Special issue: Problems of Bio-productive environment supporting the production of the short-necked clam and approaches in research



Title Biological Production Process and Food Environment for Bivalves in Tidal Flat
Authers Kinuko ITO*1, Toshiki KAGA*2 , Koichi SASAKI*1 , and Michio OMORI*1
Keywords diatom, bivalve, detritus, food resources, microenvironment, tidal flat
Citation Bull. Fish. Res. Agen. supplement No.3, 1-15, 2005
A combination of ecological research, field experiments and laboratory experiments was carried out to analyze the biological production process and food environment for bivalves in a tidal flat around Sendai Bay. Both field experiments and stable isotope analysis indicated that the important nutritional resources for Ruditapes philippinarum and Nuttallia olivacea are benthic diatoms, with a lower contribution of detritus. Macoma contabulata and Corbicula japonica, inhabiting the same site with Nuttallia olivacea, are supplied with different resources that up to now have been unknown. The food requirement for Nuttallia olivacea is estimated to be about 1500mg Cm-2day-1 at a high-density location in the tidal flat of the Natori River in spring. Conditions affecting food availabity may be linked with physical environmental conditions, and clarification of the coupling mechanisms between the biological production process and physical conditions is important for the various microenvironments. Nuttallia olivacea showed marked differences in growth at each location. Most available conditions are considered to be moderate current velocity with shallow depth, low silt-clay content and high chlorophyll a in the sediment, and presence of a wide variety of diatom species with varied size compositions. We propose a fill-in sheet for evaluation of food environment and microenvironment for bivalves at different developmental stages.

Received on January, 2004
*1 Graduate School of Agricultural Science, Tohoku University., Amamiyamachi1-1, Tsutsumidori, Aoba, Sendai 981-8555, Japan
*2 National Salmon Resources Center, Nakanoshima 2-2-4-1, Toyohira, Sapporo, 062-0922, Japan

Title Sediment environment and the characteristics on the fishing ground of Venerupis philippinarum.
Authers Masaaki YAMAMOTO*1
Keywords Japanese littleneck clam, Venerupus philippinarum, tidal flat, fluctuation of the bottom, underground temperature
Citation Bull. Fish. Res. Agen. supplement No.3, 17-25, 2005
The author investigated physical environments like as flow, bottom change, and underground temperature, etc. on the fishing ground of Venerupis philippinarum. As a result, the space and the temperature have understood as severe factors for clam larva as follows.
 The fluctuation of the bottom caused by the current was recorded 1cm or less/hr, and that caused by the wave at typhoon was recorded 3cm or less/hr. Because the living layer of the depositing larva repeats the scouring and sedimentation by the tidal current, it will be appropriate to assume a fixed larva to be moved with the sand. The fluctuation velocity of the bottom is slower than the burrowing speed of adult clam. Therefore, whether the clam takes the burrowing action is a turning point of her survival or death caused by exposing or burying.
 The soil temperature in exposed tidal flat rises rapidly in the summer sunny daytime, and the surface exceeds 37℃. At this time, though the adult shell-fish will be able to evade the high temperature by deeply diving, it is assumed that the clam larva which live in a shallow layer is caused physiological disorder and dies.

Received on January, 2004
*1 National Research Institute of Fisheries Engineering, Ebidai 7620-7, Hasaki, Ibaraki, 314-0421, Japan

Title Influence of environmental factors as oxygen deficiency, hydrogen sulfide and suspended mud on the survival and growth of Manila clam
Authers Junya HIGANO*1
Keywords Manila clam, oxygen deficiency, hydrogen sulfide, suspended mud
Citation Bull. Fish. Res. Agen. supplement No.3, 27-33, 2005
The production of Manila clam has been decreasing since early 1980s in Japan. It is presumably related to the environmental deterioration mainly caused by reclamation, barrage construction and waste discharge from watershed. Oxygen deficiency, hydrogen sulfide and suspended mud are considerably significant factors for survival and growth of Manila clam, because they affect the respiration and filtration of the clam. Manila clam shows the tolerance for anoxic condition by switching respiration to anaerobiosis that is commonly recognized in bivalve species. Manila clam also tolerates hydrogen sulfide that affects aerobic respiration. Higher concentration of suspended particle reduces the filtration of bivalves, but it isn't fatal. The cause of mass mortality of Manila clam couldn't be explained well by single factor within a short period. However, compound and long-term effects presumably influence the physiological condition of the clams and eventually cause the fatal damage. It is necessary to monitor both the environmental factors and physiological condition of the clams in order to predict the survival of the clam and to make a plan for rehabilitation of the clam habitat.

