Population Ecology of the Arctic Kelp Laminaria solidungula
Climate change and coastal development are increasingly altering the ecosystems of the Arctic Ocean. In order to anticipate the impacts of these changes, we need better understanding of species distributions within Arctic ecosystems. Where species occur, and in what number, affects ecosystem health and its ability to support biodiversity and growth. In turn, any given species’ distribution is affected by its environment, its ability to disperse, and its evolutionary history. In a changing Arctic, studies on species that photosynthesize and provide physical structure are especially important, as these species can have a disproportionate effect on ecosystems via repercussions for food webs and diversity. In shallow, rocky areas of the Arctic Ocean, kelp beds harbor biological communities that are unusually diverse and productive, relative to other Arctic marine systems.
In the Beaufort Sea, the kelp Laminaria solidungula provides important habitat and complements highly seasonal phytoplankton by providing a year-round base of the food web. This species has demonstrated food web connections to birds, fishes, and seals. As the only kelp species restricted to Arctic waters, its distribution is interesting from an evolutionary standpoint as well as an ecological one, as it may represent the limits at which kelp can persist. I am researching why and how this kelp lives where it does with the purpose of anticipating future Arctic ecosystem change, and contributing to a greater understanding of Arctic ecosystems as a whole. First, I am evaluating the continuous environmental conditions in an Alaskan Arctic kelp bed and the relationship to kelp growth. I am also determining how environmental conditions and dispersal affect kelp abundance and community diversity in the Alaskan Beaufort Sea via SCUBA surveys. Through laboratory experiments, I am then examining the effects of altered light and temperature conditions on the survival of the early life stages of Laminaria solidungula. Finally, I am investigating how Laminaria solidungula populations are (or are not) connected across the Arctic using genomics. Together, these studies represent the first in-depth investigation of the distribution of a unique and important marine alga inhabiting a rapidly changing environment.
The main study site is the Stefansson Sound Boulder Patch, located adjacent to Prudhoe Bay, Alaska. My advisor, Dr. Ken Dunton, has been visiting this site and monitoring environmental conditions since the Boulder Patch was first discovered in the 1970s.
Why Laminaria solidungula is awesome
Laminaria solidungula is the most abundant kelp in the Boulder Patch. It has a really cool annual growth pattern that highlights the two main limiting factors of kelp growth: light and nutrients. You see, L. solidungula grows in the Arctic Ocean, where the water is covered by ice for 9 months of the year. The ice blocks out whatever incoming sunlight there may be in the dark, arctic winter, essentially leaving L. solidungula in complete darkness. BUT, there’s another problem: during the summer, when there is sunlight penetrating the waters, there aren’t enough nutrients around. So, even though there’s sunlight to provide energy for L. solidungula to start growing, it simply can’t!
Now, here’s the cool part: L. solidungula does all of its photosynthesis for the entire year – gets all of the energy it can get from sunlight – in the span of those few ice-free months. It doesn’t show any growth during this time, instead using the light to make carbohydrate storage products (you can think of this as a sort of carbo-loading, only, instead of prepping for a marathon, L. solidungula is prepping for the winter). Then,when winter comes, when nutrients are available, under the cover of icy darkness, L. solidungula starts to grow.
This seasonal growth from the intercalary meristem (growing region between the stipe and the blade) results in the unique morphology of L. solidungula : each section on the blade represents one year (one winter, really) of growth. In this way, we can measure how much an individual has grown each year for up to the past four years!
Annual growth of L. solidungula tells us about the environmental conditions during that particular year. Specifically, it tells us how turbid (cloudy) the water was during that summer: if a blade section is really short, the water was really turbid during the summer previous to collection. The long term data set on annual growth can tell us about changing conditions in the Arctic : is turbidity increasing due to increased sediments coming from rivers and coastal development? How do these changes is light regime affect the energy flowing through food webs?