Current Research

 

Patterns of juvenile nekton abundance and diversity in brackish water submerged and floating aquatic vegetation

The role of marine submerged aquatic vegetation (seagrass) as essential habitat for juvenile fish and invertebrates is well established. However, the degree to which juvenile fish and invertebrates use brackish water submerged and floating aquatic vegetation as habitat is not fully understood. This work is a collaboration with Tim Carruthers (The Water Institute of the Gulf) and aims to quantify nekton abundance and assess nekton diversity within native and introduced species of submerged and floating aquatic vegetation in coastal Louisiana, where several morphologically distinct species of submerged and floating vegetation co-occur. 


linking blue crab abundance, growth and mortality to marsh fragmentation and submerged aquatic vegetation cover

Despite coastal land loss and landscape fragmentation, the Louisiana coast supports the largest commercial blue crab (Callinectes sapidus) fishery in the Gulf of Mexico, in terms of both landings and wholesale value. However, as marsh continues to fragment and the landscape changes, predicting and managing the blue crab fishery is particularly challenging. Understanding the relationship between marsh fragmentation and blue crab fishery production has been identified as a critical research need throughout the Gulf of Mexico, and in Louisiana, as climate change- and subsidence-induced marsh fragmentation is occurring at an unprecedented rate in this region. This field-based study, which is a collaborative effort with Tim Carruthers (The Water Institute of the Gulf) and Zack Darnell (Nicholls State University), is aimed at understanding the effects of marsh fragmentation and submerged aquatic vegetation cover on abundance, growth and mortality of juvenile and adult blue crabs.


gulf-wide assessment of shoalgrass dormant seed densities

Seagrass propagation can occur asexually through later extension of belowground rhizomes, or sexually, through the production of flowers, fruits and seeds. For individual species, understanding the relative importance of each reproductive mode is necessary for successful management and accurate predictions under future scenarios. Shoalgrass (Halodule wrightii), a sub-tropical seagrass species, is one of the dominant seagrasses in the Gulf of Mexico and provides essential habitat for fish and invertebrates. Shoalgrass produces small (2 mm) seeds that can remain dormant in the sediment for several years before germinating. In a collaboration with Ken Dunton (The University of Texas Marine Science Institute) and Ken Heck (Dauphin Island Sea Lab), we are quantifying shoalgrass dormant seed densities across the Gulf of Mexico. This effort spans Texas to Florida, and preliminary analyses have identified hotspots with high densities of dormant seeds.


reconstructing the reproductive history of turtlegrass along the florida panhandle

Like all seagrass species, turtlegrass (Thalassia testudinum) is capable of both asexual propagation through horizontal rhizome elongation and sexual reproduction. Each flower produced by the plant leaves a distinguishable scar on the plant’s vertical rhizome, allowing for reconstruction of the plant's reproductive history. Further, each leaf produced by the plant results in a scar, and the quantity and relative placement of the distinct leaf and flower scars provides a more complete understanding of plant age and reproductive history. This effort, which is aimed at reconstructing the reproductive history of turtlegrass in distinct meadows across the Florida Panhandle, follows previous work on spatial and temporal variability in seagrass reproductive output and environmental controls to flower production. 


submerged aquatic vegetation as a nutrient bionidicator in the northern gulf of mexico

The Louisiana coast supports a diverse assemblage of submerged aquatic vegetation that span both salinity (freshwater to saltwater) and nutrient (low to high) gradients. Freshwater and brackish water-tolerant submerged plants grow across most of the Louisiana coast, whereas saline-adapted species (seagrasses) are restricted to growing offshore along the Chandeleur Islands. Essential baseline data on plant dynamics, including species-specific nutrient content, are lacking for many of these species, despite the necessity of this information for predicting chance, and the potential for using plant nutrient content as a bioindicator of surrounding nutrient conditions. In a collaboration with Tim Carruthers (The Water Institute of the Gulf), Megan La Peyre (USGS and Louisiana State University), Kristin DeMarco (Louisiana State University) and Eva Hillmann (Louisiana State Univeristy), we are examining patterns in nutrient levels and stable isotope ratios from freshwater and brackish water submerged aquatic vegetation collected in an extensive northern Gulf of Mexico-wide survey in 2014. 

In a separate collaboration with Tim Carruthers, Patrick Biber (The University of Southern Mississippi), Ioannis Georgiou (Univerity of New Orleans), Tommy Michot (University of Louisiana at Lafayette) and Ron Boustany (USDA), we are investigating decadal-scale patterns in nutrient content of seagrasses at the Chandeleur Islands and the linkage between seagrass nutrient content and outflow from the Mississippi River.