Space–time patterns of co‐variation of biodiversity and primary production in phytoplankton guilds of coastal marine environments

• 1. The relevance of biodiversity to ecosystem processes is a major topic in ecology. Here, we analyse the relationship between biodiversity and productivity of the nano‐ and micro‐phytoplankton guilds in coastal marine ecosystems.
• 2. The patterns of variation of species richness, diversity and primary productivity (as ¹⁴C assimilation) were studied in two marine areas: a eutrophic–mesotrophic area beside the River Po delta (northern Adriatic) and an oligotrophic area around the Salento peninsula (southern Adriatic–Ionian). The study was carried out at 23 sites in the northern area and at 45 sites in the southern area. Sites were arranged on expected spatial and temporal gradients of primary productivity variation, according to distance from the coast, optical depths and seasonal period.
• 3. 167 taxa were identified in the northern area and 153 taxa in the southern area. In both areas, the taxonomic composition of the nano‐ and micro‐phytoplankton guilds exhibited greater temporal than spatial variation. The latter was much higher in the southern area than in the northern area (average dissimilarity between stations being 70.7±0.8% and 44.7±4.2% respectively).
• 4. Primary productivity varied in space and time on the gradients considered. Phytoplankton species richness and diversity exhibited significant patterns of variation in space and time; overall, these were inversely related to the primary productivity patterns in the northern area, whereas they were directly related in the southern area.
• 5. The small individual size and the high turnover rate of phytoplankton are likely to underlie the observed relationships, which emphasized a threshold response to nutrient enrichment in agreement with the ‘paradox of enrichment’. Under resource enrichment conditions, the high turnover of producers leads to hierarchical partitioning of the available resources with an increasing dominance of a few species. Therefore, the relationship observed here seems likely to be explained by the complementarity hypothesis.

Copyright © 2003 John Wiley & Sons, Ltd.     

Limit of colour vision in dim light in larvae of the giant freshwater prawn <Emphasis Type="Italic">Macrobrachium rosenbergii</Emphasis>

Colour vision depends on sufficient ambient light and becomes ineffective at a particular low light intensity. It is not known how decapod crustaceans see colour in dim light. In the present study we investigated the colour vision threshold in larvae of the giant freshwater prawn Macrobrachium rosenbergii in a tank under natural illumination. Plastic beads of different colours (blue, red, yellow and white) in various combinations were suspended in the tank. The larvae swam straight toward the beads and gathered around them. The number of larvae was highest on the blue and white beads. The luminance in the tank was then gradually decreased by covering it with different numbers of layers of black cloth, and the response of the larvae to the beads was video-recorded under infrared illumination. The preference for blue and white beads remained manifest as the luminance was reduced from 418 to 0.07 cd/m², but not at 0.02 cd/m², indicating a colour vision threshold between 0.07 and 0.02 cd/m². The larvae have apposition compound eyes with large optical parameters, comparable to those of apposition eyes of nocturnal insects, which presumably capture more light and show enhanced sensitivity, enabling the larvae to see colour in dim light.     

Effects of dietary nucleotides on growth,survival and metabolic response in whiteleg shrimp,Litopenaeus vannamei against ammonia stress condition

This trial was conducted to evaluate the effects of nucleotides on growth of whiteleg shrimp, Litopenaeus vannamei, and the survival and metabolic responses to ammonia stress test. Experimental diets were as follows: low fish meal diet (LFMD), and four LFMD test diets, each supplemented with 0.1% guanosine monophosphate (GMP), 0.1% inosine monophosphate (IMP), 0.1% mixture of GMP and IMP and 0.1% mixture of GMP, IMP, uridine monophosphate (UMP) and cytidine monophosphate (CMP). The shrimp specimens (initial body weight: 0.99 ± 0.01 g) were randomly allocated into five groups and fed four times daily for 8‐weeks. After the trial, final body weight was recorded and haemolymph was withdrawn for haematological analysis. The shrimp was then challenged with 70 mg/L ammonia (LC50) for 10 days. Survival and haemolymph of the shrimp were taken after exposure to ammonia. The highest growth performance was observed in the shrimp fed diet supplemented with GMP (p < .05), while survival was not influenced by the test diets in the feeding trial. In the ammonia challenge test, the highest survival was observed in the shrimp fed GMP supplemented diet compared to others. The plasma protein, glucose and cholesterol levels increased in all the treatments while triglycerides level decreased post challenge. Cortisol level recovered at day 10th after the challenge. Shrimps fed with nucleotides diets showed higher protein and glucose level compared to control groups post challenge. In general, nucleotides supplemented in the diet enhanced growth, improved stress resistance while modulating the haemolymph metabolites in L. vannamei under ammonia stress.     

