The importance of seaweeds and shellfishes in Japan: Present status and history

Hisashi KUROKURA*

 　Though many manufactured goods are produced from aquatic resources, people living in Japan consume them mainly as food. Among such sea foods, seaweeds and shellfishes have special religious meaning. Kombu (Laminaria), wakame (Undaria) and abalone or other shellfishes are commonly included in offerings to Shinto shrine. It was supposed from this fact that these foods were important for Japanese ancestor. In fact, many remains of seaweeds and shells were dug out from ruins of prehistoric age. In the 8^th century, Yakamochi Ohtomo, a famous poet in Nara Period, transplanted a shell species from Kishyu to Ecchyu. This is the oldest record of propagation of shellfish. Nori (Porphyra) is now indispensable for sushi. Its culture started from the 17^th century. Aquaculture of wakeme, oyster, peal oyster, and many other seaweeds and shellfishes had begun by the end of 19^th century. Aquaculture technology has been improved and the production has increased rapidly in the latter half of last century. Now seaweeds and shellfishes aquaculture encounter various difficult problems such as changes in coastal environment by pollution and land reclamation. On the other hand, the function of these aquaculture for water purification attracts attentions of people together with the increase of interest to environment issues.

Key word: shellfishes, seaweeds, Aquaculture, history
Received on June 12, 2003
* Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 113-8657, Japan

　
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The present situation and problems of oyster culture in Hiroshima Bay

Yasushi HIRATA and Satoru AKASHIGE

  Hiroshima Bay including its adjacent area is one of the most important oysters farming areas in Japan. During 1980s, the oyster production in Hiroshima Bay was about 30,000 metric tons (t) scale by fresh meat weight (FMW) a year. In the early 1990s, the oyster production began to decrease and was about 20,000t in 2000. We analyzed the present situation and problems of oyster culture in Hiroshima Bay to show the problem solution. This decrease in oyster production in the 1990s was caused directly by typhoon damages; shellfish poisoning by Alexandrium spp.; and mortality by harmful dinoflagellate Heterocapsa circularisquama: and was caused by dense cultivation indirectly. The postponing of harvesting the oyster caused by shellfish poisoning prolonged the oyster culture period. The prolongation of the culture period in a limited culture ground caused eventually dense cultivation of oyster. Aged and large-sized oysters took much feed, therefore growth of all oysters in culture grounds were slowed down under low feed level. The low growth rate accelerated prolongation of a culture period. These vicious spirals promoted dense cultivation, and changed the environment of the culture ground into favorable environment for H. circularisquama. To analyze these situations, an oyster culture process model was built. This model showed that the reduction in oyster biomass in the culture grounds is needed to escape from the vicious spiral, and shortening of the culture period was the most effective method for this reduction without reducing harvest magnitude.

Key word: oysters, Hiroshima Bay, culture process
Received on June 12, 2003
* Hiroshima Prefectural Fisheries Experimental Station, Ondo, Aki, Hiroshima, 737-1207, Japan

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The decline of Manila clam stock in Tokyo Bay

Mitsuharu TOBA*

　The fisheries production of Manila clam in Chiba Prefecture, which amounts to more than 90 ％ of the total clam production in Tokyo Bay, markedly declined to below 20,000 metric tons (mt) in 1979, after reaching 70,000 mt at its maximum in the late 1960s. This is mainly because of the large-scale reclamation of the shallow tidal areas where clam fisheries were intensively operated. However, the clam production keeps gradual decreasing even after the cessation of the series of reclamation in 1979. The periodical monitoring of clam stocking density shows decreasing of clam production since 1985 seems to be associated with the poor occurrence of wild juvenile clam. In Kisarazu Area, which is the largest Manila clam producer in Tokyo Bay, production is stably maintained between 5,000 and 6,000 mt since late 1980s, in spite of the stocking density of juvenile clam (4-11 mm in shell length) declining from 68 to 12 inds/m2 during this period. It is probably due to 2,000-3,000 mt of the transplantation of the seed clam (>20 mm) from other area in Tokyo Bay and other prefecture. On the contrary, in Northern Chiba Area, where the clam fisheries relies only upon wild clam stocks without any transplantation, the clam production has sharply declined from around 10,000 mt in late 1970s to 800 mt in 1999 reflecting directly the poor occurrence of wild juvenile clam. The cause of the substantial decline of the wild juvenile clam is still not known.

