Figure 8. Mean data reliability by species. 



Coupling of Estuarine and Marine Ecosystems 



Classifying and comparing estuaries. Although the 

 qualitative nature of the data presented precludes 

 statistical analysis of species abundances among es- 

 tuaries, comparisons can be made using data on the 

 presence/absence of species in salinity zones. This 

 information, combined with the spatial and temporal 

 distribution data, is the strength of the ELMR data 

 base. Estuaries can be loosely categorized by their 

 physical and chemical characteristics and their associ- 

 ated species assemblages (Monaco and Lowery in 

 prep). The relative importance of individual estuaries to 

 specific species may also be determined. 



The species found in an estuary are sensitive indica- 

 tors of both the mean and extreme environmental 

 conditions within that estuary. Estuaries can be classi- 

 fied by the number of species present and by whether 

 the fauna are primarily marine, estuarine, orf reshwater 

 (Tyler 1971, MacDonald et al. 1984, Ayvazian et al. 

 1 992). Species assemblages may correlate with physi- 

 cal characteristics, such as bottom substrate, vegeta- 

 tion, and spatial/temporal characteristics of salinity 

 zones. Thus, information on species presence/ab- 

 sence or other attributes may be used to determine the 

 similarities and differences among estuaries. Alter- 

 nately, a comparison of estuaries and associated spe- 

 cies can help elucidate ecological variables that might 

 account for shifts in species distribution and commu- 

 nity structure. For example, a species may show differ- 

 ing salinity tolerances among estuaries, suggesting 

 that some other factor such as temperature, competi- 

 tion, or predation may be regulating its distribution. 



Linkages to marine ecosystems Many species 

 inhabit estuaries year-round; however, a large number 

 of species only use estuaries for specific parts of their 

 life histories. Most of these latter species fall into four 

 general categories: 1 ) diadromous species, which use 

 estuaries as migration corridors and, in some instances, 

 nursery areas; 2) species that use estuaries for spawn- 

 ing, often at specific salinities; 3) species that spawn in 

 marine waters near the mouths of estuaries and de- 

 pend on tidal- and wind-driven currents to carry eggs, 

 larvae, or early juveniles into estuarine nursery areas; 

 and 4) species that enter estuaries during certain times 

 of year to feed on abundant prey and/or utilize pre- 

 ferred habitats. The biological importance of an estu- 

 ary can be assessed both by the number of species 

 present and the density, and/or abundance, of specific 

 life stages in the system relative to offshore habitats. 

 Since many offshore species use estuaries as nursery 

 areas or feeding grounds, these data may assist in 

 identifying adverse effects of estuarine degradation on 

 offshore populations. 



14 



