MEPS 160:197-207 (1997)  -  doi:10.3354/meps160197

Variability of zonation patterns in temperate microtidal Uruguayan beaches with different morphodynamic types

Luis Giménez*, Beatriz Yannicelli

Facultad de Ciencias, Sección Oceanografía, Tristán Narvaja 1674, 11200 Montevideo, Uruguay
*Present address: Biologische Anstalt Helgoland, Meeresstation Helgoland, Postfach 180, D-27483 Helgoland, Germany

Early studies on sandy beach zonation patterns have shown rather rigid schemes. Recent work has suggested that zonation changes with morphodynamic type and, in dissipative beaches, it also changes through time. This last finding leads to the conclusion that at least 1 yr of study is necessary to understand zonation patterns in dissipative sandy beaches. Here we report a 1 yr study (from March 1994 to March 1995) of 4 microtidal beaches with different morphodynamic types situated on the Atlantic coast of Uruguay. We show that zonation patterns (number of zones or belts) can change through time regardless of beach type. However, the morphodynamic characteristics of the beach seem to affect how frequently the zonation pattern can change by fusion or subdivision of zones, and which zones are involved in those processes. In beaches with flat slopes (toward the dissipative extremity), the lower zones were frequently fused and divided. The same occurred with the medium and upper zones in the beaches with steeper slopes (towards the reflective extremity). Our results suggest that spatial variability of the macrofauna is related to variability in the position of the swash zone, which in turn depends on beach slope and width. Variability of species distribution would also depend on morphological adaptations of organisms to move in such environments. We suggest 2 mechanisms of species movement to explain the variability in species distribution observed in this study: Swash Mediated Active Movement (SMAM) and Autonomous Active Movement (AAM). The first mechanism involves both an active and a passive component. AAM is independent of swash movements and affects species distribution on the upper levels of the beach.

Sandy beaches · Seasonal variability · Zonation pattern · Morphodynamic types · Uruguay

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