Biology Reference
In-Depth Information
In the underwater world, sound has two major components: an acoustic nearfield
where particle velocity dominates, and an acoustic farfield where the propagation of
pressure dominates. Marine animals perceive these two sonic fields differently: the
nearfield is perceived by sensory hair-like receptors, and membranous receptors are
used to detect the fairfield particle oscillation. These two systems are well known in
fish and marine mammals, but little is known in invertebrates. For instance, larvae
of many species of coral reefs can detect and are attracted by the sound produced by
breaking waves on the coral reef. For many other species of invertebrates, for
instance, many crustaceans, the coral reef is perceived as a hostile or dangerous
ambience, because the coral reef is a place at high risk for predation.
The pelagic larvae of reef fishes seem attracted by the noise produced by a coral
reef. To prove this hypothesis, Tolimieri et al. ( 2000 ) used light traps in a natural
condition and with natural noise broadcast by a loudspeaker to capture pelagic
larvae. They found more larvae of triplefin (a benthic reef fish) in the noise traps
than in silent traps, confirming the hypothesis that acoustic cues are used to some
extent by pelagic animals for orientation.
In a series of experiments Simpson et al. ( 2008 ) have confirmed that many
species of coral reef fishes are attracted by reef noise with different intensity
according to species and age. Further investigations have proved that behavioral
traits such as recent acoustic experience are important to modulate the response to
cliff noise. In fact, settlement-stage larval reef fishes (approximately 20 days old)
are attracted by sounds if they had a recent acoustic experience.
Vermeij et al. ( 2010 ) have observed that free-swimming larvae of tropical corals
respond to acoustic cues of the noise produced by fish and crustaceans of the coral
reef and are attracted by this sound, which represents an orientation cue to find a
favorable site where they will spend their benthic life.
Further experiments conducted by Simpson et al. ( 2012 ) with playback of coral
reef noise combined with light traps, in the Great Barrier Reef Lagoon in Australia,
have found that reef noise acts as a deterrent for many previously neglected taxa.
The animals that avoid reef noise are taxa with a pelagic or nocturnal emergent
lifestyle (Fig. 6.14 ).
This study for the first time demonstrates that a broad set of crustacean taxa with
different habitat requirements and life histories are able to detect and respond to
acoustic information provided by coral reefs. Furthermore, it has been proved that
organisms living close to the coral reefs actively avoid the reef to escape mobile and
fixed predators.
Sound produced by wave movements is a fundamental indicator of an unsafe
zone for a broad range of taxa. Zoea, the pre-settlement larval stage of Brachyura,
are attracted by reef noise, but megalops, the settlement stage of Brachyura, seem
not attracted by the reef. The mechanisms used by crustaceans to orient using noise
are not fully explained, and much research should be undertaken.
The larvae of a number of crab species have been observed to orientate and swim
toward ambient underwater sound produced by coastal settlement habitats (Stanley
et al. 2009 ). Recent laboratory- and field-based experiments conducted by Stanley
et al. ( 2012 ) have demonstrated that time of metamorphosis in the settlement-stage
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