Dr. Sebens conducts research on benthic populations and communities in both temperate and tropical locations. One project is an investigation of community and population dynamics, and long-term change in rocky subtidal habitats in Massachusetts. This project has been funded by NSF since 1979, facilitating one of the most extensive long-term studies of coastal marine communities in the world, and will be continued in collaboration with researchers at Northeastern University. He will also initiate new research on the rocky subtidal communities of the San Juan Islands.
Dr. Sebens has had over 30 years experience as a diving scientist, including six one to two week missions living and working in the underwater laboratories "Hydrolab" and "Aquarius", located on Caribbean coral reefs. His research on coral ecology has focused on the diverse sources of nutrition for reef corals, and the influence of hydrodynamics on coral particle capture and nutrient uptake from seawater, calcification and growth rate (NSF, NOAA funding since 1985). These studies have taken him to many Caribbean reef locations including Jamaica, St. Croix, Belize, and Bermuda. He also spent a sabbatical year in Australia working on the Great Barrier Reef, while based in Townsville and Lizard Island.
Commercial and recreational fishing can dramatically alter marine ecosystems. Management decisions affect not only target fishes, but also species related to targets through ecological networks. Removal of top predators from subtidal communities releases prey species from predation, allowing prey populations to increase. Examples from around the world have shown that impacts from predator removals can cascade throughout multiple trophic levels, including impacting harvestable species at lower trophic levels. Besides impacting other harvested species, predator removals also may significantly change the composition of the full marine community.
In the San Juan Islands benthic habitats, the primary species targeted by fishers is lingcod. Recently, rockfish were excluded from fishing due to concerns about dwindling numbers, but incidental capture and mortality still exists. Decades of commercial and recreational fishing for these bottomfish species in Washington waters have caused serious declines in their populations. Fisheries managers have attempted to rebuild stocks through catch limits and area closures (marine protected areas). In some instances MPAs do appear to be successfully increasing bottomfish populations.
Lingcod and rockfish are primarily predators on fishes and crustaceans, whereas the majority of predator-induced impacts from hard-bottom communities around the world involve removals of predators on sea urchins. Therefore, the impacts of changing predator abundance in Washington will likely follow different paths than those seen elsewhere. My research explores how removals of these fish species affect the benthic community in the absence of the strong predator-urchin-kelp food chain observed in other communities. I seek to answer this question with a combination of community surveys at sites with varying fish abundance (including several MPAs) and predator exclusion cages, to determine how lingcod, rockfish and other demersal fishes structure the food web.
I am broadly interested in the causes and consequences of biological diversity. The relative contribution of local and regional processes to the diversity of local communities has been a topic of lively debate, which in turn has highlighted the importance of spatial scale, an issue central to both ecological theory and conservation efforts.
I study epilithic communities found on subtidal vertical rock substrata (walls), which harbor an impressive diversity of sessile invertebrates (e.g., sponges, bryozoans, ascidians), some algae (mostly reds), and their predators (snails, stars, urchins, fish). I have conducted small-scale field experiments at three sites in the San Juan Islands, WA, testing the effects of urchins and chitons on the diversity and structure of the sessile invertebrates and algae on walls.
To place the experimental fieldwork into a broader geographic context, I surveyed 12 additional sites in the San Juan Islands and three sites in Hood Canal, Washington. The field experiments and surveys were complemented by diet analyses of urchins and chitons. These empirical data will be used to quantify the relative importance of diversity, consumers, and mesoscale oceanographic variation in this community.
Shipwrecks and other submerged structures are amazing natural laboratories where researchers can study ecological processes and community interactions resulting from localized disturbance events in our coastal oceans and deep seas. We know when man-made materials enter the ocean, a wide variety of organisms begin to aggregate and new communities form. But there are very few studies investigating these community-wide interactions and currently there are no quantitative, predictive capabilities when designing submerged structures such as piers, breakwater walls, or artificial reefs.
Given our desire to live within a few miles of every coastline on the planet, there will likely always be anthropogenic modification of existing shorelines. There will also come a time in the not-so-distant future when we need to mitigate the damage some of these modifications cause to our coastal oceans. Studying the effects of existing submerged structures, some having been acclimatizing to their ocean setting for hundreds or even thousands of years, will help inform engineers and managers how to bio-construct and monitor new structures which have the capability to enhance and promote ecosystems for a sustainable coexistence with our coastlines.