Human population growth is rapidly accelerating in coastal areas. More than half of the world’s population already lives in coastal zones. Over the next 10 years, this will increase to 75%, bringing an extra 2.5 billion people to the edges of the world’s continents.
At the same time, coastlines are becoming increasingly treacherous environments for humanity. The seas are rising as our planet warms, inundating entire communities in some locations, and posing a particularly grave threat in low-income areas (reference).
To deal with these changes, many cities have already begun massive “adaptation planning” efforts – rebuilding old seawalls, reinforcing existing shoreline armoring, and expanding the reach of coastal defense structures.
- What is the impact of these structures on marine ecosystems?
- What new assemblages of marine organisms are made possible by the increased availability of hard substrate that these structures provide?
- How can we design artificial structures better so that they facilitate ecological communities that reflect natural ecosystems and provide improved ecosystem services for future human populations?
These are the central questions that drive my research interests. I work primarily in Puget Sound, Washington, though have had the opportunity to pursue these questions through research in the Northern Adriatic, Italy, and in Sydney Harbour, Australia, thanks to the guidance and support of two amazing scientists who work on similar topics: Laura Airoldi and Emma Johnston.
In Puget Sound, my work centers around the following topics:
1. Characterizing species assemblages on artificial structures across a gradient of urbanization in Puget Sound.
Studies on the types of organisms that live on artificial structures are few. Most have come from Sydney Harbour, where researchers found that artificial structures (seawalls, artificial reefs, pontoons, marinas, etc) facilitate novel assemblages of hard-substrate organisms.
We conducted photoquadrat surveys at 39 sites throughout Puget Sound where there was artificial rocky hard substrate. We are currently evaluating the data to determine whether the composition of organisms differs according to the level of urbanization on adjacent land masses, and how these effects compare to those of other natural factors such as flow, salinity, and depth.
2. Are Giant Pacific Octopus an urban mesopredator?
In preliminary surveys of heavily urbanized areas in Puget Sound, we were surprised by the abundance of Giant Pacific Octopus (Enteroctopus dofleini). Though urban mesopredators have been well documented on land (think racoons and coyotes if you’re in North America), we know very little about the effects of urbanization underwater, and there has yet to be a documented case of a marine mesopredator that thrives in urban environments.
We’ve teamed up with the REEF Program, which empowers recreational SCUBA divers to collect observational data for science, to evaluate the spatial distribution of Giant Pacific Octopus (GPOs) in Puget Sound and determine whether GPOs may constitute the first example of an urban marine mesopredator. In addition to using observational surveys from REEF, we conducted video transects and midden collections throughout Puget Sound to quantify the effect of artificial structures on GPO densities and characterize GPO diets throughout the region. By “we”, I mean both myself and colleague/former capstone student (now Seattle Aquarium staff) Amy Green.
3. Understanding the effect of biogenic material from artificial structures to soft sediments.
Most coastal cities are positioned at the mouths of rivers or in estuarine systems where soft sediments are the dominant substrate type in marine habitats. Sediments facilitate fundamentally different assemblages of marine organisms than hard substrates. However, as a result of the expansion of artificial structures in urban areas, urban marine seascapes typically consist of a complex patchwork of soft sediment and artificial, hard-substrate environments.
The organisms that grow on hard substrate tend to produce large amounts of biomass, or organic material. These include foliose macroalgae, shell-producing encrusting invertebrates, and fleshy invertebrate growth, such as that of Metridum farcimen, a common anemone in Puget Sound (see photo above).
In observational surveys, we found that tiny pieces of red foliose macroalgae and shell material from barnacles, jingle shells, and other invertebrates that grow on artificial structures were abundant in nearby sediments.
To test the effect of these “biogenic” materials on the community of clams, worms, and other invertebrates that live in soft sediments, we performed a series of field experiments, where we added shredded red macroalgae and shell fragments to experimental plots. This was done on the western shore of Alki, in West Seattle. Plots receiving material additions were intermixed with control plots (where no material was added) in a randomized grid on the western shore of Alki, West Seattle.
We found that while single additions of algae and shell material are of limited consequence for soft sediment communities, repeated additions, which appear to more accurately reflect the ambient rate of influx surrounding artificial structures in the region, reduce the abundance and diversity of most soft sediment organisms.
The works described here are still in preparation for peer review and publication, but should be out shortly. Stay tuned for links to published articles.
Throughout the text above, I’ve used the pronoun “we” in discussing my research. This is because none of it would have been possible without many many hours of hard work by volunteer divers and lab technicians. Though our diving activities at UW are currently on hold (due to recent administrative policy changes that make it cost prohibitive), I’m always eager to hear from potential lab volunteers who are able to commit a fixed amount of time on a regular basis.
If you have questions about any of the work described here, please don’t hesitate to be in touch!