Metridium farcimen (A) before injection and injected with 1.0 mL of (B) 10% methylene blue, (C) 10% neutral red, and (D) 0.25% fluorescein. Endodermal tissue in the column and tentacles as well as cinclides are clearly marked in stained anemones. (Contributed photo)

Anemones of the San Juans | Tide Bite

  • Sun Oct 11th, 2020 1:30am
  • Life

By Christopher Wells

I first heard about UW Friday Harbor Labs, the “Mecca for invertebrate zoology,” in an Invert Zoo course during my Master’s work at the University of New Hampshire. I was told that any marine biologist worth their weight in salt needs to work at FHL, so I made it my mission to get there someday. I fell in love with sea anemones in New Hampshire and frequently read papers by Dr. Kenneth Sebens, who was the director of the Labs at the time. When I interviewed to be his graduate student, he gave me a tour around the campus and I knew I needed to be there. Being able to have an office with running seawater just a stone’s throw from the sea was my dream. Not only that, but the giant plumose anemones ( Metridium farcimen) under the docks were awe-striking; I had never seen such big anemones in my life (turns out they’re the tallest anemones in the world and the ones under the docks are small specimens!).

Anemones are particularly diverse in the northeast Pacific, with more than 22 species around the San Juans alone, but their ecology is poorly understood. Ken and I were particularly interested in the giant plumose anemone Metridium farcimen which dominated some, but not all, of the walls he was surveying. This species is a dominant competitor, and yet their distribution is patchy both at small (meters) and large scales (whole walls). Additionally, they seem to live on vertical walls only in shallow environments, becoming more abundant on horizontal and sloping surfaces as we dive deeper. Why? Are they preferentially settling in these seemingly similar environments, settling just about anywhere and then moving to the right place, or are they getting eaten in places where predators can hunt for them?

To tease apart these questions, I needed a way of tracking individuals. This was the focus of my first dissertation chapter. When all individuals are white to eggshell to cream-colored, telling the difference between anemone A and B is difficult. Ken had published a way of marking anemones in the intertidal by painting them with neutral red (Sebens, 1976), but it required taking the anemones out of the water or waiting until the tide went out. That doesn’t work with an almost strictly-subtidal species. We came up with a potential solution: inject them with dye. The only problem was that we didn’t know whether that would negatively affect their behavior and growth (the data we actually wanted to collect!), so we designed an experiment to test the stain’s efficacy. We tried three different stains: neutral red, methylene blue, and fluorescein. We collected small Metridium from the Port of Friday Harbor’s floating docks (because small ones were more likely to show measurable growth) and injected them with different dyes. Neutral red ended up marking the anemones for eight months, methylene blue lasted about six weeks, and low levels of fluorescein lasted three days. Unfortunately, high levels of fluorescein were toxic to Metridium.

We also looked at the diet of Metridium farcimen. How does this plankton eater’s diet compare to the plankton community around it? Are they preferentially eating certain species? We collected anemone gut content samples from the FHL docks, identified everything they were digesting with DNA techniques, and then compared that to what was in the plankton at the time. We found large overlap with the plankton community (as you’d expect for a plankton-eating anemone, Figure 3), and did not see any statistically significant preferential consumption. We did see that there were many species that were less abundant in the diets of the anemones, presumably because they have ways of escaping predation or were too small to eat. These included some species of copepod, many bivalve larvae, several larval worms, and many rotifers. Interestingly, 10% of the anemones’ diet was an ant species that has mating flights during the time of the gut content collection, indicating that in at least some populations, terrestrial input may be an important component of Metridium’s diet.

For part of my dissertation work I also quantified more broad-scale distribution patterns of the common coral and anemones in the San Juans to examine what abiotic and biotic factors are most important for them. This field research involved figuring out the density of different species in locations that spanned the full local breadth of flow, light and predation pressure (sea star abundances). We studied many fan-favorite locations such as the Lime Kiln Lighthouse, Cantilever Point and the subtidal below the Rosario Resort on Orcas. We found that most anemones (except the intertidal cloning anemone Anthopleura) avoid high light locations (by living deeper or on vertical surfaces, Figure 5) and low flow areas. This makes sense because high light locations are generally covered in macroalgae, and low flow areas have less food passing by as well as lower levels of oxygen. This pattern held true for both “regular” anemones and our one local hard-coral species, the cup coral Balanopyllia.

Anemones and corals are major constituents of most subtidal communities and are present from the tropics to the poles and from the shallows to the abyss. They can have major impacts on the food webs they belong to and are fierce competitors for space. Understanding how these species fit into their local habitats as well as how their distributions are impacted by competition and flow is important if we want to better understand the beautiful ecosystems around the San Juan Islands and farther afield. My research at FHL helped shine some light on what’s going on under that dock and I hope to be back there soon to continue looking at those wonderful animals.

Dr. Christopher Wells completed his Ph.D. with Dr. Ken Sebens in 2019 in the Biology Department at the University of Washington. His research was on the biology and ecology of sea anemones in the San Juan Archipelago. He is now a postdoctoral associate at the University at Buffalo, researching the recruitment and population dynamics of Caribbean octocorals. You can follow him on Twitter @the_anemone_guy.