetic burden on an organism over time.
A second class of responses can be described as evolutionary responses. Given time in selective conditions, existing genotypes conferring better resistance to change should become dominant, and new mutations that confer advantage will occur and in turn be selected for. Different organisms in the ocean have a broad spectrum of different generation times, so the capacity to evolve in response to rapidly changing oceanic conditions will vary enormously.
A final class of adaptive responses concerns biogeography and migration. Some species will simply have the capacity to move to more favorable conditions when their original habitats become less favorable for growth.