The density of the plastic particles will determine bioavailability
in the water column; hence the type of plastic ingestedmay vary between organisms. Planktivores, filter feeders and
suspension feeders inhabiting the upper water column are likely
to encounter positively buoyant, low-density plastics, such as PE
(specific gravity 0.91e0.94), on the sea surface (see Fig. 1). The
buoyancy of plastic is influenced by biofouling, for example, PE
food bags (20 28 cm) displayed a well-developed biofilm
within one week, which continued to increase throughout a
three week exposure period. By the third week, the PE food bags
had started to sink below the sea surface, indicating neutral
buoyancy (Lobelle and Cunliffe, 2011). The rate of biofouling
depends on parameters such as surface energy and hardness of
the polymer, as well as water conditions (Muthukumar et al.,
2011). De-fouling in the water column by foraging organisms
is a potential pathway for microplastic particles to return to the
seaeair interface (Andrady, 2011). This cyclic pattern may make
microplastics available to organisms occupying different depths
of the water column at different times (see Fig. 1). Alternatively,
fouled microplastics could continue to sink, as would highdensity
plastics such as PVC (specific gravity 1.38). Such particles
will become available to benthic suspension and deposit
feeders and detritivores as they sink, eventually reaching the
benthos (see Fig. 1).