Journal of Applied Phycology 6: 459-468, 1994. 459 ( 1994 Kluwer Academic Publishers. Printed in Belgium. Isolation of humic acid from the brown alga Pilayella littoralis Elham A. Ghabbourl, (the late) Ahmed H. Khairy 1 , Donald P. Cheney 2 , Verena Gross 2 , Geoffrey Davies 3 ,*, Thomas R. Gilbert 3 & Xinyu Zhang 3 l Institute of Graduate Studies and Research, Alexandria University, Alexandria, Egypt 2 Biology Department and the Marine Science Center Northeastern University, Boston, MA 02115, USA 3 Chemistry Department and the Barnett Institute, Northeastern University, Boston, MA 02115, USA (*Authorfor correspondence) Received 10 July 1994; revised 24 August 1994; accepted 25 August 1994 Key words: alga, Pilayella Littoralis, humic acid, isolation, characterization Abstract A standard humic acid extraction procedure has been used to isolate dark brown organic residues from samples of the macroscopic marine brown alga Pilayella littoralis. The residues are insoluble in water, but soluble at high pH, and are similar in elemental composition, ash content, UV-visible, IR, PMR and X-Ray fluorescence spectra, X-Ray diffractograms and scanning electron micrographs to residues of a humic acid isolated from municipal compost. These results indicate that Pilayella produces humic acids. Introduction Algal blooms caused by an unusual free-living, or unattached, form of the filamentous brown alga Pilayella littoralis (L.) Kjellman (Ectocarpales) persis- tently foul the beaches of Nahant Bay, Massachusetts. The free-living, ball-shaped P. littoralis plants wash ashore and accumulate on beaches in casts that range from 1-7 cm thick and up to several hundred meters long (V. P. Gross & D. P. Cheney, unpublished). Although the alga fouls Nahant Bay beaches through- out the year, it is most abundant in the summer and fall, when beach casts typically range from 30 to 200 t (fresh weight) of Pilayella per day (V. P. Gross & D. P. Cheney, unpublished). The frequent presence of Pilayella on public beaches discourages swimming and sunbathing. In addition, anaerobic decomposition pro- duces a hydrogen sulfide (rotten egg) odor that greatly offends local residents. Although Pilayella fouling has been limited historically to Nahant Bay, similar fouling has spread recently to nearby Broad Sound. Pilayella has fouled beaches in Nahant Bay for more than a hundred years, but surprisingly little is known about the origin of the plant or the cause of the blooms. Previous studies (Wilce et al., 1982) of the free-living form showed that it primarily repro- duces vegetatively by fragmentation. However, recent studies have suggested that it arises from plants that grow as epiphytes on other seaweeds (V. P. Gross & D. P. Cheney, unpublished). Efforts are underway to develop efficient Pilayella harvesting methods and to find uses for the large amount of biomass it produces. As part of these studies we have examined free-living Pilayella to determine its potential for composting. This paper reports the unusual finding of humic acids (HA) in such plants. HA normally result from plant and animal decay under moist conditions in a process called humifica- tion. This process occurs in seawater, soils and ocean sediments (Harvey & Boran, 1989; Flaig et al., 1975; Gillam & Riley, 1982; Rashid & King, 1970). HA are dark brown, heterogeneous organic polymers with molecular weights of 10 000 to several hundred thou- sand daltons and are insoluble in natural waters. HA in soils and sediments impart porosity, texture and work- ability and act as adsorbents and reservoirs of plant constituents, nutrients, heavy metals, pesticides and other soil components. Biomass that contains HA or is easily composted is therefore of great interest for soil improvement.