Recolonization by algae of the sublittoral habitat of Halifax County, Nova Scotia, following the demise of sea urchins

Since the first sublittoral survey off Lawrencetown, Nova Scotia in 1965--66 there has been a cycle of dominance by herbivorous sea urchins followed by mortality of these animals because of disease in 1981 and regrowth of algae. A survey of the same site in 1984 revealed that the algal communities previously recorded have returned in shallow water, with the same species attaining physical dominance (Laminaria and/or Desmarestia ). In deep water, however, certain species which used to be dominant have not returned. Their place has been taken by algae which are either resistant to herbivory or, because of their ephemeral nature, are able to occupy a wider variety of refugia.