Long‐term spatial dynamics in vegetated seascapes: fragmentation and habitat loss in a human‐impacted subtropical lagoon

Abstract

Vegetated coastal seascapes exhibit dynamic spatial patterning, some of which is directly linked to human coastal activities. Human activities (e.g. coastal development) have modified freshwater flow to marine environments, resulting in significant changes to submerged aquatic vegetation (SAV) communities. Yet, very little is known about the spatially complex process of SAV habitat loss and fragmentation that affects ecosystem function. Using habitat mapping from aerial photography spanning 71 years for Biscayne Bay (Florida, USA), we quantify both SAV habitat loss and fragmentation using a novel fragmentation index. To understand the influence of water management practices on SAV seascapes, habitat loss and fragmentation were compared between nearshore and offshore locations, as well as locations adjacent to and distant from canals that transport freshwater into the marine environment. Habitat loss and fragmentation were significantly higher along the shoreline compared with offshore seascapes. Nearshore habitats experienced a net loss of 3.31% of the total SAV mapped (2.57 km 2 ) over the time series. While areas adjacent to canals had significantly higher SAV cover, they still experienced wide fluctuations in cover and fragmentation over time. All sites exhibited higher fragmentation in 2009 compared with 1938, with four sites exhibiting high fragmentation levels between the 1990s and 2000s. We demonstrate that freshwater inputs into coastal bays modify the amount of SAV and the fragmentation dynamics of SAV habitats. Spatial changes are greater close to shore and canals, indicating that these coastal developments have transformative impacts on vegetated habitats, with undetermined consequences for the provisioning of ecosystem goods and services.

Pink ShrimpFarfantepenaeus duorarumSpatiotemporal Abundance Trends Along an Urban, Subtropical Shoreline Slated for Restoration

“…Associations between nearshore pink shrimp abundance and depth have been previously reported [75,80,94,95]. Other studies that focused on very nearshore areas (<100 m) also found higher abundances there [8–10,12,96]. Recruiting postlarval pink shrimp often concentrate in SAV near the low-tide mark along shorelines [9,12,97–102].…”

“…The seemingly weak statistical relationships with either total or species-specific SAV metrics was unexpected. Pink shrimp associations with H. wrightii have been previously reported [12,96,97,106], while other studies have reported maximal pink shrimp densities relative to total SAV biomass or % cover [10,107,108]. Although one study reports negative impacts of drift and attached algal biomass [109], the positive relationships reported by most studies suggested a stronger relationship between pink shrimp density and either species-specific or total SAV would be readily observed.…”

“…Indirectly, reduced stress on seagrass communities from extreme salinity fluctuations would yield increased pink shrimp abundance due to increased seagrass cover and spatial extent [5,8]. Higher abundance of pink shrimp has been reported in areas exhibiting higher and more stable salinities [8–10]; these same coastline stretches exhibit more continuous seagrass cover [11]. Areal expansion of shoal grass ( Halodule wrightii ) cover could further amplify pink shrimp abundance due to an apparent affinity for this seagrass species [12].…”

Resilience indicators support valuation of estuarine ecosystem restoration under climate change

“…, Santos et al. ). Therefore, nutrient and sediment loading rates, to a great extent, determine bed resilience to multiple stressors.…”

“…High nutrient loads limit the light available for photosynthesis, which decreases available energy stores and makes plants more susceptible to dying during light-limiting disturbances such as turbidity pulses during storm events (Moore et al 1997, Longstaff and Dennison 1999, Yaakub et al 2014. Under these conditions, SAV cover becomes increasingly fragmented, reducing the capacity for feedbacks that enhance habitat conditions (Montefalcone et al 2010, Santos et al 2016). Therefore, nutrient and sediment loading rates, to a great extent, determine bed resilience to multiple stressors.…”