Latest findings

Below are recent abstracts from our research lab. These talks were presented at the Coastal and Estuarine Research Federation 2011 meeting.

Metapopulation dynamics in estuarine habitat restoration: Do reference areas act as source populations?

Anna R. Armitage, Michael T. Bell, Chuan-Kai Ho, Eric N. Madrid, Antonietta S. Quigg

Consideration of metapopulation dynamics in habitat restoration can help to identify suitable source populations to supply restored areas. Metapopulation theory stipulates that source populations will have positive intrinsic growth rates; therefore, we predicted that aquatic faunal populations in reference (source) areas would have higher intrinsic growth rates than in restored (sink) areas. Second, a metapopulation exists if patches of habitat are connected and are suitable for colonization; therefore we predicted that organisms would disperse to and colonize restored areas where the habitat was suitable. To test these hypotheses, we monitored habitat characteristics and densities of three common aquatic species (sailfin molly Poecilia latipinna; rainwater killifish Lucania parva; grass shrimp Palaemonetes pugio) in three patches of recently restored brackish marsh and one reference area in the northwestern Gulf of Mexico from 2008 to 2010. All habitat patches were connected by a network of permanently inundated channels. Faunal densities were constant over time in the reference area but increased in most of the restored areas. This suggests either that (a) the reference area served as a source population that supplied the restored areas with recruits, or (b) the intrinsic growth rate was higher in restored than in reference areas. We used principal components analysis to define threshold suitability values for key habitat characteristics. Only Poecilia density was significantly related to habitat characteristics in the reference site, but Poecilia densities were not higher in restored areas with ideal habitat features than in unsuitable restored areas. Therefore, habitat suitability did not appear to be the primary driver influencing faunal colonization of restored habitat. Our results suggest that metapopulation dynamics were not strongly influencing restored site colonization at this spatial scale. 

Does ecotypic-based genetic diversity of a dominant plant impact ecosystem health and stability? A case study in a restored Spartina alterniflora marsh

Courtney T. Lee and Anna R. Armitage

Increased genetic diversity of habitat-forming species correlates with increased faunal diversity and enhances ecosystem resiliency to and recovery from disturbances. Genetic diversity at the species level may be just as important as species diversity for the long term health and stability of ecosystems. To identify the benefits of increased genetic diversity within a single plant species, I performed a common garden experiment in a constructed salt marsh in Galveston Bay, Texas. The nutrient acquisition patterns and productivity of genetically distinct Spartina alterniflora populations (ecotypes) in monoculture plots (single population) were compared to polyculture plots (two or three populations). Early trends suggest that polyculture treatments have more live plant material and increased shoot production a month after transplanting. I also examined interactions between increased genetic diversity of S. alterniflora and its colonizing insect and spider communities. At this early development stage of the restored marsh, few of these arthropods have colonized the study plots, but faunal response to plant genetic diversity may strengthen over time as the plant community develops. In an effort to maintain diverse community assemblages and ecosystem stability, increased genetic diversity of a dominant primary producer may be an important consideration. 

These projects were supported by grants from the Texas General Land Office Oil Spill Response Division and the GLO Coastal Management Program