2017 MARINE DEBRIS INVASIVE SPECIES REPORT 1

Invasive Species

Marine Debris as a Potential 

Pathway for Invasive Species

2017 NOAA Marine Debris Program Report 

Photo Credit: Oregon State University, Hatfield Marine Science Center
March 2017

National Oceanic and Atmospheric Administration 

National Ocean Service

National Centers for Coastal Ocean Science – Center for Coastal Environmental Health and Biomolecular Research

219 Ft. Johnson Rd.

Charleston, South Carolina 29412

Office of Response and Restoration

Marine Debris Program

1305 East-West Hwy, SSMC4

Silver Spring, MD 20910

Cover photograph a close-up of marine life found on a derelict dock from Japan that washed up on Agate Beach in Newport, Oregon.

Photo Credit: Oregon State University, Hatfield Marine Science Center

For citation purposes, please use: 

National Oceanic and Atmospheric Administration Marine Debris Program. (2017). Report on Marine Debris as a Potential Pathway for Invasive Species. Silver 

Spring, MD: National Oceanic and Atmospheric Administration Marine Debris Program.

For more information, please contact: 

NOAA Marine Debris Program

Office of Response and Restoration

National Ocean Service

1305 East-West Highway

Silver Spring, Maryland 20910

301-713-2989

https://MarineDebris.noaa.gov
Acknowledgements

The National Oceanic and Atmospheric Administration (NOAA) Marine Debris Program would like to acknowledge Paul L. Pennington, Ph.D. (National Centers 

for Coastal Ocean Science) for conducting this research, and Courtney Arthur (Industrial Economics, Inc.) and Keith Cialino (NOAA Marine Debris Program) for 

providing guidance and support throughout this process. Special thanks to James T. Carlton (Williams College and Mystic Seaport) and Margaret M. Brady (NOAA 

National Sea Grant Program) for reviewing this paper and providing helpful comments. Thanks also to Catherine Polk (NOAA National Ocean Service, National 

Centers for Coastal Ocean Science) for creating the graphics, Kevin McMahon (NOAA National Ocean Service, National Centers for Coastal Ocean Science) and 

Krista Stegemann (NOAA Marine Debris Program) for a copy-edit review of this report, and Emma Tonge (NOAA Marine Debris Program) for design and layout. 

Funding for this project was provided by the NOAA Marine Debris Program.

This publication does not constitute an endorsement of any commercial product or intend to be an opinion beyond scientific or other results obtained by the 

National Oceanic and Atmospheric Administration (NOAA). No reference shall be made to NOAA, or this publication furnished by NOAA, to any advertising or sales 

promotion which would indicate or imply that NOAA recommends or endorses any proprietary product mentioned herein, or which has as its purpose an interest 

to cause the advertised product to be used or purchased because of this publication.
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 4

TABLE OF CONTENTS

Executive Summary............................................................................................5

Background...............................................................................................................6

Marine Debris and Invasive Species: Two Convergent Issues.........6

NOAA’s Role with Marine Debris...............................................................6

NOAA’s Role with Invasive Species...........................................................7

What is an Invasive Species.........................................................................7

Pathways............................................................................................................8

Known Pathways for Invasive Species.....................................................8

Historical Perspective: A Shifting Baseline?...........................................9

Marine Debris and Invasions of Marine Species .........................10

How Do Aquatic Species Associate with Marine Debris?.................10

Case Studies......................................................................................................14

Framework for Invasion................................................................................16

Conclusion..................................................................................................................19

A Successful Invasion via Marine Debris................................................19

Assisted Invasion by Marine Debris.........................................................20

Summary and Knowledge Gaps................................................................21

Recommendations.........................................................................................22

References..................................................................................................................24

Glossary........................................................................................................................29
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 5

There is mounting concern over the increase 

in debris in our ocean and the potential for 

that debris to serve as a pathway for the 

introduction of non-native species. While the 

pathways associated with global shipping 

draw the greatest amount of attention 

regarding marine invasives, the purpose of 

this paper is to consider the potential role 

that marine debris may play in introducing 

non-native species that may become 

invasive. This paper is not a comprehensive 

review of either subject (marine debris or 

invasive species), as reviews are available in 

the literature for both. Rather, the objectives 

of this paper are to address:

• key terminology and concepts 

related to marine debris and 

invasive species,

• the major types of organisms 

occupying marine debris (by 

functional group),

• some key case studies regarding 

non-native species and marine 

debris,

• a basic framework to invasion 

with respect to marine debris,

• a successful invader and the role 

of marine debris,

• key information gaps and 

research needs, and

• recommendations for the 

mitigation of marine debrismediated species invasions or 

expansions.

The intersection of marine debris and 

invasive species is very complex and not well 

understood. This is because each issue is 

very complex in its own right. Determining 

the potential risk of a non-native species 

invading a new range using marine debris 

as a pathway is not possible at the present 

time due to numerous confounding factors, 

knowledge gaps, and research hurdles. 

However, given what we know about the 

barriers to invasion presented in this paper, 

we can draw some broad conclusions 

regarding the potential circumstances that 

might lead to invasion success by a nonnative species due to marine debris. 

There are four broad potential invasion 

scenarios. First, marine debris may be able 

to extend the current range of a species 

to a particular coastline, fueled by factors 

such as the impacts of climate change. 

Densely-populated coastlines are of 

particular concern, since they are found 

to have increased debris loads. Second, 

invasive species that are already established 

in an area due to another pathway (such as 

shipping) can use local pathways (such as 

marine debris) to extend their range even 

further. Third, large debris items in the open 

ocean can carry large numbers of organisms 

and species to new locations. Fourth and 

finally, reoccurring arrivals of small biofouled 

debris items from a particular locale may be 

important in leading to multiple inoculations 

of the same species, overwhelming the 

local population and introducing genetic 

constraints, as opposed to the introduction 

of any one small isolated item. 

EXECUTIVE SUMMARY
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 6

Marine Debris and 

Invasive Species: Two 

Convergent Issues

Litter in the ocean is called 

marine debris and it comes in 

many forms, shapes, and sizes. It 

ranges in size from micro-debris 

(particles < 5mm) to macro-debris 

(>2.5m) (Lippiatt, Opfer, & Arthur, 

2013), and can even include 

derelict vessels that are several 

hundred feet long. Marine debris 

is comprised of a mix of materials, 

including but not limited to plastic, 

nylon, wood, metal, and glass. 

Debris materials can be found 

free-floating at the surface of the 

ocean, within the water column, 

lying on the bottom, or littering 

shorelines (National Oceanic and 

Atmospheric Administration 

Marine Debris Program [NOAA 

MDP], 2016; United Nations 

Environment Programme [UNEP], 

2011).

