Sources of Energy for Increased Metabolic Demand During Metamorphosis of the Abalone Haliotis rufescens (Mollusca).

Abstract

Pelagic, lecithotrophic (nonfeeding) larvae of the red abalone (Haliotis rufescens) settle and subsequently metamorphose into benthic juveniles capable of feeding on particulate food. Thus, metamorphosis must be fueled by either endogenous reserves or a nonparticulate food source such as dissolved organic material (DOM) in seawater. The metabolic rates (measured as oxygen consumption) of abalone larvae were found to increase by an average of 3- to 5-fold from the larva to early juvenile stage. The total cost of development from embryo to juvenile measured for three cultures ranged from 41.6 mJ to 55.0 mJ. Meeting this cost would require 1.3 to 1.7 {mu}g of biomass (ash-free dry mass), which is similar to the initial biomass of the spawned oocyte at 1.36 +/- 0.04 {mu}g (mean of four cultures). However, there was no net loss of biomass during development from the oocyte to the juvenile. The uptake of alanine and glucose from seawater by larvae and juveniles could provide one-third of the organic material required to supply metabolism, even if the transporters were only operating at 20% of their maximum capacity throughout development. For larvae undergoing metamorphosis (between 6- and 9-days-old) the proportion of total metabolic demand supplied using aerobically catabolized biomass was only 39%. The higher metabolic rates of metamorphosis are met only in part by consuming stored endogenous reserves. Concomitant with an increase in mass-specific metabolic rate during metamorphosis, the maximal capacity (Jmax) for the transport of dissolved alanine from seawater increased 3-fold, from 61.2 +/- 1.9 (SE) to 182.0 +/- 49 pmol alanine individual-1 h-1. The majority (range: 61% to 100%) of the energy requirements of larval and early juvenile development of H. rufescens could be supplied by input of DOM from the environment. Measurements of transport rates of amino acids and sugars by these animals, and calculations of the energy input from these substrates, indicate that the cumulative transport of DOM from seawater during development to the early juvenile stage could supply an amount of energy equivalent to the initial maternal endowment of energy reserves to the oocyte of this lecithotrophic species.