are during high tide. In studies of a 

 Scandinavian species of Bledius, Larson 

 (1953) found that they evacuated tunnels 

 during high tide and could be found beneath 

 debris at the wrack line. This did not happen 

 at Tijuana Estuary. Very few beetles were 

 ever observed outside a burrow, regardless of 

 tide. 



Some insects that inhabit the salt pannes 

 are considered "threatened." Threatened 

 species are those whose range is declining due 

 to loss of habitat and/or have been proposed as 

 candidates for State or Federal listing. Among 

 such insects are the tiger beetles (genus 

 Cicindela). Tijuana Estuary supports the 

 highest diversity and abundance of tiger 

 beetles of any coastal locality in southern 

 California and possibly all of California (C. 

 Nagano, US FWS, pers. comm.). There are at 

 least four species of this genus that occur 

 here, two of which inhabit the salt pannes, 

 although they have been observed there only 

 in low numbers. These are the mudflat tiger 

 beetle (Cicindela trifasciata sigmoidea) and 

 Gabb's tiger beetle (C. gabbi, Figure 3.14). 



Tiger beetles are predaceous; they feed 

 upon any arthropods they can overpower. 

 Adults are found on mud or sand near 

 permanent bodies of water. Larvae inhabit 

 burrows in the soil in the same area as the 

 adults. The larvae (Figure 3.14) are also 

 predaceous, using hooklike mandibles to 

 capture and kill their prey, which is then 

 consumed within the burrow. Because their 

 prey includes insects that are harmful to man, 

 these beetles are considered beneficial. Tiger 

 beetles are preyed upon by other salt panne 

 and tidal flat insects including robber flies 

 (Diptera: Asilidae) and dragonflies (Odonata: 

 Anisoptera), and numerous vertebrates such 

 as birds, reptiles, and mammals (D. Mclntire, 

 pers. comm.). 



Tiger beetles are considered to be good 

 indicators of the disturbance to coastal 

 systems (Nagano 1982); the least disturbed 

 habitats have several species of tiger beetles. 

 Although quantitative data from the period 

 before closure of the estuary mouth are 

 lacking, qualitative estimates indicate that 

 populations increased significantly after the 



mouth was reopened (Mclntire, San Diego 

 naturalist, pers. comm.). 



Another group of insects that can be 

 regarded as good indicators of disturbance are 

 the true bugs of the order Hemiptera, family 

 Saldidae. Several taxa of these insects occur 

 on the least disturbed salt pannes. They have a 

 wide salinity tolerance and are carnivorous, 

 feeding on springtails, mites, and other 

 insects and spiders. One member of this 

 family, Pentacora signoreli (Figure 3.14), is 

 very abundant at Tijuana Estuary. Individuals 

 coated with salt crust have been observed on 

 salt pannes, but the mechanism for tolerating 

 such high salinities is not known (Mclntire, 

 pers. comm.). 



Salt pannes are often used as foraging 

 areas for Belding's Savannah sparrows, which 

 feed on the insects there. California least 

 terns and snowy plovers are both known to 

 nest on salt pannes. The latter two species use 

 preformed depressions, such as animal 

 footprints, in the hardpan for nest scrapes. If 

 there are patches of other substrate, such as 

 sand or small wrack, the birds will create 

 their own scrapes on these. When the pannes 

 are inundated, snowy plovers also use them as 

 feeding areas (White, pers. comm.). 



3.5 BRACKISH MARSH 



Habitats that typically have reduced water 

 salinities (between 0.5 and 30 ppt) are 

 considered brackish or mixohaline (Cowardin 

 et al. 1979). In southern California, such 

 habitats occur next to seepages or where 

 rainfall or runoff is impounded. Evaporation 

 then concentrates salts. Water levels 

 fluctuate widely but irregularly. Due to 

 differences in salinity and water levels, the 

 plants and animals of the salt marsh are 

 generally not found here. Instead, a 

 community more characteristic of the region's 

 freshwater marshes is found (Figure 3.15). 

 Cattails (Typha domingensis) and bulrushes 

 (Scirpus californica) are the usual dominants 

 among the emergent species, while the 

 submergent ditchgrass (Ruppia maritima) is 

 abundant seasonally. Red-winged blackbirds 



41 



