Diel and seasonal changes in the distribution of fish on a southeast Brazil sandy beach

The effect of diel and seasonal changes in the distribution of fishes on a subtropical sandy beach on the southeastern coast of Brazil were studied. Seine netting was carried out on both seasonal and diel scales between July 1998 and June 1999. A total of 46 fish species was recorded, six being numerically dominant: Anchoa tricolor, Gerres aprion, Harengula clupeola, Atherinella brasiliensis, Mugil liza and Diapterus rhombeus. Seasonal changes in abundance of dominant species were detected. Species dominant in winter were Anchoa tricolor, H. clupeola and Atherinella brasiliensis; in spring, Anchoa tricolor and G. aprion; in summer G. aprion and D. rhombeus; and in autumn M. liza and H. clupeola. Overall, diel patterns did not reveal any significant trends; however, if we consider each season separately, an increase in A. tricolor abundance was recorded during the day in winter/spring, being replaced at night by H. clupeola in winter, and by G. aprion in spring. Increases in number of individuals and biomass at sunset, and decreases during the night were recorded. The winter/spring inshore/offshore movements at diel scale performed by the three most abundant species demonstrate that diel fluctuation acts more at a species-specific level than at a structural one; in summer there was no evidence of diel movements due to a heavy influx of G. aprion and D. rhombeus, which use the area throughout day and night, increasing overall abundance. Seasonal movements seems to be related to ontogenetic change in species, while diel movements in the fish assemblage seem to be more related to physiological requirements, such feeding activity of each particular species, than to physico-chemical conditions.Communicated by O. Kinne, Oldendorf/Luhe     

Genetic differentiation in three Sepia species (Mollusca: Cephalopoda) from Galician waters (north-west Iberian Peninsula)

The systematics of the genus Sepia is not yet clear. Morphological evidence has led to S. officinalis Linnaeus, 1758 being considered as belonging to the subgenus Sepia sensu stricto, and S. orbignyana Férussac, 1826 and S. elegans Blainville, 1827 as belonging to the subgenus Rhombosepion. Samples of 30 individuals of S. officinalis and S. orbignyana from both sides of an oceanographic boundary off the north-west Iberian Peninsula, and a sample of S. elegans from the northern side, were collected in 1993–1994. Allozyme electrophoresis for 32 presumptive loci revealed low levels of genetic variability for the three Sepia species (mean expected heterozygosity estimates were <0.052). No significant differences in allozyme frequencies were detected among populations of either S. officinalis or S. orbignyana. The genetic identities (I) of S. officinalis and S. orbignyana (I=0.12) and of S. elegans (I=0.13) were significantly different from that of S. orbignyana and S. elegans (I=0.49). The former are typical of values for confamilial genera, and a new generic status is proposed for the latter two species, which become Rhombosepion orbignyana (Férussac, 1826) and R. elegans (Blainville, 1827).     

Ontogenetic changes in the retinal topography of the European hake, Merluccius merluccius: implications for feeding and depth distribution

Changes in the distribution pattern of cells in the ganglion cell layer were studied in the retina of the European hake, Merluccius merluccius (L.), to identify the possible adaptations of visual capabilities to different bathymetric distributions and feeding habits. From early juveniles to adults, the eye diameter increased eightfold; thus, retinal surface increased dramatically with size also. In early juveniles the retinal topography of the cells in the ganglion cell layer showed a concentric arrangement with respect to the centre of the retina. Two specialised areas were found, located at the ventral and dorso-rostral periphery, where the cell density reached 47,900 cells mm^-2, which corresponds to a theoretical visual acuity of 21' (minutes of arc). The visual axes were located upwards and downwards at around 80° from the geometric centre of the retina. In juveniles, the retina underwent important changes as the concentric topographic pattern transformed: the ventral specialised area progressively disappeared, the dorso-rostral area relocated to a rostral position and a new specialised area formed in the temporal retinal region. The visual axes were directed forward and backward. For fish with a total length of 12 cm or more, a horizontal visual streak formed along the rostro-temporal axis of the retina and a new specialised area was formed in the temporo-central region of the visual streak. In adults, acute vision could be identified with the two specialised areas at the temporal and rostral periphery, where the ganglion cell density peak decreased to 3,200-3,600 cells mm^-2 and the resolving power increased to 10'. As visual acuity is partially dependent on the cell types in the ganglion cell layer, cell populations in this layer were distinguished into either ganglion cells or displaced amacrine cells, using morphometric and histological criteria. The proportion of displaced amacrine cells was fairly uniform throughout the retinal surface, always representing between 32% and 39% of all cells in early and advanced juveniles. Only in adults did their density increase to 50%, probably as an adaptation to low light levels, which fish encounter as their distribution increases in depth. A small population of giant ganglion cells was also present in the retina. In the young and adult retinae, they represented 1.2% and 2.7% of the total cell population, respectively. Therefore, it has been shown how in M. merluccius the retinal topography undergoes important changes in relation to varying environmental demands.     

Fluoride Concentration in Drinking Water in The Province of Soria (Central Spain) and Caries in Children

The fluoride content in the water supply of the Soria province is not normally above 0.2mg L^–1 and its geographical distribution is related to the lithological and geological features of the zone, the highest concentration being associated with the Miocene clay formation of the Almazán Basin.A statistical analysis confirms a connection between this fluoride content and tooth decay among children in rural areas. However, other factors such as oral hygiene and diet have been found to affect tooth decay.     

