The Ecology of Tijuana Estuary, California: An Estuarine Profile

compared the ,chthyoplankton communities of the (Sardrnops sagax caeruleus), were imported to the
estuarine channels within Tijuana Estuary with estuary during flooding tides. These two species
those in adjacent nearshore waters. In addition, made up 6g0/o and 12% of main channel eggs and
comparisons were made between large, main 70% and 11% of nearshore eggs, respectively.
estuarine channels and tidal creeks.
However, very few larvae from nearshore species
were collected within the main channels,
A total of 28 taxa of fish larvae representing 19
families and more than 27 genera (some taxa
suggesting that imported eggs are
retained unt~l hatching. The nearshore larval
multiple genera) were collected during the dominants, weenfish (Seriphus P ~ white ~ ~ ~
period while ,8 taxa and one unknown croaker (Genyonemus lineatus) and northern
variety of fish eggs from 13 families and including anchovy (Engraulis mordax), were rarely
more than 18 genera were collected (Table 9). within the estuary.
There were distinct differences in the
fchthyoplankton assemblages collected from each Tidal flushing appears to be a determining
habitat. Estuarine larvae demonstrated patterns of factor in the distribution of ichthyoplankton in
spatial drstr~bution, related to channel rnorphometry Tijuana Estuary. The presence of postlarval
and other channel organisms, that indicated Scraenidae wlthin the estuary suggests that some
spawning habitat preferences.
nearshore-spawned eggs can hatch or develop
there. The transportation of goby species to the
Tidal creek larval collections were dominated by
longjaw rnudsucker (Gtll~chthys mtrablis)
nearshore environment is probably fatal. Brothers
(1975) measured 98% mortality for spawned
Athsrin~dae, presumably topsmelt. The longlaw cohorts of arrow goby at a similar wetland habitat
fnudsucker is known to prey upon and inhabit the in Mission Bay (25 km north of Tijuana Estuary)
burrows of the yellow shorecrab (MacDonaid and determined that tidal translocation was the
1975) High densitres of these larvae were major source of mortality for thls species.
cotlected where crab burrows were abundant.
Atherinid larvae and eggs were associated wlth
macroalgal mats, prcmarlly Enteromorpha species. The Gobi~dae larvae that dominate Tijuana
that grow In the low tidal-veloc~ty creeks Topsmelt Estuary are Common to other f~~closed bays and
attach their eggs to the blades of algae, and the estuaries of southern California While not of
juvsnifeii and adl~lts feed on the abundant plant commercial importance except as baitfish, these
nrateriai (Allen 198Q, Pdordby 1982).
low-trophic-level species are important ecoiogicaily
in that they make the primary productivity of the
A conjplex of tt,fee ~ndislingulshabie goby e"uarlne system available to higher order
larvae, comprised of arrow goby (Clevelandta IOS),
arrow gobies have been
shadow goby (Quj@tlja y-caude) and cheekspot ShCYA'n to be Important food items for California
goby (Ilypnus gtibarii), dorn~nated inaln channel as as Other Wort fishes (MacDOnald
larval cullect~ons (81"6) whrle longjaw rnudsucker 1975)
made up 29% of the total. The goby-complex
larvae were rnost dense at the sampllng statlon 3-65 Birds
closest t0 the mouth of the estuary, apparently due
to substrats preference The substrate at this s~te The channels of Tijuana Estuary are important
Was mud'sand rather than the mud and cla~/shell forag~ng and resting areas for a variety of bird life
siibstrates of the other main channel sampling such as great blue herons, which prey on channel
stations he arrow goby was the most abundant fishes (Figure 42) The estuary IS a part of the
~ostfarvaf QobY cail@cted, this species has been Paclflc Flyway, which ,s used by rnilllons of
ta live contfnensalIy with ghost shrimp waterfowl and shoreblrcfs during winter migration.
(bf,lacDorta'd 'r975), Ghost burrows were Shorebirds forage primarily for invertebrates in the
comman IcT mud/ssnd stJbstrat@ ~~s~ appears sand and mud sediments and In the water column,
that the dlstrlbutlon of gob~-cornpl@x k3rvae 1s dlvlng birds prey on fishes, wading birds use both
related substrate and lnte~actlon with another
fishes and invertebrates for food, dabbling ducks
channel organlsrn
feed on vegetation; and plovers feed on surface
~nsects Three Federally listed endangered birds
Because of thetr positlon relative to the mouth and one Callfornia endangered bird use channel
of the estuary, larvae of the goby complex were organtsms for prey These inciude the California
tidally transported to the nearshore habitat where least tern, the California brown pelican (Pelecanus
they made up 57"0 ot the totai These species oc~de,riaiis cai~iorntcusj, the l~ght-footed clapper
spawn where t~dai velocity 1s low and sediments rail, and Belding's Savannah sparrow. Other b~rd
are fine (Brothers 1975): thus, it IS doubtfui that species that feed on fishes In the channels are the
spawning occurred In the nearshore habrtat belted kingfisher (Megaceryle a/cyon), osprey
Conversely, eggs from nearshore-spawning (Pandion haliaetus), and double-crested cormoran!
species, especially Sclaenrdae and Paclfic sardine (Phalacrocorax auntus). Another Federally ilsted
48