The detrital food chain based on seaweeds. I. Bacteria associated with the surface of Laminaria fronds

The bacteria associated with the surface of fronds of the sublittoral brown alga Laminaria longicruris were investigated over a 13-month period on the coast of Nova Scotia (Canada). A psychrophilic population was found to be associated with the frond during the winter and a mesophilic population with the decaying frond during the summer. Numbers of psychrophiles varied inversely with ambient water temperature, and were present in the greatest number on the eroded tips of fronds. Laminaran hydrolyzing isolates were characteristic of the psychrophilic flora and a group of isolates hydrolyzing mannitol, protein and alginate characteristic of the mesophilic population. Increases in the numbers and proportions of bacteria utilizing plant substrates were found to accompany macroscopic evidence of frond decomposition. A comparison of the bacterial floras of L. longicruris fronds from a sheltered and exposed location showed them to be quantitatively and qualitatively comparable.