Increased oceanic microplastic debris enhances oviposition in an endemic pelagic insect

Abstract

Plastic pollution in the form of small particles (diameter less than 5 mm)--termed 'microplastic'--has been observed in many parts of the world ocean. They are known to interact with biota on the individual level, e.g. through ingestion, but their population-level impacts are largely unknown. One potential mechanism for microplastic-induced alteration of pelagic ecosystems is through the introduction of hard-substrate habitat to ecosystems where it is naturally rare. Here, we show that microplastic concentrations in the North Pacific Subtropical Gyre (NPSG) have increased by two orders of magnitude in the past four decades, and that this increase has released the pelagic insect Halobates sericeus from substrate limitation for oviposition. High concentrations of microplastic in the NPSG resulted in a positive correlation between H. sericeus and microplastic, and an overall increase in H. sericeus egg densities. Predation on H. sericeus eggs and recent hatchlings may facilitate the transfer of energy between pelagic- and substrate-associated assemblages. The dynamics of hard-substrate-associated organisms may be important to understanding the ecological impacts of oceanic microplastic pollution.

Figure 1.

Microplastic concentrations in 1972–1987 and 1999–2010. Numerical concentration (no. m⁻³) for (a) 1972–1987 and (b) 1999–2010; microplastic mass concentration (mg m⁻³) for (c) 1972–1987 and (d) 1999–2010. New data from this study include 7205 (asterisks), 7210 (inverted triangles), Southtow 13 (cross symbols), STAR (right-facing triangles), SEAPLEX (triangles) and EX1006 (diamonds). Published data are Wong et al. [7] (crossed circles), Shaw [8] (stars), Day & Shaw [9] (left-facing triangles), Gilfillan et al. [10] (filled circles) and Doyle et al. [11] (filled circles). Gilfillan et al. [10] and Doyle et al. [11] have overlapping stations. Non-peer-reviewed publicly available data from Algalita Marine Research Foundation [19] (plus symbols).

Figure 2.

Halobates sericeus adult and juvenile numerical concentration (NC) versus microplastic NC in 1972–1973 (a: Spearman rank correlation, p = 0.3644; r² = 0.019) and 2009–2010 (b: Spearman rank correlation, p < 0.0001; r² = 0.404); H. sericeus egg NC versus microplastic NC in 1972–1973 (c: Spearman rank correlation p = 0.0614; r² = 0.079) and 2009–2010 (d: Spearman rank correlation, p < 0.0001; r² = 0.512). Also shown are size–frequency histograms for all microplastic particle areas (grey) and particles with attached eggs (black) in (e) 1972–1973 and (f) 2009–2010. Symbols (a–d) represent dates of data collection: spring 1972 (grey diamonds), autumn 1972 (filled diamonds), winter 1973 (open diamonds), summer 2009 (filled circles) and autumn 2010 (open circles). Only particles in the size range used by H. sericeus were used to calculate microplastic NC (a–d). Eggs in the samples for (e) were dislodged from their original substrate (63%) are excluded from this figure.