Amir Neori

Integrating seaweeds into marine aquaculture systems: a key toward sustainability

The rapid development of intensive fed aquaculture (e.g. finfish and shrimp) throughout the world is associated with concerns about the environmental impacts of such often monospecific practices, especially where activities are highly geographically concentrated or located in suboptimal sites whose assimilative capacity is poorly understood and, consequently, prone to being exceeded. One of the main environmental issues is the direct discharge of significant nutrient loads into coastal waters from open‐water systems and with the effluents from land‐based systems. In its search for best management practices, the aquaculture industry should develop innovative and responsible practices that optimize its efficiency and create diversification, while ensuring the remediation of the consequences of its activities to maintain the health of coastal waters. To avoid pronounced shifts in coastal processes, conversion, not dilution, is a common‐sense solution, used for centuries in Asian countries. By integrating fed aquaculture (finfish, shrimp) with inorganic and organic extractive aquaculture (seaweed and shellfish), the wastes of one resource user become a resource (fertilizer or food) for the others. Such a balanced ecosystem approach provides nutrient bioremediation capability, mutual benefits to the cocultured organisms, economic diversification by producing other value‐added marine crops, and increased profitability per cultivation unit for the aquaculture industry. Moreover, as guidelines and regulations on aquaculture effluents are forthcoming in several countries, using appropriately selected seaweeds as renewable biological nutrient scrubbers represents a cost‐effective means for reaching compliance by reducing the internalization of the total environmental costs. By adopting integrated polytrophic practices, the aquaculture industry should find increasing environmental, economic, and social acceptability and become a full and sustainable partner within the development of integrated coastal management frameworks.

Integrated mariculture: asking the right questions

Reducing negative environmental impacts from aquaculture activities is a key issue for ensuring long-term sustainability of the industry. This study examines the major findings and methodology aspects from 28 peer-reviewed studies on marine aquaculture systems integrating fed and extractive organisms. All studies include seaweeds as extractive organisms. The main objective was to analyse the degree of relevance these findings have for large-scale implementation of integrated mariculture practices, and to identify necessary research areas for a future research agenda.

A sustainable integrated system for culture of fish, seaweed and abalone

A 3.3 m 2 experimental system for the intensive land-based culture of abalone, seaweed and fish was established using an integrated design. The goals were to achieve nutrient recycling, reduced water use, reduced nutrient discharge and high yields. Effluents from Japanese abalone . . Haliotis discus hannai culture tanks drained into a pellet-fed fish Sparus aurata culture tank. . The fish effluent drained into macroalgal Ul˝a lactuca or Gracilaria conferta culture, and biofilter tanks. Algal production fed the abalone. The system was monitored to assess productivity and nitrogen partitioning over a year. The fish grew at 0.67% day y1 , yielding 28-kg m y2 year y1 . y2 y1 . The nutrients excreted by the fish supported high yields of U. lactuca 78-kg m year and . efficient 80% ammonia filtration. Gracilaria functioned poorly. Ul˝a supported an abalone growth rate of 0.9% day y1 and a length increase of 40-66 mm day y1 in juveniles, and 0.34% day y1 and 59 mm day y1 in young adults. Total abalone yield was 9.4 kg year y1 . A surplus of seaweed was created in the system. Ammonia-N, as a fraction of total feed-N was reduced from 45% in the fish effluents to 10% in the post-seaweed discharge. Based on the results, a doubling of the abalone:fish yield ratio from 0.3 to 0.6 is feasible. q 2000 Elsevier Science B.V. All rights reserved.

Seaweed biofilters as regulators of water quality in integrated fish-seaweed culture units

Abstract The water-quality characteristics of a new system for the integrated culture of fish ( Sparus aurata L.) and seaweed ( Ulva lactuca L.) were examined. Seawater was recirculated between intensive fishponds and seaweed ponds. The seaweed removed most of the ammonia excreted by the fish and oxygenated the water. A model consisting of several tanks and a pilot consisting of two 100-m 3 , 100-m 2 ponds were studied. In both, the metabolically dependent water-quality parameters (dissolved oxygen, NH 4 + -N, oxidized-N, pH and phosphate) remained stable and within safe limits for the fish during over 2 years of operation. The design allowed significant increases in overall water residence time (4.9 days), compared with conventional intensive ponds, and produced a high yield of seaweed in addition to the fish. The design provides a practical solution to major management and environmental problems of land-based mariculture.