Key word: Manila clam, Tokyo Bay, stock decline, early life cycle, coastal development
Received on June 12, 2003
* Futtsu Laboratory, Chiba Prefectural Fisheries Research Center, Kokubo 3091, Futtsu, Chiba 293-0042, Japan

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Environmental conditions relevant to aggregative distribution of macrobenthos below coho salmon culture cage

Ryo SASAKI* and Akio OSHINO*

　Actual changes in environmental conditions relevant to aggregative distribution of the macrobenthos below coho salmon culture cage were examined by diving observation at Onagawa Bay in 1990s. Organic sediment derived from leftovers of moisture food pellets and fish feces were 15 cm in height at the center below culture cage. Dominant species of macrobenthos were identified Nebalia bipes, Schistomeringos japonica, Melita sp. and Capitella spp. Highest density of Nebalia bipes was found ca. 40,000 inds./m² and that of Schistomeringos japonica was ca. 5,000 inds./m² from enriched sediment on the bottom surface. Aggregative distribution of Nebalia bipes and Schistomeringos japonica were monitored at 10-m distance zone from the center point in summer, and that of Nebalia bipes and Melita sp. were monitored within 5-m distance from the center in winter. From the ecological viewpoint for these external distributions, aggregative position of macrobenthos was correlated to the marginal zone of enriched sediment. Biological activities so-called bioturbation were recognized in conjunction with synchronous patterns of the distribution between macrobenthos and organic sediment below culture cage.

Key word: coho salmon, macrobenthos, environmental condition
Received on June 12, 2003
* Kesennuma Miyagi Prefectural Fisheries Experimental Station, 119 Hajikami, Kesennuma, Miyagi 988-0247 Japan

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Influence of environmental changes in the tidal flats on the filtration and respiration of bivalve mollusks

Junya HIGANO*

　Manila clam Ruditapes philippinarum and the other filter feeding bivalves in tidal flat are not only commercially important as seafood, but also ecologically significant because of their filtration activity. The volume of water filtration by bivalves in Ariake Sound is estimated to be equivalent to daily water exchange on the tidal flat in 1970s. However, the annual catch of Japanese littleneck has been decreased during the past 20 years in Japan. Especially, rapid decrease in the clam population in Ariake Sound since 1980s forced to depress the nationwide production. Recent coastal changes such as land reclamation, dike, port, barrage, and dam construction presumably brought about the environmental impact for filter feeding bivalves through water and sediment movement. Higher intertidal zone and supralittoral zone are intercepted by artificial structure such as dike and breakwater. Consequently suspended sediments are prevented from depositing at the higher intertidal zone and are drifted in littoral zone. High concentration of mud particles suppresses the water clearance of the clams. On the other hand, reduction of water current by barrages encourages the stratification. Hypoxia and anoxia often occur in subtidal zone of eutrophied sheltered coast under the stratified layer in summer. Complex effects of mud increase and oxygen shortage are considered to be physiologically harmful to filter feeding bivalves. The ecological function of tidal flat has been destroying and it disturbs the recovery of the bivalve resources.

Key word: bivalves, coastal change, filtration, Manila clam, reclamation
Received on June 12, 2003
* National Research Institute of Aquaculture, Fisheries Research Agency 422-1 Nakatsuhamaura, Nansei, Watarai, Mie 516-0193 Japan

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The microbial loop in a eutrophic bay and its contribution to bivalve aquaculture

Takashi KAMIYAMA*

　Information on planktonic food webs around bivalve farms is important, because bivalves utilize natural suspended matter as food. Not only phytoplankton but also other heterotrophic protists are occasionally essential to bivalves. Oysters cannot use bacterioplankton, but they can ingest protists that feed on bacterioplankton, thus using microbial energy indirectly through this microbial loop. To evaluate the importance of the microbial loop in planktonic food webs, occurrences of bacteria and heterotrophic protists were studied in the eutrophic Hiroshima Bay, where oyster aquaculture is economically important. Temporal changes in microbial loop components suggested that energy flow within the microbial loop was enhanced at the end of a phytoplankton bloom. The distribution of microbes and other protists implies that transfer efficiencies within planktonic food webs including the microbial loop differed among regions of the bay. Thus, the microbial loop may play an important role in planktonic food webs in Hiroshima Bay. In some oyster ponds in France, the importance of microbial energy flow to oyster production was actually evaluated. Possibly, energy flow within the microbial loop is also important to oyster production in Japan.

