Abalone Feed Research Articles

Using Macrocystis pyrifera (L.) C. Agardh from southern Chile as a source of applied biological compounds

The exploitation of seaweeds in Chile has been carried out for more than 60 years. More recently, seaweeds have been used for the production of alginate, agar and carrageenan, agricultural fertilizers and industrial aquaculture (feed for abalone and sea urchins), increasing the added value of this natural resource. In the Magellan Region (56oS), the giant kelp Macrocystis pyrifera (L.) C. Agardh presents the most extensive kelp forest, reaching a biomass of approximately 12 kg.m-2. Recent studies have shown potential benefits from adding M. pyrifera- derived flour to salmonid feed. Research is currently underway to evaluate the useof brown algae-derived products for marine aquaculture feed of Oncorhynchus mykiss in tanks. There was no apparent adverse effect on the evaluated parameters that can be attributed to the incorporation of M. pyrifera meal in the diets fed to salmonids. Even when the control diet had numerically the best performance in zootechnical terms, the analysis of variance of all parameters evaluated showed no significant differences with regard to diets containing M. pyrifera meal. These results demonstrated that seaweed meal has important benefits for animal health and nutrition that could be applied or tested in other marine organisms of commercial importance.

Nonselective Diatom Grazing By Juveniles of Red Abalone (Haliotis rufescensSwainson, 1822) Under Experimental Culture Conditions

In abalone farms and laboratories of the Baja California peninsula in Mexico, young and postlarval abalone feed on benthic diatoms that grow on the artificial surfaces of the culture tanks, or on epiphytic diatoms growing on kelp (Macrocystis pyrifera) blades provided when a change in their diet is estimated. It is not known whether grazing selectivity occurs by postlarvae and young abalones at this time. Thus, experiments were conducted to determine whether discrimination by juveniles of red abalone (Haliotis rufescens) occurs while grazing on diatoms that grow on the rocks and kelp blades extracted from their habitat, and to determine whether the ingested diatoms are, indeed, digested. Our hypothesis was that juveniles of H. rufescens would feed nonselectively on the diatom films; thus, the characteristics of the diatom assemblages (species composition, diversity) from their gut contents should be similar to those upon which they feed. We also expected that the smaller forms of diatoms would pass through the digestive tract intact. Overall, 171 diatom taxa were identified: 123 in the tank walls, 35 on the rocks, 143 in the gut contents, and 38 in the feces. Only Amphora pediculus appeared in all the gut contents examined; however, 12 taxa accounted for 80% of the relative abundance (n = 500). Highest diversity ( = 4.46) was measured in the walls of a tank where M. pyrifera was included, but abalone specimens from this tank showed the lowest H' value in their gut contents. The hypothesis that grazing by young H. rufescens is nonselective is supported, as well as the importance of the structure of the diatom assemblage grazed upon (as in H. fulgens), which is reflected in their gut contents. Moreover, feces analysis showed that many small diatoms that are ingested are not digested, and are able to reproduce and grow after passing through the digestive tract.

A simple method for rapid estimation of Ecklonia maxima and Laminaria pallida biomass using floating surface quadrats

