Many marine fish, algae, and invertebrate species have a bipartite life history. This means that after these organisms spawn, and their eggs are fertilized, larvae spend days to months (depending on the species) drifting with ocean currents before they settle onto the habitat where they spend their adult lives. When we count the number of these settlers that have been added to the adult population, we call it recruitment. Estimates of the timing, location, and magnitude of recruitment are necessary to understand the stability of marine populations and predict how they may change over time. 

In kelp forests in California and around the world, sea urchins are voracious predators of giant kelp (Macrocystis pyrifera), a foundation species which provides essential habitat for many important marine species. In areas with a high magnitude of urchin recruitment,  urchins scour reefs of algae, thereby shifting the state of kelp forests to urchin “barrens”. Barrens can be considered a phase shift to a new ecosystem type which supports a lower diversity of species. 

Currently, a large-scale ecological shift is underway along the coast of central California. Recent changes in the abundance and grazing behavior of purple sea urchins (Strongylocentrotus purpuratus) have shifted kelp forests that have persisted for decades to a landscape now comprised of a mosaic of urchin barren-kelp forest habitats. Due to a lack of monitoring it is uncertain if the outbreak in urchin populations around the region is entirely due to a shift in urchin grazing behavior, or if it is due in part to a large recruitment event that occurred prior to the urchin outbreak. Our efforts to monitor the timing, magnitude, and locations of sea urchin recruitment may serve as an indicator for when destructive grazing might occur. Therefore, we are initiating and conducting long-term monitoring of the timing and magnitude of sea urchin recruitment throughout the Monterey Bay to determine how sea urchin recruitment dynamics underpin the stability of kelp forest.

What is CENSUS? 

CENSUS is the CENtral California Network for Sea Urchin Settlement. We are a collaboration between faculty and student researchers at UC Santa Cruz and Cal State Monterey Bay.

Our monitoring and sampling design are based on the methods employed by Schroeter et al. at the Santa Barbara Long Term Ecological Ecological Research (LTER) project. Scrub brushes serve as artificial habitat for settlement collectors for urchin larvae in the water column to settle on to and transition to adults. These brushes are suspended 1 meter above the seafloor and attached to lines that are deployed from piers and wharfs around the region. Brushes are collected weekly and processed at the lab to quantify the number of urchin settlers. We are currently sampling at the following locations around the Monterey Bay, California: Santa Cruz Wharf, Capitola Wharf, Monterey Wharf, and the Pier in Stillwater Cove.

Our aim is to create a long-term dataset of spatial and temporal variation in purple urchin recruitment for the Monterey Bay. These patterns of urchin recruitment will be useful to evaluate the role of recruitment in determining adult urchin densities and kelp forest-urchin barren dynamics.

We Ask Questions Such As:

Will periods of increased urchin recruitment predict future increases in adult urchin populations?

What oceanographic conditions are correlated with increases in recruitment?

Does recruitment occur at the same magnitude and time at different sampling stations around the region? 

Click Below for Approaches to Each Part of the CENSUS Project:

Oceanographic Modeling