Development of an inner-coastal-lagoon fauna is due to the slow rate of exchange in a large lagoon. The inner lagoon assemblage is less diverse than the outer lagoon assemblage. A high rate of foraminiferal reproduction off river mouths results in an abundant population dominated by 1 or 2 species and specimens of small size; the number of specimens per unit volume of sediment may be diluted by fast deposition. Accumulation of abundant foraminiferal tests suggests slow deposition of detrital sediments.

Marsh faunal zones are related to mean tidal ranges, and this relation can be used to estimate lagoon hydrodynamics. High diversity marsh faunas are present in low runoff areas, and low diversity faunas are found in high runoff areas. Calcareous specimens are common in many marshes, but may not be preserved in the sediments.

Nearshore open-ocean faunas differ from lagoon faunas, and have an apparent depth zonation related to water turbulence. Beach and sandy lagoon-barrier sediments contain robust open-ocean Foraminifera and may have lagoon and marsh species. Mixed faunas may be present on one or both sides of a lagoon inlet and reflect lagoon size and dominant direction of flow. Transport of marsh species into the nearshore area is a result of high runoff. Mixing of assemblages results from rise or fall of sea level, and also from upslope transport from the turbulent zone.

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