Tuesday morning, January 4, 2022. The sun rose, warming up the cool air. Sand crunched beneath my sneakers for my regular morning walk along Hobie Island Beach Park, the narrow beach that’s just north of the big Rickenbacker Bridge along Biscayne Bay. I encountered the usual suspects: seagrass washed ashore, helping to form the wrack line, debris and other detritus, a sea bean (score), and-a sea star. A juvenile sea star, maybe three inches large. “How unusual,” I thought, as never in all of my years walking along this beach, had I found a sea star. I picked it up and examined it, and placed it a few inches into the water, for it was dead. I shook my head and kept going.
I had barely taken two steps when I almost stepped on another, and another. In the span of one-quarter mile, I found eight juvenile sea stars washed up on the shoreline. They were all in the same size class, all on dry land, all dead.
There are a number of reasons that could explain this phenomenon. Sea stars are considered “pelago-benthic,” which means that their larvae ride ocean currents but once they settle, they tend to be quite stationary or travel at a crawl over the bottom (Sheehan 2019). Knowing that they don’t travel very far on their own strongly suggested to me that these animals had ended up on shore due to some sort of disturbance.
Fish and invertebrates respond to both natural (storms, temperature shifts) and anthropogenic, or human-caused (pollution, boating activity, etc.) stressors. While a slight cold front did pass through our area on Monday, the associated air and sea surface temperatures were not particularly unusual or extreme. Water quality issues are not unheard of in Biscayne Bay, but if poor water quality were the culprit, it is highly likely that I would have observed signs of other organisms in distress, like fish.
After conferring with some local experts at the University of Miami and Biscayne Bay Aquatic Preserves, it seems more likely that these sea stars were pulled from the bottom by shrimp trawlers, drifted ashore during high tide and got stranded when the tide went out. This would also explain why the sea stars were contained to a localized area. It is critical that while we are out, enjoying the beautiful resources and weather that Miami offers, we remain vigilant about what we observe. As we hear multiple times while traveling: “if you see something, say something.” Please report any unusual observations such as this one to me, Ana at: firstname.lastname@example.org.
Obtaining information like this can assist resource managers with responding quickly to events like this one in the future.
Sheehan, E. 2019. Motion in the ocean-Paradigm shift in movement ecology requires “sedentary” organisms to be redefined. Journal of Animal Ecology, Vol. 88, p. 816-819.