An assessment of marine biofouling introductions to the Puget Sound region of Washington State
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An assessment of marine biofouling introductions to the Puget Sound region of Washington State

Category: Aquatic Invasive Species

Date Published: May 2014

Number of Pages: 111

Author(s): Ian Davidson, Chela Zabin, Gail Ashton and Greg Ruiz


The Puget Sound region has a long history of marine and estuarine species invasions that have contributed to ecological alterations of the region’s ecosystem over centuries of human influence. The patterns of invasion and subsequent effects of those species are initiated by transport vectors that operate throughout the world and transfer biota to Washington. Chief among those vectors is biofouling, which is the accumulation of algae and invertebrates that settle onto submerged surfaces. This report examines the issue of marine and estuarine invasions by biofouling-mediated nonindigenous species (NIS) in Puget Sound.

Biofouling species often comprise the largest portion of species richness for NIS inventories highlighting the diversity of organisms that comprise this community and their ability to colonize and survive vector transport. The primary vectors of biofouling organisms are the submerged portions of ships and boats (vessels), but biofouling species can also be conveyed by any maritime infrastructure as well as intentional and unintentional release through aquaculture activities, live bait and other vectors. Biofouling NIS self-dispersal also plays a role in their spread after initial introductions to one part of a coastline.

This report consists of four parts:

  1. We examined the invertebrate and algal invasion history of the region and estimated the contribution of the biofouling vector to this history. We found that Washington’s NIS introductions have increased dramatically through time and there are at least 94 NIS recorded in the state, 74 of which occur in Puget Sound. Crustaceans, bivalves, gastropods, bryozoans, annelids, and tunicates are the dominant groups of NIS. Vessel biofouling may be responsible for introducing 58% of all NIS, and its strength (numbers of species attributed to this vector) has increased over time. Prior to 1950, vessel biofouling was considered a possible vector for 37% of initial NIS introductions to Puget Sound. After 1950, biofouling was a sole or possible vector of initial incursion for 64% of newly established NIS.

    We also conducted standardized searches of the scientific literature to evaluate reported impacts of the NIS that have been recorded as established in Puget Sound. The number of reports examining species’ impacts is quite low; only 28 of the 74 NIS had impact data in the literature. Prominent among the impacts for these 28 species were competition for space and over-growth of native and commercially important species, effects on ecosystem functions (e.g. nutrient cycling), parasite transmission, as well as effects on ecological communities that increase diversity through habitat creation.

  2. Section 2 examined maritime traffic patterns for commercial, recreational and fishing vessels in Puget Sound, the patterns of vessel maintenance by commercial shippers, the biofouling data for commercial vessels, and a potential approach for identifying risky vessels without biological sampling. Puget Sound is an important hub of vessel activity and our estimates of vessel traffic to the region approaches 50,000 vessels per year comprising 3,200 commercial vessel arrivals (overseas and coastwise), over 26,000 fishing vessel arrivals, and at least 20,000 overseas arrivals of recreational boat arrivals. The recreational data are likely an underestimate of the total number of arrivals each year (in terms of transient boat visits within the state and from neighboring states). Commercial vessel maintenance and operational patterns highlighted differences among ship types that may help identify biofouling risks, especially for outlier vessels within certain types (e.g. especially slow ships within a class or those with excessive lay-ups). However, analyses of our data sets and literature data on vessel biofouling suggested that high levels of variability and the difficulty in identifying clear-cut risk factors is an impediment to simple pre-arrival risk assessment. A basic model, using data from California’s hull husbandry reporting form, duration since dry-docking, and extended lay-up periods (10 days or more) suggests that between 2% and 21% of Puget Sound commercial vessels would trigger an inspection or action depending on 4-year or 400-day thresholds for dry-docking duration, respectively. Overall, the volume of traffic by all vessel types suggests that prudent vector management options should be sought to reduce biofouling introductions and NIS spread within the system.

  3. We assessed biofouling policies worldwide in Section 3 of the report, as well as in-water cleaning technology, and a suggested approach to policy-making for Washington, including potential stakeholder participation. Biofouling policies have been created or are emerging in several parts of the world, including New Zealand, Australia, California, and Hawaii, as well as at the global scale through the International Maritime Organization. The apparent floor and ceiling for potential policies for Washington range between the current status quo (do nothing different) to the most protective approaches adopted for the extraction industry in Western Australia and vessel visitors to the NW Hawaiian Islands. It is likely that any proposal for Washington will fall between these scenarios because the latter, biologically explicit approach is impractical for regular commercial shipping in the US.

    There are several options for in-water cleaning technology in the US and throughout the world, although few that are effective at cleaning and collecting debris and toxins are commercially available. This is especially true in Puget Sound where a prohibition on in-water cleaning of anti-fouling (toxin-based) paints is a deterrent for development and use of technology in the region.

  4. In the final section, we examined non-vessel vectors of biofouling and their management, as well as research and monitoring priorities for Puget Sound. Management of non-vessel biofouling vectors varies widely, from little to no knowledge of stochastic movements of maritime infrastructure, to stringent control of aquaculture imports (although gaps exists, e.g. for pathogens) and the well-managed response to the biofouling vector threat posed by Japanese tsunami marine debris.

    Multi-vector management is preferable to single-species and single-vector management, although practical considerations must also be accounted for and vessel vectors should be considered a priority for reducing NIS translocations in the absence of a multi-vector approach. Vessel biofouling appears to be the largest gap in policy for managing marine NIS in Puget Sound.

    Finally, monitoring NIS throughout Puget Sound and sampling biofouling vectors are priorities for managing NIS introductions in the region. A lack of standardized longer-term data on NIS in the region and on vectors prevents a better understanding of invasion rates, vector strength, vector management, NIS population status, impacts, and resource allocation for pre-and post- arrival management. Standardized NIS monitoring and vector analyses with sampling provide the pivotal data to underpin science-based vector management policy and a method for evaluating vector management efficacy.


Suggested Citation:
Citation: Davidson I, Zabin C, Ashton G, Ruiz G (2014) An assessment of the biofouling introductions to the Puget Sound region of Washington State. Report to the Washington Department of Fish & Wildlife and Washington Department of Natural Resources, Olympia, Washington. 111pp.