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Establishing suitable salt tolerant all-male tilapia strains with fast growth rate is a crucial requirement for successful euryhaline farming required for controlling prolific breeding and as an adaptation to the effect of climate-induced drought. This study assessed the percentage of tilapia male hybrids, their growth performance and survival rate produced by crossing female Nile tilapia (Oreochromis niloticus) and male Rufiji tilapia (Oreochromis urolepis urolepis) at different salinities. The fingerlings were reared for 70 days in triplicate concrete tanks (1 m3), each stocked with 15 fish weighing 1.62 ± 0.03 g, 1.69 ± 0.02 g and 1.41 ± 0.06 g exposed to 2, 15 and 35 ppt salinities, respectively. Acclimatization was done by adding seawater to freshwater at a rate of 2 ppt per day for 18 days. Fish sexing was done by visual assessment of the genital papilla followed by rearing the hybrids for six months to observe reproduction. Results showed that, the cross between O. niloticus (female) and O. urolepis urolepis (male) produced hybrids that were all-males without any reproduction within six months post hybridization. The hybrids reared at a salinity of 2 ppt had higher growth performance than those reared at 15 and 35 ppt. Similarly, hybrids cultured at 15 ppt had significantly higher growth performance than those reared at 35 ppt. All the hybrids produced had survival rates of 100%. This study indicated that, all-male tilapia produced by crossing between O. niloticus (female) and O. urolepis (male) can be used by fish farmers as alternative species for mariculture development to control prolific breeding and as an adaptation strategy to climate change.

The study examined different types of organic manure on the culture of marine plankton as a potential source of food for rabbitfish, Siganus stellatus, larvae. Cow dung showed significantly higher species abundance and diversity of cultured marine plankton followed by chicken and finally mixed media manure (p

An investigative field survey was performed to gather baseline data on locally available feed ingredients and fish farming practices in different regions of Tanzania. More than 80% of respondents relied on locally available feed ingredients as a major feed supplement for their cultured fish, with maize bran being the most commonly used feed ingredient in all regions. Crude protein content in most analyzed local feed ingredients was medium-high, while crude fat content was high in some animal and agricultural by-products, and medium-low in other ingredients. Most respondents were males and the majority of fish farms were owned by individuals. Earthen pond was the most common fish farming system in all regions except Dar es Salaam. Semi-intensively mixed-sex tilapia monoculture was the dominating fish farming practice. The results of the survey presented provide a good platform for future development of culture systems and feeding strategies for tilapia in Tanzania.

Snubnose pompano (Trachinotus blochii) are widely cultured in the world. Light colours are among factors affecting fish performance in captivity. Snubnose pompano larvae often reared under white light. However, no study supports its choice or informs the extent of its effect or its constituent colour. The study investigated the influence of green, blue, yellow, purple, and white lights on growth, survival, cortisol, body composition, and digestive enzymes activities of one-day post-hatch Snubnose pompano larvae reared in light magenta tanks under a photoperiod of 24 Light:0 Dark hours for 25 days. Overall, the best growth performance of snubnose pompano larvae was in purple and white, and green lights during early and late larval stages, respectively. White light promoted survival rate while that of green light reduced. Larvae were less stressed and had enhanced body contents under white and purple light environments. Purple and yellow lights influenced low trypsin and pepsin activities. The study reports for the first time the effect of the light colour environment on the digestive enzyme activities and body composition of the finfish larvae. Generally, the study provides novel insights on optimal light colour in the larval rearing protocol of this species. Through this study, the use of white light during the first feeding (zero to four days post-hatch) and purple light in later stages (five days post-hatch until metamorphosis) is encouraged while discourages green and yellow lights in the larval rearing of Snubnose pompano.

An investigation of the role of Lactobacillus plantarum and Saccharomyces cerevisiae on growth performance of hybrids from Oreochromis niloticus and Oreochromis urolepis urolepis was carried out in plastic tanks at 10 fish/m3 density and a salinity of 25 units. The probiotic treatments were 2, 4 and 6 g/kg feed while the control feed did not include any probiotics. Growth parameters were measured fortnightly and water quality parameters monitored every day. Survival rate and water quality factors revealed non-significant variations (p > 0.05). Final weight differed significantly among the treatments (p < 0.05). Furthermore, Food Conversion Ratio (FCR), Specific Growth Rates (SGR), and weight gain did not differ significantly (p > 0.05) between the control and 2 g/kg treatments. However, the 4 and 6 g/ kg feed treatments showed significant differences (p < 0.05) from the control diet and 2 g/kg for both L. plantarum and S. cerevisiae. The condition factor did not show any significant difference (p > 0.05) among the treatments. Results of this study indicate that increasing the quantity of commercial probiotics in feeds improved growth rates. Condition factor observed in the treatments could be due to the role of the tested probiotics in improving the water quality of tanks. Therefore, probiotics could potentially be used to enhance coastal aquaculture development.

