Liqia baudiniana , the rapid crabs 

 Sesarma cinereum and Cycloqrapsus 

 inteqen , and most commonly, the 

 gastropod Tectarus muricatus . The 

 vegetation generally exhibits a 

 terrestrial species composition, but 

 may vary from none at all to an 

 almost complete strand community. 

 Common flora include the white and 

 black mangroves ( Laquncularia 



racemosa and Avicennia qerminans ), 

 buttonwood ( Concocarpus erecta ), 

 seaside mahoe ( Thespesia populnea ), 

 bay cedar ( Suriana maritima ), beach 

 morning glory ( Ipomea pes-caprae 

 var. emarqinata ) , sea ox-eye ( Borri- 

 chia frutescens and B» arborescens ) , 

 saltwort ( Batis maritima ), glasswort 

 ( Salcornia perennis ), samphire 



( Philoxerus vermicularis , sea-purs- 

 lane ( Sesuvium portulacastrum ) , and 

 several coarse grasses including 

 salt grass ( Distichilis spicata ) 

 and keygrass ( Monanthochloe litto- 

 ralis ) . 



The gray zone, denoted by a 

 grayish rock, is generally vegetated 

 by many of the white zone species. 

 It is also the most upland zone on 

 the platform, to contain any signs 

 of macroscopic marine algae. The 

 occurence of the red microalgae, 

 Bostrychia tenella , and the flower- 

 ing terrestrial plants in the same 

 zone is related to the partial wet- 

 ting at spring high tide of the gray 

 zone, thus providing a suitable en- 

 vironment for both communities. All 

 three mangrove species ( Rhizophora 

 mangle , Avicennia qerminans , Laqun- 

 cularia racemosa , ) may be present 

 and, in some cases, flourish in this 

 zone. Other plant species commonly 

 found include: sea purslane ( Sesu- 

 vium potulacastrum , saltwort ( Batis 

 maritima ) , samphire ( Philoxerus 

 vermicularis ) , glasswort ( Salicornia 

 perennis ) , sea ox-eye ( Borrichia 

 frutescens ) , and the grasses Monan - 

 thochloe littoralis (keygrass) and 

 Sporobolus virqinicus (dropseed). 



The animal density and diversity 

 increases from white to gray zones, 

 as one would expect with the gray 

 zone's more moderate environment. 

 The snails Littorina ziczac , Tecta- 

 rius muricates , Nodilittorina 



tuberculata , Echinius nodalosus , and 

 Nerita peloronta are characteristic 

 of this zone. _N^_ peloronta reaches 

 maximum density in this zone. An- 

 other nerite snail ( N. versicolor ) 

 is commonly found although it reach- 

 es its maximum in the next seaward 

 zone (black). Other animals typi- 

 cally occuring in this zone include 

 the two rapid crabs Sesarma cinerum 

 and Cycloqrapsus integer , the small 

 gastropods Melampus flavus , M. cof- 

 feus qundlach , Detracia bulloides , 

 Truncatella bilabiata and T. pul- 

 chella , the isopod Liqia baudiniana , 

 and earthworms and spiders. Gener- 

 ally a beach wrack (i.e., an assort- 

 ment of marine grasses, Sarqassum , 

 and other algae) is deposited in 

 either gray or black zones by waves 

 at the high tide line. This wrack 

 harbors thousands of crustaceans 

 (primarily amphipods and isopods) 

 and insects. 



The black zone is completely 

 wetted by the higher spring high 

 tides but may be only partly wetted, 

 if at all, by lesser spring tides. 

 Because of the convolution in the 

 surface of many platforms, deter- 

 mining the actual area wetted is 

 further complicated by the way the 

 sea may invade the lower levels 

 through fissures, inlets, and hol- 

 lows before covering the crests of 

 the upper platform. The vertical 

 depth of the black zone appears 

 constant, ranging from 11.3 to 21.3 

 cm (4.4 to 8.4 in) with a mean of 15 

 cm (6 in). This consistency repre- 

 sents a departure from the more 

 variable and erratic vertical dimen- 

 sions of the white and gray zones 

 (Stephenson and Stephenson 1950). 

 The black color (dark yellow-gray) 



183 



