|Morais, P, Chicharo, M.A. & Barbosa, A.. (in press) Phytoplankton Dynamics in a coastal saline lake Acta Oecologica (aceite em Janeiro de 2003).
Chicharo MA, Chicharo L, Amaral A, Condinho S & Gaspar, M.B. Adenylic-derived indices and reburying time as indicators of the effects of dredging-induced stress on the clam Spisula solida. Marine Biology. (em publicação).
31 - Gaspar, M.B., Santos, M.N., Leitão, F., Chícharo, L., Chícharo, M.A. & Monteiro, C.C. Recovery of substrates and macro-benthos after fishing trials with a new Portuguese clam dredge. Journal Marine Biological Association U.K. (em publicação)
30 - Chícharo M.A., Amaral, A., Condinho, S., Gaspar, M.,. & Chícharo L. Study of the chronic effects of dredging induced stress on the clam (Spisula solida) using nucleic acids and lipids composition. Fisheries Research (em publicação)
29 - Gaspar, M.B., Leitão, F., Santos, M.N., Chícharo, L., Damásia, D. & Monteiro, C.C. A comparison of direct macrofaunal mortality using three types of Portuguese clam dredge. ICES Journal of Marine Science (em publicação)
28 - Alves F, Chícharo, L, Nogueira, A. & Regala, J. Changes in benthic communities due to clam dredging in the Algarve coast (South Portugal): importance of seasonal analysis for short-term impact studies. Journal of the Marine Biological Association of the United Kingdom (em publicação)
27 - Alves, F.; Chícharo L.; Serrão, E, & Abreu A. Grazing by Diadema antillarum (Philippi) upon algal communities on rocky substrates. Scientia Marina (em publicação
Reburial time and indirect mortality of Spisula solida clams caused by dredging
Chícharo, L.; Regala, J.; Gaspar, M.; Alves, F. & Chícharo M.A.
Fisheries Research. (2002) 59 (1-2), 247-258.
Clam-dredging results in the exposure of Spisula solida individuals not caught by the dredge. Subsequent survival depends on clam damage, reburial time, and the time needed by predators to reach the impacted area.We analyse these variables and discuss the importance of predation on exposed S. solida caused by dredge fishing. Sampling was performed in July 2000 off the southern coast of Portugal, at Vilamoura, a traditional S. solida sandy fishing ground.We compared the time needed for S. solida individuals to rebury themselves, relative to the abundance of potential predators. Bivalves collected by divers were placed on the seabed, and the times required for reburial were measured. These were compared with the times needed for reburial of the
clams exposed by dredge impact. At each of three dredge tracks, we analysed the number of predators that entered three equal quadrats (0.0250 m2) per minute. These results were compared with a non-affected control area. Impact caused by the fishing dredge significantly increases the number of exposed S. solida clams (p < 0.05) and the abundance of potential predatory species (p < 0.05). The brittle star Ophiura texturata was the most abundant and first species to reach the dredge track (less than 3 min after dredge impact). Other species reaching the dredge track were Pomatochistus spp. (6 min after impact), Diogenes pugilator, and Nassarius reticulatus (both 9 min after impact). Although predators reached the impacted area while S. solida bivalves were still exposed, our results suggest that predation on the non-buried clams in the dredge track is not a major factor for subsequent indirect mortality of S. solida.
Influence of mesh size and tooth spacing on the proportion of damaged organisms in the catches of the Portuguese clam dredge fishery
Gaspar, M. B., Leitão, F., Santos, M. N., Sobral, M., Chícharo, L., Chícharo, A., and Monteiro, C. C.
ICES Journal of Marine Science, . 2002, 59: 1228–1236.
Experiments to assess the eﬀect of mesh size and tooth spacing on the catch of Spisula solida were undertaken with the aim of determining an optimal combination of these two characteristics to minimize the dredging impact on by-catch species. However, our data showed that tooth spacing, mesh size and the interactions between these two factors did not affect the number of damaged macrofaunal individual’s caught. This may be because infauna entered the dredge without passing through the space between the teeth and the mesh of the net bag closed as it was stretched by the weight of the contents, preventing the escape of the caught individuals. Thus, independently of mesh size, when the dredge is towed over the sediment, the retained individuals were injured due to abrasion between animals and/or between animals and debris. The severity of injuries inflicted by dredging on diﬀerent macrobenthic species is related to their morphology and fragility.
