Silent spring revisited: Insects and spiders in Louisiana’s saltwater marshes after the Macondo blowout

The sounds of a healthy salt marsh community include buzzes, clicks, chirps, and splashes. Healthy ecosystems can handle small disturbances or stressors such as small pulses of oil from deep seeps in the Gulf of Mexico (GOM). Stressed ecosystems such as the saltwater marshes that fringe the northern GOM experienced a huge pulse of additional disturbance as a result of escaping oil from the Macondo blowout on April 20, 2010 and the subsequent cleanup efforts. We studied the effect of crude-water emulsion on the insects and spiders in saltwater marshes and compared them to the same taxa in unaffected marshes. We also compared insect and spider species richness and abundance from May 2010 – before the emulsion made landfall – to those species collected in May 2011. In most areas, we sampled for insects, spiders, and hydrocarbons not only on the edge – where we could visibly see oil – but also 20m deep into the marsh. Selected paired sites – oiled and unoiled – were sampled 100m into the marsh in 2011. All sampling had contemporaneous unoiled controls and comparable samples before the emulsion made landfall. Our sweep-net collections showed decreases in abundance of native katydids, ants, green seedbugs, and spiders in response to the intrusion of crude-water emulsion into the marsh and to the subsequent efforts to remediate it. Conversely, cordgrass bugs increased 10x in oiled saltwater marshes compared with unoiled marshes. This may provide indirect evidence of plant stress in response to a large-pulse oiling event. Our results and observations indicate widespread ‘silencing’ of insect and spider activity in Louisiana saltwater marshes affected by the BP Macondo blowout.