Oceanologia (Apr 2022)
Does topography of rocky intertidal habitat affect aggregation of cerithiid gastropods and co-occurring macroinvertebrates?
Abstract
Species aggregation has important implications for population survivorship and ecological functioning in many habitats, including rocky intertidal shores, which have been valuable to research for understanding ecological patterns and process. Intertidal gastropods of the family Cerithiidae often form extensive aggregations for which the driving mechanism may be positive thigmotaxis, i.e. movement occurring until an obstructing surface is contacted, then cessation of movement. However, it is unknown if thigmotaxis may occur by cerithiids contacting and aggregating around uneven surfaces of the rock topography, or by contacting other conspecific individuals. We quantified aggregation patterns in invertebrate assemblages and topographic complexity at intertidal rock platforms in NW India with extensive cerithiid populations. The cerithiids Clypeomorus moniliferus and Cerithium caeruleum were the most common species. Distribution analysis confirmed significant over-dispersion indicative of aggregation (densities were often around zero but occasionally reached up to 680 dm−2). Multivariate correlation analyses showed that topographic complexity contributes to overall species assemblage variability, but there was no evidence that topographic complexity correlates with cerithiid abundances or was likely to affect their aggregation. Thus the thigmotaxis producing cerithiid aggregation is probably associated with individuals contacting each other rather than any feature of the rock surface such as crevices or raised areas. Overall, while some components of species assemblages were associated with complex topography, regarding the abundant cerithiids, potential population benefits from aggregation (e.g. reduced desiccation and temperature) may be expected on rocky shores with any level of topographic complexity.