Size selectivity of the Spisula solida dredge in relation to tooth spacing and mesh size.
Gaspar, M.B., Leitão, F., Santos, M.N., Sobral, M., Chícharo, L., Chícharo, M.A. & Monteiro, C.C.
Fisheries Research (2003). 60 (2-3): 561-568
A study was undertaken on the northwestern coast of Portugal to evaluate the selectivity effect of both tooth spacing and mesh size on the catch of the white clam (Spisula solida). Two typical clam dredges, equipped with different tooth spacing and mesh size, were towed side by side. Three tooth spacing (20, 40 and 60 mm) and three mesh sizes (35, 40 and 50 mm) were investigated. The dredge selectivity experiments were performed by attaching a cover bag with a 20mm mesh to the gear. Individual hauls were analysed by the SELECT model. The Fryer’s mixed model of between-haul variation was also applied to data. The results showed that the space between teeth does not have an effect on selectivity. Tooth length was directly related to the dredge’s capture efficiency. The only factor that contributed to dredge size selection was mesh size. The 50% retention lengths estimated for mesh sizes 30, 40 and 50mm were 25.68, 26.35 and 31.94 mm, respectively. For all mesh sizes, very narrow selection ranges were observed. The most appropriate mesh size to be enforced within the Portuguese northwestern S. solida fishery should be 40 mm.
Comparison of RNA/DNA ratios obtained with two methods for nucleic acid quantification in gobiid larvae.
Esteves, E., Chicharo, M. A., Pina, T Coelho, M.L. & J.P. Andrade
J. Exp. Mar. Biol. Ecol., (2000) 243 (1): 81-94
In this paper, RNA and DNA contents and RNA/DNA ratios obtained with two fluorometric methods for the extraction and quantification of nucleic acids in individual estuarine gobiid larvae are compared. A total of 141 gobiid larvae, collected in the Mira and Guadiana estuaries (Portugal), were analysed. This study indicated that the nucleic acids content and RNA/DNA ratios of individual larvae varied with the procedure used. The two methods yielded similar log DNA values but different log RNA and log (RNA/DNA). The differences could be due to a number of factors related to specific steps of tested protocols. Comparison of nucleic acids contents and calibration of the two methods by regression analysis provided a reasonable basis for comparison although differences between estimates were evident.
The distribution of estuarine fish larvae: Nutritional condition and co-ocurrence with predators and prey.
Esteves, E., Pina, T., Chicharo, M. A & J.P. Andrade
Acta Oecologica, (2000) 21 (3): 1-13
Fish larvae were collected monthly between March and September 1997 in the Mira and Guadiana estuaries (southern Portugal). Hydrological parameters were registered and zooplankton samples were obtained simultaneously. Densities of fish larvae (ind·100 m–3) were calculated from 211 samples and larval nutritional condition measured as RNA/DNA ratios were obtained for 346 individuals, using a fluorimetric method for nucleic acid quantification. Correlating variables were further studied using multiple regression analysis in order to assess the relative importance of abiotic and biotic factors affecting within-year trends in abundance and nutritional condition of estuarine fish larvae. Results indicated that: 1) the abundance of fish larvae seems conditioned by temperature and predation; and 2) their nutritional condition is dependent on temperature and prey availability. Temperature is an important variable structuring estuaries and therefore conditions the behaviour and physiology of fish larvae. Furthermore, the co-occurrence of predators and larvae might be related to similar feeding patterns or comensalism. Whenever feeding conditions are suitable, they usually determine enhanced growth and nutritional condition. However, predation seems to control this latter relationship through its effect on larval mortality.
Algal cover and sea urchin spatial distribution at Madeira Island (NE Atlantic)
Alves,-F.M.A.; Chicharo,-L.M.; Serrao,-E.; Abreu,-A.D.
