Ecology of a key ecosystem engineer on hard coastal infrastructure and natural rocky shores

• Chthamalus stellatus were generally less abundant on hard structures than on natural rocky shores.
• Temporal population stability, growth and mortality were largely similar in both habitats.
• C. stellatus were significantly larger and recruited more onto natural rocky shores.
• Recruitment was important in determining differences in the abundance of barnacles.

The numbers of hard coastal artificial structures is increasing worldwide and there is now cumulative evidence that they support assemblages that are less diverse than natural shores. Here we investigated patterns of distribution and demography of the native barnacle Chthamalus stellatus on hard coastal structures and on natural rocky shores. Barnacles were 35% less abundant on hard structures regardless of substratum type (concrete or basalt). On a subset of sites we found that temporal population stability, growth and mortality were similar on natural rocky shores and hard structures. In contrast, barnacles were significantly larger and recruited more onto natural rocky shores. These results emphasise the important role of recruitment in determining the abundance of a key space occupier on hard coastal structures. Experimental work building on these results may generate insights that can be used as guidelines for the management of urbanised coastal areas.