It is not native. The bumpy, sharp-edged bivalve of the estuary. The Pacific oyster has a rough, grey-white shell with deep jagged edges and a distinctive purple-black muscle scar inside. The two shells are different: one is deeply cupped, the other is flat. They attach themselves to rocks, wharf piles and other hard surfaces using a strong, cement-like glue secreted from their foot. A shellfish that builds its own foundation. Ecosystem engineers of the estuary. A single oyster can filter over 100 litres of water a day, removing algae, sediment and pollutants. A bed of oysters can clean an entire estuary, creating clear, healthy water for other species. They also create habitat, with their rough shells providing shelter for small fish, crabs and other invertebrates. A bivalve that builds a city for others to live in. The oyster of the Kiwi barbecue. Pacific oysters are farmed by the million, sold in sacks and grilled over hot coals until they pop open. They are also eaten raw, fried or baked, with a squeeze of lemon and a sprinkle of salt. The taste of summer. The taste of the coast. To eat a Pacific oyster is to eat the taste of the estuary. A sharp, salty, briny bivalve that cleans the water as it feeds and fills the plate at the same time. The oyster of the barbecue, the bivalve of the summer afternoon, grilled over hot coals and washed down with a cold beer. But the Pacific oyster is not native. It came from Japan, via aquaculture, via accidental introduction. It spread faster than the native oyster could compete. Now it is everywhere. The rocky shores of New Zealand belong, in large part, to an immigrant from the north. The native oyster did not stand a chance. The Pacific oyster did not care. It just filtered and grew and multiplied. And now it is the taste of summer. No one asks where it came from. They just eat it.