The Importance of Ecosystem Engineers
It's Endangered Species Day, and we're taking a closer look at the important role that two species of protected sea turtles play as ecosystem engineers.
- Conservation •
The green sea turtle and the hawksbill sea turtle—both listed and protected under the Endangered Species Act of 1973—are two examples of ecosystem engineers, species that perform activities that significantly alter their environment, oftentimes by creating and maintaining microhabitats that would not otherwise exist.
Ecosystem engineers like green and hawksbill sea turtles highlight the importance of protecting every animal in an ecosystem since each one has a role to play. An ecosystem is a delicately woven system of checks and balances, and when this system is disrupted—for example, when a species begins to disappear—it creates a ripple effect that impacts not only the other animals in the system, but also the ability of the ecosystem to fulfill its function.
This is especially true for ecosystem engineers; if their populations start to dwindle or disappear entirely, they're not able to perform their role of creating microhabitat for other members of that ecosystem. The animals that rely on these microhabitats may begin to disappear as well, which can disrupt the food web, since larger animals may rely on the smaller animals found in microhabitats for prey. Ecosystem engineers are critical in helping to maintain the biodiversity of an ecosystem, which is a key indicator of ecosystem health.
In the case of the green and hawksbill sea turtles, their foraging behaviors—for seagrass and marine sponges, respectively—are key in helping to maintain the function and biodiversity of their ecosystems.
Green sea turtles—which are listed as threatened in the U.S. and endangered internationally by the International Union for the Conservation of Nature—will eat both plants and animals as juveniles, but as adults, they're primarily herbivores. In many parts of their range, seagrass constitutes a major part of their diet. An adult green sea turtle, which can weigh an average of 110 pounds, can eat more than 1,000 pounds of seagrass per year.
Green sea turtles form "grazing plots" in seagrass beds and help to maintain the health of these habitats. Freshly cropped seagrass quickly sends out a dense growth of new leaves that have a higher nutritional content for grazers. Additionally, as shown by a 2020 study focusing on a population of green sea turtles in the Caribbean, these turtles' grazing habits improve the growth rate of seagrass, increasing the overall productivity of this habitat.
In addition to helping to maintain the health and productivity of seagrass beds—which serve as critical breeding and nursery grounds for various species of fish and other animals—green sea turtles perform another important function for these ecosystems: creating microhabitats. Their grazing creates distinct areas with old plants, young plants and open bottom areas. This diversifies the seagrass bed habitat, which in turn improves the biodiversity of that ecosystem. Without a healthy population of green sea turtles, seagrass beds can become monocultures of old plants that slowly break down, producing excess detritus. This lessens their productivity and ability to provide microhabitats for invertebrates that are only found in clearings of seagrass beds. These invertebrates are prey for various species of fish, including species that are commercially important to humans, and are crucial to the ecosystem's food chain.
Hawksbill sea turtles–which are listed as endangered in the United States and critically endangered internationally by the International Union for the Conservation of Nature—feed almost exclusively on marine sponges in many parts of their range, which they pluck from the crevices of coral reefs with their sharp, narrow beaks.
Although coral reefs occupy less than 1% of the ocean floor, they support an estimated 25% of marine life—making them one of the most ecologically diverse habitats on Earth. Competition on a reef is fierce, with dozens of species competing for space, including marine sponges. Caribbean reefs in particular have an abundance of sponges; their biomass and diversity often exceed that of corals. A healthy population of hawksbill sea turtles in a coral reef ecosystem helps to keep the population of dominant sponge species in check, which in turn allows other species—such as reef-building corals and rarer sponge species—to colonize.
Hawksbills are key in maintaining the rich diversity of species on a coral reef; without these turtles, sponges could out-compete coral for space and the biodiversity of the reef community would decrease—along with the ability of these critical ecosystems to support so much life in the ocean.
After decades of serious decline in the 20th century, there have been significant improvements in many populations of sea turtles in U.S. waters, thanks to the Endangered Species Act. Take the green sea turtle, for example: According to data from a study of main nesting beaches in Florida conducted by the Florida Fish and Wildlife Conservation Commission, green sea turtle nest counts grew from less than 300 in 1989 to almost 41,000 in 2019.
The Endangered Species Act aims to protect at-risk animal and plant species from extinction. All six species of sea turtles found in U.S. waters are listed and protected under the Endangered Species Act. Since the act was passed, 99% of the species listed as threatened or endangered have avoided extinction, according to the World Wildlife Fund. The success stories of species that have recovered in the U.S. highlight the critical importance of the protections offered by the Endangered Species Act.
However, supporting conservation efforts that prevent species from declining in the first place is also imperative. Nationwide, more than 12,000 species of plant and animals have been identified as species of greatest conservation need. Many of these species are at risk of becoming threatened or endangered without additional conservation action. Currently, there's a bill in Congress that would do even more to protect our most vulnerable species: the Recovering America's Wildlife Act.
This legislation would provide $1.4 billion annually to states, territories and tribes for proactive conservation of at-risk wildlife, helping to restore their populations and ensure their longevity for future generations. The legislation would provide the funding and resources necessary to allow populations of vulnerable species to rebound before they become endangered. The Recovering America's Wildlife Act is based on the premise that upstream investments can prevent species from becoming endangered and keep thousands of species from reaching the brink of extinction.
In addition to our strong support for funding endangered species conservation, the National Aquarium urges Congress to pass the Recovering America's Wildlife Act, which aligns with our conservation goal of saving wildlife and habitats. When we save a vulnerable species, it doesn't just benefit that animal—every other species in its ecosystem that relies on a diversity of habitats benefits as well.
Act now and join the National Aquarium in showing your support for the Recovering America's Wildlife Act.