In addition to the 

unsightliness of marine debris, 

there are a host of serious and 

potentially damaging associated 

impacts. Ingestion, entanglement, 

ghost fishing, economic loss, 

habitat damage, vessel damage, and 

the introduction of invasive species 

are all potential impacts associated 

with marine debris (NOAA MDP, 

2016). For some of these concerns, 

such as ghost fishing (derelict 

fishing traps continuing to entrap 

fish), marine debris is perhaps the 

sole causative agent. For others, 

marine debris is one of many 

potential causative agents. This 

is the case with invasive species; 

marine debris and invasive species 

are two separate but overlapping 

issues of environmental concern.

While these two 

environmental problems are 

different at many levels in terms of 

how we study, mitigate, prevent, 

or eliminate them, they do have 

several commonalities. First, 

both marine debris and invasive 

species are of global concern 

(National Invasive Species Council 

[NISC], 2008; UNEP, 2009; UNEP, 

2011). Second, both issues are 

very complex in their own right 

and the elimination of one will 

not lead to the elimination of 

the other; each will require its 

own set of unique mitigation 

strategies. Third, human-made 

marine debris and the transport 

of species outside of their native 

ranges likely co-emerged and 

began in earnest when mankind 

took to the seas aboard vessels and 

boats several thousand years ago 

(Carlton, 1987; Carlton, 2011). 

In more modern times, shipping 

has increased globally (in terms 

of speed, size, and number of 

vessels) and has led to the dispersal 

of many non-native species 

(Carlton, 1987; Carlton, 2001; 

Lewis, Hewitt, Riddle, & McMinn, 

2003; United States Environmental 

Protection Agency [USEPA], 

2012). Concurrently, modern 

debris consists mostly of nonbiodegradable materials such as 

nylon and plastics (e.g. fiberglass, 

polyvinyls, styrofoam, etc.). In 

addition, unlike ancient litter 

which mostly degraded and sank, 

modern litter has a long life at sea 

and can float for years, transiting 

vast distances (NOAA MDP, 2016). 

NOAA’s Role with 

Marine Debris

The Marine Debris 

Research, Prevention, and 

Reduction Act was signed into law 

in 2006; it was further amended 

and renamed the Marine Debris 

Act in 2012 (33 U.S.C. §§ 1951-

1958). These pieces of legislation 

authorize the NOAA Marine 

Debris Program to “identify, 

determine sources of, assess, 

prevent, reduce, and remove 

marine debris and address the 

adverse impacts of marine debris 

on the economy of the United 

States, marine environment, 

and navigation safety.” In this 

role, NOAA serves as the federal 

lead to address marine debris in 

BACKGROUND

“While these two environmental problems 

are different at many levels in terms of how 

we study, mitigate, prevent, or eliminate 

them, they do have several commonalities. ”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 7

the United States and does this 

through research, prevention, 

removal, regional coordination, 

and emergency response.

NOAA’s Role with 

Invasive Species

NOAA’s role in addressing 

invasive species is primarily 

governed by the Nonindigenous 

Aquatic Nuisance Prevention 

and Control Act (NANPCA) of 

1990, as amended by the National 

Invasive Species Act (NISA) of 

1996. The NANPCA established 

the Aquatic Nuisance Species 

Task Force (ANSTF), which is 

co-chaired by the Director of the 

U.S. Fish and Wildlife Service and 

the Under Secretary of Commerce 

for Oceans and Atmosphere 

(NOAA Administrator). The 

NANPCA also legally defined 

the term “Aquatic Nuisance 

Species” as a “nonindigenous 

species that threatens the diversity 

or abundance of native species 

or the ecological stability of 

infested waters, or commercial, 

agricultural, aquacultural or 

recreational activities dependent 

on such waters.”

Executive Order 13112 

(1999) established the National 

Invasive Species Council (NISC) 

to ensure that federal agencies 

and programs carry out activities 

to prevent and control invasive 

species in a coordinated, effective, 

and efficient manner. The order 

also designated the secretaries 

and administrators of 13 federal 

departments to serve on this 

council. The NISC is co-chaired 

by the Secretaries of Commerce, 

Agriculture, and the Interior. 

The order also defined the term 

“invasive species” (see below) and 

authorized the NISC to prepare 

and issue a National Invasive 

Species Management Plan (NISC, 

2008).

What is an Invasive 

Species?

There is a large amount 

of inconsistency in regard to the 

concept of “invasive species” and 

with the terminology used to 

describe a species that is found 

outside of its natural range 

(Carlton, 2001; Lodge et al., 2006; 

Molnar, Gamboa, Revenga, & 

Spalding, 2008) . While Carlton 

(2001) specifically avoided 

the use of the term “invasive,” 

others have used it in various 

ways. Many have used the term 

in a broad sense to mean any 

species that exists outside of its 

natural range (Molnar et al., 

2008; Richardson et al., 2000). In 

that context, the term “invasive” 

is essentially synonymous with 

the terms “alien,” “exotic,” “nonindigenous,” “ornamental,” and 

“non-native.” It is possible to 

have a non-native species that 

does not spread prolifically and 

harmfully (Zenni & Nuñez, 2013), 

which is the case with many crop 

species or ornamental trees on 

land that require constant human 

intervention in order to sustain 

the crop or plant. However, an 

“invasive species” causes some 

amount of damage or harm to the 

new range that it has invaded.

It is recognized that human 

values and public perception 

can complicate both the concept 

of “invasive species” (NISC, 

2006) and the actions that are 

undertaken to manage that 

species. This produces a gray 

area in which the determination 

on whether or not a species is 

“invasive” is sometimes dependent 

upon human values. For 

example, salmon (Oncorhynchus 

tschawytscha) were introduced 

to the Great Lakes in the 1960s 

to rebuild a sustainable sport 

fishery after the collapse of trout 

populations, as well as to control 

an invasive fish called the alewife 

(Alosa pseudoharengus) (a move 

that would likely be very difficult 

to make today given the current 

laws). The fishery was a huge 

success and an economic boon for 

anglers and tourism along coastal 

regions of the Great Lakes. Today, 

the salmon are highly prized by 

anglers and are deemed beneficial, 

since they also feed heavily on the 

alewife. These salmon are nonindigenous, but are not considered 

to be “invasive species.” After many 

decades now, salmon and trout 

are still stocked into the Great 

Lakes and represent a multibilliondollar sport fishery. The alewife, 

while still classified as invasive, 

is considered one of the most 

“It is recognized that human values and 

public perception can complicate both the 

concept of invasive species and the actions 

that are undertaken to manage that species.”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 8

For the purposes of this paper, 

the term “invasive species” will be 

used. The definition of the concept 

will follow that of the NANPCA 

(1990) and NISA (1996), since this 

definition is more specific regarding 

the harm that a non-indigenous 

species may cause to an ecosystem.

Pathways

Species are introduced 

to new ranges through pathways 

(National Invasive Species 

Information Center [NISIC], 

2016; Ray, 2005; USEPA, 2012; 

United States Fish and Wildlife 

Service [USFWS], 2011) including 

natural processes like wind, 

currents, or a specific behavioral 

or morphological characteristic 

that a species might employ to 

disperse itself (NISIC, 2016). 

