Macroalgal growth patterns were more 

 variable. During 1985, the cover of floating 

 macroalgae never reached nuisance levels, 

 i.e., the water column did not become anoxic 

 and there were no fish kills. Maximum 

 standing crops averaged only 15 g/m 2 (n = 

 12), with a range from 0-185. Highest 

 values tended to occur in the inland lagoon. 

 This does not necessarily mean that 

 productivity was highest there, because 

 macroalgae are relocated by the prevailing 

 onshore winds. 



Rudnicki determined that several factors 

 act together to increase macroalgal biomass in 

 estuarine channels. Algal establishment 

 coincided with daytime low tides, which occur 

 primarily in winter and early spring. 

 Germination mainly occurred along the 

 shallow edge of creeks and channels where 

 current speeds and light levels were suitable. 

 Following establishment, growth was 

 stimulated by nutrient inputs from rain and 

 runoff and by afternoon exposure. When the 

 cold tidal water receded, algae became warmer 

 and received more light. However, macroalgae 

 biomass did not necessarily accumulate in all 

 areas of high productivity. Maximum volumes 

 of macroalgae developed under two conditions, 

 where circulation was reduced and where 

 prevailing winds moved the floating mats. 

 Neither Enteromorpha nor phytoplankton 

 reached peak densities in well-flushed 

 channels. Any current strong enough to scour 

 the macroalgae would certainly limit the 

 accumulation of phytoplankton as well. 



The conditions that stimulate macroalgal 

 growth were further researched by Mary 

 Kentula (unpubl. data) in the salt marsh of 

 Mission Bay (25 km north of Tijuana 

 Estuary). In winter, she collected 



Enteromorpha-dom\r\a\ed algal mats from 

 soils beneath cordgrass and measured their 

 light-saturation points. Under a broad range 

 of temperatures (17-33°C), the mats became 

 saturated at 400-600 u.Einsteins/m 2 /s. By 

 comparison, photosynthesis of the summer 

 algal mats (dominated by blue-green algae and 

 by mixtures of blue-greens and diatoms) 

 were not light-saturated until exposed to 900 

 u.E/m 2 /s. Comparing the two types of algal 

 mats under high light and temperature, the 



summer community was 30% more 

 productive than Enteromorpha. As space and 

 nutrients become limiting in spring and early 

 summer, blue-green algal mats would have 

 the competitive advantage. Furthermore, 

 Rudnicki found that Enteromorpha 

 deteriorated rapidly in warm, drying field 

 conditions, as there is no resistance to 

 desiccation. Winter conditions thus favor 

 growth of this green alga over the species that 

 dominate in summer. 



Rudnicki (1986) and Fong (1986) tested 

 the role of environmental conditions in 

 stimulating algal blooms by exposing known 

 mixtures of phytoplankton and macroalgae to 

 three salinities (10, 20, and 34 ppt) and 

 three levels of fertilization (Milorganite, a 

 dried sewage-sludge product, was added in 

 high, low, and zero levels). They devised a 

 floating rack with 27 15-liter microcosms 

 anchored in one of the estuary's tidal creeks; 

 they then followed algal growth weekly for a 

 month. Separate experiments were set up: 

 (1) in winter 1985 using Enteromorpha sp. 

 and the monad-dominated plankton, (2) in 

 spring 1985 with Enteromorpha and a 

 dinoflagellate-dominated plankton community; 

 and (3) in fall 1985 with phytoplankton 

 only, because macroalgae were rare in the 

 estuarine channels. 



In these experiments (Figure 4.2), 

 phytoplankton responded rapidly to nutrient 

 addition, with biomass increasing 

 substantially after 1-2 weeks. Macroalgae 

 took somewhat longer to reach maximum 

 biomass. Blooms of Enteromorpha developed 

 in the third week. It is likely that 

 interactions between these two groups of 

 producers occurred, through competition for 

 nutrients and/or light. The high nutrient 

 treatments of the summer experiment, which 

 lacked macroalgae, were consistently larger 

 than the winter and spring experiments, 

 which had both Enteromorpha and 

 phytoplankton. Competitive interactions were 

 later demonstrated experimentally by Fong 

 (1991), who found phytoplankton blooms 

 where macroalgae were absent. 



Salinity affected the growth of both 

 phytoplankton and macroalgae. Lowered 

 salinity delayed phytoplankton blooms, and the 



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