Key word: microbial loop, bacteria, flagellate, ciliate, oyster
Received on June 12, 2003
* Tohoku National Fisheries Research Institute, Fisheries Research Agency, Shinhama, Shiogama, Miyagi, 985-0001, Japan

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Balancing marine aquaculture inputs and extraction: Combined culture of finfish and bivalve molluscs in the open ocean

Richard LANGAN*

　Enrichment of the water column with dissolved nutrients and of bottom sediments with organic matter as a result of culturing finfish in sea cages have been identified as real and potential environmental impacts of fish culture. While severe impacts have been documented in shallow, poorly flushed waters, proper siting of sea cage operations generally results in only minor localized impacts to the benthic community on the sea floor directly beneath the cages. None the less, the perception of environmental groups and regulatory agencies in the U.S.A. that fish waste and uneaten feed will impact the marine environment regardless of siting has affected the expansion of existing sites and the establishment of new sites. In order for the industry to expand to meet the growing demand for seafood, measures to mitigate these impacts must be taken. One possible solution is to balance inputs of feed with extraction of biomass of organisms such as marine plants and bivalve molluscs that do not require external feed application.
　In 1999, the University of New Hampshire established the Open Ocean Aquaculture Demonstration Project. Funded by the National Oceanic and Atmospheric Administration, the project was designed to provide a commercial scale demonstration and research site for open ocean aquaculture in the northeast U.S.A. The project is an integrated, multi-disciplinary, regional effort that includes biology, oceanography, engineering, sociology, economics, technology transfer, and education. While the development of technologies for finfish and shellfish production in offshore environments is central to the mission of the project, demonstration of the environmental sustainability of open sea culture is critical to the social acceptance of industry development.
　Since 1999, the project has produced harvests of several species of finfish using submersible sea cages and six crops of molluscan shellfish (primarily blue mussels) using submerged longlines in close proximity to the sea cages. While not considered true polyculture, the harvest of the filter feeding bivalve molluscs represents a net removal of nitrogen, carbon and phosphorus that can be used in mass balance to offset the addition of these nutrients from finfish feeding. In this paper, data the potential for balancing inputs associated with feed application and fish wastes with extraction of fish and bivalve biomass will be examined.

Key word: bivalve mollusc culture, finfish culture, sea cages, waste feed, nitrogen
Received on June 12, 2003
* Cooperative Institute for New England Mariculture and Fisheries, University of New Hampshire, Environmental Technology Building, 35 Colovos Road, Durham, NH 03824, USA

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Seaweed resources as a source of carbon fixation

Daisuke MURAOKA*

　Approximately 2 gigatons of carbon a year is estimated to diffuse across the air-sea interface into the dissolved CO₂ pool of surface ocean water. The total area of algal and seagrass beds along the coasts of Japan is 2,012 km². We are currently estimating the macrophyte production along the coasts of Japan by estimating the annual net production and carbon content, and it is likely to be a value of ca. 2,700,000 tons of carbon a year. Additionally, the Japanese people have historically used seaweeds as food source. Economically important genera (Porphyra, Laminaria, Undaria etc.) are cultivated and harvested, with an estimated annual production of cultivated seaweeds of 530,000 tons wet weight. The total amount of annual carbon absorption by seaweed cultivation is estimated to be approximately 32,000 tons, corresponding to 1.2 ％ of the annual macrophyte production along the coasts of Japan. It is also well known that seaweeds have a positive impact on moderately eutrophic water by absorbing nutrients from surrounding waters. Seaweed resources are an important source of carbon fixation.

Key word: seaweed, carbon fixation, CO₂
Received on June 12, 2003
* Tohoku National Fisheries Research Institute, Shiogama, Miyagi 985-0001, Japan

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Environmental carrying capacity in an aquaculture ground of seaweeds and shellfish in Sanriku coast

Ken FURUYA*

　In non-feeding aquaculture of seaweeds and shellfish the culture organisms compete with natural populations for resources, viz. nutrient salts and food particles. Therefore evaluation of carrying capacity of coastal waters is crucial for sustainable exploitation of biological productivity. For this two major criteria are proposed: accurate estimation of phytoplankton primary production which governs the magnitude of total biological productivity, and understanding of oxygen dynamics based on a preliminary study in a bay on the northeastern coast of Japan.