Species are also introduced to new 

ranges by a plethora of humanmediated pathways that may 

involve intentional or unintentional 

movement (as is discussed 

throughout this report). In the 

literature, the terms “pathway” 

and “vector” are often used 

interchangeably. Some authors 

employ the term “vector” in place 

of “pathway” (Barnes, Galgani, 

Thompson, & Barlaz, 2009; Carlton, 

1999; Carlton, 2001; Carlton, 2011; 

Roman & Darling, 2007; Williams 

et al., 2013), while others use 

the term “pathway” rather than 

“vector” (Carson et al., 2013; Lewis, 

Riddle, & Smith, 2005). In keeping 

with the terminology employed 

by the NISC (established under 

Executive Order No. 13112, 1999) 

and other federal agencies (ANSTF, 

1994), the term “pathway” will be 

used throughout this document 

when referring to dispersal 

mechanisms in a broad sense, and 

used to encompass all possible 

human-made or human-mediated 

mechanisms.

Known Pathways for 

Invasive Species

Globalization, or the 

integration of views, products, 

cultures, and ideas on an 

international scale, has vastly 

increased world travel and 

commerce. This process has led 

to an increase in the rate and 

magnitude of non-native species 

introductions through a variety 

of pathways (Ruiz, Carlton, 

Grosholz, & Hines, 1997; USEPA, 

2012). In a report to the Pew 

Oceans Commission, Carlton 

(2001) identified pathways 

particularly susceptible to aiding 

marine invasions. These include 

ships (ballast water and hulls), 

drilling platforms, dry docks, 

aids to navigation, seaplanes, 

canals, public aquaria, research 

laboratories, marine debris, 

scuba and snorkeling equipment, 

fisheries (including aquaculture/

mariculture and bait), the aquarium 

pet industry, habitat restoration 

activities, and releases from 

educational institutions.

Pathways associated 

with global shipping (e.g., 

ballast water and biofouling) 

are widely considered to be the 

most significant cause of humanmediated transoceanic dispersal of 

valuable food sources supporting 

that fishery (Fenichel, Horan, & 

Bence, 2010). 

Whereas no definition 

to date is perfect, the federal 

government has defined the 

concept of “invasive species” in 

two different ways. The following 

definition of “invasive species” was 

defined in Executive Order 13112 

(1999).

Invasive Species: “a species that 

is non-native to the ecosystem 

under consideration and whose 

introduction causes or is likely to 

cause economic or environmental 

harm or harm to human health 

(Executive Order No. 13112, 

1999; NISC, 2006).”

A white paper (NISC, 2006) 

produced by the National Invasive 

Species Council provides a nonregulatory policy interpretation of 

the concept of invasive species (in 

Executive Order No. 13122, 1999) 

by identifying what is meant, and 

just as important, what is not meant 

by the concept.

Prior to that, the NANPCA, 

as amended by the NISA, defined 

the concept as follows:

Aquatic Nuisance Species: “a 

nonindigenous species that 

threatens the diversity or 

abundance of native species 

or the ecological stability of 

infested waters, or commercial, 

agricultural, aquacultural, or 

recreational activities dependent 

on such waters.”

“Pathways associated with global shipping 

are widely considered to be the most 

significant cause of human-mediated 

transoceanic dispersal of non-native 

marine and estuarine species.”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 9

non-native marine and estuarine 

species (Carlton, 1987; Carlton, 

2001; Lewis, Hewitt, Riddle, & 

McMinn, 2003; USEPA, 2012). 

Ballast water carried perhaps 

the greatest overall threat for 

transoceanic dispersal until recent 

times, as it is now controlled in 

part by national and international 

management policies (International 

Maritime Organization, 2016). 

The roles that many other 

pathways play in the dispersal of 

marine organisms are not well 

characterized (Williams et al., 

2013). Marine debris is one of the 

least understood anthropogenic 

pathways.

Historical Perspective: 

A Shifting Baseline?

The scale and extent of 

invasions by marine organisms may 

“The scale and extent of invasions by marine 

organisms may be greatly underestimated, 

seriously skewing our understanding of 

the history and ecology of many marine 

communities.” 

be greatly underestimated, seriously 

skewing our understanding of 

the history and ecology of many 

marine communities. Carlton 

(2011) suggests that many of the 

commonplace assumptions that 

we have regarding native species 

(crustaceans in the case of Carlton 

[2011]) may be erroneous. This 

is because global oceanic voyages 

for exploration, commerce, and 

fishing began in and have increased 

since the 1500s, yet the first marine 

biologists did not arrive on the 

shores of some continents to begin 

the process of identifying and 

cataloguing species until several 

centuries later. It is entirely possible 

that many of the indigenous or 

cosmopolitan species that we are 

trying to conserve are non-native 

species that “hitched a ride” or were 

purposefully introduced not more 

than a few hundred years ago.

Figure 1. Small vessel at Cape Disappointment (Photo Credit: Washington State Department of Ecology).
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 10

MARINE DEBRIS AND INVASIONS 

OF MARINE SPECIES

successful and unsuccessful 

invasions, and suggest knowledge 

gaps for further research to better 

understand the importance and 

impact of marine debris as a 

pathway for invasive species.

How Do Aquatic 

Species Associate with 

Marine Debris?

Aquatic species associate 

themselves with marine debris 

in a number of ways that stem 

directly from their natural 

ability to adjust and acclimate to 

changing conditions. On large 

pieces or aggregates of debris, it 

is likely that one would be able to 

document many, if not all, of the 

following groups. An extensive 

literature review by Thiel and 

Gutow (2005) reported over 

1,200 species of sessile and motile 

organisms associated with natural 

and human-made debris from 

sources all over the globe. They 

grouped the organisms into two 

groups– facultative and obligate. 

The facultative species (959 

species) were those known to live 

in natural benthic habitats and on 

debris items, whereas the obligate 

rafters (41 species) are known only 

A wide range of organisms 

occur on marine debris, including 

microbes, protists, plants, fungi, 

and members of many animal 

phyla. Which, if any, of these 

species are invasive? In keeping 

with the aforementioned definition 

of invasive species, we must 

recognize that for a species to be 

invasive, it needs to cause harm 

(or be likely to cause harm). We 

cannot assume that any species 

that attaches itself to marine debris 

is an invasive species, nor can we 

discount the possibility that it may 

become invasive. 

The U.S. Department of 

Agriculture’s National Invasive 

Species Information Center’s 

website maintains a listing of 

invasive aquatic plants and animals 

in the United States (NISIC, 

2016). The NISIC is a gateway to 

information about invasive species, 

created to meet the informational 

needs of the National Invasive 

Species Council (established under 

Executive Order No. 13112, 1999) 

and the public. Their website also 

contains a “watch list” of aquatic 

organisms that are known to be 

invasive on other continents, 

but have not made it to North 

American shores. In addition, the 

website maintains links to other 

global databases of introduced 

aquatic species.

