CHAPTER 4 

 SECONDARY PRODUCERS 



4.1. ZOOPLANKTON 



The diverse zooplankton represent an 

 important link between the phytoplankton 

 and higher levels of the estuarine food 

 webs. Almost every ma.ior qroup of 



organisms is represented in the 

 zooplankton, either as larvae or as 

 adults; great variety is also evident in 

 the relatively extensive size range of 

 individuals. Zooplankton have marked 



differences in swimming ability and are 

 often dispersed in patch v, somewhat 

 irregular spatial distributions. 



Zooplankton repackage organic matter 

 produced by phytoplankton into larger 

 particles, thereby concentrating energy 

 into forms more useful to higher 

 predators. At the same time, they excrete 

 nutrients that may again contribute to 

 phytoplankton productivity. 



of the estuary (Figure 26). Overall 

 seasonal peaks of copepods in Apalachicola 

 Bay are noted from March to August with 

 minimum densities in January and February. 

 Optimal salinities for the dominant 

 species, Acartia tons a , range from Ifi to 

 22 ppt. East Bay, characterized by low 

 but variable salinity, has the highest 

 variability in zooplankton numbers over 

 time. Coastal waters have been most 

 stable in terms of seasonal changes in 

 zooplankton abundance. Apalachicola Bay 

 also has the highest species richness of 

 the three areas studied. Cladocerans and 

 chaetoqnaths are located primarily in 

 coastal waters. Decapod larvae throughout 

 the estuarv are primarily crab zoeae; 

 other zooplankton include polychaete 

 larvae, ostracods, amphipods, isopods, 

 mysids, echinoderms, ctenophores, and 

 coelenterates. 



Zooplankton (Table 12) are among the 

 least known assemblages in the 

 Apalachicola estuary. While the 



dimensions and interrelationships of the 

 zooplankton community are relatively 

 poorly understood in the Apalachicola 

 estuary, certain factors such as 

 temperature, salinity, wind, nutrients, 

 primary (phytoplankton) productivity, and 

 predator-prey relationships are known to 

 contribute to processes involving this 

 group of organisms. Net zooplankton are 

 composed largely of holoplankton (plankton 

 for entire life cycle; about '^0%) , while 

 meroplankton (temporary plankton) 



constitute less than lO?;! of the total 

 (Table 12; Edmisten 1QZ9). The 



holoplankton are composed mainly of 

 copepods, cladocerans, larvaceans, and 

 chaetognaths. Copeoods, notably Acartia 

 tonsa , are dominant throughout the 

 estuary. Apalachicola Bay supports higher 

 numbers of copepods than any other portion 



The zooplankton mean standing crop 

 (dry weight) in East Bay approximates 4.0 



3 



mg m"-^ annually; in Apalachicola Bay, 32.1 



mg m 

 m~3 yr~l 



yr 



-1. 



in coastal areas, 16.7 mg 

 Peak dry-weight biomass occurs 

 in May throughout most of the study area 

 with secondary increases during .luly and 

 August (Figure 26). Zooplankton 

 distribution is influenced by changes of 

 temperature and salinity through time 

 (Table 13). Edmisten (1979), using 

 analysis of covariance with temperature 

 and salinity as covariates for factors 

 such as Acartia numbers, percent abundance 

 (of Acarti a ) , total zooplankton numbers, 

 zooplankton biomass, and Shannon 

 diversity, found significant station and 

 month differences in all cases (p - 0.02). 

 Temperature significantly influenced 

 numbers of Acartia , total zooplankton 

 numbers (p < 0.01), and biomass. Salinity 

 significantly affected zooplankton 

 numbers, biomass, and diversity (p < 0.01) 



43 