In South Africa two species of kelp, Ecklonia maxima and Laminaria pallida, occur in quantities sufficient for commercial use. Currently, the former species is harvested in large quantities (about 5 000 tonnes wet weight per year) as abalone feed. In order to set limits to the amount of kelp that may be harvested, it is necessary to obtain reasonably accurate measurements of kelp biomass. Biomass estimates are traditionally obtained by destructive sampling of kelp sporophytes from quadrats placed on the bottom. Scuba divers harvest the plants and weigh them ashore. This method is slow and labour-intensive, and severely limits the area of kelp bed that can be sampled. This study investigates several alternative methods to determine an easier, quicker method of estimating kelp biomass. First, morphometric data on both species of kelp were collected to investigate if there were easily measurable characters that correlate with the weights of individual sporophytes, which then could be used as proxies for destructive sampling. Second, floating quadrats were used to establish correlations between the density of kelp heads at the water surface during low spring tides and kelp biomass. Good correlations were found between (1) individual sporophyte weight and stipe weight for E. maxima (p = 0.0000; r2 = 0.5693) and L. pallida (p = 0.0000; r2 = 0.6175), and (2) individual sporophyte weight and stipe length for E. maxima (p = 0.0000; r2 = 0.5828) and L. pallida (p = 0.0000; r2 = 0.4817). Such measurements are time consuming and labour intensive, and require scuba and destructive sampling. However, using floating 1 m2 surface quadrats, good correlations were found between the density of kelp heads at the surface and the biomass of kelp (E. maxima, p = 0.0000, r2 = 0. 3469; L. pallida, p = 0.0000, r2 = 0.4785). Surface density measurements are more than eight times quicker than the traditional biomass determination method, are non-destructive, require fewer personnel, can be done by snorkelling and are unaffected by water clarity. Furthermore, harvesting for abalone feed is boat-based and targets only surface-reaching kelp. Sporophytes of E. maxima that reach the surface at low water spring tide comprise on average 62% of the total biomass of kelp in these beds, so scuba should still be used where observations and measurements of subcanopy biota are required.

Growing Ulva (Chlorophyta) in integrated systems as a commercial crop for abalone feed in South Africa: a SWOT analysis

Over 1,000t fresh weight of Ulva was cultivated on South African abalone farms in 2007, primarily for feed, but in one case to allow partial re-circulation by nutrient removal. The potential of this new commercial crop is analysed. Material is collected from natural free-floating populations and at least four species are commonly grown, with different ecophysiological characteristics. A brown epiphyte, Myrionema strangulans, causes a disease of the Ulva, which is currently managed by farmers by re-stocking. The main potential threat is that some farmers are wary of integrated systems, fearing they may promote disease in abalone, although Ulva has been grown in abalone effluent and fed back to the abalone on one farm for 6 years without adverse effects. Opportunities exist for the expansion of Ulva cultivation via further spread of the abalone industry, the inclusion of seaweed raceways in proposed fish-farming activities, or the potential for the inclusion of high quality cultivated Ulva as a constituent in aquafeed. A conservative estimate of production over a full year from these raceway systems was 26.1 g dw m−2 day−1 (2006) and 19.7 g dw m−2 day−1 (2007), similar to maximum figures for total annual microalgal biomass production in outdoor systems.

Integrated seaweed cultivation on an abalone farm in South Africa

Land-based abalone aquaculture in South Africa, based on the local species Haliotis midae, started in the early 1990s and has grown rapidly in the last decade, with 13 commercial farms now producing over 850 t per annum. Over 6,000 t per annum of kelp Ecklonia maxima are now harvested for this purpose, and some kelp beds are reaching maximum sustainable limits. Research into seaweed aquaculture as feed (Ulva and some Gracilaria) for abalone started in the late 1990s on the southeast coast (where there are no kelp beds) using abalone waste water. A growing body of evidence suggests that a mixed diet of kelp plus other seaweeds can give growth rates at least as good as compound feed, and can improve abalone quality and reduce parasite loads. A pilot scale Ulva lactuca and abalone integrated recirculation unit using 25% recirculation was designed and built on the south west coast of South Africa using one 12,000-L abalone tank containing 13,200 15 ± 2.5 g abalone, connected to two 3,000-L seaweed tanks containing an initial starting biomass of 10 kg of seaweed, replicated 3 times. In an 18-month period, there were no significant differences in abalone health or growth rates, sediment build up and composition, mobile macro fauna densities and species between the recirculation or the flow-through units. Transfer of oxygen generated by the seaweeds to the abalone tanks was poor, resulting in the recirculated abalone tanks having lower (33%) dissolved oxygen concentrations than a comparable flow-through abalone unit. Seaweed nutrient content and specific growth rates in the units were comparable to seaweeds cultivated in fertilized effluent (SGR = 3.2 ± 3.4%.day−1; Yield = 0.2 ± 0.19 kg.m2.day−1). Indications were that at this low recirculation ratio the seaweeds in the units were nutrient limited and that there were no negative effects to the abalone being cultivated in such a recirculation unit at this recirculation ratio.

