Filamentous Brown Seaweeds vs. Tube-forming Diatoms

Filamentous Brown Seaweeds vs. Tube-forming Diatoms in Maine

In Maine’s intertidal, it is common to see fuzzy or slimy-looking brown mats or tufts comprised of very thin (< 0.5 mm) threads. These may be growing on seaweed, or attached to rock, shells, pilings, docks, boat hulls, or free-floating.

Many species fit this general description, but they fall into two primary categories: filamentous brown seaweeds (macroalgae) and tube-forming diatoms (microalgae). Both are in the phylum Ochrophyta, but brown seaweeds are mostly in class Phaeophyceae and tube-forming diatoms are in the Baccilariophyceae. Despite only distant relatedness, these groups can be challenging to differentiate in the field.