Key word: carrying capacity, shellfish culture, seaweed culture, Sanriku coast
Received on June 12, 2003
* Graduate School of Agricultural and Life Sciences, The University of Tokyo Bunkyo, Tokyo 113-8657, Japan

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Review: Production of Gracilaria parvispora in two-phase polyculture systems in relation to nutrient requirements and uptake

Erin RYDER*1 , Stephen NELSON*2, Edward GLENN*2, Pamela NAGLER*2, Sherman NAPOLEAN*3 and Kevin FITZSIMMONS*3

　Gracilaria parvispora Abbott is highly valued in Hawaiian seafood markets. Due to the over-harvesting of natural beds. G. parvispora is scarce on the open reef ; and harvesting is strictly regulated. On Molokai, Hawaii, a community-based operation was established to develop a sustainable, integrated culture system for this species. Previous research suggested that ammonium was the limiting factor for sufficient growth on the reef. Therefore, on Molokai, a polyculture system was developed using fish/shrimp effluent to load thalli with nitrogen before placement in a low-nutrient lagoon for growout. The research described here demonstrates how small-scale, commercial culture of seaweed can be successfully integrated with the production of fish and shrimp. Two benefits of a two-phase polyculture system are: 1) a waste product from the first phase (i.e. ammonia nitrogen) becomes a resource for the second phase and 2) integrated systems are financially more stable because of improved cash-flow and product diversification. A modest biomass of fish can support a substantial production of seaweed. The type of cage-based, polyculture system developed on Molokai could be applicable to other rural coastal areas.

Key word: Gracilaria parvispora, polyculture, tank culture, effluent, nitrogen
Received on June 12, 2003
*1 University of Maryland, Center for Environmental Science, P.O.Box 775, Cambridge, MD 21613 USA
*2 University of Arizona Dept. of Soil, Water, and Environmental Science, 2601 East Airport Drive, Tucson, AZ 85706, USA
*3 Ke Kua'aina Hanauna Hou, HC01 Box 741, Molokai, HI 96748-0741, USA

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Preliminary examination of the bioremediation and mariculture potential of a Northeast U.S.A. and an Asian species of Porphyra

George P. KRAEMER* 1, Raquel CARMONA* 2,3, Christopher NEEFUS* 4, Thierry CHOPIN* 5, Sheryl MILLER* 3, Xiaogeng TANG* 3,6 and Charles YARISH* 3

　Finfish and shrimp mariculture operations produce nutrient-rich effluent that can threaten the health of coastal ecosystems if not properly managed. As part of an effort to develop an economically viable system of integrated polyculture, we have begun to evaluate the bioremediation and mariculture potential of Northeast U.S.A. and Asian species of Porphyra. We present here preliminary results based on short- and long-term experiments. Short-term nitrogen (N) uptake measurements were conducted over ca. 20 min in 50 mL tubes at 5-15 ℃ and at high (10 g FW L^-1) stocking density. During long-term (28-d) experiments at 15 ℃ and at 0.4 g FW L^-1, we examined the growth, N assimilation into Porphyra tissue, and phycobiliprotein contents at three- to seven-day intervals as a function of N concentration (25, 75, 150, 300μM). Performance (growth rate and bioremediation) was maximal at 150-300μM inorganic N. Induction of archaeospore production reduced growth rates. Porphyra purpurea removed 96-100 ％ of N within 3.5 days at 150μM NH₄⁺ . Overall, Porphyra appears to be an excellent choice for bioremediation of moderately eutrophic effluents, with the added benefit that tissue may be harvested for sale.

Key word: Porphyra, eutrophication, aquaculture, mariculture, nitrogen, phosphorus, bioremediation, seaweed
Received on June 12, 2003
*1 Department of Environmental Sciences, State University of New York, Purchase College, Purchase, NY 10577 USA
*2 Department of Ecology and Evolutionary Biology, University of Connecticut, Stamford, CT 06901 USA
*3 Faculdade de Ci＾encias do Mar e do Ambiente, Universidade do Algarve, PORTUGAL
*4 Department of Plant Biology, University of New Hampshire, University of New Hampshire, Durham, NH 03824
*5 Centre for Coastal Studies and Aquaculture, University of New Brunswick, Saint John, New Brunswick E2L 4L5 CANADA
*6 College of Marine Life Sciences, Ocean University of Qingdao, PRC

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An assessment of the beneficial roles of Nannochloropsis oculata in larval rearing of marine finfish