Tilapia hatcheries in Tanzania rely heavily on importing germplasm. Nevertheless, the genetic structure of the imported stocks is poorly understood. In the current study, the level of genetic diversity and differentiation of eight populations of Nile tilapia (Oreochromis niloticus) strains imported in Tanzania was investigated. Four of the studied strains originated from Thailand, three from Uganda, and one from the Netherlands. Double-digest restriction site–associated DNA sequencing (ddRAD-seq) was applied to identify and genotype single nucleotide polymorphisms (SNPs). In total, 2214 SNPs passed all the quality control steps and were utilized for downstream analysis. Mean heterozygosity estimates were higher for the Thailand strains (Ho, 0.23) compared with the strains from Uganda (Ho, 0.12). Low genetic distance was observed amongst populations from the same geographic origin (Fst, 0.01–0.04). However, genetic distance between populations from different geographic origins was substantial (Fst, 0.24–0.44). Bayesian model–based clustering (STRUCTURE) and discriminant analysis of principal components (DAPC) grouped the studied animals into three distinct clusters. A cross-validation approach (where 25% of animals from each population were considered of unknown origin) was conducted in order to test the efficiency of the SNP dataset for identifying the population of origin. The cross-validation procedure was repeated 10 times resulting in approximately 97% of the tested animals being allocated to the correct geographic population of origin. The breeding history and hatchery practices used to manage these stocks prior and after import appear to be the main factors for the genetic diversity observed in this study. Our study will help inform hatchery stock management and future breeding program designs in Tanzania.

Five introduced strains of Nile tilapia (Oreochromis niloticus) were tested for growth performance both in fresh- and brackish-water (2 salinity units) environments for 56 days. The BIG NIN, GIFT, Chitralada, “Ruvu Farm” and Silver YY strains with initial mean average weight (± standard error) of 96.4 ± 6.90 g, 104.1 ± 7.19 g, 137.2 ± 7.21 g, 53.2 ± 6.98 g and 95.3 ± 7.11 g, respectively were used. Individuals were tagged and pooled in hapas (12 m × 8.5 m × 2 m each), aligned into different ponds (20 m × 20 m each). Stocking density of 5 fish/m2 and 350 g/kg crude protein diet were used. Overall, the average weight gain for GIFT strain was 7.5%, 32%, 45% and 86.5% higher than BIG NIN, Chitralada, “Ruvu Farm” and Silver YY strains, respectively, across both environments. All strains performed significantly better (p

IntroductionThe decline in fishery resources from the wild has led to an ever increasing focus on aquaculture in recent years. With increasing aquaculture of animal species, there is an increasing need for suitable microalgae in the production of these animals. However, cultivation of microalgae in expensive pure chemical media is one of the major challenges facing large-scale cultivation of microalgae.PurposeThe present study investigated the suitability of aquaculture wastewater (AWW) supplemented with NPK (nitrogen:phosphorus:potassium) fertilizer as a cheap source of nutrient to cultivate a microalgaChlorella vulgaris(C. vulgaris).MethodsC. vulgariswith an initial cell density of 0.8 × 106cells/mL was batch cultured in AWW supplemented with NPK at 0.1, 0.5, 1.0 g/L and BBM for 20 days under laboratory conditions using 2000 mL Erlenmeyer flasks. The proximate composition, chlorophyll, minerals, and vitamins analysis ofC. vulgarisbiomass were done using standard analytical methods.ResultsThe highest values in optical density (4.872 ± 0.025), dry cell weight (2.858 ± 0.015 g/L), specific growth rate (0.2097 ± 0.0038 day–1), and biomass productivity (0.1701 ± 0.0007 g/L/day) were obtained inC. vulgarisgrown in AWW + 1.0 NPK medium. The total chlorophyll, protein, lipid, and carbohydrate content of the microalgae biomass were in the range of 0.05–0.862%, 44.062–57.089%, 17.064–23.260%, and 15.217–21.896%, respectively. Furthermore, microalgae grown in AWW + 1.0 NPK showed good vitamin and mineral content compared to BBM grown alga.ConclusionThese findings indicated that the AWW + 0.1 NPK, AWW + 0.5 NPK, and AWW + 1.0 NPK are potential growth media forC. vulgariscultivation and can replace the BBM medium, which is very expensive and less accessible to users.

