Salt pannes and pools

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Salt pannes and pools are shallow, water-holding depressions in salt and brackish marshes. Pools stay wet longer, especially between tides, while pannes often dry out. Pannes begin when a layer of organic debris (wrack) covers and kills existing vegetation, creating a small hollow that can hold water. Over time, repeated flooding and drying raise the salinity, which then shapes which plants and animals can live there. Salt pools are similar, but their exact formation is less clear and they may become more common as sea levels rise.

These places are unique microhabitats dominated by salt-tolerant plants, bottom-dwelling vegetation, and estuarine animals. The plant and animal communities vary a lot with salinity, water, and other conditions.

Variants
- Low salt marsh panne: usually little or no vegetation. If present, plants may include smooth cordgrass (Spartina alterniflora), brown seaweeds such as knotted wrack (Ascophyllum nodosum) and rockweeds (Fucus spp.). The ground is soft, silty mud.
- High salt marsh panne: briefly flooded and shallow, with more vegetation dominated by arrow-grass (Triglochin maritimum). Some deeper spots may have little or no vegetation. Short smooth cord-grass (Spartina alterniflora) is common.
- Salt marsh mosquito panne: little vegetation on the upper part of the high marsh and typically deeper than other pannes. It is flooded by the higher spring tide and may hold water for 2–3 weeks after. The eastern salt marsh mosquito (Aedes sollicitans) lays eggs on exposed surfaces, which hatch when the panne floods again.
- Widgeon grass–marsh minnow deepwater pool: high marsh pools that stay semi-permanently or permanently flooded. They support small fish like sheephead minnow (Cyprinodon variegatus variegatus) and mummichog (Fundulus heteroclitus) and other aquatic plants. These pools can occur near the upper edge of the low marsh.
- Brackish marsh panne: found in brackish marshes, often with spike grass (Distichlis spicata) and sometimes the invasive Typha angustifolia. These pannes are shallow with a mixed group of grasses and flowering plants.
- Saturated mud panne (transition zone): in the edge zone near forested uplands, shaded by trees. This habitat can host seaside crowfoot (Ranunculus cymbalaria) and small patches of prostrate plants. Other grasses and forbs commonly seen around the panne edge include Virginia wild rye (Elymus virginicus), seaside grasses like carex species, marsh goldenrod (Solidago sempervirens), salt-meadow cordgrass (Spartina patens), and smooth cordgrass (Spartina alterniflora).

In short, salt pannes and pools are temporary, salty wet spots in marshes that support a range of salt-tolerant plants and small aquatic life, with the specific mix shaped by salinity and water conditions.