Halodule wrightii and sediment biogeochemistry response to bioturbation

Seagrasses are one of the most productive ecosystems in the world performing important ecological functions and providing nursery habitats for many marine organisms. Seagrass productivity and sustainable growth depend on sediment porewaters as a primary nutrient source. In nutrient-filled conditions, microbial processes taking place within seagrass sediments can provide an additional nutrient source. Nutrient availability, seagrass structure, and beneficial microbes present within vegetated sediments are susceptible to change as sediments become disturbed. Large bioturbators such as stingrays use seagrass nurseries as prime foraging locations. They excavate sediments forming pits both in and outside seagrass beds. We examine how organic matter, porewater nutrients, and microbial presence in H. wrightii beds in the Pensacola Bay System are impacted by stingray bioturbation. As rhizomes, roots, and sediments are excavated or exposed, we anticipated that ray pits would have lower nutrient concentrations than the surrounding bed. However, preliminary results have shown higher NH₄⁺ concentrations in ray pits than surrounding seagrass beds. Future sampling will examine seasonal difference between the ray pits and surrounding bed.
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Abstract/Description: Seagrasses are one of the most productive ecosystems in the world performing important ecological functions and providing nursery habitats for many marine organisms. Seagrass productivity and sustainable growth depend on sediment porewaters as a primary nutrient source. In nutrient-filled conditions, microbial processes taking place within seagrass sediments can provide an additional nutrient source. Nutrient availability, seagrass structure, and beneficial microbes present within vegetated sediments are susceptible to change as sediments become disturbed. Large bioturbators such as stingrays use seagrass nurseries as prime foraging locations. They excavate sediments forming pits both in and outside seagrass beds. We examine how organic matter, porewater nutrients, and microbial presence in H. wrightii beds in the Pensacola Bay System are impacted by stingray bioturbation. As rhizomes, roots, and sediments are excavated or exposed, we anticipated that ray pits would have lower nutrient concentrations than the surrounding bed. However, preliminary results have shown higher NH₄⁺ concentrations in ray pits than surrounding seagrass beds. Future sampling will examine seasonal difference between the ray pits and surrounding bed.
Subject(s): Sediments