CHAPTER 4 



ECOSYSTEM FUNCTIONING 



Studies of energy flow and nutrient cycling 

 in the salt marsh were initiated in 1976, 

 when researchers began to test the "East Coast 

 dogma" about coastal wetlands. Research on 

 the extensive coastal plain marshes in Georgia 

 and elsewhere had indicated extremely high 

 rates of vascular plant productivity, which in 

 turn subsidized coastal food chains. The early 

 work in southern California indicated that salt 

 marshes were indeed different, with rates of 

 primary productivity lower for vascular 

 plants and higher for epibenthic algae 

 underneath the open canopy (Sections 4.2- 

 4.3). Functional models of the ecosystem 

 were not developed, because the system 

 simply was not stable long enough for energy 

 flow rates to be characterized. Later work 

 focused on short-term growth rates in 

 response to variations in specific 

 environmental factors. For example, studies 

 of the algal growth in channels were initiated 

 in 1984, when problems of sewage spills and 

 threats of year-round wastewater discharges 

 indicated the need to understand what triggers 

 nuisance algal blooms. Our ability to 

 characterize ecosystem functioning has thus 

 been limited by variability. On the other 

 hand, our understanding of species 

 composition (Chapter 5) has been aided by 

 witnessing responses to environmental 

 fluctuations. 



4 . 1 PRIMARY PRODUCTIVITY OF 

 CHANNEL ALGAE 



The research of Rudnicki (1986) and Fong 

 (1986) characterized temporal patterns of 

 algal abundance in five habitats at Tijuana 

 Estuary, and manipulative experiments have 

 shown how algae respond to different 

 salinities and nutrient inputs. Throughout 



this section, the observations on macroalgae 

 are based on Rudnicki's work, and information 

 on phytoplankton is based on Fong's research. 

 The term macroalgae generally refers to 

 Enteromorpha and/or Ulva, as these genera 

 are not always easy to distinguish. As used 

 here, phytoplankton includes all microscopic 

 algae suspended in the water column, whether 

 derived from the channel sediments or 

 continuously planktonic (free-floating). 



Chlorophyll concentrations and cell 

 counts, rather than changes in productivity 

 rates, have been used to measure responses to 

 nutrient influxes. Maximum concentrations 

 of chlorophyll in the plankton occurred during 

 the 1984 nontidal episode, when Fong 

 documented a bloom of unicellular blue- 

 greens (Table 4.1). On the other hand, 

 maximum populations of macroalgae may have 

 occurred during the winters of 1983 and 

 1984 when tidal flushing was sluggish and 

 nutrient concentrations were high due to 

 sewage spills. However, our only evidence of 

 this is the March 1984 air photo, which 

 shows substantial macroalgal growth along the 

 shores of the inland lagoons and within the 

 northern tidal creeks. After tidal flushing 

 was reinstated, neither algal type developed 

 blooms of nuisance proportions. 



Rudnicki and Fong's joint monitoring 

 program began in 1985 and provided monthly 

 data on the seasonal dynamics of channel algae 

 (Figure 4.1). Three tidal creeks, the dredged 

 channel, and the inland lagoons were sampled 

 for phytoplankton, by collecting water 

 samples to measure chlorophyll concentration 

 and count cells. The same sites were sampled 

 simultaneously for macroalgae by determining 

 their cover and maximum biomass. 

 Macroalgae germinate and develop on the 

 sediments under shallow water. At some later 



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