Distribution, Abundance, and Potential Larval Connectivity of the Non-Native Bryozoan Watersipora on Offshore Oil Platforms and Natural Reefs

Mark Page1, Susan Zaleski2, Rachel D Simons3, Robert J. Miller4, Jenifer Dugan5, Brandon Doheny1 and Donna M Schroeder6, (1)Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA, United States, (2)Bureau of Ocean Energy Management, Department of Interior, Camarillo, CA, United States, (3)Earth Research Institute, University of California, Santa Barbara, Santa Barbara, CA, United States, (4)University of California Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States, (5)University of California, Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States, (6)U.S. Department of the Interior, Bureau of Ocean Energy Management, Camarillo, CA, United States
Abstract:
The invasion and spread of exotic species is considered one of the greatest threats to biological diversity and the functioning of aquatic ecosystems today. The non-native foliose bryozoan, Watersipora subtorquata (=W. subatra?), commonly reported from harbors and embayments, also occurs on offshore oil platforms in the southern California Bight. To better understand and manage the spread of Watersipora among platforms and other artificial and natural reef habitats, we are assessing the current distribution of this bryozoan and evaluating dispersal pathways using empirical and modeling results. We surveyed 23 oil and gas platforms offshore of California from San Pedro Bay in the south to Pt. Conception in the north and 27 natural reefs bordering the mainland coast and northern Channel Islands using photographic methods and diver searches. Watersipora occurred on approximately half (13) of the platforms, with most of those (11) located in the south (San Pedro Bay) or southeastern portion of the Santa Barbara Channel. Where present, Watersipora cover varied widely among platforms. Watersipora occurred on 6 of the 12 mainland natural reefs surveyed within the Santa Barbara Channel, but only 2 of 15 reefs on the northern Channel Islands. Where present on reefs, Watersipora cover was low and patchy. Preliminary particle tracking modeling using ROMS suggests potential larval connectivity of Watersipora among some platforms, but little connectivity between platforms and natural reefs due to the short planktonic larval duration of this bryozoan and the direction of prevailing currents. These preliminary results suggest that dispersal from harbors or through hull fouling is the most likely vector of dispersal to natural reefs. Our study will inform mitigation measures to manage the spread of Watersipora among offshore structures, including future renewable energy installations, and to natural habitat, as well as decisions on future Rigs-to-Reefs alternatives in California.
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