3.2 ALGAL MAT PRODUCTIVITY 



Studies of intertidal algal 

 productivity along Pacific Coastal marshes 

 are more numerous than studies of algal 

 composition. However, most of the work 

 deals with mud- or sandflat algae (e.g. 

 Pamatmat 1968, Riznyk et al. 1978, Onuf et 

 al. 1978). Again, only the work at 

 Tijuana Estuary (Zedler 1980) has dealt 

 with soil algae found under a marsh canopy 

 and general results are presented in order 

 to suggest the role of algal mats in the 

 productivity of southern California 

 coastal marshes. 



As with measurements of vascular 

 plant productivity, there are different 

 methods and assumptions for measuring and 

 calculating annual algal productivity. 

 Methods based on the measurement of oxygen 

 produced do not give the same results as 

 methods based on carbon dioxide uptake. 

 The former method measures gross 

 productivity (net productivity plus 

 respiration), while the latter gives 

 something closer to net productivity. 

 Furthermore, assumptions must be made in 

 extrapolating from hourly incubation 

 measurements to daily and yearly 

 estimates. Hence, annual algal 

 productivity measurements are subject to 

 large errors »and comparisons from study to 

 study should be made with caution. Even 

 comparisons made with the same methods can 

 be faulty if different assumptions have 

 gone into the annual calculations. 



At Tijuana Estuary, it appeared that 

 algal mats might be more productive, both 

 on an absolute basis (more grams of 

 carbon/m /yr) and on a relative basis (a 

 larger proportion of the total marsh 

 productivity) , than in the eastern United 

 States marshes. Hence, caution was used 

 in making the assumptions necessary to 

 convert short-term productivity 

 measurements to annual net productivity 

 (Zedler 1980). 



Algal productivity was measured 

 biweekly in the same four habitats for 

 which compositional information was 

 obtained, namely under canopies of 



cordgrass ( Spartina foliosa ) , Jaumea 

 carnosa , saltwort ( Batis maritima ) , and 

 shoregrass ( Monanthochloe littoralis ) . 

 Again, both seasonal and spatial patterns 

 were found, with winter having the lowest 

 values, followed by a spring peak in early 

 March and a second low in April. The 

 winter low was attributed to cool 

 temperatures, while the April low 

 coincided with a period of little tidal 

 inundation, no rainfall, and dry algal 

 mats. An April depression would not be 

 expected in years of early spring rains. 

 Values in late spring through fall were 

 again high, in response to the long period 

 of favorable temperatures. 



Spatial differences in productivity 

 (Figure 34) related to (1) elevation, with 

 the higher, drier elevations being less 

 productive than the low marsh habitatsj 

 and (2) the type of overstory canopy. The 

 two sampling stations at low elevation 

 differed significantly from one another, 

 with mats under the tall, dense cordgrass 

 canopy being less productive than those 

 under the more open Jaumea canopy. Both 

 desiccation and shading appear to be 

 stresses for southern California marsh 

 algae. 



On an absolute basis, the annual 

 productivity estimates for Tijuana Estuary 

 marsh algae (net productivity up to 340 

 gC/m /yr) are among the highest recorded 

 for epibenthic algae in soft sediments. 

 What features of these marsh habitats 

 would prove so favorable for algal growth? 

 The year-round warm climate is no doubt 

 one important factor in promoting algal 

 growth, especially for the bluegreen 

 algae. Substrate stability may well be 

 another. Algal growths in the channels of 

 Tijuana Estuary are never as persistent as 

 within the marsh canopies (Zedler et al. 

 1978). Diatoms are abundant on the creek 

 banks, but the few patches of bluegreen 

 algae seem to be readily eliminated either 

 through herbivore consumption or removal 

 by currents. When tidal circulation is 

 sluggish, large floating colonies of green 

 algae ( Ulva and Enteromorpha ) develop and 

 become entrained on the edges of the 

 marsh, but these soon become desiccated. 



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