Márcia Regina Denadai

Along‐ and across‐shore components of the spatial distribution of the clam Tivela mactroides (Born, 1778) (Bivalvia, Veneridae)

Beach clam fisheries often provide an alternate income for traditional fishermen, but this activity is highly vulnerable to urbanization of coastal areas. Tivela mactroides is a beach clam commonly harvested in the Caribbean (Venezuela) and on the south‐eastern Brazilian coast. Only localized records on its spatial structure in size and abundance are available to support management of this clam. The present study showed that the spatial distribution in abundance and size of T. mactroides in Caraguatatuba Bay, state of São Paulo, Brazil, has both along‐ and across‐shore (intertidal and subtidal) components. The nature of this distribution should be taken into account in the design of further population or monitoring studies concerning this species. Clam density varied along‐shore, with a tendency towards higher numbers of individuals in the stations near the northern side of river mouths of this bay. Lower densities were related to the occurrence of sea‐stars and sand‐dollars. The intertidal and subtidal across‐shore distribution of clam abundance and size varied between and within areas (southern and northern). The individuals from the southern area were concentrated at intermediate tidal levels (0.2–0.6 m in relation to mean low water), whereas in the northern area the clams were more homogeneously distributed. The uppermost limit of their distribution was 0.8 m (southern) and 0.4 m (northern), and an upwards tendency towards increased size was more evident in the northern area. In the subtidal, abundance and individual size tended to increase from the deepest (4.5 m) to the shallowest (0.5 m) levels only in the southern area. Individual clams in the northern area tended to be smaller and more abundant than in the southern area. The species had an ontogenic distribution: small‐sized individuals were recorded only in the subtidal. Possible causes for these patterns and for the differences between areas (human exploitation, organic pollution, beach morphodynamics, differential recruitment, and adult–larvae interactions) are discussed, and specific studies are suggested to evaluate formally the proposed hypotheses.

Levantamento de Mollusca, Crustacea e Echinodermata associados a Sargassum spp. na Ilha da Queimada Pequena, Estacao Ecologica dos Tupiniquins, litoral sul do Estado de São Paulo, Brasil

This work represents the first effort to assess the phytal macrofauna of Queimada Pequena island and was focused in mollusks, crustaceans and echinoderms associated to Sargassum spp. Sampling of the macrofauna was performed by random collections of 6 Sargassum fronds 6 m deep using SCUBA. The fronds were sealed underwater in individual 200 mm mesh bags and detached from the rocky shore. The samples were preserved in recipients in 10% formalin and carried to the laboratory to remove and identify the associated fauna. Forty one taxa were registered, with dominance of peracarid crustaceans. Mollusk composition is different from that of northern Sao Paulo coast. From the sixteen mollusk species recorded, only the gastropod genera Anachis and Odostomia and the bivalves Musculus and Modiolus were recorded in the Sargassum macrofauna at both coastal regions of Sao Paulo state, although the genus Fissurela had already been recorded at Santos region associated with the alga Amphiroa fragilissima. The occurrence of the exotic bivalve Isognomon bicolor was also confirmed. Our data suggest differences in the composition of molluskan fauna between southern and northern coasts of the state. Extensive investigations are necessary to confirm these results and to support management strategies in this conservation unit.

Structure of molluscan assemblages in sheltered intertidal unconsolidated environments

A malacofauna de 13 ambientes oceânicos, protegidos, entremares e nao-consolidados e sua relacao com os fatores abioticos foram estudados com o intuito de conhecer a riqueza de especies e compreender o papel dos fatores abioticos na estruturacao das associacoes. Quatro tipos distintos de ambiente entremares foram reconhecidos com base nos descritores da comunidade (diversidade, riqueza e densidade) e nas caracteristicas abioticas. O tamanho medio do grao de areia (em phy) e a inclinacao da praia mostraram uma relacao negativa com a diversidade, riqueza e densidade. Sedimentos grossos foram favoraveis a fauna de moluscos nas areas estudadas, contrastando o bem conhecido efeito negativo deste tipo de areia sobre a fauna em praias oceânicas tipicas. Os terracos de mare baixa, tipicos de areas dominadas pela mare, e a presenca de estruturas biogenicas, tais como fragmentos rochosos e cascalho, estiveram tambem associados aos altos valores de riqueza. O grande numero de especies registrado na area estudada como um todo parece ser uma consequencia direta desta heterogeneidade ambiental, uma vez que esta e composta por tipos de ambientes altamente distintos.

