THE ROLE OF SEABIRDS AND SEALS IN THE SURVIVAL OF COASTAL PLANTS - LESSONS FROM NEW-ZEALAND LEPIDIUM (BRASSICACEAE)

Six of the eight indigenous New Zealand Lepidium species are coastal, and have restricted or reduced distributions. One is extinct and the r emainder are considered threatened with extinction. This limited distr ibution is in marked contrast to their apparent abundance in the eight eenth and early nineteenth centuries (1760s-1830s). Accounts from the voyages of Cook, Surville and d'Urville describe L, oleraceunz as an a bundant coastal plant which was collected extensively for use as an an tiscorbutic. However, by the late 19th century, resident botanists wer e expressing concern about the marked decline in coastal species of Le pidium, a decline which has continued to the present. Ecologically, co astal species of Lepidium are similar, being restricted to open sites often close to the high tide mark. They are commonly associated with b ird colonies, and occasionally with fur seal colonies. Traditionally t heir decline has been attributed to introduced herbivores. However, wi ld grazing animals were not common until the end of the 19th century, well after the initial decline had occurred. Other possible reasons fo r their decline include herbivory and predation by rats, and by fungal and invertebrate pests of cultivated Brassicaceae, overcollecting and coastal development. However, we suggest that a major factor in the d ecline of coastal Lepidium species was a decline in coastal seabirds t hrough predation and seals through culling. Seabirds and seals are cri tical for the survival of Lepidium species by keeping sites open throu gh disturbance, dispersing seed, and providing nutrient enrichment for plant growth, and their loss has resulted in decline of habitat for L epidium.