This paper describes a method of estimating the limiting factors for the distribution of eelgrass beds using a neural network from the results of an environmental investigation. After conducting the environmental investigation in eleven areas of the Seto Inland Sea, we used the back propagation method to model a layered neural network to determine the degree of eelgrass growth under differing environmental conditions. The explanatory variables of this network are water depth, net photosynthetic rate, wave height, gradation of bottom material (the proportion of gravel, sand, silt and clay), and oxidation-reduction potential of bottom material. We performed a neural network simulation to estimate the limiting factors for the distribution of eelgrass beds along the coast near Kasaoka-shi, Okayama Prefecture. Our simulation assumed the following four cases about the input values for the environmental conditions at each prediction point in the simulation range from the results of the environmental investigation on this coast: 1) present environmental condition, 2) extinction coefficient (index of sea water turbidity) half of present condition, 3) wave height half of present condition, and 4) proportion of silt and clay half of present condition. For each case, the range of possible prediction points with eelgrass growth present was extracted as the potential area of eelgrass bed distribution. The limiting factors were estimated by comparing these results. The potential area of distribution was dramatically larger for case 2 than case 1. Case 3 increased the area slightly, with little or no increase in case 4. This simulation revealed that sea water turbidity, or loss of light, is the most powerful limiting factor, but wave height also limits the distribution of eelgrass beds on this coast. Given the results of an environmental investigation, this method is a simple, useful way to estimate the factors limiting the distribution of eelgrass.

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In order to apply individual-based fish school behavior model to evaluate fishway effectiveness, parameters in the model e.g. parameter of rheotaxis should be improved. In this study, upstream behavior of Japanese dace school was observed in an experimental vertical-slot fishway installed in an indoor flume channel, and rheotaxis of individual fish was examined. In the upstream passage, fish school seldom entered the pools created between the vertical-slot baffles. Flow velocity was 0.2m/s at the no-baffle area in the flume channel. In contrast, water flow was accelerated at the slot area of vertical-slot fishway because the channel width was narrowed by the baffles, and the velocity was over 0.5m/s at the center of the slot area. However, there was a zone of low flow velocity (0.2m/s) close to the pools in the slot area, and fish school ascended at the low-velocity zone. When fish traversed fast flow area at the upper part of the slot area, the rheotaxis appeared to become strong. Fish employed the burst speed against fast flow, while they swam at their sustainable speed in ascending in the low-velocity area. In vertical-slot fishway, the flow velocity varied largely, and the flow pattern was complicated. Fish were likely to ascend through the low-velocity zone, and appeared to change their swimming speed according to the flow velocity to maintain the ground speed.

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In some Japanese coastal areas, seaweed beds have recently declined and changed into barren ground, so-called Isoyake. It is known that Isoyake in pacific coastal areas depends on the rout of Kuroshio Current, which is high water temperature and low nutrient concentration. An approaching of Kuroshio Current leads to a decrease of seaweed growth rate and an increase of herbivore grazing rate. At Muroto coastal area in Shikoku Island, many of seaweed beds have declined since over fifteen years ago. Deep ocean water (DOW) is low water temperature and high nutrient concentration. Thus DOW may leads to an increase of seaweed growth rate and a decrease of herbivore grazing rate. It has been reported that the DOW discharge may restore seaweed bed from Isoyake condition at Muroto coastal area. In this study, numerical simulations using a seaweed bed ecosystem model, which was based on the data of field surveys and biological experiments, were performed to clarify the mechanism of the recovery of seaweed bed. The results of numerical simulations showed that the nutrient concentration and grazing pressure, which depend on the deep ocean water content, are the important factors for the seaweed bed recovery.

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The excessive over population of some algae eating fish are known as one of the cautions of isoyake. Such phenomenon supposed to be resolved by introducing those fish in value-added seafood development. Based on this fact, we assessed the potential utilization of algae eating rabbit fish Siganus fuscescens and bassy chub Kyphosus spp. as the raw material for value-added thermal gel products development. Based on our experimental findings, we consistently proclaimed that rabbit fish meat is useful raw material for high quality thermal gel product production other than that of spawning and spent ones. Consequently, unlike rabbit fish bassy chub meat functions well for quality thermal gel product production throughout the year, though low whiteness may limit its wide application in food industry. However, further studies in this line are needed to explore algae eating fishes in high quality seafood production.

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The barren ground, known as "isoyake" in Japanese, is a phenomenon of the disappearance of seaweeds caused by certain factors. It is also a serious environmental problem in the conservation of coastal biodiversity and fisheries resources. Since 1971, the Kagoshima Prefectural Fisheries Technology and Development Center (KPFTDC, formerly Kagoshima Prefectural Experimental Station) had been conducting field studies in identified barren grounds so as to introduce some interventions to restore the seaweed communities. The hypothesis was that the seaweed communities were negatively impacted by fish and sea urchin grazing. We reviewed recent studies of the barren ground phenomenon that focused on removing the limiting factors of the growth of seaweed communities. Results of the survey in 2002 and 2003 revealed that the composition of seaweed grazers, water temperature and other environmental factors of the barren grounds showed no significant differences compared to those of the natural seaweed communities. However, the former had higher biomass of grazers compared to the latter. Based on this information, we suggested the possible influence of maximum grazing and its detrimental effects to the primary growth of seaweeds. I also discussed some factors that led to the occurrence of barren grounds and its continuance, and what methods to consider for the optimum restoration of such 'lost' seaweed communities.

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Recently, browsing by herbivorous fishes has been paid attention as a causative agent of seaweed/seagrass bed reduction in warm temperate waters of Japan. Although occurrence of these fishes has been known for > 100 years, information on their ecology and resource levels has been quite limited. To evaluate the above phenomenon, roles and interactions of marine plants and herbivores were reviewed with special reference to the feeding ecology of herbivorous fishes in the world. The recent prevalence of destructive herbivorous fishes in Japan is very unique enough to reconsider coastal changes and overfishing rather than elevation of water temperature.

