Sediment Fauna, Fisheries Catches and Land Earning from the Korean Tidal Flat
Sediment Fauna, Fisheries Catches and Land Earning from the Korea and Tidal Flat
Koh Chul-Kwan(Professor, Department of Oceanography, Seoul National University)
This paper reports that the coastal use of the Korean west sea has been concentrated rather in the mass land earning than the nature conservation. Faunal records, secondary production of bivalves and fisheries catches are described to emphasis the ecological importance of the tidal flat. Studies on sediment fauna and annual production of bivalves inhabiting tidal flats were carried out at 167 stations of 8 localities along the whole coast from 1989 to 1997. A total of 94 taxa were identified. Dominant species were: Heteromastus sp., Umbonium thomasi, Latenula cf. limicola and Lingula anatina. The high biomass of edible bivalves at different localities were shown by Sinonovacula constricta (2,678 g TWW m-2, Total Wet Weight including the shell), Ruditapes philippinarum (1,221 g TWW m-2) and Mactra veneriformis (629 g TWW m-2). Annual production of those species calculated from the growth rate and biomass were 1,358, 1,635, and 2,998 g TWW m-2, respectively. Important fisheries catches were mollusces. The areal dimension of land earning from the tidal flat was recorded as 405 km2 from 1917 to 1945, 625 km2 from 1946 to 1994 and 764 km2 including the project in progress. Those deterioration threatens the coastal ecosystem and, therefore, a change in policy of land earning is needed.
The Korean (South) West Sea located in the eastern Yellow Sea belongs to a macrotidal regime where the tidal height reaches up to 10 m on the coast in the north. The high tidal ranges and the gentle bottom slope produce broad tidal flats which rival those on the North Sea coast. Tidal flats are developed to about 10 km wide in many places and occupies an area of about 2,800 km2. The coast is one of the rias with dented geomorphology.
The coastal use on the West Sea has mostly been directed to a reclamation of tidal flats by separating them from the sea by sea walls. Dikes has been constructed at the mouths of bays if there a wedge-shaped tidal flat is developed. Land earning is the prime interest and, therefore, tidal flats have frequently been diked and land-filled.
This study is aimed primarily to present biological data to give an overview of sediment infauna occurring on the Korean tidal flat. Biological resources are evaluated based on data of secondary production estimated for edible bivalves. Statistics on fisheries catches are also included to demonstrate the high productivity of the Korean tidal flats. By referring the historic records of the tidal flat reclamation, we have discussed the future strategies of an wise use of the Korean coast. It was of our question how political economy and collective action concerning the utilization of such unique ecosystem should be structured in the future.
MATERIALS AND METHODS
Field surveys has been carried out at 167 stations assigned to different tidal flats from the north to the south along the whole west coast (Fig. 1). We named the surveyed tidal flats by the villages located nearby as Youngjongdo, Songdo, Panweol, Hwasung, Daesan, Kunsan, Kimje, Buan tidal flat.
Subjects which were concentrated during the surveys were the occurrence of sediment fauna by species and individual numbers, and the biomass and seasonal growth edible bivalves. As an environmental factor, grain size of the sediment has been analyzed at every stations. Occurrence of the tidal flat animal was investigated at 8 localities along the coast. A box core of 0.1 x 0.2 x 0.3 m (surface area: 0.02 m2) was mostly used to collect the benthic animal. The collected sediments were washed on a 1 mm mesh sized sieve, and the animals retained were fixed with 10 % formalin solution in seawater. After identification and counting the individuals in the laboratory, individual numbers were converted to the numbers per 1 m2.
Object animals for the production studies were Mactra veneriformis common to the sand flat, and Sinnovacula constricta, a typical bivalve on the mud flat, and Ruditapes philippinarum frequently found on silty to sandy sediments. The production study of M. veneriformis was conducted on the Songdo tidal flat at 17 occasions from March 1989 to September 1990. The bivalve M. veneriformis was collected from ten 0.5 x 0.5 m quadrates randomly laid on the lower intertidal. The shell length and flesh dry weight of more than 100 individuals was measured at every survey. A multiplication of the individual dry weight with individual numbers counted from the sample quadrates produced the biomass (B) which was applied to an estimation of the secondary production. The production, P, was then calculated by a multiplication of the relative growth rate, G, with the biomass (Ricker, 1946). The production was estimated for every age class obtained by counting the growth ring. The annual yield of M. veneriformis was the sum of the production calculated for every age class.
