The Sand Beach Ecosystem of Chile
225
absent from Chilean sandy beaches, even between closely related species
like Excirolana braziliensis and E. hirsuticauda (Jaramillo 1987a). Fishes
(Eleginops maclovinus) and birds, like the whimbrels (Numenius phaeopus) and sanderlings ( Calidris spp.), prey on Emerita analoga in the
swash zone of exposed beaches (Pequeno 1979), though predation does not
appear to regulate the abundance of the population. The adults of upper
shore species like 0. tuberculata and the tenebrionid beetle Phalerisida
maculata display similar patterns of nocturnal surface locomotor activity
(Jaramillo et al. 1980), probably to escape predation by visually feeding
shorebirds as well as to avoid desiccation at high temperatures and low
humidity during daylight. The slope and water content of the sandy substrate probably influence daily migrations between different beach zones
(Kennedy 1997).
15.4 Human Impacts
The surf clam Mesodesma donacium is the only invertebrate species widely harvested in the surf zone and the shallow subtidal area of exposed
sandy beaches between 19°S and 42°S (Tarifefto 1980). In some areas clams
("machas") are collected by divers behind the surf zone. However, clams
are mostly harvested during low tide by the fishermen ("macheros") who
use their feet and body weight to excavate the sand until clams come up to
the sediment-water interface. In north-central Chile {30°S), surf clams
reach commercial size (70 mm) after 4-5 years. The maximum size of
109 mm at an age of 15 years decreases to 86 mm from north-central Chile
to southern beaches at 37-38°5 (Alarcon 1979; Tarifefto 1980, 1984). Landing data suggest a significant decrease in clam fisheries from
12,000-17,000 tons in 1987/89 to about 6,000 tons during 1995-1997 due to
overexploitation.
The disposal of liquid and solid wastes along the Chilean coast has
increased over the years. Accidental oil spills and the deposition of mine
tailings have changed the zonation patterns of the intertidal macroinfauna
and caused a decrease in macroinfaunal species richness and abundance
(Castilla et al. 1977; Castilla 1983). Furthermore, Chilean sand beaches
represent an important recreational resource due to their proximity to
major urban centers. The mechanical disturbance of sands in the intertidal
area by beach visitors is common during the summer holiday season,
though it seems to have little effect on intertidal macroinfauna (Jaramillo
et al. 1996).
225
absent from Chilean sandy beaches, even between closely related species
like Excirolana braziliensis and E. hirsuticauda (Jaramillo 1987a). Fishes
(Eleginops maclovinus) and birds, like the whimbrels (Numenius phaeopus) and sanderlings ( Calidris spp.), prey on Emerita analoga in the
swash zone of exposed beaches (Pequeno 1979), though predation does not
appear to regulate the abundance of the population. The adults of upper
shore species like 0. tuberculata and the tenebrionid beetle Phalerisida
maculata display similar patterns of nocturnal surface locomotor activity
(Jaramillo et al. 1980), probably to escape predation by visually feeding
shorebirds as well as to avoid desiccation at high temperatures and low
humidity during daylight. The slope and water content of the sandy substrate probably influence daily migrations between different beach zones
(Kennedy 1997).
15.4 Human Impacts
The surf clam Mesodesma donacium is the only invertebrate species widely harvested in the surf zone and the shallow subtidal area of exposed
sandy beaches between 19°S and 42°S (Tarifefto 1980). In some areas clams
("machas") are collected by divers behind the surf zone. However, clams
are mostly harvested during low tide by the fishermen ("macheros") who
use their feet and body weight to excavate the sand until clams come up to
the sediment-water interface. In north-central Chile {30°S), surf clams
reach commercial size (70 mm) after 4-5 years. The maximum size of
109 mm at an age of 15 years decreases to 86 mm from north-central Chile
to southern beaches at 37-38°5 (Alarcon 1979; Tarifefto 1980, 1984). Landing data suggest a significant decrease in clam fisheries from
12,000-17,000 tons in 1987/89 to about 6,000 tons during 1995-1997 due to
overexploitation.
The disposal of liquid and solid wastes along the Chilean coast has
increased over the years. Accidental oil spills and the deposition of mine
tailings have changed the zonation patterns of the intertidal macroinfauna
and caused a decrease in macroinfaunal species richness and abundance
(Castilla et al. 1977; Castilla 1983). Furthermore, Chilean sand beaches
represent an important recreational resource due to their proximity to
major urban centers. The mechanical disturbance of sands in the intertidal
area by beach visitors is common during the summer holiday season,
though it seems to have little effect on intertidal macroinfauna (Jaramillo
et al. 1996).