Spatio-temporal variation of anthropogenic marine debris on Chilean beaches

Highlights

• Anthropogenic marine debris (AMD) is found on all Chilean beaches but no temporal tendency of AMD densities was observed.

• Plastics and cigarette butts presented the highest percentages of AMD in all three surveys, attributed to local sources.

• The Antofagasta Region in northern Chile had highest AMD densities.

• Most AMD was found at the upper stations of beaches in most of the country.

• We suggest that socio-economic development alone cannot explain temporal trends in AMD densities.

Abstract

We examined the hypothesis that in an emerging economy such as Chile the abundances of Anthropogenic Marine Debris (AMD) on beaches are increasing over time. The citizen science program Científicos de la Basura (“Litter Scientists”) conducted three national surveys (2008, 2012 and 2016) to determine AMD composition, abundance, spatial patterns and temporal trends. AMD was found on all beaches along the entire Chilean coast. Highest percentages of AMD in all surveys were plastics and cigarette butts, which can be attributed to local sources (i.e. beach users). The Antofagasta region in northern Chile had the highest abundance of AMD compared with all other zones. Higher abundances of AMD were found at the upper stations from almost all zones. No significant tendency of increasing or decreasing AMD densities was observed during the 8 years covered by our study, which suggests that economic development alone cannot explain temporal trends in AMD densities.

Introduction

Anthropogenic marine debris (AMD), mostly composed of plastics, has been characterized as a global and persistent environmental problem that has considerably increased over the last decades (Galgani et al., 2015). The accumulation of AMD has multiple impacts that can be categorized into three types: biological, ecosystemical, and socio-economical (Kuo and Huang, 2014). Biologically, marine organisms can be affected by AMD through ingestion and entanglement (Gregory, 2009, Kühn et al., 2015), which can lead to physical and chemical damage and even death (Rochman et al., 2013, Vegter et al., 2014). In terms of ecosystems and biogeography, AMD may serve as dispersal vehicle for invasive species, which can modify local ecosystems (Amaral-Zettler et al., 2015, Kiessling et al., 2015, Thiel and Gutow, 2005). With respect to socio-economic factors, since coastal AMD is aesthetically detrimental, it can affect the perception of beach-users and eventually coastal tourism, requiring high beach cleaning costs and causing losses in revenue (Jang et al., 2014, Newman et al., 2015, Santos et al., 2005).

Marine debris can be classified according to two main source categories: ocean- and land-based debris, depending on where AMD entered the marine environment (Galgani et al., 2015). Ocean-based AMD sources include waste from shipping, fishing, oil platforms, and aquaculture (Astudillo et al., 2009, Edyvane et al., 2004, Hinojosa and Thiel, 2009, Hong et al., 2014, Sheavly and Register, 2007, Watters et al., 2010). Land-based AMD might enter the marine environment by rivers, outflow from industries, harbors, unmanaged landfills, sewage waters, extreme events (tsunamis, hurricanes), or through direct littering by beach visitors (Aguilera et al., 2016, Goto and Shibata, 2015, Green et al., 2015, Khordagui and Abu-Hilal, 1994, Rech et al., 2014). It has been estimated that > 8.4 million tons of plastic waste enter the oceans annually from land-based sources (Jambeck et al., 2015).

A major part of AMD studies have been conducted in coastal areas, because of their proximity to sources, facility of access, and due to potential aesthetic impacts (Galgani et al., 2015). These studies provide insights about dominant types of AMD, their abundance, potential origins and accumulation rates. Nevertheless, these characteristics might be highly variable, e.g. due to the influence of urban cities, coastal use, river flushing, and the geomorphology, hydrodynamics and oceanography of each coastal area (Galgani et al., 2015, Moriarty et al., 2016). Consequently, studies with standardized methods that extend over a certain region and time are needed to evaluate the spatio-temporal variability of AMD abundances and composition (Browne et al., 2015, Hong et al., 2014, Moreira et al., 2015, Thornton and Jackson, 1998).

Temporal changes of AMD have been studied over different spatial scales, but most of them have been done on a small scale, such as single beaches, bays or islands (e.g. Agustin et al., 2015, Tourinho and Fillmann, 2011), or during shorter periods of time (e.g. Madzena and Lasiak, 1997, Storrier et al., 2007). Only few studies extend over a large temporal and spatial scale (for examples see Gago et al., 2014, Nelms et al., 2016, Ribic et al., 2010, Ribic et al., 2011, Schulz et al., 2015a, Schulz et al., 2015b). The generated results are contrasting: in some cases trends of AMD densities can be identified, either increasing in Indonesia (Willoughby et al., 1997), decreasing in Australia (Edyvane et al., 2004), or being consistent over time in Canada and Scotland (Lucas, 1992, Storrier et al., 2007). But in other cases, the results are highly variable and no temporal tendencies are observed (Cheung et al., 2016, Eriksson et al., 2013, Nelms et al., 2016). Consequently, no consistent global long-term trend has been identified for AMD densities on beaches (Browne et al., 2015).

Changes of AMD abundance over time might be related to the socio-economic and educational conditions of a country; pro-environmental behavior (e.g. adequate waste disposal) is generally higher in developed countries (Morren and Grinstein, 2016). Developed economies might have educational programs to increase environmental awareness in the population, such as environmental campaigns, frequent clean-up campaigns (e.g. NOAA, Ocean Conservancy), and well-established recycling infrastructure (Borja et al., 2011, Veiga et al., 2016). On the other hand, developing countries might focus on economic growth, often at the expense of environmental care. Environmental degradation might increase as the economy grows, up to a point where economic development leads to higher environmental awareness, and amounts of AMD are likely to be lower on beaches of developed countries, with a tendency to decrease over time. For an emerging economy such as Chile we should thus expect that the amounts of AMD of beaches are high, with a tendency to increase over time.

The Chilean citizen science program Científicos de la Basura (“litter scientists”) has been studying the problem of AMD in the SE Pacific for approximately 10 years, conducting the first national survey of AMD on beaches in 2008 (for further details of the program, see Eastman et al., 2014). The mean density of AMD was by that time 1.8 items m^− 2 (which included wood and “others”) and the most common AMD types were plastics, cigarette butts and glass (Bravo et al., 2009). Nevertheless, these results represented only a first snapshot of the general situation, and there was no information on the spatio-temporal dynamics of beach litter in the SE Pacific. Therefore, the national AMD survey was repeated during the years 2008, 2012 and 2016 along the entire Chilean coast, in order to (1) determine composition, (2) estimate abundance and spatial patterns, and (3) explore temporal trends of AMD densities on beaches from the SE Pacific.