The integrated culture of seaweed, abalone, fish and clams in modular intensive land-based systems : II. Performance and nitrogen partitioning within an abalone (Haliotis tuberculata) and macroalgae culture system

A pilot-scale system for the intensive land-based culture of abalone was established using an integrated design aimed at eliminating the dependence on external food sources, whilst reducing water requirements and nutrient discharge levels. The system was the first and simplest trial in a series of progressive complexity of the concept of integrated culture of seaweed, abalone, fish and clams in modular and intensive land-based facilities. Relative sizes of the modules, their stocking densities and the rate of nutrient supply were determined based on earlier results to be optimal. Effluents from two abalone (Haliotis tuberculata) culture tanks drained into macroalgae (Ulva lactuca or Gracilaria conferta) culture and biofilter tanks, where nitrogenous waste products contributed to the nutrition of the algae; net algal production from each algal tank was harvested and used to provide a mixed diet for the abalone. Excess algal yield was used elsewhere. The system was monitored to assess productivity and nitrogen partitioning over a year, while improvements were made based on the accumulating results. Total annual N-budgets were combined with mean production figures to determine a suitable ratio of abalone biomass to algal culture vessel productivity, towards commercial application of the concept. The abalone grew on average 0.26% and 0.25% body weight/d in the two culture tanks; reduced growth and increased food conversion ratios (food eaten/biomass gain; w/w) were associated with high summer water temperatures (max. 26.9°C). U. lactuca showed reliable growth and filtration performance (mean production of 230 g fresh weight/m2/d, removing on average 58% of nitrogen supplied). Conversely, G. conferta growth was highly erratic and was deemed unsuitable for the current application. It is estimated that 1 kg of abalone biomass would require food supplied by 0.3 m2 of U. lactuca culture, reducing N inputs required by 20% and N in effluent by 34% when compared to the two organisms grown in monoculture.

A proposed model for “environmentally clean” land-based culture of fish, bivalves and seaweeds

Abstract A model system is proposed, in which particulate and dissolved metabolites from the effluents of fish culture are removed by biofilters of bivalves (Crassostrea gigas and/or Tapes semidecussatus) and seaweeds (Ulva lactuca). The design utilizes ecological principles and the results of long-term pilot-scale trials with each of the four components of the system. Fresh sea water enters the fishponds, drains through an earthen sedimentation pond, a bivalve filtration unit and a seaweed filtration/production unit, and is finally discharged back into the sea. An additional loop recirculates water from the sedimentation pond through a bivalve production unit. The performance of each of the different components of the system is assessed in terms of total nitrogen budgets, which yield the following results: fish yield, 26% of the N introduced in the feed; bivalve yield, 14.5%; seaweed yield, 22.4%; settled feces, 32.8%; suspended and dissolved discharge back into the sea, only 4.25%. The harvested yields contain 63% of the N budget. The production of 1 kg of fish, requiring 3 kg of feed, is accompanied by the production of 3 kg of bivalves and 7.8 kg of seaweed. Each 100 m2 of fishponds requires 50 m2 of sedimentation ponds, 33 m3 of bivalve troughs and 42 m2 of seaweed ponds.

A semi-recirculating, integrated system for the culture of fish and seaweed

Abstract Biofiltration allows for environmentally sustainable mariculture. An intensive, biofiltered recirculating integrated system producing fish and seaweed on a semi-commercial scale was evaluated with respect to production and to nutrient and heat budgets. The system consisted of abalone (Haliotis discus hannai) and sea urchin (Paracentrotus lividus) tanks, an intensive fishpond (Sparus aurata), and a three-stage Ulva lactuca biofilter, which cleaned and recirculated 50% of the effluent back to the fishpond. To preserve water heat, the shellfish and fishpond units were both covered with greenhouses; the biofilter unit was covered with a greenhouse only during winter. Seaweed yield was variable and averaged 94 and 117 g m−2 day−1 (fresh weight) in periods with and without greenhouse cover, respectively. Protein content of U. lactuca averaged above 34% of dry weight. The biofiltration of only 50% of the water through the seaweed biofilter reduced the export of dissolved nutrients to the environment by nearly 30%. Peak ammonia excretion by the morning-fed fish coincided with maximum seaweed light-dependent ammonia uptake and concentrations of ammonia in the fishpond remained within nontoxic limits. Also, daytime photosynthesis of U. lactuca (uptake of CO2) met fish respiration (production of CO2), thus balancing fishpond pH levels within safe limits regarding ammonia toxicity. Daytime oxygen demand by the fish was partially met by the photosynthetically generated oxygen. Before covering the biofilter with a greenhouse, it lost much heat, reducing the temperature in the fishpond. Following the greenhouse covering of the biofilter, heat loss ceased and consequently the fishpond temperature was raised. Recirculation through the biofilter improved system sustainability; it reduced water use, lowered negative environmental impact, and maintained stable and safe water quality conditions in the fishpond.

