EVSC20004 Lecture Notes - Lecture 4: Seagrass, Microfauna, Filter Feeder
18 May 2018
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LECTURE 4: ESTUARIES – HABITATS
• Large variety of habitats, all subject to changes in salinity
• Mostly seen as sediment habitats, from river and ocean
Soft Sediments - Unvegetated - Benthic
• Macrofauna >500 micrometres: worms, crabs, amphipods, molluscs
• Meiofauna 62-500 micrometres: nematodes, copepods, gastrotrichs
• Microfauna <62 micrometres: bacteria, diatoms, flagellates
Moving within Sediments
• Burrowing through sediments - or move through interstitial spaces
o Digging (some crustaceans) or hydrostatic pressure (some worms) – use muscle
contraction
• Moving between grains
o Very small organisms, often wormlike, no sediment displacement
Feeding Types
• Deposit feeding: ingest sediment to extract food, then get rid of sediment
o Forms: tentacles, buried within sediment, probe on surface while buried, burrow
• Suspension feeding: feeding on organic particulates suspended in water
o Active (filter feeding) - through pumping of water through the system
o Passive - cilia or mucous to move food particles - starfish
• Scavenging: feeding on dead organic matter - e.g crabs, shrimps, some gastropods
• Predation: hunting or consuming other animals
Seagrass Beds - Benthic
• Seagrasses: requirements = soft sediments (most species), sheltered waters, wide range of
salinity
o Most grow subtidal, but some intertidal species
o Are a substrate for sessile species - not found in unvegetated sediment
o Allows higher diversity of organisms present
o Habitat for motile animals: crabs, rays, branchiopods, molluscs
• As a food: largely cellulose, hard to digest - eaten by few species (swans, turtles, few fish,
dugongs)
• Nursery areas: provide shelter from predators for juveniles
• Ecosystem engineers:
o Leaves baffle water movement - sediments settle
o Rhizomes & roots bind sediments
• Carbon sinks: extensive roots beneath sediment, carbon sequestration
Mangrove Forests
• Sheltered waters, soft sediments, largely tropical, halophytes
• Roots:
o Pneumatophores - allow gas exchange during high tide
o Provide structure in water column
o Substrate for seaweeds, barnacles, tubeworms & bivalves
• Around roots:
o Species move with tide: burrowing crabs, gastropods, fish (many juveniles)
