conditions within that estuary. Estuaries can be clas- 

 sified by the number of species present and by whether 

 the fauna are primarily marine, estuarine, or freshwa- 

 ter. Species assemblages may correlate with physical 

 characteristics, such as bottom substrate, vegetation, 

 and areal and temporal characteristics of salinity zones. 

 The informationon species presence/absence or other 

 attributes can be used to determine the faunal similari- 

 ties and differences among estuaries. 



A comparison of estuaries and associated species can 

 identify differing factors among those estuaries that 

 might account for shifts in species distribution and 

 relative abundance, helping to define ecological vari- 

 ables controlling species distributions. For example, a 

 species may show differing salinity tolerances among 

 estuaries, suggesting that some other factor, such as 

 temperature, competition, or predation may be regulat- 

 ing its distribution. 



Linkages to marine ecosystems. Estuaries are home 

 to many aquatic species year-round, however, a large 

 number of species only use estuaries for specific parts 

 of their life histories and spend the rest offshore. Most 

 of these latter species fall into four general categories: 

 1) diadromous species, which use estuaries as migra- 

 tion corridors and, in some instances, nursery areas; 2) 

 species that use estuaries for spawning, often at spe- 

 cific salinities; 3) species that spawn in marine waters 

 near the mouths of estuaries and depend 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. The importance of an estuary can 

 be assessed by the intensity with which species use 

 estuarine habitats. Importance can be estimated both 

 by the number of species present as well as the density 

 of specific life stages in estuaries relative to offshore 

 habitats. These data may assist in identifying adverse 

 effects of estuarine degradation on offshore popula- 

 tions. 



East Coast Strategic Assessment. Development of 

 a capability to define and interpret the effects of anthro- 

 pogenic and natural phenomena on living marine re- 

 sources will be a component of the Strategic Environ- 

 mental Assessments Division's East Coast of North 

 America Strategic Assessment Project begun in FY 92 

 (NOAA 1 991 ). This project will characterize the biologi- 

 cal, physical, chemical, and economic characteristics 

 of the east coast of North America to address multiple 

 resource use conflicts. The data compiled for the 

 ELIVIR southeast and northeast study regions will be 

 major components of this project. The new initiative 

 will include electronic mapping of the distribution and 

 relative abundance of living marine resources. The 

 study area begins at the head-of-tide in estuaries and 



encompasses the continental shelf as defined by the 

 200-m isobath. Beyond the shelf, the study area 

 contains epipelagic waters. The areal coverage will 

 extend from the Straits of Belle Isle, Newrfoundland, to 

 Tampa Bay, Florida. The ELMR distribution and abun- 

 dance data will be the primary source of fish and 

 invertebrate informationforeast coast estuaries. These 

 data will be integrated with the coastal and offshore 

 living resource information to develop a consistent 

 data base on species found from the head-of-tide to 

 past the continental shelf. This will enhance NOAA's 

 capability to define and understand the coupling of 

 estuarine and marine habitats based on species" spatial 

 and temporal distributions and life history characteris- 

 tics. 



Additional data sets developed or under development 

 (e.g., National Status and Trends, O'Connor 1990) in 

 NOAA programs will enable regional environmental 

 assessments of anthropogenic effects on living marine 

 resources. The integration of biological and physical 

 data will significantly improve our ability to identify and 

 define the biological linkages and physical interchanges 

 between estuarine and shelf habitats. As it becomes 

 apparent that the cumulative effects of small alterations 

 in many estuaries have a total systemic impact on 

 coastal ocean resources, it is more important than ever 

 to compile consistent information on the Nation's es- 

 tuarine fishes and invertebrates. Although the knowl- 

 edge available to effectively conserve and manage 

 living resources is limited, the ELM R data base provides 

 an important tool for assessing the status of estuarine 

 fauna and examining their relationships with other 

 species and their environment. The ELMR data base 

 provides baseline information on the zoogeography 

 and ecology of estuarine fishes and invertebrates, and 

 identifies gaps in our knowledge of these resources. 

 When combined with data sets under development in 

 the East Coast of North America Strategic Assessment 

 Project, our ability to conduct interdisciplinary assess- 

 ments that identify strategies to balance resource 

 development and conservation efforts will be signifi- 

 cantly enhanced. 



Acknowledgments 



We thank those individuals that provided information 

 and reviewed the data in this report. Without their 

 efforts, a study of this magnitude and complexity would 

 not be possible. In addition, we thank the many other 

 scientists and managers who provided contacts and 

 references. 



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