7. IS THE TRANSPLANTING FEASIBLE AND APPROPRIATE? [Excerpt]
One of big questions about the landfill project is whether its mitigation method is appropriate or not. The EIS said that the large-scale transplanting of important sea grass beds is feasible, basing only on a small-scale transplanting test. The following is an excerpt of overall transplanting scheme:
1. OVERVIEW OF CONSERVATION METHODS
(1) Conservation of Important Wildlife Species (Blue mud hopper and Vaucheria constricta)
Since endangered fish species - blue mud hoppers (Scartelaos histophorus) and algae species Vaucheria constricta are found within the planned reclamation area and surroundings, suitable conservation measures are to be carried out for each species.
Blue mud hoppers (Scartelaos histophorus)
Status quo
- (endangered) fish species found in mud flat areas
- their only habitats in Japan are found within Nakagusuku Bay, Okinawa Island
- Nakagusuku Bay is the northern limit of their world distribution
- Their number has gradually increased in recent years and is now approximately 2,700 individuals in Nakagusuku Bay
- Of 2,700, over ten individuals are found in Awase area
Conservation measures
- existing mud flat where this species is found will be excluded from the reclamation area
- artificial mud flat, in which this species can live, will be created around the reclamation area
- cultivating techniques already established in laboratories will be kept and managed
Vaucheria constricta
Status quo
- (threatened) Xanthophyceae algae species found in sand flat areas
- their only habitats in Japan are found only in three coastal areas in Okinawa Island
- habitat size in Awase area is about 1.7 ha
- inevitably most habitats in Awase area will be lost due to this reclamation project
Conservation measures
- Transplanting temporarily to neighboring Yakena area where V. constricta habitat expands up to 106 ha, and then from there to a newly established artificial mud flat area around the reclamation area.
- Developing cultivating techniques in laboratories
2. TRANSPLANGING AND CONSERVATION OF SEA GRASSES
Inevitably a part of sea grass beds is to be lost due to the reclamation project. Thus, approximately 25 ha of dense sea grass beds will be transplanted around the reclamation area.
A transplanting test has been carried out since July 1998 in Awase area, taking into consideration of previous transplanting cases in offshore of Minami-hama, Itoman City, and offshore of Arakawa area, Ishigaki City. It is thought that transplanting is technically feasible since a good development has been observed in spite of many typhoon landings.
(1) Transplanting Test of Sea Grasses (sea grass beds)
As regards the transplanting survey of sea grasses, two species of large tropical sea grasses - namely Cymodocea serulata and Syringodium isoetifolium - were selected since both are dominant in the area. Three sites, where sea grasses are sparsely distributed in the western side of vessel route in Awase area (see Figure 1), were selected for transplanting tests. The tests were initiated by transplanting both species into 2 m by 2 m quadrates. The "method of law plantation" was used for transplanting. Monitoring surveys were carried out six times from October 1998 through February 2000.
Of these three sites, most transplanted sea grasses have survived (developed their roots) in the area. Sea grasses in two sites are growing well and forming sea grass beds. Sea grasses in another site have survived, but are not forming sea grass beds due to not good conditions for their growth (see Table 1 and Figure 2). From these results, transplanting of sea grasses in the area is considered to be technically feasible.
Regarding a large-scale engineering method for transplanting sea grasses, measures taken in five cases were compared and reviewed in 1999. As a result, the most suitable method for a large-scale transplanting method for sea grasses in this area is the method of combining backhoe dredgers and collecting boxes.
(2) Transplanting Test of V. constricta
V. constricta is an algae species belongs to Xanthophyceae. In Japan, V. constricta are found in three areas, where small sea grass species such as Halodule pinifolia are found and little movement of sand is observed on mud flats, in Okinawa Island: offshore of Yakena area, Yonashiro Town (total habitat area is about 106 ha as of February 2000, see Figure 3); offshore of Awase area, Okinawa City (habitat area is about 1.7 ha as of March 2000, see Figure 4); and offshore of Ota area, Onna Village (habitat area is about 2 ha as of March 2000, see Figure 5). V. constricta has its resting phase as eggs in sands (thallus/an algal body withers) during summer seasons when water temperature is high, and forms its thallus only in winter seasons. Therefore their thalli can be observed only from January through May.