A novel three-stage seaweed (Ulva lactuca) biofilter design for integrated mariculture

Seaweed biofilters have proven their usefulness in the treatment of fishpond effluents. However, their performance poses a dilemma: TAN (Total Ammonia N) uptake rate – and with it seaweed yield and protein content – is inversely proportional to TAN uptake efficiency. The ideal for a seaweed biofilter performance would be a high uptake rate together with high uptake efficiency. The novel three-stage seaweed biofilter design described here has solved this dilemma. The design used the finding that the performance of seaweed ponds depended on the flux of TAN through them, and that therefore effluents with reduced TAN concentration could provide the seaweed with a high TAN flux if the water flow increased proportionally. Effluents from a seabream fishpond were passed through a series of three successively smaller (25, 12.5 and 6.25 m2, respectively) air-agitated Ulva lactuca ponds. The diminished inflow TAN concentrations to the second and third ponds of the biofilter system were compensated for by the increased water exchange rates, inversely proportional to their sizes. The biofilter performance was evaluated under several TAN loads. TAN was efficiently removed (85–90%), at a high areal rate (up to 2.9 g N m-2 d-1) while producing high protein U. lactuca (up to 44% dw) in all three stages, although with mediocre yields (up to 189 g fresh m-2 d-1). Performance of each seaweed biofilter pond correlated not with TAN concentration, but with areal TAN loads. The novel three-stage design provides significant functional and economic improvements in seaweed biofiltration of intensive fishpond water.

A Total Nutrient Budget for an Experimental Intensive Fishpond with Circularly Moving Seawater

Abstract A total nutrient budget was measured in an experimental intensive fishpond with circularly moving seawater and a water retention time of 2 days. The pond was stocked with gilthead sea-bream, Sparus aurata . An important feature of this pond design was the significant reduction of the excess organic load of particulate matter by daily draining of the settled detritus. The major nutrient pathways consisted of fish excretion coupled with phytoplankton uptake. All inputs and outputs of phosphorus and nitrogen were measured daily over a 1-month period. Fish food accounted for more than 95% of the nutrient input, sustaining dense phytoplankton populations with up to 450 μ g chlorophyll a l −1 . Fish assimilated 21% of P and 26% of N inputs. On a monthly average, ca. 50% and 46% of the P and N inputs, respectively, were found in the particulate phase of the water column. This phase was dominated by a phytoplankton community which exhibited “bloom and crash” cycles due to microflagellate grazing. As the pond progressed from a bloom to a crash, the fractions of entering nutrients which ended in the particulate phase changed from 76% to 32% for P and from 63% to 34% for N. The drained settled detritus contained on average only 17% of the P and 10% of the N inputs. The outflow of dissolved matter contained 22% of P and 13% of N inputs. On a monthly average, surpluses (inputs minus outputs) of −10% for P and 5% for N were estimated in the budget, which balanced within experimental error. On a daily basis, however, the deviations from a balanced budget were occasionally larger, with surpluses ranging from −29% to 6% for P and from −3% to 8% for N. Attached macroalgal growth and decomposition are thought to be likely causes of these periodic deviations. The significant nonalgal conversion of dissolved total N into particulate N during phytoplankton crashes (as much as 20% of ammonia-N and 75% of dissolved organic-N) was probably due to uptake by bacteria and heterotrophic flagellates. Intensive bacterial activity, in particular sulphate reduction, was observed in the drained detritus.

The integrated culture of seaweed, abalone, fish and clams in modular intensive land-based systems: I. Proportions of size and projected revenues

Three environmentally friendly modular designs for integrated mariculture are described. The basic design consists of modules for the culture of seaweed (Ulva lactuca or Gracilaria spp.) and abalone (Haliotis tuberculata). Modules for the culture of fish (Sparus aurata) and then clams (Tapes philippinarum) are subsequently connected in two progressively complex systems. The modular design allows flexibility in the allocation of resource shares to each product according to operational and economic constraints. Reduction in nutrient release to the environment results from increasing the fraction of supplied ammonia or protein-N that ends up as commercial products relative to current monoculture practices. As much as half or more of the nitrogen supplied to the proposed systems is expected to be utilized by harvestable yields of seaweed, molluscs and fish. System dimensions and projections of yields and revenues allow readers to roughly estimate profitability for the three designs under their own conditions.