Comparative growth and mortality of Bonamia ostreae -resistant and wild flat oysters, Ostrea edulis, in an intensive system. I. First year of experiment

Since the early nineteen-seventies, the parasitic protozoans Marteilia refringens and Bonamia ostreae have consistently deleteriously affected the French production of Ostrea edulis (Linné). Purification and inoculation of B. ostreae that were achieved in the late nineteen-eighties allowed a selection program to be initiated. Two O. edulis strains, S85 and S89, were raised that displayed significant resistance to B. ostreae in the field. Growth was monitored to ensure that the resistant strains grew at a rate comparable to that of controls, using two crosses between the first generation of S89 and the second generation of S85 (G1G2), and between the first generation of S89 and wild oysters (G0G1). Growth and mortality were monitored for seven consecutive months in an intensive open circulating system at the IFREMER station of Bouin (Vendée, France). A Chapman-Richards model of growth revealed that the two “resistant” crosses grew significantly better than two controls from Quiberon Bay (Brittany), an area in which B. ostreae is endemic, and Palavas (Mediterranean Sea), where oysters are less infested by this parasite. The asymptotic values for growth curves ranged between 27.2 and 28.2 g for G1G2 and G0G1 vs 21.0 and 22.8 g for the controls. There was a similar trend in mortality, with G1G2 (11.8%) surviving better than the three other populations (from 28.7 to 57.5%). B. ostreae was not detected during the experiments and mortalities were attributed to feeding conditions that were not optimal, reinforced by gametogenesis and high temperatures during the summer. It is suggested that the better performance of G1G2 and G0G1 resulted from their increased resistance to stress. Received: 10 March 1997 / Accepted: 4 August 1997     

Determination of canthaxanthin in the red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>) from Marseille by HPLC combined with UV and MS detection

Corallium rubrum is the most famous and precious coral due to the intense characteristic red colour of its skeleton. We have determined the presence of carotenoids in natural samples of C. rubrum from Marseille, Riou, and investigated their chemical composition. Analysis was performed both on soft tissues and hard tissues including spicules and skeleton. Since hard tissues are made of a mineral fraction and an organic fraction obtained after demineralization, extraction was performed both with and without demineralization by EDTA. The extracts were analyzed by complementary methods of TLC, HPLC/DAD and HPLC/MS. The components were separated by RP-18 chromatography column using acetonitrile/methanol for HPLC/DAD and acetonitrile/water gradient for HPLC/MS analysis. Our results give the first evidence of the presence of canthaxanthin, 4,4′-diketo-β-carotene, as the major carotenoid in all samples. Spicules exhibited higher content in carotenoids than skeleton. Demineralization treatment improved the efficiency of carotenoid extraction by an average factor of 5 and showed that organic matrix contains canthaxanthin.     

On the gains of committing to inefficiency: Corruption, deforestation and low land productivity in Latin America

We present a new explanation and empirical evidence showing that rural subsidies to large farmers tend to be associated with low land productivity and excessive deforestation. We develop a lobbying model where wealthy farmers trade bribes or political contributions to government politicians in exchange for subsidies; farmers are able to tilt the terms of the bargaining game with policy makers in their favor by pre-committing to an inefficient choice of semi-fixed inputs. Government proneness to accept political contributions or bribes and its willingness to provide subsidies cause farmers to adopt inefficient modes of production as a mechanism to capture such subsidies. Our predictions are consistent with stylized facts on land use in Latin America, and suggest that subsidy schemes have been counterproductive—distorting and constraining development, and triggering excessive depletion of natural resources. We validate some of the predictions of the model through econometric analyses using a new data set for nine countries in Latin America.     

Larval fish assemblages in Independencia Bay,Pisco, Peru: temporal and spatial relationships

The structure of the larval fish assemblages in Independencia Bay on the coast of Peru was examined using a combination of univariate and multivariate techniques. The plankton of Independencia Bay was sampled during 2000, to ascertain ichthyoplankton composition, abundance, and seasonality. These data were used to assess the function of the bay as spawning and nursery grounds and were related to the regional oceanography. In total, 16,156 fish larvae, representing 34 families, 48 genera, and 48 species were collected. Engraulidae, Normanichthyidae, Blenniidae, Gobiesocidae, Haemulidae, Labrisomidae, Pinguipedidae, and Atherinidae comprised 96.8% of the larvae captured; the remaining 3.2% included 26 families. Greatest mean larval fish densities, 319–1,381 per 100 m³, were recorded between September and November, suggesting a major spring spawning period. The most abundant fish larvae during this period were preflexion stage mote sculpins (Normanichthyidae) and newly hatched and preflexion stage anchovies (Engraulidae). A second, smaller summer peak was dominated by preflexion stage anchovies, followed by preflexion stage mote sculpins. The occurrence of high larval fish densities and the wide range of larval stages suggest that Independencia Bay is a regionally important spawning and nursery ground for marine fish. The principal component analysis showed that temperature and salinity were the dominant variables within the first two principal components, which accounted for 74.4% of the variation in environmental conditions. These conditions varied over time, station, and depth; however, interaction terms could not clearly be identified. Fitting a multinomial logistic model showed that larval fish assemblages and environmental conditions were associated in a complex way. The spring and summer ichthyoplankton abundance peaks in Independencia Bay coincided with high zooplankton standing stock and also coincided approximately with the periods of increased upwelling in the area.Communicated by O. Kinne, Oldendorf/Luhe