Kelp forests

Kelp forests are highly productive areas in the subtidal zone. As with the intertidal zone, the subtidal zone of the Auckland Islands is missing many species found around mainland New Zealand. In particular, there are very few species of large brown algae, resulting in a sparse understorey beneath the giant kelp in deeper, sheltered areas of the islands. At the Auckland Islands, the kelp is grazed by a small endemic pāua – the Subantarctic or virgin white-foot pāua.

Why do you think the subtidal zone of the Auckland Islands is missing many kelp species found on mainland New Zealand?