Francesca M.C. Fazey, Peter G. Ryan, Biofouling on buoyant marine
plastics: An experimental study into the effect of size on surface
longevity, Environmental Pollution, Volume 210, March 2016, Pages
354-360, ISSN 0269-7491, http://dx.doi.org/10.1016/j.envpol.2016.01.026.
(http://www.sciencedirect.com/science/article/pii/S0269749116300264)
Abstract: Recent estimates suggest that roughly 100 times more plastic
litter enters the sea than is found floating at the sea surface, despite
the buoyancy and durability of many plastic polymers. Biofouling by
marine biota is one possible mechanism responsible for this discrepancy.
Microplastics (<5 mm in diameter) are more scarce than larger size
classes, which makes sense because fouling is a function of surface area
whereas buoyancy is a function of volume; the smaller an object, the
greater its relative surface area. We tested whether plastic items with
high surface area to volume ratios sank more rapidly by submerging 15
different sizes of polyethylene samples in False Bay, South Africa, for
12 weeks to determine the time required for samples to sink. All samples
became sufficiently fouled to sink within the study period, but small
samples lost buoyancy much faster than larger ones. There was a direct
relationship between sample volume (buoyancy) and the time to attain a
50% probability of sinking, which ranged from 17 to 66 days of exposure.
Our results provide the first estimates of the longevity of different
sizes of plastic debris at the ocean surface. Further research is
required to determine how fouling rates differ on free floating debris
in different regions and in different types of marine environments. Such
estimates could be used to improve model predictions of the distribution
and abundance of floating plastic debris globally.
Keywords: Marine plastic debris; Buoyancy; Biofouling; Fragment size;
Microplastics