No abstract

A construction of breakwaters and other shoreline structures on part of a coast influences drift sand transport in the bay, and causes comprehensive topographic changes on the beach. This study investigated shoreline and coastal changes, taking as an example of Shiraragahama Beach in Miiraku on the northwestern end of Fukue Island, Nagasaki Prefecture (Kyushu, Japan). Miiraku, adjacent to Saikai National Park, appears in the revered 8th century poetry collection “Manyoshu” and served as a port for a ship taken by the Japanese envoy to China during the Tang Dynasty (618-709). Because of the recent development of breakwaters for a fishing harbor, the shore environments of this beach have changed significantly. In this study, the status of silt deposits and topographic changes on this beach arising from the construction of a harbor breakwater were evaluated by comparing aerial photographs taken in different years. Next, the changes in the shoreline visible from aerial photographs from 1947 to 2014 were analyzed. Lastly, the altitude of the beaches was measured using accurate survey methods. The following results were obtained: 1) coastal erosion made rock cliffs to fall off along the shore and deposited sand on this beach; 2) the more serious advances or retreats of the shoreline took place around shoreline structures; 3) sandbars and beach cliffs were formed.

Variations in the fish community structure in Omura Bay, an enclosed bay in the East China Sea, were investigated using long-term fishery landing data over the past five decades . We confirmed that the fish community structure in Omura Bay showed three conspicuous regimes during the study period. Anchovies dominated in the pelagic domain with abundant and various demersal fish species in the first phase (1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978). Demersal fish declined remarkably with the dominance of sardines in the pelagic domain during the second phase (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987), and the fish community was simplified with the return of anchovies and no recovery of demersal fish in the third phase (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006). These changes were significantly related with periodic largescale climate changes and cumulative regional-scale human impacts. The replacement of sardine/anchovy caused by a climate regime shift in the North Pacific contributed to the fish community regime shifts in Omura Bay. Moreover, habitat degradation such as depletion of dissolved oxygen combined with climate-induced changes in food web systems resulted in a rapid reduction in demersal fish. Contraction of the habitat volume due to an increase in oxygen-restricted water simplified the fish community structure and eventually reduced fishery landings in Omura Bay. These findings demonstrate that long-term fish community responses to largescale climate changes and regional-scale human impacts can be observed in a coastal enclosed bay, providing useful information for fisheries management in areas with climate and human-induced changes.

This study focuses on rounded fields, or “Maruhata” in Japanese, on the Miiraku Peninsula located in northwest Fukue Island, one of the Goto Islands, Nagasaki Prefecture. Maruhata fields are normally used for agriculture, but they may have multiple functions, for example in preventing floods by temporarily holding water during heavy rains. We conducted a field survey at a three-tiered Maruhata field in the Take District in Miiraku in to measure its latitude, longitude, and elevation. The presence of Maruhata fields smooths out the inclined plane and offers a flood prevention function by retaining water within during heavy rains and ameliorate flows by breaking the gradient. In addition, Maruhata fields have a function to prevent mud and soil to flow into the sea and reduce pressure on the fishing ground. We conclude that Maruhata fields have a disaster prevention function owning to their topographic features in addition to their function as agricultural fields.

A construction of breakwaters and other shoreline structures on part of a coast influences drift sand transport in the bay, and causes comprehensive topographic changes on the beach. This study investigated shoreline and coastal changes, taking as an example of Shiraragahama Beach in Miiraku on the northwestern end of Fukue Island, Nagasaki Prefecture (Kyushu, Japan). Miiraku, adjacent to Saikai National Park, appears in the revered 8th century poetry collection “Manyoshu” and served as a port for a ship taken by the Japanese envoy to China during the Tang Dynasty (618-709). Because of the recent development of breakwaters for a fishing harbor, the shore environments of this beach have changed significantly. In this study, the status of silt deposits and topographic changes on this beach arising from the construction of a harbor breakwater were evaluated by comparing aerial photographs taken in different years. Next, the changes in the shoreline visible from aerial photographs from 1947 to 2014 were analyzed. Lastly, the altitude of the beaches was measured using accurate survey methods. The following results were obtained: 1) coastal erosion made rock cliffs to fall off along the shore and deposited sand on this beach; 2) the more serious advances or retreats of the shoreline took place around shoreline structures; 3) sandbars and beach cliffs were formed.