Estuarine Intertidal Sand or Mixed-Fine: Lagoon, Hyperhaline and Euhaline

Lagoons are formed when longshore water-borne sediments are deposited to form a spit closing off (partially or totally) an embayment.  Open lagoons are regularly flushed by freshwater and tidal action through a channel, while enclosed ones have no permanent channel and rarely flush.  The latter are usually filled gradually by salt marsh vegetation.  Some lagoons drain completely at low tide, while others retain water because of a sill in the channel. Water in the lagoon evaporates, concentrating salts. Interstitial salinities can reach as much as 80 ppt, but are more commonly in the euhaline range. Toward the landward end of these lagoons, the salinity can grade to < 0.5 ppt if there is freshwater influence.  Productivity is high because of marsh vegetation, eelgrass, microalgae, and terrestrial input. Shorebirds, waterfowl, river otters, and hawks all use these habitats.  Tidal creeks draining lagoons tend to contain mixed-coarse substrata and are occupied by a unique set of plants and animals using this high-flow, variable-salinity habitat.  Probably the inhabitants of each lagoon creek are different, although all will contain filter feeders, epifaunal and infaunal.  Few surveys of benthic organisms in lagoons were found.

Diagnostic Species (Marsh)

The same vascular plant communities which occur in the Estuarine Intertidal Sand:  Partly Enclosed, Eulittoral, Euhaline habitat occur in this habitat. This habitat is dominated by Salicornia virginica, but a Jaumea carnosa-Salicornia virginica community also occurs.

Common Associates (Marsh)

Puccinellia spp., Distichlis spicata, Spergularia spp.

Common Benthic Species

Zostera marina, benthic diatoms, ulvoids, mats of Ceramium pacificum and Polysiphonia paniculata; dominant animals are the polychaete Axiothella rubrocincta and the clams Macoma nasuta and Transennella tantilla.  Other bivalves include Protothaca staminea, Psephidia lordi, Tapes philippinarum, and Mya arenaria. Other worms include Ophiodromus pugettensis, Armandia brevis, Polydora ligni. The brittle star Amphipholis squamata is also abundant.

Sites Surveyed

Foulweather Salt Marsh, American Camp Lagoons, Argyle Lagoon, Spencer Spit, White Point, Mud Bay, Westcott Bay, Jefferson Point Marsh, Perego’s Lagoon, Lake Hancock, Elger Bay, Thorndyke Bay.


Kunze, 1984; Albright et al., 1980; Friday Harbor Labs unpublished reports.