Louisiana Sea Grant

Impact of black mangrove expansion in coastal Louisiana

Expansion of black mangroves on trophic dynamics in coastal Louisiana: Implications of climate change and coastal restoration to estuarine fisheries

Duration:
Two years

Other Author(s): Mike Polito (LSU) and Christina Powell (LSU)

The Challenge

With fewer winters experiencing extended periods of freezing temperatures, the black mangrove has been expanding in south Louisiana for the past 20 years. That condition is expected to continue into the future as climate change continues warming winters and producing drought conditions. As black mangroves become more of a presence in Louisiana salt marshes, traditionally dominated by Spartina alterniflora, and as they are used more often as part of coastal restoration strategies, how will this change in vegetation impact food webs, including the fisheries that depend upon the salt marsh ecosystem. 

The Approach

Three plots were selected in the wetlands of south Lafourche near Port Fourchon and Grand Isle representing three habitats – a salt marsh dominated site, a black mangrove dominated site, and then a site that represented an intermixing of the two. Samples were taken from the water’s edge and juvenile organisms (brown shrimp and blue crabs) were collected and analyzed to determine what type of vegetation made up most of their diet. The goal is to find out whether black mangroves are providing the same amount of habitat and food sources as traditional salt marsh environments, or if black mangroves could be a concern if they become too plentiful along the coast and are not contributing to the food sources.