Introduction

When most people mention reefs, they usually mean coral reefs, without realising that reefs can be extensive in cooler (temperate) waters. The temperate zone is generally defined as lying between the latitudes 23º 27' and 66º 33' north or south. There are fundamental differences in the structure and dynamics of tropical and temperate reefs.

Temperate reefs consist of a rocky substrate, which is colonised by a range of algae and attached invertebrates. Coral reefs are built up by small animals that secrete a calcium carbonate skeleton (corals). Temperate waters are cooler and nutrient levels tend to be higher compared to reefs in tropical waters.

In contrast to the domination by corals on tropical reefs, the dominant biota on temperate reefs are generally macroalgae where there is enough light. In temperate systems, the majority of carbon fixed is via these large algae. In tropical systems, the majority of carbon fixed is by the symbiotic relationship of microscopic algae living in the tissue of sponges and corals. Contrary to common belief, corals are common in temperate waters, but they do not build reefs here.

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