Seasonality, Dietary Overlap and the Role of Taxonomic Resolution in the Study of the Diet of Three Congeneric Fishes from a Tropical Bay

Not only seasonality but also taxonomic resolution of prey categories has been shown to affect diet studies. We analyzed the stomach contents of three sympatric species, Stellifer rastrifer, S. brasiliensis and S. stellifer, sampled monthly from August 2003 to October 2004 in Caraguatatuba Bay, southeastern Brazil. General characteristics and similarities among their diets were evaluated by considering high taxonomic ranks of all prey groups, and also the lower taxonomic ranks of the main prey groups. Dietary similarity was relatively high among species and low between seasons, and both evaluation criteria gave the equivalent results. The rare items, however, provided information about resource partition, and the species compositions of the most important groups were apparently good indicators of food availability.

Life history of three catfish species (Siluriformes: Ariidae) from southeastern Brazil

Este estudo teve como objetivo avaliar a distribuicao espaco-temporal, reproducao e dieta dos bagres Genidens genidens, G. barbus e Aspistor luniscutis na Enseada de Caraguatatuba. Seus tamanhos foram registrados e o sexo e o estagio reprodutivo identificados. A abundância foi comparada entre areas (sul e norte) e entre meses (agosto/2003 a outubro/2004). As especies tiveram distribuicoes espaciais distintas, permitindo sua coexistencia. A distribuicao temporal reflete sua tendencia por migrar no perioo reprodutivo, evidenciado pela dominância de individuos pequenos e imaturos na enseada. Houve uma tendencia de G. genidens reproduzir no inverno e A. luniscutis na primavera. G. genidens teve sua dieta constituida de crustaceos, moluscos (conchas), escamas de peixes, ostracodes e sifoes de bivalves. G. barbus revelou uma grande dominância por misidaceos, seguido por peixes (ossos e escamas). Para A. luniscutis, a dieta foi baseada em escamas de peixes e crustaceos. Grande quantidade de material orgânico particulado foi observado na dieta das especies, como ja conhecido para bagres estuarinos. O consumo de escamas de peixes pode refletir um habito lepdofagico. Pequena sobreposicao na dieta foi observada entre as especies, refletindo distincoes no ambiente como tambem nas proporcoes ingeridas de cada item.

Feeding habits of whitemouth croaker Micropogonias furnieri (Perciformes: Sciaenidae) in Caraguatatuba Bay, southeastern Brazil

Abstract This study examined the feeding habits of Micropogonias furnieri in Caraguatatuba Bay. Samples were collected monthly between May 2003 and October 2004 by trawling in two areas (southern and northern parts of the bay). The fish were measured and their stomach contents identified. The abundance was compared between areas and among months. M. furnieri was more abundant in the southern area and in the spring of 2003. The population was dominated by small immature individuals. This species had a varied diet, feeding on crustaceans, bivalve siphons, and polychaetes. The ingestion of bivalve siphons may be an opportunistic behavior, due to the presence of a large bank of the bivalve Tivela mactroides in the study area. The high proportion of unidentified organic matter in the stomach corroborates published reports that this species eats continuously and has rapid digestion. These results demonstrate that M. furnieri can be considered a carnivore, with a preference for benthic organisms.

Population Dynamics and Diet of the Madamango Sea Catfish Cathorops spixii (Agassiz, 1829) (Siluriformes: Ariidae) in a Tropical Bight in Southeastern Brazil

The madamango sea catfish, Cathorops spixii (Siluriformes: Ariidae), is often among the most abundant fishes on the South American Atlantic coast. In the present study, conducted in shallow, non-estuarine coastal areas of Caraguatatuba Bight in southeastern Brazil, collections of this species, the most abundant member of the ichthyofauna, included primarily medium-sized individuals, indicating that the area may play a specific role in their development. Although studies of the local ichthyofauna have been much neglected, the area is economically important and its ecological significance is undervalued. This study primarily treats habitat use by C. spixii, assessing certain population parameters and the dietary composition. Monthly samples were taken from August 2003 through October 2004, with three trawls in two areas, corresponding to depths of about 1 to 4 m. The catfish showed two main peaks of abundance in the area, in April/May and July 2004. A mode around 9 cm SL persisted through time, and the entrance of younger recruits peaked from January to April. The low estimate for body-growth parameters (K = 0.16) corroborates some K-strategist characteristics of the species. The asymptotic length was 27.3 cm SL and total mortality (Z) was 1.01 yr−1. Cathorops spixii showed an omnivorous feeding habit, preying mainly upon polychaetes, copepods and bivalves, with considerable seasonality in its diet.

