Reef Sound as an Orientation Cue for Shoreward Migration by Pueruli of the Rock Lobster, Jasus edwardsii

Abstract

The post-larval or puerulus stage of spiny, or rock, lobsters (Palinuridae) swim many kilometres from open oceans into coastal waters where they subsequently settle. The orientation cues used by the puerulus for this migration are unclear, but are presumed to be critical to finding a place to settle. Understanding this process may help explain the biological processes of dispersal and settlement, and be useful for developing realistic dispersal models. In this study, we examined the use of reef sound as an orientation cue by the puerulus stage of the southern rock lobster, Jasus edwardsii. Experiments were conducted using in situ binary choice chambers together with replayed recording of underwater reef sound. The experiment was conducted in a sandy lagoon under varying wind conditions. A significant proportion of puerulus (69%) swam towards the reef sound in calm wind conditions. However, in windy conditions (>25 m s-1) the orientation behaviour appeared to be less consistent with the inclusion of these results, reducing the overall proportion of pueruli that swam towards the reef sound (59.3%). These results resolve previous speculation that underwater reef sound is used as an orientation cue in the shoreward migration of the puerulus of spiny lobsters, and suggest that sea surface winds may moderate the ability of migrating pueruli to use this cue to locate coastal reef habitat to settle. Underwater sound may increase the chance of successful settlement and survival of this valuable species.

Fig 1. Map of the experimental site.

Castle Point experimental sites used for collection of Jasus edwardsii pueruli and experimentation with behavioural choice chambers. “X” = positions of underwater speakers. The coastline was extracted from https://www.ngdc.noaa.gov/mgg/shorelines/ and redrawn.

Fig 2. Experimental set up and choice chamber.

(A) Schematic of experimental set up, and (B) behavioural choice chamber design.

Fig 3. Broadcast sounds from a natural reef habitat.

Power spectra of the broadcast sounds from a natural reef habitat during the summer replayed in the Jasus edwardsii behaviour field experiment. Solid black line represents the median spectra for the 6 minute recording and dashed grey lines represent the spectral variability (5 & 95 percentiles) determined from a series of non-overlapping 10 s duration windows (S1 Sound File).

Fig 4. Predicted probability and observed proportion of puerulus choosing to move towards the reef sound for the range of wind gust speeds experienced over the study period.

Predicted probability of a Jasus edwardsii puerulus choosing to move towards the reef sound moderated by the wind gust speed (m s^-1), based on a logistic regression (grey area represents the 90% CI) (Wald Z = -2.4; P = 0.02; n = 59). Black dots in the graph represent the observed proportion of the puerulus per night choosing to move towards the reef sound, while the numbers adjacent to the black dots represents the total puerulus sample size used to generate the proportion.

Fig 5. Underwater sounds at the experimental site.

Power spectra of underwater sound recorded for each night at the experimental site in January 2015 (A) immediately prior to the artificial source of underwater sound commencing (S2 Sound File), and (B) during the experiments with the artificial source of underwater sound present (S3 Sound File).