• 1) Estuaries are an interface between fresh and salt water habitats; sometimes are "nurseries", often depauperate in permanant spp.

• 2) Estuaries are categorized either by geologic origin or by patten of mixing of fresh and salt water

  • origin: a) coastal plain estuary, b) fjord, c) tectonic estuary, d) bar-built estuary (first 3 are due to flooding of coastal features due to isostatic or eustatic changes in sea level, only the last is created by oceanic processes- waves and currents)
  • mixing: a) vertically-mixed estuary, b) slightly stratified estuary, c) highly stratified estuary, d) salt-wedge estuary (reflect a continuum of relative rates of fresh water flow & tidal mixing)

• 3) Because salinity in estuaries varies greatly in space & time, organisms that live there must have adaptations to salinity stress

  • organisms may osmoconform, osmoregulate, or do some of both
  • physiological response can depend on rate of change of salinity

• 4) Upper reaches of estuaries (3 - 12%o) are often most depauperate

  • poorly suited to both marine and freshwater species
  • salinity fluctuations most unpredictable in frequency and duration
  • larvae of estuarine specialists exhibit adaptations to remain in one place or to leave the estuary and return later

• 5) Salt-marshes are formed and dominated by rooted, vascular plants (halophytes) at interface between estuarine and terrestrial habitats

  • most common at mid latitudes, they often exhibit a distinct vertical zones of plants, similar to zonation on rocky shores
  • compared to mud flats and open water, productivity is very high
  • they support a detrital food web including polychaetes, crustacea, gastropods, bivalves (often only a few common species)

• 6) Mangrove forests are like salt marshes except they are dominated by peculiar trees and shrubs specialized for life in salt water

  • common at low latitudes; include a great variety of organisms

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