Ke Alahou, Volume I, Number 5, 1 April 1980 — Continuous Flow Essential to Stream Life Cycles [ARTICLE]

Continuous Flow Essential to Stream Life Cycles

by John Ford, U.S. Army Corps of Engineers, Environmental Research Section (from Hawai'i Coastal Zone News)

Ikahe mau ke kahawai e ola ana na i'a iloko la, 'oia ka 'o'opu, 'opae ame ka hihiwai. E niau iho ana ka wai a e holoi i ka lepo ame ka pilau ma ka papaku a e ho'olako ike ea, ka mea nui no ka ulu 'ana oke kowau o ka 'o'opu i hanau 'ia a kau malalo o na 'ili'ili me na pohaku iloko o ka wai. I kahe ka wai a e ho'olako no ho'ii na mea 'ai a ka 'opae a e ho'okaulike mau no ho'i i k anu o ka wai i ka niau 'ana o ka wai. A 'o ka mea nuipaha e 'ike aku ai i ke kahawai, 'oia no ka hopena o ke au ola (life cycle) o na i'a kahawai. I ka wa kahiko, e mana'o ana napo'e 'imi a huli na'auao, he i'a no ke kai. A ua kapa 'ia he "diadromus" ('o ka mana'o pili pono, 'oia no lio'i: e 'au i kai a ho'ihou i ka wai). A i keia manawa e ho'au iho ma ke kahe o ka wai a i ke kai. Mahope, kau ma ke kahua o ke kai a lilo ipua (he mea i'a li'ili'i) a nui, ua kapa 'ia he "hinana" a ho'i hou mai i ka nuku wai. Ma ka nuku wai, e 'ohi ana i ka hinana ka'o'opu ma ke kahawai. Alaila, ua kapu 'ia ka 'ohi 'ana e aupuni Panala'au. Nolaila, he mea nui ka kakou e malama. pono i ke kahe mau 'ana o ka wai e ho'ola hou ai i na Lanauna hou o ka i'a kahawai. A ina, e malama hewa, alaila, emi no ka nui o ka i'a kahawai a nalowale no ho'i e lilo i mealahcr'qle. The maintenance of continuous flow is particularly important to the 'o'opu (goby), 'opae (shrimp), and hihiwai (snail, shellfish), whieh ,are indigenous, or native to Hawaii's waters. Swift currents cieanse the stream bed of silt whieh would otherwise coilect in the gravel and smothēFTāluable habitat. Riffle waters, ormini-rapids, are supersaturated with oxygen whieh sustains life in 'o'opu eggs that are deposited underneath rocks in the stream bed. Food for the mountain 'opae is provided by the drifting particles of algae and detritus whieh the animals filter

> i "■"* " from the passing currents. The continuous flow of water protects all stream life from undergoing frequent and wide changes in temperature and serves toprevent thermal stress. » Perhaps the most important role that continuous streamflow plays is that it is essential in allowing the native species to complete their life cycles. Our fresh water 'o'opu, 'opae and the hihiwai demonstrates a marine ancestry through the retention of a. mariae larval stage. Scientists eall this life cycle "diadr®mous," and it literally means/'two runs." After tne eggs of these animals hatch iri the stream, eurrents carry the tiny larvae into the oeean. During this time, the larvae may be passively transported by coastal currents, and there is little evidence ihat they must return to the stream r of their birth. After a period ranging from severar weeks to as mueh as seven months, depending upon the species, the larvae metamorphose into juveniles, ,settle to the bottom at the stream mouths, and begin their migration back inlo freshwater where they will grow to maturity. At this point in their life cycle of the 'o'opu, the juveniles are called hinana by Hawaiians. The native Hawaiian people used to collect hinana in large baskets atjstream mouths. So great wds.the effect of this harvest upon the populations of 'o'opu that the practice was eventually outlawed by the Territorial Government. The maintenance of flow to the sea is the only mechanism by whieh indigenous, diadromous*species ean replenish their own populations in Hawaiian streams. WitJiout it, streams cannot supportsufficient numbers of these valuable.animalsfox subsisience, or recreational or commercial fishery uses. Diversion of streamflow mau also jeopardize the existence of 'o'opu hiukole (Lenlipe? concolor), a species unique to Hawaii, whieh some scientists believe is rare.