Settlement of crown-of-thorns starfish: role of bacteria on surfaces of coralline algae and a hypothesis for deepwater recruitment
Johnson, CR and Sutton, DC and Olson, RR and Giddins, R (1991) Settlement of crown-of-thorns starfish: role of bacteria on surfaces of coralline algae and a hypothesis for deepwater recruitment. Marine Ecology Progress Series, 71 (2). pp. 143-162. ISSN 0171-8630
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Settlement trials conducted with larvae of crown-of-thorns starfish Acanthaster planci
revealed a moderate degree of substratum specificity. Highest rates of settlement and metamorphosis
occurred on coral rubble and the crustose coralline alga (CCA) Lithothamnlum pseudosorum, but rates
were more vanable on the coralline. Interpretation of settlement on the rubble is difficult because rubble
always supported some CCA. Settlement was significantly lower on other CCA (Porolithon onkodes and
Neogoniolithon foslei), non-calcareous crustose red algae (Peyssonellia sp.), and fouled ceramic tdes.
These results were consistent irrespective of whether larvae were offered a choice of substrata or not.
When larvae were separated from L. pseudosorum by mesh, settlement was highly variable but
sometimes occurred at high rates, suggesting that contact with the algae is not obligatory for induction.
Larvae were not induced to settle by GABA (y-amino butyric acid), elevated K+ concentrations, or coral
blocks fouled for 9 d, and settlement rates were virtually zero in controls without a known added
inducer. Treatment of highly inductive shards of L. pseudosorum with antibiotics reduced their
Inductive activlty to low levels, suggeslng that induction of settlement and metamorphosis of A. planci
by L. pseudosorum may be mediated by epiphytic bacteria. Other results were consistent with the
notion of bacteria-mediated induction. The inductive ability of different regions on individual L.
pseudosorum plants varied greatly, as did densities of bacteria on the plant surface. Larvae always
settled on sections of thallus having high densities of bacteria, but never on adjacent areas where
epiphytic bacteria were sparse. The inductive stimulus is likely to be chemical since it was inactivated
by boiling or autoclaving, and may be a relatively large molecule since it was not detected in water,
ethanol or chloroform extracts of lnductlve algae or coral rubble, and was retained by dialysis tubing of
pore size 10000 Daltons. The spatlal distribution of coral rubble and L. pseudosorum on and around
GBR midshelf reefs, the location of hydrodynamic retention cells around reefs, and the pattern of
outbreaks on the GBR, suggest that mass settlements of A. planci are more likely to occur in deep than
in shallow water. This would explain the paradox that outbreaks of A. planci on the GBR are not
heralded by increases in abundances of juveniles in shallow water, but are first observed as adult
starfish ascending from deepwater Prehminary deep water videotransects off Davies Reef showed that
rubble and CCA were abundant m deep water (30 to 65 m) adjacent to the area where aggregations of
adult starfish were first seen moving up from deep water, but the substratum in deep water off other
sections of the reef was sand.
|Deposited By:||Professor Craig R. Johnson|
|Deposited On:||24 Jun 2007|
|Last Modified:||18 Jul 2008 19:58|
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