Growth performance and survival of giant freshwater prawn Macrobrachium rosenbergii larvae fed coloured feed

This study examined the behavioural response on the preference and acceptance, growth performance and survival of Marcobrachium rosenbergi larvae fed with isonitrogenous and isolipidic yellow (YCF) and blue (BCF) coloured feed. In the behavioural response test, single and paired feed drop test of YCF and BCF were introduced at the middle of a tank about 15–20 cm from the edge of the white colour tank wall to larvae zoea IV–VI. The number of larvae attracted to each coloured feed was recorded. For the growth and survival performance, each coloured feed was fed to triplicate groups of larvae (zoea V–VI) at stocking density of 30 larvae/L in 12 ppt brackish water for 28 days until they reached postlarval (PL) stage. In the behavioural test, the number of larvae that attracted and accepted the BCF was significantly higher than those fed YCF (p < 0.05). The body weight and length of PL fed BCF was 28% and 5.6% bigger than those fed YCF respectively. However, the survival of the PL was almost similar in both treatments. This study shows that the freshwater prawn larvae were attracted more to the BCF and able to detect and capture the preferred BCF by vision and this contributed to higher growth of the larvae.     

Touch-sensitive bristles on the carapace of the mud crab Scylla paramamosain may be receptors for courtship signals

Fisheries Science - Bristle patches on the carapace behind the eyes were found for the first time in both males and females of the four species of mud crab Scylla spp. Electrocardiography revealed...     

Growth performance and physiological responses in striped knifejaw, Oplegnathus fasciatus, held under different photoperiods

The growth performance and stress response in striped knifejaw, Oplegnathus fasciatus (body weight 100–300 g) reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) were investigated. Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. A trial of acute handling and confinement stress was also carried out to investigate the stress-induced levels of different stress indicators in O. fasciatus. Blood was also collected from undisturbed fish which was considered as control. Although there were no significant differences in weight gain, specific growth rate (SGR) and feed conversion efficiency (FCE) in fish exposed to 6L:6D, 16L:8D and 24L:0D photoperiods, all parameters in these photoperiods were significantly higher than those of 12L:12D photoperiod (P < 0.05). There was no significant difference in protein retention efficiency (PRE) between fish exposed to 16L:8D and 24L:0D photoperiods, but PRE in both photoperiods was significantly higher than that of 12L:12D photoperiod.Acute stress significantly increased the plasma levels of cortisol (110.3 ng ml^− 1) and glucose (195.4 mg dl^− 1), and decreased plasma levels of total protein (0.8 g dl^− 1); however, all parameters were returned back to the levels indistinguishable from those of control, undisturbed fish within 24 h. The levels of cortisol, glucose and total protein in fish exposed to different photoperiods during the study were far from the stress-induced levels (P < 0.05). The results demonstrated that the growth performance of O. fasciatus reared from 100 to 300 g can be stimulated significantly by using the manipulated photoperiods where feeding time may be playing an important role to increase food intake and feed conversion efficiency. It also revealed that the artificial photoperiods did not cause significant stress response in fish.     