Masanori OKAUCHI*

　From points of both water quality management by algal nutrient absorption and a good live food of rotifer, the role of Nannochloropsis oculata supplied to larval rearing water was examined by a larval rearing experiment in this study. Larvae of Japanese red sea bream, Pagrus major, were reared being fed rotifers and subsequently an artificial diet during the thirty-day experimental period. In the four test tanks (100-L capacity) each with 1,000 Japanese red sea bream larvae in addition to the rotifers, N. oculata was maintained at a density of 5-10×10⁵ cells/mL while in the four control tanks, no N. oculata supplemented, but all the other experimental conditions were the same as the test tanks.
　At the end of the experiment, the concentrations of inorganic nitrogen (NH₄-N, NO₂-N, and NO₃-N) and inorganic phosphate (PO₄-P) in the control tanks were 1.5-2.0 times higher than those in the test tanks. While, the number of rotifers with eggs in the test tanks was remarkably higher in comparison with that in the control tanks. Moreover, rotifers in the test tanks contained much more eicosapentaenoic acid (EPA) and n-3 highly unsaturated fatty acid (n-3 HUFA), so that their nutrient value is concluded as higher than that in the control tanks. From the results of this experiment, supplementation with N. oculata into the rearing water is concluded to produce beneficial effects on maintaining water quality and also enhancing the nutrient quality of the rotifers.

Key word: Nannochloropsis oculata, larval rearing, water quality management, Pagrus major, rotifer, Brachionus, food organism
Received on June 12, 2003
* National Research Institute of Aquaculture, Fisheries Research Agency, Nansei, Mie 516-0193, Japan

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Integrating Intensive Aquaculture of the Red Seaweed Chondracanthus exasperatus

J. Robert WAALAND*

　Washington State has a significant history of experimental seaweed aquaculture. Early experiments involved the carrageenophytes Mazzaella splendens and Chondracanthus exasperatus in both open water net culture and semi-closed tank systems on land. Later, net culture of Porphyra for nori and long line culture of the edible kelps Nereocystis and Macrocystis were tested successfully. Further development of these culture systems was halted due to combinations of market, regulatory, political and social considerations. When a Seattle company developed a high value product from the Turkish Towel Seaweed, Chondracanthus exasperatus, there was renewed interest in intensive tank and pond based aquaculture because Washington has a long term moratorium on commercial seaweed harvesting from wild seaweed populations. The initial phase of this research was conducted at Mukilteo, Washington, where strategies for long term cultivation in tanks were tested, and a new custom cultivation tank design was developed for pilot scale cultivation research at a larger site on the shore of Clam Bay near Manchester, Washington. Long term cultivation is now being tested in tanks of up to 5,000L volume supplied with natural seawater, nutrient supplemented seawater, and seawater effluent from nearby fish culture tanks. Seawater from Clam Bay is naturally rich in nutrients from tidal driven upwelling and nearby commercial salmon aquaculture operations. Supplemental nutrients (commercially available "f/2" enrichment and agricultural fertilizers) and halibut culture tank effluent have both been tested for their ability to support C. exasperatus growth with relatively low seawater turnover rates. Compared to seawater at the Clam Bay site, halibut tank effluent differs in both nutrient composition and quantities. Initial results indicate that halibut tank effluent is a satisfactory source of nutrients for C. exasperatus in intensive culture and that this seaweed scrubs significant quantities of nutrients from halibut tank effluent, especially ammonium. Recent experiments with several bioreactor designs have investigated the culturing of C. exasperatus at very high loading densities in recirculated natural and artificial seawater in both submerged and spray culture.

Key word: seaweed, red algae, Chondracanthus, aquaculture
Received on June 12, 2003
* Department of Biology, University of Washington, Seattle, Washington 98195, USA

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Economic value of tideland as place for recreational clam digging, a case study at Kajishima Island

Yasuji TAMAKI*

　Clam digging produces large revenue for fishery cooperative associations and produces a large additional income to fishermen. Although many urban residents enjoy clam digging, an evaluation of the economic value has not been carried out until now. Therefore, I estimated the recreational benefits of clam digging by the travel cost method by using the embarkation lists of the ferryboats for recreational clam digging visitors at Kajishima Island, Kira Town. The results totaling 35.65 million yen were calculated as the recreational benefits of Kajishima Island's surroundings of about 6 ha from the clam digging bed. This amount with Manila clam fishing amount of the Kira Fishery Cooperative Association of 38 million yen. It is evident that urban residents gained a large benefit from recreational clam digging. Mitigation by artificial tidal land is necessary for the tidal land lost by land reclamation as a future policy.

