Estimates of Marine Debris Accumulation on Beaches Are Strongly Affected by the Temporal Scale of Sampling

Stephen D A Smith,Ana Markic,Brock Fenton

doi:10.1371/journal.pone.0083694

Abstract

Marine debris is a global issue with impacts on marine organisms, ecological processes, aesthetics and economies. Consequently, there is increasing interest in quantifying the scale of the problem. Accumulation rates of debris on beaches have been advocated as a useful proxy for at-sea debris loads. However, here we show that past studies may have vastly underestimated the quantity of available debris because sampling was too infrequent. Our study of debris on a small beach in eastern Australia indicates that estimated daily accumulation rates decrease rapidly with increasing intervals between surveys, and the quantity of available debris is underestimated by 50% after only 3 days and by an order of magnitude after 1 month. As few past studies report sampling frequencies of less than a month, estimates of the scale of the marine debris problem need to be critically re-examined and scaled-up accordingly. These results reinforce similar, recent work advocating daily sampling as a standard approach for accurate quantification of available debris in coastal habitats. We outline an alternative approach whereby site-specific accumulation models are generated to correct bias when daily sampling is impractical.

Highlights

Marine debris is a key threatening process for marine organisms, with reports of fatal interactions becoming all too frequent [1,2,3]
While this study was conducted on a single small beach, the results support those from other studies that have assessed accumulation over a range of temporal scales [10,13,14] - once deposited, debris is rapidly lost from the surface of beaches
Ryan et al [10] reported that daily accumulation rates on beaches in South Africa were 100–600% greater than estimates based on weekly sampling: the modelled value in our study was,360%

Summary

Introduction

Marine debris is a key threatening process for marine organisms, with reports of fatal interactions becoming all too frequent [1,2,3]. Gaining accurate information on how much debris is in the marine environment is a critical step in targeted management, and assessments of accumulation rates on beaches are often used to provide such estimates for coastal environments [10,11,12]. There has been increasing recognition that accumulation studies may underestimate available debris and that the scale of this underestimation is dependent on the interval between accumulation studies [13,14]. In the majority of accumulation and trend assessment studies, sampling was conducted at a minimum frequency of monthly [15,16,17,18]. The highest time-standardised accumulation rates result from daily surveys, but this timeframe is impractical for ongoing monitoring across numerous sites or for protracted periods

Methods

Results

Conclusion