Research

Linking community and food-web approaches to restoration: An ecological assessment of created and natural marshes influenced by river diversions

Coastal land loss in Louisiana has claimed more than 4,800 km2 since the 1930s. Without preventative action, an additional 4,500 km2 of land will disappear in the next 50 years. Restoration efforts have included modifying hydrologic patterns and construction of tidal marshes and river diversions to reconnect the Mississippi River to adjacent estuaries. While these restoration efforts have shown promise for reducing land loss, little is known about their impacts on the composition of the plants and animals in a coastal marsh and their food web structure. This research is funded by the NOAA Restore Science Program and seeks to expand knowledge of the effects of river diversions on natural versus created marshes in Louisiana. We are determining species composition, abundances, and food web structure in natural marshes along varying levels of salinity that result from a river diversion. We are also examining species composition, abundances, and food web structure in created marshes that differ in age influenced by this same river diversion. Finally, the data collected from the marshes will be incorporated into an ecosystem model to predict the impact of salinity changes and habitat restoration efforts on marsh food web structure, function, and resilience. This project will increase understanding of how river diversions impact the marsh food webs and provide the means for predicting how certain types of restoration will impact the species living in a marsh. This project will consider the majority of components in marsh food webs and make it possible for managers to take an end-to-end ecosystem perspective when making management decisions. More information can be found at our project website: https://restorefoodweb.lumcon.edu/

Trophic Ecology and Paleohistory of Antarctic Krill Predators

A key species in the Antarctic marine ecosystem is Antarctic krill, which in addition to being commercially harvested, is the principle prey of a wide range of marine organisms including penguins, seals and whales. The aim of this study is to use penguins and other krill predators as sensitive indicators of the Antarctic marine food web. Specifically this study will recover and analyze modern (<20 year old), historic (20-200 year old) and ancient (200-10,000 year old) penguin and other krill predator tissues to track their past diets and population movements relative to shifts in climate and the availability of Antarctic krill. This will be achieved by coupling advanced stable and radio isotope techniques, particularly compound-specific stable isotope analysis, with unprecedented access to modern, historical, and well-preserved paleo-archives of Antarctic predator tissues dating throughout the Holocene. This NSF funded research will help place recent ecological changes in the Southern Ocean into a larger historical context by examining decadal and millennial-scale shifts in the diets and population movements of Antarctic krill predators. Understanding how krill predators were affected by these factors in the past will allow us to better understand how these predators, the krill they depend on, and the Antarctic marine ecosystem as a whole will respond to current challenges such as global climate change and an expanding commercial fishery for Antarctic krill.

Mangrove Ecosystem Services and Fisheries in Coastal Tanzania

More than 35% of coastal mangrove areas worldwide have been degraded or lost entirely in the past 20 years. This NSF funded research seeks to understanding the relationship between mangrove ecosystem services and mechanisms that cause poverty to persist in low income coastal communities in Tanzania. Working with a larger group of both natural and social scientists, we are using bulk and compound-specific stable isotope analysis determine: 1) the relative use of mangroves habitats and carbon derived from mangroves versus other estuarine and near-shore habitats by adult fish and crustaceans targeted by subsistence and commercial fishers, and 2) the ontogenetic movements and use of mangrove habitats by juvenile fish that are subsequently targeted by subsistence and commercial fishers when they move outside of mangrove habitats as adults. Our results will be integrated into larger studies of ecosystem services to help inform mangrove policies that benefit communities facing climate change and coastal habitat loss.

Impact of the Deep Water Horizon Oil Spill on Coastal Food Webs

We are using compound-specific stable isotopic analysis of amino acids to assess how trophic structure and carbon flow in marsh food-webs were impacted by the Deep Water Horizon oil spill. Using archived and newly collected samples we are comparing trophic structure and primary producer contributions to marine and terrestrial food-webs in oiled and unoiled marshes to understand how these ecosystems respond during the recovery process. This work is part of a multi-institution team of researchers on the Coastal Waters Consortium (CWC) project funded by the Gulf of Mexico Research Initiative. It complements CWC organismal level studies on invertebrate, fish, birds, mammals and will aid in the interpretation of large-scale marsh mesocosms experiments conducted by CWC researchers.

Expansion of Black Mangroves and Marsh Food Webs in Coastal Louisiana

Climate change, winter warming and drought conditions in coastal Louisiana are projected to increase the spread of tropical black mangroves (Avicennia germinans) into salt marshes (Spartina alterniflora). In addition, recent coastal restoration efforts in Louisiana’s marshes have promoted and used the planting of black mangroves as a method of trapping sediments to reduce coastal erosion. This research is funded by Louisiana Sea Grant and examines how shifts from saltmarsh grasses to mangrove dominated systems in Louisiana will influence the abundance of juvenile nekton and carbon flow through marsh food-webs. We are conducting field surveys using drop traps, suction sampling and net collection to examine the abundance and species composition of marsh and mangrove-associated fish and invertebrates. In addition we are using isotopic approaches to quantify the relative importance of primary production sources (e.g. marsh grass, mangrove, microalgae, etc.) to these marsh consumers. This will help determine how climate-driven changes in the carbon sources influence trophic dynamics in Louisiana’s productive estuaries that support Louisiana’s commercially and recreationally valuable fisheries.

Trophic Ecology of an Expanding New England Gray Seal Population

While considered locally extinct in the U.S. prior to 1958, gray seals (Halichoerus grypus) populations have recovered substantially since then along the Gulf of Maine and New England coast. The growing population of seals has lead to concerns in coastal communities about interactions between seals and commercial and recreational fisheries. This project aims to aid in our understanding of the diets and ecological role of gray seals in the Gulf of Maine and New England coast. Working with NOAA and Duke University we are using stable isotope analysis to provide a better understanding of the diets and movements of gray seals. This will help us to understand their predation pressure on commercially important fish stocks and develop research, conservation and management strategies that benefit both seals and fisheries in collaboration with scientists, natural resource managers and the fishing community members of the Northwest Atlantic Seal Research Consortium.

Impact of Invasive Mice on California Seabird Islands

As part of a collaborative project with Point Blue Conservation Science we are using stable isotopes to examine the direct and indirect impacts of non-native house mice on the seabird and terrestrial communities of the Farallon Islands. This approach has allowed us to track seasonal variation in the direct impact of mice on seabirds as well as the island’s endemic salamander and insect populations. When combined with stomach content and pellet analyses, it appears that the major impact of mice on seabirds may relate to the facilitated predation by migratory Burrowing owls, which feed on mice when they are abundant but switch to sensitive seabird species like the Ashy-storm petrel when mice populations seasonally decline. In addition, preliminary results suggest that mice directly impact native plants and insects by direct predation and indirectly impact endemic salamanders via competition. These ongoing studies are helping to inform U.S. Fish and Wildlife Service policy as it develops and seeks approval for a mouse eradication program.