Received on January, 2004
*1 National Research Institute of Aquaculture, Nakatsuhamaura 422-1, Nansei, Watarai, Mie, 516-0193, Japan

Title Importance of network system among benthic-animal local populations in bay waters
Authers Toshio FUROTA*
Keywords bay water, metapopulation, network, tidal flat, zoobenthos
Citation Bull. Fish. Res. Agen. supplement No.3, 35-46, 2005
Most macrobenthic animal species inhabiting in tidal flats and subtidal bottoms in bay waters have a dispersal phase by plankton larvae in the early life history. During the plankton stage, larvae tend to be passively transported to new benthic habitats far from the natal habitat. This means that local benthos populations mainly consist of immigrants released from other local populations.
 In case of the introduced spider crad, Pyromaia tuberculata, in the inner Tokyo Bay where summer bottom hypoxia is severe, population of the crab quickly recolonize in every fall when the bottom have recovered from the hypoxia. This recolonized population quickly reaches maturity by next spring, then can release plankton larvae prior to catastrophic mortality of the benthic animals caused by next summer hypoxia. The larvae released in the inner bay disperse to entire area of bay water, and can settle in the mouth part of the bay where DO is enough to maintain crab population during summer. This mouth part population also reaches maturity before next fall, then produces larvae for recolonization of the crab in the inner bay. Thus, seasonal trade of the crab larvae between local populations, which are esrablished in the inner and mouth areas of the bay, is the essential process to maintain the crab population in the entire area of the bay.
 During 1980s in Tokyo Bay, 6 species of the tidal-flat mud snails belonging to Family Batillariidae and Potamididae commonly occurred in several tidal flats where escaped from large-scale reclamation of the flats along the entire coast line of the bay conducted during late 1960s to early 1970s. During 1990s, however, 5 species (Batillaria multiformis, B. zonalis, Cerithidea rhizophorarum, C. cingulata and C.djadjariensis) that have a plankton larval stage, had been extinct or had become endangered, but local populations of B. cumingi that develops directly without larval stage tended to increase. Extinction or decline of mud snail populations that have a plankton-dispersal process is probably resulted from the failure of larval immigration relating with isolation of each flat from others caused by the reclamation, and by bottom hypoxia which the larvae should encounter before approach to the shore.
 These studies suggest that a viewpoint of network system between local populations of benthic animals through larval dispersal is important to understand the mechanism of the population maintenance of the benthic animals in bay waters.

Received on January, 2004
* Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba, 274-8510, Japan

Title Larval abundance, distribution, and size composition of the clam Ruditapes philippinarum in Tokyo Bay
Authers Tomoyuki KASUYA*
Keywords bivalves, R. philippinarum, larva, reproduction, larval transport
Citation Bull. Fish. Res. Agen. supplement No.3, 51-58, 2005
As the first step in clarifying the larval transport processes of R. philippinarum in Tokyo Bay, short-term spatial and temporal variations in abundance and size-frequency distribution of R. philippinarum planktonic larvae were investigated. To do so, measurements were taken at 65 stations throughout the Tokyo Bay area on August 2, 6, and 10 in 2001. The size-frequency distributions of the larvae indicated that the growth rate (shell length) was 15-18μm d-1 during the summer in the bay. Based on the large numbers of small D-shaped larvae found shortly after hatching in waters around the Banzu, Futtu, and Sanmaizu-Haneda areas, it can be deduced that the spawning populations in these areas probably contribute greatly to the larval supply in the bay. Small larvae were also found in abundance around both the Kawasaki-Yokohama and Ichihara port areas, suggesting that these regions also play an important role in larval supply and recurrence areas into Tokyo Bay. In addition, the abundant spatial distribution variations of the cohort, observed on August 2 and 6, demonstrated that larval populations were concentrated within the central area of the bay, where a distinct upwelling front induced by strong southwestward wind was found on August 6. These findings indicate that physical processes, such as divergence and convergence in the frontal area of the bay, seem to greatly influence the advection of R. philippinarum planktonic larvae in the bay.

