UPTAKE OF DISSOLVED ORGANIC-MATTER BY LARVAL STAGE OF THE CROWN-OF-THORNS STARFISH ACANTHASTER PLANCI

The life-history of the crown-of thorns starfish (Acanthaster planci) includes a planktotrophic larva that is capable of feeding on particul ate food. It has been proposed, however, that particulate food (e.g. m icroalgae) is scarce in tropical water columns relative to the nutriti onal requirements of the larvae of A. planci, and that periodic shorta ges of food play an important role in the biology of this species. It has also been proposed that non-particulate sources of nutrition (e.g. dissolved organic matter, DOM) may fuel part of the nutritional requi rements of the larval development of A, planci as well. The present st udy addresses the ability of A, planci larvae to take up several DOM s pecies and compares rates of DOM uptake to the energy requirements of the larvae. Substrates transported in this study have been previously reported to be transported by larval asteroids from temperate and anta rctic waters. Transport rates (per larval A, planci) increased steadil y during larval development and some substrates had among the highest mass-specific transport rates ever reported for invertebrate larvae. M aximum transport rates (J(max)(in)) for alanine increased from 15.5 pm ol larva(-1) h(-1) (13.2 pmol mu g(-1) h(-1)) for gastrulas (J(max)(in ) = 38.7 pmol larva(-1) h(-1) or 47.4 pmol mu g(-1) h(-1)) to 35.0 pmo l larva(-1) h(-1) (13.1 pmol mu(-1) h(-1)) for early brachiolaria (J(m ax)(in) just prior to settlement = 350.0 pmol larva(-1) h(-1) or 161.1 pmol mu g(-1) h(-1)) at 1 mu M substrate concentrations. The instanta neous metabolic demand for substrates by gastrula, bipinnaria and brac hiolaria stage larvae could be completely satisfied by alanine concent rations of 11, 1.6 and 0.8 mu M, respectively. Similar rates were meas ured in this study for the essential amino acid leucine, with rates in creasing from 11.0 pmol larva(-1) h(-1) (or 9.4 pmol mu g(-1) h(-1)) f or gastrulas (J(max)(in) = 110.5 pmol larva(-1) h(-1) or 94.4 pmol mu g(-1) h(-1)) to 34.0 pmol larva(-1) h(-1) (or 13.0 pmol mu g(-1) h(-1) ) for late brachiolaria (J(max)(in) = 288.9 pmol larva(-1) h(-1) or 11 0.3 pmol mu g(-1) h(-1)) at 1 mu M substrate concentrations. The essen tial amino acid histidine was transported at lower rates (1.6 pmol mu g(-1) h(-1) at 1 mu M for late brachiolaria). Calculation of the energ y contribution of the transported species revealed that larvae of A, p lanci can potentially satisfy 0.6, 18.7, 29.9 and 3.3% of their total energy requirements (instantaneous energy demand plus energy added to larvae as biomass) during embryonic and larval development from extern al concentrations of 1 mu M of glucose, alanine, leucine and histidine , respectively. These data demonstrate that a relatively minor compone nt of the DOM pool in seawater (dissolved free amino acids, DFAA) can potentially provide significant amounts of energy for the growth and d evelopment of A. planci during larval development.