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Critical Review pubs.acs.org/est
Spatial and Temporal Patterns of Stranded Intertidal Marine Debris: Is There a Picture of Global Change? Mark Anthony Browne,*,†,‡ M. Gee Chapman,§ Richard C. Thompson,∥ Linda A. Amaral Zettler,⊥ Jenna Jambeck,# and Nicholas J. Mallos∇ †
National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, 735 State Street, Suite 300, Santa Barbara, California 93101-3351, United States ‡ Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney NSW 2052, Australia § School of Biological Science, University of Sydney, Sydney NSW 2006, Australia ∥ School of Marine Science & Engineering, Plymouth University, Plymouth PL4 8AA, U.K. ⊥ The Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, Massachusetts 025431, United States # College of Engineering, University of Georgia, Athens, Georgia 30602, United States ∇ Ocean Conservancy, 1300 19th Street, NW, Eighth Floor, Washington, D.C. 20036, United States S Supporting Information *
ABSTRACT: Floating and stranded marine debris is widespread. Increasing sea levels and altered rainfall, solar radiation, wind speed, waves, and oceanic currents associated with climatic change are likely to transfer more debris from coastal cities into marine and coastal habitats. Marine debris causes economic and ecological impacts, but understanding the scope of these requires quantitative information on spatial patterns and trends in the amounts and types of debris at a global scale. There are very few large-scale programs to measure debris, but many peer-reviewed and published scientific studies of marine debris describe local patterns. Unfortunately, methods of defining debris, sampling, and interpreting patterns in space or time vary considerably among studies, yet if data could be synthesized across studies, a global picture of the problem may be avaliable. We analyzed 104 published scientific papers on marine debris in order to determine how to evaluate this. Although many studies were well designed to answer specific questions, definitions of what constitutes marine debris, the methods used to measure, and the scale of the scope of the studies means that no general picture can emerge from this wealth of data. These problems are detailed to guide future studies and guidelines provided to enable the collection of more comparable data to better manage this growing problem.
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INTRODUCTION
there are millions of tonnes of hazardous debris added to coastal habitats11 through increased runoff12 and wind.13 Changes in currents14 and upwelling may cause debris to arrive in previously unimpacted places, and increased wave action8 may bring floating subtidal debris onto shores.15 Increasing solar radiation will accelerate the rates at which stranded intertidal debris photodegrades into smaller fragments, resulting in more microdebris.16 It is essential to understand spatial and temporal patterns of stranded intertidal marine debris at a global scale, so future changes can be predicted and managed.
Climatic change and contamination by marine debris are global problems that degrade biological systems by impairing physiological functions, growth, and survivorship. Recently, plastics are replacing traditional materials, making goods lighter and able to travel longer distances.1 Although plastic goods may reduce emissions of carbon dioxide, policy makers believe the amount of waste generated and emitted (see Jambeck et al.2 for estimates of emissions) is challenging environmental management because of perceived increases in plastic debris in the environment.3 More than 80% of the associated impacts to wildlife are caused by plastic.4,5 As plastic production and global climatic change accelerate, larger quantities of debris will be added to coastal habitats, because of global changes in sea levels,6 rainfall, wind speed,7 and wave height8 and increased risk of floods, storms, hurricanes, and tsunamis.9,10 Each year, © 2015 American Chemical Society
Received: Revised: Accepted: Published: 7082
December 15, 2014 April 15, 2015 May 4, 2015 May 4, 2015 DOI: 10.1021/es5060572 Environ. Sci. Technol. 2015, 49, 7082−7094
Critical Review
Environmental Science & Technology Because of large coastal populations,17 there is widespread contamination of intertidal regions.18,19 Concerns about ecological impacts,4,5 along with its visibility, have led to many studies of stranded debris (Figure 1). Most measured visible debris, such as household goods,20,21 or fishing gear,22 but recently, there is more emphasis on microplastics.13,19,23,24
scale; e.g., how do the amounts or composition of debris vary among oceans, deep and shallow waters, and different habitats, what are the major trends and are they determined globally or locally, and how is debris related to climatic change, waste management, and coastal usage? Data on sources, pathways, and sinks are needed to understand and predict the location and extent of the problem. As has been previously stated,30 this requires rigorous quantitative data synthesized at appropriate (large/global) scales. Currently, our understanding comes from two major sources. Most large-scale studies of marine debris have focused on cleaning the environment, e.g., the ICC (International Coastal Clean-up) Programme which collected debris over 28 years31 and the OSPAR (Convention for the Protection of the Marine Environment of the North-East Atlantic) Programme which measures debris annually on 51 European beaches.32 Numerous cleanup programmes in Britain are detailed in Storrier et al.33 The results of such programmes are not generally published in peer-reviewed scientific journals (but see Schulz et al.34), where most papers focus on local issues. Although the emphasis is on cleanup, if methods are comparable, data from such studies should be able to contribute to a global picture. Alternatively, numerous reviews35−38 have attempted to summarize large-scale patterns or long-term trends in marine debris by summarizing published data. Most have not, however, evaluated how sampling methods might affect the measures obtained. As one example, Claereboudt39 provided the amounts of debris per linear meter from studies that included measures of standing stock,40,41 or accumulation over days42 or months,43 data collected from a site,44 from vertical transects of different sizes,40,45 or from new42 or old46 strandlines. All of these methods can affect the amounts and types of debris measured and, thus, confound spatial or temporal patterns if the measures are treated as equivalent. They also included different size ranges and components in their measures of debris, so were not measuring equivalent material. Synthesis of information from multiple small studies can only test for generality if methods do not vary in ways that influence results,47 including the type and size of sampling units, replication, and temporal and spatial scales, etc.48 A global synthesis of spatial patterns and trends in the amounts and
Figure 1. Trends demonstrating increasing interest in marine debris within the literature published in the past 5 decades (a) and annually for the past decade (b). The search was performed in the Web of Science using the terms “marine” AND “debris”. Papers were further sorted to retain only those associated with marine debris. The asterisk (*) indicates the search was performed in July 2014.
Industry and policy makers disagree about how to tackle marine debris and whether plastic products cause more marine debris and impacts (Figure 2).25−29 It is currently essential to gather robust data to answer important questions about changes in the amounts and types of marine debris at a global
Figure 2. Advertisement from the 18th International Association of Packaging Research Institutes (IAPRI) World Packaging Conference, San Luis Obispo, CA, USA, 2012. Reprinted with permission from Dow Chemical (Australia) Pty. Ltd. Copyright 2012. 7083
DOI: 10.1021/es5060572 Environ. Sci. Technol. 2015, 49, 7082−7094
Critical Review
Environmental Science & Technology
Figure 3. Global map of studies about intertidal debris.
evaluation unless they provided original data, with description of methods. References were then used to find papers from underrepresented habitats or areas. We identified where and why the study was done, how habitats and sites were selected, the number of sites, and whether standing stock or accumulation was measured. Methods were evaluated in relation to the aims, with respect to spatial and temporal replication, pseudoreplication, balanced or unbalanced sampling, the areas sampled, and the data collected. We identified the measures, the level of quantitative information, characterization of the debris, whether buried debris was included, and the size ranges of debris. There were 83 papers on macrodebris (>1 mm) and 19 papers on microplastics (
