VARIATION IN BURROW-WALL MICROMORPHOLOGIES OF SELECT INTERTIDAL INVERTEBRATES ALONG THE PACIFIC NORTHWEST COAST, USA: BEHAVIORAL AND DIAGENETIC IMPLICATIONS

Burrow-wall micromorphologies produced by nine different intertidal invertebrates were characterized by scanning electron microscopy. Minimally disturbed burrows and host sediment associated with Heteromastus filiformis, Saccoglossus bromophenolosus, Corophium volutator, Clymenella sp., Phoronopsis viridis, Cirriformia luxuriosa, Arenicola marina, Nereis virens, and Upogebia pugettensis were collected from various locales along the western coast of Washington and California. Scanning electron micrographs show several unique sedimentary characteristics present in the burrow lining of each invertebrate. Three traits-grain orientation and grain-size distribution, the nature of the mucus lining, and the presence of wall sculpture-appear significant in describing the microscale burrow lining. In several burrow types, the burrow structure was distinguishable from the matrix by changes in the modal grain size and sorting of the burrow-wall sediment. Variations in the type of packing-cubic versus rhombohedral packing-between the burrow and sediment often accompanied grain-size variations. In addition to the alterations to grain distribution and orientation, most burrows surveyed showed mucus-stabilized walls. The style of the mucus secretion-globules, threads, or ribbons-and the resultant structure-smooth blankets or woven mats-used to stabilize the burrow wall can characterize burrow linings. Wall sculpture (microbioglyphs or micro-surficial morphology) was observed rarely but when present was highly distinctive of Corophium volutator burrow linings. The observed variation in burrow-wall micromorphologies; provides evidence of trace-maker behavior, burrow-preservation potential, and sediment diagenesis.