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  1. Seagrass beds in Florida Bay are home to many ecologically and economically important species. Anthropogenic press perturbation via alterations in hydrology and pulse perturbations such as drought can lead to hypersalinity, hypoxia, and sulfide toxicity, ultimately causing seagrass die-offs. Florida Bay has undergone two large-scale seagrass die-offs, the first in the late 1980s and early 1990s and the second in 2015. Post-die-off events, samples were collected for stable isotope analysis. Using historical (1998–1999) and contemporary (2018) stable isotope data, we examine how food webs in Florida Bay have changed in response to seagrass die-off over time by measuring contributions of basal sources to energy usage and using trophic niche analysis to compare niche size and overlap. We examined three consumer species sampled in both time periods (Orthopristis chrysoptera, Lagodon rhomboides, and Eucinostomus gula) in our study. Seagrass production comprised the majority of source usage in both datasets. However, contemporary consumers had a mean increase of 18% seagrass usage and a mean decrease in epiphyte usage of 7%. The shift in trophic niche from epiphyte usage (green pathway) toward seagrass usage (brown pathway) may indicate that food web browning is occurring in Florida Bay. 
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  2. Abstract

    Tropicalization is a phenomenon that is changing the structure of ecosystems around the world. Mangrove encroachment is a particular form of tropicalization that may have cascading consequences for resident fauna in subtropical coastal wetlands. There is a knowledge gap regarding the extent of interactions between basal consumers and mangroves along mangrove range edges and the consequences of these novel interactions for consumers. This study focuses on the key coastal wetland consumers,Littoraria irrorata(marsh periwinkle) andUca rapax(mudflat fiddler crabs), and their interactions with encroachingAvicennia germinans(black mangrove) in the Gulf of Mexico, USA. In food preference assays,Littorariaavoided consumingAvicenniaand selectively ingested leaf tissue from a common marsh grass,Spartina alterniflora(smooth cordgrass), a preference that was also previously documented inUca. The quality ofAvicenniaas a food source was determined by measuring the energy storage of consumers that had interacted with eitherAvicenniaor marsh plants in the lab and the field.LittorariaandUcaboth stored ~10% less energy when interacting withAvicennia, despite their different feeding behaviors and physiologies. The negative consequences of mangrove encroachment for these species at the individual level suggest that there may be negative population‐level effects as encroachment continues. Many studies have documented shifts in floral and faunal communities following mangrove replacement of salt marsh vegetation, but this study is the first to identify physiological responses that may be contributing to these shifts.

     
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