Scientia-Marina-Barcelona [Sci-Mar-Barc] 2001 vol. 65, no. 4, pp. 383-392
This study describes sea urchin spatial distribution in relation to environmental factors, and the relationship between Diadema antillarum density and algal abundance. Twenty-three transects around Madeira Island were surveyed by scuba divers, and sea urchin density and algal cover were determined in situ. Sampling sites along these transects were characterised in terms of distance from the tide line, water depth, substratum type, bottom declivity and water turbulence. Diadema antillarum was the dominant sea urchin species. Paracentrotus lividus and Arbacia lixula occurred at shallower depths (2-6 m), contrasting with the distribution of Sphaerechinus granularis, which occurs among D. antillarum (4-20 m). Surveys found two alternative types of communities on rocky shores: 1) a community with high algal cover and low numbers of sea urchins, along the north and south-west coasts and; 2) a community with little algal cover and high densities of sea urchins, along the south-east coast. Macroalgal cover and D. antillarum densities were inversely correlated (adjusted R super(2)=75.6%; n = 429; p<0.05). The results showed that water turbulence was the most important factor limiting the distribution of D. antillarum on rocky substrates. We propose a multiple non-linear regression model (using backward stepwise analysis) to explain D. antillarum abundance on the rocky shores: D. antillarum/m super(2) ( square root square root )= 0.121 -0.209 distance from shore (in m) ( square root square root ) + 2.052 water depth (in m) ( square root square root ) - 1.778 water turbulence level ( square root square root ) - 0.007 water turbulence level super(4) ( square root square root ); where square root square root indicates data are square-root transformed (adjusted R super(2) = 60.99%; n = 454; p<0.05).
The influence of dredge design on the catch of Callista chione (Linnaeus, 1758)
Gaspar,-M.B.; Dias,-M.D.; Campos,-A.; Monteiro,-C.; Santos,-M.N.; Chicharo,-A.; Chicharo,-L.
Hydrobiologia 2001 vol. 465, no. 1-3, pp. 153-167
To evaluate a possible introduction of a new dredge in the fishery of Callista chione (Linnaeus, 1758), IPIMAR has conducted a study with the objective of comparing the efficiency of two dredges (traditional dredge and the new dredge design) and evaluating their impact on the benthic community. The experiments were carried out during March 1999 on the Southwest coast of Portugal, from a site off Troia. Three different tow durations of 5, 10 and 20 min were investigated. A total of 24 hauls were accomplished, 4 for each tow duration and dredge. The experiments were conducted by attaching a cover bag with a 20 mm mesh to the gear. After each haul, the catches in the bag and in the cover were sorted separately. All individuals retained were attributed scores on a scale of 1-4 in which 1 equates to good and 4 equates to dead. The results obtained showed that catches from the traditional dredge (TD) are composed of a great fraction of juveniles of C. chione, while in the new dredge (NDD) catches are composed, almost entirely, by individuals with a superior size to the minimum legal length (50 mm). This result indicates that the mesh of the bag of the TD used in the exploitation of this resource is not adequate. For the 3 different tow durations, the mean fishing yield obtained for the NDD was always superior to the TD, due to its greater efficiency in capture. The proportion of by-catch is significantly higher when the TD is used. For all 3 tow duration, the TD caused mortalities on the target species and on the macrobenthic community in the same order of magnitude as the NDD. Since the fishery of C. chione is managed by daily quotas per boat, when using the NDD the impact on the macrobenthic community is reduced by about 50% due to its greater efficiency of capture. Another advantage in the usage of the NDD relatively to the TD, is to allow the smallest individuals (independently of the species) to escape rapidly through the metallic bars on the grid, increasing their probability of survival.
Macrofauna spatial differences within clam dredge-tracks and their implications for short-term fishing effect studies
Chicharo,-L.; Regala,-J.; Gaspar,-M.; Alves,-F.; Chicharo,-A.
Fisheries-Research-Amsterdam [Fish-Res] 2002 vol. 54, no. 3, pp. 349-354
In situ observations of clam dredging showed that the effects of the dredge on the benthic macrofauna may not be constant during a tow. A sand buffer forms in front of the gear approximately 10 m after the beginning of a tow, and this pushes the sediment partially aside. In this study, we analyze differences in abundance, the number of taxa present, diversity, and evenness within sections of dredge-tracks in a disturbed, fished area and a non-fished area along the southern coast of Portugal. These areas were sampled by divers before and after dredge-fishing activity. At each site, three dredge-tracks were produced. These tracks were divided in three longitudinal sections (start, middle and end) and two transverse sections (track and edge). Six quadrats were used to sample macro.
