Biotic Recovery Following Ice-Rafting in a Salt Marsh

Abstract

Salt marshes provide critical ecosystem services and functions including habitat provision and coastal community protection from storms. Chronic disturbances (e.g., anthropogenic inputs, climate change) and episodic disturbances (e.g., storms, oil spills) can affect the species composition and abundances of salt marsh biota, thus influencing ecosystem function and service provision. One such disturbance typical of the northeastern USA is annual nor'easter storms which deposit ice-rafted sediments on the salt marsh surface. In the winter of 2018, however, the extratropical cyclone, winter storm Grayson, deposited sediments equivalent to 15 years of accumulation on portions of the Great Marsh in Ipswich, Massachusetts, USA, potentially causing historic impacts. The recovery of the plant and invertebrate communities were evaluated 3 months, 6 months, and 18 months post ice-rafting from winter storm Grayson. We hypothesized sediment deposits would smother underlying plants, surface-dwelling invertebrates (i.e., epifauna), and surface-feeding infauna, such as polychaetes, although we expected little to no impact to subsurface-feeding infauna, such as oligochaetes. As predicted, plant, epifauna, and surface-feeding infauna were all impacted initially by sediment deposition, with lower abundances in deposits than in references, whereas subsurface-feeding infauna were unaffected. Despite historic volumes of sediment deposited by winter storm Grayson, we saw full recovery of the biotic community within 18 months. Sediment deposits had a maximum thickness of 6.5 cm and were patchily distributed throughout the marsh, and quick revegetation and invertebrate recolonization may ultimately have been from nearby, undisturbed areas. The fast recovery of the biotic community suggests minimal impacts to ecosystem services and functions and indicates an overarching resilience of the salt marsh to natural disturbances such as nor'easters.

Resource availability and plant age drive defense against herbivory in salt marshes

“…Littoraria snails used in the feeding assays had an average height of 22.9 ± 1.1 mm and an average width of 17.8 ± 1.0 mm (Wittyngham 2022). Littoraria consumption of Spartina was not affected by treatment (herbivory only: p = 0.414; nutrients only: p = 0.101; herbivory plus nutrients: p = 0.691; Fig.…”

“…This stem density (~ 144 stems per m 2 ) was slightly less than average stem densities at this site (~ 208 per m 2 ). At the time of planting, Spartina plants had an average height of 73.8 ± 14.2 cm, stem diameter of 9.9 ± 2.1 mm, and 9 ± 1.5 leaves (Wittyngham 2022) and there were no initial differences in morphometrics by pot or by treatment. A waterproof paint line was added to each stem at the sediment surface so that stem height could be tracked throughout the course of the experiment.…”

“…Data were submitted through the Virginia Coast Reserve (VCR) Long‐Term Ecological Research (LTER) repository and are publicly available from the Environmental Data Initiative: https://doi.org/10.6073/pasta/0b70b4ed9cd773475609eb1a97cec9bd (Wittyngham 2022).…”