Revista Chilena de Historia Natural 79 (3): 337-351, 2006
RESEARCH ARTICLE
Algal wrack deposits and macroinfaunal arthropods on sandy beaches of the Chilean
coast
Four Chilean sandy beaches were sampled during the summer of 2000, to study the role
of stranded algal wrack deposits on the population abundances of three detritus feeder species of the macroinfauna that inhabit the
upper shore levels of that beaches: the talitrid amphipod Orchestoidea tuberculata Nicolet, the tylid isopod Tylos
spinulosus Dana and the tenebrionid insect Phalerisida maculata Kulzer. The beaches were Apolillado (ca. 29°S),
Quidico (ca. 38°S), Guabún and Mar Brava (ca. 42°S). Replicated samples were collected with a plastic cylinder (25 cm in diameter)
from algal wrack deposits including the sediments beneath the wrack and nearby bare sand areas. Samples were collected at two
beach levels, one closer to the sea with fresh deposits and other located on the upper beach with dry alga. Algal wrack deposits were
mostly composed of the brown algae Macrocystis pyrifera (L.), Durvillaea antarctica (Chamisso) Hariot and
Lessonia nigrescens Bory. O. tuberculata was found in the algal wrack deposits and bare sands collected
from Apolillado, Quidico, Guabún and Mar Brava. On the other hand, T. spinulosus was just found at Apolillado, while
P. maculata occurred in the sands beneath algal wrack deposits and bare sands collected from Apolillado, Quidico and
Guabún. In general, the mean abundances of O. tuberculata, P. maculta and T. spinulosus
were significantly higher in those samples collected from sands beneath algal wrack deposits; i.e., 56, 61 and 14 times higher
(overall means) than in bare sands, respectively. It is concluded that stranded algal wrack deposits indeed promote an increase in
population abundances of sandy beach detritus feeders, either because that deposits provide their main food source or shelter against
variable environmental conditions (e.g., air temperature and humidity) during daylight hours. That might well explain the patchiness
shown by these organisms, either across or along shore. This conclusion has important implications for sampling design of sandy
beaches characterized by high inputs of algal wrack deposits.
Key words:
algal wrack deposits,
sandy beach arthropods, Chilean coast
