Burrowing activity of the Neohelice granulata crab (Brachyura, Varunidae) in southwest Atlantic intertidal areas

espanolEl cangrejo cavador y semiterrestre Neohelice granulata construye sus cuevas activamente y constantemente en la zona inter-mareal del estuario de Bahia Blanca durante la marea baja. Se analizaron diferencias en la morfologia estructural de las cuevas y la actividad excavadora de N. granulata en microhabitats contrastantes (marisma y planicie de marea) y se relacionaron con diversas condiciones, como el nivel de las mareas, el tipo de sustrato, las propiedades del sedimento y la densidad poblacional. En la planicie de marea la mayor densidad de cuevas totales en el otono (172 cuevas·m–2) se relaciono con el fenomeno de muda, y la mayor densidad de cuevas activas durante el verano (144 cuevas·m–2) se relaciono con la migracion reproductiva. Los sedimentos de los monticulos biogenicos (removidos por cangrejos) presen-taron mayor contenido de agua y penetrabilidad que los sedimentos superficiales (control), lo cual sugiere que la bioturbacion incrementa los valores de estos parametros. La granulometria y mineralogia no variaron entre los microhabitats ni entre las estaciones. Todas las cuevas presentaron forma de tunel y solo aquellas provenientes de la marisma presentaron camaras dentro de los tuneles, posiblemente usadas con propositos reproductivos. Las cuevas de la marisma exhibieron entradas angostas y tuneles profundos, y las de la planicie de marea presen-taron entradas muy angostas y tuneles superficiales. Se confirmaron diferencias en las caracteristicas de las cuevas y en la actividad excava-dora de N. granulata entre los distintos ambientes y se relacionaron con los factores bioticos y abioticos, lo cual indica que esta especie tiene un comportamiento excavador adaptativo. EnglishThe burrowing and semiterrestrial crab Neohelice granulata actively and constantly builds its burrows in the intertidal zone of the Bahia Blanca Estuary during low tide. Differences in structural morphology of N. granulata burrows and burrowing activities in contrasting microhabitats (saltmarsh and mudflat) were analyzed and related to several conditions, such as tide level, substrate type, sediment properties, and population density. In the mudflat the higher density of total burrows in autumn (172 burrows·m–2) was associated with molt timing, and the higher density of active burrows in summer (144 burrows·m–2) was associated with reproductive migration. Sediments from biogenic mounds (removed by crabs) showed higher water content and penetrability than surface sediments (control), suggesting that bioturbation increases the values of these parameters. Grain size distribution profiles and mineralogical composition did not vary between microhabitats or between seasons. Burrows were all tunnel-shaped and only those from the saltmarsh had chambers inside the tunnels, possibly used for reproductive purposes. Burrows from the saltmarsh had narrow entrances and deep tunnels, and burrows from the mudflat presented very narrow entrances and surface tunnels. Differences in burrow features and burrow activity of N. granulata between microhabitats were confirmed and associated with biotic and abiotic factors, indicating that this species has an adaptive burrowing behavior.