One of the most iconic destinations on the California coastline is Monterey Bay. From the historic cannery row to an internationally recognized aquarium, the bay offers a wide variety of attractions for people from all over the world. A plethora of marine life also find the area ideal to visit or live, including the southern or California sea otter.
On my most recent visit to Monterey, after spending most of the morning at the aquarium, I sat down at one of my favorite places on cannery row overlooking the water to enjoy a steaming bread bowl of clam chowder. Just beyond the outdoor patio where I sat, a lone sea otter was close enough for her raw, pink nose to distinguish her as a female. Although there were no other otters nearby, she was not exactly alone. A juvenile gull was at her side, asking for food like it would of its mother. The otter was floating leisurely on her back, eating something I couldn’t quite make out from my vantage point. While she wasn't about to share any of it, she didn’t seem to be bothered by the gull either, and watching the odd couple caused me to consider their contrasting lifestyles.
Despite their differences and the otter’s apparent denial of direct interaction, as a part of the same ecosystem, they’re still linked. At the ecosystem level, a species’ niche is essentially their role in that system, defined by their habitat needs, and the way in which they fulfill those needs. For a few species, this role is more significant than others' in the system (i.e. their impact on the ecosystem is greater than that of the size of the animal itself and/or of its population in the system). These species are called keystone species, and sea otters are one of the most well understood examples.
Sea otters consume about one third of their body weight daily, an appetite that is satiated by a wide range of predominantly marine invertebrates found among the subtidal zones within their home ranges. Much of the areas where otters forage are dominated by large brown algae species, commonly known as kelp. Kelp are anchored to the sea floor by a root-ball-esque ‘holdfast’, from which they grow quickly up to sea surface where their broad blades can absorb sunlight and photosynthesize. In areas where multiple kelp organisms are growing in water depth of 15-100 feet, they essentially create an underwater forest.
Just like forests on land, these kelp forests are complete with a canopy and an understory that create the structural complexity within which many marine organisms find food and shelter. It's in the understory where sea otters forage. One of the most important prey items for the southern sea otter are purple sea urchins. Sea urchins in California kelp forests normally feed on 'drift kelp' or pieces of the large kelp blades that break off and decompose over time, like leaf litter in a terrestrial forest. The urchins trap the drift kelp in their spines as it settles toward the sea floor. But if there are too many urchins in a given kelp forest, there won't be enough drift kelp to go around, and the hungry urchins will begin to use their scraping jaws to eat away at the holdfasts that are rooting the live kelp to the sea floor. Without their holdfasts to anchor them, the kelp will be carried away by tidal currents or wind-generated surface turbulence. No kelp, no kelp forest habitat, and the organisms that are both directly and indirectly connected to it are affected. This includes the gulls that naturally rely on productivity in the subtidal zone to supply the shoreline and sea surface with scavenging opportunities. By keeping the urchin populations in check, sea otter foraging reduces the vulnerability of kelp forests to direct urchin predation, thus contributing to the overall integrity of the habitat for all of the organisms that live in it and interact with it.
I looked away from the otter and the gull, at my own meal of shellfish and thought of myself as part of the ecosystem. Many humans are more like the gulls, living in circumstances that necessitate opportunistic living. But some of us have options. Today, there are many opportunity for us to be keystone individuals within our communities, where the significance of our role is greater than we may currently realize. As keystones, we can work together to make significant lifestyle choices that help to maintain balance within the ecosystems to which we are connected. Sometimes, this will demand creativity, but like the otters, we can use tools to tackle the more challenging opportunities for sustainability.
Another critical part of realizing the human keystone niche can be learned from the otters, too. Scientists have observed that sea otters pass on their feeding habits and preferences to their offspring (and sometimes their friends), which ensures that their keystone niche will be filled for generations to come. When we use the tools we have to find and create opportunities to live sustainably, it’s important that we also spread the word...
Pondering the sea otter niche over a meal reminded me of one tool that is well worth sharing. Many of the choices we are faced with every single day concern food. Thanks to the Monterey Bay Aquarium and their Seafood Watch Program, sustainable seafood choices are one of the easiest ways we can start. Download your free regional seafood pocket guide or the sustainable seafood app by clicking on the highlighted link above, but don't stop there! Even when our human lifestyles seem as different as that of a seagull and an otter, a dependence on a balanced earth for survival is something we’ll always have in common, and the effort will be well worth the reward. So, for those of us who have the choice and can access the enabling tools, let's be the sea otters of humanity and live as keystone individuals of balanced communities, ecosystems, and the earth.