“Myotis macropus” by Michael Pennay is licensed under CC BY-NC-ND 2.0
Although the coast is an extremely popular place to live, commercial development is causing a ghoulish decline in bat inhabitants. While coastal areas account for only 4% of the land on earth, 60% of the global population lives along the coast (UNEP/UN, 2006; Bellio and Kinsford, 2013). The coastal ecosystems are frighteningly disrupted as commercial development continues in these areas, and fewer bats are haunting the coast as a result. Is there a reason to be concerned with these changes?
The degradation of coastal lagoons causes a decrease in activity and species richness of bats in Australia. Many insectivorous bats live in the coastal lagoons in Australia. As development of these areas increases, so do threats to the bat species living there. To many people, bats are creepy blood sucking monsters, closely associated with Halloween. In reality, bats are an important part of ecosystems and benefit us in ways you may not realize. The presence of unhealthy bat populations is an ecological indicator of problems in the entire ecosystem. Bats serve important roles in ecosystems by pollinating plants, consuming significant numbers of insects including many agricultural pests, dispersing seeds for ecologically important plants, and guano (bat poop!) provides rich, natural fertilizer (“Why Bats Matter”).
In a recent study published in Biological Conservation, Dr. Bradley Clarke-Wood and colleagues of the University of New South Wales investigated the difference in insectivorous bat species richness and bat activity in nine coastal lagoons around Sydney, Australia (Clarke-Wood et. al., 2016). Using Anabat detectors, the researchers recorded bat calls to determine the amount of activity and species richness of bats in low, moderate, and high quality lagoons. The lagoons sampled were classified as high, moderate, or low quality based on the water quality, amount of habitat destruction, and human population living in the area (Clarke-Wood et. al., 2016).
When exploring the lagoons of coastal Australia, you might run into one of the sixteen total species that the research team identified over the course of the study. Of the sixteen species, 7-8 species were found on any given night of sampling in high and moderate quality lagoons while only two species were found in low quality lagoons. Eight were not found in any low-quality lagoons and only three were found in every one of the lagoons sampled. The researchers recorded bat calls and used the number of bat calls recorded to measure bat activity. They also used the number of species found to determine the “species richness.” Not surprisingly, they found both activity and richness to be directly related to the quality of the lagoon sampled. In fact, the “total activity was on average 19 times higher in high quality than low quality and seven times higher in high quality than moderate quality lagoons” (Clarke-Wood et. al., 2016). This result shows clearly that the quality of the lagoons affects the species present (Clarke-Wood et. al., 2016). The most likely explanation for the decrease in bat richness is a decrease in roosting places (i.e. trees are being cut down) and poor water quality (Clarke-Wood et. al., 2016).
The study also tested the lagoon sediments for metals that result from urbanization and pollution. Scientists are worried that these metals could make the bats sick and be another source of terror for the populations. The low-quality lagoons had the highest concentrations of eight of the nine metals found. Some of these metals were also detected in aquatic invertebrates and bat hair.
Bradley Clarke-Wood stated that “when coastal systems are urbanized, habitat quality for biota declines because of loss and alteration of native vegetation, eutrophication and poor water quality” and that “this decline changes community dynamics of both vertebrates and invertebrates as well as the community health and biodiversity.” This means that without necessarily intending to, we are hurting important species and ecosystems in many ways.
On the other hand, the study did note that there was no significant difference between the invertebrate richness and biomass, or total mass of all invertebrates living there, between different lagoon qualities. This means that invertebrates seem to be uninterrupted by coastal development. In addition, the level of pollutants detected in bat fur was the same across all of the lagoons. Because the invertebrates (which the bats eat) are not affected and pollutants are not directly affecting the bats, some people might argue that coastal urbanization is not affecting bat populations. However, the authors note that the focus of their study was on bats, not invertebrates and they did not have a large sample size of invertebrates. If they had, lagoon quality may have been shown to affect invertebrates as it had in other studies. Bats also go through seasonal moulting, or shedding, which could explain the lack of pollutants in their fur. Despite these findings, the results of the study are clear, bats are very much affected by the quality of lagoons.
Jones and colleagues point out that insectivorous bats can be “considered indicators of wider ecosystem health” based on their sensitivity to urbanization “at the species and community level” (Jones et. al. 2009). The decrease in bat richness could therefore indicate poor ecosystem health due to urbanization of coastal lagoons. Not only are bats at risk, but other animals and plants can also be in danger due to loss and disruption of habitat. Loosing insectivorous bats means that we are losing an important means of pest control, seed dispersal and plant pollination. Part of the appeal of coastal life is the wildlife that accompanies it. Would these places really be so spectacular if we lose a vital member of the ecosystem? These changes cannot be tolerated.
Consideration must be given to the ecologic implications of increased urbanization and development along coastal regions. Greater urbanization does not correlate to improved diversity of the environment, nor can the ecologic status quo be maintained with increased commercial development. Are these consequences important? While fewer bats may be haunting coastal regions, we cannot afford to annihilate entire ecosystems just to enhance the enjoyment of coastal vacationers.
Bellio, M., Kingsford, R.T., “Alteration of Wetland Hydrology in Coastal Lagoons: Implications for Shorebird Conservation and Wetland Restoration at a Ramsar Site in Sri Lanka.” Biological Conservation 167 (2013): 57-68.
Clarke-Wood, Bradley K., Jenkins, Kim M., Law, Brad S., Blakey, Rachel V. “The Ecological Response of Insectivorous Bats to Coastal Lagoon Degradation.” Biological Conservation 202 (2016): 10-19. Web. http://www.sciencedirect.com/science/article/pii/S0006320716303172
Jones, G., Jacobs, D.S.,Kunz, T.H., Willig, M.R., Racey, P.A., “Carpe noctem: The Importance of Bats as Bioindicators.” Endanger. Species Res. 8 (2009): 93-115. Web.
UNEP/UN, “Marine and Coastal Ecosystems and Human Well-Being.” WWW Document. http://www.unep.org/pdf/completev6_LR.pdf
“Why Bats Matter.” (n.d.). Retrieved September 6, 2016, from http://www.bats.org.uk/pages/why_bats_matter.html