Forests of the Sea
The role of kelp forests in oceanic carbon cycling
When you’re setting up your towel for a beach day, you avoid the dried seaweed on the sand – this dried seaweed is “kelp wrack”. While it may catch your feet in the surf, it’s catching rays of sunlight to create energy and oxygen out in the ocean.
In fact, the immense amount of energy the Giant Kelp (Macrocystis pyrifera) creates enables it to grow up to 2 feet per day!
The Giant Kelp is commonly found along the California coast, where it creates kelp forests that rival the productivity of tropical rainforests. Kelp forests provide habitat and food to an abundance of organisms.
By Priya Shukla, M.S.
The Giant Kelp is anchored on the seafloor and grows to the ocean’s surface. The canopy, pictured above, is responsible for a majority of the photosynthesis that occurs in an individual kelp.
Kelps are photosynthetic, which means they convert sunlight and carbon into usable organic energy and produce oxygen as a byproduct. The carbon-based energy that kelps produce is cycled through the food web. Carbon can also be stored in the kelp itself, where it eventually becomes absorbed into the deep ocean. These processes are all part of the oceanic carbon cycle. Overall, kelp photosynthesis is important for coastal zone health. To better understand the role of kelps in the carbon cycle, I studied how the oceanic environment affects kelp photosynthesis during my Master’s degree with Dr. Matthew Edwards’ at SDSU.
I investigated how nutrients influence photosynthesis in the kelp canopy, using both laboratory experiments and stable isotope analysis.
Laboratory experiments allow us to see how kelps respond in real time, while stable isotopes act as longer term records of kelp photosynthesis and nutrient uptake. We can compare results from both of these approaches to paint a fuller picture of kelp health!
For my laboratory experiments, I exposed two species of kelp (the Giant Kelp and the Feather Boa Kelp, Egregia menziesii) to different nutrient levels to see if this altered kelp photosynthetic patterns. These different nutrient levels represented natural changes in nutrient availability in the ocean: nutrient-poor conditions frequently occur during the summer, while nutrient-enriched conditions occur during the spring. I also collected kelps for stable isotope analyses that measure the proportion of carbon and nitrogen in a kelp blade, to see if similar trends occur in nature.
A close up view of the Giant Kelp. This seaweed will grow straight to the surface and is held upright by air bladders that are attached to the kelp blades.
Laboratory experiments showed that each kelp species responded differently to nutrient availability. The Feather Boa kelp was able to withstand nutrient-poor conditions, while the Giant Kelp preferred nutrient-enriched conditions. The stable isotope analysis similarly shows that the Giant Kelp and Feather Boa Kelp do not invest in carbon production and nutrient uptake at the same rate. This might be because unlike the Giant Kelp, the Feather Boa Kelp is commonly found in the shallower intertidal zone, where it is used to stressful conditions.
These results indicate that kelp species do not respond to changes in the oceanic environment in the same way, and therefore do not contribute to carbon cycling equally.
Priya grinds kelp blade samples to prepare them for stable isotope analysis. Kelp samples must be dried and ground up into a fine powder before they can be analyzed, this is a very labor intensive process.
Kelp forests harbor a broad diversity of fishes and invertebrates, and are sensitive to changes in the ocean climate. The current El Niño will bring warm, low nutrient waters, which may provide us a window into understanding how climate change influences kelps.
My research will improve our understanding of how changes in the marine environment will affect kelp forest health, their role in the carbon cycle, and ultimately, the organisms that rely on them.
I hope that my research better informs scientists, managers, and policymakers about how kelps respond to environmental change.
Why is being a biologist awesome?
Being a biologist is awesome because it allows me the freedom to ask questions that are pertinent to scientists and to our society. Asking questions about environmental change means I communicate with scientists across biology, chemistry, and oceanography, this greatly expands my knowledge and network. SDSU provided an excellent environment for fostering collaborations across labs, institutions, and disciplines during my Master’s degree.
Author: Priya Shukla, M.S. Contact Priya at firstname.lastname@example.org or find her on Twitter: @priyology