The maturity of V. constricta was observed in February 2000, and transplanting from Awase area to Yakena and Katsuren areas was carried out (see Figure 6). As a result, 70 to 80% of its colony survived one month after transplanting. Since V. constricta is an annual plant, transplanted individuals withered and were washed away from spring to summer. However, their eggs rest within sands of transplanted sites. Appeared thalli were observed in two out of three transplanted sites in January 2001.
Eggs resting within sands in Awase area were also transplanted to Yakena area in late September 2000. About four months later, thalli were observed at one out of three transplanted sites in late January 2001.
It is known that eggs of V. constricta do not disperse in large area and therefore is found in the same area next year. Thus, it is thought to be feasible to maintain their annual life cycle if conditions such as movement of surface sands and ground level of beds are to be kept.
3. TRANSPLANTING METHODS (Sea Grass Beds and V. constricta)
(1) Transplanting Method of Sea Grasses
In order to carry out a large-scale transplanting of inevitably disappearing sea grass beds, it was suggested to use a backhoe dredger and a collecting box for protecting sea grasses as well as for smooth and cost-efficient operations.
By loading a backhoe dredger on a deck barge and attaching a collecting box into its bucket, sea grasses will be collected and transplanted from the vessel. This method will allow quick and easy collecting/transplanting of sea grasses.
Figure 6 shows the flow of operations using a backhoe dredger and a collecting box, and Figure 7 shows collecting and transplanting.
Procedures of collecting, transferring and transplanting of sea grasses by using a backhoe dredger and a collecting box is as follows:
(a) Collecting and transferring of sea grasses
After divers confirm sea grass beds to be collected, a deck barge with a backhoe dredger will be deployed.
Sea grasses will be put into a collecting box which is attached to a backhoe dredger. The vessel will transfer collected sea grasses.
(b) Transplanting of sea grasses
After divers confirm a suitable transplanting site, a collecting box attached to a backhoe dredger will put down on to the bottom of sea. Then collected sea grasses will be transplanted.
Concerning this machine-operated method, a pilot transplanting will be carried out in March 2001. Taking into consideration of its result, the major operation will then be implemented.
(2) Transplanting Method for V. constricta
The overview of transplanting method for V. constricta is shown in Figure 8.
[1] Transplanting test of V. constricta
The purpose of this transplanting test is to establish a primary transplanting method by monitoring and reviewing results of the test. V. constricta is to be transplanted from its original habitat in the Awase area to the surrounding areas of major habitats in Yakena Area and Katsuren Area (see Figure 9).
Two methods are to be used. They are the "thallus transplanting" before their maturity and the "sand sea bottlm transplanting". The latter method transplants sands which include eggs after their dispersal.
(a) Transplanting of thalli
This method is carried out during the spring tide. V. constricta will be collected from marginal areas of its dense habitats in daytime at low tide. Paying attention not to harm its rhizoid (or holdfast), sands around V. constricta will be dug. V. constricta with sand material will be put into a container. The body of V. constricta will immediately transferred to a transplanting site and then be put in.
(b) Transplanting of sand sea bottom
After confirming the dispersal of eggs, sand bed surfaces will be collected within V. constricta communities. Then sands are transferred to a transplanting site and then replacing bed surfaces.
[2] Cultivating test of V. constricta in laboratories
The purpose of this test is to develop techniques for cultivating and protecting eggs from the viewpoint of species conservation as well as to understand suitable conditions for the growth and maturity of V. constricta in details.
The cultivating test will use collected eggs from fertile (matured) thalli of V. constricta as well as sand beds with many eggs. Necessary conditions for germination will be sorted out, by repeating artificial germination tests step by step with different conditions of temperature, light and water quality found in fields.
<Test methods>
Fertile (matured) thalli of V. constricta or sand beds which include many eggs were transferred to a laboratory (which belongs to the Okinawa City Fishermen's Association shown in Figure 9), put in laboratory dishes and have been observed. The following experiments have been already started:
- Conditions for egg germination with different water temperature
- Germination experiments from the (summer) resting phase with different water temperature
- Conditions for egg germination with different light exposure
- Germination experiments from the (summer) resting phase with different light exposure
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