Nurdle drifters around South Africa as indicators of ocean structures and dispersion

Abstract

Dispersion processes in the ocean typically involve wind, ocean currents and waves. All these factors were included in an analysis to model nurdle dispersion from an accidental spill in Durban Harbour, South Africa, in October 2017. Nurdle sightings on beaches by members of the public are used as indicators of the dispersion which extended over 2000 km of the South African coastline in a period of 8 weeks. Using known oceanographic current structures, satellite imagery, wave data and surface wind drift values of between 5% and 8% of wind speed, good agreement was found between the modelled dispersion and nurdle sightings. In particular, it was found that nurdles remained in specific sections of the coast for long periods, and that sporadic wind events were required to move them into new coastal areas. Such results may also contribute to understanding the dispersal behaviours and strategies adopted by larval stages of marine organisms, particularly fishes, that have pelagic larval durations that extend over weeks to months. The event was recognised as a major pollution incident rivalling other nurdle spillages reported worldwide, and extensive efforts were made to collect the nurdles, particularly along the northern KwaZulu-Natal coast. However, 9 months later, less than 20% had been recovered. The results emphasise the connectivity of different ocean regions, and in particular that pollution of the ocean is not a localised activity. Matter discharged at one point will disperse over a wide area -in this case, significantly further afield than the area of recovery operations. Significance:•Wind drift in the upper metre or two of the ocean has been notoriously difficult to quantify, and the spread of nurdles along the South African coastline can only be explained by using drift percentages two or three times the generally accepted value of 3% or less. Nonetheless, it is important to realise that there are substantial differences in dispersion rates between the upper few centimetres of the ocean and that even a metre or two deeper. •The rapid manner in which nurdles, and other microplastics, can be dispersed is important in terms of understanding the spread of this form of pollution in the world's oceans. The results also confirm the important role that wind can play in the movement of eggs, larvae and invertebrates and the significance of vertical migrations in and out of the surface layers.• Finally, the results confirm many of the accepted coastal current regimes on the east and south coasts of South Africa. Moreover, it is shown that certain sections can have very long residence times, where drifters are only removed under sustained wind conditions.

Dispersal and coastal geomorphology limit potential for mangrove range expansion under climate change

“…Propagule dispersal in south‐east Africa occurs predominantly in a south‐westward direction, which reflects the primary flow direction of the Agulhas Current, while the few northward tracks represent the prevailing direction of longshore drift (Lutjeharms, 2007). Similar dispersal patterns have been observed for drifting plastic nurdles (Schumann et al, 2019) and plastic drift cards that were used in a field study to estimate dispersal and transport rates for A. marina propagules along the South African coastline (Steinke & Ward, 2003). Overall, there is high potential for along‐shore connectivity between estuarine mangroves in the region, as shown by the particle concentration map and the report of drift cards being transported rapidly southwards (~600 km in 3 weeks).…”

Plastics in the Indian Ocean – sources, transport, distribution, and impacts

“…For comparison, the potential discharge of 78 t of nurdles released by the X-Press Pearl is the second-worst release of nurdles from shipping accidents. This includes the 150 t released into Hong Kong harbour in 2012 during a typhoon, and 49 t released into Durban harbour in South Africa in 2017 (Schumann et al, 2019). On 25 May, large quantities of nurdles were washed up on the beaches closest to where the X-Press Pearl was anchored (Fig.…”

The M/V X-Press Pearl Nurdle Spill: Contamination of Burnt Plastic and Unburnt Nurdles along Sri Lanka’s Beaches

“…The fire changed the nurdles, leading to a wide range of appearances that complicated already challenging cleanup efforts, monitoring, and damage assessment for nurdle spills. ,,, On the beach, unburnt nurdles have been reported to be easy to identify; though, unburnt nurdles may blend in with shells and sand (Figure S4). Similarly, the burnt plastic may camouflage among natural materials (Figure ).…”