The origins of the coastal and marine flora and fauna of the Azores

Abstract

The Azores Archipelago is geologically young, and the nine islands are from 8 million (Santa Maria) yr old. Evidence of endemism among the Azorean marine and maritime biota is sparse and clearly apparent only with regard to the supralittoral, maritime, vegetation Probably no alga nor marine animal is endemic, although a few species in several phyla are currently recognised as having this status. The marine fauna shows little evidence of colonisation by species with an eastern Pacific origin following the closure of the Isthmus of Panama and the opening of the Bering Strait in the Late Pliocene. The majority of the Azorean coastal and marine biota is very modem and comprises species that have arrived predominantly from the eastern Atlantic, especially the area between southern Europe (Lusitanian Region) and northwest Africa (Mauretanian Region), including the Mediterranean, but also contains species from other Atlantic sources. Regardless of their geographic origin, most representatives of the coastal Azorean marine biota are chance survivors of recent chance immigrants probably delivered to these shores in a variety of ways. It is likely, however, that the majority, but unknown percentage, of species were delivered by currents. Species with teleplanic larvae, for example, are present from both the western and eastern Atlantic. It is also likely that some, especially representatives of the Hydroida and species exhibiting direct development, were delivered by rafting and there are some examples of possible delivery by migratory birds (phoresy) which may also be more significant with regard to inter-island transport and especially between wetland feeding and roosting sites. The majority of terrestrial plants, all mammals, reptiles, amphibians and freshwater fishes (except Anguilla anguilla) of the Azores were introduced by man. Some marine colonisers have received human assistance, particularly the maritime vegetation and other well known exotics but in the latter case, unlike elsewhere, their impacts appear minimal. Following a brief introduction to the Azores, the geology of the islands and the ocean currents by which they are influenced, the marine, especially intertidal, flora and fauna are discussed in terms of their origins and possible means of arrival. The algae are represented by >300 species, the fauna by some 2100. The depauperate marine biota is characterised by simple communities notably lacking significant numbers of suspension feeders, perhaps to be expected in mid-Atlantic waters and, thus, by just as simple food chains. The uniformity of shore types also limits recruitment, even of successful immigrants, and coastal diversity and sources of primary productivity are only enriched in a few significant wetlands.