The Confluence of Sod and Sea with Sara Wickham
Complex, dynamic, and deeply dependent, ecologist Sara Wickham shares the unexpected ways in which seaweed harmoniously weaves marine and terrestrial ecosystems together.
The most integral and supportive relationships are often the most unassuming. Ecologist, Sara Wickham, studies the often overlooked but incredibly crucial role of sea wrack, or dead, washed-ashore seaweed, on Pacific Northwest food webs. Seemingly humble, sea wrack provides nutrient subsidies to terrestrial ecosystems that could change the way we think about island ecology. Only with the knowledge of these complex, deeply dependant, and perpetually fluctuating ecosystems can we begin to understand the fragility and connectivity of their symbiotic relationship.
FCLTY: So I looked up your research station and must say it is ridiculously remote and incredibly beautiful. Can you tell us about your research and the 100 Islands Project?
My research takes place on the central coast of British Columbia, Canada in and around an area called the Hakai Lúxvbálís Conservancy—its sexy name being, the “Great Bear Rainforest”. This beautiful territory is a remote, exposed, boat-access only region. My team and I spend our summers based out of a research station on Calvert Island from which we take 12-14 day camping trips to nearby island archipelagos to conduct biodiversity surveys.
The broad goal of the project is to investigate how Island Biogeography (IB) theory is affected by ecosystem subsidies. To do this we are surveying 100 islands (hence the project’s name) for terrestrial plants, invertebrates, songbirds, mammals, and sea wrack.
FCLTY: That sounds like a great way to spend the summer. Can you tell us more about ecosystem subsidies and the role of sea wrack in nutrient transfer?
Ecosystem subsidies refers to the transfer of organisms or nutrients across environmental boundaries, to the advantage of a resident population or populations. On the central coast of British Columbia, the terrestrial environment has the potential to be heavily subsidized by marine nutrients. Nitrogen rich bird guano, spawning salmon, intertidal invertebrates, and herring eggs are all deposited and/or consumed by terrestrial animals. However, these sources of marine nutrients can be highly seasonal events and occur in very localized areas.
A more consistently available source, both seasonally and spatially, are dead seaweeds (aka sea wrack) that have washed up on shorelines.
Sea wrack is an overlooked but hugely important component of BC’s terrestrial food webs. It is the main food and habitat food resource for amphipods, wrack flies, and coleopteran beetles, which in turn are eaten by birds, mice, shrews, minks, black bears, wolves and many more.
One of the more famous ecosystem subsidies in the Pacific Northwest is the migration of salmon from the ocean to their freshwater natal streams. The salmon carcasses (which are chalk full of marine-derived Nitrogen) fertilize terrestrial plants and feed a vast amount of terrestrial mammals, birds, and invertebrates. However, salmon spawn and die in freshwater streams—not many of which exist on the small islands we study. Sea wrack, on the other hand, is found consistently throughout the 100 Islands study region. They only differ in species composition depending on where you are and what time of year it is.
FCTLY: I never realized dead sea weed was such an integral component of nutrient transfer between ecosystems. What’s your favourite aspect of your research focus?
Overall I feel passionate about my research because I believe it exemplifies the pervasiveness of interconnectivity between ecosystems. The reality is that the health of the terrestrial environment is entirely dependent on the health of the marine environment, and vice versa.
Using something as banal as rotting seaweeds to highlight this dependency seems to me like a fantastic way to reiterate the narrative of ecosystem connectivity.
FCLTY: I really enjoy how the relationships of this inter-ecosystem narrative are unexpected but incredibly rich. What about in reverse? How do the terrestrial environments benefit the oceans?
One instance that’s particularly relevant up here is rivers, creeks, and streams flushing organic matter and cycling carbon into the ocean. The nutrients in this organic matter feed microbes and zooplankton. These organisms are the basis of the marine food web and are responsible for nourishing everything from clams, barnacles, and crabs to massive baleen whales.
FCLTY: What do you think is the most valuable takeaway from your work in the way we think about ecosystem dynamics and dependency as a whole?