Effects of environmental conditions on planktonic abundances, benthic recruitment and growth rates of the bivalve mollusc Ruditapes decussates in a Portuguese coastal lagoon
Fisheries-Research-Amsterdam [Fish-Res] 2001 vol. 53, no. 3, pp. 235-250
Controlling environmental parameters for the early stages of marine invertebrates have received little attention, particularly in field studies. This study involves measurement of abundances and growth rates of the bivalve Ruditapes decussates Linnaeus 1758 during its planktonic larval and early benthic life stages in a coastal lagoon: Ria Formosa, Portugal. Measured abundances were compared with tidal amplitude, water temperature, salinity, wind velocity and direction, and a food availability indicator (chlorophyll a). Data were obtained on abundance and prodissoconch length of the larvae, measured two to three times per week, and of post-larval stages individuals that had settled in artificial collectors over 10 months. Larval and juvenile cohorts were identified using size-frequency distributions and larval ages estimated by larval shell growth lines. Data were fitted to linear, exponential, and Laird-Gompertz growth models. Larval growth rates best matched a linear model: 3.78 plus or minus 0.55 per day, r super(2) = 0.75, p < 0.001. Early benthonic growth rates best matched a Laird-Gompertz model: 3.97 plus or minus 0.15 per month, r super(2) = 0.98, p < 0.001. It was concluded that there was a significant relationship between planktonic and recruitment abundances. Water temperature (as a coarse factor) and advection (as a fine factor) effects were inferred to be the prime environmental factors affecting early life stages of this species in this coastal lagoon system.
A juvenile recruitment prediction model for Ruditapes decussates (L.) (Bivalvia: Mollusca)
Fisheries-Research-Amsterdam [Fish-Res] 2001 vol. 53, no. 3, pp. 219-233
Despite the importance of larval abundance in determining the recruitment of benthic marine invertebrates and as a major factor in marine benthic community structure, relating planktonic larval abundance with post-settlement post-larvae and juveniles in the benthos is difficult. It is hampered by several methodological difficulties, including sampling frequency, ability to follow larval and post-larval or juvenile cohorts, and ability to calculate growth and mortality rates. In our work, an intensive sampling strategy was used. Larvae in the plankton were collected at weekly intervals, while post-larvae that settled into collectors were analyzed fortnightly. Planktonic larval and benthic post-larval/juvenile cohorts were determined, and growth and mortality rates calculated. Integration of all equations allowed the development of a theoretical formulation that, based on the abundance and planktonic larval duration, permits an estimation of the future abundance of post-larvae/juveniles during the first year of benthic life. The model can be applied to a sample in which it was necessary only to measure larval length.
An ecohydrologic study of the Guadiana estuary (south Portugal)
Um estudo ecohidrologico do estuario do Guadiana (sul de Portugal)
Chicharo,-M.A.; Chicharo,-L.M.; Galvao,-H.; Barbosa,-A.; Marques,-M.H.; Andrade,-J.P.; Esteves,-E.; Gouveia,-I.; Miguel,-C.
Revista-de-Biologia [Rev-Biol-Lisboa] 2000 vol. 18, no. 1-4, pp. 139-156
Ecohydrology is considered a tool for sustainable management of aquatic resources. This is the basis of a study on the Guadiana Estuary carried out within the Fifth Phase of UNESCO's International Hydrological Programme. The construction of the Alqueva dam in the near future will pose problems for water quantity and quality in the Guadiana Estuary. The aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary before the construction of the Alqueva dam (1996-1998). This was carried out to determine how environmental factors affect the aquatic biota. The results of available information on the subcatchments of the estuary (including urban, agricultural, forested areas and pollution point sources, both domestic and industrial) were integrated into a geographic information system (GIS)-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. The N/P ratios indicate some limitation by phosphorus, except for the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occur in the upper/middle estuary. The fish larval life cycle phase, especially sensitive to environmental alterations, was in a good ecophysiological condition with high RNA/DNA ratios. It was concluded that the estuary subcatchment basin is under low anthropogenic pressure and the aquatic biota characteristics seem to indicate a general good water quality.
