272
J.R. Cantera and J.F. Blanco
oyster Crassostrea columbiensis, and shipworms (Teredinidae). Although
organisms move vertically with tidal oscillations (Blanco and Cantera
1999), clearly defined vertical zones are characteristic (Cantera 1991; Blanco 1995). Muddy bottoms among mangroves down to 30 em depth are
occupied by endofaunal organisms like bivalves (Anadara, Mytella, Protothaca, Corbula) and deposit-feeding polychaetes (i.e., Nereis). Most species live on the mud surface where the mud whelk Cerithidea and other
gastropods (Anachis, Theodoxus, Melampus, Marinula) feed on detritus.
Crustaceans (i.e., Uca, Alpheus, Synalpheus) are represented by 24 species
and fishes, such as wizards or gobies ( Gobionellus, Gobiosoma, Gobiomorus), flatfishes (Cynoglossidae, Bothidae, Soleidae), and toadfishes
(Batrachoides pacifici, Daector dowi), are common (Cantera et al. 1983).
18.3.4 Mud Flats
Extensive mud flats occur around creeks in the inner bay. The sediments
are generally less than 125 J.Lm but are occasionally mixed with river-borne
sand or gravel from cliff erosion. The structure of the community is typically related to characteristics of soft bottoms (i.e. grain size, organic matter, REDOX potential, temperature, etc.). Despite the apparent absence of
organisms, mud flats are rich in species (157), notably deposit-feeders and
detritivores, most of which occupy the aerobic upper subsurface layers of
sediments, while some bivalves and polychaetes burrow into deeper layers.
In general, tidal zones are not well defined. Owing to high temperature and
desiccation stress, the upper littoral is poor in species, with few dominants
like Marinula, Cerithidea, Eurypanopeus, and bivalves (Protothaca, Tagelus, Chione, Polymesoda) which remain buried most of time. Theodoxus,
Clibanarius, and Uca dominate the upper intertidal zone but, where sediments are mixed with gravel, other species (Petrolisthes, Anachis, Panopeus, Eurypanopeus) are present. Species richness (32) increases in the midintertidal zone ( 423 in d. m- 2 ), with polychaetes (Capitella, Glycera,
Thelepus, Streblosoma, Neanthes) representing the principal component
(Cantera 1991). The lower intertidal zone (up to 67 species) diplays high
diversity and evenness and is inhabited by gastropods (Natica, Nassarius,
Theodoxus, Anachis, Cerithium), bivalves (Tagelus, Anadara, Chione, Polymesoda), stomatopods (Squilla), polychaete worms (Amphinomidae, Capitellidae, Glyceridae, Nereidae), crabs (Panopeus, Eurypanopeus, Alpheus,
Callinectes), and benthic fishes ( Gobionellus, Gobiesox, Citharichthys, Symphurus).
J.R. Cantera and J.F. Blanco
oyster Crassostrea columbiensis, and shipworms (Teredinidae). Although
organisms move vertically with tidal oscillations (Blanco and Cantera
1999), clearly defined vertical zones are characteristic (Cantera 1991; Blanco 1995). Muddy bottoms among mangroves down to 30 em depth are
occupied by endofaunal organisms like bivalves (Anadara, Mytella, Protothaca, Corbula) and deposit-feeding polychaetes (i.e., Nereis). Most species live on the mud surface where the mud whelk Cerithidea and other
gastropods (Anachis, Theodoxus, Melampus, Marinula) feed on detritus.
Crustaceans (i.e., Uca, Alpheus, Synalpheus) are represented by 24 species
and fishes, such as wizards or gobies ( Gobionellus, Gobiosoma, Gobiomorus), flatfishes (Cynoglossidae, Bothidae, Soleidae), and toadfishes
(Batrachoides pacifici, Daector dowi), are common (Cantera et al. 1983).
18.3.4 Mud Flats
Extensive mud flats occur around creeks in the inner bay. The sediments
are generally less than 125 J.Lm but are occasionally mixed with river-borne
sand or gravel from cliff erosion. The structure of the community is typically related to characteristics of soft bottoms (i.e. grain size, organic matter, REDOX potential, temperature, etc.). Despite the apparent absence of
organisms, mud flats are rich in species (157), notably deposit-feeders and
detritivores, most of which occupy the aerobic upper subsurface layers of
sediments, while some bivalves and polychaetes burrow into deeper layers.
In general, tidal zones are not well defined. Owing to high temperature and
desiccation stress, the upper littoral is poor in species, with few dominants
like Marinula, Cerithidea, Eurypanopeus, and bivalves (Protothaca, Tagelus, Chione, Polymesoda) which remain buried most of time. Theodoxus,
Clibanarius, and Uca dominate the upper intertidal zone but, where sediments are mixed with gravel, other species (Petrolisthes, Anachis, Panopeus, Eurypanopeus) are present. Species richness (32) increases in the midintertidal zone ( 423 in d. m- 2 ), with polychaetes (Capitella, Glycera,
Thelepus, Streblosoma, Neanthes) representing the principal component
(Cantera 1991). The lower intertidal zone (up to 67 species) diplays high
diversity and evenness and is inhabited by gastropods (Natica, Nassarius,
Theodoxus, Anachis, Cerithium), bivalves (Tagelus, Anadara, Chione, Polymesoda), stomatopods (Squilla), polychaete worms (Amphinomidae, Capitellidae, Glyceridae, Nereidae), crabs (Panopeus, Eurypanopeus, Alpheus,
Callinectes), and benthic fishes ( Gobionellus, Gobiesox, Citharichthys, Symphurus).