Acute Disturbance of Lake Pontchartrain Benthic Communities by Hurricane Katrina

Abstract

In 2005, Hurricane Katrina produced a distinct, acute ecological disturbance of the benthic invertebrate community of Lake Pontchartrain, LA, USA. The bivalve Rangia cuneata and other community dominants were lost from 50% (815 km 2 ) of the lake bottom. The storm surge directly killed benthic organisms and produced salinity stratification that caused episodes of detrimental low dissolved oxygen concentration at depths >3.7 m. Past disturbance of the bottom by shell dredging and intrusion of higher salinity bottom water through deep shipping channels appears to have contributed to the severity of this impact. Colonization by tolerant opportunistic taxa occurred, but low rainfall after Katrina has slowed the recovery of the typical rangia community. A decrease in water transparency and an increase in turbidity and chlorophyll a were associated with the loss of clam biomass. Other hurricanes may have produced less obvious but similar effects on smaller spatial and temporal scales.

Rangia cuneata clam decline in Lake Pontchartrain from 2001 to 2014 due to an El Niño Southern Oscillation shift coupled with a period of high hurricane intensity and frequency

“…The decrease in clam density during the hurricane years, 2005, 2008 and 2012 indicated distinct hurricane effects. These effects are supported by previous studies of benthic invertebrate impacts from Katrina and Rita (Poirrier et al 2008, Engle et al 2009) and Ike and Gustav (Ray 2009). We found that density changes in 6-20 mm clams accounted for most of the differences.…”

“…Anthropogenic climate change may have also directly increased hurricane intensity (Burkett 2008). Severe hurricane surges can have a direct lethal effect on benthic invertebrates (Poirrier et al 2008): they disturb sediments, which bury clams, abruptly increase salinity, and produce water column stratification with anoxic and hypoxic bottom water .…”

“…A severe disturbance should be expected when a 3.7-4.9 m storm surge, such as the one that occurred during Katrina, enters a soft-bottomed estuary with a mean depth of 3.7 m. Damage and burial from storm surges were important factors in R. cuneata clam decline. Poirrier et al (2008) found recently dead and dying R. cuneata after Katrina. After Isaac, articulated shells with non-weathered periostraca from dead R. cuneata clams were common in sediment samples ).…”

Temporal and Spatial Variability in Culturable Pathogenic Vibrio spp. in Lake Pontchartrain, Louisiana, following Hurricanes Katrina and Rita

“…We cannot resolve such acute effects with our limited data, but could the hurricanes have had longer-lasting effects on vibrio abundance? One significant effect of the storms was on the benthic communities, which showed declines in abundance and diversity as a result of scouring and changes in bottom water chemistry (20,57). We found that vibrio abundance was correlated with turbidity, and an increase in the turbidity of the lake appears to be correlated with the loss of the community services of benthic filter feeders, such as the clam Rangia cuneata (57).…”

“…One significant effect of the storms was on the benthic communities, which showed declines in abundance and diversity as a result of scouring and changes in bottom water chemistry (20,57). We found that vibrio abundance was correlated with turbidity, and an increase in the turbidity of the lake appears to be correlated with the loss of the community services of benthic filter feeders, such as the clam Rangia cuneata (57). Given the known association of vibrios with particles and plankton and the enrichment of vibrios in filter-feeding bivalves, it seems possible that the dramatic hurricane-related losses of filter feeders in this shallow estuarine lake could have led indirectly to a chronic increase in pathogenic vibrios in the plankton.…”