three areas (Marsh A, Marsh B and Lagoon) of Wild Bird Park, which was laid out on reclaimed ... 1) has been open to bird-watchers since September. 1983.
Succession of Benthic Assemblages in Wild Bird Park, a Sanctuary Established on Reclaimed Land in Osaka Port HISASHI YOKOYAMA, TATSUMI UMEHARA and KUNIO ODA Osaka City Institute of Public Health and Environmental Sciences, 8-34 To]o, Tennoji, Osaka, 543 Japan In order to obtain data relevant to increasing the numbers of prey organisms for shorebirds, the population of benthic animals and the environment were surveyed from 1982 to 1989 in three areas (Marsh A, Marsh B and Lagoon) of Wild Bird P a r k , which was laid out on reclaimed land in Osaka Port. In Marsh A, formed by standing rainwater, marine benthic organisms intruded as seawater was introduced. In Marsh B, created by the pumping in of s e a w a t e r , i n t e r t i d a l g a m m a r i d s d i s a p p e a r e d a n d chironomid l a r v a e d o m i n a t e d as f r e s h w a t e r g r a d u a l l y replaced the s e a w a t e r . In the L a g o o n , connected to the sea by ducts, a large biomass and high species diversity were found but large, intertidal animals were scarce. A comparison with the results of surveys made on the tidal flat at the mouth of Onosato River suggests that natural features should be introduced into Wild Bird P a r k for the future development of an intertidal assemblage.
Wild Bird Park in Osaka Port (Fig. 1) has been open to bird-watchers since September 1983. The park, which was reclaimed from the sea by the deposition of sludgy sediments dredged f r o m the harbor area, has a s/~ndy area of 12.8 ha, a planted area of 6.5 ha, and three c o t t a g e s for o b s e r v a t i o n s . In the sandy area there are two marshes and a lagoon, each of which was f o r m e d by a different process: M a r s h A was formed in a depression in which rainwater has collected since August 1981; Marsh B was created by the pumping in of seawater from December 1981 through February 1982, then the seawater was gradually replaced by freshwater as time passed; the Lagoon was made via a connection with the sea formed by ducts in October 1982. t35"OO"
10"
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Fig. 1 Wild Bird Park in Osaka Port. Marine Pollution Bulletin, Vol. 23, pp. 7 3 9 - 7 4 2 , 1991. Printed in Great Britain 0025-326X/91 $3.00+0.00 © 1991 Pergamon Press plc
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Results of the first six surveys of benthic organisms in the bird sanctuary were reported by Yokoyama et al. (1984). In this report, we describe the succession of benthic organisms and their h a b i t a t s in Wild Bird Park, and we suggest environmental f a c t o r s t h a t are essential for the improvement of the park from results of a comparison with the environment on a natural tidal flat. Methods Twenty three surveys were conducted during the period between November 1982 and November 1990 in Wild Bird Park. Benthic animals were collected with a 0.0225-m 2 Ekman-Birge grab and a 1-mm-mesh sieve from 2 to 5 stations in each area. Numbers of individuals and wet weights were determined for each species. Samples of w a t e r and sediment were collected and analyzed in the laboratory. To obtain data applicable to the improvement of the park, benthic fauna, configuration of the ground, and the nature of the sediment such as grain size, ignition loss, COD and quantity of debris of terrestrial plants contained in it were surveyed seasonally on the natural tidal flat at the mouth of Onosato River (Fig. 1) from May 1986 to January 1987. Results and Discussion
Marsh A In this area, the w a t e r quality has been getting worse, as indicated by the increasing val.ues of COD (Fig. 2). This tendency seems to depend on the enrichment by organic matter that originates in the debris from aquatic plants, such as the green alga Oedogonium inversum and the angiosperm Ruppia maritima, and in exudates from the bottom sediments. To improve the water quality, the water was pumped out of the marsh at the beginning of August 1986, and then seawater was pumped into the marsh at 17-22 September 1986. As a result, increased chlorinity and decreased COD were recorded in November 1986. Marsh A was dominated by chironomid larvae t h a t included Polypedilum sp., Pentaneura sp. and Chironomus sp. before the seawater was pumped into this marsh. The seawater brought the chironomid Chironomus salinarius, which occurs in saline waters at the seashore, as well as marine animals, such as the gammarid Corophium insidiosum and the polychaetes Capitella capitata and Polydora sp., into Marsh A. As a result, the biomass increased markedly. However, the numbers of these animals decreased as the s e a w a t e r was exchanged for freshwater. The value of COD increased again and reached 30rag g -~ in August 1987. Therefore, in order to introduce seawater into Marsh A through the Lagoon at high tide, a channel (Fig. 1) was made in March 1988. Then COD decreased, and the density and biomass increased again as a result of the intrusion of marine animals.
