Category New Zealand – sub-tropical

The horse or fan mussel (Atrina zelandica) is an endemic, filter-feeding bivalve mollusc that is particularly conspicuous because of its size and abundance. It often lives in groups that occupy 10 sq m or more, mainly on muddy-sand substrates of sheltered waters. It is widespread in the lowest intertidal and subtidal waters, including estuaries and harbours, but is also found in deeper waters of up to 50 metres off open coasts.

This filter-feeding bivalve produces waste biodeposits that are rich in organic matter and support animal aggregations that are distinctly different from, and more diverse than, those further away. Horse mussels therefore play an important role in enhancing habitat food supply and fuelling metabolism.

The horse mussel further enhances biodiversity on soft se...

Pagrus auratus

Strictly, or scientifically speaking, the New Zealand snapper (Pagus auratus) is not actually a “snapper” at all!

The snappers are a large and diverse group of robust-bodied, carnivorous fishes and belong to the family Lutjanidae. Like many other southern hemisphere species, the New Zealand snapper inherited its name from the northern species it most closely resembles, but is in fact a member of the family Sparidae, which are sea bream or porgies.

In New Zealand waters, this indicator can be found from the tip of the North Island down to the northern areas of the South Island. They are mostly encountered in deep water over offshore reefs and gravel beds, around islands and near undersea pinnacles.

The snapper is also known by the Maori name, ‘tamure’ and is a very ...

When people talk about coral reefs, fishermen tend to shrug their shoulders and complain about snagged lines and torn nets. But when you talk about groupers, they suddenly sit up and pay attention. Groupers are among the economically most important fishes of the coral reef, because of their popularity as food. Yet without the coral reef there would probably be no groupers. For this reason, groupers are an extremely important indicator species and your record of their existence or non-existence during your dive tells us a lot.

The giant grouper (Epinephelus lanceolatus) is one of the largest reef-dwelling fish. It may grow to more than 270 cm and reach weights of 300 kg...

Lobsters, like shrimps and crabs, are decapods – literally meaning 10 legs – and can be found in all of the world’s tropical and sub-tropical seas as well as more temperate waters. They are predatory, nocturnal animals with a vividly decorated coat. They are often numerous locally; they linger in crevices (with their long antennae sticking out) during the day and hunt small benthic organisms at night, but they also feed on organic detritus whenever they happen across it. As with all crustaceans, the lobster moults or sheds its shell to grow.

Lobsters have recently suffered a dramatic demographic decline; intensive fishing has annihilated entire populations, especially where tourism abounds.

The lobster families that you may encounter are the spiny rock lobsters, Palinurida...

The marine habitats in which marine communities live are many and varied and are created, or caused, by a number of physical factors. These factors combine to determine which animal and plant communities can co-exist within a particular habitat, with the interplay of the communities themselves playing a large determining factor.

The physical factors include elements such as temperature, depth, tides and currents, relative salinity, wave action, light or shade, sea-bottom substrate, aspect and inclination. Extreme physical factors, such as a rise in sea temperature can have a significant and sudden impact on habitats, such as the El Nino effect on the coral reefs in the Maldives, where a small rise in sea temperature caused widespread coral bleaching.

In addition to the physical fact...