The study on the production of S. constricta was carried out on the Hwasung mud flat for one year from September 1992. The production biology of the Manila clam, R. philippinarum, was studied on the Daesan tidal flat on 13 occasions from September 1991 to 1992 at monthly intervals.
Type of sediments
The predominance of sand and silty sand sediments was observed on the Songdo tidal flat, while the finer silts were typical of the Yongjongdo tidal flat. The majority of the Hwasung tidal flat was characterized by silts, whereas the sediments on Panweol tidal flats contained higher percentage of clay. The broadest tidal flat around Kunsan, Kimje and Buan were `composed of sand to silt sediments.
In brief, the tidal flat of Yeongjongdo, Panweol and Hwasung belonged to silt-mud flat, while Songdo, Kunsan, Kimje and Buan tidal flats could be described as sandy-silt to sand flat.
Fig. 1. Distribution of the Korean (South) tidal flat. Areal dimension is estimated as about 2,810 km2. Tidal flats located in the northern part is broader due to the high tidal range (up to 9 m). Sediment fauna was investigated at 8 tidal flats marked by arrow.
Among the total of 167 stations, silty sand (23.6%), sandy silt (24.2%) and silt faces (23.6%) were predominated and then the sand face (15.8) followed. Less mud faces were found (7.3%). Most stations were characterized by well sorted sediment, but several stations showing a mixture of mud with sand near Kunsan (5.5%) were found.
A total of 94 taxa have been collected. The polychaete involved the largest number of taxa (50 among 94 species) and then the pelecypod (16 species), crabs (12 species) and gastropod (7 species). Two of holothurian species were found: one of which Protankyra bidentata was considered for typical of the outer tidal flat. The living fossil species belonging to the brachiopod, Lingula anatina, was found overall on the coast, but mostly near Kimje, especially in the middle intertidal in so far as the sediment was a mixed type of silt with mud.
Data on density (individual numbers per m2) and frequency (% occurrence at sampling stations) of the most abundant 19 taxa on 8 tidal flats are presented in Table 1. The taxa listed in Table 1 belonged mostly to infauna. Occurrence of epifauna would be poorly described by samplings with a box core covering an area of 0.02 m2 employed in this study. The most dominant species listed in Table 1 would, therefore, give a different perception from that obtained when we observe the tidal flat at a glance. For example, the gastropods such as Bullacta exarata and Hinia festiva were frequently found with naked eye on the silty sediments, however, those taxa ranked second dominant group in Table 1. In spite of those shortages, we could define characteristic species at different localities and sediment faces. Followings describe the characteristic species of each tidal flat from north to south.
Table 1. Densities (number of individuals per m2) and occurrence (Frequency in percent of number of stations occurred among total stations (n) investigated) of dominant species on the Korean tidal flat. Frequencies are indicated in the parenthesis. The species are sorted by the similarity of occurrence and listed by that order. Abbreviations are as P: polychaetes, G: gastropods, Br: brachiopods, H: holothurians, B: bivalves, D: decapoda.
Taxon Songdo Young-jongdo Panweol Hwasung Daesan Kunsan Kimje Buan
(n=23) (n=16) (n=22) (n=16) (n=23) N=17) (n=31) (n=19)
Heteromastus sp. (P)Umbonium thomasi (B)Lingula anatine (Br)Protankyra bidentata (H)Mactra veneriformis (B)Lumbrineris nipponica (P)Nepthys polybranchia (P)Laternula cf. limicola (B)Potamocorbula amurensis (B)Sinonovacula constricta (B)Magelona japonica (P)Ilyoplax dentimerosa (D)Nephtys californiensis (P)Nitidotellina minuta (B)Perinereis aibuhitensis (P)Ilyoplax pingi (D)Mediomastus sp. (P)Bullacta exarata (G)Hinia festiva (G) 9 (13)115 (70)13 (48)27 (5)22 (39) 5 (56)245 (44)2 (6)50 (88)221 (63)3 (6)7 (25)9 (50)36 (81)7 (56) 1006 (18)+66 (59)8 (68)22 (45)++ 33 (63)59 (13)8 (19)11 (69)16 (56)26 (69)13 (56) 55235 (100)8375 (13)100 (9)950 (39)1425 (35)25 (4)1075 (43)225 (13) 3 (41)2 (24)45 (71)4 (18)3256 (24)2 (12)6 (41)5 (41) 2 (10)27 (55)34 (81)3 (35)14 (48)130(6)2 (16)6 (55)6 (29) 4 (41)929 (82)20 (88)+10 (12)17 (18)2 (24)4 (29)13 (65)
The most dominant species on the Songdo tidal flat was the holothurian species Protankyra bidentata which occurred largely in sandy sediments. Eleven species are listed as characteristic of the Panweol tidal flat, among them the pelecypod, Potamocorbula amurensis, ranked the first dominant. However, the Panweol tidal flat is an area located in the inner-most area of a tidal inlet and the burrows and the sediment mounds of crabs constituted the conspicuous surface structures of the tidal flat. Crabs such as Helice tridens sheni and Macrophthalmus japonicus were typical of the mud flat zone. The small crabs, Ilyoplax dentimerosa and I. pingi, whose carapace length is less than 1 cm were dominant in terms of abundance, but most crabs wandering around and to be seen because of the active behavior were the larger-sized crabs as H. tridens sheni and M. japonicus. The bivalve P. amurensis was mostly found in the channel sediment and, therefore, not conspicuous to the observer. The occurrence of the large-sized polychaete, Periserrula leucophryna, could be reported. The largest specimen was 56 cm in length and 1.3 cm in width. The bell-shaped sediment mounds on the middle intertidal belonged to this polychaete.
