Maíra Pombo

Issues to be considered in counting burrows as a measure of Atlantic ghost crab populations, an important bioindicator of sandy beaches.

The use of indirect estimates of ghost-crab populations to assess beach disturbance has several advantages, including non-destructiveness, ease and low cost, although this strategy may add some degree of noise to estimates of population parameters. Resolution of these shortcomings may allow wider use of these populations as an indicator of differences in quality among beaches. This study analyzed to what extent the number of crab burrows may diverge from the number of animals, considering beach morphology, burrow depth and signs of occupation as contributing factors or indicators of a higher or lower occupation rate. We estimated the occupation rate of crabs in burrows on nine low-use beaches, which were previously categorized as dissipative, intermediate or reflexive. Three random 2-m-wide transects were laid perpendicular to the shoreline, where burrows were counted and excavated to search for crabs. The depth and signs of recent activity around the burrows were also recorded. The occupation rate differed on the different beaches, but morphodynamics was not identified as a grouping factor. A considerable number of burrows that lacked signs of recent activity proved to be occupied, and the proportions of these burrows also differed among beaches. Virtually all burrows less than 10 cm deep were unoccupied; the occupation rate tended to increase gradually to a burrow depth of 20–35 cm. Other methods (water, smoke, and traps) were applied to measure the effectiveness of excavating as a method for burrow counts. Traps and excavation proved to be the best methods. These observations illustrate the possible degree of unreliability of comparisons of beaches based on indirect measures. Combining burrow depth assessment with surrounding signs of occupation proved to be a useful tool to minimize biases.

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.

Population biology of Stellifer rastrifer, S. brasiliensis and S. stellifer in Caraguatatuba Bay, northern coast of São Paulo, Brazil

Os ecossistemas podem refletir mudancas ambientais em muitos aspectos, desde o enfraquecimento dos individuos ate alteracoes na composicao da comunidade. Do mesmo modo, os parâmetros populacionais podem fornecer indicacoes confiaveis de mudancas ambientais. Sciaenideos do genero Stellifer sao peixes geralmente muito abundantes e em suas populacoes e frequente a ocorrencia de duas ou mais especies simpatricas. No presente trabalho, a dinâmica populacional de tres especies de Stellifer do sudeste do Brasil foi avaliada. A amostragem ocorreu em aguas rasas das zonas marinhas da Baia de Caraguatatuba, de agosto de 2003 a outubro de 2004. As especies avaliadas foram Stellifer rastrifer (n = 3.183), S. brasiliensis (n = 357) e S. stellifer (n = 116). Os resultados mostraram que a area sob maior influencia continental tende a suportar um numero maior de individuos menores. Variacoes de tamanho ao longo do tempo foram semelhantes entre as especies e negativamente correlacionadas com o Krel, que apresentou flutuacoes suaves. De modo geral a distribuicao de frequencia de comprimento ficou concentrada entre 6,0 e 9,0 cm e para a grande maioria das femeas as gonadas se apresentaram imaturas durante o periodo avaliado. Os resultados suportam a existencia de estratificacao populacional por tamanho dentro destas especies, indicando que a area e apropriada para o desenvolvimento de juvenis. A desconsideracao de tais caracteristicas pode acarretar serias implicacoes para a gestao dessas areas.

Harvesting the Beach Clam Tivela mactroides: Short- and Long-Term Dynamics

Abstract Small-scale fisheries are frequently overlooked for research and management, and their social and environmental impacts are often overlooked as well, preventing the implementation of appropriate actions for their sustainability. Additionally, the dynamics of beach clam fisheries and their importance for local communities are not well understood. A study on the population biology of the clam Tivela mactroides in Caraguatatuba Bay, southeastern Brazil, revealed intense harvesting of this resource by both residents and tourists. To assess the extent and dynamics of clamming, the number of harvesters was recorded during the course of the day in vacation and nonvacation periods throughout 2003–2005 and 2007–2008; the number of other beach users, weather conditions, and tide height were also recorded. The overall amount of clams harvested was estimated based on censuses of clammers and interviews to calculate the amount of clams harvested per collecting event. The intensity and dynamics of the harvesting activity varied on all the temporal scales evaluated. The estimated amount of clams harvested per year decreased from the first (24.6 kg/year) to the second (8.8 kg/year) group of sampling years, presumably due to clam mass-mortality events and smaller shell sizes in 2007–2008, although clam abundance increased enormously. Vacation periods (presence of tourists) influenced the number of harvesters and the daily dynamics of clamming activity, although this relationship was only evident during 2003–2004. The number of harvesters increased with the number of tourists, except in periods of very high tourist activity, when harvesting decreased. Clamming was more widespread during the day under high tourist activity but during nonvacation times was concentrated in morning low-tide periods. Weather had a partial influence on clamming, with harvesters absent only during intense rain occasions. The understanding of the dynamics of this Tivela mactroides fishery highlights key points for planning and implementing management measures, which will involve continuous monitoring of stocks, harvesting, and food safety.

