SUMMARY AND PROSPECT OF THE SURVEY
Taiji Kikuchi *
１．Between 1978 survey and the present survey(1989-1992), whole areas of tidal flats, macrophyte beds and scleractinian coral communities around Japan are considerably reduced. Three thousand eight hundred and fifty seven ha of tidal flat was lost during 13 years and the rate of loss is 7.0％ of the area existed in 1978. Almost all of the loss of tidal flat was caused by land filling. Reduction of whole macrophyte beds during the period was 6,403ha, the rate of loss against whole macrophyte beds in 1978 was 3.3％. Among them 19.9% in area was seagrass (Zostera marina) bed, 22.2% was Sargassum bed, and 36.0％ was kelp (Laminaria, Ecklonia, Eisenia and Undaria)bed. High percentage of reduction of seagrass and Sargassum beds was reported in Seto Inland Sea, most of such loss was caused by land filling and other human impact. Moreover, some part of the loss of macrophyte beds qualified by unknown causes may be influenced eutrophication and lowering of transparency related human activity. In Mikawa Bay and Ise Bay, Pacific coast of Central Honshu, ca. 200ha of seagrass bed was lost by land filling. Large area of Seagrass bed and Sargassum bed disappeared in Ariake Sea and Amakusa coast, west Kyushu, considerable area of seagrass bed declined in Mutsu Bay, northern end of Honshu. As the human impact is not so serious in west Kyushu and Mutsu Bay, reason of disappearance was unclear.
Anyway, land filling and other maritime civil engineering, discharge of civil and industrial waste to the sea give serious influence to conservation of tidal flats，macrophyte beds and scleractinian corals. Legal control and more prudent development in and around those habitats are strongly needed.
２. Relationship between long term fluctuation of seawater temperature and fluctuation of seagrass bed and Sargassum bed was discussed. Large scale decline of the seagrass Zostera marina in south and southwest Kyushu where the southern border of its biogeographical distribution range may be blamed to duration of high seawater temperature years since 1980s. Loss or decline of kelp bed was reported in various local provinces, but the causes reported in the inquiry was "isoyake", "change of marine climate", or "unknown". "Isoyake" is a word in Japanese fisherman, designating the replacement of subtidal kelp bed on the rocky bottom by crust of unsegmented coralline algae. Recent theory and evidence of "isoyake"or coralline flat formation by Japanese algal ecologists, and proposal of partial recovery of kelp bed by manipulation of grazing invertebrates are introduced. This technique may serve rehabilitation of a part of damaged kelp bed, direct cause of kelp loss may be some physical impact such as high water temperature and strong wave action, prevension of coralline flat development in wide range may be difficult.
３. More than half of coral reef area in Ryukyu Archipelago ( Okinawa Ken) was low in coral coverage. Destruction of coral communities in shallow part may be caused heavy predation by crown－of－thorn starfish Acanthaster planci in 1980s, decline and weak recovery of coral communities along the coast of Okinawa Island is blamed to human impact such as maritime development, discharge of waste water and red clay run off from the terrestrial arable land and civil engineering works. In the small islands around the Okinawa Island, coral communities are preserved much better condition. In Sekisei shoko (Sekisei lagoon) which is located southern end of Ryukyu Archipelago, remarkable recovery of coral communities were reported recent two or three years (after this national－wide survey).
In the non coral reef building area in the Japan mainland, more than 50ha of coral communities which have more than 25% coverage were discovered in south Kyushu (Miyazaki, Oita, Kagoshima, Kumamoto Ken), south Shikoku (Ehime and Kochi Ken) and southern part of kii Peninsula (Wakayama Ken), central Honshu. Table shape Acropora is most common, Acropora hyacinthus is dominant in open sea coast of south Japan, and A. solitaryensis becomes dominant in more protected environment. There are some endemic species in northern marginal area of coral growing region.
４. Generally speaking, coral damage by human impact is not serious in the Japan mainland. Though the information on coral mortality was lacking in this national－wide investigation, I tried to gather and review the previous reports on coral mortality in the Japan mainland. Mass mortality by occasional very cold winter, and break down the table shape colonies by strong surge at typhoon caused serious decline. Predation by the crown－of－Thorn starfish (Acanthaster planci) is very occasional and not serious.
There are some reports on the outbreak of Muricid whelks of genus Drupella and Morula, and their predation damaged corals. Stamping out of the predatory snails by diver's team was done in some localities. Fortunately, damage by those predatory snails is very limited in spatial range.
５. There are some technical problems about judgement of the degree of coverage of macrophytes and scleractinian corals, and estimation of the areal extent of the community. Estimation of areal extent of tidal flat is rather easy, if we can measure the aerial photo at the low tide of spring tide. For subtidal macrophyte beds and coral communities, determination of coverage classes depends on subjective judgement of the investigator. Another problem is determination of the outline of single community.
For example, whether there is single wide community with coverage class +, or there are several separated patches of coverage class +, I,II etc. scattered in bare substrate, must be determined by subjective judgement. The criteria of judgement must be improved if we make joint training under instruction of coral specialists, however, it will not be possible in the national－wide simultaneous survey in which many investigators, research groups or informant join together. In time sequential comparison between two census, if former survey overestimated the areal extent of seagrass bed or coral community and result of the second survey is exabtly estimated, the area of decline or rate of loss between two census survey will be overestimated.
６. In this survey, coral communities in both coral reef areas and non coral reef building areas were examined both qualitatively and semi－quantitatively. Adoption of the "manta method" (observer towing method) made possible continuous observation of shallow subtidal bottoms along the shore line. Of course there are many critiques on accuracy of identification, influence of transparency on the result, technical difficulty of recording, mistake of judgement by poor experience of observers in some provinces etc. In spite of these defects of the method, I will highly appreciate adoption of this method in this survey. Elaborate survey of non coral reef building areas is very important contribution. Improving of accuracy both in field work and taxonomic identification may be the task remained in future.
７. In this survey, cause of decline or disapperance of the habitat or community was recorded by witness of informant. Except the land filling at the place, it is difficult to determine the cause of decline or disappearance of macrophyte beds or coral communities at single survey. To investigate the real causality of decline, gathering of the record of physical environmental factors such as long term variation of sea water temperature, record of extreme thermal rise or fall, long term variation of nutrient concentration, transparency and turbidity near the macrophyte beds or coral communities are needed. Such information has been deposited in Marine observatories, meteorological observatory or weather stations, and Fishery Experiment Station of each local province. Extraction of data and statistical analysis of the influence of those factors to macrophyte beds and coral communities need another project study.
８. Biological factors, space competition among benthic plants or plants and scleractinian corals, decline of corals by pedation impact of starfish and Muricid snails are also important. Not only the stamping out campaign at their outbreak, basic studies on their ecology and life history, and the environmental cue of their outbreaks are needed.
* Amakusa Marine Biological Laboratory, Kyushu University．