Introduction Materials and methods

1. Introduction

The discharge of low-quality water from intensive land-based mariculture facilities causes environmental and economic concerns, since fish excrete to the water 70–80 of Ž . their ingested protein N, 80 of it in dissolved forms Porter et al., 1987 . The development of practical and non-polluting land-based maricultural practices is therefore of great importance, both for mariculture and for the coastal environment. A useful approach of integrated mariculture has been designed at the National Center Ž . for Mariculture NCM , Eilat, for solving the effluent problem by nutrient recycling. Water from fishponds recirculates through biofilters of seaweed, which remove most of Ž . the ammonia from the water Cohen and Neori, 1991; Neori et al., 1993, 1996 . The financial return from the low-value seaweed biomass by-product can be raised greatly by feeding it to valuable macroalgivores, such as sea urchins and abalone. Ž . Abalone is a commercially valuable marine gastropod Oakes and Ponte, 1996 . Its Ž culture worldwide is severely limited by supplies of suitable seaweed Uki and Watan- . abe, 1992 . This situation makes it only natural to add abalone to the integrated culture Ž . system for fish and seaweed Shpigel and Neori, 1996 . The integrated culture of two Ž organisms, abalone and seaweed, has been tested on a laboratory scale Neori et al., . 1998 . In this study, we describe the performance of a more complex system, for integrated culture of three organisms — abalone, fish and seaweed. The system is intended to be fully integrated, that is, the fluxes of water and nutrients between the three modules are adjusted to optimize water use, nutrient recycling and marketable production. The system is also intended to be sustainable, one that allows increased supply of marketable marine organisms with minimal increases in pollution and in burden on natural populations.

2. Materials and methods

Ž The experimental system was a modification of our model design design B in . Shpigel and Neori, 1996 , with a water saving modification, by which the abalone culture water were recycled for the fish culture. It consisted of one unit each for abalone, Ž y1 . finfish, and seaweed. Unfiltered seawater 2400 l day was pumped to two abalone tanks, drained through a fish tank, and finally through a seaweed filtrationrproduction Ž . Ž unit back to the sea Fig. 1, gray rectangles . The fish were fed with fish feed Matmor, . Israel . Ammonia and other nutrients excreted by the fish were removed by the seaweed and supported their growth. The seaweed was harvested and fed to the abalone. The integrated culture was operated for a year, beginning in October 1995. 2.1. Abalone unit Ž . Fig. 1. A schematic diagram of the integrated mariculture system gray rectangles . The processes defining the Ž y1 . nitrogen budget are illustrated. Rounded values grams N year quantify each process; solid vertical arrows are seawater flows; heavy dashed arrows are N inputs and outputs; the fine dashed line is seaweed recycling to the abalone. The abalone unit consisted of two 120-l rectangular bottom drained tanks. The tanks Ž were elevated, allowing effluents to drain into the fish tank. A removable screen 1-cm . mesh covered the whole area 10 cm above the flat bottom, and retained the abalone while allowing feces and detritus to drain. The tanks were completely flushed and cleaned once a week. Two parallel air diffusers suspended the algae, which were added as feed. Two 160-mm diameter half pipes were stacked on the netting to provide surface area and shelter for abalone attachment. Two size groups of Japanese abalone, Haliotis discus hannai, were stocked in Ž . Ž . separate tanks, 1200 juveniles of 11 2.3 mm mean sd length 0.23 0.04 g in Ž . Ž . one tank Group I and 251 adults of 44.2 2 mm length 15.7 4.6 g in a second tank Ž . Group II . The juveniles were kept in the system 374 days. Six hundred juveniles were culled out after 184 days. The adults were kept in the system at stocking densities of 20–30 kg m y3 . After 184 days they were harvested, measured for the parameters described below, and then replaced by 600 smaller individuals of 16.6 3.1 mm length Ž . Ž . 0.7 0.1 g for an additional 224 days Group III . One hundred animals in each adult group were individually tagged. Once a month the tagged animals were washed free of debris, drained to remove surplus water and dried on absorbent paper. Wet weight measurements were used to calculate specific growth Ž . Ž rates SGR for each time interval, i.e., the percent body weight gain per day Shpigel . et al., 1996, based on Day and Fleming, 1992 w x SGR s lnW ylnW rt = 100 1 Ž . Ž . t where W is the wet weight of an animal at the beginning of each monitoring interval and W is the weight after t days of growth, at the end of the interval. Shell length t measurements were used to calculate shell growth Shell growth mmrday y1 s L yL rt 2 Ž . Ž . Ž . 2 1 where t is time interval in days, L is the length of an animal at the beginning of each 1 monitoring interval and L is the length at the end of the interval. Food conversion ratio 2 Ž . FCR was calculated from feed intake and growth FCR s feed intake g fw rweight gain g fw 3 Ž . Ž . Ž . Additionally, the cumulative yields of the three abalone groups and the supplied seaweed were used to calculate overall production FCR. 2.2. Fish unit Ž . Three hundred gilthead sea bream Sparus aurata with an average weight of 40 g Ž . Ž 2 . 12 kg total weight were stocked in a 600-l 1 m surface area rectangular aerated tank. The fish were fed a 45 protein pellet diet. The bottom of the tank was drained daily to remove feces and uneaten food. Stocking density was maintained below 15 kg m y3 . Excess fish were culled regularly. Once a month a sample of 50 fish was weighed. Specific growth rates and FCR were calculated as mentioned above. 2.3. Seaweed unit Two species of seaweed, UlÕa lactuca and Gracilaria conferta, were grown in two Ž 2 . Ž . 600-l 1 m surface area tanks as described in Vandermeulen 1989 . The algae were suspended in the water column by air diffusers situated at the bottom. Total seaweed biomass was kept approximately at 1.5 kg of U. lactuca and 5–13 kg of G. conferta. Twice a week, excess seaweed biomass was harvested. The seaweed was drained of surplus water and weighed. The biomass was fed to the abalone as needed and the rest discarded. Several crashes of the G. conferta stock occurred, necessitating biomass imports. 2.4. Abiotic parameters and nitrogen budgets Ž . Abiotic parameters oxygen, temperature, pH and ammonia levels were monitored Ž . twice a day at 0800 and 1400 h in all components of the system. Ammonia levels were Ž . monitored by an electrode Ingold NH Electrode Type 15-230-3000 . In addition, 24-h 3 intensive measurements were carried out several times a year. During the intensive Ž . measurement periods, ammonia-N was measured by an autoanalizer Technicon AA-II Ž . as in Neori et al. 1996 . Nitrogen content of the abalone and the seaweed tissue were Ž . measured by a CHN analyzer Perkin Elmer . Nitrogen levels of the abalone mucus, and fish and abalone feces were measured in preliminary experiments and were estimated for this experiment according to the actual sizes of the abalone.

3. Results