Outline

Efforts are currently underway to expand the present uniform method of water quality management in the Seto Inland Sea to bay and open sea management that takes into consideration social and geopolitical characteristics and seasonal fluctuations, and to preserve and restore nutrient management and biological habitat environments, in order to develop highly sustainable coastal management methods with the aim of achieving healthy substance circulation and high biological productivity that are not impaired by red tides or the like.

Subtopic (1) Development of methods for managing nutrient concentrations

Description of Research (FY 2014 – 2016 Achievements)

While narrowing down the target ocean regions for research and conducting verifications such as identifying and resolving issues with research locations, methods, items etc., we performed biological research into nutrients, phytoplankton and zooplankton, sand eels, anchovies and other sea creatures that feed on plankton and so on, in order to determine the current state of water quality and ocean life. We established basic water quality items for Hiroshima Bay and Osaka Bay and completed measurements of primary and secondary production, and we were able to calculate transfer efficiency. In tidal flats, we were able to determine the main source of food (benthic microalgae) for the clams that constitute an important species for the marine products industry, and to determine primary and secondary production and calculate transfer efficiency. With regard to transparency properties, we succeeded in calculating the percentage of contribution of each of the light attenuation factors in the ocean water in bays and open ocean regions, and developed methods for identifying region-specific transparency (light attenuation caused by particles that do not include phytoplankton) and regions of the Seto Inland Sea where “red tides” are likely to occur due to water quality properties. We also developed a new DNA marker that can be used to estimate sand eel population dynamics and gene flow and, for the first time, scientifically corroborated that the sand eels that inhabit the Seto Inland Sea come from a single genetic population. An analysis conducted using a particle tracking model suggested that it may be possible to deduce the locations of sand eel breeding grounds, and we identified the environmental characteristics of breeding grounds through studies and cultivation experiments, in order to identify the stocks and current state of reproduction of the fish species that play a crucial role in the overall ecosystem of the Seto Inland Sea.

Description of Research (FY 2017 Plan)

Based on the knowledge obtained from past surveys conducted in the central western part of the Seto Inland Sea and the results of the survey conducted this fiscal year, we will analyze the structure of the ecosystem of Osaka Bay, for which abundant knowledge has been obtained in the past, and organize the characteristics specific to this ocean region, such as region-specific transparency and fragility with respect to increased phytoplankton, and identify the differences in ecosystem structure depending on ocean region and the factors that have caused these differences, in order to pursue typification for the purposes of coastal management. In addition, we will use the integrated model for the Seto Inland Sea developed in Topic 5 to further refine the aforementioned typification. In order to understand the behavior of creatures that feed on plankton and the reasons for their decline, we will work to explain these ecosystems and at the same time study the feeding habits of fish-eating fish with regard to the chain leading from plankton-eating creatures to higher trophic level ecosystems.

Subtopic (2) Determination of the function of tidal flats and seaweed beds in nutrient circulation and biological reproduction

Description of Research (FY 2014 – 2016 Achievements)

By determining the nutrient inflow and outflow in the Zostera (eelgrass) beds in the Bisan Seto ocean region, we were able to identify the process of nitrogen utilization by eelgrass and show quantitatively the importance to eelgrass growth of the intermittent supply of nutrients when it rains. We also conducted observations using side-scan sonar and underwater cameras that enabled us to successfully distinguish the distribution areas within the Zostera beds in which eelgrass does and does not flourish.

Description of Research (FY 2017 Plan)

In order to identify the functions that enable the desired nutrient circulation and biological reproduction in tidal flats and seaweed beds in very fragile ocean areas, we will conduct a study of the Maehama Tidal Flat during this fiscal year to assess the functions of the tidal flat through a comparison with the estuarine tidal flat.