The Estuary Ecosystem of Buenaventura Bay, Colombia
269
dant echinoderms (i.e., the sand dollars Encope and Mellita), are common
in the lower intertidal (Cantera 1991).
18.3.2 Cliffs and Rocky Shores
The tectonic processes along the Pacific coast of Colombia have given origin to abundant steep cliffs (>45° slope) and to rocky shores with more
gently sloping platforms, composed of boulders, pebbles, and gravel from
cliff erosion. The slope, tidal- and wave-dependent dampening, substrate
characteristics, wave impact, pore water temperature and salinity, and
competition for space and food determine the species composition and
structure of cliff and rocky shore communities along the northern coast
and in the interior of Buenaventura Bay. As opposed to sand beaches, these
substrates display clear vertical zonation patterns with a diverse flora and
fauna and especially rocky shores are among habitats with particularly
high species diversity (Shannon diversity index 3.48-3.63 bits/ind.; Cantera 1991). Desiccation-tolerant blue-green and green algae and a lichen
inhabit the upper littoral (spray) zone of cliffs and rocky shores. The periwinkle Austrolittorina aspera is very abundant (115 ind. m- 2 ) and cooccurs with Littoraria zebra (3.6 ind. m- 2 ), the rock crab Grapsus grapsus
(2 ind. m- 2 ), and the isopod Ligia baudiana (28 ind. m- 2 ). About 20 species
occupy the upper intertidal zone where the periwinkle L. zebra
( 6.8 in d. m- 2 ) becomes increasingly abundant. The crab Pachygrapsus
transversus (14 ind. m- 2 ) is common on less wave-exposed cliffs, while
barnacles ( Tetraclita, Chthamalus ), limpets (Fissurellidae, Acmaeidae,
Siphonariidae), crabs (i.e. Grapsus grapsus), and some green algae occur
on exposed cliffs. The mid-intertidal zone is inhabited by 41 species and is
dominated by bivalves of the families Mytilidae (Brachidontes), Isognomonidae, and Ostreidae (oysters), which occur together with crabs of the
families Xanthidae (Eriphia squamata <1 ind. m- 2 ) and Grapsidae (Pachygrapsus transversus 12.0 ind. m- 2 ), as well as the red calcareous alga Lithothamnion. Apart from barnacles, anemones, and sponges, the gastropods
Acanthina brevidentata and Thais kiosquiformis and some crabs (i.e.
Pachygrapsus transversus) occur in the lower intertidal zone.
The outstanding feature of the lower intertidal is the increasing number
of perforations (up to 54.8% inside the bay and 60.2% outside the bay)
caused by abundant boring organisms. The dominant borers on protected,
soft limestone are bivalves of the families Pholadidae ( Cyrtopleura crucigera and Dyplothyra curta; up to 216.8 perforations m- 2 ) and Petricolidae
(Petricola denticulata; 132 perforations m- 2 ). Species of the family Mytilidae (Lithophaga aristata, L. plumula; 62.9 ind. m- 2 ) perforate hard conglo-
269
dant echinoderms (i.e., the sand dollars Encope and Mellita), are common
in the lower intertidal (Cantera 1991).
18.3.2 Cliffs and Rocky Shores
The tectonic processes along the Pacific coast of Colombia have given origin to abundant steep cliffs (>45° slope) and to rocky shores with more
gently sloping platforms, composed of boulders, pebbles, and gravel from
cliff erosion. The slope, tidal- and wave-dependent dampening, substrate
characteristics, wave impact, pore water temperature and salinity, and
competition for space and food determine the species composition and
structure of cliff and rocky shore communities along the northern coast
and in the interior of Buenaventura Bay. As opposed to sand beaches, these
substrates display clear vertical zonation patterns with a diverse flora and
fauna and especially rocky shores are among habitats with particularly
high species diversity (Shannon diversity index 3.48-3.63 bits/ind.; Cantera 1991). Desiccation-tolerant blue-green and green algae and a lichen
inhabit the upper littoral (spray) zone of cliffs and rocky shores. The periwinkle Austrolittorina aspera is very abundant (115 ind. m- 2 ) and cooccurs with Littoraria zebra (3.6 ind. m- 2 ), the rock crab Grapsus grapsus
(2 ind. m- 2 ), and the isopod Ligia baudiana (28 ind. m- 2 ). About 20 species
occupy the upper intertidal zone where the periwinkle L. zebra
( 6.8 in d. m- 2 ) becomes increasingly abundant. The crab Pachygrapsus
transversus (14 ind. m- 2 ) is common on less wave-exposed cliffs, while
barnacles ( Tetraclita, Chthamalus ), limpets (Fissurellidae, Acmaeidae,
Siphonariidae), crabs (i.e. Grapsus grapsus), and some green algae occur
on exposed cliffs. The mid-intertidal zone is inhabited by 41 species and is
dominated by bivalves of the families Mytilidae (Brachidontes), Isognomonidae, and Ostreidae (oysters), which occur together with crabs of the
families Xanthidae (Eriphia squamata <1 ind. m- 2 ) and Grapsidae (Pachygrapsus transversus 12.0 ind. m- 2 ), as well as the red calcareous alga Lithothamnion. Apart from barnacles, anemones, and sponges, the gastropods
Acanthina brevidentata and Thais kiosquiformis and some crabs (i.e.
Pachygrapsus transversus) occur in the lower intertidal zone.
The outstanding feature of the lower intertidal is the increasing number
of perforations (up to 54.8% inside the bay and 60.2% outside the bay)
caused by abundant boring organisms. The dominant borers on protected,
soft limestone are bivalves of the families Pholadidae ( Cyrtopleura crucigera and Dyplothyra curta; up to 216.8 perforations m- 2 ) and Petricolidae
(Petricola denticulata; 132 perforations m- 2 ). Species of the family Mytilidae (Lithophaga aristata, L. plumula; 62.9 ind. m- 2 ) perforate hard conglo-