Key word: clam digging, recreational benefits, travel cost method
Received on June 12, 2003
* National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan

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Large-scale restoration of tidal flats and shallows to suppress the development of oxygen deficient water masses in Mikawa Bay

Teruaki SUZUKI*

　Development of hypoxia has been confirmed in the inner-part of almost every major bay of Japan on the Pacific coast from Tokyo southward. Mikawa Bay, where Japan's most serious hypoxia occurs, is used to this report to present the effects and causes of hypoxia, such as impact upon fisheries, historical development and nutrient budget between sediment and water. Although hypoxia basically results from an increase in nutrient load input, intense reclamation in Mikawa Bay of about 1,200 ha of shallows in the 1970s, including tidal flats, has drastically accelerated a deficiency in dissolved oxygen. This is mostly due to losses in the rich filter-feeding macrobenthic community that largely control the high water-purification capacity of those areas. Currently, oxygen deficient water masses in Mikawa Bay are large enough to strip the precious water purification capacity of the remaining shallows by killing the remaining filter feeders. Consequently, the considerable shallows have turned from being a purifier of water quality to a source of excess nutrients, thus sending the Bay into a spiral of deterioration. In order to break this vicious cycle, the dissolved oxygen deficiency of the Bay must be contained to the extent that the purification capacity of the shallows can be brought into full play. To this end, the first thing to do is to restore the tidal flats and the shallows having the effective depth so designed as not to be affected by oxygen deficient water masses, over an extensive area. This may be a more urgent imperative than reducing the nutrient load input. Since 1998 to 2001, about 350 ha of artificial shallows, including tidal flats, have been restored in Mikawa Bay using sand dredged from the Nakayama sea channel. Recovery of abundant benthic organisms, such as bivalves, has been confirmed already by monitoring. Additional tidal flat restoration is now in progress.

Key word: hypoxia, tidal flat, restoration, Ruditapes philippinarum
Received on June 12, 2003
* Aichi Fisheries Research Institute, 97, Wakamiya, Miya-cho, Gamagori, Japan, 443-0021

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Linking watershed loading and basin-level carrying capacity models to evaluate the effects of land use on primary production and shellfish aquaculture

Mark W. LUCKENBACH* and Harry V. WANG*

　Aquaculture production of hard clams, Mercenaria mercenaria, in the lower Chesapeake Bay, Virginia, U.S.A., has increased dramatically within the last decade. In recent years concern has been raised that some growing areas may be approaching the exploitation carrying capacity for clam production. Preliminary calculations indicate that large-scale intensive clam aquaculture may be controlling nutrient and phytoplankton dynamics in this system. To date, carrying capacity models have not been applied to this system, but we are in the process of building models for that purpose. Moreover changing land use in the watersheds surrounding the clam-producing areas raises the need for an improved understanding of how these changes will affect water quality, primary production and shellfish production. We describe an ongoing project linking a watershed-based loading model with a physical transport-based water quality model to simulate primary production and predict carrying capacity for clam aquaculture. Extensive calibration and verification of the water quality model has demonstrated its utility for simulating primary production and water quality parameters in the Chesapeake Bay. In our present efforts, watershed loading models have been developed and tested for predicting both surface and groundwater inputs into the coastal waters. We are currently coupling the water quality and watershed loading models, and developing clam physiology and population-level sub-models. Also, under development is a sediment deposition/resuspension sub-model. Each of these components will be linked to estimate exploitation carrying capacity for clam production in this system. Our goal is to use the coupled models to predict how varying land use scenarios impact water quality, primary production and shellfish carrying capacity of coastal waters.

