Microplastics detected in every sponge sample from three Wellington bays

By Krystal Gibbens for RNZ

Researchers collecting sponges on the Wellington coastline have found microplastics in every sample, and it could have implications for our seafood.

Victoria University of Wellington researchers collected 45 sponges of six different species, from Evans Bay, Shark Bay and Māhanga Bay.

The sponges in Evans Bay had the highest concentrations of microplastics, which the researchers said was likely due to its proximity to high-density urban areas.

Marine Biology professor James Bell said the variation in the levels of particles found “probably reflects differences in the kind of water flow patterns” in the harbour.

There are 10 stormwater pipe outlets within 1km of the site, compared with one and two outlets at Shark and Māhanga Bay respectively.

Given that an estimated 80 per cent of plastics in the marine environment come from land-based sources, the study suggested that microplastic abundance in sponges was mainly explained by the amount of microplastics in the environment, rather than species identity.

Bell said sponges were “filter feeders”. When they were filtering out tiny particles from the water, they were likely capturing microplastic particles at the same time.

Bell said their results suggested that other filter feeders in the harbour such as mussels and clams, which people ate, were “quite likely to have microplastic particles in them too”.

The study which was conducted as part of a masters student degree programme was one of the first studies in New Zealand exclusively studying microplastics in sponges.

Bell noted that the masters student, Rachel Parry, found more microplastics than they were initially expecting.

He said in the future they would be interested to research what impact microplastics had on the sponges.