(-3.7 m ) mean low water, while the 

 channel was dredged to -15 ft (-4.6 m) 

 mean low water. Cement bulkheading 

 and rock riprap were used for the sides 

 of the marina. Benthic studies were 

 conducted by Reish (1963) from August 

 1959 to April 1962, following the comple- 

 tion of dredging of the three additional 

 basins and the channel. No benthic 

 animals were found in the first samples 

 taken following the dredging; specimens 

 were found in samples taken in Septem- 

 ber 1959. Species numbers increased 

 rapidly for the first 9 mo after that 

 time, then held constant in the channel 

 for the following 14 mo (Reish 1962). 

 Over 50% of the species collected were 

 polychaetes. Over the period of the 

 study, no significant decrease in popu- 

 lation occurred after about 1 yr in the 

 first basin and in the inward portions 

 of the additional three basins. This 

 drop in species was related to a drop in 

 dissolved oxygen and appearance of sul- 

 fide odor. These findings reinforced 

 Reish's theory that poor water circula- 

 tion was the cause of the decrease, 

 since the water circulation in the chan- 

 nel was not restricted. According to 

 Reish (1963), it apparently takes about 

 1 yr for the effect of limited water 

 movement to alter the benthic environ- 

 ment of a newly established marina. No 

 successional patterns of benthos were 

 observed . 



Reish (1961) also observed that 

 succession of attached organisms did 

 occur on the floats in the marina. The 

 apparent climax community of My til us 

 and Ulva was noted after the floats had 

 been in the water for 6 mo. Up to 30 

 associated species might have been pre- 

 sent. Reish (1962) notes that succession 

 on solid substrates in the southern Cali- 

 fornia waters is more rapid than what 

 has been observed in other geographical 

 areas. This may be due to longer breed- 

 ing seasons and relatively restricted 

 annual water temperature ranges. 



Because of the apparent correlation 

 between benthic population decrease and 

 poor water circulation, it is recommend- 

 ed that measures be taken to maintain 

 proper circulation in marinas. Poor wa- 

 ter circulation affects the benthic com- 

 munity and may also adversely affect 



fishes, shellfishes, and other aquatic 

 life in the area. 



CASE HISTORY - BULKHEADS IN 

 COASTAL REGION 3 - GULF OF 

 MEXICO 



Within the Gulf of Mexico, a num- 

 ber of studies are available documenting 

 the effects of bulkheads or seawalls on 

 certain components of an ecosystem 

 (Corliss and Trent 1971, Gilmore and 

 Trent 1974, Mock 1966, Moore and 

 Trent 1971, Trent et al. 1972, 1976). 

 These studies are primarily concerned 

 with structures on the coast of Texas, 

 but the results are generally applicable 

 along the Gulf coast of the United 

 States. 



The purpose of bulkhead or sea- 

 wall construction in this region is to 

 provide protection of upland areas from 

 erosion and also to provide waterfront 

 real estate. This latter function is 

 achieved by constructing a bulkhead 

 along a vegetated shoreline and then 

 filling the area behind the bulkhead to 

 provide land for development. Such 

 artificial creation of real estate is com- 

 mon in Galveston Bay, Texas, and in 

 Florida. Bulkheads also provide mooring 

 facilities . 



The creation of bulkheaded water- 

 front housing developments in this 

 region has clear socioeconomic signifi- 

 cance, regardless of the level of envi- 

 ronmental impact. Their success in pro- 

 viding desirable real estate is obvicus. 

 Alternate structures are generally not 

 considered because of the economic ben- 

 efits gained from filling behind a bulk- 

 head or seawall. Their effects on coast- 

 al processes and the biota require more 

 detailed study. 



Trent et al. (1976) studied an area 

 in the West Bay of Galveston Bay, Tex- 

 as, which had been a natural marsh 

 before bulkheading. The marsh was 

 altered by channelization, bulkheading, 

 and filling. The altered area consisted 

 of a series of dead end canals with 

 houses built on the strips of land sepa- 

 rating the canals. Approximately 111 

 acres (45 ha) of emergent marsh vege- 

 tation (pri marly Spartina alterniflora ), 



114 



