[Tide Bites] Understanding the Effects of Ocean Acidification on Predator-Prey Interactions

This article comes from “Tide Bites”, the monthly newsletter of UW Friday Harbor Laboratories. Seroy, S. (2017, July). Understanding the Effects of Ocean Acidification on Predator-Prey Interactions. Retrieved from https://fhl.uw.edu/about/news-and-events/newsletters/. [link to original article]. Applications for undergrads wishing to study and research at Friday Harbor Labs this autumn are still being accepted.

Understanding the Effects of Ocean Acidification on Predator-Prey Interactions

by Sasha Seroy

Sasha Seroy is a graduate student in the Oceanography Department at the University of Washington, advised by Dr. Daniel Grünbaum.

Marine organisms are experiencing dramatic environmental changes due to global climate change. As atmospheric carbon dioxide concentrations rise, the oceans absorb increasing amounts of carbon dioxide, which results in acidification. While ocean acidification affects several different types of organisms, calcifiers — those that make their shells or skeletons from calcium carbonate like shellfish or corals — have been identified as particularly vulnerable. Acidification not only increases the likelihood of shell or skeleton dissolution, it can also make it more difficult for organisms to create calcium carbonate in the first place. Several studies have investigated the effects of ocean acidification on calcifiers in isolation; however, in nature, organisms interact with a wide variety of other organisms, from predators to prey to competitors. These interactions have the potential to amplify or reduce the effects of acidification with consequences that could propagate up to population and community levels. I am particularly interested in how interactions between predators and prey are influenced by changing ocean chemistry.

bryozoan colonies
Fig. 1: Individual feeding zooids within a bryozoan colony (left), an entire single bryozoan colony (center), and multiple bryozoan colonies growing on kelp (right).

The encrusting bryozoan Membranipora membranacea is commonly found in the waters around San Juan Island and presents a good model system to investigate the effects of acidification on predator-prey interactions. Membranipora forms large circular colonies composed of zooids — the individual units within a colony (Figure 1) — on kelp blades. As they grow, colonies add subsequent rings of zooids to their outer edge. This structure makes it simple to divide colonies like cutting a pizza, and then expose genetically identical slices of the same colony to different environmental conditions via laboratory manipulations. Membranipora exhibits an inducible defense — a defense that is only formed in the presence of predators — which helps protect them from being eaten. Upon receiving chemical cues that the predatory sea slug Corambe steinbergae is close by, Membranipora produces spines on skeletons of newly-formed zooids along the outer growing edge of the colony (Figure 2). While these inducible spines are beneficial, they present a trade-off because they require energy to make, and leave less energy to put toward colony growth. Therefore, the cost associated with increased protection is a reduction in overall colony growth. Thus, similar to tree rings, we can see which rings of zooids were formed at a time of high predation by looking for defensive spines. Since these interactions are easy to quantify and Membranipora forms its skeleton from calcium carbonate, this system is a good model to understand how ocean acidification might affect predator-prey dynamics.

[read the full post at FHL Tide Bites]