The upwelling current brings up dense, cold and nutrient-rich water from the subsurface towards sea surface. By supplying the nutrients into the euphotic zone, primary productivity will be enhanced and the high-level productions will increase there as a result of a food chain. Therefore, in order to make rich fishing ground, studies on artificial upwelling devices such as marine structures installed on the sea bottom were made so far. Vertical stratification of water density may often occur in oceans, depending on season and latitude. The flows in these regions result in the stratified density current. In the present study, in order to investigate the effect of the stratification on the upwelling induced by the marine structures, flow visualization tests in the homogeneous and stratified flows were carried out in the small towing tank. The stratification was achieved by salt water and fresh water. Two kinds of stratification were used in the experiments, i.e. linear density profile and two-layer flows with different densities. A sea mountain range, V-shaped and X-shaped structure models were used in the present flow visualization tests. It is shown that the density stratification suppresses uplifting of water due to upwelling induced by the artificial marine structure significantly. Richardson number and densimetric Froude number are recognized to be important parameters for upwelling in the stratified density flow. An internal gravity wave in the two layer flow becomes steepest at internal Froude number of 0.8.
Along the southwestern coast of Hokkaido, the urchin barren has been persistently dominated by sea urchin for a long time, which has restricted the kelp beds to shallow waters, largely less than 2m in depth. Because of overgrazing of sea urchins that were settled onto the artificial kelp reef on the urchin barren, a loss or decline of kelp has been observed. This report illustrates some proposals about developing the kelp nursery in the urchin barren. It is important to reconcile the crown depth of the substrata for the kelp with the depth which the sea urchin cannot exist. It is desired to make the uneven crown of the substrata in a range of depth which the kelp can distribute. Also if the factor which was obstructing the growth of the kelp was observed, it is important to understand the limiting factor and to recover the kelp nursery through an adaptive management process.
Effect of marine environment on annual changes in first year biomass of Saccharina japonica var. ochotensis in summer (hereinafter referred to as Kelp biomass) were investigated from 1998 to 2010, at Rishiri Island, Japan. Relatively large fluctuations were observed for both Kelp biomass (mean 257g m^<-2>; range 0-1571g m^<-2>) and sea urchin biomass (mean 153g m^<-2>; range 40-348g m^<-2>) during study period. The correlation coefficient between Kelp biomass and sea urchin biomass was negative (r=-0.34, n=12, p=0.28). The relationship between Kelp biomass and each temperature from January to April was unclear. DIN (NO_3-N+NO_2-N) concentration decreased from January to April, on the other hand PO_4-P concentration was relatively uniform. Changes in the NP ratio from January to April indicated that exhaustion of DIN occurred in March and April. The correlation coefficient between Kelp biomass and DIN concentration in March was significantly positive (r=0.83, n=9, p<0.01). These results suggest that DIN concentration in March is limiting factor of Kelp growth at Rishiri Island. We use a generalized linear model (GLM) to statistically analyze the field survey data. The model using DIN concentration in March and sea urchin biomass as explanatory variable was selected by AIC. This result suggests that DIN concentration in March and sea urchin biomass are important for changes in first year biomass of Kelp at Rishri Island.
Fertilization effects promoting growth of Saccharina japonica var. religiosa (Miyabe) and reforming seaweeds community with density control of sea urchins were investigated in southwest coast of Japan Sea off Hokkaido, Japan which is characterized as oligotrophy. Fertilizer-controlled dissolved inorganic nitrogen (DIN) was carried out by adding NH_4-N ((NH_4)_2SO_4) in the coastal sea area of Kaminokuni, Hiyama, Hokkaido, Japan for 24 hours from autumn to early summer next year. By adding NH_4-N, DIN concentration at the fertilization point could be maintained at 1mg/L greater. The algal body of Saccharina at the fertilization point became significantly larger than that at the non-fertilization point. Fertilizing with removing sea urchins, seaweeds community was reformed. However, without removing sea urchins, seaweeds community was not reformed even if fertilization. It was confirmed that fertilization with density control of sea urchins was necessary to reform seaweeds community there. Here we also suggest applicability of nitrogen stable isotope (δ^<15>N) signature in algal tissue as a new indicator of detecting fertilization effects. The δ^<15>N value of Saccharina collected from fertilization point was significantly depleted. This result indicated that Saccharina had assimilated high concentrated DIN of fertilization origin.
Production of kelp in Japan was decreasing sharply, especially in eastern Hokkaido Japan, Saccharina longissima. To conserve the kelp forest, Hokkaido Government has tried some methods for increasing production of kelp. This paper introduce present situation of kelp fisheries in eastern Hokkaido and weed control weed control (removing algae and sea weed) as methods of kelp ground conservation. Future direction and present situation of removing procedure are also shown.
In order to conserve kelp bed of Saccharina japonica with maintenance of genetic diversity, we investigated the genetic diversity using AFLP and microsatellite markers, and also searched proteins of which the expression level change depending on environmental condition with the objective of developing diagnostic technic to detect an environmental stress. As results of AFLP analysis, genetic difference was detected between collecting sites. It is recognized that, except for several populations, genetic similarity coefficient (S) between populations was correlated with regional continuity. Developed 10 microsatellite markers could detect polymorphisms between individuals. The results from proteomic profiling, the expression of 51 spots was enhanced under high temperature condition, and of nine spots under oligotrophic condition. The genetic parameters obtained from AFLP analysis suggested that several local populations existed. In other words, extinction of these populations indicated the loss of genetic diversity. Therefore, persistence of them becomes major issue for conservation of genetic diversity of this species. It seems that the diagnostic technic to detect the environmental stress plays a key role in maintaining kelp beds in the future.
Present situation of fisheries resourse of kelp (remarks and system of fisheries, research) in southern Sakhalin, Russia, are intrduced. Second year kelp individual only catch by hand of diver or using fisheries hook. Their fisheries season are different in area, in eastern coast, the duration ranged from 15th April to 30th September, in western side is from 1st May to 30th September. Quota of kelp was determined based on present fisheies resourse of kelp, genereally the production of kelp is different between easter coast and western coast. To decide the quota of kelp, more accurate scientific research are conducted in Sakhalin, distribution, life cycle, reproductive biology, morphology, molecular, oceanography and their affect for kelp bed are currently studied.
The kelp, Saccharina japonica var. ochotensis, is one of the most important fisheries resources for Northern Hokkaido, Japan, and Southern Sakhalin, Russia. Recently, the resources are decreasing in two areas, it make serious issues. Based on previous studies, we guess that warmer water temperature bring poor nitrate and higher grazing pressure of sea urchin for kelp, it cause decreasing the production of the kelp. However, it has not yet confirmed in kelp ground, so oceanographic condition during winter season (February) and biomass of kelp and sea urchins during summer season (from June to August) were observed in Hokkaido (Otaru and Rishiri) and Sakhalin (Yablochnyy and Bogdanovitch). At the most warm station, Otaru, there is no kelp but many long-spine sea urchin Strongylocentrous nudus appeared, whereas the most cold station, Yablochnyy, have abundant kelp and short-spine sea urchin S. intermedius. Concentration of nitrate does not show much difference among each station. In this study examined affection of water temperature, nitrate, grazing pressure of sea urchin for kelp. It is clear that water temperature and the grazing effects for kelp, but nitrate does not show efficiency for the kelp ground.
From past decade, kelp fisheries in Hokkaido Japan have several issues and catch volume is decreasing sharply. Present situation, future direction, and policy for increasing kelp production are explained.