Experimental manipulations of the organic compositions of seawater: implications for studies of energy budgets in marine invertebrate larvae

Abstract

Correct measurement of changes in biomass and metabolic rates over time are two essential elements for the accurate construction of energy budgets for invertebrate larvae. Both components of larval energetics are altered by changes in the organic chemistry of the seawater. Axenic (bacteria-free) veliger larvae (88 μm shell length) of the bivalve Crassostrea gigas (Thunberg, 1795) had a 53% enhancement of their metabolic rate relative to control values (5.8 ± 0.6 pmol larva −1 h −1, x ± 1 se ) when exposed to seawater to which 1 μM glucose had been added. Gastrulae, prism-stage, and pluteus-stage, larvae of the sea urchin Lytechinus pictus (Verrill, 1867) had significantly higher metabolic rates when 1 μM amino acids (16 amino acids at 62.5 nM each) was added to seawater. Gastrulae increased their rate of respiration by 35%, from 10 ± 0.9 to 13.5 ± 1.4 pmol O 2 embryo −1 h −; prism-stage larvae by 33% from 40.9 ± 2.0 to 54.4 ± 2.8; and pluteus-stage larvae by 50%, from 33.4 ± 1.5 to 50.3 ± 3.1. Lecithotrophic larvaei of the gastropod Haliotis rufescens Swainson, 1822, either had no change (Day 1, trochophore larvae) or a significant increase (Day 2, veliger larvae) in dry organic weight when reared in natural seawater that had been passed through a filter of 0.2-μm pore size (to remove particles). In contrast, sibling larvae always decreased in dry organic weight when reared in seawater which had first been passed through a sand-filter (a treatment that alters the organic chemistry of seawater), and then a 0.2-μm (pore size) filter. These data show that alterations of the organic chemistry of seawater can affect the growth and metabolism of invertebrate larvae. If such modifications are not controlled, energy budgets constructed from laboratory experiments on larvae in altered seawater may bear little resemblance to the energetics of larvae in the field.