Microbial mats and thalassinid shrimp: Spatial and geochemical interactions in a modern intertidal environment

ABSTRACT This research examines the spatial and geochemical interactions between mat‐forming microorganisms and thalassinid shrimp in an intertidal flat situated on the shores of Willapa Bay, Washington, USA. The study serves as a contemporary analog for the relationships between mats and burrowing organisms in deep time. This methodological approach uses (i) field data to investigate sedimentological characteristics along a transect from heavily burrowed to mat‐dominated sites, (ii) orthophotogrammetry to analyse and quantify mat extent and shrimp burrow density, (iii) porewater samples collected using Rhizon samplers and inductively coupled plasma mass spectrometry to determine porewater elemental concentrations, (iv) statistical analysis of the position of burrow openings and mat extent and (v) DNA analysis to characterise the microbial community composition of this site. These findings reveal a complex relationship between burrowing organisms and mat‐forming microorganisms, suggesting a potential benefit to burrowing organisms in colonising sediment that is spatially proximal to mats, or covered in discontinuous microbial mats. These findings challenge oversimplified interpretations of the AR that are based on a rigid dichotomy between matgrounds and mixgrounds. A key simplification is the depiction of the AR as a sudden, one‐way shift from matgrounds to bioturbated sediment. While burrowing organisms contributed to the decline of microbial mats, factors such as sediment supply, hydrodynamics and chemical conditions also play a significant role in their spatial distribution. This work highlights that burrower–mat interactions, both past and present, are more nuanced than previously understood.