Revista Chilena de Historia Natural 76 (4): 543-561, 2003
RESEARCH ARTICLE
Population abundances, growth and natural mortality of the crustacean macroinfauna at two
sand beach morphodynamic types in southern Chile
Monthly samplings were carried out during 1994-1996 at an intermediate and at a sandy
beaches of southern Chile (Calfuco and Mehuín, respectively; ca. 39º S), to evaluate the predictions of the swash exclusion hypothesis
on the population abundances and life history of the crustacean macroinfauna inhabiting the intertidal of that beaches. It is
hypothesized that only true intertidal species (i.e., that directly affected by the swash) will be affected by differences in beach
morphodynamic types. That species were the cirolanid isopods Excirolana braziliensis and Excirolana hirsuticauda
and the anomuran crab Emerita analoga. On the other hand, the almost supralittoral amphipod
Orchestoidea tuberculata should not be affected by differences in beach morphodynamic types. The total population
abundances of O. tuberculata and E. analoga were significantly higher at the intermediate beach of Calfuco,
that of E. braziliensis and E. hirsuticauda at the dissipative beach of Mehuín. While the
abundances of ovigerous females of O. tuberculata and E. analoga were higher at Calfuco, that
of the ovigerous females of E. braziliensis and E. hirsuticauda did not differ between beaches.
Juveniles of O. tuberculata had higher abundances at Calfuco, while that of the other species peaked at Mehuín. The
reproductive period of amphipods and isopods peaked at the same spring-summer months at both beaches. E. analoga
also reproduced during springsummer months, but their abundances peaked at different months. While juveniles of O.
tuberculata peaked at similar times at both beaches, those of Excirolana braziliensis and E.
hirsuticauda peaked later at Mehuín. Juveniles of E. analoga had very low abundances during the first spring
summer period of this study; during the second one they peaked at the same month (October) at both beaches. The growth curves
and growth parameters of O. tuberculata, E. braziliensis and E. hirsuticauda did not
differ significantly between beaches, even when O. tuberculata tended to growth faster at Calfuco. The growth curves and
growth parameters for E. analoga were different only for females, which had higher growth at the dissipative site. The
natural mortality of the four species showed no significant differences between beaches. Thus, most of the results of this study do not
support our hypothesis, suggesting that other factors, apart from beach morphodynamics are important in explaining spatial variability
in population abundances and population biology of the sandy beach macroinfauna.
Key words:
sandy beach
macroinfauna, crustaceans, beach morphodynamic types, southern Chile
