Spectacular bluffs and steep hillsides provide a dramatic backdrop to Horoirangi Marine Reserve, which is north of Nelson city along the eastern side of Tasman Bay. The 904ha reserve extends from Glenduan to Ataata Point and offshore for one nautical mile.The bluffs that overlook the reserve are not just a spectacular landscape, they also act as the rock source for the distinctive inter-tidal and sub-tidal boulder reefs found within the reserve. These reefs are the beginning of the Nelson Boulder Bank, a geologically unique landform.Overall, the reserve straddles a transition from bedrock reefs at Ataata Point to boulder bank habitats at Glenduan - a transition zone which is not found elsewhere in Tasman Bay. While the upper intertidal boulders are too mobile to provide a reliable habitat for sea creatures, the stable boulder or bedrock habitats lower down support an array of reef dwelling species - molluscs, crustaceans, starfishes, urchins, sponges, ascidians, seaweeds and fishes. Ambush starfish are particularly numerous. The offshore sediments, like much of Tasman Bay, are dominated by assorted deposit and suspension feeding invertebrates such as urchins, brittle-stars and bivalves.The southern end of the marine reserve at Glenduan (known locally as ‘The Glen’) is only a short drive from Nelson. The reserve is accessible by foot from here, but keep an eye on the tide and take care walking over the boulders. At low tide the boulder reef is a fun place to explore and study.A slightly longer drive away is Cable Bay, which provides kayak and boat access to the northern end of the marine reserve. Some of the best diving and snorkelling is found towards the north of the reserve, especially near Ataata Point. Look for crayfish lurking in overhangs and crevices, and some of the more common reef fish – wrasses, triplefins, goatfish, blue cod, blue moki, tarakihi and the occasional snapper. Sponges, some quite large, are a notable reef feature.