Taxon-specific ecological drivers of diatom-dominated microphytobenthos: Experimental and spatio-temporal insights from a temperate hypertidal mudflat

Abstract

Photosynthetic microorganisms form the productive base of many coastal ecosystems. Yet, the relative importance of ecological drivers underlying variability in their abundance, diversity, and species composition remains poorly resolved. To address this, I examined variability in microalgal assemblages in relation to infaunal and epifaunal grazers, heterotrophic microorganisms, and sediment physico-chemical properties in a Bay of Fundy intertidal mudflat. These variables were quantified using environmental DNA metabarcoding, chlorophyll a fluorescence, microscopy, and field measurements. Data were obtained from a field experiment that manipulated epifaunal grazer abundance with exclosures and nutrient availability with fertilizers. My findings suggest differing sensitivities of the biomass and species composition of the diatom-dominated microphytobenthos to ecological drivers. Species composition was more closely linked to biotic interactions, whereas biomass varied under resource-driven control within the broader environmental context. My thesis contributes to ongoing efforts to clarify ecological controls on the productive, carbon-sequestering base of coastal ecosystems.