Status of the Guadiana Estuary (south Portugal) during 1996-1998: An ecohydrological approach
Chicharo,-M.A.; Chicharo,-L.M.; Galvao,-H.; Barbosa,-A.; Marques,-M.H.; Andrade,-J.P.; Esteves,-E.; Miguel,-C.; Gouveia,-I.
Aquatic-Ecosystem-Health-and-Management [Aquat-Ecosyst-Health-Manage] 2001 vol. 4, no. 1, pp. 73-89
The aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary (1996-1998) before the construction of the Alqueva dam. This work was carried out to determine how environmental factors affect seasonal and tidal variations of plankton populations in the estuary. The available information on the subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated into a geographic information system-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. River flow near Mertola (ca 50 km upstream from the mouth) reached 3400 x 10 super(6) m super(3) in winter and decreased to 42x10 super(6) m super(3) in summer. With respect to nutrients, nitrogen to phosphorus ratios indicated some limitation by phosphorus, except at the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may significantly influence the retention of zooplankton in the estuary. The fish larval life cycle, especially sensitive to environmental alterations, showed high ratios of ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was concluded that an ecohydrological approach, allowing integration of different elements from the cellular to the habitat level into a geographic information system, can contribute to a better understanding of the processes that influence the aquatic biota of the estuary. The approach will be a useful assessment tool for monitoring the estuary following dam completion.
Diel variation of the RNA/DNA ratios in Crassostrea angulata (Lamarck) and Ruditapes decussatus (Linnaeus 1758) (Mollusca: Bivalvia)
Chicharo,-L.M.Z.; Chicharo,-M.A.; Alves,-F.; Amaral,-A.; Pereira,-A.; Regala,-J.
Journal-of-Experimental-Marine-Biology-and-Ecology [J-Exp-Mar-Biol-Ecol] 2001 vol. 259, no. 1, pp. 121-129
The aim of this study was to investigate the effect of time of day on RNA/DNA ratios among fed and starved Crassostrea angulata and Ruditapes decussatus juveniles. Sampling to investigate the day and night condition of juveniles was carried out for 48 h. A highly sensitive method for nucleic acid quantification was applied to bivalves. The results suggest that there is some variation in nucleic acid quantities with the time of the day. For the two species analysed, the RNA/DNA ratio was particularly high during the night and was higher in the fed animals. The results seem to indicate that there is some endogenous rhythm in the production of RNA. If there are diel changes in RNA/DNA ratios, it follows that average RNA/DNA ratios can be unrepresentative if there is any day or night bias in sampling.
Marine plankton of the Bijagos Archipelago (Guinea-Bissau, West Africa) and its relationship with fish eggs and larvae.
Poissons et Peches Africains Diversite et Utilisation
Esteves,-E.; Gomes,-T.M.; Anibal,-J.; Teixeira,-T.; Jardim,-J.E.; Chicharo,-L.; Ferreira,-L.
International Conference for the Paradi Association and The Fisheries Society of Africa, Grahamstown (South Africa), 13-18 Sept 1998
African-Fishes-and-Fisheries-Diversity-and-Utilisation-Poissons-et-Peches-Africains-Diversite-et-Utilisation Coetzee,-L.-(ed.); Gon,-J.-(ed.); Kulongowski,-C.-(ed.) Grahamstown-South-Africa FISA; PARADI 1998 p. 275
Results of the joint Guinean-Bissau (CIPA)/Portuguese (UCTRA) marine sciences survey in the Bijagos Archipelago (Guinea-Bissau, West Africa) carried out in May June 1995 are presented here. Water surface temperature and salinity were measured in 15 stations with T-probe and refractometer. Nitrite, ammonia and phosphates concentrations were obtained from water samples collected at 1-m depth and analysed using a Hach DR/3 portable photometer. In nine of these stations phytoplankton was sampled with a Nansen bottle at 1m depth and zooplankton was collected with a FAO conical net (0.37 x 1.60 m, 0.5 mm mesh size) towed 0.5 mm mesh size) towed 0.5 m below the surface at a constant velocity of 3 knots. The system had lower salinity (mean=34.4 ppm plus or minus 0.77 SD) and higher temperature (mean=28.6 degree C plus or minus 2.02 SD) than surrounding open oceanic water. Nitrite, ammonia and phosphates concentration ranged between 0.05-0.47,0.29 and 0.8-12.1 mu mol/L, respectively. Phytoplankton abundance was greater in the periphery of the archipelago and its diel variation at Canogo station seemed more related to tidal influence than with hour of sampling. Malacrostaceans determined the general variability of the zooplankton community. Fish eggs and larvae represented less than 5.5% of total zooplankton abundance. A day-night rhythm of zooplankters abundance could be depicted from the eulerian sampling plan done at Canogo station. Integrated analysis of oceanographic data and the data collected did not permit us to establish inter-relationships among factors.
