Energy-Dispersive X-ray spectrometry (EDX) was applied to the gut-content analysis of benthic animals, and its validity for easier estimation of the origin of gutcontents was evaluated. We analyzed the elemental composition of various reference samples and compared it with the elemental composition of the gut-contents. EDX analysis showed eight principal elements and five scarce elements. We used eight principal elements for analysis which were characteristic of the origin of gut-contents. We could not discriminate flocculent material of supposedly planktonic origin from bottom sediment because both were rich in iron, aluminum, and silicon. We could, however, easily distinguish sea floor sediment mainly composed of inorganic substances from fresh sediment that is rich in bioelements such as calcium, phosphorus, potassium, and sulfur. The calcium content was especially high in crustaceans, and sulfur in fish muscle. Six-rayed radar charts, with the weight percentages of Ca, S, P, K, and Mg (representative bioelements) and Fe+A1+Si (representing sediment) as the ordinates, showed three characteristic patterns for different sets of items. Geodesic similarity indices of the food items of six deep-sea fishes and nine control items were calculated. The UPGMA showed three distinct clusters, i.e., stomach contents with sediment remains, Ca-rich contents, and supposedly protein-rich contents. The present method could elucidate the fishes' general food habits objectively, and it has wide scope of applicability independent of location, season, and prey species.

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The spatial variability of the density of sea urchins (Strongylocentrotus nudus) soon after settling and metamorphosis and after having grown to at least 1 cm was analyzed in relation to offshore marine algal zonation. Newly settled sea urchins occurred throughout, from the shoreward cobblestone area to the offshore area dominated by crustose coralline red algae, where the highest density was observed. Individuals smaller than 2 cm diameter occurred mainly in the crustose corallines-dominated area. Sea urchins 2-4 cm in diameter occurred with a high density in the crustose corallines-dominated area and with a low density in a narrow zone in the Eisenia bicyclis-dominated area close to the crustose corallines-dominated area. These results suggest that they had settled in the crustose corallines-dominated area, survived and later dispersed during growth toward the E. bicyclis-dominated area.

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A method established to culture a free-living nematode, Microlaimus sp., from a tidal flat was applied to free-living nematodes from subtidal mud sediments. Two Chromadorids, Prochromadorella sp. and Spiliphera sp., successfully completed their life cycle in the laboratory at a temperature of 20°C. Eggs of Prochromadorella sp. hatched as juveniles 170-190μm long 3.5-4 days after spawning. Females 900-1000μm long started to deposit eggs 30 days after hatching and they deposited 42 eggs on average in 40 days. The generation time of the species was about 34 days. Eggs of Spiliphera sp. hatched as juveniles 350-360μm long 5-6.5 days after spawning. Females 1350-1500μm long started to deposit eggs 46 days after hatching and deposited 14 to 19 eggs in 40 days. The generation time of the species was about 51 days. Since all three nematode species that were able to complete their life cycles in the laboratory are epigrowth feeders, the present culture method may be applicable to other nematodes of similar feeding habits.

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Behavioral rhythms of marine animals have often been investigated in the field by use of an artificial light at night. This study was carried out to test whether such lighting affects the timing of behavior, thus causing a modification of the rhythmic patterns. Emergence patterns of a marine midge and several small crustaceans monitored without light showed various degrees of synchrony with day-night and tidal cycles; patterns of some species are well-demarcated, and others show only a weak rhythmicity. In comparison, artificial lighting may indeed have affected the number of specimens collected, but the characteristics of each species' emergence pattern were unchanged. The animals may not respond positively to the artificial light except initially, and then they may escape it. We speculate that light habituation takes place in the animals, and that because of this, night activity patterns monitored using the field light are very similar to those monitored without the light. In conclusion, use of a field light for monitoring the activity of animals at night is fully acceptable procedure.

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