The total penetration of photosynthetically active radiation (i.e. light useful for
plant growth) to depth depends on the water type.
The numbered lines show the % of surface irradiance that penetrates to different depths
for water of oceanic types I-III (above heavy line) and for coastal waters of types 1-9
(below heavy line). Lower limit of multicellular algae = lower limit of crustose
corallines. For example, in Coastal 7 water, this would occur at 14 m, whereas in Oceanic
I water the lower limit of crustose corallines is at c. 160 m. (From Dring, 1982.)