Date of Award

Winter 2024

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Gregg E Moore

Second Advisor

Alyson Eberhardt

Third Advisor

Michelle Fournet

Abstract

Salt marshes are intertidal, vegetated habitats that develop in protected, low energy areas within temperate estuaries. Notably, the North American coast comprises approximately 40% of the world's salt marshes which are valued for their numerous ecosystem services including coastal protection, carbon sequestration, and outdoor recreation. Additionally, salt marshes are vital habitats for estuarine nekton (fish and crustaceans), which rely on creeks, channels, the vegetated marsh, and isolated pools within the marsh surface for reproduction, foraging, and refuge from predators. In New England, the historic practice of salt marsh ditching for agricultural development and mosquito management has resulted in significant changes to the geomorphology of many salt marsh habitats, with a primary concern being the formation of large “mega-pools” created by the collapse of the marsh platform following ditching and subsequent marsh inundation during high tides. The formation and expansion of mega-pools threatens the overall stability of the salt marsh by promoting mass vegetation die-off, negatively affecting both the quality of the habitat and the ecosystem services it provides. To reduce prolonged marsh inundation and mitigate the formation of mega-pools, a novel restoration technique known as compaction runneling has been proposed as a restoration strategy in the Great Marsh Estuary, MA. Compaction runnels have been shown to effectively reduce the size of mega-pools and in some cases transform mega-pools into a collection of smaller pools that mimic those which occur naturally on the marsh platform. Despite the promising results following runnel installation, little is known about the relationship between runneling activity and the estuarine nekton communities reliant on the affected habitats. To address this knowledge gap, two studies were established to monitor nekton community response to runnel implementation in the Great Marsh Estuary. The first study employed the use of lift nets to conduct manual nekton sampling within treated (runneled) and untreated (control) pools before and after runnel implementation. Overall nekton and Fundulus heteroclitus density showed no response to runnel activity while Palaemonetes spp. density had a negative response to runnel activity that was trending towards significance (0.05 < p < 0.07). The second study employed an increasingly popular method of marine habitat monitoring, passive acoustic monitoring (PAM), to establish the first soundscape analysis study in a New England salt marsh. Hydrophones were deployed in treated (runneled) and untreated (control) salt marsh pools and recorded the ambient soundscape (0-24 kHz) from June 2023 - August 2023. While underwater biological sound signals were limited in diversity, a strong diel pattern was observed with pronounced acoustic activity of a crustacean, thought to be Palaemonetes spp., during daylight hours. There was no relationship observed between acoustic activity of Palaemonetes spp. and pool treatment. These studies provide a strong foundation for future monitoring of nekton communities with respect to runnel activity, which has been estimated to require 3-5 years to reach its management goal of 80% mega-pool drainage. With further research on the acoustic behavior of Palaemonetes spp., coupled with its documented potential as an indicator species of marsh health, PAM has the capacity to be a cost-effective and highly accessible approach to nekton monitoring in salt marshes.

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