Abstract:
Main trophic relationships that occur along the exposed sandy shores in southernmost Brazil
(,336 S) are established taking into account several biological compartments operating at
morphodynamically distinct environments. Beaches are predominantly of the intermediate type but
some stretches of coastline are truly dissipative (Cassino Beach) or tending-to-reflective (Concheiros
Beach), presenting thus diverse biological compartments and inhabitant macrobenthic assemblages.
Dense concentrations of the surf-zone diatom Asterionellopsis glacialis are responsible - at least for the
intermediate shorelines - for the most year-round primary production, sustaining several consumers up to
tertiary level. Among them, bivalves Amarilladesma mactroides, Donax hanleyanus and the hippid crab
Emerita brasiliensis can account for more than 95% of all the surf-zone secondary production, in addition
to the elevated biomass of the suspension-feeder polychaete Spio gaucha and the scavenger isopod
Excirolana armata. Crabs, whelks, carnivorous polychaetes, seabirds and surf-zone fishes may also be
present and occupy superior trophic levels depending on the beach morphodynamics. Based on the high
species richness, abundance and the role of macrobenthic fauna in transferring matter and energy to
seabirds and the surf-zone fish assemblages, we address this important issue on the Southwestern Atlantic
ecology. Conservation efforts should be implemented for the southernmost Brazilian sandy shores, at
least for those non urbanized areas.
As principais relac¸o˜ es tro´ ficas observadas ao longo da costa arenosa exposta do extremo sul do
Brasil (,336 S) sa˜o estabelecidas levando-se em considerac¸a˜o os va´ rios compartimentos biolo´ gicos que
operam em ambientes morfodinamicamente distintos. Estas praias sa˜o predominantemente do tipo
intermedia´ rio, embora alguns trechos sejam dissipativos (Praia do Cassino) ou apresentem tendeˆncias
reflectivas (Praia dos Concheiros), possuindo compartimentos biolo´ gicos diversificados e associac¸o˜es
macrobentoˆnicas residentes. Densas concentrac¸o˜ es da diatoma´cea Asterionellopsis glacialis sa˜o
responsa´ veis - pelo menos para as praias intermedia´ rias - por grande parte da produtividade prima´ ria
anual, sustentando va´ rios consumidores ate´ o nı´vel tercia´ rio. Entre estes, os bivalves Amarilladesma
mactroides, Donax hanleyanus e o crusta´ceo Emerita brasiliensis sa˜o responsa´ veis por mais de 95% de toda
a produc¸a˜o secunda´ ria da zona de surfe, em adic¸a˜o a` elevada biomassa do poliqueta suspensı´voro Spio
gaucha e do iso´pode necro´fago Excirolana armata. Caranguejos, gastro´ podes, poliquetas carnı´voros, aves
marinhas e peixes da zona de surfe tambe´m podem estar presentes, ocupando nı´veis tro´ ficos superiores
dependendo da morfodinaˆmica praial. Baseado na alta riqueza de espe´cies, na abundaˆncia e no papel da
macrofauna bentoˆ nica em transferir mate´ria e energia para as aves marinhas e as assemble´ias de peixes da
zona de surfe, esta importante questa˜o ecolo´ gica do Atlaˆntico Sudoeste foi investigada. Esforc¸os de
conservac¸a˜o devem ser implementados nas praias arenosas do extremo sul do Brasil, pelo menos naquelas
a´ reas na˜o urbanizadas.
