THE ENVIRONMENTAL BIOLOGY OF THE EMBRYOS, EGG MASSES AND NESTING SITES OF THE LINGCOD, OPHIODON ELONGATUS.

摘要

The nature and extent of egg mortality was examined in the lingcod, Ophiodon elongatus (Hexagrammidae). Comparisons between nests at different areas in Puget Sound, Washington, indicate that certain spawning grounds are unsuitable for proper embryo development due to prevailing weak tidal currents which do not adequately ventilate nests. Hypoxic conditions which develop at the interior of poorly ventilated egg masses cause embryo mortalities by asphyxiation, protract the hatching time of the egg mass and result in disparate larval size among siblings at hatch. The ecological implications of these factors is discussed.;Data presented in this investigation suggest that water movement is an important stimulus for nest site selection by lingcod. In areas where tidal currents are weak, nest deposition occurred in shallow water, where waves and vertical tide motion create water movement. Nests were consistently deposited in deeper water at swift current areas.;In situ predation on nests was investigated. Small gastropods, Amphissa columbiana and Calliostoma ligatum, were the most commonly observed egg predators. Guardian male lingcod were not effective at eliminating gastropods. Although they consume relatively few eggs, gastropod foraging activity may promote nest dislodgement at swift current areas.;Respiration rates of lingcod embryos were estimated at various oxygen tensions. Embryos reduce their oxygen consumption with increasing hypoxia. Not all oxygen consumed by an egg was due to embryo respiration, epibiota on the chorion can account for up to 24% of the total oxygen uptake of an egg. Epibiota may restrict gaseous exchange and consume oxygen necessary for developing lingcod embryos perhaps of particular concern in poorly ventilated egg masses.;The interstitial environment of lingcod egg masses was examined under a variety of current conditions including slack water. Oxygen, pH and ammonia were monitored in unventilated nests.