In addition to the 

NISIC, the NEMESIS Database

(Smithsonian Environmental 

Research Center, 2016) provides 

informational resources on nonnative marine and estuarine 

species that occur in the coastal 

waters of the United States; it is 

maintained by the Smithsonian 

Institution. The United States 

Geological Survey (USGS) also 

maintains the Non-indigenous 

Aquatic Species (NAS) database

(USGS, 2016), which contains 

an inventory of informational 

resources for introduced 

freshwater and marine aquatic 

species, with spatial references of 

biogeographical accounts.

It is important to note, 

however, that many modern-day 

invasions consist of species that 

were not on any watch list. A few 

examples include the Asian shore 

crab (Hemigrapsus sanguineus), 

now widespread along the Atlantic 

coast of the United States; the 

Chinese clam (Corbula amurensis), 

abundant in the San Francisco Bay; 

and the Australian green seaweed 

(Caulerpa taxifolia), which was 

introduced to Europe and other 

regions. None of these species 

were known to have a previous 

invasion history or were predicted 

to invade.

This paper will review the 

types of organisms that commonly 

associate with marine debris 

through several case studies 

from the literature. The goals are 

to describe how aquatic species 

associate with marine debris, 

provide context for understanding 

“We cannot assume that any species that 

attaches itself to marine debris is an invasive 

species, nor can we discount the possibility 

that it may become invasive.”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 11

to associate with floating debris, 

where they spend their entire life 

cycle.

BIOFILMS

Microorganisms (bacteria, 

microalgae, and fungi) have the 

ability to colonize various surfaces 

(Decho, 2000) of both organic 

(animals, plants [e.g. wood], 

protists, and fungi) and inorganic 

(sediments and rocks) origin. As 

part of the colonization process, 

microbes form a consortium and 

secrete a matrix of extracellular 

polymers (EPS) to create a 

“microbial biofilm” (Decho, 

2000). In addition to serving as 

protection, this mucilaginous 

Figure 2. Wakame kelp (Undaria pinnatifida), native to Japan and a known invasive species, was found in Oregon attached to debris that 

resulted from the Japan tsunami in 2011 (Photo Credit: Oregon State University, Hatfield Marine Science Center).

biofilm allows the various species 

of microbes within the matrix 

to mutually share nutrients, 

extracellular enzymes, and other 

essential compounds. Biofilms 

are also known to sequester 

metal contaminants and attract 

pathogens (Decho, 2000) and 

harmful algal bloom (HAB) 

species (Maso, Garces, Pages, & 

Camp, 2003). 

It is widely accepted 

that microbes will colonize any 

surface in the marine environment 

(Lobelle & Cunliffe, 2011). To 

that end, biofilms are common 

on marine debris, yet only a 

few studies have addressed the 

issue (Lobelle & Cunliffe, 2011; 

Maso et al., 2003; Saldanha et al., 

2003; Webb, Crawford, Sawabe, 

& Ivanova, 2009; Ye & Andrady, 

1991). Thiel and Gutow (2005) 

reported 72 microbial species 

found on marine debris in their 

extensive literature review, 

including cyanobacteria (11 

species), fungi (32 species), and 

microalgae (29 species). A study 

by Zettler, Minceer, and AmaralZettler (2013) revealed that there 

is an incredible host of microbes 

associated with small plastic 

marine debris (approximately less 

than 5mm), some of which may 

harbor pathogens, such as some 

members of the genus Vibrio. 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 12

SESSILE ORGANISMS: 

ENCRUSTERS/

BIOFOULERS

The encrusting or biofouling 

community is perhaps the most 

recognized group of organisms 

on floating and beached marine 

debris. The encrusters consist of 

a variety of sessile organisms (i.e., 

those that do not move) including, 

but not limited to, bryozoans, 

barnacles, ascidians, hydroids, 

macroalgae, encrusting species of 

foraminiferans, and some mollusks 

and polychaetes (Winston, 

Gregory, & Stevens, 1997). Like 

biofilms, encrusters will attach to 

nearly any surface in the marine 

environment. Much attention has 

been particularly paid to fouling 

on boat hulls. In fact, hull fouling 

has been an impediment to marine 

transportation since humans 

first took to the ocean in boats. 

Encrusters significantly reduce 

hull speed and efficiency (Schultz, 

Bendick, Holm, & Hertel, 2010), 

so a great amount of effort and 

money is spent on preventing the 

fouling of ship hulls. For example, 

Schultz et al. (2010) estimated the 

overall cost associated with hull 

cleaning, hull coating, and fuel loss 

due to fouling to be approximately 

$56 million per year for the United 

States Navy’s mid-size destroyer 

fleet (Arleigh Burke class destroyer 

DDG-51) of about 60 ships. 

When this cost is extrapolated to 

all of the commercial, military, 

and private vessels around the 

world, the enormity of the cost to 

control biofouling becomes highly 

apparent. 

Knowledge of fouling on 

marine debris pales in comparison 

to that associated with the 

fouling of ships, but the impact 

of marine debris and its potential 

as a pathway for invasive species 

cannot be discounted. A variety of 

studies have observed encrusting 

organisms on marine debris, 

with some studies documenting 

non-native organisms present 

on beach- or shoreline-stranded 

debris (Barnes & Fraser, 2003; 

Barnes & Milner, 2005; Winston et 

al., 1997), and others focusing on 

floating debris (Astudillo, Bravo, 

Dumont, & Thiel, 2009; Bravo et 

al., 2011; Goldstein, Carson, & 

Eriksen, 2014). Thiel and Gutow 

(2005) reported that the vast 

majority of the species reported 

(of more than 1,200 species) on 

marine debris were from the phyla 

Cnidaria (Hydrozoa), Crustacea 

(Amphipoda), and Bryozoa.

To date, no studies 

document marine debris as being 

the sole pathway responsible for an 

invasion of encrusting organisms 

into a particular area. Given the 

multitude of potential pathways 

for the introduction of invasive 

species, the degree to which marine 

debris plays a role in the invasion 

of encrusting communities remains 

unclear. 

MOBILE ORGANISMS: 

HITCH-HIKERS/

HANGERS-ON/AQUATIC 

RAFTERS

Gregory (2009) noted the 

possibility that mobile organisms 

may be associated with marine 

debris. In a recent study (Goldstein 

et al., 2014), a variety of plasticassociated rafting organisms 

were observed during Eastern 

and Western Pacific Ocean 

cruises from 2009 to 2012, with 

various sessile and mobile species 

reported. Ninety-five different 

taxa (largely arthropods, mollusks, 

and cnidarians) in 11 phyla were 

found on the debris, with an 

approximately equal distribution 

of mobile and sessile species. The 

taxa included many mobile grazers 

and predators, and were found on 

debris objects that were varied in 

size and diverse in composition. 

Many of the taxa found on the 

debris were known invaders 

(Goldstein et al., 2014). Previously, 

Thiel and Gutow (2005) reviewed 

this topic and found 410 arthropod 

species were associated with 

debris, with more than 100 mobile 

arthropod species. In another study 

(Astudillo et al., 2009), mobile 

species were identified as a major 

functional group found on floating 

detached aquaculture buoys off the 

coast of Chile.

