Ocean Acidification; What it means for Kelp Forests, Sea Urchins, and Sea Otters

The Monterey Bay Trifecta

Along the west coast of the United States lies the California city of Monterey. Monterey is popular not only because it resides along the sea, but because it is home to important marine species. One of the largest species of algae in the world, giant kelp is displayed at the Monterey Bay Aquarium, where the first living kelp forest exhibit opened to the public. Monterey is also a popular spot due to its sea otter population. You will see these furry creatures floating on their backs, gnawing on mussels and sea urchins. You may even see them floating around and holding hands with other sea otters to prevent drifting. They also may be seen floating around with pieces of kelp. Why are sea otters seen with sea urchins and kelp in hand?

What is the importance of the three species?

Sea urchins are a primary food source for sea otters. Sea urchins are grazers that eat much vegetation when given the opportunity, and along the west coast of the United States, they are allowed to feed on kelp. If there are no predators present in the ecosystem, they will continue to graze until there is no vegetation left. Kelp forests, also known as underwater forests, display similarities to terrestrial forests. They house many different species and act as protection to predators of said species. They are also a food source for many organisms. When the kelp dies, they sink to the bottom of the ocean, allowing benthic organisms to obtain nutrients. While providing nutrients and protecting organisms within their forest, they are photosynthesizers, taking in sunlight and converting it into nutrients. Giant kelp forests have integral roles in their ecosystem due to their ability to take in carbon dioxide and convert it to oxygen and nutrients.

What is ocean acidification?

Due to climate change, we have seen increasing seawater temperatures in many regions, and Monterey is no exception. According to data from the National Oceanic and Atmospheric Association, the pH has increased over time. These decreases in pH are due to increases in atmospheric carbon dioxide entering the sea surface. The idea of overall decreases in pH in the oceans over time due to increasing oceanic uptake of atmospheric carbon dioxide is ocean acidification. As carbon dioxide entering the ocean surface, it will react with water to form carbonate and then react again to form bicarbonate and positive hydrogen ions. The pH scale has an inverse relationship with hydrogen ion concentration. Therefore, when we see increases in hydrogen ion concentration, this means there are decreases in pH.

How will ocean acidification affect the three species?

With oceans predicted to decrease in pH with time, we may begin to see decreases in sea urchin populations, especially along the west coast of the United States. The California current, starting from Southern British Columbia going down to Baja California Sur, is known for its strong upwelling episodes. Upwelling is when deep, nutrient-rich waters are brought to the surface, which leads to higher productivity, but excess upwelling may increase ocean acidification. With the decomposition of organic matter sinking to the ocean floor, this naturally increases the carbon dioxide concentration. When upwelling occurs, there will be an increase of carbon dioxide concentration to the surface, ultimately leading to increases in ocean acidification.

So, what next?

With increasing ocean acidification, solutions need to be researched to maintain the populations of the three species. We do not know how the effects of ocean acidification will affect the giant kelp forest population across the west coast of the United States. It is worrisome as giant kelp forests have integral roles in these ecosystems. Ocean acidification also harms organisms such as sea urchins, as decreases in carbonate levels inhibit the sea urchin from creating their outer shell. There is not much known about how ocean acidification affects sea otters, but future research could lead us to understand how the effects on one species in a symbiotic relationship could affect all organisms within the relationship. There are no clear indicators to how it would affect all but sea urchins, but the future may hold the key to the solutions.