La experienca del desarrollo del cultivo de abalón (Haliotis spp.) en Chile : oportunidades y desafíos

Intensive abalone farming--specifically of the red abalone (Haliotis rufescens) and the green (or Japanese) abalone (Haliotis discus hannai)--has expanded rapidly in Chile since the late 1990s, and this article presents an overview of the challenges facing the industry and the factors which favour its development. At present, 100% of Chile's abalone enterprises farm the H. rufescens species, owing to its suitability for full-cycle culture. In the analysis of factors that facilitate the development of abalone farming in Chile, those that stand out include the characteristics of the aquatic ecosystem, existing entrepreneurial and professional skills, decisive government support in co-financing scientific and technological projects, infrastructure and associated services to support these development initiatives and a market where prices have remained stable and demand for abalone products has been steady. The greatest challenges facing intensive abalone farming in Chile are providing a constant supply of macroalgae for abalone feed and developing complementary feed, as well as updating current legislation on intensive abalone farming, strengthening producer associations and establishing health certification. The article discusses examples of the impact that native organisms can have on animals introduced into an aquatic ecosystem and the international transmission of agents such as withering syndrome and sabellid polychaete infestation disease, associated with the movement of abalone seeds and broodstock. The article also emphasises the importance of implementing the recommendations of the World Organisation for Animal Health.

The growth of disk abalone, Haliotis discus hannai at different culture densities in a pilot-scale recirculating aquaculture system with a baffled culture tank

The growth rate of disk abalone, Haliotis discus hannai, energy consumption and changes in water quality were monitored in a pilot-scale recirculating aquaculture system (RAS) for 155 days. Baffles were installed in the RAS culture tanks to enlarge the attachment area and clean out solid waste materials automatically by hydraulic force only. The experimental disk abalones, of shell length 24.5 ± 0.5 mm, were cultured at three stocking densities, 700, 1300 and 1910 individuals/m 2 bottom area, in triplicate. The abalones were fed with sea mustard, Undaria pinnatifida, once a week. The abalone feed conversion rates and daily growth rates ranged from 24.5 to 25.9 and 0.32 to 0.36%, respectively. Their daily shell increments and survival rates ranged from 67.7 to 78.6 μm/day and 87.6–92.2%, respectively. The growth in weight tended to decrease at a culture density of 1300 individuals/m 2 bottom area, while shell increments and survival rates were acceptable at this density. The total power consumption for heating was 1185.4 kW, comprising 30.2% of the total power consumption, while the average water exchange rate was only 2.9% per day. The total ammonia nitrogen stabilized below 0.07 mg/L, after conditioning of the biofilter. The NO 2 −–N, NO 3 −–N and total suspended solid concentrations were also maintained within acceptable ranges for the normal growth of disk abalone. The use of the RAS with these newly designed culture tanks for disk abalone culture produced 1300 individuals/m 2 bottom area with a water exchange rate of only 2.9% per day and used about one-tenth of the heat energy of a conventional flow-through system.

Opportunities and challenges for the development of an integrated seaweed-based aquaculture activity in Chile: determining the physiological capabilities of Macrocystis and Gracilaria as biofilters

Seaweed production is a reality in Chile. More than ten species are commercially used to produce phycocolloids, fertilizers, plant growth control products, human food or animal fodder and feed additives. These multiple uses of algae offer a number of possibilities for coupling this activity to salmon, abalone and filter-feeder farming. In this context, different experiments carried out in Chile have demonstrated that Gracilaria chilensis and Macrocystis pyrifera have great potential in the development of an integrated aquaculture strategy. The present Integrated Multi-Trophic Aquaculture (IMTA) approach study showed that Gracilaria can be cultured best at 1 m depth whereas Macrocystis has an especially good growth response at 3 m depth. Both species use available nitrogen efficiently. On the other hand, high intensities of solar radiation (UV and PAR) can be critical at low depths of cultivation, and our results indicate that both species show photosynthetic susceptibility mainly at noon during the summer. The demand of Macrocystis for abalone feeding is increasing, thus improving the opportunity for developing an integrated nutrient waste recycling activity in Chile. Although Gracilaria shows a higher nitrogen uptake capacity than Macrocystis, its market value does not yet allow a massive commercial scaling.

