Marine Algae Adapt to Climate Change

By: Sarah McGhee UHM MOP Student

Marine algae can be found in all parts of the ocean across the globe. They are a vital part of the food chain and are some of the most diverse groups of organisms in the sea. It is no secret that climate change has affected ocean life, and marine algae are no exception.

Phytoplankton is one of the most common and important examples of marine algae. These small, photosynthetic protists provide about half of the oxygen we breathe. They are also responsible for absorbing carbon dioxide as part of their photosynthetic process, which plays a large role in the removal of carbon from the atmosphere.

At the base of the food chain, phytoplankton are primary producers, providing a food source for larger species of plankton as well as small fish. If they were to be bothered by climate change, like most species are, the effects would be felt all the way up to the top consumers, humans, who rely on fish as a staple of some diets. So how are they coping?

Phytoplankton live in the photic zone which is, unsurprisingly, more impacted by climate change than deeper waters. As the water closer to the surface warms, it becomes more stratified, meaning the cooler, more nutrient-dense water sinks, leaving the algae in the warmer water with depleted nutrients. However, recent data have shown that even in nutrient depleted waters, the algae?s productivity may be sustained in a unique way.

Along with carbon, phytoplankton require nitrogen and phosphorus to photosynthesize. Under some conditions, these adaptable algae are able to substitute sulfur in place of the phosphorus they need, through a mechanism known as nutrient uptake plasticity.

A team from the Hawai?i Ocean Time-series study program ran an experiment in which the plasticity mechanism was ?turned off?for some algae and left on for others. With the mechanism turned off, and all other conditions remaining the same, there was an 8%decrease in phytoplankton productivity. With the mechanism remaining unchanged, and all the conditions the same, there was actually a 5%increase in the phytoplankton productivity.

While this was only a small sample in a very specific region, Dr. Eun Young Kwon, first author of the study and a researcher at the IBSCenter for Climate Physics at Pusan National University, South Korea, believes that in some subtropical regions, the percent of increase in productivity may be much higher. Marine dissolved organic matter (DOM) is already one of the largest carbon sinks in the ocean, and this increase in phytoplankton productivity would also increase the sea?s ability to sequester carbon dioxide from the environment. However, while phytoplankton are very adaptable organisms, they may not be entirely immune to the effects of climate change. Along with the depletion of nutrients, other issues include ocean acidification. Ocean acidification refers to the decrease in the ocean?s pH level, and this could have dramatic effects on calcifying phytoplankton organisms, as well as other species that are highly sensitive to pH changes such as corals. It is important for us to understand that even the smallest creatures on our planet are being affected by climate change. While we may not directly see the harm, eventually we will understand the importance every species has and why it is necessary to protect and preserve them while we can.