240 



200 



160 



o) 120 



80 



40 



o- 



MARMAV JUL SEP NOV JANMARMAY JUL SEPNOV JANMARMAYJUL SEP 



I —1976 1 1977 — | 1?78— 1 



Figure 4.7. Seasonal dynamics of litter in the 

 salt marsh of Tijuana Estuary. Vertical bars 

 are ±.1 standard error, n = 25. Reprinted 

 with permission from T. Winfield 



and mortality through time with differences 

 in disappearance rates of species and plant 

 parts shows high temporal variation in 

 detritus production. 



4.5.2 Feeding and Growth Rates 



Plant material produced by the salt marsh 

 is used both directly (herbivory) and after 

 fractionation to detrital particles (detri- 

 tivory). We are virtually ignorant of the 

 first process at Tijuana Estuary. But the 

 abundance of insects found on various salt 

 marsh plants insures that it is an important 

 energy flow pathway (e.g., outbreaks of 

 Diptera on cordgrass documented by Covin 

 1984; Coleopteran damage on pickleweed 

 documented by Beare and Beezley, both 

 discussed in Section 4.4). 



lated through May in 1976 but decreased 

 through November in 1977. August values 

 were high in 1976 (about 200 g/m 2 ) and low 

 in 1977-78 (100-130 g/m 2 ). The proces- 

 ses responsible for litter removal are 

 likewise variable, and tracing the fate of plant 

 losses is a complex problem. Casual obser- 

 vations indicate that the coincidence of high 

 tides and strong winds results in major 

 transport of litter from the low marsh to the 

 high tide line. Large wrack deposits are 

 occasionally obvious, but there are many 

 months when debris lines are hard to locate. 



Data on decomposition rates (Table 4.7) 

 show large differences between: species, 

 leaves and stems, live and dead fractions, and 

 locations of litter bags in the marsh. While 

 litter bags were deployed in the marsh only 

 during one year, other data indicate year-to- 

 year differences in the availability of plant 

 parts for various marsh species (Section 

 4.3). Furthermore, some of the succulent 

 plants are highly susceptible to breakage 

 (e.g., saltwort, Batis maritima), while the 

 grasses are not. Leaves of saltwort are 

 readily detached and floated away at the end of 

 the growing season, as are their fleshy fruits. 

 Coupling the differences in plant production 



Table 4.7. Decomposition rates of selected 

 plant material (from Winfield 1980). 



a Ecotone = upper extent of cordgrass zone. 



93 



