Recently, restoration and creation of seaweed bed have been regarded as important. The Fisheries Engineering contributes to development of formation of seaweed bed greatly. However, it is difficult to form seaweed bed in a barren ground zone. Because some studies about mechanisms of barren ground occurring by over-grazing by sea urchin progressed, directionality of some countermeasures is becoming clear. However, mechanisms of barren ground occurring by over-grazing of herbivore fish still are not almost understood. It will be important that an action of herbivore fish is grasped in order to make seaweed bed. For researchers studying Fisheries Engineering, a symposium about formation of seaweed bed in a barren ground zone was held. Because a lot of suggestive argument was done in this symposium, it was wished that development of formation of seaweed bed technique progressedmore.

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The contents of stomach and intestines of specimens of Siganus fuscescens from Futaoi Island in the Sea of Hibiki were analysed and the percentages of each algal species and animal taxanomic groups were determined. 64 specimens, ranging from 168 to 312 mm body length, were collected by bottom gill net and commercial trap net in autumn (September and October) of 1998 and late spring (May) of 1999. The diet of S. fuscescens consisted dominantly of laminarian and fucoid algae, with an animal component of less than 2% by wet weight. The degrees of similarity and diversity, on a weight basis, in the diet of S. fuscescens were compared between autumn and Spring. The dietary composition in spring was greatly different from that in autumn, and two annual species of undaria pinnatifida and Sargasstm horneri overwhelmingly dominated in spring, whereas diverse perennial species of laminarian and fucoid algae constituted the diet in autumn. There was evidence of selection of reproductive receptacles of fucoid algae as an important food source. These results emphasize the unusual feeding pattem of adult S. fuscescens among the members of the family Siganidae.

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Grazing pressure for kelp forest formation was conducted from 1997 to 1999. Experimental fields established in two 'Isoyake areas', Otaru and Tomari. To control the grazing pressure, two fields were encIosed by fence, and the sea urchin, Strongylocentrotsu, was removed in the fence. The fence prevents the invasion of sea urchin from outside of fence to inside. At the experimental fields,sSea urchins were no grazing over the winter, whereas the urchins add grazing during summer. Vegetation was observed in both of inside and outside of the fence. Kelp forest appeared only inside of fence, but Isoyake continued in outside of fence. Gonad of sea urchin at the new kelp forest increased in qualitative and quantitative.

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Many photographs of seascapes were collected from seven sites in 'Isoyake areas' (sea deforestation areas) on the southwest coast of Japan, namely from Wakayama, Miyazaki and Kagoshima Prefectures. The features were compared in order to clarify their common points and the differences among their seascapes. There were wide variations in the seascapes in 'Isoyake areas' on the southwest coast of Japan. Especially, the algal vegetation in 'Isoyake areas' varied, i.e. 1) only crustose corallin red algae occurred, 2) short-lived small algae dominated, and 3) long-lived macro brown algae Sargassum spp. dominated. In 'Isoyake areas', a high density of sea urchins and snails were observed on the rocky bottom and grazed marks by fish were observed on lamina of Eisenia and Ecklonia plants. The 'Isoyake areas' faced to open sea, and had a high transparency around the coast of Wakayama Prefecture. The importance of continuous monitoring on bio-communities and environmental conditions through from in the seaweed.beds adjacent to 'Isoyake areas' is discussed.

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In recent years, it has showed that the algal bed is severely affected by the over-grazing of herbivorous fishes, particularly in the southwestem sea of Japan. Although the present utilization of the herbivorous fishes is limited locally in Japan, they should be effectively utilized from the viewpoint of the total ecosystem with the consideration of the grazing impact on algal bed. In this report, the potential for marine food of herbivorous fishes is examined based on fact-finding research for local utilization and the fisheries for herbivorous fishes in Japan.

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Various types of episodic decrease or disappearance of seaweed bed, resulting in the formation of barren grounds (not necessarily coralline community), have been called Isoyake in Japan. Among the barrens, offshore types are more popular than the other types (inshore, middle, whole and spotted). It should be noticed, however, that they include stable barrens just below the lower limits of algal vegetation. Recent literatures of 'Isoyake' in domestic and other areas in the world suggest that anthropological reasons (e.g., overfishing of predating animals, eutrofication) as well as oceanographic natural disasters (e.g., El Nino, inshoring of Kuroshio) can induce barrens. Therefore, the targets of 'Isoyake' research should be placed on the establishment of ruled fisheries and balanced utilization of coastal waters.

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The investigation concerned artificial reefs that are creating kelp, Laminaria lerigiosa, habitat at Biya, Hokkaido, Japan. Since the water on the shore side of reefs was shallow, the velocity of water particles due to waves was high, restraining feeding pressure from sea urchins, Strongylocentrotus nudus, and assisting in the formation of kelp forests. However, regarding the reefs on the open sea, the water was deep and wave velocity was low, resulting in intensive feeding pressure from sea urchins and subsequent barren ground. Sea urchins on reefs at the shore side grow faster than ones at the open sea. By adjusting the water depth using rocks and blocks, wave velocity could restrain feeding pressure from sea urchins, thus making it possible to create kelp forests for the fishery of sea urchin.

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