Fauna on the Hwasung tidal flat located about 10 km to the south of Panweol was characterized by the dominance of bivalve Sinnovacula constricta which has long been used for human food in Korea. The predominance of crabs was similar to the Panweol tidal flat. The polychaete Perinereis aibuhitensis which ranked the fifth in abundance is a worm used for bait by angler. Catches have been exported to Japan.
The Daesan tidal flat was represented by diverse fauna due to the diverse sediment types. This tidal flat was an area of strongest current flow. Heterogeneous mixture of mostly poorly sorted sediments were found. Large ripples, gullies and channel were well developed. Predominant current flow is from Asan Bay into Garolim Bay, which is reflected in the derivation of many of the tidal flat organisms. The predominance of the polychaete, Heteromastus sp. which was mostly found in fine sediments around Korean waters, was unique for the silty to sandy faces near the channel of the Daesan tidal flat. The gastropod Umbonium thomasi was typical of the outer flat.
The Kunsan, Kimje and Buan tidal flat produced the largest number of species in unique combination for this habitat (Table 2). The highest occurrence of the bivalve Laternula cf.
Table 2. List of species occurred on Kunsan, Kimje and Buan tidal flats. Individual numbers presented in the table are total counts from 69 stations investigated. +: occurred but not counted.
Species name No. of indiv. Freq. (%) Species name No. of Indiv. Freq. (%)
CNIDARIA Pennatulacea indet. MOLLUSCA Batillaria multiformis Bullacta exarata Coelomactra antiguata Cyclina sinensis Dosinorbis japonicus Hinia festiva Laternula cf. Limicola, Mactra chinensis Mactra veneriformis Meretrix lusoria Moerella irridescens Neverita didyma Potamacorbula amurensis Ruditapes philippinarum Scapharaca subcrenata Sinonovacula constricrta Solen strictus Umbonium thomasi,BRACHIOPODA Lingula anatina,CRUSTACEA Calianasa sp. Helice tridens sheni Hemigrapsus penicillatus Iloplax pingi Iloplax dentimerosa Macrophthalmus japonicus Macrophthalmus dilatatus Orithyia sinica Philyra pisum Scopimera globosa Sesarma plicatum 20115033516173044459563110464141012261153+8518526219891221662710022+1077+ 15.94.343.513.013.023.231.913.04.330.413.015.923.25.815.94.331.952.2184.108.40.206.326.18.730.411.610.130.4 Uca arcuata Amphipoda indet. Anomura indet. ECHINODERMATA Paracudina chilensis Protankyra bidentata Holothuroidea indet. Ophiuroidea indet. POLYCHAETA Amphictene japonica Arabella semimaculata Diopatra sugokai Glycera chirori Glycera subaenea Glycera sp. Glycinde sp. Haploscoloplos elongatus Lumbrineris sp. Neanthes japonica Nectoneanthes latipoda Nectoneanthes oxypoda Nepthys caeca Nepthys ciliata Nepthys oligobranchia Nepthys sp. Owenia fusiformis Perinereis aibuhitensis Periserrula leucophryna Scolelepis sp. Marphisa sanguinea Capitellidae indet. Nereidae indet. Phyllodocidae indet. Polynoidae indet. Sigalionidae indet. SUM 5+1531508+1197+33321193531171017++121282836910641030917111084556 220.127.116.1118.104.22.168.28.727.526.111.639.130.422.214.171.124.958.08.717.4126.96.36.199188.8.131.52.95.8100.0
Limicola on the Kunsan tidal flat was due to the center of abundance near the channel connected to the Mangyung River. This taxon ranked also the first in abundance on the Kimje tidal flat, but the distribution was limited to stations located on the slope edge of the channel leading into the Dongjin River. The occurrence of a lingulid brachiopod Lingula anatina which has ranked the second in abundance on the Kunsan, Kimje and Buan tidal flat was found as a living species on the world coasts. The predominance of Umbonium thomasi in sandy to silty bottom was observed as shown on the Daesan tidal flat. The bivalve Mactra veneriformis which has ranked the fourth on the Kimje tidal flat is a representative species for cultivation on the Korean tidal flat.