Seaweed future cultivation in Chile: perspectives and challenges

Production of seaweeds in Chile has fluctuated between 120,000 and 316,000 wet metric tons per year during the last ten years. The most important Phaeophyta are exploited for alginate production and as abalone feed. Among the Rhodophyta, Chilean production comes mainly from wild stocks, as at present cultivation on a commercial scale is restricted to Gracilaria. Large-scale production of this species has been the result of a sharp increase in the number of farms. During the last five years an important trend towards diversification of seaweed exploitation and cultivation has developed. The demand for brown algal materials for the alginate industry, abalone cultivation, seaweed flour production for human and animal feeding and the development of novel food products has encouraged the farming of Macrocystis pyrifera and of red edible seaweeds, such as Chondracanthus chamissoi and Callophyllis variegata, is also promoting the development of cultivation activities.

Population structure and growth of polydorid polychaetes that infest cultured abalone Haliotis midae

Polydorid polychaetes can infest cultured abalone thereby reducing productivity. In order to effectively control these pests, their reproductive biology must be understood. The population dynamics and reproduction of polydorids infesting abalone Haliotis midae from two farms in South Africa is described using a length-based, age-structured model. Shells were infested mainly by introduced Boccardia proboscidea. Polydora hoplura and Dipolydora capensis were also present but in numbers too few to identify factors influencing infestation. At both farms, B. proboscidea lived for a minimum of 12 months. Growth rate, size at maturity, maximum size, infestation intensity, recruitment, percentage of the population brooding and mortality appear to be affected by abalone feeding regime and water temperature, and these factors need to be considered in controlling infestation. Brooders and recruits were present throughout the year, but increased significantly during mid- to late winter/early spring when water temperature and day length increased. Treatment measures should therefore be implemented throughout the year but with increased effort when water temperature increases.

Mapping and quantifying the South African kelp resource

Two species of kelp are exploited commercially in South Africa. Use of beach-cast Laminaria pallida is limited, although it comprises the bulk of the biomass on the northern West Coast. Ecklonia maxima dominates the southern West Coast and provides most of the material for the South African kelp industry. Harvests of E. maxima fronds for abalone feed have reached 3 000–5 000 tonnes fresh weight (t f wt) y−1, whereas beachcast material of both species (about 1 000t dry wt y−1) is collected mainly for alginate extraction. For the first time, a South African kelp inventory has been compiled using all available data for the 900km-long West Coast (Cape Agulhas to the Orange River), although a few gaps remain. Beds of E. maxima and L. pallida reaching the surface at low spring tides were mapped using one or several methods: infrared aerial photography, digital multispectral aerial imagery, Landsat satellite imagery, and physical mapping with a hand-held GPS. The data are on a GIS database. Landsat 5 TM imagery could identify the presence of kelp beds, but only infrared aerial imagery and multispectral imaging at low spring tides accurately quantified surface areas of kelp beds. Biomass of the main kelp (E. maxima) is variable in space (between 3kg f wt m−2 and 24kg f wt m−2) and time (changes of up to 50%), making estimates for management difficult. Using an average biomass value of 12kg m−2, the total biomass of surface-reaching kelp beds on the West Coast is estimated to exceed 593 000t f wt, but extensive subsurface beds remain unquantified. Results are discussed in relation to sustainable limits to harvesting, gaps in knowledge, and the improved management of kelp resources.

