Sanctuary Integrated Monitoring Network
Monitoring Project

Monitoring growth and spread of the invasive bryozoan Watersipora in Monterey Harbor

Principal Investigator(s)

  • Steve Lonhart
    Monterey Bay National Marine Sanctuary
  • Chad King
    Monterey Bay National Marine Sanctuary
Start Date: February 01, 2010

This project began as a Senior Thesis project for Sarah Traiger, a UC Santa Cruz undergraduate in 2010. Sarah was interested in the competitive interactions between Watersipora and native invertebrates. The abstract from her paper can be found under the Discussion section tab.

Six cement pilings on A tier inside Monterey Harbor were selected and we established permanent plots to monitor through time. Pilings were wrapped with clothesline, which served as fixed points, and at two depths for two of the pilings: one just below the lowest tide line and one 2 m above the bottom. Since the cement pilings have four equal sides, and because we took photos both above and below the clothesline, each line on a piling constituted 8 photos. During each sampling dive 64 photos were taken.

Photos were taken with a Canon 300D digital SLR attached to a PVC framer that had a fixed distance and orientation. Each photo covers 0.025 square meters of the cement piling face. Photos were then analyzed by overlaying a grid of fixed points (49) and identifying to the lowest taxonomic level possible what was under each of the 49 points. These data were then used to estimate percent cover for each of the categories.

Summary to Date

The bryozoan Watersipora is a seasonal inhabitant of the pier pilings, and the precent cover varies both by season and depending on the type of natives also in the same area.

Monitoring Trends

  • Analyses are currently underway.


Abstract from Sarah Traiger's UCSC Senior Thesis: Invasive species are a conservation concern because they often change the ecological communities they invade. Invasive species can compete with or prey on native species, or alter the structure of the habitat (ecosystem engineers). The invasive bryozoan Watersipora subtorquata, is abundant in the Monterey harbor and has been sighted in kelp forests in the Monterey Bay. We examined whether there is evidence that Watersipora has affected the “fouling community”, i.e. sessile invertebrates and algae that inhabit man-made structures, by studying the differences between photoquadrats with various levels of Watersipora cover. Corynactis californica negatively responded to increasing abundance (percent cover) of Watersipora, while Membranipora fusca positively responded. Diplosoma listerianum had high percent cover when there was high cover of Watersipora and when Watersipora was low or absent, but D. listerianum was much less abundant at moderate levels of Watersipora. Our results suggest that Watersipora influences this fouling community because of the differences between the communities with different levels of Watersipora. However, experimental manipulations of the community would be necessary to confirm that Watersipora is the cause of these differences. It will be interesting to following changes in Watersipora abundance and its interactions with other species, both in the Monterey harbor and in the kelp forests, to see how Watersipora affects the native community.

Study Parameters

  • Non-indigenous species
  • Growth
  • Dispersal & Recruitment
  • Distribution

Study Methods

We use fixed plots on cement pier pilings to capture monthly photographs of the benthic cover. These photos are a fixed area (0.025 square meters) and taken with a digital camera. Images are then analyzed for percent cover of the invasive bryozoan Watersipora and other organisms attached to the piling.