Key word: Mercenaria mercenaria, aquaculture, carrying capacity, water quality model
Received on June 12, 2003
* Virginia Institute of Marine Science, College of William and Mary. P. O. Box 350, Wachapreague, VA, USA, 23480

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Environmental change in the coastal environment: challenges for the selection and propagation of filter feeding species in aquaculture, stock enhancement and environmental rehabilitation

Roger MANN*

　Selection of species for aquaculture, fishery stock enhancement and environmental rehabilitation or restoration in the coastal zone requires consideration of the fact that species have evolved over geological time whereas changes in the coastal environment have occurred predominantly over recent historical time, often with the largest changes occurring within the past decades of human activity. The evolutionary issue is particularly noted with filter feeding molluscs, where extant species supporting both major natural fisheries and aquaculture have ancient lineages and evolved in environments that may have differed considerably from the locally turbid, nutrient enriched, disturbed (through watershed change and local activity) waters in which they now survive. We cannot presume that native species are strongly selected to survive in the environments in which they currently reside. Neither can we presume that they will be successful candidates for aquaculture, fishery stock enhancement, environmental rehabilitation (the restoration of ecological services in community structure), or environmental restoration (restoration of native community structure with associated ecological services). Watershed and coastal use impacts have, over recent human history, altered community structure in coastal waters, and diminished the ability of surviving community members to perform the ecological services that are one end product of their evolution. A challenge is therefore presented to students of intensive species culture, extensive fishery enhancement, and ecological rehabilitation or restoration: how to best use the tools of husbandry in concert with large and small scale environmental manipulation to promote progress in the designated area of interest? Ecological rehabilitation or restoration centered on cornerstone filter feeding species must employ local environmental rehabilitation, but this will only be successful if it is accompanied by a wider commitment to watershed management protocols that protect all life history stages, including the delicate early stages. A numerical argument for this approach, based on Paulik life history models, will be presented. Intensive aquaculture, by comparison, may be able to progress in marginal environments where delicate early life history stages are cultured in controlled situations, thus limiting mortality, before transfer to open systems. Fishery enhancement resides between these options, where a dual role of supplementing local reproduction is balanced against increased exploitation of commercial product.

Key word: bivalve molluscs, aquaculture, stock enhancement, environmental rehabilitation
Received on June 12, 2003
* Virginia Institute of Marine Science, Gloucester Point, VA 23062 USA

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Integrated aquaculture systems for nutrient reduction in agricultural wastewater: potential and challenges*

Andrew M. LAZUR* 1 and Frank LETEUX* 2

　The integration of aquaculture with agriculture, such and fish production with poultry , has been practiced for hundreds of years and takes advantage of the nutrient output of one crop to increase pond primary productivity, subsequently, enhancing herbivorous fish production. Applying this integration concept for the purpose of reducing the environmental impact of agriculture via the nutrient extraction ability of various shellfish, plant and fish species, is however, a relatively new concept and is increasingly justified by nutrient discharge regulations and associated increasing effluent treatment costs. Agricultural operations, such as animal feedlots, are specific nutrient point sources in which integration with extraction aquaculture could reduce environmental impact. In addition to playing a key role in nutrient reduction, extraction aquaculture species can be an important source of income, critical to offsetting increasing nutrient treatment costs and increasing farm profitability. This paper will review current strategies to apply this concept in the field, present an overview of specific efforts in Florida and summarize the challenges of implementation of integrating production of various aquaculture species to reduce nutrients in agricultural wastewater.

Key word: Integration, aquaculture, agriculture, nutrient reduction
Received on June 12, 2003
*1 University of Maryland Center for Environmental Sciences, Horn Point Laboratory, P.O. Box 775, Cambridge, MD 21613 USA
*2 Florida Department of Agriculture and Consumer Services, Office of Agricultural Water Policy, 1203 Governor's Square Blvd., Suite 200 Tallahassee, FL 32301 USA
* Presented in the Satellite Symposiun held in Shiogama on Oct. 21, 2002.

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Understanding the influence of bivalve suspension-feeder populations on water quality in eutrophic coastal waters

