Carlos Werner Hackradt

Ichthyofauna composition across a wave: energy gradient on Southern Brazil beaches

Wave action in sandy beach surf zones and its influence on species composition were evaluated at three sites at Pontal do Parana, Parana State, between June/2004 and May/2005. At each sampling site, five hauls were performed monthly using a 15 m long, 2.6 m height beach seine with a 5 mm mesh-size. Samplings were carried out at low water spring tides during daylight. A total of 26,866 fishes were collected, amounting to a total weight of 84,838 kg, which were distributed amongst 28 families and 63 taxa. Multi- and univariated methods used indicated that sheltered and moderately exposed beach samples had similar ichthyofaunal composition, being clupeids and engraulids the most abundant at these beaches. Although abiotic factors differed significantly between beaches, depth appears to exert the major influence on ichthyofauna structure by providing less turbulent waters which might have permitted shoals maintenance. Conversely, exposed beach samples differed largely from the other beaches and were influenced primarily by wave height and salinity variables. These were displayed at CCA diagram and through the occurrence of P. virginicus, M. littoralis and T. goodei.

Diel and tidal variation in surf zone fish assemblages of a sheltered beach in southern Brazil

Diel and tidal variations of fish assemblages were assessed at Pontal beach, southern Brazil, using a seine net. Species richness was greater at night, whereas fish number, weight, and richness (community indicators) were all influenced by the tidal state. Samples from rising tides were more representative, probably due to onshore fish movements for feeding purposes. However, lower catches were associated with high tides, mainly through net avoidance, indicating that sampling in these conditions is not highly informative. Clupeoids exhibited greater variation in a 24 h period, and the night occurrence of A. tricolor and daylight shoaling of Harengula clupeola, Anchoa parva and Sardinella brasiliensis suggested distinct strategies for avoiding daylight predators. In some species, this behaviour may have been induced by the bottom morphology and tidal state, facilitating nearshore grouping. In addition to being caught at night, the occurrences of Menticirrhus littoralis, Pomadasys corvinaeformis, Umbrina coroides and Hyporhamphus unifasciatus indicated a spatial niche partition according to tidal state. Although not evaluated properly, temporal fluctuations could reflect species recruitment patterns. Seasonal fluctuations have to be considered when analysing short-term changes in the community as such fluctuations are synchronized with the natural history of the species, making it difficult to interpret short-term variations in isolation.

Factors influencing spatial patterns of the ichthyofauna of low energy estuarine beaches in southern Brazil

Estuarine beaches are low energy environments found along the coast in several protected places around the world, such as estuaries, bays or areas protected by submerged bars or coral reefs. Although common, these places have been poorly studied. Using a seine net, six beaches were sampled along an environmental gradient for 12 months. During this period, an increase of the dominant species following the increase in salinity and energy values was observed, whilst the opposite pattern occurred for species richness and abundance. Univariate and multivariate analyses showed spatial and temporal variations between beaches and months. Depth and marginal habitats appear to be more important factors than wave height and period, temperature, salinity and pH, which are normally used to describe fish habitat utilization patterns in beaches and estuaries. Nevertheless, specific sampling designs should be proposed to evaluate properly these questions.

Assembléia de peixes associados a ambientes consolidados no litoral do Paraná, Brasil: uma análise qualitativa com notas sobre sua bioecologia

Recentemente, estudos com peixes recifais vem recebendo cada vez mais atencao dos pesquisadores. Na costa brasileira cinco provincias zoogeograficas foram determinadas, sendo o Parana incluido na provincia sul-sudeste. Utilizando-se do censo visual sub-aquatico para acessar a fauna de peixes recifais, avaliou-se os ambientes naturais e artificiais. Observou-se que a heterogeneidade de ambientes na regiao configura diferencas na estrutura da ictiofauna influenciada pela matriz arenosa que envolve os ambientes artificiais e pelo efeito atrator destas estruturas evidenciado pela maior presenca de especies pelagicas, efeito diluido no entorno dos ambientes insulares avaliados. A aparente pobreza de especies, quando comparado com outros locais pertencentes a mesma provincia, pode ser efeito de um filtro biologico local ou apenas um reflexo da inexistencia de estudos na regiao.

Effect of marine protected areas on distinct fish life-history stages

The role of Marine Protected Areas on distinct life stages of Mediterranean reef fish species (classified on the basis of their economic value and mobility categories) was assessed in a network of marine reserves in SE Spain. Only abundance and biomass of adult of both commercial and demersal species were positively affected by protection. Gradients across reserve boundaries (as a clue to the occurrence of spillover) were observed for fish abundance but not for biomass, indicating a protected fish assemblage with a predominance of small-sized individuals. Also, post-larvae of commercial species were negatively related to protected zones. Active selection of settlement preferred habitats, larval accumulation favoured by the geomorphological configuration of the coast or mixed effects has been proposed as possible explanations. Juveniles showed high spatial variability resulting in a lack of response to fishing protection measures. We highlight the need of including early life stages and overall suitable habitats for them when designing MPA networks due to the crucial importance of these stages to successful fulfillment of MPA objectives.

Genetic diversity and gene flow of the threatened Brazilian endemic parrotfish Scarus trispinosus (Valenciennes, 1840)

The greenback parrotfish, Scarus trispinosus, is the largest herbivorous fish inhabiting Southwestern Atlantic reefs, and was recently included in the IUCN red list of threatened species as endangered due to the overexploitation of their populations. The aim of this work was to evaluate the existence of structured populations (i.e. genetic unities) along a coast of approximately 2000 km of the NE Brazilian coast. The transferability of 17 primers synthesized for Scarus rubroviolaceus was tested for S. trispinosus and five transferable loci were validated and used. Two localities within the Abrolhos Bank, off the Central Brazilian coast (Corumbau and Caravelas) and in close proximity to the MPA, which encompasses the largest remnants of the S. trispinosus population, exhibited higher levels of genetic richness. Remaining locations, Pernambuco, Porto Seguro and Rio Grande do Norte exhibited lower genetic diversity. We found no genetic differences among sampled localities however, when those samples were gathered into latitudinal groups (northern vs southern) a subtle but significant genetic substructuring was revealed. It is proposed that a combination of high local individual admixture favoured by habitat connectivity drived genetic homogeneity at regional scales while larval dispersal contributed to heterogeneities observed at large scales maintaining gene flow through oceanographic currents.