Patterns of Growth and Erosion of blades of the kelp Saccharina latissima

Abstract

Kelp, large seaweeds of the Phylum Ochrophyta (or Phaeophyta), Order Laminariales provide many essential functions to intertidal habitats all over the world, yet the factors that govern their productivity are understudied. This is becoming an increasingly important issue as kelp productivity and population sizes have decreased over time due to an overabundance of predation and changes in the environment, resulting in kelp deforestation with decreased resilience (Steneck et al. 2002; Krumhansl and Scheibling 2012, Wernberg et al. 2019). Kelp deforestation not only posits a biological problem to its surrounding ecosystem but also an economic problem as they are an important aspect of aquaculture, are utilized in many commercial products and support many commercial fisheries by providing habitats and food web support. The increasing vulnerability of these kelp forests has become a growing problem, especially as we find out more about the vital role that kelp plays in its ecosystem. Kelp forests play in important role in fighting climate change; they sequester carbon and provide blue carbon sinks, ameliorate ocean acidification, and provide complex habitats that encourage intertidal biodiversity. This suggests that kelp aquaculture is key to fighting climate change as well (Duarte et al. 2017).They are autotrophic and are primary producers that serve as a food source, both for herbivores as live plants that are fed on as well as through the detritus that they shed (Mann 1973). They exude dissolved organic material (DOM) from their blades that contribute to both the biotic composition of their surroundings as well as to epiphyte activity (James et al. 2020). Kelp provide structural functions as well; their detritus often forms complex habitats that allow for greater biodiversity of micro-organisms that live on the ocean floor, and the kelp beds can provide a similar function as well for macro-organisms such as juvenile fish (Figure 1, Branch and Griffiths 1988).

As we increasingly discover the ways in which kelp are essential contributors to its local ecosystems, it becomes more important that further studies are conducted to learn more about their rates of growth and erosion and to study which factors may affect these rates. In this study we looked specifically at Saccharina latissima (sugar kelp), a brown alga that grows along the western coast of the US and is ecologically important to its surrounding habitat in the Salish Sea where this experiment took place. This experiment was conducted over the course of 6 years as a part of a spring quarter class at Friday Harbor Labs and we used a simple but effective method that can measure growth and erosion of S. latissima that was used at different depths and thus at different light levels. With this data we ask what the patterns of growth and erosion are in S. latissima and estimate the rate of growth and erosion in April and May.