Award: OCE-1851286

Since the discovery of deep-sea ecosystems fueled by chemical energy—such as hydrothermal vents and cold seeps—more than 40 years ago, one of the biggest mysteries has been how these isolated communities of specialized animals are maintained and connected. Because these ecosystems are separated by vast stretches of ocean, scientists have long wondered how their microscopic larvae travel between sites. Larvae are carried by ocean currents, but they are so small and so widely scattered that tracking their journeys is extremely difficult. Our project investigates how larval behavior—like how long they spend in the plankton, how they move vertically through the water, and whether they remain near the seafloor—interacts with ocean currents to shape the distribution of cold-seep animals on both sides of one of the world’s most famous biogeographic barriers: the Florida peninsula.

Cold seeps are found from ~500 m to ~3000 m throughout the Gulf of Mexico (GoM) and the Western Atlantic Margin (WAM). Both regions host beds of symbiont-bearing mussels that use methane for energy. These mussels—Gigantidas childressi, Bathymodiolus brooksi, and B. heckerae—provide habitat for a diversity of other animals. Although the GoM and WAM have similar seep habitats and the mussels are on both sides of the Florida peninsula, WAM seeps support only a subset of the other animals found in the GoM. We hypothesized that the ability of larvae to disperse through the relatively shallow waters of the Florida Straits may be constrained by where the adults spawn and by the depths at which their larvae drift. If larvae of some species spend more of their larval lives at depths that do not allow them to cross the Straits, this could explain why some species never establish populations on the other side.

To test these ideas, we sampled larvae repeatedly at seeps at three depths in the Gulf of Mexico and three on the Western Atlantic Margin. Using the recently-developed SyPRID sampler deployed on autonomous underwater vehicle Sentry, we collected larvae from precise depths in the water column and near the seafloor. We also used a multiple-closing net system and deployed larval traps on the seafloor at several depths to determine what fraction of larvae remain very near the seafloor. After collection, larvae were carefully identified and biological parameters (swimming speeds, physiological measurements) were recorded for some key species.

Larvae of mussel species were found at both GoM and WAM sites—including at locations that do not match the adults' current distributions. We even detected mussel larvae in the upper water column around the Florida Keys. These measurements will provide realistic estimates of biological parameters—vertical distributions, swimming speeds, and physiological tolerances—that can be included in larval tracking models that are currently being produced. These models can predict which cold seeps will be connected by larvae released at different depths.

Understanding larval dispersal is essential for conserving deep-sea ecosystems. Cold seeps are major natural filters that remove methane—a potent greenhouse gas—from entering the atmosphere. These cold seep ecosystems are also known also provide essential habitat for deep-sea fisheries and corals and provide energy for broader food webs, making knowledge of their connectivity increasingly important for management.

This project also provided substantial educational benefits. It supported eight undergraduate researchers—three through NSF’s REU program and one as capstone thesis student—and a postbaccalaureate intern who later became an NSF Graduate Research Fellow and continued to study methane seeps. Additionally, two master’s theses resulted from this project, both now in preparation for publication. Six students gave eight presentations on this work at national and international scientific conferences.

Formal education and informal, public education were important components of the project as well. In 2020, we taught a shipboard course on cold-seep science aboard the R/V Atlantis, giving students hands-on experience with the HOV Alvin, shipboard oceanographic research, and cold-seep ecology. Research from this project also contributed to a 2025 undergraduate course at Western Washington University on methane seep ecology. Learning opportunities are also available to people of all ages through a student-created interactive StoryMap project, aimed to leave the user more excited about what seeps below and to bring these unseen ecosystems into the public eye. Finally, we are in the final stages of developing interactive video exhibits on deep-sea biology, cold seeps, and larval ecology produced for small museums and aquaria on the coasts of Oregon, Washington, and North Carolina.

 

 

Last Modified: 11/30/2025
Modified by: Shawn M Arellano