The Ecological Response of Insectivorous Bats to Coastal Lagoon Degradation

The Ecological Response of Insectivorous Bats to Coastal Lagoon Degradation

 

Bradley Clarke-Wood

 
Supervisors


2013

Abstract

Coastal lagoons, while providing crucial habitat for a wide range of biodiversity, are often under intense urbanisation pressures resulting in their degradation.  Insectivorous bats utilise these highly productive ecosystems and are directly impacted by their decline in quality. We compared bat activity and richness with prey biomass across a gradient of lagoon quality in coastal lagoons of  Greater Sydney to determine the extent to which bats and their prey were impacted by lagoon degradation. Next, we honed in on the mechanisms behind insectivorous bats’ decline in degraded lagoons by examining food web structure (using analysis of δ13C and δ15N stable isotopes) and heavy metal contamination of lagoon sediment, invertebrates and bat tissue.  Insectivorous bat communities were found to comprise of more species and be more active at undisturbed lagoons. Australia’s only trawling bat, Myotis macropus, was absent from all low quality lagoons. Heavy metal contamination of coastal lagoons is a significant source of degradation. Analysis of heavy metal concentrations in sediments, invertebrates and insectivorous bats confirmed that these contaminants were present at degraded lagoons and were operating within the trophic structures of these habitats.  While trophic structure structure did not differ significantly with lagoon quality, M. macropus showed a small shift towards more δ13C enriched diets in low quality lagoons, potentially indicating avoidance of contaminated aquatic prey resources.  The present study demonstrates that while coastal lagoons support a rich bat community, ongoing development of these habitats is likely to negatively impact on insectivorous bat species. Degradation has led to a disruption of food webs at coastal lagoons likely as a result of past contamination events rather than current contamination level. 

 

 

 

 

 

 

 

 

 

 

 

Key Findings

  • The present study found that the quality of coastal lagoons was strongly linked to the amount of insectivorous bat activity. As these lagoons declined in quality, there was a marked reduction in insectivorous bat activity. Insectivorous bats were 19 times more active at undisturbed lagoons than their degraded counterparts. Coupled with this degraded lagoons did not support the full assemblage of species found at the higher quality lagoons
  • Despite the lack of contrast in trophic area in this study there were significant shifts in the ranges of δ15N and δ13C across lagoon quality. A wider than expected δ15N range and δ13C at degraded lagoons may be due to nitrogen enrichment in polluted areasand confounding effects of relative δ13C enrichment of marine sources that enter into the coastal lagoon from the saltwater inlet.
  • Zn, Cu and Pb were detected at higher concentrations in sediments and invertebrate communities from highly degraded lagoons and these concentrations were at environmentally significant levels. Moderately degraded coastal lagoons also exhibited environmentally significant concentrations of these contaminants, despite being less concentrated than the highly degraded sites.
  • Due to a highly specialised feeding ecology, M. macropus has a distribution restricted to coastal regions and inland rivers. The present study has identified a threshold below which M. macropus appears to be excluded from coastal lagoons. Degraded lagoons below this threshold are characterised by high proportions of cleared land and high human population densities.

 
Publications
In Preparation 
 
Collaborators, partners and sponsors

 

Research Program: 
Aquatic Species Ecology
Research Themes: 
Rivers and Wetlands

Publications for this project

Author Date Title Description PDF
Clarke-Wood et al. 2016 The ecological response of insectivorous bats to coastal lagoon degradation

Coastal lagoons provide key habitat for a wide range of biota but are often degraded by intense urbanization pressures. Insectivorous bats use these highly productive ecosystems and are likely to be impacted by their decline in quality. We compared bat activity and richness and invertebrate biomass and richness across a gradient of lagoon quality (9 lagoons) in the Greater Sydney region, Australia to determine the extent to which bats and their prey were impacted by lagoon degradation. Bats were more diverse and 19 times more active at higher quality lagoons. The trawling bat, Myotis macropus, was absent from all low quality lagoons, but these lagoons were used by other species such as Miniopterus schreibersii oceanensis. Invertebrate richness and biomass did not differ significantly across lagoon quality. We examined potential mechanisms of insectivorous bat decline at degraded lagoons by measuring toxic metal concentrations in bat fur, invertebrates and sediment. Lead and zinc were detected at environmentally significant levels in the sediments of lower quality lagoons. Furthermore, lead concentrations were 6 times the lowest observable adverse effects level for small mammals in the hair of one individual M. macropus. The present study demonstrates that coastal lagoons support a rich bat community, but ongoing development and pollution of these habitats is likely to negatively impact on insectivorous bat species, especially trawling species.

Online: http://www.sciencedirect.com/science/article/pii/S0006320716303172

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