Orientation of the Beach Hopper 'Notorchestia' sp. (Amphipoda: Talitridae)

Abstract

Littoral talitrid amphipods in the Northern Hemisphere and equatorial regions use a variety of cues to orient along the y-axis (land-sea axis) of the intertidal zone. Little is known as to whether similar cues are used in Southern Hemisphere taxa. The response to three cues commonly used in littoral amphipods was tested for in the Australian intertidal talitrid 'Notorchestia' sp. (originally identified as 'Talorchestia quadrimana' (Dana, 1852), but material not available for further identification). These cues were slope, geomagnetic field, and solar azimuth. The results provide some evidence that 'Notorchestia' individuals could favour the geomagnetic field and solar azimuth to orient along the y-axis of the intertidal zone rather than use beach slope. Orientation toward the land or sea appeared to be related to the presence or absence of seawater in the test vessels. Talitrids from two different beaches with differing land-sea axes were found to be broadly oriented according to the direction of the beach from which they were collected. Inconsistencies in some of the results could stem from the amphipods using an integrated orientation system that relies on the presence of a number of cues. These amphipods appear to be broadly oriented in favourable directions rather than oriented along angular paths with specific numeric values. The results presented in this study parallel those found in other littoral amphipod species in other parts of the world.