Patterns of movement of the limpet Cellana tramoserica on rocky shores and retaining seawalls

Abstract

Artificial structures are becoming common features of the landscape in shallow waters of urban areas, but very little is known about their ecology. In Sydney Harbour (NSW, Australia), intertidal seawalls replace considerable portions of natural habitats, including rocky shores. Previous studies have shown that seawalls and rocky shores generally support similar assemblages of plants and animals, with important differences in relative abundances of some species. The behaviour of key consumers can have a fundamental role in structuring benthic assemblages, and it is, therefore, necessary to assess whether it is changed by the replacement of natural habitats with artificial structures. This study compares patterns of movement of the common patellid limpet Cellana tramoserica between seawalls and vertical rocky shores. The distances displaced, the orientation of movement and the homing behaviour of marked individuals were recorded from day to day, over a period of several tidal cycles (14 d) and for a longer period (ca. 3 mo), on several seawalls and rocky shores. Short-term patterns of movement (1 to 14 d) did not differ between structures. In contrast, after 3 mo, although the orientation of the movement remained random on both kinds of structures, limpets on seawalls had dispersed longer distances and tended not to retain their original positions. These results suggest that long-term dispersal of C. tramoserica, rather than foraging bouts, could be altered by the replacement of rocky shores with artificial structures. Differences in use of habitat by key consumers should be incorporated in models aimed at identifying the mechanisms responsible for the occurrence of different assemblages on natural and artificial structures.

Inter-individual variation partially explains patterns of orientation on steeply sloped substrata in a keystone grazer, the limpet Cellana tramoserica

“…Manipulative experiments would be needed to establish whether individuals are active selecting steeply sloped microhabitats or if other processes are driving this pattern. Homing is unlikely to explain this pattern as previous studies have found only 10-15 % of Cellana home after 14 days on vertical surfaces (Bulleri et al 2004) compared to the 62 % of individuals consistently being found on steeply sloped surfaces in this study. Consistently being located on steeply sloped substrata is not associated with an increased chance of orientating downwards.…”

“…The behaviour of intertidal animals on steeply sloped substrata has been relatively understudied compared with that of organisms on horizontal substrata and within specific microhabitats (see Della Santina 1994;Della Santina et al 1995;Chelazzi et al 1998;Bulleri et al 2004 for some exceptions). Global sea levels are predicted to rise as a result of climate change (Pachauri and Reisinger 2007), and consequently, the intertidal region may shift in many areas from predominately horizontal surfaces to increasingly dominated by steeply sloped and vertical surfaces (Vaselli et al 2008;Jackson and McIlvenny 2011), and the abundance of different habitat types will change (Thorner et al 2014).…”

Recruitment determines differences between assemblages on shaded or unshaded seawalls

“…Alternatively, they may migrate into shaded patches only when temperatures are very hot and move back onto the unshaded wall when conditions are more benign. Whether the observed difference between shaded and unshaded portions of seawalls may be explained by behavioural responses to habitat differences cannot be tested here because there are few data on patterns of movement of mobile animals on intertidal seawalls (Bulleri et al 2004).…”

Differential patterns of distribution of limpets on intertidal seawalls: experimental investigation of the roles of recruitment, survival and competition

“…Despite many papers in recent years documenting patterns of assemblages on seawalls, few have compared ecological interactions among animals between artificial and natural shores. Bulleri et al (2004) showed grazing by Cellana tramoserica on walls differed from that on natural shores in NSW, which could have major impacts on assemblages because of its strong interactions with other species (Underwood et al 1983, Underwood 1984. Intertidal shores in NSW are generally extensive wave-cut platforms, so interactions among grazers might be expected to be stronger on seawalls where the intertidal area is reduced and species are crowded into a limited area.…”