CHAPTER 3 

 ALGAL MATS ON THE MARSH SOILS 



3.1 ALGAL COMMUNITY STRUCTURE 



The low-growing, open canopies of 

 vascular plants in southern California 

 marshes allow light penetration to the 

 soil surface and subsequent development of 

 lush algal mats. Filamentous bluegreen 

 and green algae and dozens of species of 

 diatoms form mats up to 1 cm thick on the 

 moist soils and on the lower part of the 

 halophyte stems (Figure 32). However, one 

 cannot appreciate the beauty or complexity 

 of these communities without a microscope 

 (Figure 33). Unfortunately, the 

 composition of these marsh algal mats has 

 been studied only at Tijuana Estuary 

 (Zedler 1980). Elsewhere in southern 

 California, the mudflat algae (Riznyk et 

 al. 1978) and subtidal epibenthic algae 

 (Wilson 1980) have been examined. As a 

 result of the paucity of information on 

 species composition, it is uncertain 

 whether the conclusions drawn from the 

 Tijuana Estuary work would hold throughout 

 the region. 



Light penetration, temperature, and 

 soil moisture are likely to be important 

 factors for algal species distribution. 

 These factors vary both seasonally and 

 spatially over the elevation gradient of a 

 marsh. Hence, in attempting to 

 characterize the algal mat composition of 

 Tijuana Estuary's marsh, sampling was 

 carried out biweekly in four parts of the 

 marsh chosen to allow comparisons with 

 elevation (low, medium and high, differing 

 in inundation, soil moisture, and 

 salinity) and with different overstory 

 canopies (at the same elevation, but with 

 a short, open canopy of Jaumea carnosa and 

 taller canopy of cordgrass [Spartina 

 foliosa ; Zedler, unpub. ms.b]). 



The total species list which resulted 

 from examining 1,680 wet-mounted 



microcores of the algal mats included 2 

 green algae, 7 bluegreen algae. and 74 

 diatoms. Of these, 38 species were 

 considered common; they occurred in more 

 than 5% of the microcores. The bluegreen 

 and green algae form the matrix of the 

 algal mats and probably contribute most of 

 the biomass. However, their occurrence is 

 patchy, perhaps due to herbivory and 

 disturbance by crabs and snails. The 

 species most commonly encountered are 

 listed by algal group in order of 

 decreasing frequency of occurrence for the 

 marsh as a whole (Table 8). The habitat 

 and season of greatest abundance are noted 

 to indicate the general environmental 

 conditions which seem to favor each 

 species. All species except Nitzschia 

 obtusa V . nana showed differential 

 frequencies with sampling station 

 (habitat), and all except Amphora exigua 

 and Rhopalodia musculus differed with 

 sampling season. Spatial and temporal 

 patterns are the general rule for Tijuana 

 Estuary marsh algae. Still, the sampling 

 stations averaged 64J similarity, with the 

 greatest difference in composition 

 occurring between the highest and lowest 

 stations sampled. These similarities are 

 much greater than those for the overstory 

 vegetation at the same sampling stations, 

 and one can speculate that (1) algal 

 communities have broader ranges of 

 tolerance since algae readily go dormant 

 and readily revive with favorable 

 conditions, (2) that the environment for 

 algae differs far less than that for 

 vascular plants because of the 

 ameliorating influence of the overstory 

 canopy, or (3) that tides move the algae 

 through the intertidal marsh and species 

 are continually replenished at all 

 habitats. Perhaps all are true. Much 

 research remains to be done before a 

 conceptual model can be suggested. 



4A 



