Scales of Spatial Heterogeneity of Plastic Marine Debris in the Northeast Pacific Ocean

Miriam C Goldstein,Andrew J Titmus,Michael Ford,Judi Hewitt

doi:10.1371/journal.pone.0080020

Abstract

Plastic debris has been documented in many marine ecosystems, including remote coastlines, the water column, the deep sea, and subtropical gyres. The North Pacific Subtropical Gyre (NPSG), colloquially called the “Great Pacific Garbage Patch,” has been an area of particular scientific and public concern. However, quantitative assessments of the extent and variability of plastic in the NPSG have been limited. Here, we quantify the distribution, abundance, and size of plastic in a subset of the eastern Pacific (approximately 20–40°N, 120–155°W) over multiple spatial scales. Samples were collected in Summer 2009 using surface and subsurface plankton net tows and quantitative visual observations, and Fall 2010 using surface net tows only. We documented widespread, though spatially variable, plastic pollution in this portion of the NPSG and adjacent waters. The overall median microplastic numerical concentration in Summer 2009 was 0.448 particles m−2 and in Fall 2010 was 0.021 particles m−2, but plastic concentrations were highly variable over the submesoscale (10 s of km). Size-frequency spectra were skewed towards small particles, with the most abundant particles having a cross-sectional area of approximately 0.01 cm2. Most microplastic was found on the sea surface, with the highest densities detected in low-wind conditions. The numerical majority of objects were small particles collected with nets, but the majority of debris surface area was found in large objects assessed visually. Our ability to detect high-plastic areas varied with methodology, as stations with substantial microplastic did not necessarily also contain large visually observable objects. A power analysis of our data suggests that high variability of surface microplastic will make future changes in abundance difficult to detect without substantial sampling effort. Our findings suggest that assessment and monitoring of oceanic plastic debris must account for high spatial variability, particularly in regards to the evaluation of initiatives designed to reduce marine debris.

Highlights

Plastic debris has been documented in a wide variety of marine ecosystems, including the coastlines of remote islands, the coastal water column, the deep sea, and subtropical gyres [1,2,3]
3,464 pieces of plastic marine debris were sighted through visual observation, 30,518 microplastic particles were collected by manta tow, and 324 microplastic particles were collected by bongo tow
The size distribution of particles collected by net tow was skewed towards the smaller end of the size spectrum, with the most abundant particles having an area of approximately 0.01 cm2 (Fig. 2)

Summary

Introduction

Plastic debris has been documented in a wide variety of marine ecosystems, including the coastlines of remote islands, the coastal water column, the deep sea, and subtropical gyres [1,2,3]. Environmental impacts of large pieces of debris ranging from centimeters to tens of meters in diameter, termed ‘‘macroplastic,’’ include habitat alteration and damage, entanglement, and ingestion by megafauna such as cetaceans, seabirds, and sea turtles [4,5]. Plastic debris abundance increased between the late 1960s through the 1990s as documented by at-sea surveys [12,13], seabird ingestion studies in the Arctic and Atlantic [14,15], a Continuous Plankton Recorder study in the northeast Atlantic [16], and coastal deposition on remote islands [17]. Since the 1990s, there is some question as to whether plastic density has continued to increase, since high spatial and temporal heterogeneity make shorter-term trends difficult to discern [18]

Methods

Results

Conclusion