Diatoms provide attachment sites for other diatoms: a natural history of epiphytism from southern California

Abstract

Large epiphytic and epilithic diatom species were observed to act as substrata for other diatoms at freshwater, brackish and marine sites in southern California, USA. The most commonly encountered examples involved species that form long filaments attached to rocks or macroalgae. Biddulphia biddulphiana, B. tridens, Odontella aurita, Triceratium pentacrinus f. quadrata and Trigonium arcticum were commonly observed hosts in marine sites. Brackish water examples were Bacillaria paxillifer, Melosira varians, Pleurosira laevis and Terpsinoë musica, and Hydrosera whampoensis and P. laevis provided attachment sites in freshwater habitats. These large diatoms had other diatoms attached, usually to the girdle bands or to flat or concave surfaces of the valve face and mantle. Occasionally, the mucilage pads connecting the cells served as substrata for small epiphytic diatoms. The attached flora comprised several unrelated genera of centric and pennate diatoms, both raphid and araphid. Thus, large epiphytic and epilithic diatoms provide suitable attachment sites for other diatom species in water bodies spanning a wide salinity range, and it appears that this phenomenon is more common than previously recognized. The frustule geometry of the ‘host’ diatom apparently plays an important role in determining the location of attachment.