In the summer of 2017, I travelled to FHL for one of my usual short visits of reconnecting with resident scientists and diving into the waters to see how the seaweed communities have changed at favored sites (Reuben Tarte, Cattle Point, Deadman Bay). I also travelled there to catch a ride north: I jumped onto a 42’ Nordic Tug and steamed directly from FHL’s breakwater to Prince of Wales Island (POW, Southeast Alaska) via the Inside Passage, with the ultimate goal of relocating for a postdoctoral fellowship that was to investigate the role of sea otters in eelgrass habitat (UAF, Eckert Lab).
It must be said: sea otters are unforgiving. Their tenacity, in fact, is not quite appreciated until one has the opportunity to observe their daily foraging habits. As we rounded the northern point of POW Island into a calm, fog-enshrouded Shakan Bay, we noticed dozens of sea otters simmering to the surface around us, each returning with a prize to dismember and consume: clam, clam, clam, sea cucumber, clam, clam, basket star…BASKET STAR? Like I said, sea otters are unforgiving. Although their role as a predator is canonized in texts that describe the cascading effects of their consumption of urchin and abalone (Estes et al. 1978, Duggins 1980), this should not suggest that their activity is limited to rocky areas. Sea otters are generalist predators that consume over 200 species across a spectrum of rocky and soft substrates. Diet analysis suggests that butter clams are their preferred prey in Southeast Alaska (La Roche 2020). What wasn’t apparent from the surface as we cruised through the corridor of sea otter carnage in Shakan Bay was what effect the foraging activity had on the soft seafloor below, which was what I was to later investigate in eelgrass habitat.
I was introduced to Alaskan eelgrass systems by Wendel Raymond (now PhD!), a recent FHL alumnus who had already been investigating food webs within eelgrass communities on POW Island for two summers. On my first day in the field, Wendel donned a dry suit and assumed “floating log” formation as he drifted along a transect counting eelgrass densities. I walked around the intertidal to make my first observations of an eelgrass site known to have a moderate sea otter presence (based on local population counts). This was one of those natural history moments of just taking it all in; I expected to see a number of excavated pits within the eelgrass as evidence of foraging activity (otters digging up clams, which they do by diving and digging with their front paws), but only a couple of pits were present within a 100 meter transect. However, along the
upper edge of the eelgrass bed where butter and littleneck clams are more abundant, the bed looked as if it had been bombed. A cluster of pits existed where there used to be a mosaic of clams and eelgrass, and many pits had exposed eelgrass rhizomes (roots) along the perimeter (Figure 1). It appeared as if sea otters could cause reductions in the upper extent of an eelgrass bed via “bioturbation,” which is disturbance caused by an organism (as opposed to waves or other physical factors).
