About This Project

Kelp forests are important ecosystems that support diverse marine communities globally. They face severe losses from climate-driven marine heatwaves and subsequent sea urchin overpopulation. My previous research established a threshold of 2 urchins/m², currently used in California, to sustain healthy kelp. I will now examine how environmental variables such as salinity affect this threshold. This will help create site-specific thresholds for more efficient kelp management.

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What is the context of this research?

Kelp forests are among the most biodiverse temperate marine ecosystems globally. These underwater forests are vulnerable to heatwaves exacerbated by climate change, showing declines in most regions of the world. In northern California, bull kelp experienced a 95% coverage decline in 2014-2016 due to an intense El Niño effect. This, combined with a local collapse of the predators of sea urchins, which are the main kelp consumers, led to kelp overgrazing. Restoration efforts have been ongoing ever since.

Previously, I identified a threshold of 2 urchins/m2 to allow kelp to naturally recover from urchin grazing. This threshold has been implemented in restoration plans for bull kelp. However, biological factors such as predator presence making urchins hide and environmental factors such as substrate complexity and salinity affect grazing behavior. This raises a question of how local biological and environmental conditions may affect this threshold of 2 urchins/m2.

What is the significance of this project?

This project will inform future kelp restoration management plans in northern California to create site-specific thresholds that account for the environmental conditions of the sites being managed. For example, if I identify regions with lower salinity allow a higher urchin density threshold, then those regions can have more lenient management policies than regions with higher salinity. Different environmental variables could be antagonistic and cancel each other out, so a region with high salinity and high substrate complexity could have a similar threshold to a low salinity and low substrate complexity.

Furthermore, the modeling techniques that I will be using during this project will be usable in other regions and with other species of kelp being affected in a similar way by grazing activity.

What are the goals of the project?

The main goal of this project is to evaluate how the urchin density threshold for kelp persistence varies across different environmental conditions in northern California. To do this, I will identify environmental variables in recent literature that have a correlation with urchin grazing activity in kelp forests and compile sites where those environmental variables, urchin, and kelp densities are all available. Second, I will fit a simple mathematical model based on my prior research that describes the urchin threshold using the data of each site. I will use publicly available data such as Kelp Watch or CENCOOS. Finally, I will use these estimated thresholds to identify correlations between the identified environmental variables and the numerical value of these thresholds, as well as using historical kelp density data to identify if the new threshold is better at predicting population persistence than the default threshold of 2 urchins/m2.