Science Centres: Aquatic Biodiversity and Biosecurity

A horse mussel bed.

Many of New Zealand’s estuaries and shallow coastal waters are experiencing increased sediment loads because of coastal development. Recent NIWA research has investigated the effects of suspended sediment concentrations on species that live on the seafloor.

In many systems there are key species which influence the abundance and diversity of organisms around them through their effects on food, nutrients, movement, and the provision of habitats. NIWA research has shown that the horse mussel (Atrina zelandica) is a key species in Kawau Bay, north of Auckland.

Our research compared the effects of horse mussels on the abundance and diversity of seafloor species at three sites with different levels of suspended sediment. We found that, in clear waters, the abundance and diversity of small sediment-dwelling animals and nutrient production from the sediment was higher in the vicinity of horse mussels. In murky waters, the opposite was true, both for small animals and algae.

How does this come about? ‘In clear waters, horse mussels provide a source of organic and nutrient enrichment that is used and enhanced by small animals, but in murky waters, their contributions make less difference. Plus, the rain of mucus bundles the mussels produce in high sediment concentrations may disturb other organisms’, explains marine ecologist Dr Judi Hewitt, who led the research.