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.

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.

Several studies have used the abundance of ghost crabs (Ocypodidae) as an indicator of human impacts on sandy beaches. Such studies have used assessment of burrows, even if the ratio between the number of burrows and crabs might not be consistent across beaches over time. The activity period of crabs frequently mentioned in such studies is always assumed to be during daylight. The few published studies on the daily activity of OcypodeWeber, 1795 preclude generalizations. Our study assessed the activity of O. quadrataFabricius, 1787 over six 24-hour cycles, using the most affordable filming devices on a restricted-access beach, thus excluding the influence of observers and tourists. The number of individual crabs and the time spent outside the burrows were calculated for every ten minutes of filming. These variables were assessed for correlation to each other, tidal height, temperature, and time of day. Both activity variables were significantly related to tide height, regardless of temperature or time of day. Peaks of activity in O. quadrata occurred during both day and night, and were mostly influenced by circatidal rhythms.

The Amazon region is one of the Earth’s hotspots of biodiversity and has a pivotal role in climate regulation. Yet, little is known about its coastal biodiversity. Here, we performed the first assessment of macrobenthic diversity and ecological patterns of sandy beaches north of the Amazon River delta, the world’s largest freshwater input into the oceans. By assessing spatial and temporal changes in the soft-bottom biodiversity and environmental variables of three beaches (Goiabal, Nazaré, and Sumaúma) in the northernmost stretch of the Brazilian coast, we found low richness (14 taxa, overall; Goiabal: 3.27 ± 1.78; Nazaré: 2.34 ± 1.29; Sumaúma: 2 ± 0.67) and diversity (Goiabal: 0.72 ± 0.52; Nazaré: 0.62 ± 0.46; Sumaúma: 0.55 ± 0.39) across 2949 individuals with great dominance of estuarine species (notably Nephthys fluviatis and Sphaeromopsis mourei). Abundance was higher during rainy periods, and the same pattern was observed for richness and diversity in comparison to transitional periods, at least on Nazaré Beach. Environmental heterogeneity was reduced during rainy periods, resulting in a higher abundance of dominant species and lower beta diversity. Most species presented aggregated distribution at the upper intertidal zone, and changes in macrobenthic assemblages were linked to variations in rainfall and organic matter content in the sediment. Given the ecological uniqueness and the severe erosional process affecting the northern coast of the Amazon region, our results provide essential baseline knowledge to better understand the patterns and processes influencing its understudied biodiversity. We advocate that further studies expand our findings to support the conservation of this region.

The population biology, life history parameters and diet of the shorthead drum Larimus breviceps were assessed in Caraguatatuba Bight, a shallow non-estuarine environment. Two homogeneous areas, South and North, were selected, avoiding major sources of continental waters. Monthly from October 2003 to October 2004, three random samples were taken by trawling from 800 to 1600 m outward from the waterline. Larimus breviceps was the third most abundant species during the study period, and was considerably more abundant from February to May 2004. Smaller individuals were also more abundant during this period, which we therefore considered the main recruitment period of the species. The predominance of individuals of a limited size range (6–12 cm total length) seems to indicate that the area functions as a nursery for L. breviceps, sheltering late-juvenile individuals. This feature complicated the estimation of life history parameters, but by taking into account the peculiarities of the area and the identification of similar modal progressions during the sampling period, we obtained reasonable values for the parameterization of the von Bertalanffy Growth Model (L_∞ = 32.25 cm, K = 0.72, t_max 4.38 y, Z = 12.104). The total mortality index does not reflect mortality rates only, but also the migration of older individuals to other, probably deeper, areas. The diet was based mainly on Crustacea, specifically Decapoda shrimps, with slight seasonal alterations.