Barbeau, M. A. | bioRxiv Science

bioRxiv2025

Integrating nekton communities, salt pool dynamics, and fish foraging patterns to assess salt marsh restoration success in Maritime Canada

Salt marsh restoration aims to recover areas and ecological functions that have been impacted by human activities. We evaluated different structural and functional metrics to assess the response of nekton to salt marsh restoration in two distinct case studies in Maritime Canada in 2022-2023. We compared the visiting nekton communities in intertidal creeks and on marsh platforms, the abiotic conditions and small-bodied faunal communities in salt pools, and the foraging patterns of two fishes between reference and restoring marshes. In both case studies, similar nekton species were observed between reference and restoring marshes; however, nekton communities differed by site type (14-52% of the variation). Pools in restoring marshes were providing basic nekton functions but had yet to offer the enhanced habitat support as those in reference marshes. Gut fullness was similar in tomcods (Microgadus tomcod) and mummichogs (Fundulus heteroclitus) between site types suggesting that restoring marshes were fulfilling foraging function for these species despite site type differences (11-44% of the variation) in prey composition being detected. Although the nekton community structure and functions in restoring marshes did not mirror those in references marshes, our findings highlight the value of restoring salt marshes in terms of nekton habitat. This study also demonstrates the advantages of implementing a multifaceted approach to understand the response of biotic communities to salt marsh restoration.

ecology↗

bioRxiv2017

Stochastic dispersal increases the rate of upstream spread: a case study with green crabs on the northwest Atlantic coast

Dispersal heterogeneity is an important process that can compensate for downstream advection, enabling aquatic organisms to persist or spread upstream. Our main focus was the effect of year-to-year variation in larval dispersal on invasion spread rate. We used the green crab, Carcinus maenas, as a case study. This species was first introduced over 200 years ago to the east coast of North America, and once established has maintained a relatively consistent spread rate against the dominant current. We used a stage-structured, integro-difference equation model that couples a demographic matrix for population growth and dispersal kernels for spread of individuals within a season. The kernel describing larval dispersal, the main dispersive stage, was mechanistically modeled to include both drift and settlement rate components. It was parameterized using a 3-dimensional hydrodynamic model of the Gulf of St Lawrence, which enabled us to incorporate larval behavior, namely vertical swimming. Dispersal heterogeneity was modeled at two temporal scales: within the larval period (months) and over the adult lifespan (years). The kernel models variation within the larval period. To model the variation among years, we allowed the kernel parameters to vary by year. Results indicated that when dispersal parameters vary with time, knowledge of the time-averaged dispersal process is insufficient for determining the upstream spread rate of the population. Rather upstream spread is possible over a number of years when incorporating the yearly variation, even when there are only a few \"good years\" featured by some upstream dispersal among many \"bad years\" featured by only downstream dispersal. Accounting for annual variations in dispersal in population models is important to enhance understanding of spatial dynamics and population spread rates. Our developed model also provides a good platform to link the modeling of larval behavior and demography to large-scale hydrodynamic models.

ecology↗