1. Benthic macroalgae
Gas bladders like in this thallus of Fucus keep seaweeds afloat
Red algae may be filamentous (left; nuclei stained, fluorescence microscopy) or thallous (right, Porphyra sp.)
Green algae can also be filamentous (left, Acrosiphonia) or form thalli (right, Ulva).
Take a look at photographs of kelp forests and much more marine life by clicking here -- and more photographs, sorted according to species and groups, are found here
Seagrass damage by prop scars, Dade County, FL: green = little affected, yellow = moderately affected, re = strongly affected