The role of containerships as transfer mechanisms of marine biofouling species

Abstract

Fouling of ships is an important historical and enduring transfer mechanism of marine nonindigenous species (NIS). Although containerships have risen to the forefront of global maritime shipping since the 1950s, few studies have directly sampled fouling communities on their submerged surfaces, and little is known about differences in the fouling characteristics among commercial ship types. Twenty-two in-service containerships at the Port of Oakland (San Francisco Bay, California) were sampled to test the hypothesis that the extent and taxonomic richness of fouling would be low on this type of ship, resulting from relatively fast speeds and short port durations. The data showed that the extent of macroorganisms (invertebrates and algae) was indeed low, especially across the large surface areas of the hull. Less than 1% of the exposed hull was colonized for all apart from one vessel. These ships had submerged surface areas of >7000 m², and fouling coverage on this area was estimated to be <l7 m² per vessel, with zero biota detected on the hulls of many vessels. The outlying smaller vessel (4465 m²) had an estimated coverage of 90% on the hull and also differed substantially from the other ships in terms of its recent voyage history, shorter voyage range and slower speeds. Despite the low extent of fouling, taxonomic richness was high among vessels. Consistent with recent studies, a wide range of organisms were concentrated at more protected and heterogeneous (non-hull) niche areas, including rudders, stern tubes and intake gratings. Green algae and barnacles were most frequently sampled among vessels, but hydroids, bryozoans, bivalves and ascidians were also recorded. One vessel had 20 different species in its fouling assemblage, including non-native species (already established in San Francisco Bay) and mobile species that were not detected in visual surveys. In contrast to other studies, dry dock block areas did not support many organisms, despite little antifouling deterrence in some cases. Comparisons with previous studies suggest that the accumulation of fouling on containerships may be lower than on other ship types (eg bulkers and general cargo vessels), but more data are needed to determine the hierarchy of factors contributing to differences in the extent of macrofouling and non-native species vector risks within the commercial fleet.

Keywords:

• containerships
• biofouling
• fouling
• hulls
• species introductions
• vectors

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Erratum

Acknowledgements

We are grateful to the Port of Oakland, especially Jody Zaitlin and Phil Granger, for access and logistical assistance throughout the project. We very much appreciate all the terminal and shipping line operators, staff and agents for arranging access to vessels as well as participating ship operators for their cooperation and insight. We thank George Smith for planning and advice; Bill Morrison, Don Ockrassa and Kevin Nekinaken for diving expertise; Michael Wright and Underwater Resources Inc for ROV expertise; Christina Simkanin for assistance in the field; Maurya Falkner, Lynn Takata and Suzanne Gilmore for discussions and advice. We also thank three anonymous reviewers for comments and suggestions that improved the manuscript. The Port of Oakland and the California State Lands Commission funded this research.