Over the years, kelp bed canopies have varied considerably in size and extent. The reasons for fluctuations in both the size of kelp bed canopies and the health of the plants have been studied and debated for decades. Over-harvesting, waste discharge, storms, oil spills, turbidity and warm water are all thought to have contributed to the loss of kelp beds. To date, no single cause has been identified, and the luxuriant regrowth of kelp in areas from which it had disappeared seems to reassure scientists that declines are reversible.
However, it does seem that availability of adequate nutrients is a major influence on the health and survival of kelp. Large, destructive storms have also caused damage to these plants, as in 1983 and 1988 when storms destroyed much of the kelp canopy.