Our Livin<^ Resources — Coastal <& Moriiw Ecosvslciiis 



277 



The bloom is so dense in some locations that it 

 reduces light penetrating 1 m (3.3 ft) by more 

 than 5U9f (Dunton 1994). This light reduction is 

 leading to loss of shoal grass in the deep areas 

 most influenced by the brown tide. 



Displacement of shoal grass by manatee 

 grass was not evident in the upper laguna in 

 1988 but is now. In all likelihood, the same 

 processes responsible for the profound changes 

 in the composition of seagrass meadows in the 

 lower laguna will now take hold in the upper 

 laguna. The greater isolation of the upper lagu- 

 na from a source population of the invader prob- 

 ably accounts for the much later initiation of the 

 replacement process than in the lower laguna. 



A final factor further magnifies the impor- 

 tance to redheads of these changes in seagrass- 

 es of the Laguna Madre of Te.xas. The Laguna 

 Madre de Tamaulipas. just south of the delta of 

 the Rio Grande, is an integral part of the winter 

 life-suppon system of redheads. In most years, 

 more redheads overwinter in Texas than 

 Mexico: however, in years of drought in Texas, 

 more ducks continue south into Mexico. The 

 large geographic extent of available habitat 

 apparently buffers the population by increasing 

 the probability that suitable conditions prevail 

 somewhere in the system eveiy year. The gov- 

 ernor of the State of Tamaulipas, however, is 

 now promoting the extension of the Gulf 

 Intracoastal Waterway through the Laguna 

 Madre in Mexico. In all likelihood, this devel- 

 opment will reduce the support capacity of the 

 laguna in Mexico for redheads, further increas- 

 ing the reliance of the ducks on the laguna in 

 Texas. 



Modification of dredging practices in Texas 

 and planning of waterway construction in 

 Mexico hold the most promise for sustaining 



.seagrasses and habitat for redheads to the max- 

 imum extent possible. At present, most dredge 

 disposal is to submerged receiving areas along 

 the channel, where bay resources are directly 

 affected and wave-caused resuspension some- 

 times impairs water clarity for long periods 

 after dredging. Land-based or deep-sea disposal 

 would alleviate these problems. In Mexico, con- 

 ducting an inventory of key resources, promi- 

 nently including seagrasses and redheads, rout- 

 ing the waterway to avoid concentration areas, 

 and implementing environmentally sound con- 

 struction and disposal practices will ensure the 

 greatest security for the wintering habitat of 

 redheads and other resources linked to seagrass 

 meadows. 



References 



Adair. S.E., and J.L. Moore. 1990. A survey of seagrass dis- 

 tribution of the middle Texas coast. Chapter 1 1 in S.E. 

 Adair. J.L. Moore. W.H. Kiel. Jr. and M.W. Weller. eds. 

 Winter ecology of redhead ducks in the gulf coast region. 

 Final Rep.. Cooperative Agreement 14-16-0009-87-909 

 between Texas A & M University and the U.S. Fish and 

 Wildlife Service. National Wetlands Research Center. 



Adair, S.E.. J.L. Moore, and C.R Onuf. 1994. Distnbutional 

 ecology of submerged aquatic vegetation in estuaries of 

 the upper Texas coast. Wetlands 14(2): 1 10-121. 



Dunton. K.H. 1994. Seasonal growth and bioniass of the 

 subtropical seagrass HaloJiile wrightii in relation to con- 

 tinuous measurements of underwater irradiance. Marine 

 Biology 120:479-489. 



Onuf, C.R 1994. Seagrasses. dredging and light in Laguna 

 Madre. Texas, USA. Estuarine, Coastal and Shelf 

 Science 39:75-91. 



Quanimen. M.L.. and C.R Onuf. 1993. Laguna Madre: sea- 

 grass changes continue decades after salinity reduction. 

 Estuaries 16:.^02-310. 



Texas Parks and Wildlife Department. 1965-67. Coastal 

 waterfowl project. Federal Aid Rrojects W-29-R- 1 8 to 24. 

 Austin. TX. 



Weller, M.W. 1964. Distribution and migration of the red- 

 head. Journal of Wildlife Management 28:64-103. 



For further information: 



Christopher P. Onuf 



National Biological Service 



Southern Science Center 



Campus Box 339 



6300 Ocean Or 



Corpus Christi.TX 78412 



The conterminous United States has nearly 

 142,000 km (88,182 mi) of tidal shoreline 

 that exists in a delicate balance with the forces 

 of nature (CuUiton et al. 1990). Much of this 

 shoreline and the coastal barriers in particular 

 are experiencing greatly increased pressures as 

 a result of rapid population growth and accom- 

 panying development. Although coastal areas 

 are highly desirable for their abundant natural 

 resources and habitability, they are also 

 extremely dynamic environments in which con- 

 ditions hazardous to humans (e.g., erosion, 

 Hooding, pollution) may be present. In many 

 regions, these hazards, which threaten not only 

 humans but also valuable marine resources and 

 even entire ecosystems, are increasing at alarm- 

 ing rates as coastal development, recreation, 

 and waste disposal increase, often in direct con- 

 flict with long-term natural coastal processes. 

 This article defines coastal barriers, summarizes 



their changes, and discusses the U.S. 

 Department of the Interior's (DOI) Coastal 

 Barrier Resources System (CBRS). 



Coastal Barriers Defined 



Coastal barriers are geologically recent 

 depositional sand bodies that are highly variable 

 in shape, size, and their response to natural 

 processes and human alterations. They may 

 stretch many kilometers in length and contain 

 high sand dunes — such as the Outer Banks of 

 North Carolina — or they may be small and iso- 

 lated islands, so low in relief that they are rou- 

 tinely overwashed by spring tides and minor 

 storms. Their dynamic nature means coastal 

 barriers are constantly shifting and being modi- 

 fied by winds and waves, but scientific field 

 investigations over the past several decades are 

 revealing some disturbing trends. 



Coastal 

 Barrier 

 Erosion: Loss 

 of Valuable 

 Coastal 

 Ecosystems 



by 

 S. Jeffress Williams 

 U.S. Geological Survey 

 James B. Johnston 



National Biological Service 



