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Table 1 Division of the Sylt coastal zone into tidal levels. Plant associations according to Ellenberg [22]

From: Uncharted biodiversity in the marine benthos: the void of the smallish with description of ten new Platyhelminth taxa from the well-studied North Sea

Tidal level Description
Upper supratidal Beach zone higher than 1 m above mean high tide (MHT) level and salt marshes grown with the plant association Armerietum maritimae (ungrazed) or Juncetum gerardii (grazed), also starting about 1 m above MHT. This zone is only flooded during storm tides, interstitial salinity mostly meso- to oligohaline (18–3 psu)
Lower supratidal Zone between MHT and 1 m above. In salt marshes with the plant association Puccinellietum maritimae. Interstitial salinity mostly in the polyhaline range (30–18 psu)
Upper intertidal Sand- and mudflats between mid-tide level and MHT. May not be submerged during strong offshore winds. Salinity occasionally drops to the polyhaline range
Lower intertidal Sand- and mudflats between mid-tide level and neap low tide level (NLT). Regularly submerged, salinity rarely beyond ambient level
Infratidal Zone between NLT and 1 m below mean low tide (MLT); may fall dry during strong offshore winds. Earlier studies often failed to sample this zone because the actual low water level was too high to reach it from the landward side, or too low to reach it by ship
Shallow subtidal Sediments 1–10 m below MLT
Deeper subtidal Water depth > 10 m. In the vicinity of the island this level is only represented by tidal channels with medium to coarse sand