Material type weakly affects algal colonisation but not macrofaunal community in an artificial intertidal habitat

Abstract

The urbanisation and hardening of shorelines is likely to continue in response to coastal population growth and climate change. To mitigate associated ecological impacts, ecological engineering is being increasingly applied to enhance local biodiversity. This includes retrofitting topographically complex tiles or units onto intertidal artificial structures to mimic features of the natural hard-bottom habitats that were lost. However, the effect of material (different rock types) on the biotic colonisation of these habitat enhancements has rarely been investigated. We constructed complex tiles using a range of materials (concrete, granite, limestone, pink sandstone, violet sandstone, and a composite of the natural stones) to test their effects on the colonisation and establishment of intertidal algae and macrofaunal communities on seawalls in Singapore. We found no significant differences in macrofaunal species richness, total abundance, and community composition among treatments. There were only minor differences in algal community composition, total algal cover, and algal succession patterns among tile types. For both macrofaunal and algal communities, site-specific differences significantly affected colonisation. Our study suggests that material does not substantially influence biotic colonisation on habitat enhancement units and, therefore, other factors such as the associated environmental impacts of potential fabrication materials could be weighted more heavily when planning ecological engineering solutions for hardened shorelines.