Reproductive cycle of the trigonal clam Tivela mactroides (Bivalvia, Veneridae) in Caraguatatuba Bay, southeastern Brazil

Abstract Tivela mactroides is an important fishery resource for local artisanal fishermen in Brazil and the establishment of management programmes for this species requires information about its reproductive cycle, the main focus of this study. The reproductive pattern of T. mactroides from Caraguatatuba Bay on the southeast coast of Brazil was analysed by means of histological techniques from November 2003 to October 2004. The species had heterogeneous continuous gametogenesis, with no resting period and the sex ratio did not differ significantly from 1:1. Maturity indices varied over the months, with slightly higher proportions of mature gametes from May 2004 to October 2004, which indicates a high proportion of spawning in winter and spring; however, small releases of gametes may also have occurred during summer and autumn. As the reproductive cycle is heterogeneous and temporal seasonality in gametogenesis is not predictable, it is not possible to designate a closed fishing season for the present population as a management strategy to avoid overexploitation.

Population biology of the barbel drum Ctenosciaena gracilicirrhus (Metzelaar, 1919) (Perciformes: Sciaenidae) in Caraguatatuba Bay, Southeastern Brazil

Este estudo levantou dados sobre a biologia populacional de Ctenosciaena gracilicirrhus (Perciformes: Sciaenidae) em uma regiao costeira rasa, nao-estuarina, do sudeste do Brasil. Amostras mensais foram realizadas de outubro de 2003 a outubro de 2004, em duas areas distintas e similares, com variacao batimetrica de 1-4 m. A especie esteve, em geral, entre os peixes mais abundantes. No entanto, sua densidade foi significativamente maior em um unico mes e area, maio de 2004 na area sul. O fato pode ser explicado pelo seu comportamento migratorio e uma preferencia por regioes mais profundas. Esse comportamento pode levar a vieses em estudos de comunidade ictiica que usam poucas amostras, ou apenas amostras sazonais. Individuos de C. gracilicirrhus de 4,0 a 10,2 cm de comprimento total foram amostrados, apresentando uma moda principal de 7,5-9,0 cm e uma reducao significativa do tamanho de junho de 2004 em diante. As estimativas de parâmetros de crescimento foram comprometidas pelas caracteristicas peculiares da populacao no local. De forma semelhante, a identificacao das presas foi comprometida devido ao elevado nivel de deterioracao do conteudo estomacal. Foi possivel concluir, entretanto, que os crustaceos foram nitidamente os itens mais importantes ingeridos. Amphipoda mostrou ser o unico subgrupo identificavel, principalmente devido a construcao de tubos.

Non-linear curve adjustments widen biological interpretation of relative growth analyses of the clam Tivela mactroides (Bivalvia, Veneridae)

Evaluation of relative (allometric) growth provides useful information to understand the development of organisms, as well as to aid in the management of fishery-exploited species. Usually, relative growth analyses use classical models such as the linear equation or the power function (allometric equation). However, these methods do not consider discontinuities in growth and may mask important biological information. As an alternative to overcome poor results and misleading interpretations, recent studies have suggested the use of more complex models, such as non-linear regressions, in conjunction with a model selection approach. Here, we tested differences in the performance of diverse models (simple linear regression, power function, and polynomial models) to assess the relative growth of the trigonal clam Tivela mactroides, an important fishing resource along the South American coast. Regressions were employed to relate parameters of the shell (length (L), width (W), height (H) and weight (SW)) among each other and with soft parts of the organism (dry weight (DW) and ash-free dry weight (ASDW)). Then, model selection was performed using the information theory and multi-model inference approach. The power function was more suitable to describe the relationships involving shell parameters and soft parts weight parameters (i.e., L vs. SW, DW, and AFDW, and SW vs. DW). However, it failed in unveiling changes in the morphometric relationships between shell parameters (i.e., L vs. W and H; W vs. H) over time, which were better described by polynomial functions. Linear models, in turn, were not selected for any relationship. Overall, our results show that more complex models (in this study polynomial functions) can unveil changes in growth related to modifications in environmental features or physiology. Therefore, we suggest that classical and more complex models should be combined in future studies of allometric growth of molluscs.