Environmental implications of plastic debris in marine settings--entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien invasions

Abstract

Over the past five or six decades, contamination and pollution of the world's enclosed seas, coastal waters and the wider open oceans by plastics and other synthetic, non-biodegradable materials (generally known as 'marine debris') has been an ever-increasing phenomenon. The sources of these polluting materials are both land- and marine-based, their origins may be local or distant, and the environmental consequences are many and varied. The more widely recognized problems are typically associated with entanglement, ingestion, suffocation and general debilitation, and are often related to stranding events and public perception. Among the less frequently recognized and recorded problems are global hazards to shipping, fisheries and other maritime activities. Today, there are rapidly developing research interests in the biota attracted to freely floating (i.e. pelagic) marine debris, commonly known as 'hangers-on and hitch-hikers' as well as material sinking to the sea floor despite being buoyant. Dispersal of aggressive alien and invasive species by these mechanisms leads one to reflect on the possibilities that ensuing invasions could endanger sensitive, or at-risk coastal environments (both marine and terrestrial) far from their native habitats.

Figure 1.

Debris (mainly plastic) collected during an annual beach clean at Mason Bay, South Island, New Zealand.

Figure 2.

Examples of entanglement from New Zealand that draw immediate public sympathy and anger: (a) Karoro (southern black-backed gull, Larus dominicanus) caught and hooked in nylon filament fishing line; (b) a New Zealand fur seal trapped in discarded netting and (c) Ghost fishing—derelict fishing gear dredged from >100 m on the Otago shelf.

Figure 3.

Examples of ingestion: (a) Laysan Albatross (Phoebastria immutabilis, at Kure Atoll, Courtesy of AMRF); (b) plastic from the stomach of a young Minke whale (Balaenoptera acutorostrata) that had been washed ashore dead in France (Courtesy of G. Mauger & F. Kerleau, Groupe d’Études de Cétacés du Cotentin GECC) and (c) stranded sea turtle disgorging an inflated plastic bag. One infers that it has been mistaken for an edible jellyfish (medusoid).

Figure 4.

Example of colonization and encrustation on plastic debris from the New Zealand coastline: (a) heavy and varied colonization of a plastic slab recovered (note the hard bodied encrustations and soft fleshy epibionts; (b) cuttings from a tangled mass of synthetic rope, carrying a cargo of the warm-water Indo-Pacific oyster, Lopha cristagalli, a species that is alien to New Zealand waters (appendix A(ii)); (c) plastic pellet (raw material for manufacture of plastic products) encrusted by the bryozoan Membranipora taberculata, see appendix A(i); (d) small bryozoan colony (Galeopsis mimicus) attached to a frayed plastic flake (arrowed) recovered from a depth of 393 m off the east coast shelf off the South Island (appendix A(xii)); scale bar 200 µm. Recently a tropical hermatypic coral has also been reported on a remote South Island shoreline (J. Lindqvist, personal communication).

Figure 5.

The Subtropical Convergence and strong easterly flowing Antarctic Circumpolar Polar Current are frontal zones and are ‘leaky barriers’ which some organisms are now traversing.