Rufiji tilapia (Oreochromis urolepis urolepis) is an endemic cichlid in Tanzania. In addition to its importance for biodiversity conservation, Rufiji tilapia is also attractive for farming due to its high growth rate, salinity tolerance, and the production of all‐male hybrids when crossed with Nile tilapia (Oreochromis niloticus). The aim of the current study was to assess the genetic diversity and population structure of both wild and farmed Rufiji tilapia populations in order to inform conservation and aquaculture practices. Double‐digest restriction‐site‐associated DNA (ddRAD) libraries were constructed from 195 animals originating from eight wild (Nyamisati, Utete, Mansi, Mindu, Wami, Ruaha, Kibasira, and Kilola) and two farmed (Bwawani and Chemchem) populations. The identified single nucleotide polymorphisms (SNPs; n = 2,182) were used to investigate the genetic variation within and among the studied populations. Genetic distance estimates (F st) were low among populations from neighboring locations, with the exception of Utete and Chemchem populations (F st = 0.34). Isolation‐by‐distance (IBD) analysis among the wild populations did not detect any significant correlation signal (r = .05; p‐value = .4) between the genetic distance and the sampling (Euclidean distance) locations. Population structure and putative ancestry were further investigated using both Bayesian (Structure) and multivariate approaches (discriminant analysis of principal components). Both analysis indicated the existence of three distinct genetic clusters. Two cross‐validation scenarios were conducted in order to test the efficiency of the SNP dataset for discriminating between farmed and wild animals or predicting the population of origin. Approximately 95% of the test dataset was correctly classified in the first scenario, while in the case of predicting for the population of origin 68% of the test dataset was correctly classified. Overall, our results provide novel insights regarding the population structure of Rufiji tilapia and a new database of informative SNP markers for both conservation management and aquaculture activities., The objective of the current study was to assess the genetic variation among 10 Rufiji tilapia populations of both wild and farmed origin using ddRAD‐seq. We investigate for the existence of putative genetic clusters, test for the existence of isolation by distance, and assess the efficiency of predicting population of origin‐based only on the genomic profile using cross‐validation schemes.

Understanding population structure and genetic diversity within and between local Nile tilapia lines cultured in Tanzania is important for sustainable aquaculture production. This study investigated the genetic structure and diversity among seven Nile tilapia populations in Tanzania (Karanga, Igunga, Ruhila, Fisheries Education and Training Agency, Tanzania Fisheries Research Institute, Kunduchi, and Lake Victoria). Double-digest restriction site-associated DNA (ddRAD) libraries were prepared from 140 individual fish (20 per population) and sequenced using an Illumina HiSeq 4000 resulting in the identification of 2,180 informative single nucleotide polymorphisms (SNPs). Pairwise Fst values revealed strong genetic differentiation between the closely related populations; FETA, Lake Victoria, and Igunga and those from TAFIRI and Karanga with values ranging between 0.45 and 0.55. Population structure was further evaluated using Bayesian model-based clustering (STRUCTURE) and discriminant analysis of principal components (DAPC). Admixture was detected among Karanga, Kunduchi, and Ruhila populations. A cross-validation approach(25% of individual fish from each population was considered of unknown origin) was conducted in order to test the efficiency of the SNP markers to correctly assign individual fish to the population of origin. The cross-validation procedure was repeated 10 times resulting in 77% of the tested individual fish being allocated to the correct population. Overall our results provide a new database of informative SNP markers for both conservation management and aquaculture activities of Nile tilapia strains in Tanzania.

