Lecture Series 1: Soft Sediment Systems Slides Notes

Soft-Sediment Systems Overview

Subject Title: MB2050: Functional Biology of Marine Organisms
Coordinator: A/Prof Jenni Donelson

Key Lecture Topics:

• Physical characteristics of soft-sediment systems

• Biological organization within these habitats

• Challenges of living in soft sediment

Characteristics of Soft-Sediment Systems

Sediment Types:

• Sand: larger particles; grain size allows water movement

• Mud: finer particles; retains more moisture

• Gravel: consists of > 30% larger sediment

• Pore Water: water between sediment particles, affects habitat properties

Sediment Sorting and Types

Sorting:

• Indicates particle size spread in a sample

• Grain Size Categories:

  • Cobble: -6 to -8, 64-256 mm

  • Coarse Gravel: -4 to -5, 16-32 mm

  • Others include: fine gravel, sand, silt, clay

Environmental Influences on Sediment

Environmental Characteristics:

• Coarse-Particle Beaches:

  • Steep slopes, high instability

  • Low oxygen; fewer organisms due to harsh conditions

• Fine-Particle Beaches:

  • Stable environment, shallow water

  • More organic matter; higher bacterial presence

Challenges of Living in Soft-Sediment

Stability of Substratum:

• Constant wave action causes particle instability

• Implications:

  • Risk of smothering for organisms

  • Difficult locomotion due to loose particles

  • Limited attachment surfaces for organisms

• Oxygen Availability:

  • Particle size affects how much water can move, influencing oxygen levels

• Sediment Composition Impacts:

  • Aerobic zones (oxygen-rich) vs. anoxic layers (low oxygen)

Infauna and Community Structure

Infauna Categories:

• Macrofauna: > 2mm; includes polychaetes, bivalves, crustaceans

• Diversity: Increases in lower energy environments with finer sediments

• Meiofauna: < 2mm; inhabit spaces between sediments

• Microfauna: Bacteria and other microbes; denser in finer grains

Burrowing and Burying Behaviors

Burrowing:

• Excavation of cavities by organisms (e.g., polychaetes, mollusks)

• Burying: Movement into sediment; direct body contact helps

• Mechanisms of Entry:

  • Hydraulic Mechanism: Common in soft-bodied organisms

  • Mechanical Displacement: Common in hard-bodied organisms

Respiratory Strategies in Infauna

• Option 1: Maintain contact with oxygenated water via siphons or other adaptations

• Option 2: Adaptations for low oxygen environments: respiratory pigments; anaerobic respiration

Feeding Strategies of Soft-Sediment Taxa

Deposit Feeding: Ingesting sediment; examples include:

• Non-selective feeders

• Surface browsers

• Head-down deposit feeders

• Suspension Feeding: Less common; may change based on water currents

• Carnivory: Predators that hunt on the surface or underground

Ecological Implications of Feeding and Sediments

• Biogenic Grading: Alters sediment structure; includes production of fecal pellets

• Trophic Group Amensalism: Impact of deposit feeders on suspension feeders

  • Increased sediment instability can reduce feeding efficiency for suspension feeders

Summary

• Major challenges include:

  • Instability of habitat

  • Limited surfaces for attachment

  • Varying oxygen availability

• Organisms have adaptations and behaviors that help them survive in soft-sediment environments, influencing their roles ecologically.