EFFECT OF WATER VELOCITY AND BENTHIC DIATOM MORPHOLOGY ON THE WATER CHEMISTRY EXPERIENCED BY POSTLARVAL ABALONE

The water bathing postlarval abalone often lies within the diffusive boundary layer (DBL) so its chemistry is greatly influenced by the metabolism of the biofilm on which the abalone feed. This study used microelectrodes to investigate the influence of water velocity and diatom morphology on dissolved oxygen and pH in the DBL. Decreasing water velocity increased the thickness of the DBL, thereby increasing the amplitude of changes in oxygen concentration. Over a film of the prostrate diatom Nitzschia ovalis Arnot, DBL thickness averaged 71, 139, 177, and 406 μm at water velocities of 78, 15, 7, and 1 mm s−1 respectively. Corresponding oxygen concentrations at the biofilm surface under moderate light (75 μE m−2 s−1) and temperature (15°C) averaged 111%, 120%, 125%, and 151% of air saturation respectively, at the four velocities. The presence of a 1-mm tall diatom canopy (Achnanthes longipes Agardh) over a Nitzschia ovalis film thickened the DBL by 3-fold at 1 mm s−1 and 6-fold at ∼80 mm s−1. The thickened DBL and higher diatom biomass generated extreme conditions at the biofilm surface. Dissolved oxygen concentrations as high as 440% of air saturation, and pH as high as 9.8 were recorded beneath the canopy in moderate light (105 μE m−2 s−1) and temperature (15°C) at a water velocity of 1 mm s−1. Changes during darkness were less extreme, with 53% oxygen saturation and pH 7.7 the minima recorded. These measurements demonstrate the extreme water chemistry that can develop in the microhabitat of postlarval abalone. The changes will be amplified by the presence of filamentous diatoms, by increased light intensity, and by lack of water movement. Standard aeration will greatly reduce the extremes experienced by postlarvae by generating water movement sufficient to thin the DBL.

Farming of the Giant Kelp Macrocystis Pyrifera in Southern Chile for Development of Novel Food Products

This study explores the potential cultivation of the giant kelp Macrocystis pyrifera (L.) C.A. Agardh in southern Chile, for the development of novel food products. The study demonstrates the importance of considering the collection site of the parent sporophytes for successful cultivation. This study also shows that the ropes must be seeded with 10,000 to 40,000 spores ml−1, depending on the culture method used. We also demonstrated that under environmental conditions in southern Chile, the seeded ropes must be put at sea at the latest during autumn (April) in order to reach the harvesting season in December. However, several other management aspects must be considered to improve the quality of the product. Our final estimation indicates that over 14.4 kg m−1of rope (fresh weight) can be produced and from this total production, over 70% can reach the quality to produce different food products that are already being introduced in oriental countries. The remaining 30% can be used for abalone feeding and is also available for the organic fertilizer industry located in Chile.

Abalone farming in South Africa: An overview with perspectives on kelp resources, abalone feed, potential for on-farm seaweed production and socio-economic importance

The South African abalone cultivation industry has developed rapidly and is now the largest producer outside Asia. With a rapid decline in wild abalone fisheries, farming now dominates the abalone export market in South Africa. Kelp (Ecklonia maxima) constitutes the major feed for farmed abalone in South Africa, but this resource is now approaching limits of sustainable harvesting in kelp Concession Areas where abalone farms are concentrated. This paper gives an overview of the development of the South African abalone industry and analyses how abalone farming, natural kelp beds and seaweed harvesting are interlinked. It discusses options and constraints for expanding the abalone industry, focussing especially on abalone feed development to meet this growing demand.Kelp will continue to play an important role as feed and kelp areas previously not utilised may become cost-effective to harvest. There are many benefits from on-farm seaweed production and it will probably be a part of future expansion of the abalone industry. Abalone waste discharges are not at present regarded as a major concern and farming brings important employment opportunities to lower income groups in remote coastal communities and has positive spillover effects on the seaweed industry and abalone processing industry.

