Size, depth and position affect the diversity and structure of rock pool communities in an urban estuary

Abstract

Rock pools provide a range of ecological niches that can support diverse assemblages on rocky shores. As intertidal shores are increasingly lost to developments, understanding the drivers of diversity in rock pools is important for the conservation and construction of these key habitats. In this study we investigated relationships between physical characteristics of rock pools and their biota in an urban estuary. We sampled the biota every 6 weeks for 1 year at sites in the inner and outer zones of Sydney Harbour. In the well-flushed and exposed outer zone, sessile and mobile taxa richness was positively related to rock pool width, whereas only mobile taxa richness was related to depth and volume. In the more urbanised and less exposed inner zone, mobile taxa richness was positively related to rock pool width and volume. In both zones, sessile taxa richness decreased with increasing height on shore. Our results suggest that the biodiversity of intertidal rock pools varies depending on their position in Sydney Harbour and the available species pool. Therefore, restoration efforts should consider rock pool size parameters and local environmental conditions, including location, so designs can be optimised to maximise species diversity in these pools.

Artificial rockpools: Seaweed colonisation and productivity vary between sites but are consistent across environmental contexts

“…The available literature indicates that in terms of seaweed, shallow pools tend to support a higher number of species than deeper pools, while sessile faunal taxa appear to have no relationship to depth (Browne & Chapman, 2014;Firth, Schofield, et al, 2014). The richness of mobile faunal taxa has been shown to increase with both depth and volume of the rock pool unit (Schaefer et al, 2018). We therefore expect that the pools used in this investigation were able to develop a full algal assemblage.…”

Understanding the role of microhabitats in intertidal rock pools to guide future eco-engineering designs

“…This may suggest that diversity within pools is driven by other factors, not considered here, rather than microhabitats. Alternatively, the low numbers of rock pools with overhangs or pits observed in the harbour zones may partly explain the overall low number of species of mobile taxa in rock pools at these sites (Schaefer et al 2019), since there is compelling evidence that microhabitats increase niche availability (Menge and Sutherland 1976), which generally positively affects diversity.…”

“…For benthic invertebrates, the effect of rock pool size characteristics varied. For example, rock pool diameter had no effect on mobile species (Underwood and Skilleter 1996), whereas rock pool depth had no consistent effect on mobile species (Astles 1993;Firth et al 2014;Schaefer et al 2019), which may be linked to species-dependent effects (Astles 1993;Bugnot et al 2018), or the local environmental conditions (Schaefer et al 2019). To date, artificial rock pool designs have been of simple shape and based on variations in these characteristics (e.g., total size and/or depth), but have not considered smaller-scale topographical complexity features (microhabitats) within rock pools.…”

“…loose shells), which suggested a level of habitat selectivity (White et al 2015). Observations done during surveys of the size, depth, and position of rockpools on intertidal rocky shores in Sydney (Schaefer et al 2019) suggest that features of pools may also influence the distribution of mobile macro-invertebrates. Assessing microhabitats within rock pools may therefore provide an important link for detailed habitat-diversity relationships that can be used to build more sophisticated rock pool designs that target mobile macro-invertebrates.…”

“…Rock pools come in various shapes and sizes, and previous research has shown that a variety of rock pool characteristics can influence mobile diversity (Metaxas and Scheibling 1993;Bugnot et al 2018;Schaefer et al 2019). For example, deeper and larger pools support an increased diversity of fish (Bugnot et al 2018).…”