Acanthaster planci

The crown-of-thorns (COTS) starfish, Acanthaster planci (Fig. 26.1A) is probably the best-studied asteroid in the world because of the effect that periodic outbreaks of this species have on coral reefs (see Additional reading). We have comprehensive knowledge of the ecology, reproduction, and feeding biology of A. planci. This species is an unusual asteroid in being a specialist corallivore and outbreaks result in marked decrease in live coral cover to below 1-5% in some reports. Acanthaster planci generally prefers acroporid and pocil-loporid corals, but other corals are also consumed. The outbreak ends when coral prey is exhausted. Reef recovery following intense predation by COTS is variable with some reefs not recovering for 10-15 years. The eggs of A. planci contain saponins, a chemical toxic to fish and presumed to protect the eggs and embryos from predation.

There are three hypotheses on the causes of A. planci outbreaks: (1) the predator removal hypothesis proposes that overfishing of COTS predators (triton shells, fishes) influences the increase in numbers; (2) the natural phenomenon hypothesis, and (3) the terrestrial runoff hypothesis that proposes that nutrient runoff from the land leads to an increase in the phytoplankton food of A. planci larvae, leading to enhanced recruitment. Recent data analyses provide strong support for the nutrient hypotheses, emphasising the need to control nutrient runoff from anthropogenic sources into the GBR lagoon (see Chapter 11). While it was thought that COTS outbreaks might be due to a major pulse of recruitment, it now appears that they are comprised of individuals from multiple recruitment years.

Desierto Atacama

Figure 26.2 Asteroidea. A, Cryptasterina hystera (x 1.67) (photo: from Byrne and Walker 2007); B, Cryptasterina pentagona (x 1.67) (photo: from Dartnall et al. 2003); C, Aquilonastra byrneae (x 1.67) (photo: from Byrne and Walker 2007); D, Ailsastra sp (x 0.30) ; E, Disasterina sp. Holothuroidea (x 1.25). F, Afrocucumis africana (x 0.92); G, Polyplectana kefersteinii (x 1.10); H, Euapta godeffroyi (x 0.10); I, Synapta maculata (x 0.23). (Photos: M. Byrne, unless noted.)

Figure 26.2 Asteroidea. A, Cryptasterina hystera (x 1.67) (photo: from Byrne and Walker 2007); B, Cryptasterina pentagona (x 1.67) (photo: from Dartnall et al. 2003); C, Aquilonastra byrneae (x 1.67) (photo: from Byrne and Walker 2007); D, Ailsastra sp (x 0.30) ; E, Disasterina sp. Holothuroidea (x 1.25). F, Afrocucumis africana (x 0.92); G, Polyplectana kefersteinii (x 1.10); H, Euapta godeffroyi (x 0.10); I, Synapta maculata (x 0.23). (Photos: M. Byrne, unless noted.)

complexes comprising a number of species. A number of cryptic species have been recently identified in tropical Queensland based on differences in reproduction and development.

Echinaster luzonicus (Fig. 26.1H) is a common species in the GBR. This multiarmed (6+ arms) species often has an irregular profile with unequal portions due to its propensity to autotomise distal portions of its arms followed by regeneration. The pincushion star Culcita novaeguineae is also common (Fig. 26.1F, G). Juvenile Culcita are flatter and have more distinct rays than the adult (Figs 26.1G).

Coral Reproduction And Development

Figure 26.3 Holothuroidea. A, Holothuria atra (x 0.27); B, Holothuria atra with commensal crabs (x 0.50); C, Holothuria atra with commensal worm (x 0.67); D, Holothuria edulis (x 0.38); E, Holothuria leucospilota (x 0.17); F, Holothuria dof-leinii (x 0.21); G, Holothuria difficilis (x 0.63); H, Holothuria fuscogilva (x 0.19); I. Holothuria whitmaei (x 0.15) (photo: H. Eriksson). (Photos: M. Byrne, unless noted.)

Figure 26.3 Holothuroidea. A, Holothuria atra (x 0.27); B, Holothuria atra with commensal crabs (x 0.50); C, Holothuria atra with commensal worm (x 0.67); D, Holothuria edulis (x 0.38); E, Holothuria leucospilota (x 0.17); F, Holothuria dof-leinii (x 0.21); G, Holothuria difficilis (x 0.63); H, Holothuria fuscogilva (x 0.19); I. Holothuria whitmaei (x 0.15) (photo: H. Eriksson). (Photos: M. Byrne, unless noted.)

The feeding biology of sea stars varies from specific to general diets. Many species are predators on molluscs, sponges, corals and other echinoderms. Other species are surface grazers and scavengers. These asteroids predominantly feed off hard substrata such as coral rubble, eating sponges, microscopic organisms, or coral mucus. Culcita novaeguineae feeds on corals, other invertebrates and benthic films. Coral mortality caused by individual Culcita is less than that caused by individual Acanthaster, but its selective feeding habits may influence the relative abundance of some coral species.

Was this article helpful?

0 0
Going Green For More Cash

Going Green For More Cash

Stop Wasting Resources And Money And Finnally Learn Easy Ideas For Recycling Even If You’ve Tried Everything Before! I Easily Found Easy Solutions For  Recycling Instead Of Buying New And Started Enjoying Savings As Well As Helping The Earth And I'll Show You How YOU Can, Too! Are you sick to death of living with the fact that you feel like you are wasting resources and money?

Get My Free Ebook


Post a comment