hackberry ( Celtls laevigata ) , Hercules- 

 club ( Zanthoxylum clava-herculls ) , and 

 wax myrtle ( Myrica cerifera ). 



Although the rate of primary pro- 

 duction in dune areas is considerably 

 lower than in marsh habitats, the role 

 of dune plants in stabilizing and ac- 

 cumulating sediments is critical. 

 Plant stems trap wind-blown sand that 

 would otherwise be lost to the beach 

 system, and the roots, which sometimes 

 extend far beneath the surface, bind the 

 sand together. Vegetation in the beach 

 habitat also supports populations of 

 rabbits and other small mammals, birds, 

 and reptiles. 



The intertidal portion of the beach 

 habitat is the focus of rapid energy 

 flux, but much of this activity is not 

 apparent, because it occurs beneath the 

 sand surface and it involves small 

 organisms. A characteristic group of 

 burrowing organisms feeds on the organic 

 matter that is pumped through beach 

 sands by tidal and wave energy. These 

 organisms are eaten in turn by predatory 

 burrowers and by shorebirds that feed in 

 the swash zone. An excellent descrip- 

 tion of the dynamics of the intertidal 

 beach community can be found in Peterson 

 and Peterson (1979), although the com- 

 parison between high tidal energy North 

 Carolina beaches and low energy northern 

 gulf coast beaches is not perfect. 



MDPR beaches tend to be muddy and 

 carbonate rich. The beach intertidal 

 community includes meiobenthic and 

 macrobenthic fauna, the former con- 

 sisting primarily of the so-called 

 interstitial fauna, tiny crustaceans 

 that live in the spaces between sand 

 grains. The most conspicuous of the 

 larger animals that occupy the lower 

 beach are molluscs, including bivalves 

 (e.g., Mulinia sp., Gemma gemma ) , gas- 

 tropods, and Crustacea (e.g., Orches- 

 toidea sp., Emerita sp., Ocypode qua- 

 drata) . Some benthic beach inhabitants 

 are deeply burrowing forms that are 

 rarely seen unless core samples are 

 taken. These include polychaetes like 

 Diopatra sp.; hemichordates like Balan- 

 oglossus sp.; and crustaceans like 

 Callianassa sp . Burrowing forms are 

 important food sources for specialized 



shorebirds like plovers, willets, san- 

 derlings, and sandpipers, that forage in 

 the swash zone during low tide. During 

 times of inundation, the benthic fauna 

 in the beach habitat provide food for 

 predatory nekton, which includes members 

 of the family Dasyatidae (stingrays) , 

 Cyprinodontidae (killif ishes) , Engraul- 

 idae (anchovies) , and Scianidae (drums) , 

 among many others. The functional par- 

 titioning of this intertidal food source 

 by various fish and bird groups is des- 

 cribed by Peterson and Peterson (1979) . 



Besides the feeding areas of the 

 intertidal sand and mud flats, the 

 higher beach and dune areas are also 

 important to birds. Migrating species 

 like warblers use them as resting 

 points, and shorebirds as nesting 

 grounds. In a 1972 study of dune ridges 

 inland from Caminada Bay (Barataria 

 hydrologic unit) , 69 species of mi- 

 grating birds were identified as using 

 the dune habitat during the spring 

 migration period (Hebrard, unpublished 

 data cited by Bahr and Hebrard 1976). 

 Nesting colonies of black skimmers, 

 Sandwich terns, royal terns, least 

 terns, Caspian terns, gull-billed terns, 

 and laughing gulls are all found on the 

 barrier island beach and dune habitats 

 in the MDPR. 



Because of the vulnerability of 

 beaches and dunes to storm erosion, and 

 because the entrainment of the Missis- 

 sippi has caused a lack of sediment 

 enrichment in many parts of the MDPR, 

 the erosion of barrier islands and 

 retreat of shore lines is a serious 

 problem. Penland and Boyd (1981) esti- 

 mate that the Chandeleurs have been 

 receding at rates of from 1 to 20 m/yr 

 (averaging 7) or 3 to 65 ft/yr (aver- 

 aging 23) during the past 60 years. It 

 is likely that these islands will to- 

 tally disappear during the next century, 

 causing increased marsh erosion in the 

 Pontchartrain hydrologic unit (Baumann 

 et al., in preparation). 



Although there has been some oil 

 and gas industry activity on Timbalier 

 Island, the only barrier island in Lou- 

 isiana that has been extensively de- 

 veloped is Grand Isle. By 1970, more 

 than one-third of the island had been 



42 



