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Note: Session titles beginning with an asterisk (*) have student presenters.
AUTHORS: Clay Stroud, Louisiana State University; Kevin Ringelman, Louisiana State University; Michael Poirrier, University of New Orleans; Claire Walker, University of New Orleans
ABSTRACT: Lake Pontchartrain provides wintering habitat for a continentally-significant proportion of Lesser Scaup (Aythya affinis), though surveys indicate dramatic variation in annual abundance (221–1,194,907). Previous studies indicate that scaup feed primarily on mollusks, and so changes in the benthic community, in response to hurricanes, droughts, and spillway openings, could potentially create a lagged bottom-up trophic cascade that ultimately affects scaup populations. To diagnose trophic linkages and variation in scaup abundance, we collected ducks (n=60) and paired benthic samples from the field to evaluate diet preferences, and then analyzed pre-existing long-term datasets on scaup and benthic populations. The most commonly consumed prey species was Rangia cuneata, accounting for 42.54% of all food items. Compared to 2004 (255 individuals/m2), R. cuneata practically disappeared from the lake in the winter of 2005 due to Hurricane Katrina (31 individuals/m2), but rebounded to above pre-Katrina levels (384 individuals/m2) the following year. Likewise, there were less than 500 scaup estimated in 2005, but over 800,000 birds the following winter. Droughts and spillway openings produced similar patterns of immediate decline in R. cuneata and scaup abundances with increased populations the following year. These disturbances appear to reset the size-class succession of benthic invertebrates; the intervening periods were characterized by an increasing abundance of larger bivalves, and accordingly fewer scaup. Scaup populations on Lake Pontchartrain appear to be closely linked to R. cuneata populations. Our results provide valuable information on trophic linkages in an estuarine system that is particularly prone to increasingly frequent disturbance events predicted with climate change.
Monday October 30, 2017 2:00pm - 2:20pm EDT
Carroll Ford