Plankton of Guadiana Estuary: seasonal distribution and relation with environmental parameters - preliminary results
Plancton do Estuario do Guadiana: sazonalidade e relacao com os parametros ambientais - resultados preliminares
Gouveia,-I.; Miguel,-C.; Chicharo,-M.A.; Marques,-M.H.; Chicharo,-L.M.
Revista-de-Biologia [Rev-Biol-Lisboa] 1999 vol. 17, no. 1-4, pp. 179-192
The aim of this study was to investigate the spatial and temporal distribution of plankton communities from the Guadiana Estuary and related environmental parameters. Between March 1997 and March 1998, with a variable periodicity, sampling was done along five sampling stations (from the mouth of the river to 40 km upstream) during flood tide. Temperature, salinity, turbidity (with a Secchi disc) and chlorophyll a were measured. Mesozooplankton was sampled by sub-superficial tows, of ten-minute duration, using a 500 mu m net. The plankton taxonomic composition and density were determined. Phytoplankton and zooplankton abundance was higher in the beginning and in the end of spring and summer, respectively than in the other months. High densities of phytoplankton occurred generally in higher estuary, were the Chlorophyceae dominated (namely Ankistrodesmus spirilliformis and Pediastrum simplex). In the middle estuary the small flagellates and the Cryptophyceae were the predominant, and in the lower estuary were the Baccillariophyceae (Leptocylindrus danicus) and the small flagellates. The zooplankton abundance was higher in the lower estuary. Crustacea dominated in the obtained samples, in spit of changes in it specific composition along the estuary. So, in the lower estuary the Cladoceros (Podon, Evadne e Penilia) and Decapoda larvae were the dominant, while in the upper estuary the Copepodes and Cladoceros (Bosmina, Diaphanosoma and Ceriodaphnia) were the most abundant. The environmental parameters significantly related with the planktonic densities were the temperature and salinity, as well as, in an indirect way, the nutrients chlorophyll a seems to act as an indicator of food availability, for the herbivore mesozooplankton.
Estimation of the life history parameters of Mytilus galloprovincialis (Lamarck) larvae in a coastal lagoon (Ria Formosa - south Portugal)
Journal-of-Experimental-Marine-Biology-and-Ecology [J-Exp-Mar-Biol-Ecol] 2000 vol. 243, no. 1, pp. 81-94
The life history parameters of early stages of marine invertebrates, particularly field estimations, have received relatively little attention. The aim of this research was to estimate in situ abundance and growth of Mytilus galloprovincialis planktonic larvae. Plankton samples were filtered through gauze of 63 mu m mesh and identified, counted and measured using an inverted microscope. Short-term fluctuations in Mytilus galloprovincialis larvae abundance and environmental parameters (water temperature, salinity, wind velocity direction, tidal amplitude and chlorophyll a) were monitored (two to three times a week). Larval cohorts were identified using size-frequency distributions and age estimates compared with larval shell growth lines. Data were fitted to the linear, exponential, von Bertalanffy and Laird-Gompertz growth models. Larval growth adjusted better to the Laird-Gompertz model (0.525 plus or minus 0.073 mu m d super(- 1); r super(2) = 0.768; P < 0.05). Reduction of shell growth after 1 to 1.5 months in the plankton suggests the occurrence, in this period, of a 'delay of metamorphosis' phase. The results of our study indicate that advection and availability of settlement substratum may be the key factors for the life history parameters of this species in a coastal system such as the Ria Formosa.
