Sea Urchins Keep Surviving as Marine Life Deteriorates in the Florida Keys

Marine life in the Florida Keys is negatively impacted by two nefarious forces: human activity and climate change. The former involves fishing, tourism, and diving, while the latter causes a spike in intense hurricanes. As such, when Florida museum researchers started looking for sea urchins on the ocean floor off the coast of the Florida Keys back in the summer of 2020, they uncovered some good news: their population was relatively stable since the 1960s.

The researchers, who published the analysis of their survey in the journal PeerJ, visited 27 sites along a 20-mile stretch of coast near Long Key looking for tracks and dimples in the sediment that reflected the presence of burrowing echinoids (sand dollars, sea biscuits, and heart urchins) concealed just beneath the surface. "The Florida Keys have had some 'ah ha' moments for us," study co-author Tobias Grun tells Treehugger. "The number of burrowing echinoids that can co-exist in one spot, or the sheer abundance of some burrowers was remarkable."

Since the scientific community doesn't know much about the role burrowing echinoids play in creating and maintaining marine environments, the findings are significant.

"The findings that burrowing echinoids have been highly resilient against climate change and environmental pollution over the last 60 years was a huge discovery for us," says Grun. "Even though burrowing echinoids are of such high ecological importance, we don't know much about their current distribution, population size, and health. The reason, therefore, is by far not the lack of interest by the scientific community but lies more in the nature of the research itself: fieldwork is very expensive."

"The more we worked with burrowing sea urchins, including research using these echinoids as role models for sustainable building constructions, the more we understood that our knowledge was extremely limited and mostly based on research conducted between the 1960s and 1990s with all the technical limitations of these eras. We are now able to overcome many of the technical limitations our colleagues have encountered in the past, but very little progress has been made since then."

Sea Urchins Are Important to Marine Ecosystems

Sea urchins—the name is a mix of Greek and Latin that translates to "spiny skin"—are echinoderms related to starfish, sea lilies, brittle stars, and sea cucumbers. They come in two variants: regular and irregular. Regular sea urchins are spherical with spines. Irregular sea urchins are burrowers and include sand dollars, sea biscuits, and heart urchins. Both types are essential for healthy marine ecosystems.

Grun explains that regular sea urchins—"those well-known ball-shaped spiny critters that can be found on rocks and reefs"—are crucial to their ecosystems for controlling algae and other microbial coverage. As for burrowing echinoids—irregular sea urchins that live in sandy and muddy parts—they also have a critical role in the marine ecosystem.

"They dig through the sediment and thereby ventilate and oxygenate the upper sediment layers of the sea floor. This is thought to allow aerobic micro-organisms to settle in interstitial spaces between the sediment and decompose organic material as well as other matter," says Grun. "In addition, burrowing echinoids feed on organic material in the sediment and so clean the ocean floors."

"Finally, some of the burrowers crack sediment grains with their powerful jaws to get access to organic material on and in the porous sediment grains. By doing so, they actively control the sediment’s grain size in their habitats. Altogether, they can be considered ecosystem engineers that play a critical role in the development, maintenance, and health of soft-bottom habitats."

As the climate crisis progresses, it's important to understand why some marine creatures are more resilient in withstanding the impacts of a deteriorating environment than others. Grun says evolution may be at play. "Some marine animals are very opportunistic," he says. "They can tolerate a wide range of abiotic factors like pH, temperature, and salinity, to name a few. They are evolutionarily built that way."

That said, Grun warns that being able to survive under certain poor conditions does not necessarily mean that populations are stable and unaltered over time.

"At this point, our data indicate that burrowing echinoids are more resilient than other marine species and are doing comparatively well. That does not mean that we can push our luck and keep going the way we are right now. Our study provides some hope that these critters are resilient, but this is a temporal and geographical snapshot and much more work is needed to translate our findings into a larger scale. The reasons for their resilience are also widely unknown."

This article was written by the Treehugger editorial team and the interview with Tobias Grun was conducted by Mary Jo DiLonardo.