TERRESTRIAL RAFTERS

Perhaps the earliest 

documented case of terrestrial 

organisms rafting on floating 

objects is an account of ants rafting 

on a floating log (Wheeler, 1916). 

There are few other reported cases 

of terrestrial flora or fauna rafting 

“The impact of marine debris and its 

potential as a pathway for invasive 

species cannot be discounted. ”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 13

on floating items. In the case of the 

ants, they had reportedly floated a 

short distance from the mainland 

of Brazil to San Sebastian Island. 

There are great impediments to 

survival of terrestrial organisms 

rafting great distances, including 

lack of shelter, exposure to salt 

water, wave action, lack of food, 

and lack of potable water, which 

likely explains why we do not 

see many documented cases of 

these organisms traveling great 

distances. In the review by Thiel 

and Gutow (2005), a small number 

of non-marine or terrestrial species 

associated with mostly natural 

floating material was reported, but 

most were found in relatively close 

proximity to their native ranges. 

These included 12 species of nonmarine arthropods, three species of 

amphibians, 17 species of reptiles, 

and two small mammal species. 

While these occurrences are 

rare, it is believed that terrestrial 

species arrived and were established 

on many islands and distant shores 

by rafting on natural material 

over the millennia. A paper by 

Eldredge and Gould (1972) offered 

a controversial view on this topic 

when it was released, but is now 

considered a landmark paper. They 

suggested that speciation occurred 

not gradually over the course of 

Figure 3. A small derelict boat washed ashore on the remote Spring Island, British Columbia, Canada, and was positively identified as a vessel 

lost during the 2011 Japan tsunami (Photo Credit: Kevin Head).

millennia, but through punctuated 

events not unlike the Japan tsunami 

in 2011. There is geologic evidence 

for giant tsunamis, earthquakes, 

volcanic eruptions, and even 

meteor strikes, which likely ejected 

a great amount of natural drifting 

material (rafts) into the ocean that 

may have carried terrestrial species 

to distant shores.

“There are great impediments to survival of terrestrial organisms 

rafting great distances, including lack of shelter, exposure to salt 

water, wave action, lack of food, and lack of potable water, which 

likely explains why we do not see many documented cases of these 

organisms traveling great distances. ”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 14

Case Studies

REGIONAL STUDY: 

PLASTIC BEACH DEBRIS; 

EAST COAST OF FLORIDA

Three studies conducted 

in 1980, 1988, and 1994 along the 

East Coast of Florida surveyed 

beach-stranded debris items 

and associated biota (Winston et 

al., 1997). The studies primarily 

focused on plastic items that 

were largely colonized by 

encrusting organisms. Over 64 

taxa were observed from nine 

phyla, and the dominant groups 

were foraminiferans, bryozoans, 

hydroids, algae, tube-building 

polychaetes, and barnacles. Four 

of the five dominant species were 

native species. These encrusters 

and benthic species appeared to 

have originated from Caribbean 

or Floridian coasts and islands. 

There was possibly one exotic 

bryozoan species reported, 

perhaps originating from the coast 

of Brazil. These studies also noted 

seasonal differences in the diversity 

of organisms and evidence of 

reproduction by the encrusters.

The plastic debris that was 

surveyed was predominantly of 

U.S. origin and probably originated 

from within 500 miles of the 

study site (Winston et al., 1997). 

To a lesser extent, some items 

originating from the Caribbean 

were noted, which agrees with 

prevailing current patterns in the 

region. Items manufactured in 

Portugal, Greece, and Scandinavia 

were observed, but the debris 

point of origin (i.e. where they 

were discarded) was not known. 

Since the majority of the debris 

and the associated species on the 

debris originated from within the 

region, range expansion of current 

inhabitants is more likely than new 

invasions by non-natives. There 

was no evidence found to suggest 

possible establishment or invasion 

by transoceanic, non-native 

species.

REGIONAL STUDY: 

AQUACULTURE BUOYS; 

SOUTHEASTERN 

PACIFIC, COAST OF 

CHILE

Astudillo et al. (2009) 

studied organisms associated with 

detached aquaculture buoys in the 

Southeastern Pacific off the coast 

of Chile from 2001 to 2005. Thirtyfour detached buoys were surveyed 

and contained a total of 134 species 

representing 14 phyla. About 54% 

of the species were common across 

all buoys, and the overwhelming 

majority of them were indigenous 

to the region. The most common 

species were mobile species and 

suspension feeders, of which the 

majority had sexual reproduction 

strategies such as separate sexes, 

internal fertilization, and direct 

or very short larval development. 

Encrusting communities were 

found to be very mature and wellestablished. 

These plastic buoys were 

found to originate from a common 

aquaculture operation in the Bay 

System of Coquimbo, Chile. Plastic 

buoys float higher out of the water, 

resulting in high windage which 

can cause them to be transported 

farther distances (Astudillo et al., 

2009), as opposed to other types of 

plastic debris.

GLOBAL STUDY: OPEN 

OCEAN AND COASTAL 

DEBRIS; ATLANTIC 

OCEAN

In 2002, Atlantic Ocean 

shipboard surveys were conducted 

between hemispheres (from 68°S 

to 78°N) to compare floating openocean marine debris to debris 

stranded on beaches (Barnes & 

Milner, 2005). The Eastern North 

Atlantic (off of Europe) had the 

greatest amount of floating debris, 

and debris stranding densities 

were greatest in equatorial regions. 

Plastic pieces were the dominant 

debris type found in both the open 

ocean and stranded on beaches. 

While sampling was limited 

compared to the scale of the study, 

there was no change detected in 

the amount of debris collected 

when compared to a survey 

conducted ten years earlier. 

During this study, 

organisms were only documented 

from beach-stranded debris and 

were predominately encrusters, 

such as balanomorph barnacles, 

pedunculate barnacles, byrozoans, 

hydroids, and polychaetes from 

sites across both hemispheres 

(Barnes & Milner, 2005). One 

exotic species (the invasive 

barnacle, Elminius modestus, now 

known as Austrominius modestus) 

was found attached to plastic 

debris in the Shetland Islands, 

United Kingdom. The barnacle 

is native to Australia, but was 

introduced to Britain in the 1940s 

during World War II (Crisp, 1958), 

presumably via biofouling from 

ships. In a prior survey, Harms 

(1990) found ten plastic debris 

items during a benthic survey in 

the Elbe Estuary (Germany Bight, 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 15

North Sea), of which eight had A. 

modestus attached. In total, 104 

individuals of A. modestus were 

found (Harms, 1990). Barnes 

and Milner (2005) discussed that 

the impacts of marine debris on 

animal introductions are difficult 

to measure and that future oceanic 

surveys are warranted for a more 

inclusive picture.

