Macrofaunal Loss and Microhabitat Destruction: The Impact of Trampling in a Temperate Mangrove Forest, NSW Australia

Abstract

Trampling paths are a feature of estuarine habitats in southeastern Australia. An experimental investigation quantified the impact of trampling over a 3 year period on the microhabitat features and macrofaunal assemblages in a temperate mangrove forest in New South Wales, Australia. The magnitude of the impact varied between 0 and 25 passes (representing a visit by 25 people), which reduced the biomass of the Bostrychia–Caloglossa algal association by 50%. The frequency of trampling varied between one and four, simulating a single and seasonal visits by a group of people to the mangrove forest. The main impact of trampling was an alteration to the microhabitat structures of the forest floor including a decrease in the number and vertical height of pneumatophores, an increase in the proportion of bent and broken pneumatophores in trampled lanes and a decrease in the biomass of the epiphytic Bostrychia–Caloglossa algal association. The macrofauna most impacted by trampling were the gastropods most commonly associated with the pneumatophores and algal assemblages and included Ophicardelus spp. and Assiminea buccinoides. Those gastropods least impacted by trampling were commonly associated with the surface of the sediment or were known to move over the surface and included Bembicium auratum and Cassidula zonata. There was little impact on the main burrowing crab, Heloecius cordiformis. There were some indirect impacts of trampling with the recruitment of Ophicardelus spp. Assiminea buccinoides and Salinator solida reduced in the subsequent year after trampling had ceased. People can create walking paths in mangrove forests that have long term effects on the habitat. An appropriate management emphasis may lie in maintaining the structural features of the habitat.