MICROBIAL COLONIZATION OF COPEPOD BODY SURFACES AND CHITIN DEGRADATION IN THE SEA

Next to cellulose, chitin (composed of N-acetyl-D-glucosamine sugar un its) is the most frequently occurring biopolymer in nature. Among the most common sources of chitin in the marine environment are copepods a nd the casings of their fecal pellets. During the mineralization of ch itin by microorganisms, which occurs chiefly by means of exoenzymes, n itrogen and carbon are returned to the nutrient cycle. In this study, the microbial colonization of the moults (exuviae), carcasses and feca l pellets of Tisbe holothuriae Humes (Copepoda: Harpacticoida) was exa mined in the laboratory. Results obtained with DAPI staining indicated that a succession of microorganisms from rodshaped bacteria and cocci to starlike aggregates took place, followed by the yeastlike fungus A ureobasidium pullulans (de Bary) Arnaud. No differences were noted bet ween moults from various developmental stages, from nauplius to adult. The ventral sides and extremities of exuviae and carcasses were more rapidly colonized than other parts of the bodies. The casings of fecal pellets were frequently surrounded by bacteria with fimbriae or slime threads. In situ studies of chitin degradation (practical grade chiti n from crustacean shells) with the mesh bag technique showed that abou t 90 % of the original substance was lost after 3 months exposure in s eawater at temperatures between 10 and 18 degrees C. Chitinase activit y was measured in the water at two stations near Helgoland, an island in the North Sea. A higher exoenzymatic activity was found in the rock y intertidal zone, compared to the Station Cable Buoy located between the main and Dune island. These values correspond to the higher bacter ia numbers (cfu ml(-1)) found in the rocky intertidal: 10 to 100x grea ter than those found at the Cable Buoy Station.