Cultivation of Laminaria japonica (Laminariales, Phaeophyta) in Udo Coast, Jeju, Korea

【In order to produce Laminaria japonica in Jeju as feed for abalone, a transplant experiment was performed with the Baekryungdo and the Wando cultivar stocks at the Udo aquafarm from January to July 2003. Eight water conditions at the aquafarm and eleven traits of the two cultivar stocks were measured once a month. The water temperature ranged from 12.9 $^{\circ}C$ to 23.5 $^{\circ}C$ . The salinity was 31.3-36.8‰ the DO was 5.40-9.86 mg ${\cdot}$ $l^{-1}$ the pH was 7.82-9.61. Concentrations of $NO_2-N,\;NO_3-N,\;NH_4-N\;and\;PO_4-P$ were 0.02-0.15 $\mu$ M, 2.27-3.49 $\mu$ M, 0.16-0.56 $\mu$ M and 0.07-0.99 $\mu$ M, respectively. The whole frond length of the Baekryungdo and the Wando specimens were 173.84 and 153.67 cm. The blade width, stipe length, blade length, fascia length, blade thickness, total weight and substantiality of the Baekryungdo and the Wando specimens were 14.61 and 13.05 cm, 3.94 and 3.02 cm, 169.88 and 150.65 cm, 155.81 and 137.10 cm, 1.01 and 0.96 cm, 258.04 and 200.96 cm, and 101.56 and 94.62, respectively at the conclusion of the experiment in July. The measurements of the Baekryungdo specimens were slightly higher than those of Wando specimens. The fascia width, stipe thickness and fascia thickness of the Wando specimens were slightly higher than those of the Baekryungdo specimens. The relative growth rates of these traits of two cultivar stocks during the growth test were very similar. Generally, the performance of the Baekryungdo cultivar stock seems to be better than that of the Wando samples. Further study of the physiological ecology for cultivation and breeding is needed in the future.】

Suitability of three red macroalgae as a feed for the abalone Haliotis tuberculata coccinea Reeve

A 60-day feeding trial was conducted to assess the suitability of three red algae, Hynea spinella, Hynea musciformis and Gracilaria cornea, as potential feed for the culture of juvenile abalone, Haliotis tuberculata coccinea R. Seaweeds were reared in a biofiltration unit with fishpond waste water effluents. The three algal species were found to contain high protein contents which would be related to its production under the high nitrogen culture conditions of the biofilter system. Protein and carbohydrate contents were highest in H. musciformis and lowest in G. cornea. Survival rates of juvenile abalone were very good, regardless of the algae fed. Feed intake of H. spinella was highest, followed by H. musciformis. Growth rates of abalone were within the range obtained under commercial conditions, final shell length and weight being significantly highest in animals fed H. spinella and lowest in those fed G. cornea. Feeding G. cornea lead to the lowest growth performance due to the lowest feed intake, whereas feed conversion ratios were significantly highest for H. musciformis and protein efficiency ratios were higher for both H. spinella and G. cornea. This study suggested the good potential of any of the three red seaweeds tested—successfully produced by the biofilter system, their nutritional composition being similar to other macroalgae used as feed for abalone and matching the abalone protein and lipid requirements—hence promoting growth and survival. Nevertheless, the biofilter produced macroalgae H. spinella showed the highest dietary value for juvenile of H. tuberculata coccinea.

The influence of culture conditions on the growth and biochemical composition of an algal feed for juvenile greenlip abalone (Haliotis laevigata)