Comparisons have been made between faunal composition and sediment faces. Assigning the dominant taxa at 167 stations into sediment faces from sand to silt and clay, we could define typical taxa of every sediment type . Typical animals are slightly different at a specific locality, but an general tread can be described as in Table 3.
Table 3. Typical dominant species assigned to different sediment types. Percent in parenthesis is the ratio of the number of stations showing the sediment type among 167 stations.
Sediment type Dominant species Sediment type Dominant species
Sand(15.8%) Protankyra bidentata Laternula cf. limicola Lingula anatina Sandy silt(24.2%) Bullacta exarataHinia festivaSinonovacula constricta Nitidotellina minuta
Silty sand(23.6%) Ruditapes philippinarumUmbonium thomasi Lumbrineris nipponica Lingula anatinaMactra veneriformis Silt (23.6%) Ilyoplax pingiPerinereis aibuhitensis
Muddy sand(5.5%) Lingula anatina Mud (7.3%) Ilyoplax dentimerosaMacrophthalmus japonicaMacrophthalmus dilatatusHelice tridens sheni
The sand faces were characterized by Umbonium thomasi accompanied with Protankyra bidentata. The brachiopod Lingula anatina extended its distribution into the silty sand and muddy sand flat. The bivalve Mactra veneriformis was considered as typical of muddy sand faces, however it also occurred broadly on silty sand flat. Sandy silt sediment was populated by the epifauna Bullacta exarata, but the polychaete Nephtys polybranchia was comparatively rich in the sandy silt sediment without any preference of the locality. The razor clam Sinnovacula constricta was mostly present on the Hwasung tidal flat. Nitidotellina minuta counted as typical bivalve of silty sediment, but this species was confined to the Yeongjongdo tidal flat. Mud faces were found at 7.3% among 167 stations, however, the fauna was rich and diverse: Crabs as Helice and Macrophthalmus were conspicuous over the whole Korean tidal flat. The small crab Ilyoplax dentimeros is listed as typical, because of the highest counts in core samples.
A general pattern of zonation could be described: Crabs Helice and Macrophthalmus, the gastropod Bullacta exarata, the brachiopod Lingula anatina, the clam Mactra veneriformis and the gastropod Umbonium thomasi occurred from higher to lower intertidal.
Secondary production of bivalves: Mactra, Ruditapes and Sinonovacula
Table 4 summarizes the annual production of clams estimated by Ricker뭩 model based on data collected from the field observations at different localities. The production described in Table 3 is the net production in which the fisheries catches and losses by death are excluded. The highest production was shown by the razor clam Sinnovacula constricta and the lowest by surf clam Mactra veneriformis, but the latter showed the highest P/B ratio. The mean biomass of M. veneriformis was 629 g TWW m-2 and this estimate comprised to the weight of about 200 individuals. The individual weight of 3 g was then resulted. This size of individuals are less than two years old. The highest biomass of 2,678 g TWW m-2 was recorded by the razor clam S. constricta. The mean individual weight of 20 g, which weighed seven times of M. veneriformis, could also be estimated from the mean density data recorded as 130 g TWW m-2 on the Hwasung tidal flat.
Table 4. Mean density (indiv.m-2), biomass (g DW m-2) and annual production (g DW m-2yr-1) of edible bivalves on the Korean tidal flat. In the parenthesis are the total wet weight (g TWW) including shells.