GLOBAL STUDY: OPEN 

OCEAN DEBRIS; NORTH 

PACIFIC OCEAN

A study conducted in 

the North Pacific (Goldstein et 

al., 2014) documented the taxa 

associated with floating debris 

in the open ocean between 2009 

and 2012. Eighty-seven percent 

of the 242 debris items collected 

were rigid plastic fragments, and 

approximately 25% of those were 

larger than 2 cm in diameter. 

Ninety-five taxa from 11 phyla 

were observed associated with 

the debris, the majority of which 

were suspension feeders, with 

arthropods being the most 

dominant group. Ominvores, 

grazers, and predators were also 

present in significant numbers. 

Most of the taxa found were 

those commonly associated with 

rafting and fouling on debris, 

although about a quarter were 

not previously documented as 

being part of rafting assemblages. 

Goldstein et al. (2014) indicated 

that some of the observed taxa 

were known invaders, but they 

did not determine whether the 

populations that were encountered 

originated from their home range 

or from a new or expanded range. 

NATURAL DISASTERS 

AND MARINE DEBRIS

Natural disasters can 

cause severe damage to property, 

loss of life, economic losses, and 

extreme environmental damage. 

Hurricanes, tsunamis, landslides, 

and floods can destroy property 

and can generate an extreme 

amount of debris in a very short 

period of time. This debris can 

be scattered in many directions 

and deposited in upland areas, on 

coasts and shorelines, or washed 

out to sea. In recent years, there 

have been a number of natural 

disasters that have generated a 

great deal of marine debris. One 

of the more serious events in 

recent years was the March 11, 

2011 earthquake (9.0 magnitude) 

in Japan that triggered a tsunami, 

with waves up to 40 meters 

(NOAA, 2013b; Figure 4). The 

event devastated over 200 miles 

of coastline and resulted in great 

loss to human life and property. 

The debris generated from this 

event consisted of nearly any item 

imaginable, ranging from small 

plastics to derelict fishing vessels 

tens of meters long. Items began 

showing up along the West Coast 

of the United States about a year 

later in 2012.

Debris from a natural 

disaster can be different than other 

debris discarded into the ocean. 

Items such as floating docks, 

anchored buoys, and watercraft can 

get ripped loose or dislodged from 

moorings and washed out to sea. 

These items typically have mature, 

well-colonized communities of 

marine organisms. In addition, 

a great amount of debris from 

terrestrial sources can be injected 

into the ocean, and subsequently 

become colonized by marine life. 

Such disaster-generated debris is 

capable of floating across the ocean 

and stranding on foreign shores, 

resulting in a number of potential 

introductions (NOAA MDP, 2016). 

For example, four docks from 

the Port of Misawa, Japan were 

dislodged from their moorings 

during the Japan tsunami (Barnea 

et al., 2014). Two of these docks 

drifted across the Pacific Ocean 

and stranded on the West Coast 

of the United States: one in 

Oregon (June 2012) and one in 

Washington (December 2012), 

while the third dock resurfaced 

in Hawai'i, but was not recovered. 

The dock that washed ashore in 

Oregon was covered in growth 

and contained numerous nonnative species., while the dock that 

washed ashore in Washington had 

less coverage of biota. This could 

possibly be due to scouring in 

the surf zone, but more than 400 

pounds of biota were removed 

from the dock, representing more 

than 60 species from coastal Japan 

(NOAA, 2013a). Both docks, 

which spent more than a year 

“Hurricanes, tsunamis, landslides, and 

floods can destroy property and can 

generate an extreme amount of debris in a 

very short period of time.”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 16

Figure 4. Disaster-generated debris is capable of floating across oceans and stranding on foreign shores, resulting in a number of potential 

invasive species introductions. This figure shows the possible introductions resulting from marine debris generated by the March 11, 2011 

earthquake (9.0 magnitude) and resulting tsunami in Japan. 

at sea, contained significant and 

thriving communities of organisms 

at the time of their stranding on 

the West Coast of the United 

States.

Framework for 

Invasion

Numerous frameworks or 

models have been proposed for 

the invasion process (Richardson 

et al., 2000; Shea & Chesson, 

2002; Williamson & Fitter, 1996; 

Williamson, 1996). Blackburn 

et al. (2011) developed a unified 

framework that combined many 

of the concepts and ideas of 

previous models, outlining four 

stages for an organism to become 

an invasive species in a new 

range. First, the species must be 

transported to the foreign range 

via a pathway. Second, the species 

must be introduced to the foreign 

range. Third, the species must 

become established in the foreign 

range, which includes survival and 

reproduction. Finally, the species 

must spread in that range to 

become invasive.

The reality is that there 

are far more failed invasions as a 

result of species introductions than 

successful invasions (Blackburn 

et al., 2011; Lockwood, Cassey, & 

Blackburn, 2005; Zenni & Nuñez, 

2013). This is due to the numerous 

barriers in each stage of the 

invasion framework. In order to 

understand the likelihood that an 

introduced species will successfully 

invade a new range, it is important 

to gain an understanding of past 

failed invasions and the reasons 

for those failures (Zenni & Nuñez, 

2013).

Zenni and Nuñez (2013) 

found five main factors that 

contribute to the failure of a 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 17

species invasion. These include 

poor propagule pressure, abiotic 

resistance, biotic resistance, genetic 

constraints, and mutualist release. 

As a pathway for invasive species 

introduction, marine debris adds 

additional complexity and barriers 

to the transportation stage of the 

framework. These barriers include 

distance and transit hurdles, harsh 

environments, and complications 

for reproduction such as dispersal 

issues associated with differing 

developmental strategies.

One of the first and most 

obvious barriers to invasion for 

a species utilizing marine debris 

as a pathway is that it first must 

establish itself on the debris. 

Encrusting organisms, for example, 

are particularly well-adapted to 

colonizing human-made surfaces, 

including the hulls of ships, marine 

debris, docks, buoys, jetties, and 

platforms. There is also the case of 

coastal structures and vessels (such 

as docks, barges, derelict watercraft, 

lost/adrift buoys, etc.) that are often 

completely colonized with biota 

at the point of origin or release. 

Debris cast off of ships can then 

become colonized by organisms 

as it drifts into various regions 

or ecosystems. Non-encrusting 

organisms are often embedded into 

the encrusting communities on 

marine debris.

For short or regional 

transits, the species may survive 

without the need for extensive 

habitat resources. For longer 

transits, a species or community 

of species will require all of the 

necessary resources to survive 

Figure 5. A worker uses a 30% bleach spray to decontaminate and reduce the spread of possible marine invasive species on the Japanese dock 

which made landfall on Washington’s Olympic Peninsula in December 2012 (right; Photo Credit: Allen Pleus, Washington Department of Fish 

& Wildlife).

the transit. In many respects, they 

must first become established on 

the debris. Many of the barriers 

associated with the introduction of 

a species to a new range also exist 

with respect to an organism being 

associated with the marine debris.

