Invertebrates

Striped shorecrab

Invertebrates, which include intertidal organisms such as aquatic insects, worms, clams, and crabs, and terrestrial insects and spiders, are likely major consumers in the salt marsh food chain and in turn are an important food source for the fishes and birds of the marsh.


Crabs are perhaps the most prominent invertebrates.  Burrows of several species of crab occur throughout the lower marsh, the most commonly seen one being fiddler crabs and lined shore crabs.

 

Continuing studies have helped characterize the benthic community at the Tijuana Estuary. The species composition and dominance change with the distance from the River's mouth. Captellid and spionid polycheates are found in both the estuary's northern and southern arms. Protothaca staminea and Tagelus californianus are the most common bivalves in the tidal channels (Williams et al 1996). California horn snail (Cerithidea californica) is abundant throughout the year, but especially in the winter. 

 

Relatively little research has been done on the terrestrial invertebrates of the estuary and their ecological role, except for recent work on invasive Argentine ants conducted by a NERRS Graduate Research Fellow from 2004-2007. This non-native species forms extremely aggressive colonies, forcing out native ants and depleting the key food source of the horned lizard, which does not eat Argentine ants. Installation of new irrigation lines has been blamed for Argentine ant invasion, as the ants require a year-round water source. In general, most insects here probably feed on vascular plants, algae, and decaying plants, while others are carnivores. They serve as a food source for birds and other marsh vertebrates. Marsh insects are also important to the pollination of marsh flowering plants. The endangered salt marsh bird's beak, for example, is pollinated by specific native bees (Zedler, 1982d).

 

Rove beetles (Staphylinidae spp.) burrow in mud and salt flats. They are abundant in the estuary and appear to play a role in aerating soils and in reversing soil compaction resulting from off-road vehicles. Studies suggest that the largest population of the wandering skipper (Panoquina errans) in the United States may be at the Tijuana Estuary (Zedler, 1982d). The estuary also supports a diverse and abundant population of coastal tiger beetles (Cicindela sp.), of which four species may be threatened (U.S. Fish and Wildlife Service, 1982). The Reserve is also a location for the globose dune beetle (Coelus globosus), a federal Category 2 species.

 

At least eleven species of salt marsh mosquitoes breed in the saline and brackish (fresh and saltwater mixing) pools of the estuary (U.S. Fish and Wildlife Service, California Department of Parks and Recreation, and Department of the Navy, 1983). Three species (Aedes taeniorhynchus,Anopheles hermsi, and Culex tarsalis) are of particular concern because of their potential as pests and possible disease vectors. Currently, biochemical control methods are being used to combat larvae and adults in areas where there is a high concentration of these mosquitoes.