Ecological significance of deformed chaetognaths associated with bacteria
Preserved samples of chaetognaths (S. crassa) from Tokyo Bay contained normal animals and deformed ones, associated with bacteria. Bacterial colonization occurred inside the body rather than on the body surface. Due to bacterial growth, muscles degenerated and chaetognaths became abnormally knotty and flabby. Some preserved specimens (S. nagae) from Suruga Bay had head damage and were attacked by large numbers of bacteria. Thus, bacteria appear to be important primary or secondary invaders. Abnormal specimens of S. crassa occurred more frequently in July 1979 (12.4%) than in June 1982 (3.9%). The percentage of head-damaged specimens of S. nagae varied with depth, ranging from 1.6 to 13.3%. This suggests that the fraction of the population suffering from bacterial invasion is similar in both species. Food containing ratio (FCR) values, an indication of feeding activity, of the abnormal animals in Tokyo Bay were less than 10% and no feeding rhythm was found, whereas normal animals had high FCR values with a maximum peak (more than 60%) between 2000 and 2300 h. Abnormal specimens sometimes had spermatophores on the body surface. It was obvious that abnormal animals were still alive in the sea and that some of them not only fed on copepods but also copulated. However, feeding activity and reproductive behavior were much lower in abnormal animals than in normal ones. The lack of abnormal animals larger than 9.0 mm and their smaller mean body length compared with normal animals and those infected by parasites suggest that mortality of the chaetognath population is affected by bacterial infection rather than by parasitic infection.
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Document Type: Research Article
Publication date: 1985-09-01
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