PROPAGULE PRESSURE

The issue of propagule 

pressure is not unique to organisms 

using marine debris as a pathway 

of introduction. Propagule pressure 

is defined as the composite 

number of viable, non-native 

individual organisms introduced 

into a new range (Lockwood et 

al., 2005; Roman & Darling, 2007; 

Zenni & Nuñez, 2013). There are 

two components to propagule 

pressure— size and number, which 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 18

Figure 6. The marine organisms that were found on the derelict Misawa floating dock that washed ashore on Agate Beach in Newport, Oregon 

(Photo Credit: Oregon State University, Hatfield Marine Science Center).

refer to the number of individuals 

in a single release and the number 

of release events. The size of a 

piece of marine debris is directly 

proportional to its potential 

propagule size since the larger the 

debris, the more individuals it can 

carry. Goldstein et al. (2014) found 

the size of the debris is positively 

correlated with the number of taxa 

found on the debris. The number 

of pieces of debris originating 

from a particular locale is a 

contributor to propagule number. 

The concept of propagule quality 

has also been introduced (National 

Research Council [NRC], 2011), 

which relates to the viability of the 

organisms and/or their capacity to 

reproduce.

The significance of 

small, isolated pieces of marine 

debris with minimal associated 

biota remains unclear. Given 

the extremely poor propagule 

pressure attributed to a small, 

isolated piece of debris, we can 

speculate that the risk for invasion 

is decreased. Conversely, large 

pieces of marine debris, such as 

the Misawa docks (Barnea et al., 

2014), have significantly increased 

propagule pressure and, in turn, 

the risk of invasion success is 

increased. Many small pieces of 

debris originating from the same 

area, such as the aquaculture 

buoys off of Chile (discussed on 

page 14; Astudillo et al., 2009), 

can also have a significantly 

increased risk of invasion success. 

While the propagule size for an 

individual detached buoy is small, 

the numerous buoy losses over 

time from Chilean aquaculture 

facilities constitute a significantly 

increased invasion risk due to the 

high propagule number (multiple 

releases).
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 19

CONCLUSION

A Successful Invasion 

via Marine Debris

The early thinking was that 

a successful invasion could include 

one male and one female, or a 

single fertilized female, to cause 

the establishment of a species 

in a new range (Wheeler, 1916). 

However, given the many barriers 

to transportation, introduction, 

establishment, and spread, we 

see the process is much more 

complicated.

Currently there are no 

reported invasions solely due to 

marine debris as a pathway (J.T. 

Carlton, personal communication). 

This is, in part, because teasing out 

which of many pathways brought 

a species to a new region has often 

proved challenging (Carlton & 

Ruiz, 2005). Molecular genetic 

techniques may assist in ferreting 

out probable source populations 

and thus may be useful in helping 

to identify possible pathways 

of introduction. Despite these 

challenges, we cannot dismiss 

marine debris as a potential 

pathway in invasion biology. There 

are several scenarios whereby 

marine debris may play a role in 

species invasions.

REGIONAL INVASIONS 

AND RANGE 

EXPANSIONS:

In any given region, the 

majority of marine debris likely 

originates from the region itself 

or nearby locations (Winston 

et al., 1997) and in populated 

coastal areas, increased debris 

loads have been observed (Barnes 

& Milner, 2005; Ribic, Sheavly, 

Rugg, & Erdmann, 2012; Wei, 

Rowe, Nunnally, & Wicksten, 

2012; Winston et al., 1997). 

Marine debris, in concert with 

other pathways, may play a role 

in the range expansion of native 

and introduced species when 

coupled with climate change 

impacts (Mainka & Howard, 2010; 

Figure 7). Climate change impacts 

that may drive range expansions 

and new invasions include 

changing temperatures, changing 

precipitation patterns, changing air 

and ocean chemistry, and changing 

ocean circulation (Mainka & 

Howard, 2010). 

Regional dispersal via 

marine debris could foster the 

range expansion of organisms that 

reproduce sexually or asexually. 

Due to the sheer amount of debris 

that can be present, propagule 

pressure is greatly increased, 

allowing the organism to overcome 

genetic constraints and have 

increased mate encounters. 

Organisms that have larval 

developmental strategies are at an 

advantage in regional dispersal 

scenarios. If adult forms of 

organisms are able to associate 

with debris or other pathways 

and reproduce, then they can 

potentially extend the maximum 

‘reach’ of their larvae’s dispersal 

limits (Mainka & Howard, 2010).

TRANSOCEANIC 

INVASIONS:

For global or transoceanic 

introductions via marine debris, 

barriers to invasion are numerous 

and thus the potential for invasion 

is more limited. Like regional 

dispersal mechanisms, species 

encrusted on oceanic pieces of 

marine debris must have sufficient 

propagule pressure. However, large 

debris items (such as Japanese 

tsunami debris—the Misawa 

docks) with mature communities 

of organisms are of particular 

concern. These communities have 

greatly increased propagule size 

and quality, containing many 

individuals of many different 

species at various life-history 

stages. While there are a number of 

variables at play, the communities 

of organisms on this large debris 

can have reduced founder effects 

and increased mate encounters 

once they reach a foreign range. 

Increased debris loads in the ocean 

“For global or transoceanic introductions 

via marine debris, barriers to invasion 

are numerous and thus the potential for 

invasion is more limited.”
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 20

Figure 7. Regionally, marine debris, in concert with other pathways, may play a role in range expansion of native and introduced species when 

coupled with climate change impacts. 

resulting from extreme events may 

increase the chance of transoceanic 

species introductions.

Assisted Invasion by 

Marine Debris

While much attention is given to 

marine debris’ potential to start 

prolific and damaging invasions by 

non-native species, marine debrisassisted invasion of established 

invasive species (Winston et al., 

1997) is also a concern, although 

this has not been well documented 

(Figure 8). A possible scenario 

could be an invading organism 

arriving to a new range as larvae 

via ballast water or hull biofouling 

from a home range thousands 

of miles away. Through high 

propagule pressure, the organism 

may settle, become established, 

and reproduce in the new range. 

A variety of local or regional 

pathways, including marine debris, 

may then assist in the continued 

spread of the invasion.

As an example, the invading 

Australian barnacle A. modestus 

(as discussed on page 14) was 

introduced via ballast water to the 

United Kingdom during World War 

II (Crisp, 1958). Since that time, the 

barnacle has spread throughout the 

U.K. and Europe, predominantly by 

larval dispersal on coastal currents. 

Barnes and Milner (2005) observed 

high densities of floating debris 

in those waters off of Europe and 

the U.K. and found A. modestus 

attached to plastic debris on the 

shores of the Shetland Islands. 

In another study, newly-settled 

individuals of A. modestus were 

found on plastic debris from a 

benthic trawl in the Elbe Estuary 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 21

near Germany (Harms, 1990). 

In that case, the debris was not 

serving as a transport mechanism, 

but rather as a mechanism that 

serves to increase the number 

of individuals in a given area by 

providing more habitat. This may 

lead to increased larval dispersal, 

which is the primary mechanism 

Figure 8. A variety of local or regional pathways, including marine debris, can assist in the continued spread of established invasive species 

introduced to the area through other pathways, such as shipping.

