HAWAIIAN STREAM ORGANISMS
Biologists have long recognized the role of
Hawaii's extreme geographical isolation in shaping its flora and
fauna. The Hawaiian Islands are about 4,000 km from the nearest
continental source of species making it the most isolated
archipelago on Earth. As a result of this extreme isolation,
Hawaiian streams have relatively fewer species compared to their
continental counterparts with many groups of organisms entirely
missing. The Hawaiian aquatic insect fauna, for example, has no
native stoneflies, mayflies, caddisflies, alderflies, or
dobsonflies; however certain insect taxa such as the odonates
(damselflies in particular) and certain diptera (flies) exhibit
spectacular radiation of species into specialized stream
environments.
The larger organisms (macrofauna) native to
Hawaiian streams generally have marine connections. All of the
native macrofauna exhibit amphidromy in that they all have marine
larval phases. Five species of fishes, generally all referred to
as 'o'opu by the early Hawaiians, are native to Hawaii. Natives,
incidentally, include both endemic species, which are only found
in a particular area, as well as indigenous species which
naturally occur in a particular area but are found in other
locality as well. All of Hawaii's stream fishes are now believed
to be endemic except one, Awaous guamensis ('o'opu-nakea). Two
gastropod snail species, Neritina granosa (hihiwai) and Neritina
vespertina (hapawai), are endemic to Hawaii. The edible hihiwai
inhabits mountainous stream reaches while the hapawai is found in
deep estuaries of streams near the ocean. Two decapod crustaceans
complete the list of amphidromous native Hawaiian stream
macrofauna. Atyoida bisulcata ('opae-kalaole) is a swift-water
inhabitant of mountainous stream reaches and a popular delicacy
among island residents. The Hawaiian prawn (Macrobrachium
grandimanus - 'opae-'oeha'a) is a relatively small endemic (less
than 3 inches) which inhabits Hawaiian estuaries.
Hawaii's stream environments are poorly
surveyed and to date there has not been a systematic inventory of
extant or search for new aquatic species within- and
among-islands. Little is known, for example, about Hawaii's
native aquatic and semi-aquatic lymnaied snail fauna which may
rival the extraordinary and well-documented radiation of Hawaii's
terrestrial snails. The algae of Hawaiian streams, which support
most food webs, are virtually unstudied taxonomically. It is
critically important that such surveys and inventories be
undertaken immediately to protect Hawaii's remaining freshwater
biodiversity.
Threats to stream environments in Hawaii are many. Alien species introductions into streams are rapidly escalating on all islands disrupting natural stream functioning and increasing predation and competition on native species with few natural defenses. Water withdrawals from streams for potable water, agricultural and hydropower development has been identified as one of the primary factors degrading the biological quality of streams in the Hawaiian Islands. These disruptive forces are only expected to increase and intensify in the coming century in Hawaii unless conservation policies are strengthened and needed information and technologies are developed.