A Greater Gray: Students investigate ecological connectivity in national marine sanctuaries
By Sam Furtner, Stephanie Gad, Isabella Marill, and Adam Qian
September 2017
Like us, marine species need insurance policies. Identifying areas of ecological connectivity and creating a network of properly placed marine protected areas can provide this insurance.
To identify areas ecologically connected to Gray's Reef National Marine Sanctuary, and therefore important for conserving pressured species, NOAA's Office of National Marine Sanctuaries proposed an ecological connectivity assessment as a master's thesis group project to the Bren School of Environmental Science & Management's class of 2017. To help support effective marine protected areas, we – four students in the Bren School's class of 2017 – worked with Gray's Reef National Marine Sanctuary to understand how fish species at the sanctuary are connected regionally and how these connections can inform management decisions.
By understanding which areas in the ocean are connected to each other through species migration and dispersal, we can create a network that offers protection to species over a larger geographic range. Additionally, if one of the connected areas becomes heavily impacted and can no longer provide adequate protection, the remaining network can substitute protection and help replenish the impacted area, essentially acting as that insurance policy. This is particularly beneficial for fisheries because it helps keep populations sustainable for harvest.
Marine protected area networks like these are advantageous to smaller marine sanctuaries, just like at Gray's Reef National Marine Sanctuary. Even though it is on the smaller side of most national marine sanctuaries, Gray's Reef is home to a spectacular array of biodiversity. Unlike typical coral-based reefs, Gray's Reef is made up of a unique “live bottom” ecosystem, referring to the hundreds of animals, like sea squirts, sponges, and barnacles, that carpet every inch of its rocky ledges. The sanctuary is also frequented by over 180 fish species, many commercially and recreationally important to the southeast Atlantic region.
Unfortunately, reports have shown these species are either facing or have historically faced heavy fishing pressure, resulting in population decline and subsequent impacts on both the ecosystem and the surrounding fisheries. An effective way to enhance the protection of these fish species is to figure out what surrounding areas are connected and design a network of protected areas that incorporates them.
We approached our project by considering the distribution of fish larvae. Larvae, the microscopic juvenile stage of marine organisms, are a great way to illustrate ecological connectivity because they are dispersed by ocean currents, allowing them to be modeled by computer software. They are also safer from human pressures like fishing when moving between protected areas than their much larger adult counterparts.
When fish larvae are released from one reef and end up at another, their start and stop points are considered ecologically connected. Using larvae to model connectivity can identify networks of areas that, when protected, can increase protection for species in areas where fishing pressure is high. Potentially “connected” areas may be adjacent to the sanctuary, but they could also be far away.
To identify areas larvae might settle and mature, our team used geographic information system (GIS) software to model larvae by releasing them from known spawning locations and simulating their dispersal using ocean currents data. We modeled four fish species: gag grouper, scamp grouper, red snapper, and black sea bass. Our goal was to find which areas delivered the most fish larvae to Gray's Reef National Marine Sanctuary. Model results showed where larvae were released, where they ended up, and how strong the connection between the areas were based on the quantity of larvae delivered. Areas with the highest larval contribution possessed the strongest ecological connectivity to Gray's Reef and were regarded as candidates for a protective network.
We devised several maps that show the exact network sizes with corresponding conservation goals to help managers visualize management decisions. However, when considering the design of a marine protected area network, there are a number of important next steps, such as the incorporation of potential socioeconomic costs and modeling for different environmental scenarios (e.g., impacts of climate change).
Lastly, we created a framework of our model that can be used by other sanctuaries to explore the ecological connectivity of their region. Our framework can readily be coupled with a socioeconomic analysis to determine the most cost-effective way to attain target levels of protection.
Ocean acidification, sea temperature rise, pollution, overfishing, and other human- and naturally-induced pressures are causing our ocean to change. Now more than ever we need insurance policies to ensure the health of our ocean and the sustainable growth of marine species. A deeper understanding of how the ocean is connected provides a foundation for impactful spatial management, benefiting our marine ecosystems and fisheries.
