Gulf of Mexico Region. The location of the 31 

 selected ELMR Gulf of Mexico estuaries are shown 

 in Figure 13 (next page), and the common and 

 scientific names of the 44 selected ELMR Gulf of 

 Mexico species are listed in Table 14 (p. 35). Results 

 of the ELMR study in the Gulf of Mexico region are 

 summarized in Distribution and Abundance of Fishes 

 and Invertebrates in Gulf of Mexico Estuaries, Volume 

 1: Data Summaries, ELMR Report No. 10 (Nelson et 

 al. 1992). These results were also previously pub- 

 lished in three separate reports for the Western Gulf 

 of Mexico (Texas) (Monaco et al. 1989); Eastern Gulf 

 of Mexico (Florida, Alabama) (Williams et al. 1990); 

 and Central Gulf of Mexico (Louisiana, Mississippi) 

 (Czapla et al. 1991). Life history summaries and 

 tables for the species in this region were published 

 in Volume II: Species Life History Summaries (Pattillo 

 etal. 1997). 



Estuaries of the Gulf of Mexico were formed on a 

 vast coastal plain of sedimentary deposits. In Loui- 

 siana, the Mississippi River has transported enor- 

 mous quantities of sediment to coastal waters, build- 

 ing up the delta and alluvial plain. Barrier islands 

 and lagoons are common along the Texas coast. 

 Tidal range is small throughout the region, gener- 

 ally less than a meter (NOAA 1990a). Hurricanes 

 may occasionally impact Gulf estuaries with storm 

 surges and episodic freshwater inflow. 



The 44 species selected are generally of the warm- 

 temperate fauna of the Gulf of Mexico portion of the 

 Carolinian marine biogeographic province. The 

 actual fauna of the south Florida estuaries, Florida 

 Bay and Ten Thousand Islands, includes many spe- 

 cies from the tropical Caribbean marine province. 

 Therefore, the selected ELMR species list does not 

 adequately represent the actual south Florida es- 

 tuarine fauna. 



Table 15 (p. 36) readily conveys the occurrence of 

 the selected 44 ELMR species in each of the 31 Gulf 

 of Mexico estuaries. This table depicts the highest 

 relative abundance of the adult or juvenile life stage 

 of each species, in any month, in any salinity zone 

 within each estuary. The spawning, egg, and larval 

 life stage categories are not considered. This table 

 also suggests the zoogeographic distribution of spe- 

 cies among Gulf of Mexico estuaries. For example, 

 the Florida stone crab is found from Florida Bay to 

 Apalachicola Bay, whereas the closely related Gulf 

 stone crab occurs from Pensacola Bay westward. 

 Some species occur in the higher-salinity estuarine 

 waters of Florida and Texas, but are absent from the 

 low-salinity areas of Louisiana, such as bay scallop, 

 snook, code goby, and gulf flounder. A few euryha- 

 line species, such as blue crab, bay anchovy, and 



hardhead catfish are ubiquitous, considered at least 

 common in all 31 Gulf of Mexico ELMR estuaries. 

 Alabama shad, an anadromous species closely re- 

 lated to the American shad, is now rare or extir- 

 pated through much of its former range (Mettee et 

 al. 1996). It is therefore being considered as a 

 candidate species for protection under the federal 

 Endangered Species Act (NMFS 1997). 



To examine seasonal patterns of species presence/ 

 absence in Gulf of Mexico estuaries, the revised and 

 updated ELMR data sets (NOAA 1997a) for Florida, 

 Alabama, Mississippi, Louisiana, and Texas were 

 selected and merged. The revised Gulf of Mexico 

 ELMR data set utilizes five salinity zones: 0-0.5 ppt 

 (tidal fresh), 0.5-5 ppt, 5-15 ppt, 15-25 ppt, and >25 

 ppt. The revised ELMR data consider the presence 

 of eggs and spawning as distinct life stages, just as 

 in the original three-zone ELMR data (Nelson et al. 

 1992). Numbers of species present, ranked as "rare" 

 or greater, were counted by month and by salinity 

 zone for the adult, juvenile, and larval life stages. In 

 Figure 14 (p. 38), the numbers of species were aver- 

 aged across estuaries and plotted by month for the 

 adult, juvenile, and larval life stages. In Figure 15 

 (p. 39), the mean annual maximum number of spe- 

 cies is plotted by salinity zone for the adult, juve- 

 nile, larval, spawning, and egg life stages. 



• The number of species appears to be lower in 

 the tidal fresh (0-0.5 ppt) and seawater (>25 ppt) 

 zones. However, this may have been partially 

 because the selected ELMR species are prima- 

 rily estuarine, not freshwater or marine resi- 

 dent species. 



• Juveniles and adults are the predominant life 

 stages present in estuaries, followed by larvae, 

 eggs, and spawning. 



• The number of species present as juveniles and 

 adults is generally highest from March through 

 October, and lowest from December through 

 February. However, this seasonal variation is 

 much less dramatic than in the North Atlantic 

 and Mid-Atlantic regions. 



• The number of species present as larvae is gen- 

 erally highest in the 15-25 ppt zone. This num- 

 ber peaks in April in the 15-25 ppt zone, but 

 peaks in September in the >25 ppt zone. 



Text continues on p. 40. 



33 