Effect of Azospirillum inoculants on arbuscular mycorrhiza establishment in wheat and maize plants

Plant growth-promoting rhizobacteria and arbuscular mycorrhizal (AM) fungi represent two main groups of beneficial microorganisms of the rhizosphere. The role of different strains of Azospirillum on AM fungi development was evaluated by measuring the percentage of AM colonisation of the root system in durum wheat and maize plants, grown under both greenhouse and field conditions. The effect of wild-type Azospirillum brasilense strain Sp245 and genetically modified (GM) derivatives overproducing indole-3-acetic acid was assessed at greenhouse level in (1) three different cultivars of durum wheat, in the presence of indigenous AM fungi and (2) maize plants artificially inoculated with Glomus mosseae and Glomus macrocarpum. In addition, the establishment of natural AM fungal symbiosis was evaluated using Azospirillum lipoferum CRT1 in maize plants at field level. Despite the stimulatory effect of the different Azospirillum inocula on root growth, no significant differences in AM colonisation were found, independently of the AM fungus involved, either in wheat or in maize plants. Similarly, GM A. brasilense, which strongly stimulates root development, did not affect AM formation. Although these results were obtained in conditions in which the mycorrhization rate was moderate (15–30%), overall considered they indicate that the use of wild-type or GM Azospirillum phytostimulators does not alter mycorrhization.     

Evaluation on the potential of betaine,taurine, nucleotide and nucleoside as feeding stimulant for juvenile marble goby <Emphasis Type="Italic">Oxyeleotris marmoratus</Emphasis> through behavioural assays

This study was conducted to evaluate the potential of betaine, taurine, inosine (INO), inosine 5′-monophosphate disodium (IMP·Na₂), and guanosine 5′-monophosphate disodium (GMP·Na₂) as a feeding stimulant for juvenile marble goby (Oxyeleotris marmoratus) (total length 6.6–8.5 cm) through behavioural assays using agar gel pellets. All fish were conditioned to accept agar gel pellet before the behavioural assays started. Each chemical substance was tested on 50 replicates of individual fish once, and the overall ingestion rate was calculated as the representative data. The pure agar gel pellet was totally rejected by the fish (0 % ingestion rate). Therefore, any added test substance which can significantly improve the fish ingestion of the agar gel pellet can be the potential feeding stimulant. Of all the chemical substances tested at 0.1 M concentration, the ingestion rates of both INO and IMP·Na₂ were the highest (both 100 %) and were significantly higher (P < 0.05) than those of the other chemical substances tested. However, INO was identified as the most potent feeding stimulant as it could function perfectly (100 %) even at the lower concentrations tested (0.01 and 0.001 M). The ingestion rates of IMP·Na₂ were found significantly decreased (P < 0.05) at the concentrations of 0.01 and 0.001 M (78 and 2 %, respectively). The ingestion rate of GMP·Na₂ at 0.1 M was 60 %, hence higher concentration (>0.1 M) may be required to improve its efficiency as the feeding stimulant. Taurine was not a feeding stimulant, and betaine was neither a feeding stimulant nor feed enhancer for the juvenile O. marmoratus.     

The giant freshwater prawn Macrobrachium rosenbergii alters background colour preference after metamorphosis from larvae to postlarvae: In association with nature of phototaxis

The giant freshwater prawn Macrobrachium rosenbergii larvae have apposition eyes and are positively phototactic, whereas the postlarvae (PL) have superposition eyes and are negatively phototactic. M. rosenbergii has colour vision as early as larval stage. We discovered that M. rosenbergii alters background colour preference after metamorphosis from larvae to PL in association with nature of phototaxis. The test circular glass aquaria covered with a pair of two‐colour papers contained with a group of 100 larvae or 20 Pl, and the number of individuals in each colour background was recorded five times for each colour pair. The background colours tested were light blue, green, yellow, red, white and black. The numbers of larvae or PL in each colour background of different pairs were analysed by the Thurstone's law of comparative judgment. In the larvae, significant bias towards yellow was evident. In the PL, of the four pairings of black with other colours, all biased to black. The mean z‐scores were highest for yellow in the larvae, and for black in the PL. To determine the possible background brightness preference of the larvae and PL, six different colour backgrounds were presented in pairs. The larvae significantly preferred light blue over dark blue, white over yellow and white over black. The PL exhibited reversed preference. The relationship between z‐scores and light reflectance levels of five colour papers was significantly positive in the larvae and negative in the PL. The observed background colour preference was probably due to relative brightness rather than chromaticity difference.