The effects on growth performance, feed utilization, survival and whole fish body proximate composition of replacing fishmeal (Rastrineobola argentea) with a locally available spirulina species (Arthrospira fusiformis) as a protein ingredient in the feed of Rufiji tilapia (Oreochromis urolepis urolepis) fry was examined. Fishmeal replacement with A. fusiformis was carried out at 5%, 15%, 25%, 35% and 100% (S5, S15, S25, S35 and S100), and the effect of the replacement was compared with the control diet (S0, 0% spirulina). Fish fry were stocked at an average initial weight of 0.57 g at 10 fish per 0.1 m3 and cultured for 60 days using full strength salt water (30-35 ppt). A. fusiformis was isolated from Momela Lake in Arusha National Park, Tanzania and propagated using selected culture media. It was observed that fish fry fed spirulina at a 5% fishmeal substitution level diet had better (p0.05). Spirulina supplementation had no effect on fish survival rates and meat quality. It appears that the Momella Lake spirulina may be an appropriate growth-stimulating plant protein when used as a feed additive in Rufiji tilapia mariculture.

Tropical marine seagrasses live in environments with low nutrient concentrations. However, as land development intensifies along tropical coastlines, the marine environment in which these organisms grow is becoming more nutrient-rich. Nitrogen (N) uptake, assimilation, translocation and storage under a diversity of N sources in enriched conditions were investigated in two tropical seagrass species, Cymodocea serrulata and Thalassia hemprichii, from an oligotrophic marine environment. Both seagrasses were able to take up different inorganic and organic N sources through their above- and belowground tissues when enriched with high N concentrations. The uptake rates of T. hemprichii were generally higher than C. serrulata in leaves and rhizome, whereas root uptake was systematically higher in C. serrulata. Acropetal and basipetal translocation was observed in both species. Reduction and assimilation of N, measured in terms of their nitrate reductase and glutamine synthetase activity, were correlated with nitrate and ammonium uptake rates, respectively. Cymodocea serrulata showed a tendency to immediately use the available N, whereas T. hemprichii allocated more N in assimilation and storage investment. The responses of these seagrasses to N-enrichment demonstrate their ability to adapt to over-enrichment by varying N sources in the first step of the eutrophication process.

Pollution, turbidity and coral bleaching history, as well as coral diversity, vary along the Tanzanian coastline. Prior to this study, it was not known whether exposure to such environmental variation might have influenced the diversity and distribution of Symbiodinium along this coastline. Such information can provide insight into whether Tanzanian reef-building corals develop adaptation to current trends of climate change. Here, 10 reef-building coral samples were collected from different reefs along the Tanzanian coast with different micro-environments and bleaching histories. The ITS-2 region of ribosomal DNA was employed in the characterisation of Symbiodinium harboured by reef-building corals. DGGE fingerprints and DNA sequences showed that most coral species host a single Symbiodinium type, which is maintained throughout the coast regardless of local environmental differences. We present polymorphic symbioses in Acropora spp., Millepora sp. and Galaxea fascicularis in mainly turbid and warm environ...

Coastal vegetative habitats are known to be highly productive environments with a high ability to capture and store carbon. During disturbance this important function could be compromised as plant photosynthetic capacity, biomass, and/or growth are reduced. To evaluate effects of disturbance on CO2 capture in plants we performed a five-month manipulative experiment in a tropical seagrass (Thalassia hemprichii) meadow exposed to two intensity levels of shading and simulated grazing. We assessed CO2 capture potential (as net CO2 fixation) using areal productivity calculated from continuous measurements of diel photosynthetic rates, and estimates of plant morphology, biomass and productivity/respiration (P/R) ratios (from the literature). To better understand the plant capacity to coping with level of disturbance we also measured plant growth and resource allocation. We observed substantial reductions in seagrass areal productivity, biomass, and leaf area that together resulted in a negative daily carbon balance in the two shading treatments as well as in the high-intensity simulated grazing treatment. Additionally, based on the concentrations of soluble carbohydrates and starch in the rhizomes, we found that the main reserve sources for plant growth were reduced in all treatments except for the low-intensity simulated grazing treatment. If permanent, these combined adverse effects will reduce the plants’ resilience and capacity to recover after disturbance. This might in turn have long-lasting and devastating effects on important ecosystem functions, including the carbon sequestration capacity of the seagrass system.

