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Marine-based activities that put pressure on coastal marine habitats

Some of the marine-based activities that put pressure on our coastal marine habitats include:

  • competition from invasive species (marine pests) accidentally introduced from boats and ships
  • dredging to clear shipping and access channels and dumping of dredge spoils
  • plastic and oil-based pollution
  • accumulation of shells, feed, and faeces on the seabed from aquaculture
  • anchoring of ships and boats, particularly on reef habitats (MacDiarmid et al, 2012a).

In this section we report on pressures from non-indigenous species, which can become marine pests. Commercial and recreational fishing are also important pressures in coastal waters, and are discussed in Our fisheries and the impact of fishing on marine ecosystems.

Non-indigenous species in our marine environment are increasing

Non-indigenous (exotic) species are generally introduced into New Zealand waters attached to boat or ship hulls or in ballast water. Some have little impact or cannot survive in New Zealand waters; others can become pests.

Marine pests compete with, and prey on, indigenous species, modify natural habitats, affect marine industries, and alter ecosystem processes. They are largely a threat to coastal marine habitats rather than the deeper ocean (MacDiarmid et al, 2012a). Their impact on native species and habitats means they pose a risk to our natural and cultural heritage and to commercial and recreational fishing, shellfish harvesting, and aquaculture.

In 2015, 351 non-indigenous species were identified in New Zealand’s coastal waters, of which more than half (187) had established a breeding population in our marine environment. Since 2009, the number of non-indigenous species in New Zealand has risen by 10 percent, with 33 new species recorded between 2010 and 2015.

Data on eight species can demonstrate how the threat of marine pests is changing

In the absence of certainty about the future impact of any particular non-indigenous species, we chose eight species to represent the threat of non-indigenous species to our marine environment (see figure 9).

The species occur in a variety of different marine environments, and represent species across a range of scientific classes of organisms, that established at various dates in New Zealand waters (see table 1).

The Australian droplet tunicate (a sea squirt) in Rangaunu Harbour in the far north of the North Island. The tunicate smothers beaches, rocks, and tide pools and is a pest of aquaculture (Photo: Crispin Middleton, NIWA)

Figure 9

Click to enlarge view

Note: Undaria has been found as far south as the subantarctic Snares Islands.

This map illustrates the maximum north-to-south extent and expansion of selected non-indigenous species in New Zealand coastal waters. Visit the MfE data service for the full breakdown of the data.

Table 1

Eight marine species representing the threat of marine pests to our marine environment

Marine species


Impact and history

Asian bag (or date) mussel Arcuaatula senhousia

Small, thin-shelled mussel that lives in estuaries

  • Modifies native habitats
  • Established in Auckland in the 1970s

Asian paddle crab
Charybdis japonica

Large, aggressive swimming crab

  • Predator of native species
  • First recorded in the Auckland region in 2000

Australian droplet tunicate Eudistoma elongatum

Sea squirt that forms long, white cylindrical tubes

  • Smothers beaches, rocks, and tide pools and a pest of aquaculture
  • First reported in Northland in 2005

Greentail (greasy back) prawn Metapenaeus bennettae

Prawn that grows to about 13cm in length

  • Estuarine deposit feeder
  • First recorded in Waitemata harbour in 2009

Mediterranean fanworm Sabella spallanzanii

Very large, fast-growing worm that builds long, flexible tubes up to 1 metre in length

  • Pest of aquaculture and other industries
  • Modifies natural habitats
  • Affects cycling of nutrients within natural ecosystems
  • Establishment date not reported

Clubbed tunicate
Styela clava

Rapid growing sea squirt that forms dense colonies

  • Pest of aquaculture and other industries
  • Establishment date not reported

Fragile clam
Theora lubrica

Small bivalve (shellfish with two hinged shells)

  • An indicator of marine pollution
  • Present since at least the 1970s

Undaria pinnatifida

Fast-growing brown kelp

  • Pest of aquaculture and other industries
  • First reported in New Zealand in 1987

Source: Inglis and Seaward (2016)

There is limited research on the economic and non-market costs of pests in the marine environment. Biosecurity New Zealand’s 2009 study estimated the economic output loss from marine pests at $15 million a year – this did not include ongoing expenditure on restricting pests. Another report estimated the initial one-off costs of responding to incursions of the clubbed tunicate and Mediterranean fanworm to be $2.2 million and $1 million, respectively (Biosecurity NZ, 2010). Non-market costs from pest invasions could include losing shellfish beds for harvesting and children being unable to paddle at the water’s edge (Bell & Yap, 2008; Royal Society of New Zealand, 2014).

For more detail see Environmental indicators Te taiao Aotearoa: Marine non-indigenous species.