Species name Mean density Biomass Annual productin P/B Ratio Locality
Mactra veneriformisRuditapes philippinarumSinonovacula constrictaBenthic microalgae 205292130 31.5 (629)62.0 (1221)134 (2678) 68 (1358)83 (1635)150 (2998)50 gC m-2 yr-1 2.151.341.12 Incheno-SongdoDaesanHwasungIncheon-Songdo
The commercially important fisheries catches around the Korean coast are drawn from four groups: shell fishes, crustaceans, echinoderms and macroalgae. Of these groups, the various shell fishes constitute by far the greatest tonnage (Table 4). The oysters, short necked clams (Manila clam), mussels and cockle shells account for the largest tonnages of catches. Of the mollusks, surf clams, razor clams and Venus clams have catched mostly on the west coast. All those are bivalves catched from the tidal flat, beside the pen shell inhabiting the sand bottom of the subtidal area in the west.
Table 5. Important commercial catches (metric tons per year) on the Korean tidal flat (1997)
Species name Common name Fisheries catchews (ton yr-1)
Acetes japonicusRuditapes philippinarumTegillarca granosaMactra veneriformisMeretrix lusoriaSinonovacula constrictaCyclina sinensis Shrimp Manila clam Cockle shell Surf clam Hard clam Razor clam Venus clam 1019371982744933496206113
In recent years, there have been abundant examples of the decline of fisheries catches of all types around Korean coast. Some of these declines are exemplified by landings of bivalves on the west coast. Until 1986, the annual catch of the surf clam M. veneriformis was about seven thousands metric tons, however, it declined to about one thousand metric tons after 1986. The yield which we had reached before 10 years has not recovered till today. Ruditapes philippinarum was the clam of which the annual catch was two-folds higher than that of M. veneriformis, however, the catch at present is only about 60 thousands metric tons per year. The total catch of the Venus clam Cyclina sinensis is much lower than the above two bivalves species, but the decline in the catch is clearly shown. The hard clam Meretrix lusoria was known to be the best tasted bivalve in Korea and large portion of the landings had been exported to Japan. The annual yield in 1997 is only about 500 metric tons. Meretrix lusoria was a typical clam for sand bottom on the Incheon-Songdo and Kimje tidal flat in the west. The only catch which are not declined is the razor clam Sinnovacula constricta, but the occurrence is restricted rather to the mud flat, and therefore the annual catch is only in small amount.
Although not depicted in a Figure, commercial catches in the Kyeonggi Bay which possesses the broadest tidal flat in the west showed a sharp decline in the catch of M. veneriformis from 1988. Monthly catch of about 60 metric tons recorded in the Kyeonggi Bay comprised to about 80% of the total catch from the Korean coast. R. philippinarum was catched around 800 metric tons per month in 1987, but decreased sharply after 1988. The decline in the catch of Cyclina sinensis is also clear, however, the yield was down from 1990. The recent landings of M. lusoria is extremely small compared with those recorded in the beginning of 1980뭩.
Land earning from the Korean tidal flats during 20th century
A short historic review of the land earning from the Korean tidal flat given in Table 6 indicates that a significant portion of the tidal flat is reclaimed in recent years. But those alterations have begun in the 1920뭩 during the period of Japanese occupation. Rice production was the main purpose. The area of salt marshes had been considerably modified at that time. Statistics in 1987 reported that the areal extent of the tidal flat as about 2,800 km2, but the total tidal flat area must be summed with 405 km2 which was dammed before 1945. If we add the area of 500 km2 reclaimed during 1946-87, then the total dimension of the Korean tidal flat was about 3,700 km2.
Table 6. Historic review of the land earning from Korean tidal flat from 1917 to 1998
Length of the coast line, west sea, Korea (South) 3,341 km
Dimension of tidal flats in 1987 2,815 km2
Area of land earned from the tidal flat in the recent history (Km2)
1917 – 38 405.4 1946 – 60 6.3 1961 – 69 172.2
1970 – 79 193.7 1980 – 89 93.1 1990 – 94 98.5
1995 ?continuing 764.0
total area including the continuing 1733.2
The largest land earning is in the progress on the Kimje tidal flat. The government agency of Rural Development Coorperation (RDC) has launched the so called 멣aemankeum?project in 1991 with an expectation of accomplishing the project in 2004 (RDC, 1994). The 33 km long sea wall is constructing. The land which will be earned from this project is amounted to about 400 km2. The lake produced after cutting the tidal flat covers an area of 120 km2.