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.

Frequency, Magnitude, and Possible Causes of Stranding and Mass-Mortality Events of the Beach Clam Tivela mactroides (Bivalvia: Veneridae)

Stranding combined with mass-mortality events of sandy-beach organisms is a frequent but little-understood phenomenon, which is generally studied based on discrete episodes. The frequency, magnitude, and possible causes of stranding and mass-mortality events of the trigonal clam Tivela mactroides were assessed based on censuses of stranded individuals, every four days from September 2007 through December 2008, in Caraguatatuba Bay, southeastern Brazil. Stranded clams were classified as dying (closed valves did not open when forced) or dead (closed valves were easily opened). Information on wave parameters and the living intertidal clam population was used to assess possible causes of stranding. This fine-scale monitoring showed that stranding occurred widely along the shore and year-round, with peaks interspersed with periods of low or no mortality. Dead clams showed higher mean density than dying individuals, but a lower mean shell length, attributed to a higher tolerance to desiccation of larger individuals. Wave height had a significant negative relationship to the density of dying individuals, presumed to be due to the accretive nature of low-energy waves: when digging out, clams would be more prone to be carried upward and unable to return; while larger waves, breaking farther from the beach and with a stronger backwash, would prevent stranding in the uppermost areas. This ecological finding highlights the need for refined temporal studies on mortality events, in order to understand them more clearly. Last, the similar size structure of stranded clams and the living population indicated that the stranded individuals are from the intertidal or shallow subtidal zone, and reinforces the ecological and behavioral components of this process, which have important ecological and socioeconomic implications for the management of this population.

A new species of philichthyid copepod (Crustacea: Cyclopoida) parasitic on Stellifer spp. (Perciformes: Sciaenidae) from southeastern Brazil

A new species of copepod, Colobomatus stelliferi n. sp., belonging to the cyclopoid family Philichthyidae Vogt, 1877 is proposed based on female specimens collected from the mandibular canals of three species of sciaenid teleosts: Stellifer brasiliensis (Schultz) (type-host), S. rastrifer (Jordan) and S. stellifer (Bloch), collected in Caraguatatuba Bay, State of São Paulo, Brazil. The new species can be distinguished from its closest congeners by the absence of lateral processes in the genital somite, the presence of one cephalic process in the cephalosome and one pair of dorso-lateral processes on the fused pedigerous somites. This is the first species of Colobomatus Hesse, 1873 described as parasites of species of the teleost genus Stellifer.

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.

Ghost crab burrows simulation shows differential across-shore persistence

Ghost-crab abundance is often used as an indicator of sandy beach environmental quality. Most studies use an indirect approach, assuming a direct relationship between the number of burrows and individuals. We here hypothesized that burrows could remain open for different periods of time according to the beach strata. We performed a field manipulation to simulate burrows, with persistence of each one individually assessed over a month. Results succeeded in demonstrating a significant differential persistence of burrows among beach compartments (backshore, frontal dune, and coastal vegetation, i.e., in a landward oriented sequence), which can affect abundance estimates and are thus prone to overestimating larger size classes, which inhabit the landward limit of the species’ range of occurrence. We recommend that this information is taken into consideration in population studies, and encourage the development of similar studies over broader spatial and temporal scales.

Novel structure in sciaenid fish skulls indicates continuous production of the cephalic neuromast cupula

The presence of a conspicuous and frequent but never-described structure in the skull cavities of sciaenid fish was noted during population studies in an urbanized bay. The ultrastructure closely resembles the cupula of neuromasts, an organ associated with the perception of the environment in teleost fish. The bodies were recorded detached in both preserved and freshly sampled individuals and without associated cilia. Prominent characteristics are acellularity, the elliptic-conic shape composed of stack-like protein lamellas, and a mesh-like appearance in cross section. These acellular lamellar cephalic bodies (ALCBs) were more abundant in larger individuals and showed temporal peaks of abundance independently of the fish size. The conic and lamellar features suggest that the deposition of protein layers follows fish growth, and the bimodality of the size of these structures in individuals indicates temporal peaks of production. These results indicate that these ALCBs are a consequence of the accretion of the cupula of neuromasts at a faster rate than they degrade. Given the novelty of this structure and the increasing records of diseases of marine organisms worldwide, an important question is whether these bodies occur subsequently to some environmental change and whether their accumulation in the skull cavities has consequences to fish health.