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Recently, it becomes clear that the herbivorous fishes such as Rabbitfish eating seaweed too much is one of the main factors which cause the Isoyake (Sea deforestation) in the south part of Japan. Therefore we have to make decrease the inhabiting density of these fishes by fishing to preserve and expand the seaweed bed against over-eating by the herbivorous fishes. But there are few regions in Japan to catch herbivorous fishes as main targets of fishing, it has been hardly studied about the fishing methods of the herbivorous fishes at the Isoyake areas. To study effective fishing method of the herbivorous fish, I examined some cases of fishing for these fishes in every place in Japan. Many Rabbitfish were captured by the gillnet in Okinawa prefecture where most Rabbitfish are captured in Japan. The effective fishing method for the Rabbitfish by gillnet are particularly considered in this report.

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Seasonal and diurnal feeding patterns were studied on the herbivorous fish Siganus fuscescens, which was reported to be the causative agents of deforestation of kelp beds in southern coasts of Kii Peninsula, Wakayama Prefecture, Japan. Culture experiments revealed that S. fuscescens feeds Ecklonia most vigorously in late September, ranging from 26 to 29℃ in water temperature. The highest averaged feeding rate recorded during the decade was 3.97%. The feeding time of S. fuscescens in a day was found to be 9:00 to 17:00 with a notable peak from 13:00 to 15:00. To find effective methods of protecting kelp in larger scales, auditory stimuli were challenged in tanks and/or cages using iron drums driven with water and wind energies, respectively. Although auditory stimuli were effective to lowering the feeding rate of S. fuscescens, further studies are needed to overwhelm the acclimatization.

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Laboratory experiments were conducted to evaluate the effects of wave-induced oscillatory flow and temperature on feeding by the rabbitfish Siganus fuscescens on the kelp Ecklonia cava or Eisenia bicyclis. With a constant temperature of 20℃, feeding rates were very low from July to August and then increased until November. When feeding activity was highest, oscillating flow reduced feeding to 50% at the velocity amplitude of l.lm/s and to nil at ca 1.5m/s. An experiment with variable temperatures showed that temperature threshold for initiating feeding on kelp were variable with time, from 23℃ in late July to 17℃ in early November. Once reached maximal, feeding rate remained high until temperature was lower than 19℃ and then decreases to zero at 16℃. Contrary to expectations, the experimental results and wave-induced water velocity predictions lead to the conclusion that destructive feeding by S. fuscescens on kelp is very unlikely to be inhibited by waves on the Pacific coast of central Honshu, requiring further studies of the feeding ecology of S. fuscescens.

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To detect the trend on seaweed restoration techniques on barren grounds in Japan, domestic literature (> 1,000) published since 1970 were surveyed. The literature contains local survey (18%), experiments and detailed observations (23%), recovery trials (43%) and reviews (16%). The literature increased chronologically with a temporal maximum in 1980-85. Among the local areas, literature was particularly abundant in western coasts of Hokkaido and Pacific coasts of middle Honshu (from the Kii Channel to Cape Inubo). The target seaweed bed types were mostly kelp and Sargassum forests and the dominant causative agents of these bed reductions were intensive grazing by sea urchins and herbivorous fishes. The literature analysis revealed that 'removal' of sea urchins and 'defense' of seaweeds were unreasonably preceded by employing stones or concrete blocks and transplanting seaweeds. Grazing by herbivorous fishes is a recent problem in southern Japan; the literature abruptly increases after 2000. These may represent some of the reasons why barren ground recovery projects were unsuccessful.

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Using the database (number of literature > 1,000, 1970 to 2005) on barren ground reported from Japanese coasts, component techniques in 'Isoyake' recovery technology were summarized as a systematic tree to seaweed review restoration technologies were reviewed. The component techniques are termed as 'module' of individual techniques. The systematic trees are composed of two main branches, 'control of intensive grazing by herbivores' and 'stock enhancement of seaweeds'. The former main branch was divided into two branches, 'sea urchins' and 'herbivorous fishes', which are comprised of nine and six component techniques, respectively. In each of these branches; the techniques are categorized into three groups, 'removal', 'dispersal' and 'exclusion'. The latter main branch is composed of thirteen techniques categorized into five groups, 'transplantation', 'illumination', 'fertilization', 'employment of substratum' and 'removal of sedimentation'. In order to recover the seaweed community on intensively grazed areas, the techniques in the first main branch should not be preceded by those in the latter branch.

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As a beginning of a nationwide 'Isoyake' project (2004 to 2006), we surveyed the current status of reduction of seaweed beds in Japan by hearing from 39 coastal prefectural governments. The survey revealed that seaweed beds reduced at least from 86 areas of 37 prefectures. The most prominent trend is the increase of urchin barrens and deforestation by herbivorous fish in southern Japan; these two phenomena are sometimes coupled together. The southern type of urchin barren is inhabited by Anthocidaris, Diadema, Echinometra or Hemicentrotus, while the northern type is dominated by Strongylocentrotus. Deforestation by fish browsing is caused by Siganus, Calotomus, Priomirus and Kyphosus (the latter two are limited to exposed coasts), among which Siganus was shown to extend up to warm temperate Sea of Japan coast of northern Honshu. In Siganus, juveniles rather than adults are becoming frequently found by divers or caught by set nets. Fluctuations of Kuroshio, elevation of water temperature, change of coastal currents, increase of turbidity and local accumulation of volcanic ash are also enumerated as the causative agents of the recent seaweed bed reductions.

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