Bay of Islands is our rich tapestry

This aerial photograph illustrates the distribution within the Bay of Islands of these, its most widespread ecosystems. (M is for mangroves.) Photo / Land Information New Zealand - Dean Wright

It's Sea Week - here Fish Forever's John Booth takes a look at the Bay of Islands' unique marine ecosystems.

There's an extraordinarily complex assortment of form and colour in the marine life of the Bay of Islands - often classified for convenience into 'ecosystems'.

An ecosystem is a particular combination of interacting living and non-living elements (for example, a seagrass bed on a soft shore). Many of the Bay of Islands' marine ecosystems are representative of those also to be found elsewhere in the country. But others are rare - special to the Bay of Islands.

And in a world desperately seeking to protect at least some of what's left of its natural marine heritage, it's important to have a handle on both the representative and the rare.

Within its two bold capes, the Bay of Islands is home to everything from mangroves to marlin.

Take the eastern part of the Bay of Islands. In this one really-quite-small area you can paddle your waka in a couple of hours (10 minutes in the tinnie) from an estuary bordered by well-over-a-century-old mangrove trees, out onto the grounds of the big mommas.

You glide past shores sheltered from the elements to those which, from time to time, face swells of unlimited fetch, the metres of plantless cliff above the sea demonstrating the point. You traverse estuarine waters containing so little salt that you could drink it - out to ones you'd swear grew crystals. Waters as murky as a mud-wallow to those simply transparent. Dark places, and light. Swirling currents, and then perfect tranquillity. Rocky reef to mudflat - and everything between.

And that's before you even take the plunge.

The snorkeller glides over great areas of 'biogenic' seafloor composed almost entirely of the hard parts of animals that used to live on the seafloor and in the water column above, and after-lunch lolls in a mangrove channel to listen to its snapping shrimps and watch an eagle ray fly by.

With scuba gear and torch, the filter-feeding animals on the walls and dark recesses of giant caves on exposed cliffs come into view.

There is much more diversity - both in hue and structure - among the fish in these deeper, more open-water reefs than back up the estuaries.

And below 30 metres, seafloors vary from those soft and muddy to ones comprised of shingle, cobble or reef. There are few seaweed here, the living world being dominated by fish and by filter- and deposit-feeder invertebrates.

Arras - a rich tapestry indeed.