Marine Debris Time and Space Variability in a Remote Island: Faial (Azores, NE Atlantic)
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1
University of the Azores, Department of Oceanography and Fisheries, Portugal
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2
University of the Azores, Department of Biology, Portugal
It is increasingly accepted that marine pollution is a growing problem in the Oceans. Early reports in the 70´s already expressed this environmental concern (Carpenter and Smith, 1972). Deliberately or accidentally discarded waste items (i.e. marine debris) are mainly composed by plastics (60-80%; Derraik, 2002), a reflection of their widespread utilization, production and waste mismanagement (275 million metric tons of plastic waste were generated in 192 coastal countries in 2010; Jambeck et al., 2015). Moreover, the characteristics of the material itself (e.g. lightweight, resistant), provide ideal conditions to be carried or transported (through storm drains, rivers and other water waterways, etc.) until previously non-impacted places (Browne et al., 2015) (e.g. remote islands). Hence, it is estimated that more than 5 trillion pieces of plastic are presently floating in the Ocean surface (Eriksen et al., 2014).
The abundance, composition and potential sources of stranded marine debris were investigated on Faial Island (Azores Archipelago), for the second consecutive year. During a six-month period (December 2013 to May 2014), two sandy beach sites (Conceição (38°32’35’’N, 28°37’08’’W),) – PC and Porto Pim (38°31’29’’N, 28°37’32’’W) - PP) were monitored based on the proposed methodology of Opfer et al. (2012). In order to study the standing-stock (i.e. the amount of accumulated anthropogenic debris on the beach) (Moreira et al., 2016), 10 random transects (10m wide each) were monitored during low tidal phases at each study area (100m length; parallel to the water), during a period of six days per month. All target-sized items (2-30 cm) were visually sorted while reading transects (limited by the back of the shoreline towards the water’s edge), recorded and organized into main categories (plastics, cloths/fabric, glass, metal, rubber, processed lumber, others and large). This sampling season (B) followed the same guidelines as the ones performed in the first research year (A) (November 2012 until May 2013; Pieper et al., 2015), to allow comparison of results. Marine debris density was calculated per transect using the formula D = n/W*l, where D = density of debris items (number of debris items m-2); n = number of target-sized debris observed; w = width (m) of shoreline section recorded during sampling, and l = length (m) of shoreline sampled.
A total of 16,259 pieces were counted throughout the sampling months (12,812 items at PP; 3447 items at PC), and all main debris categories were detected at both sites. Densities varied between 0 to 2,746 items m-2, differing from one location to another: PP = 0,722±0,054; PC = 0,239±0,037 (M±SE), as well as the month were concentration of items was more evident (March revealed highest densities at PP: 1,009±0,216; December had highest densities at PC: 0.563±0.144). Category plastics formed the majority of all debris recorded on both beaches (12,812 pieces in total) during the survey period (95% at PP and 90% at PC), followed by category glass (556 pieces in total), that represented 4% at PP and 7% at PC.
The weighted arithmetic means of the total abundances were calculated for all main categories in order to verify how some of the data points contributed more than others to the variables Time (years A and B) and Space (Porto Pim and Conceição) for the stranded marine debris. That way, three ratios were assessed: Time Ratio (analysis of the contribution of each debris category from the same site between the different two years); Space Ratio (analysis of the contribution of each debris category between different sites within the same year); and Space/Time Ratio (overall analysis of Space and Time ratios to evaluate which of these two influenced the most the abundance of debris).
The results show that both years (A and B) exhibit similar tendencies in terms of general debris abundances. The computed ratios also show that plastics are more abundant in Porto Pim than in Conceição beach, and that Space (i.e. the sampling site) tends to have a stronger influence than Time (i.e. the sampling year), when concerning washed ashore plastic debris during the monitoring program. Nevertheless, when we consider the way in which debris tend to accumulate within the same sampling year and between different sampling years, some dissimilarities start being noted. The Time Ratio results enhance the fact that there was a decrease on abundances of plastics from year B to year A; plus, abundances of debris did not reach the highest measurements in the equal months (year A: February for PP and January for PC; year B: March for PP and December for PC).
Fluctuations of marine debris depositions tend to respond to several factors that are not easy to recognize upfront (Browne et al., 2015). Such examples are the relationship between wind and tide forcing-inflow processes (e.g. resuspension or burial of pieces), which act in combination with the study area, and the time of year/day (e.g. tidal type, tidal stage, height oscillations, changes in wave action and wind forces) (Moreira et al., 2016), changing in a consistently way the standing-stock of beached debris items. Moreover, there are many extrinsic factors that are difficult to account in a numerical form which can lead to misinterpretation of obtained results (e.g. sporadic clean-up actions performed by citizen to reach environmental awareness; or cleaning of beach by municipal employees, after storm events).
These outputs bring up the hypothesis that intra-annual variability could differ from inter-annual variability of washed ashore waste. In order to ascertain this assumption, and to measure the impact of marine pollution on remote oceanic islands (e.g. Faial Island), long-term monitoring is needed, so potential debris trends can be understood. Taking this into consideration, a third year of sampling is currently being conducted, allowing improved data robustness, while shedding better light about possible (internal and external) influencing factors that can contribute to the presence of anthropogenic items in the remotest archipelago of the Northeast Atlantic Ocean: The Azores.
Acknowledgements
This research was supported by through a ESTAGIAR-L Program (Grant No. PL 132721). We thank Clara Loureiro (CIBIO-InBio DOP/UAç) and João Reis for helping during the beach surveys conducted in this study. Computer logistics and facilities were provided by Department of Oceanography and Fisheries at the University of the Azores.
References
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Keywords:
marine pollution,
Plastics,
beach,
Remote island,
Azores archipelago
Conference:
IMMR | International Meeting on Marine Research 2016, Peniche, Portugal, 14 Jul - 15 Jul, 2016.
Presentation Type:
Poster presentation
Topic:
Biodiversity, Conservation and Coastal Management
Citation:
Pieper
C,
Ventura
MA,
Cunha
RT and
Martins
A
(2016). Marine Debris Time and Space Variability in a Remote Island: Faial (Azores, NE Atlantic).
Front. Mar. Sci.
Conference Abstract:
IMMR | International Meeting on Marine Research 2016.
doi: 10.3389/conf.FMARS.2016.04.00077
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Received:
30 Apr 2016;
Published Online:
13 Jul 2016.
*
Correspondence:
Ms. Catharina Pieper, University of the Azores, Department of Oceanography and Fisheries, Horta, 9901-862, Portugal, catharina.pieper@gmail.com