Field Guide to Seagrasses of the Red Sea - Seagrass-Watch

Habitats
The Red Sea contains examples of all the major tropical marine habitats
except estuaries. For the purpose of this guide, three main seagrass
habitats are identified: i) shallow coastal; (ii) reef; and (iii) deep coastal (refer
to illustration and photographs on pages 6 and 7). These three broad habitat
types differ in terms of water depth and seafloor type (sand versus rock).
Water depth has a major influence on light levels reaching seagrasses and
light is critical for photosynthesis. Seafloor type is important because most
species can only grow in sand, but a few species can be found on reef.
The shallow coastal habitat, also referred to as a back reef environment, is
characterized by depths shallower than 10 m and a seafloor dominated by
sand. The deepwater coastal habitat relates to waters ranging from 10 to
70 m in depth, the latter being the maximum depth in which seagrasses are
known to persist in the Red Sea. This habitat is also characterized by sand
on the seafloor. The reef habitat is characterized by calcium carbonate rock
mainly formed by coral. Very shallow water habitats are periodically exposed
to air at low tide (the intertidal zone). Exposure to air in the intertidal zone and
extreme levels of light can greatly limit seagrass growth and diversity.
Field Guide to Seagrasses of the Red Sea 5