Spirulina species are world widely known for their ability to produce high quantities of useful metabolites such as protein, fatty acids and vitamins. One of the major challenges in production of this microalgae is the cost and composition of culture medium. In the present study, effect of two culture media with agricultural fertilizers as nitrogen sources viz . urea containing medium (UM) and N: P: K containing medium (NPKM) on production of a locally found spirulina ( Arthrospira fusiformis ) was investigated. Zarrouk medium (ZM) was used as a standard, other culture conditions included 67.5 μmol m -2 s -1 radiation, 10 pH and 30 oC temperature. A. fusiformis was isolated from Momela Lake in Arusha National Park Tanzania. There was no difference ( p > 0.05) in mean biomass production (BM mean ) and doubling time (DT) between ZM (1.205 g/L, 1.437 days respectively) and UM (1.168 g/L, 1.63 days respectively). Significantly higher ( p < 0.05) maximum biomass BM max production and exponential growth rate (μ) in a sequential order was from ZM (1.844 g/L, 0.483/day respectively), UM (1.6 g/L, 0.425/day respectively) and NPKM (0.57 g/L, 0.273/day). It appeared that the wild-isolated A. fusiformis was able to grow well in less costly UM showing high potential for mass production. © 2019 International Formulae Group. All rights reserved. Keywords: Momela Lake’s spirulina, biomass production, agricultural fertilizers, nitrogen sources

Some ecophysiological adaptation strategies of the tropical seagrass Halophila ovalis were investigated with respect to this plant's ability to grow in the upper intertidal in either monospecific pools (but not together with other intertidal species) or emergent and exposed to high temperatures and irradiances during several hours every day. It was found that Halophila ovalis could raise the pH in simulated pools to 8.6, while the two other major (biomass wise) intertidal seagrasses raised the pH to 8.8 ( Cymodocea rotundata ) and 9.2 ( Thalassia hemprichii ). In situ, midday pH values of 8.5, 8.7 and 9.0 were recorded in pools inhabiting the three species, respectively. It was further found that photosynthetic electron transport rates (ETR) measured continuously in situ for one leaf during a diurnal cycle followed the irradiance up to a daily maximal value of 2200 μmol photons m −2 s −1 , but dropped by ca. 50% when the leaf became air exposed just before noon. This drop in ETR upon emergence was verified by “point measurements”, while ETRs of leaves that grew in small pools formed as the tide receded followed the irradiance more closely. Similarly, F v / F m measured after 15 min of dark adaptation decreased by ca. 50% in emergent leaves during midday, but maintained higher daily values in the submerged leaves. Based on the above results, we suggest that Halophila ovalis can not grow in intertidal pools together with the other major intertidal species because the latter raise the pH above its pH compensation point, thus restricting its utilisation of inorganic carbon. For emergent leaves, while F v / F m values drop during the day, ETRs are still high enough so as to contribute significantly to the daily photosynthetic production of Halophila ovalis . The drop in F v / F m indicates photoinhibition during midday, especially in emergent leaves, but this is a dynamic process that apparently repairs itself during the late afternoon.

Spatial and temporal dynamics of submerged aquatic vegetation (SAV) cover were studied in the relatively pristine and seagrass-dominated area of Chwaka Bay, Zanzibar (Tanzania) by using satellite remote sensing. Through complementary field work the potential of the technique for change detection was verified. The general changes in SAV cover were examined using Landsat images from 1986, 1987, 1998, 2001 and 2003. Two of these images, from 1987 (Landsat TM) and 2003 (Landsat ETM+), were specifically analysed to create a map of the change in SAV cover. Overall, the general distribution of SAV stayed fairly stable over the period investigated, but the result also showed regions where significant alterations, both losses and gains, had occurred between the two years. Based on our findings and anecdotal information from local fishermen and seaweed farmers potential causative factors are discussed. It was concluded that a repeated mapping with satellite remote sensing is a suitable tool to monitor changes of seagrass and seaweed distribution in shallow tropical environments.

Seagrass species diversity and abundance were studied in East African back-reef lagoons with contrasting groundwater-outflow rates. The selection of the lagoons was based on a groundwater flow model. A total of 10 seagrass species was observed at all sites together. Sites with a higher groundwater outflow displayed a lower species diversity than sites with a lower groundwater outflow. Thalassodendron ciliatum dominated at sites with high groundwater outflow rates, while Thalassia hemprichii showed higher coverage at sites with low groundwater outflow. Porewater salinities were up to 5 psu lower at locations with predicted high groundwater-outflow rates indicating supply of freshwater. The reduction in porewater salinity at groundwater outflow sites is relatively low, which makes it unlikely that a difference in optimum salinity for growth is the main factor causing reduced diversity at these sites. Nitrogen-stable isotope signatures of seagrass leaves showed a significant increase with increased groundwater outflow rates. This suggests that the nitrogen source for these plants was, at least in part, groundwater. Differences in competition for nitrogen may explain the observed pattern in species diversity and abundance. To establish a substantive link between the observed reduced seagrass diversity or enhanced δ15N values of T. ciliatum leaves on the one hand and increased groundwater outflow rates on the other, further exploration through detailed measurements of groundwater outflow rates and groundwater nitrogen isotopic composition are needed., This research is part of the GROFLO project which was supported by grant no. IC18-CT96-0065 of the Commission of the European Communities within the framework of the INCO Programme. This is NIOO-CEMO publication no. 2854

