Marine biological zones and the factors determining them

 
Table 5 Marine biological zones and the factors determining them
 
 
Zone
Typical upper boundaries around Britain and Ireland
 
Immersion
 
Thermal stability
 
Light
 
Salinity
 
Wave action
Adlittoral
 
Spray only
Highly variable
Photic
Saline influence
None
Supralittoral
+10 to +6 m
Spray and splash
Highly variable
Photic
Euryhaline
Highly variable
Eulittoral
+7 to +4 m MHWS
Regular immersion and emersion
Highly variable
Photic
Euryhaline
Highly variable
Infralittoral
+1 to 0 m MLWS
Immersed (intermittent spring tide emersion of sublittoral fringe)
Variable - eurythermal
Euphotic
Euryhaline
Variable
Circalittoral
-5 to -20 m
Immersed
Moderately variable - mesothermal
Mesophotic (sparse algae, algal crusts)
Mesohaline / Stenohaline
Moderately variable
Circalittoral offshore
-40 to -80 m
Immersed
Stable - stenothermal
Aphotic
Stenohaline
Stable
Bathyal
-200 m
Immersed
Very stable - stenothermal
Aphotic
Stenohaline
Stable