Received on January, 2004
* National Institute for Land and Infrastructure Management, 3-1-1 Nagase, Yokosuka, Kanagawa 239-0826, Japan

Title Numerical simulation on advenctive process of planktonic leavae of the clam Ruditapes philippinarum in Tokyo Bay
Authers Hirofumi HINATA*1 Koji TOMISU*2
Keywords numerical simulation, clams, planktonic larva, Tokyo Bay
Citation Bull. Fish. Res. Agen. supplement No.3, 59-66, 2005
Numerical simulation based on the Princeton Ocean Model (POM) was performed to investigate advective process of plankton larvae of the clam Ruditapes philippinarum during the period from July 31 to August 10, 2001 in Tokyo Bay. Simulation results indicated that spatial distribution of wind velocity field strongly influenced flow patterns in the bay which play a crucial role in the advective process, and that the number of the larvae was reduced during the pelagic term due to depredation by Noctiluca scintillans and Aurelia aurita. In addition, the results suggested that the modeling of swimming movement of the larvae and the investigation of abundance of the clam in shallow regions including harbor areas were required to clarify precise process of recruitment and the existence of the network between shallow regions through exchange of the larvae.

Received on January, 2004
*1 National Institute for Land and Infrastructure Management, Nagase 3-1-1, Yokosuka, Kanagawa 239-0826, Japan
*2 Tokyo University of Science, Yamasaki 2641, Noda, Chiba, 278-8510, Japan

Title Larval transportation and settlement mechanism to tidal flat in Japanese littleneck clam Ruditapes philippinarum
Authers Nobuo KURODA*
Keywords larval movement, Ruditapes philippinarum, vertical distribution, tidal flat, settlement
Citation Bull. Fish. Res. Agen. supplement No.3, 67-77, 2005
We studies larval vertical distributions of a clam Ruditapes philippinarum in Mikawa Bay and near the tidal flats to know the transportation and settling processes. In the bay, larvae tended to assemble in the bottom water column as they mature. As the result of this vertical movement, it seems that matured larvae are transported to the interior bay by landward flow at depth. At the spring tide, the matured larvae descended to the bottom water particularly at ebbs and low tides. they may avoid being transported offshore by this behavior. Near the tidal flats, the larvae also descended to the bottom water at low tides of the spring tide, but ascended to upper layer at floods and were transported to the interior tidal flats by the flood current. The ascending behavior was, mainly observed at the mature stage. The matured larvae were considered to settle on the sediment when they made contact with the slopes of tidal flats, because the density of only the transported matured larvae in the tide water decreased during floods, and because most of the newly settled juveniles were found on the slopes of tidal flats.

Received on January, 2004
* Marine Resources Research Center, Aichi Fisheries Research Institute, Toyohama, Minamichita, Aichi 470-3412, Japan

Title Immunological and molecular biological technique for identification of early life history stages short-necked clam, Ruditapes Philippinarum
Authers Masami HAMAGUCHI*
Citation Bull. Fish. Res. Agen. supplement No.3, 79-82, 2005
Species identification is major limiting step in the study of early Life history stages of bivalves. Due to the morphological similarity of veligers, sorting large numbers of plankton samples by traditional methods is a laborious and time-consuming task. The use of monoclonal antibodies and indirect immunofluorecsence technique provides the means to rapidly discriminate among species. In 1998, we have developed the monoclonal antibodies to the clam. In this summary, I will describe the strategy about development of new monoclonal antibodies for settled juvenile clam.

Received on January, 2004
* National Fisheries Research Institute of Seto Inland Sea, Maruishi 2-17-5 Ohno Saeki, Hiroshima 739-0452, Japan

Title Some comments on recovery on the manila clam resource and present state of inshore ecosystem
Authers Taiji KIKUCHI*
Keywords manila clam, critical life stage, resource management, inshore ecosystem
Citation Bull. Fish. Res. Agen. supplement No.3, 87-92, 2005
The annual yield of the Manila clam in Japan decreased in recent years but the cause of mortality is unclear. To analyze the long time decrease of the clam, both studies on habitat conditions for both juvenile and adult clam, and studies on settlement of pelagic larvae in adequate habitats, and recruitment of benthic stage. To estimate the size of stock population and stability of recruitment and young immature shells, the author proposed establishment of manira reserve. In sand flat of Ariake Sea, the smallest legal fishing size of the clam is nearly with the minimal size reproduction, and most them were caught before or just after the first reproduction. It seems important to guarantee the seed source adult population. The importance of filter-feeding bivalves to the purification mechanism of eutrophicated inshore ecosystem was pointed out, recovery of manila clam resource from the aspect was expected.

Received on January, 2004
* Kyusyu Lutheran college, Kurokami 3-12-16, Kumamoto, 860-8520, Japan