The diatom Navicula jeffreyi was cultured in seawater media of low, standard or high nitrate content (2.47, 12.35 and 24.71 mg NO3-N L-1, respectively) in high (22 ± 3 mol photons/m2/s) and low (4.7 ± 0.8 mol photons/m2/s) light conditions. The growth, survival and grazing rates of juvenile Haliotis laevigata Donovan, 1808 were monitored in response to the density and biochemical composition of N. jeffreyi cultured in each of the six treatments. Navicula jeffreyi Hallegraeff et Burford grown in high light had a proportionally lower protein content and a higher carbohydrate and fat content (22 ± 0.6%; 17.6 ± 1.5%; 7.5 ± 0.7%, respectively) compared to the content of diatoms grown in low light (30 ± 0.6%; 14.3 ± 2.5%; 4.7 ± 1%, respectively). Under low light, the carbohydrate content of N. jeffreyi was marginally higher in low nitrate treatments (17%) compared to standard (14%) and high (12%) nitrate. Juveniles grazed a larger number of diatoms when the protein content of the diatoms was low, possibly compensating for the lower protein levels. In high light, dense N. jeffreyi biofilms produced elevated pH levels which most likely resulted in the mortality of a large number of juvenile H. laevigata. This study indicates that changes in light intensity and nitrate concentration under which the diatom N. jeffreyi were cultured, affected the growth, survival and grazing rates of juvenile H. laevigata.

Morphological and taxonomic studies of Gracilaria and Gracilariopsis species (Gracilariales, Rhodophyta) from South Africa

Southern Africa has an extremely rich and diverse seaweed flora with a wide variety of marine habitats. Increased commercial interest in these seaweed resources has been the stimulus for biodiversity studies. The Gracilariaceae (Rhodophyta) has emerged as one of the families that possess economic potential as a source of agar and as a potential feed for abalone. A lack of knowledge concerning the taxonomic status of many members of this family is a concern. Gross morphological characters have been the main means of identification and incorrect applications have led to a number of misidentifications. Consequently, a comprehensive reappraisal and revision of these species was carried out. The species count for the South African Gracilariaceae is now two Gracilariopsis species, and nine Gracilaria species. Gracilaria crassa has been reduced to a synonym of G. canaliculata. It is believed that G. foliifera was erroneously identified and specimens in South Africa referred to as G. millardetii and G. protea are assigned to G. corticata. South African Gracilariopsis, previously referred to as Gs. lemaneiformis, is confirmed to be conspecific with European Gs. longissima. This species occurs along the west and south coasts of South Africa, co-existing in a few habitats with G. gracilis. The taxonomic identity of G. vieillardii specimens from South Africa and the differentiation of G. canaliculata and G. salicornia has been confirmed based on morphology. Three species of Gracilaria (G. aculeata, G. beckeri and G. capensis) are endemic or near endemic to the South African coast, and a fourth species, G. denticulata is localised in southeast Africa.

The influence of light intensity on the density of different diatoms as feed for juvenile greenlip abalone ( Haliotis laevigata)

The diatoms Cocconeis sp. and Navicula jeffreyi, were cultured in aquaria under high and low light levels. Diatom density and juvenile Haliotis laevigata growth, survival and behaviour were monitored. In contrast to N. jeffreyi, growth of Cocconeis sp. was not inhibited in low light (<200 lx), however, the density of both species increased in high light (800 lx). Juvenile H. laevigata growth rates were strongly correlated to the density of N. jeffreyi but not to the density of Cocconeis sp. Juvenile growth rates did not differ between diatom species or shading condition. A reduction in the photophobic behaviour of juvenile H. laevigata was observed in shaded aquaria, suggesting that abalone are not strictly nocturnal feeders. Results demonstrate the importance and effect of light intensity on the growth of diatom species and the growth, survival and behaviour of juvenile H. laevigata. Results also show that light intensity for diatom culture and husbandry of juveniles in a hatchery needs to be considered carefully.

Potential new applications for the southern African kelps

The extensive kelp beds comprising four species, off the west coast of South Africa, provide a large source of raw material that can be used for various applications. Current uses are: (1) the export of the unprocessed kelp for alginate extraction, which generates low prices that fluctuate depending on the world market, (2) processing of Ecklonia maxima for use as agricultural stimulant, and (3) as abalone feed. However, these operations use only a fraction of the total annual yield. The future of the South African seaweed industry lies in developing value-added products. Two such possibilities include their use as biosorbents in heavy-metal wastewater remediation and their potential medicinal value.