Macrofauna of sheltered and pocket beaches located in embayments, estuaries or landward of protective reefs has not been adequately assessed in beach ecology. In this setting, the concurrent role of large‐scale morphodynamics and wave‐exposure gradients in shaping biological patterns is still uncertain. To examine variations in community descriptors and the influence of physical factors on macrofauna, 12 sandy beaches on five islands within Sepetiba Bay (SE Brazil) were characterized in terms of beach morphodynamics and dimensions (length and width), such as geographical position relative to the bay mouth. A total of 80 species were collected and identified. Community descriptors of macrofauna responded to morphodynamics and exposure gradients. Increases in species richness, and abundance, from harsh reflective (coarse sands, steep slopes) to benign dissipative (fine sands, gentle slopes) beaches, and from the bay mouth (exposed beaches) towards the inner bay (sheltered beaches) were observed. Mollusks were the most abundant macrofaunal group, followed by crustaceans and polychaetes. Crustaceans dominated the beaches near the bay mouth, whereas mollusks were more abundant on the beaches farther from the bay mouth. Canonical correspondence analysis showed that the degree of exposure, distance from the bay mouth, beach index, and beach length and width significantly affected the macrofauna distribution and abundance, creating an environmental gradient along Sepetiba Bay. Differences in macrofauna composition among the beaches studied were associated with beach length and width. In this sense, spatial variation of macrofauna among beaches can be a function of intertidal area. These results indicate that community characteristics in the sandy beaches studied are affected by several physical characteristics, but also by other factors that are affected by coastal processes.

Aim: While geographical patterns of species richness are reasonably well explored for single wellstudied taxa, less is known about aggregate patterns of total richness for major biomes and their environmental correlates. Here we analyse continental-scale aggregate patterns of macrofaunal diversity for sandy beaches, a dominant habitat along the Atlantic and Pacific coasts of South America.Location: South American coastlines.Time period: Present day (data amassed from studies performed since 1971).Major taxa studied: Benthic macrofauna, including crustaceans, polychaetes and molluscs.Methods: We compiled richness information for all macrofaunal groups on 263 sandy beaches in South America using standard criteria. We further matched these data with environmental variables including sea surface temperature (SST), chlorophyll a, grain size, beach slope, tide range and various morphometrics. We used generalized linear mixed models to relate environmental factors to observed variation in total macrofaunal richness across all beaches, testing competing hypotheses about environmental correlates and possible drivers of latitudinal diversity.Results: Macrofaunal richness decreased from tropical to temperate beaches in the Pacific and followed a parabolic trend in the Atlantic, with the highest biodiversity found at tropical and midlatitudinal bands. Beach slope, tidal range and chlorophyll a mostly explained latitudinal trends in macrofaunal richness, followed by grain size, SST and ocean basin.Main conclusions: This study indicates that richness of macrofaunal species at a given beach is most closely related to characteristics of the physical habitat, such as beach slope, area and grain size. At this scale, planktonic food supply also appeared to be more important than temperature, which is a dominant explanatory variable of global-scale variation in species richness. K E Y W O R D S benthic macrofauna, environmental correlates, latitudinal diversity, macroecology, sandy beaches, South America

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