The mass land earning on the Korean coast in recent years was remarkable, however, the values of Korean tidal flats have not been assessed in an ecological and environmental view point. Primary and secondary productions recorded in the study areas rival those of Wadden Sea area. The reclamation projects have frequently been supported by the Ministry of Agriculture, Korea, with emphasis on an earning of rice field. The annual income of fishermen by catching the bivalve, Mactro veneriformis, amounted to about 0.8 million US$ per km2. In the case of the razor clam, Sinnovacula constricta, the annual income has been reached to about 2 million US$ per km2 because of the higher market price. Although the economic importance of fisheries has generally been declined on the Korean coast, the tidal flat sustains the capacity of fisheries catches and possibilities in economic uses are still remained.
The levels of pollutants in the Korean coastal waters have been increased in recent years and a reason for that was supposed to be related with those embankments of tidal flat area (MEK, 1995; Koh, 1996). A concrete example can be shown from the saline lake Sihwa which was isolated from the sea by a dike construction in 1994. A sharp increase in concentrations of heavy metals and organic materials in lake sediments are reported (Lee and Koh, 1998). The bottom fauna was changed to the polychaete, Polydora ligni, which was known to be tolerant to higher concentration of organic matters in sediments with high sulfide. Even an azoic zone of several square kilometers was found. The reason of the higher concentration of pollutants and its bioeffects in the lake was the locality of the enclosure. The dike closed the seawater which received discharges from the industrial complex and the city of Ansan populated by more than 0.3 million people.
We are collecting data on ecology, fisheries, and social economy concerning the Korean tidal flat. It was clear, however, that the Korean tidal flat has been deteriorated through the land earning without less assessment of environmental impacts. Comparing the coastal uses in Korea with developed countries as German on the North Sea coast, it can be indicated that the Korean government policy on the conservation is still in primitive stage.
The coastal countries of Wadden Sea have established the concept of wise use and sustainable development enforcing a better conservation strategy to manage the Wadden Sea ecosystem (CWSS, 1990). Three countries including German have decided to develop a common approach which can be characterized by a complex strategy. Assessments of the quality of tidal flat ecosystem have been performed (NNW, 1994, NSHW, 1994).
Study on the tidal flat ecosystem in Schleswig-Hostein includes various aspect of ecology in tidal flat (NSHW, 1994): The study involved plankton, benthos with emphasis on crabs, bivalves and their fisheries, waterfowl, and wild life, especially the seals. Chemical data on heavy metals and organic compounds have also been produced. The relationship between the human and tidal flat ecosystem was also an important aspect raised by this report. All the information was displayed with GIS system and, therefore, informative to the public.
The situation in Korea should better be improved as far as it concerns with conservation strategies of tidal flats. Even an assessment of tidal flat ecosystem have little been attempted. Many works are needed to develop a program for conservation and wise use. A more important aspect is, however, that the ecological assessment should be included in planning of land uses and inevitable setting of industrial complexes. Still yet, policy makers tend to establish projects of tidal flat reclamation rather in developmental aspects, not in ecological.
Common Wadden Sea Secretariat (CWSS), 1992. Wise use and conservation of the Wadden Sea. The Common Wadden Sea Secretariat.
Koh, C. H. 1996. Coastal pollution in relation to coastal development. In Symposium on the problem of marine pollution, Korea, Association for Marine and Fisheries Research of the Tokdo Area, 53-80.
Lee, J. H. and C. H. Koh, 1998. Soft bottom fauna in and off a heavily polluted saline lake after embankment on the west coast of Korea (submitted).
Ministry of Environment, Korea (MEK), 1995. Environmental status, Korea. Ministry of Environment, Korea. Seoul.
Nationalpark Niedersaechsisches Wattenmeer (NNW), 1994. Oekosystem Forschung, Wattenmeer Niedersachsen. Nationalparkverwaltung Niedersaechsisches Wattenmeer. Wilhelmshaven, Germany.
Nationalpark Schleswig-Holsteinisches Wattenmeer (NSHW), 1994. Oekosystem Forschung Schleswig-Holsteinisches Wattenmeer. Schriftenreihe Heft 5. Landesamt fuer den Nationalpark Schleswig-Holsteinisches Wattenmeer.
Ricker, W.E., 1946. Production and utilization of fish population. Ecol. Monogr., 16: 373-391.
Rural Development Corporation (RDC), 1995. Tideland Reclamation in Korea. Seoul.
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