Bottom-up effects of mangrove encroachment on basal consumers in the Gulf of Mexico

Coastal wetlands are complex ecosystems that are shaped by the interaction of multiple environmental factors. As human activities alter the climate however, the structure of wetlands is changing. One such shift is occurring throughout the Gulf of Mexico where mangrove trees are encroaching into salt marshes as a result of climatic drivers including sea level rise and decreased frequency of winter freeze events. Along the Gulf Coast of Texas, black mangroves (Avicennia germinans), the primary encroaching species, are increasing in abundance and displacing salt marsh plants. The marsh plants being replaced are the primary food sources for many consumers at the base of salt marsh food webs, including fiddler crabs (Uca spp.) and marsh periwinkle snails (Littoraria irrorata). My research aimed to determine how these basal consumers respond to this shift in plant communities and the disappearance of their primary food sources. Through surveys and stable isotope analyses, I identified shifts in the distribution and diet of basal consumers in mangrove encroached marshes. Basal consumers in encroached wetlands were physically associated with mangrove structures but did not consume mangrove-derived plant matter. Lab mesocosm studies examined the trophic interactions of Uca and Littoraria with Avicennia in more detail through food preference and food quality experiments. I found that Avicennia was both an unpreferred and poor-quality food source that lowered the body condition of consumers to which it was fed. Field-collected consumers from mangrove encroached sites also had lower body conditions. Consumers at mangrove encroached sites replaced the marsh plants in their diet with fine organic matter, suggesting that either fine organic matter is less nutritive than marsh plants, or the presence of mangroves has negative non-consumptive effects on basal consumers. This research indicates that mangrove trees are not equivalent to the marsh plants they are replacing and that their encroachment has negative trophic effects on basal consumers. These results have important implications for managing coastal wetland ecosystem functions such as nursery habitat and fisheries support and evaluating the restoration uses of mangroves

Coastal woody encroachment reduces food quality for basal consumers

Abstract Woody plant encroachment (the replacement of grasses and forbs by woody shrubs and trees) is reshaping communities in both terrestrial and coastal environments, but little is known about its effects on basal consumers. We used interactions between fiddler crabs (Uca spp.) and the encroaching mangrove Avicennia germinans in Gulf of Mexico salt marshes to explore trophic interactions between basal consumers and encroaching shrubs. In a series of food preference trials, fiddler crabs consumed over five times more marsh (Spartina alterniflora) plant matter when given a choice between mangrove and marsh diets. In food quality trials, fiddler crabs stored 50% less energy, as measured by hepatopancreas lipid content, when restricted to a mangrove diet. These results demonstrate that mangrove encroachment may have negative consequences for salt marsh basal consumers, which may lead to deleterious population‐level effects and altered ecosystem carbon flows. As fiddler crabs are generalist consumers and mangroves share many physical and chemical characteristics with other encroaching woody species, negative consequences for basal consumers may be widespread in other environments undergoing woody shrub encroachment

A sea anemone of many names: a review of the taxonomy and distribution of the invasive actiniarian Diadumene lineata (Diadumenidae), with records of its reappearance on the Texas coast

Volume: 706Start Page: 1End Page: 1

Figure 6 from: Hancock ZB, Goeke JA, Wicksten MK (2017) A sea anemone of many names: a review of the taxonomy and distribution of the invasive actiniarian Diadumene lineata (Diadumenidae), with records of its reappearance on the Texas coast. ZooKeys 706: 1-15. https://doi.org/10.3897/zookeys.706.19848

Diadumene lineata (Actiniaria: Diadumenidae) is a prolific invader of coastal environments around the world. First described from Asia, this sea anemone has only been reported once from the western Gulf of Mexico at Port Aransas, Texas. No subsequent sampling has located this species at this locality. The first record of the reappearance of D. lineata on the Texas coast from three locations in the Galveston Bay area is provided, and its geographic distribution and taxonomic history reviewed

Human actions alter tidal marsh seascapes and the provision of ecosystem services

Tidal marshes are a key component of coastal seascape mosaics that support a suite of socially and economically valuable ecosystem services, including recreational opportunities (e.g., fishing, birdwatching), habitat for fisheries species, improved water quality, and shoreline protection. The capacity for tidal marshes to support these services is, however, threatened by increasingly widespread human impacts that reduce the extent and condition of tidal marshes across multiple spatial scales and that vary substantially through time. Climate change causes species redistribution at continental scales, changes in weather patterns (e.g., rainfall), and a worsening of the effect of coastal squeeze through sea level rise. Simultaneously, the effects of urbanization such as habitat loss, eutrophication, fishing, and the spread of invasive species interact with each other, and with climate change, to fundamentally change the structure and functioning of tidal marshes and their food webs. These changes affect tidal marshes at local scales through changes in plant community composition, complexity, and condition and at regional scales through changes in habitat extent, configuration, and connectivity. However, research into the full effects of these multi-scaled, interactive stressors on ecosystem service provision in tidal marshes is in its infancy and is somewhat geographically restricted. This hinders our capacity to quickly and effectively curb loss and degradation of both tidal marshes and the services they deliver with targeted management actions. We highlight ten priority research questions seeking to quantify the consequences and scales of human impacts on tidal marshes that should be answered to improve management and restoration plans