Individual study: Use of a pump system helps enhance conditions for fish and crustaceans in the Port of Sakai-Semboku, Kansai region, Japan
Yamochi S. & Oda K. (2002) An attempt to restore suitable conditions for demersal fishes and crustaceans in the Port of Sakai-Semboku, north Osaka Bay, Japan. Aquatic Ecology, 36, 67-83
Low seawater oxygen conditions developed in the summer of 1995 and 1996 in the lower water layer in the Port of Sakai-Semboku, north Osaka Bay (Japan). This led to deterioration of sediment quality and benthic fauna, especially in the innermost part of the port (Dejima Fishing Port) where anoxic conditions prevailed and no benthic animals were found. The study summarised here investigated the possibility of Sakai-Semboku becoming a nursery ground or a 'summer shelter' for benthic fishes and crustaceans (large number of juveniles being present during the winter and spring during periods of better oxygen conditions) by countering the effects of summer hypoxia through installing an oxygenating pump system.
Surveys were conducted (before and after pump installation) of environmental factors (e.g. temperature, salinity and percentage saturation of oxygen of the seawater) and benthic fauna (along transects covering 350 m²) at the Port of Sakai-Semboku in 1995-1998.
A jet streamer pump system (Mitsubishi Type MJS-100) was installed on the sea bed in the Dejima Fishing Port (c. 80,000 m² in area; 4 m maximum depth) and operated from June to September 1998 to improve oxygen conditions. This section of the port has stagnant water with low re-oxygenation potential via tidal exchange. The pump system used can transport oxygen-saturated surface waters to the bottom at a rate of 42,000 mó a day.
Vertical profiles of percentage saturation of oxygen were measured at about 70 m from the pump at intervals during June to September 1996 (before pump installation) and July to August 1998 (after installation).
The overall number of species in transects increased from 0-7 in June-August 1996 to 12-17 in June-August 1998; the number of individuals per 35/m² increased from 0.1-0.7 to 7.7-14.4. This equates to average values in June to August 1998 being 7-times higher for the number of species and 51-times higher for the number of individuals compared to 1996 (total average of number of species: 2.0 in 1996 and 14 in 1998; total average of number of individuals: 0.21 in 1996 and 10.9 in 1998).
The jet pump system in summer 1998 led to an increase of oxygen saturation of the lower seawater layer of about 10% compared to 1996; this appears to have been responsible for improvement in richness and abundance of benthic fishes and crustaceans in 1998.
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