Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Sediment cores (9.6 cm inner diameter) were collected with an Ocean Instruments MC-400 multicorer or via SCUBA diving at each site and timepoint. Grain size was measured in the top 8-12 cm of sediment. 1-2 cores were sectioned into 1 cm increments and dried at 65 °C for 48 h. Dried samples were placed in a muffle furnace at 550 °C for 4 h to combust sediment organic matter. Porosity and organic content were calculated from the sediment mass differences before and after drying and combusting, respectively. Combusted sediment was then placed in a 1% sodium hexametaphosphate solution for at least 3 weeks to deflocculate. After weeks of deflocculating, clumps of mud often remained intact in muddier samples, so all samples were gently rubbed with a gloved finger on a 63 μm sieve to break up mud clumps. The mud was then washed through the sieve and combined with the sand retained on the sieve. After breaking up clumps, we measured grain size distribution using a Malvern Mastersizer 3000. For each sample, 5 measurements were averaged and then analyzed using Gradistat (Kenneth Pye Associates, LTD.).

Bottom water salinity and temperature (° C) measured at each site and timepoint using a CTD (conductivity, temperature, depth) instrument array.

For each sediment sample, 5 Malvern Mastersizer measurements were averaged and then analyzed using Gradistat v9.1 (Kenneth Pye Associates, LTD.).

NSF abstract:
Marine sediments are important habitats for abundant and diverse communities of organisms that are important as food sources for higher trophic levels, including commercially important species. Through burrowing, constructing tubes, and feeding on sediments, these animals modify their physical and chemical environments to such an extent that they are considered ecosystem engineers. Bioturbation, the mixing of sediments by animals, is important in regenerating nutrients and transporting pollutants and carbon bound to mineral grains. Despite its importance, our ability to predict bioturbation rates and patterns from the community structure is poor, largely due to a lack of understanding of the mechanisms by which animals mix sediments. This project builds on earlier work showing that animals extend burrows through muddy sediments by fracture to test the hypothesis that the mechanical properties of sediments that affect burrowing mechanics also affect sediment mixing. More broadly, this project examines the relative contributions of (i) the functional roles of the organisms in the community, (ii) the mechanical properties of sediments, and (iii) factors that might increase or decrease animal activity such as temperature and food availability to bioturbation rates. Burrowing animals modify the physical properties of sediments, and this project quantifies these changes and tests the hypothesis that these changes are ecologically important and affect community succession following a disturbance. In addition to this scientific broader impact, this project involves development of instrumentation to measure sediment properties and includes a substantial education plan to introduce graduate, undergraduate, and middle school students to the important role that technology plays in marine science.

Through burrowing and feeding activities, benthic infauna mix sediments and modify their physical environments. Bioturbation gates the burial of organic matter, enhances nutrient regeneration, and smears the paleontological and stratigraphic record. However, current understanding of the mechanisms by which infaunal activities mix sediments is insufficient to predict the impacts of changes in infaunal community structure on important sediment ecosystem functions driven by bioturbation. This project tests specific hypotheses relating infaunal communities, bioturbation, and geotechnical properties with the ultimate goal of understanding the dynamic changes and potential feedbacks between infauna and their physical environments. This project integrates field and lab experiments to assess the relative importance of infaunal community structure and activities to bioturbation rates. Additionally, this project builds on recent work showing that muddy sediments are elastic gels through which worms extend burrows by fracture to propose that geotechnical properties of sediments mediate bioturbation by governing the release of particles from the sediment matrix during burrow extension. Finite element modeling determines how the release of particles by fracture during burrowing depends on the fracture toughness (cohesion) and stiffness (compaction) of sediments and complements laboratory experiments characterizing the impact of geotechnical properties on burrowing behaviors. The proposed research also aims to determine whether impacts of infauna on geotechnical properties are ecologically important. Changes in infaunal communities and geotechnical properties following an experimental physical disturbance address the hypothesis that ecosystem engineering of bulk sediment properties facilitates succession.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.