Jenni Stanley, Craig Radford & Andrew Jeffs Post-doctoral Fellow

Background Final stage of larval development in benthic marine organisms involves selecting a suitable settlement habitat. Involves specific cue or combination of cues Physical Chemical Can be both general and species specific

Settlement and Metamorphosis Not the same process Tightly coupled in biofouling organisms Capability of “delaying metamorphosis” in some species Ecological costs because it extends time in the plankton Physiological costs as it reduces post-metamorphic growth rate

Crab Settlement Studies Most crab studies that have occurred in the last decade Blue crab (Callinectes sapidus) Common mud crab (Panopeus herbstii) Fiddler crab (Uca pugnax) Estuarine mud crab (Rhithropanopeus harrisii) Focus on cues that shorten or lengthen time to metamorphosis (TTM) In brachyuran crabs TTM can be shortened by 15 – 25% with exposure to chemical cues (Forward Jr. et al., 2001)

Ambient Underwater Sound Composed of a wide range of frequencies Abiotic 50 – 1000 Hz – wind and waves Biotic 50 – 50,000 Hz – biological Anthropogenic – infrasound to ultrasound – human activities The major component of the sound emitted from a reef is produced by the inhabitants A cue which communicates a lot of habitat information would be of great value to larval settlers

Unique Habitat Signatures Significant differences in ambient sound associated with different coastal habitats in subtropical New Zealand Differences in acoustic profiles due to fish communities and benthic characteristics.

Unique Habitat Signatures 0000 Fringing Reef Lagoon Back Reef

Percentage Prms 2 Time Fringing Reef Unique Habitat Signatures Lagoon Back Reef

Unique Habitat Signatures Fringing Reef LagoonBack Reef

Ambient underwater sound may act as a long distance orientation cue as well as a settlement cue Jeffs et al., 2003; 2005; Simpson et al., 2005; Radford et al., 2007; Stanley et al., 2010 Ambient Underwater Sound Studies

Induction of settlement in crab megalopae by different habitat sound signatures Aim: Investigate the influence that sound signatures from different habitat types have on triggering settlement behaviour and/or shortening TTM

Four habitat treatments: distinct acoustically and biologically Continuous frontal fringing coral reef Isolated back reef habitat interrupted with areas of sand and coral rubble Sandy bottomed lagoon Silent (control) Methods - Laboratory Based Experiments

Results – Laboratory-based experiments 48/102 48/114 60/138 72/138 Reduction of 33% 30/84 36/108 66/120 Reduction of 47% Percentage metamorphosed Time (h) Cymo andreossyi Grapsus tenuicrustatus

Results – Laboratory-based experiments Percentage metamorphosed Time (h) Schizophrys aspera 24/48 24/60 42/78 42/84 Reduction of 33%

Methods - Field Based Experiments Isolated back reef habitat interrupted with areas of sand and coral rubble Sandy bottomed lagoon Two Habitat treatments: distinct acoustically and biologically

Results – Field-based experiments Percentage metamorphosed 48/87 48/144 Reduction of 29% 48/87 48/159 Reduction of 32% Grapsus tenuicrustatus Cymo andreossyi Time (h)

Results – Field-based experiments Percentage metamorphosed 48/87 48/159 Reduction of 25% Time (h) Schizophrys aspera

Conclusions Similar results in both tropical and temperate species Clear preference for optimal adult habitat type Ability to discriminate habitat by sound signatures The acoustic cue mediates an endogenous physiological development process Remote habitat identification using acoustic cues Integration of all the available cues now needs to be investigated

Acknowledgements Thanks To: Associate Professor Andrew Jeffs Dr Craig Radford NZMSS Student Research Funding Leigh Marine Laboratory Staff and students Lizard Island Research Station Staff and visiting students