I think most people view these ecosystems as separate entities, largely unaffected by each other’s processes. In reality, terrestrial and marine ecosystems are inherently connected.
There are many cases where land has been protected in order to save habitat for a certain species – say for example bears. But bears are dependent on salmon as a food source and overfishing has caused massive declines in salmon populations. So in order to restore or maintain a population of bears one would also have to address the issues facing salmon populations.
Food webs are complex, opportunistic, and always fluctuating. They are definitely not confined to a single ecosystem or environment.
FCLTY: What do you think would help people understand this more?
Education and awareness! In as many forms as possible. Science communication is great, but I think many of the questions we are asking and answering as scientists are part of a larger narrative. And this narrative is relatable to many people, it’s just not intriguing to many in its current form. And so communicating our research through stories and art can increase the capacity for a larger audience to connect to the work.
FCLTY: Are there ways in which humans can leverage the benefits of sea wrack by cultivating and supplementing areas that are lacking in nutrients?
On a small scale, savvy gardeners who live near coastlines have been gathering seaweeds and putting them into their gardens and composts for hundreds of years – it’s a technique seen all over the world in many cultures. Seaweeds absorb mineral from the ocean which can fertilize soils with trace elements. And the fibers in the brown kelps aid in soil moisture retention. However, I don’t think seaweeds are used to fertilize crop lands on an industrial scale, the cost of cultivating, drying and transporting the seaweeds to agricultural areas may be too prohibitive.
FCLTY: What about existing land management practices that have a positive impact on the area? For instance, First Nations land management techniques and how these have affected the intertidal ecosystems?
First Nations people have occupied this area since time immemorial and so their ecosystem management techniques have been informed by thousands of generations of local knowledge. This knowledge manifests itself as a sustainable and respectful use of resources. Common modifications to the landscape that we see now (as archeological sites), that would be ancient resource harvesting sites are fish traps, culturally modified trees, intertidal root gardens, and shell middens. Fish traps, although now defunct, trap sediments and provide habitat for intertidal organisms. And new research has shown that trees located near shell middens grow taller, wider, and healthier (Trant et al. 2016).
So although human land use is generally associated with deteriorated landscapes, up here it is the opposite, and historical First Nations use of the land has actually enhanced the ecosystem.
FCLTY: What changes to the volume and distribution of sea wrack have you seen in the Great Bear rainforest in general?
It’s interesting because the north end of our study area has been recently recolonized by sea otters, who haven’t quite made it down to the south end just yet. So on the north end we see the classic otter-urchin-kelp trophic cascade. The otters chow down on the sea urchins, and sea urchins eat kelps. So with less urchins around the north end of our study region, the kelp forests are increasing.
Down south, urchins abound. They literally mow down kelps forests to bare rock. The resulting underwater wasteland is called an urchin barren. Obviously with less seaweeds and kelp growing in the ocean, there is less wrack to wash up on shore. So sea-otter colonized areas may have increased amounts of wrack washing ashore, which would increase the transport of marine nutrients to the beaches and forests. Otters could potentially affect wrack in a positive way!
FCLTY: What’s one particular experience that comes along with this work that you absolutely love? Is there something sensorial or personal that makes the day to day of the project great for you?
I love the region I work in. Despite the unrelenting rain, bugs, and lack of showers I look forward to my three months in the field all year.
Day to day I feel so damn lucky to be exploring such a remote and beautiful part of the world, one that few people have the opportunity to visit.
And I get to share my field experiences with a rad group of people and we are supported by the equally as rad staff at the the Hakai Institute.
FCLTY: Can you tell me one of your crazy/most special/totally weird moments in your field work?
I had a staring contest with a wolf once. That was pretty bananas! It was only about 5 meters away, we stumbled upon each other in the woods. Eventually it got bored of me and sauntered away. Well actually, it walked away when I reached for my camera. Classic wildlife move!
Interview and text: Brynn Catherine McNab
(Image Source: Hakai Institute & Sara Wickham)