A Faithful Analogue of Modern Marine Ecosystems Lies Just Beneath the Surface

Biologists striving to restore and preserve depleted environments face a significant challenge due to their limited understanding of pre-human ecological conditions. This knowledge gap is particularly pronounced in coastal ecosystems, which had already undergone substantial transformations from pollution and overharvesting long before scientific monitoring began.

However, a recent study published in the esteemed journal PeerJ presents an intriguing revelation: a faithful representation of modern marine ecosystems resides just beneath the surface. Building upon more than two decades of conservation paleobiology research, the findings indicate that fossils of various marine groups, including worms, mollusks, crabs, and sea urchins, are preserved in proportion to their diversity.

Michal Kowalewski, the Florida Museum Thompson Chair of Invertebrate Paleontology and co-author of the study, expressed, “This has been a topic in paleontology for decades.

“People have looked at modern ecosystems in a variety of habitats to see how well the fossil record reflects what’s living there. But most previous studies looked at how species are recorded within a specific group. We wanted to know how groups are recorded within the entire system.”

Fossils serve as a partial and imperfect record of Earth’s past, with organisms primarily composed of soft tissues being less likely to be preserved compared to those with hard, durable parts like bones and shells. The durability and strength of these hard parts, which vary depending on the organism and its developmental stage, influence their preservation likelihood.

To circumvent this challenge, researchers have used mollusks as proxies for assessing overall ecosystem health. Mollusks have a robust representation in the fossil record and previous studies have demonstrated their reliability as indicators of past diversity. Notably, recent research in Europe has revealed the nearly complete collapse of native molluscan biodiversity in the eastern Mediterranean Sea due to global warming, suggesting that other marine groups in the region may be approaching similar thresholds.

Much like a doctor gauges a patient’s vital signs, scientists can broadly infer the health and stability of an environment by examining fossil mollusks. However, to discern specific patterns related to population declines, shifting ranges, and the introduction of invasive species, a comprehensive examination is necessary.

Lead author Carrie Tyler, an assistant professor at the University of Nevada, Las Vegas, elaborated, “Most of what we know, in terms of biases in the fossil record, is based on mollusks.”

They designed their “study to determine whether those biases are consistent when you include many types of organisms, not just mollusks. What happens when you have worms and sea urchins and all other groups in a marine ecosystem?”

Before arriving at their conclusions, Tyler and Kowalewski sought a suitable marine ecosystem for comparing living and fossil organisms and studying discrepancies between past and present communities. They selected a relatively pristine area off the coast of North Carolina, comprising both living animals and skeletal remains. The researchers collected samples from 52 localities along transects extending from near-shore coastal waters to the open sea.

Kowalewski explained, “We chose this system because it included a spectrum of habitats along an onshore-offshore gradient, from estuary to open shelf.”

Each habitat supported specialized communities, enabling Tyler and Kowalewski to assess the preservation potential for various organisms under different environmental conditions.

Over a span of two years, the researchers meticulously documented over 60,000 living and dead specimens representing hundreds of marine invertebrates. As anticipated, the robust shells of mollusks led to their overabundance in the fossil record compared to other groups. However, fragments of deceased corals, sand dollars, tube-forming worms, and other non-mollusk organisms were broadly represented at similar levels of abundance and diversity as their living counterparts.

Groups with limited existing diversity in the region, such as sea stars and brachiopods, were not recovered from the fossil record due, in part, to their low numbers. Additionally, past and present habitats often featured different dominant species. For instance, a common type of hermit crab today did not appear in the fossil record. However, the overall number of species across different groups remained relatively consistent.

Most marine ecosystems lack a comprehensive inventory of their inhabiting species, and the current roster is dwindling as some species decline in abundance or face extinction. Nevertheless, if other marine ecosystems exhibit similar fidelity to those in North Carolina, researchers will possess a new baseline to evaluate the long-term viability of supported communities.

Tyler emphasized the significance of these findings, stating, “We can use the whole fossil assemblage as a picture into the past for a particular place despite differences in preservation among animals. By comparing it to the living community, we can see how much an ecosystem has changed and decide on the best conservation strategies based on those changes.”

Source: 10.7717/peerj.15574

Image Credit: Florida Museum of Natural History