Research Students Present their Study of the Effect of Climate Change on Corals at the Partnership for the Delaware Estuary 2023 Meeting

Julia Rakowsky, Gabriela Pendos, Kayla Cayemitte, Hannah Snyder, and Ivy Foster presented their research on the effects of climate change on coral in January at the 2023 meeting of the Partnership for the Delaware Estuary in Atlantic City, NJ. They study Astrangia poculata, the northern star coral, a non-reef building stony coral found in shallow waters of the western North Atlantic Ocean including the Delaware Bay. It is part of benthic communities, growing on boulders, ledges, pebbles, docks, and empty mollusk shells. Most corals depend on algae that lives within their tissues (an “endosymbiotic” relationship) for much of their energy although the coral polyps (individuals) also feed on plankton. Astrangia poculata is unusual in that polyps can be brown in color–stuffed with endosymbiotic algae, or white in color-having relatively few endosymbiotic algal cells and depending more on eating plankton, yet be quite healthy. This relationship is “facultative” rather than obligatory as it is in reef corals. Astrangia poculata is considered a model organism from which several research groups on the eastern seaboard hope to learn about why corals “bleach” (lose their endosymbiotic algae) when they are stressed.

In addition to ocean temperature changes, climate change is causing more frequent and more severe storms. The students are currently investigating the effects of decreased salinity on A. poculata. Near shores where A. poculata is found, substantial, rapid decreases in salinity due to heavy rains or increases in salinity due to storm surge can occur. The students are currently investigating the effects of decreased salinity on A. poculata. They work in Dr. Kate Goddard’s laboratory where they are further developing this project which was originated by honor’s student Hannah Merges. Hanna has graduated and is in graduate school studying the effect of climate change on reef corals.

Salinity can drop very low in nearshore areas, but is usually around 20-34 parts per thousand (2% to 3.4% salts). The students have found that when Astrangia poculata is stressed by decreased salinity of 5-15 ppt, that they lose vast quantities of endosymbiotic algae and the photosynthetic efficiency of the algae that remains in the tissues drops. At 5 ppts, the polyps lose their tentacles, and cannot feed. Very few coral polyps (individuals) survive at 5 ppt, even for only 48 hours. The researchers are currently testing whether polyps that have very large numbers of endosymbiotic algae (brown in color) survive low salinity better than white polyps. They hypothesize that the endosymbiotic algae will maintain the polyp while it recovers from being unable to feed itself.

At the meeting the students had the opportunity to reconnect with recent graduate Marie Gazzillo who attended the meeting to learn about current research and job opportunities in the geographical area. They had the opportunity to meet Ursinus College graduate Matt Kenwood who gave a talk on his honors thesis on the population genetics and mutations involved in pollution resistance of Fundulus heteroclitus, a small fish found in the Delaware estuary. Matt is now a PhD student at the University of Texas Health Science Center at San Antonio. His work is also currently being continued by researchers in Dr. Goddard’s laboratory. The students also met Ursinus College graduate Lauren McGrath who is the Watershed Protection Program Director at the Willistown Conservation Trust and had the opportunity to talk about career paths and options.