Center for Lakes and Reservoirs 

Environmental Science and Management Programs 

Assessing Hull Fouling as a Vector of Invasive Species: A Case 

Study in the Lower Columbia River 

Contact Information 

Ian Davidson

idavidso@pdx.edu 

Portland State University 

Center for Lakes and Reservoirs 

PO Box 751 - ESR 

Portland OR 97207-0751 

Ph: 503-725-8104 

Fax: 503-725-3834 

Introduction 

Q: What is the extent and composition of hull biofouling entering the Columbia River ? Does this vector pose a significant threat of 

invasion to the system? 

 

Shipping has been identified as the major vector of organism transfers on a global scale. Of the two sub-vectors associated with shipping, 

there has been huge bias in ecological research toward ballast-mediated transfers of organisms, perhaps at the expense of hull fouling. 

Hull fouling transfers of organisms are historically and contemporaneously important in aquatic nonindigenous species ( NIS ) 

introductions, yet very little quantitative data exist to rigorously examine the current rates, extent and composition of organism transfers 

via vessel hulls. 

 

Research at Portland State University has shown that eight of the 81 established introduced species in the Lower Columbia River were 

possibly hull mediated invasions. Analysis of shipping patterns, hull fouling loads and biofouling organism ecology will provide an 

insight into current rates of biofouling transfers and the possibility of future successful invasion resulting from this vector. The data may 

be used to implement management strategies to reduce the risk of hull transfers into and out of the Lower Columbia River . 

 

Ian Davidson sampling hull biofouling on the waterline of a barge on dry dock. 

 

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Personnel: 

Primary: Ian Davidson (Principal Investigator and project Coordinator), Mark Sytsma (Principal Investigator), Greg Ruiz (Principal 

Investigator) 

Additional field and database assistance: Christina Simkanin 

 

Funding/collaborators: 

The US Coast Guard is funding the work as part of the CRANSI program. 

Whitman Miller, at SERC, is a collaborator 

An example of a bulk carrier on dry dock at the ship yard in Portland (left). Notice a clump of fouling (hydroids) on the hull in an area 

where antifouling paint could not be previously applied because of dry docking blocks (right). 

 

Accomplishments/results: 

There are four avenues of research being pursued: 1) Wetted surface area (WSA) analysis, 2) Sampling of vessel hull biofouling, 3) 

Fouling assemblage diversity, abundance and settlement in the Columbia River 4) Fouling assemblage viability in a freshwater system. 

 

1) Preliminary results have shown that >42 million m 2 of WSA has arrived into the Columbia River between 2002 and June 2005. Bulk 

carriers have provided the majority of this figure with >58%, followed by container ships (13%) and roll on/roll off car carriers (11%). 

Current analysis is focusing on the origin and distance traveled by these vessels to ascertain the primary source regions of Columbia 

River port vessels and associated hull fouling biota. 

 

2) Sampling of ships hulls has been divided between two sources: direct sampling of hulls during dry docking and video analysis of 

underwater hull surveys carried out by local maritime companies. To date, nine dry docked vessels have been sampled with proportions 

of fouling on hulls ranging from <1% to 90%. Vessels analyzed from hull video analysis generally had lower levels of fouling (<1% to 

22%), although one vessel that had been out of commission for a period of years had approximately 80% of its hull fouled. The high 

variability recorded from the 22 vessels analyzed thus far is probably a function of different patterns in voyage routes, exposure to 

freshwater and hull husbandry schedules. However, this analysis has been primarily qualitative and vessels surveyed may not be fully 

representative of the commercial fleet entering Lower Columbia River (LCR) ports. Fouling organisms encountered thus far include 

species of algae, mollusk, bryozoan, hydroid, cnidarian, polychaete, and crustacean (including the introduced barnacle Balanus 

improvisus ). The majority of organisms were not alive upon collection and a finalized species list will be made. 

 

3) A preliminary study of rocky substrates near ports revealed very low diversity of fouling organisms with only ephemeral 

Enteromorpha and Cladophora type algal species present. As a result, fouling surveys and settlement panels were restricted to areas near 

the mouth of the river (<40 miles from the mouth) where seawater intrudes to create estuarine conditions. Fouling panels have been 

placed at low tide/immediate subtidal levels for approximately 3 months. To date, analysis of three sites (18 panels) has revealed fouling 

loads have been minimal (<10% panel area covered). These low levels of settlement occurred in sites of both high fouling density (rocks 

dominated by mussels, barnacles and limpets) and low fouling density (areas where fouling loads were characterized by green ephemeral 

algae and almost no fauna). After the predetermined submersion time, more panels will be collected from boat harbors and other rocky 

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sites near the mouth. 

 

4) Settlement panels have been deployed at a site of high salinity and fouling abundance along the Oregon coast (near Tillamook Bay ). 

These panels will be used in an experiment which will mimic the change in salinity that occurs when ships enter the Columbia River (salt 

wedge) system. The aim is to determine the levels of mortality and 'drop off' of random fouling assemblages in freshwater. 

 

Discussion: 

The colonizable surface, or wetted surface area, of ships' hulls has the potential to inoculate the receiving waters of a port on every 

voyage. The same is not true of ballast water whereby large quantities of water transported to a port are not always released in that port. 

Therefore, the underlying potential for invasions to occur via hull fouling is intrinsically linked to WSA arrivals. Analyses of ballast 

water volumes being released into US ports has been conducted (Minton et al, in press), and one coarse analysis of WSA arrivals to the 

US revealed that over 400 million m 2 (or 1.5 × the area of Vermont ) of WSA arrives annually from different bioregions (Miller & Ruiz, 

in prep). 

In the previous 3 1⁄2 years, >42million m 2 WSA has arrived into the LCR. Fouling levels on vessels sampled have been highly variable, 

ranging from >1% to 90% of the wetted surface area. Estimates of the commercial fleet in general suggest that even the best maintained 

vessels have between 5% and 20% or their hulls covered in biofouling. A crude estimate would then suggest that, since 2002, between 

2.1million and 8.4million m 2 of fouled surface area has entered the system. 

However, a major limiting factor for fouling organisms in this system is low salinity, which acts as an abrupt barrier to these organisms 

soon after vessels cross the mouth of the river. Further analysis of ships' hull from the LCR and experimental analysis of fouling 

assemblages exposed to severe reductions in salinity will provide further evidence to the extent of the threat that hull fouling carries in 

terms of species invasions in the LCR. 

Two previous studies regarding hull fouling have involved the LCR. In both, only one ship was examined and it was assumed that no 

fouling organisms survived after visiting the system. Despite this, approximately 10% of introduced species in the LCR may have arrived 

via hull fouling and in the context of the larger issue of invasions within the system, data is required for any management steps that may 

be required to accurately assess and reduce the threat of the hull fouling vector. 

 

Further work: 

Relative to ballast water research, hull fouling is poorly studied and the majority of studies have been primarily qualitative. This is partly 

because vessel hulls are difficult to sample in a standardized way. As a result, basic knowledge of the extent and composition of 

biofouling transfers arriving at US ports is unknown. The relative importance of shipping characteristics such as hull husbandry, origin, 

voyage duration, and docking durations are also unknown. We previously developed a protocol to sample ships hulls, using ROV 

technology in conjunction with the US Navy Power and Protective Systems (Caderock) division. We plan to undertake multiple 

deployments of this technology to build a database of many tens of vessels sampled at various Pacific coast ports. Combined with a 

broader scale and detailed examination of vessel (WSA) activity on the west coast, this will provide a baseline of quantitative data from 

representative ships to determine the threat from the hull fouling vector to US coastal ecoysystems. 

 

 

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