Several characteristics of Thalassodendron ciliatum populations were evaluated along the coasts of Kenya and Zanzibar Island, with the aim to study spatial variability in this species. A reconstruction technique, using scars left by abscised leaves and flowers, was employed to determine leaf production, shoot demography, and flowering frequency. Eight subtidal sites in different back-reef lagoons were sampled along with a subtidal site that was not protected by a reef, a site with intertidal rack pools, and a subtidal site in a mangrove bay. Leaf- production rates were lowest for the population of the unprotected subtidal site and for the population from the intertidal rock pools (30 leaves per shoot per year). At these sites, leaf life-span was almost twice as long (94 days). Low leaf-formation rates seem to be compensated by long leaf life- spans to maintain similar numbers of standing leaves per shoot. Highest leaf-production rates were found at the mangrove-bay site (53 leaves per shoot per year). The mangrove-bay population showed internodal lengths of almost 7 mm and stem lengths of almost 90 cm. The stems were two- to four-fold longer than those at the other sites. A short leaf life-span of 51 days at the mangrove site indicates that the investment in stem growth occurs at the expense of leaf maintenance. Median ages of the populations varied almost four-fold from 0.5 to 1.8 years. All meadows showed shoot-recruitment rates that were either the same as or larger than shoot mortality rates, suggesting that the environmental quality in this region is still suitable for sustaining vigorous seagrass vegetation. Flowering frequencies were generally low and seedlings were not found. [KEYWORDS: seagrass; leaf production; demography; flowering; east Africa; Thalassodendron ciliatum Cymodocea-nodosa; reconstructive technique; seagrasses colonization; population-dynamics; den hartog; growth; pollination; amphibolis; biomass; lagoon]

Eucheuma denticulatum has been shown to release bromoform, diiodomethane, dibromochloromethane, perchloroethylene, chloroiodomethane, chloroform, sec-butyl iodide, methyl iodide, methylchloroform, carbon tetrachloride, trichloroethylene and butyl iodide into its growth media, with bromoform (310 ± 25 μg kg DW−1 h−1) and diiodomethane (182 ± 9 μg kg DW−1 h−1) being the dominant volatile halocarbons (VHCs). The production of VHCs was always higher at a photon flux density of 1500 than at 400 μmol photon m−2 s−1. The influence of pH was minimal at 400 μmol photon m−2 s−1. The addition of azide decreased mean VHC production at pH 8·2 ± 0·2 and 8·8. Algae kept in media where extracellular hydrogen peroxide was decomposed by addition of manganese dioxide showed a decrease in VHC production at pH 8·2 ± 0·2 and an increase at pH 8·8. We suggest that high light intensity and carbon dioxide deficiency caused by high pH in E. denticulatum promote VHC production through induction of hydrogen peroxide synthesis.

Growth of Eucheuma denticulatum was studied in the field and in laboratory experiments. Field co-cultivation of E, denticulatum with the green alga Ulva reticulata or the seagrass Thalassia sp, reduced daily growth rate (DGR)bf a Tanzanian and a Philippin

