Tidal water exchange drives fish and crustacean abundances in salt marshes

Abstract

Coastal salt marshes provide important habitat for fishes and crustaceans, including species of commercial value that feed or take refuge in the marsh. Yet population abundances vary considerably between sites, often without clear explanation. We hypothesised that faunal abundance and mean size would be positively related to 2 physical properties that govern marsh accessibility to water-dependent species, as has been found on the southeastern coast of the USA: (1) the volume of water exchanged by tidal flooding, which gives access to the marsh, and (2) edge amount, the length of the water-vegetation borderline per unit area where species can take refuge and feed. Digital terrain models and tidal information were used to select 5 marshes in Wales, UK, that differed in edge amount and water exchange (52°N, 4°W). Fishes and crustaceans were sampled using baited traps, fyke nets and seine nets. In total, 15 species were caught, including commercially valuable brown shrimp, European eel and sea bass. We found water exchange volume, but not edge amount, boosted fish and crustacean abundances. Crab and sea bass sizes were both negatively affected by water exchange, while shrimp and fish sizes were unaffected. Our findings show how the mechanisms that drive fish and crustacean abundances and sizes vary between geographical regions. Feasibly, fisheries associations with marsh hydrogeomorphology might operate differently as well.

Effects of structural complexity and water depth on the juvenile blue crabCallinectes Sapidusin a simulated salt marsh mesocosm

“…This implies that even in areas of very shallow water, adult blue crabs experience minimal impediments to foraging. The refuge effects of shallow water may be dependent on the predator-prey interaction, such that only piscine predators too large to access shallow water are hindered (de la Barra et al, 2022). In contrast to piscine predators, adult blue crab predators are unique in their ability to withstand exposure to air, such as when adult and subadult blue crabs exploit shallow pools of muddy water at ebb tide to ambush prey when the marsh surface is exposed (Johnson, 2022).…”

“…Aquatic organisms must either leave the vegetated marsh or seek shelter in residual tide pools along the pitted marsh surface (Allen, Ogburn and Kenny, 2017). Prey survival is likely a function of both structural refuge as well as shallow water refuge, with the relative importance of each determined by tidal amplitudes, marsh surface inundation times and species characteristics (de la Barra et al, 2022).…”

Model-based evaluation of critical nursery habitats for juvenile blue crabs through ontogeny: abundance and survival in seagrass, salt marsh, and unstructured bottom

“…As access to salt marsh vegetation for aquatic organisms is controlled by marsh flooding and tidal regimes, the importance of marsh structural complexity in governing survival is likely regulated by hydrology (Minello, Rozas and Baker, 2012). In Chesapeake Bay, SME utilization is limited by mesotidal inundation profiles characteristic of mid-Atlantic estuaries (Minello, Rozas and Baker, 2012;de la Barra et al, 2022). Aggregate survival in SME is therefore a combination of the survival conferred by both structured and unstructured components of salt marshes.…”

“…These findings have additional implications for intertidal habitats such as salt marshes. As SME remains inundated for only a portion of the full tidal cycle, a high proportion of small juveniles must leave the vegetated marsh surface to adjacent unstructured subtidal habitat at low tide (de la Barra et al, 2022), though some fraction of juveniles may bury in the exposed marsh surface (Johnson and Eggleston, 2010) and adults may remain in tidal pools to opportunistically forage (Johnson, 2022). Although survival in adjacent unstructured habitat in these locations maybe be higher than in similar deeper habitat (Ruiz, Hines and Posey, 1993), these areas nevertheless provide lower refuge quality relative to structured habitat (Ryer, van Montfrans and Moody, 1997).…”

Blue carbon benefits from global saltmarsh restoration

“…Saltmarshes provide an array of other ecosystem services besides climate regulation, including delivering natural flood defence and water quality enhancement, and supplying habitat for biodiversity, commercial fish species and migratory birds (Adams et al, 2021; de la Barra et al, 2022; Fairchild et al, 2021; Sharps et al, 2017). In the United States, coastal wetlands were valued at US$23.2 billion year −1 for storm protection services alone (Costanza et al, 2008), and saltmarsh services globally are worth Int$1.07 trillion year −1 (Davidson et al, 2019, using 2007 ‘International’ $).…”