Sedimentology, ichnology, ecology and anthropogenic modification of muddy tidal flats in a cold-temperate environment: Chignecto Bay, Canada

Abstract

In Chignecto Bay, upper Bay of Fundy, Canada, the muddy tidal flats exhibit distinctive sedimentological and ichnological characteristics indicative of winter conditions and the development of ice. From late spring to autumn (May–October: mean temperature +13.6 °C), the mud flats sustain a high infaunal biomass and sediment deposition is dominated by tidal processes. Neap–spring tidal rhythmites, fluid-mud deposition and high levels of bioturbation are all characteristic of summer deposits. During the winter, temperatures remain below zero (December–March: mean temperature −6.3 °C), and ice forms in the bay and periodically on the mud flats. Ice rafts and blocks are common on the tidal-flat surface, and these blocks deform the muddy sediment, cut deep scours and deposit allochthonous sediment (including gravel) across the flats. Intermittent storms in the autumn and winter also contribute to sediment scouring and erosion. Annual die-offs of infauna are reflected by reduced bioturbation in winter deposits. Each spring, renewed larval recruitment and opportunistic colonization results in increasing levels of bioturbation, and the trace suite is dominated by a low-diversity assemblage of diminutive, vertical burrows. The summer–winter cyclicity in infaunal colonization manifests, ichnologically, as a distinctive bioturbated–non-bioturbated bedset character.Infaunal populations in Chignecto Bay peak in the late spring and in the late summer–early autumn. Both population peaks are exploited by vertebrates, including migrating Atlantic sturgeon (late spring) and migratory shorebirds (late summer–early autumn). In particular, the upper Bay of Fundy, including Chignecto Bay, is a staging ground for approximately 42–74% of the world’s Semipalmated sandpipers (Calidris pusilla) on their annual migration from the Arctic to South America. Fortunately, anthropogenic modification of Chignecto Bay, and its associated bays and rivers (e.g. construction and dismantling of a causeway over the Petitcodiac River), has not had a significant effect, to date, on the mud-flat habitat or the infaunal biomass.

Structuring forces of intertidal infaunal communities on the northern coast of British Columbia, Canada: assessing the relative importance of top-down, bottom-up, middle-out, and abiotic variables

“…2). As in other studies, the infaunal community varied significantly with top-down (Heck Jr. and Valentine 2007;Hughes et al 2014), middleout (Prugh et al 2009;Johnson et al 2014), and abiotic variables (Lu et al 2008;Dashtgard et al 2014), but these variables accounted for a minority of the community variation (0%-9% each; 10% total). The overall low proportion of the variation accounted for by these covariates does not mean that these variables are unimportant in structuring the infaunal community, since our analyses use correlational data to report on relative importance and not on absolute effect size.…”

“…Here, we examine possible species performance forces (predation, competition, and response to certain abiotic conditions) underlying community structure. For instance, envi-ronmental or abiotic variables, such as water salinity, temperature, or sediment properties, coupled with variations in exhibited tolerances of organisms for these conditions (Stillman 2002;Lu et al 2008;Dashtgard et al 2014;Sizmur et al 2019) can play an important role in structuring communities (Kelaher et al 2001;Ferguson et al 2013;Gerwing et al 2022a). As well, interactions among the living components of an ecosystem can affect communities, namely top-down predation, which in our analysis, and as discussed below, may be indistinguishable from bioturbation (Heck Jr. and Valentine 2007;Hughes et al 2014;Johnson et al 2014) and bottom-up forces, such as the availability and competition for nutrients (Davis et al 2014;Schuldt et al 2014;Pilditch et al 2015a).…”

Short-Term Response of a Downstream Marine System to the Partial Opening of a Tidal-River Causeway

“…Absence of a short-term impact of opening the causeway on these mudflats likely stems from the macrotidal nature of the Bay of Fundy, where tidal amplitudes range from 8-15 m (Bleakney 1972;Desplanque and Mossman 2004). Any changes in hydrodynamics that occurred when the causeway was opened were likely overwhelmed by the substantial daily water movement in and out of the Bay (Dashtgard et al 2014;Desplanque and Mossman 2004;Wu et al 2011). In fact, sediment deposition after opening the causeway appears to be primarily occurring subtidally in the middle of Shepody Bay, not on the intertidal mudflats (AMEC 2013;AMEC 2015).…”