Roger I.E. NEWELL*, Jeff C. CORNWELL*, Raleigh R. HOOD* and Evamaria KOCH*

　Suspension feeding bivalve molluscs serve to couple pelagic and benthic processes because they filter particles with high efficiency from the water column and transfer undigested remains in their biodeposits to the sediment surface. This feeding activity, combined with their often high abundance as natural stocks and in intensive aquaculture farms, can make bivalves extremely important in regulating water column processes in shallow coastal waters. Of all bivalve species worldwide, eastern oysters are among the most powerful in this regard because of their unusually high weight specific filtration rates ( 7 to 10 L h^-1 g-¹ dry tissue weight at typical summer water temperatures of 25 ℃.) The eastern oyster is well adapted to living in estuaries where inorganic particles comprise a large fraction of the seston because it can sort filtered particles prior to ingestion and reject less nutritious particles as pseudofeces. Currently in the nutrient enriched Chesapeake Bay, where phytoplankton are in high abundance, eastern oysters maintain high filtration rates but now reject large amounts of undigested algal cells in their pseudofeces. Newell (1988) initially drew attention to the possible ecosystem benefits of the original huge stocks of eastern oysters in Chesapeake Bay by comparing water column turnover times before oysters were commercially exploited to the situation today when oysters are at an all time low abundance.
　In contrast to Newell's (1988) proposition that oyster populations may once have exerted "top-down" control on phytoplankton stocks others claim that oysters may simply recycle inorganic nutrients rapidly back to the water column and hence there would not have been any long-lasting reduction in phytoplankton biomass. To help distinguish between these scenarios, Newell et al. (2002) explored in laboratory incubations changes in nitrogen fluxes and denitrification under anoxic and oxic conditions in response to loading by different amounts of phytoplankton cells, representing an experimental analog of oyster biodeposits. When organics were regenerated under aerobic conditions, typical of those associated with shallow water oyster habitat, coupled nitrification-denitrification was promoted, resulting in denitrification of 〜20 ％ of the total added nitrogen. In contrast under anoxic conditions, typical of current summertime conditions in main-stem Chesapeake Bay where phytoplankton is microbially degraded beneath the pycnocline, nitrogen was released solely as ammonium from the added organics. Such denitrification of particulate nitrogen remaining in the biodeposits of benthic suspension feeders will enhance nitrogen removal from eutrophied coastal waters (Newell, 2004).
　It is likely that reduced oyster filtration by the much diminished oyster populations has contributed, in part, to observed higher turbidites in Chesapeake Bay and the consequent reduction in light reaching the sediment surface. In aerobic incubations of sediment cores with even low light levels (70μmol^-2 s^-1), Newell et al. (2002) found that a benthic microalgal/cyanobacterial community grew that not only absorbed the inorganic nitrogen released from oyster biodeposits but also fixed N2. This suggests that an ecosystem dominated by benthic primary production may develop in shallow waters when reduced turbidity associated with bivalve feeding increases light penetration to a level that can sustain benthic microalgal production.
　Over the last four decades seagrass beds have either declined or have disappeared throughout much of the Chesapeake Bay due to high water turbidity leading to reduced light availability for these benthic plants. In order to explore the possible interactions between oyster and seagrass declines we have developed a numerical model to simulate the interaction between wave-induced sediment resuspension, bivalve filtration, and seagrass growth. This model, which is parameterized based upon direct measurements of oyster filtration and seagrass wave dampening effects, shows that under high wave height conditions the presence of oysters can reduce suspended sediment concentrations by nearly an order of magnitude, which significantly increases water clarity and the depth to which seagrasses can grow (Newell, 2004).

* Horn Point Laboratory, University of Maryland Center for Environmental Science, PO Box 775, Cambridge, MD 21631 USA

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DEVELOPMENT OF A NOVEL GENE TRANSFER METHOD IN PORPHYRA

Chum-Mean LIN* 1, Charles YARISH* 2 and Thomas CHEN* 1

　Foreign genes have been successfully transferred into both animal and plant by transgenesis, but introduction of foreign genes into many important algae species is still in its infancy. Although nuclear and organelle transformations in Chlamydomonas reinhardtii, a green microalgal species, have been well established, attempts to develop transformation methods for macroalgae, such as Volvox carteri and several diatom species have just begun. Currently, there is no report of success of genetic transformation in Porphyra species (seaweed).
　To facilitate applications of seaweed in both basic research and integrated aquaculture biotechnology, we have undertaken initiatives to develop gene transfer technology for Porphyra, and made significant progress. A plasmid DNA with a selection marker was transferred into archaeospores of P. leucosticta by electroporation. Total DNA was then prepared from those electroporated samples at various times of incubation including 24 hrs, one week, two weeks and up to two years. PCR analysis showed the consistent presence of plasmid DNA in all samples tested, strongly suggesting the success of gene transfer in Porphyra. The thalli developed from those transformed archaeospores grow well under continuous presence of selection pressure over two years with serial transfers. Reverse transcription (RT)/PCR analysis of RNA samples isolated from transgenic thalli showed expression of the transgene. These observations provide us with great confidence that genetic manipulation and production of transgenic Porphyra is feasible.

*1 1 Department of Molecular and Cell Biology, and * 2 Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269 USA *Corresponding author