Estimation of starvation and diel variation of the RNA/DNA ratios in field-caught Sardina pilchardus larvae off the north of Spain
Chicharo,-M.A.; Chicharo,-L.; Valdes,-L.; Lopez-Jamar,-E.; Re,-P.
Mar.-Ecol.-Prog.-Ser. 1998 vol. 164, pp. 273-283
Incl. bibliogr.: 65 refs.
The aim of this study was to analyse the general larval condition, to determine the incidence of starvation and to investigate the effect of time of day on RNA/DNA ratios among field-caught Sardina pilchardus larvae. The larvae were collected during 4 research cruises off northern Spain, during March, April, May and June 1992. A highly sensitive fluorometric method for nucleic acid quantification was applied to larvae of S. pilchardus. The means of the RNA/DNA ratio were relatively high, so the larvae collected off northern Spain were generally in good condition. Low percentages of starving larvae (RNA/DNA ratio less than 1.3), ranging from 0 to 3.23%, were found over the 4 mo. The RNA/DNA ratios were significantly correlated with zooplankton biomass. Larvae collected at night revealed higher RNA/DNA ratios compared to larvae caught during the day. This seems to indicate that there is some endogenous rhythm in the production of RNA. It would then follow that, if there are diel changes in RNA concentrations, average RNA indices can be unrepresentative if there is any day /night bias in sampling.
Starvation percentages in field caught Sardina pilchardus larvae off southern Portugal
Sci.-Mar.-Barc. 1997 vol. 61, no. 4, pp. 507-516
Starvation has been proposed as a major event only in small larvae that are learning to feed on planktonic prey. However, there are few comparisons of percentages of starving larvae either among locations, times or phases of larval development. The percentage of starvation of Sardina pilchardus larvae of different lengths was analysed in four distinct areas off southern Portugal. A highly sensitive fluorometric method for RNA/DNA quantification was applied to field caught S. pilchardus larvae during April and May 1992. Using in situ determination of critical RNA/DNA ratio (1.3), we classified as starving only a small percentage (2.22%) of first-feeding (<8 mm) sardine larvae, but bigger larvae appeared to be more vulnerable to starvation. We concluded that sardine larvae analysed were generally in good condition (total percentage of starving larvae - 4.64%), but with some variation within each region.
Nutritional condition and starvation in Sardina pilchardus (L.) larvae off southern Portugal compared with some environmental factors
J.-Exp.-Mar.-Biol.-Ecol. 1998 vol. 225, no. 1, pp. 123-137
The aim of this study was to determine the condition and the incidence of starvation among field-caught Sardina pilchardus larvae, using RNA/DNA ratios and to compare them with various abiotic and biotic factors. S. pilchardus larvae were collected off southern Portugal, during April and May 1992. A highly sensitive fluorometric method for quantifying larvae nucleic acid was applied. Sardine larvae were generally in good condition. The means of the RNA/DNA ratios were relatively high and low percentages of starving larvae (RNA/DNA ratio < 1.3) were recorded, ranging from 0 to 12.5%. These two results were associated with high prey availability, which contributes to enhanced condition, and with a high density of potential predators, which may result in fewer larvae in poor condition.
The DNA/RNA ratio as a useful indicator of the nutritional condition in juveniles of Ruditapes decussatus
8. Iberian Symposium on Marine Benthos Studies, Blanes (Spain), Feb 1994
SCI.-MAR.-BARC. 1995 vol. 59, no. supplement 1, pp. 95-101
Condition indices have been widely used to assess how healthy individuals are under certain circumstances. It has been shown that the RNA/DNA ratio is a good indicator of the nutritional condition of several marine organisms. A very sensitive fluorometric method for RNA/DNA quantification (Clemmesen, 1990) was applied to fed and starved post-larvae laboratory-reared clam, Ruditapes decussatus. The presented study shows that the RNA/DNA ratio is a useful indicator of nutritional stress for bivalve spat. The decrease in RNA/DNA ratio recorded here, under starved conditions was lower than in similar experiments on fish. A lower metabolic rate in clams may result in a slower response with respect to RNA /DNA ratios than that observed in vertebrates.8>