“The debris was not serving as a transport 

mechanism, but rather as a mechanism 

that serves to increase the number of 

individuals in a given area by providing 

more habitat.”

for dispersal of A. modestus. While 

the role of marine debris is perhaps 

very minimal in this case, it may 

assist in the proliferation of the 

established invasive species by 

providing additional pathways or 

increased habitat areas.

Summary and 

Knowledge Gaps

The issues surrounding marine 

debris as a pathway for invasive 

species are complex and not well 

understood. What we do know 

is that while there are numerous 

barriers for a species to overcome, 

thousands of aquatic and terrestrial 

invasions have been successful 

through a variety of pathways. 

On one hand, we might predict 

that invasion risk is very low 

with regard to marine debris as a 

pathway given these barriers. On 

the other hand, invasion risk may 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 22

be high under certain situations and scenarios. We 

must also consider the fact that debris loads are still 

increasing (Jambeck et al., 2015). This suggests that 

the overall risk for impacts due to marine debris is 

increasing. While definitive examples of invasion via 

marine debris elude scientists, there is a potential risk 

of invasion based on the weight of evidence. Here is 

what we know:

• The amount of debris in the ocean is increasing.

• Organisms from distant shores are found attached 

to or associated with marine debris.

• Some of the organisms associated with debris are 

known invaders.

• Debris loads are heaviest in populated areas.

• Large pieces of debris can harbor more organisms 

and can float long distances.

• Extreme events such as cyclonic storms, 

earthquakes, and tsunamis can produce enormous 

amounts of debris.

• During the introduction of a non-native species, 

increased numbers of individuals may increase the 

chances of invasion success.

Concerns regarding invasions of organisms 

have prompted many studies in both terrestrial and 

aquatic systems. Awareness of marine debris and 

the various issues associated with it are beginning to 

gain national and global attention. Despite a number 

of studies documenting the association of various 

species with marine debris, there are significant gaps 

in the knowledge base and a multitude of questions 

persist. While this list of questions is by no means 

comprehensive, it serves as a starting point to begin 

the dialog to understand the problem:

• As a pathway of introduction, how large of a role 

does marine debris play in species invasions when 

compared with other pathways, such as shipping?

• What are the settlement densities of organisms on 

marine debris?

–By debris type/composition/size?

–By point of origin?

–For debris discarded in the open sea versus debris 

discarded in estuaries that then float out to sea?

• Are microplastics in the ocean pathways for the 

introduction of microorganisms? Do microplastics 

harbor pathogens?

• How do communities of organisms change over 

time (ecological succession) on large debris pieces 

in the open ocean? Do some organisms outcompete others on the debris?

• Do species assemblages on floating marine debris 

differ significantly from species assemblages on 

beach-stranded items within the same region?

Recommendations

Based on the information discussed in the 

body of this report, the following recommendations 

are meant to assist in the further study and reduction 

of the potential for marine debris to act as a pathway 

for invasive species.

• Work with the National Invasive Species Council to 

integrate marine debris into the National Invasive 

Species Management Plan.

• Develop targeted approaches to reduce the 

potential spread of invasive species via marine 

debris. 

–Regionally:

• Identify major debris generation points.

–Work with regional agencies to engage the 

responsible parties to reduce and

 eliminate debris at its source.

–Identify operations or generation points that 

consistently release the same type of debris 

(i.e. aquaculture or fishing operations).

• Identify new types of gear or new practices 

that will reduce or eliminate the release of the 

debris.

• Conduct beach and river sweeps; network 

with beach cleanups to gather data on 

encrusters and growth rates on debris and 
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 23

provide debris to the scientific community for 

analysis.

–Globally:

• Identify large pieces of debris in the ocean.

–Explore international efforts to mark and 

track (GPS) the large items.

–Remove large items if feasible.

–Disaster Debris:

• As part of an overall emergency response 

plan/standard operating procedure:

–Compile a listing of large resources, facilities, 

vessels, docks, etc. that are unaccounted for 

in the aftermath of the event. 

–Use models and remote sensing technologies 

to find and/or predict the location of large 

floating debris.

–Explore international efforts to mark and 

track (GPS) the large items.

–Remove large items if feasible.
2017 MARINE DEBRIS INVASIVE SPECIES REPORT 24

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GLOSSARY

Abiotic resistance – Physical or chemical factors that inhibit the introduction and establishment of a non-native 

species to a new range, such as temperature, light availability, sediment/substrate type, or flow dynamics.

Aquatic invasive species (AIS) – Refers specifically to invasive species that reside in aquatic environments 

(Smits & Moser, 2009).

Aquatic Nuisance Species – A nonindigenous species that threatens the diversity or abundance of native species 

or the ecological stability of infested waters, or commercial, agricultural, aquacultural or recreational activities 

dependent on such waters (NANPCA, 16 U.S.C. §§ 4701-4751).

Biofilm – A consortium of microorganisms living in a matrix of extracellular polymers on surfaces.

Biotic resistance – Biological factors that inhibit the introduction and establishment of a non-native species to a 

new range, such as competition or predation.

Dispersal – Any movement of a species that ultimately results in increased gene flow (Ronce, 2007).

Founder effect – A loss in genetic diversity in a population that was established by a small number of 

individuals.

Genetic bottleneck – An extreme reduction in the demographic size of a population.

Introduced species – Refers to a species that is transported by humans or human activities into areas outside 

of their natural ranges. The means of introduction may be intentional or unintentional escape, release, 

dissemination, or placement (Executive Order No. 13122, 1999).

Invasive – Tending to spread prolifically and undesirably or harmfully.

Invasion success – The successful introduction, reproduction, and invasion by a non-native species to a new 

range.

Invasive species – A species that is non-native to the ecosystem under consideration and whose introduction 

causes, or is likely to cause, economic or environmental harm or harm to human health (Clinton, 1999; NISC, 

2006).

Mutualism – A symbiotic relationship between two species when both partners benefit from the association.

Native species – Refers to a species in a particular ecosystem that historically occurred or currently occurs in 

that ecosystem and was not introduced (Executive Order No. 13122, 1999); a species in its natural range.

Non-native species (synonyms: alien, exotic, non-indigenous, ornamental) – Refers to any species residing 

outside of its currently-reported natural range. 

Pathway – A dispersal mechanism that encompasses all possible human-made or man-mediated mechanisms.
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Phenotypic plasticity – The ability of an organism to change its physical characteristics or traits in response to 

changes in the environment. 

Polyphagous – Able to eat many different types of food.

Propagule pressure – The composite number of viable, non-native individual organisms introduced into a new 

range (Lockwood et al., 2005; Roman & Darling, 2007; Zenni & Nuñez, 2013).
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United States Secretary of Commerce

Benjamin P. Friedman

Acting Under Secretary of Commerce for Oceans and Atmosphere

Dr. Russell Callender

Assistant Administrator, National Ocean Service