Marsh B Marsh B was dominated by the gammarids Corophium volutator and Grandidierella japonica at the time of the first two surveys, when the chlorinity was 3°~ (Fig. 2). It is estimated that these marine species were carried into the marsh with the seawater pumped up into it when the marsh was made. However, these species disappeared and chironomid larvae, including Chironomus sp. and Polypedilurn sp., predominated as the water was replaced by accumulating rainwater.
Lagoon The Lagoon was characterized by the high density and occurrence of a rich variety of species, which included the polychaetes Capitella calntata, Polydara sp. and PseudoPolydora sp., the chironomid Chironomus salinarius, and the g a m m a r i d s Corophium insidiosum and Grandidierella japonica (Fig. 2). Large biomasses of >100g m-" or high densities of >30000 individuals m -2 were often found in summer. However, large benthic organisms (e.g., the polychaete Neanthes japonica, the g a s t r o p o d Batillaria multiformis, and the brachyurans Scoln'mera globosa, Ilyoplax pusilla and Macrophthalmus japonicus), which are c o m m o n on Japanese tidal flats, were scarcely found in this area. Their absence may be caused by the fact that water remains present at low tide because of the higher position of the ducts as compared with the bottom of the lagoon.
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Marsh A t 15
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Fig. 2 Long-term trends with respect to chlorinity, COD and macrobenthic organisms in Marsh A and with respect to macrobenthic organisms in Marsh B and in the Lagoon at Wild Bird Park.
Tidal flat at the mouth of Onosato River The m o u t h of Onosato River is sheltered from the sea by a sandbank, and a small tidal flat with an area of 1 ha, which has a tidal creek and a tide pool, is formed in this area. The tidal flat is characterized by the presence of three brachyurans, namely, Macrophthalmus japonicus, Helice tridens tridens, and Uca lactea lactea, which m o s t likely fall prey to shorebirds. H. tridens tridens was unevenly distributed on the tidal flat. The other two species had their own specific p a t t e r n s of d i s t r i b u t i o n . M. japonicus occurred as the dominant species in wettish, muddy sediments, while U. lactea lactea was distributed only in a sandy area. Heights of the four sampling s t a t i o n s ranged f r o m CDL (chart d a t u m level) +100cm to CDL +116cm (cf., mean sea l e v e l - CDL +94cm). The lowest station had fine (median diameter = M d ~ , 2 . 8 - 3 . 1 ) , wettish sediments t h a t contained a large quantity of organic matter (ignition loss, 3 . 4 - 3 . 9 %; COD, 5 . 4 - 6 . 0 m g g-1 dry mud; dry weight of debris of terrestrial p l a n t s , 306g m-2), while the highest s t a t i o n had coarse ( M d ¢ , 1 . 4 - 1 . 7 ) , drier sediments t h a t contained a small q u a n t i t y of organic m a t t e r ( i g n i t i o n loss, 1 . 9 - 2 . 5 g ; COD, 2 . 2 - 3 . 0 m g g-1 dry m u d ; dry weight of debris of t e r r e s t r i a l p l a n t s , 62g m-~). Such a v a r i e t y of h a b i t a t m a y be responsible f o r the segregation of the constituent species. Details of results of the surveys have already been described by Yokoyama & Yamanishi (1987a, b).
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Tidal f l a t s , where emersion and submersion a l t e r n a t e with the tidal cycle, are valuable feeding areas for m i g r a t i n g shorebirds. E x p a n s i o n of t h e a r e a of the t i d a l f l a t is necessary f o r r e c r u i t m e n t of large i n t e r t i d a l a n i m a l s in Wild Bird Park. D a t a o b t a i n e d from the tidal f l a t a t the m o u t h of Onosato River such as details of the n a t u r a l features, changes in the height of the ground above sea level and variations in the grain size of the sediment should assist in plans for the improvement of Wild Bird Park.
Conclusions T h e i n t r o d u c t i o n of s e a w a t e r i n t o the m a r s h of the artificial b i r d - s a n c t u a r y was v e r y useful for the i m p r o v e m e n t of the w a t e r q u a l i t y and the increase in p o p u l a t i o n of the benthic animals. For the f u r t h e r development of the benthic assemblage in the s a n c t u a r y , it is necessary to expand the intertidal area with reference to the data obtained from the natural tidal flat.
References Yokoyama, H., Kawai, S. & Oda, K. (1984). Macrobenthic fauna in the Natural Bird Sanctuary in Osaka Port. An. Rep. Osaka City Inst. Publ. Hlth & Envir. Sci., 46, 10-18 Yokoyama, H. & Yamanishi, R. (1987a). Maerobenthic animals and their habitats on the tidal flat at the mouth of Onosato River (1). Nature Study, 33, 101-104. Yokoyama, H. & Yamanishi, R. (1987b). Maerobenthic animals and their habitats on the tidal flat at the mouth of Onosato River (2). Nature Study, 33, 111-115.
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