Accumulation and the effects of copper and zinc on the macroalga Padina gymnospora were assessed in the laboratory after artificial exposure to copper and zinc (separately or in combination). Exposure concentrations of copper used were 0, 25, 50, 100, 500 and 1,000 μg l-1. Concentrations of zinc exposure were 0, 50, 100, 250, 1,000 and 5,000 μg l-1. The simultaneous (or combined) addition of copper and zinc (Cu+Zn) involved 25+50, 50+100, 100+250, and 500+1,000 μg l-1. Accumulation patterns were determined by measuring tissue contents of copper and zinc, while the tolerance was assessed by measuring growth rate and photosynthetic performance, as maximum quantum yield (Fv/Fm). Furthermore, the influence of major nutrients (phosphates and nitrates) on algal-metal-accumulation was estimated after additions of nitrate (1, 10 and 20 mg l-1) and phosphate (0.1, 1 and 2 mg l-1). The data obtained showed that the accumulation increased linearly with the increase in metal concentration in the growth media. However, the presence of additional nitrate and phosphate reduced both the metal accumulation and their toxic effects. Both algal growth rate and maximum quantum yields were negatively affected in proportion to the increase in metal concentrations and exposure time. At exposures to 50, 100 and 500 μg l-1 copper, inhibition in growth was greater than 50%, while an exposure to 1,000 μg l-1of zinc was needed to cause the same effect on growth and Fv/Fm. Growth rate was a more sensitive indicator of stress than maximum quantum yield in response to exposure to copper and zinc.

Keywords: ammonia assimilation, glutamate dehydrogenase, GDH, Gracilaria sordida , red alga, enzyme activity Glutamate dehydrogenases (GDH, EC 1.4.1.2-4) catalyse the entry of ammonium into the organic cycle via amination of a-ketoglutarate and its release via deamination of Lglutamate. NAD-GDH facilitates NAD-/NADP-dependent deamination while NADPH-GDH facilitates NADH-/NADPH-dependent amination reactions. In the study reported here, GDHs were extracted from the red alga Gracilaria sordida and purified 10- to 180-fold before examining their amination and deamination reaction properties. NAD-/NADP- and NADH-/ NADPH-dependent activities were the order of 11:1 and 1:1.8, respectively. The pH optima for amination and deamination were 8.2 and 8.4 under NADH- and NADPH- and 8.4 and 9 under NAD- and NADP- dependent activities, respectively. Whereas both NAD- and NADP-dependent deamination activities were activated by calcium ions (Ca 2+ ), only NADPH-dependent amination was activated. The K m values (in mM) were 3.0–3.6 for ammonia, 2.0–3.3 for a-ketoglutarate, 0.00286 for NADH, 0.0033 for NADPH),1.7–2.1 for L-glutamate, 0.344 for NAD and 0.476 for NADP. It appears that the GDHs in G. sordida are dominated by NAD-dependent deamination enzyme and that in NADH-NADPH- dependent amination reactions, NADPH is more preferred. It is suggested that NAD-GDH\'s role in G. sordida could be as a catabolic shunt facilitating respiration. Anabolic functions could be assimilation of ammonia released during photorespiration and synthesis of N-rich transport compounds. Western Indian Ocean Journal of Marine Sciences Vol.2(2) 2003: 179-186

Flooding and salinity fluctuations are common in mangrove systems. Sometimes these events are long-lasting, persisting several months. With an increased frequency of heavy rainfalls and terrestrial run-off, subsequent floods have been associated with massive mangrove mortality and failure to regenerate in the region. Owing to climate change, these events are expected to be more common in the future. We investigated how three weeks of submergence in water of different salinities affected the photosynthetic rates in seedlings of three common mangroves: Bruguiera gymnorrhiza (L.) Lamk.; Avicennia marina (Forssk.) Vierh.; and Heritiera littoralis Dryand. We found that photosynthesis and survival rates declined with increasing salinity and submergence time for all species. Prolonged submergence caused a significant decline in photosynthetic rates (as electron transport rate – ETR) for B. gymnorrhiza (P = 0.021) and H. littoralis (P = 0.002), whereas significant effects of both salinity (P = 0.003) and submergence (P = 0.023) were observed between species. Maximum diurnal values of ETR declined in the order of A. marina > B. gymnorrhiza > H. littoralis. After submergence, survived seedlings were tended normally, watered twice a day with freshwater. Three seedlings of B. gymnorrhiza from freshwater and 33% seawater treatments and of A. marina from freshwater treatment displayed signs of recovery for the first 3–5 days, but after that they died. We conclude that submergence time and water salinity will affect the performance of mangrove areas, such that areas experiencing prolonged submergence with flooding dominated by saline water might be most severely impacted.

Samples were collected monthly from Oyster Bay, Dar es Salaam. Light, temperature, salinity, pH, seawater nitrogen and phosphorus were determined on each sampling period. Mean carrageenan yield was significanlly higher during the SE monsoon period (t = 6.15, P