210 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



preliminary results of the work east of the 

 Mississippi delta (carried out by R. H. Parker) 

 indicate that there is a density of 100 individual 

 mollusks (mostly Mulinia lateralis) per orange 

 peel bucket sample of 100 cu. in. capacity on some 

 muddy bottom areas in this region. It would 

 appear that we have here a community comparable 

 to the Syndosmya {=Abra) community of "shallow 

 and protected waters of an estuarine character" 

 (Jones 1950). Such a community, composed of 

 small, rapidly growing species, may have a rapid 

 overturn and thus have a higher productivity 

 in terms of harvestable crop than a community 

 composed of larger, slower growing species. It 

 would also be less stable. 



SERPULOID REEFS 



While the serpuloid reefs of Bermuda are fairly 

 well-known to biologists, at least by hearsay, it is 

 not generally realized that similar reefs occur in 

 the Gulf of Mexico. There is a smaU area of 

 scattered serpuloid reefs at the junction of Baffin 

 Bay and the Laguna Madre, south of Corpus 

 Christi, Texas, and a larger area near Veracruz, 

 Mexico. Recent efforts to collect the worm that 

 caused these growths in Baffin Bay have been un- 

 successful, and there is some question as to 

 whether this reef is still actively growing. Ac- 

 cording to W. Armstrong Price, there is evidence 

 that these reefs had been actively growing within 

 the last 80 years. The only information of the 

 reefs near Veracruz is the brief paper by Heilprin 

 (1890). Two reefs are mentioned; one, near 

 Punta Gorda, was, at the time, lying parallel to 

 shore about }i mile from land, about /(e mile wide 

 and about % mile in length. The other, off Punta 

 de Hornos, was about the same size and in the 

 same relative position to the shore line but about 

 half as wide. A modern survey of these reefs 

 should provide interesting information as to 

 growth and ecology. 



The serpuloid reefs of Baffin Bay are of peculiar 

 interest in view of the high salinities which occur 

 in this region. Salinities as high as 80 parts per 

 thousand have been recorded, and during the pe- 

 riod from July 1946 to October 1948 the lowest 

 recorded salinity was 41.6 parts per thousand. 

 Samples of serpuloid rock from this region have 

 yielded two species of polychaetes, two amphipods 

 and a barnacle. All the species are well-known 

 estuarine forms. 



THE JETTY COMMUNITY 



There are no naturally rocky shores in the 

 eastern or northern Gulf of Mexico, hence, there 

 are no extensive hard-bottom communities. A 

 limited fauna and flora has become established on 

 the various jetties along the Texas coast and also 

 on the short jetties at Calcasieu Pass near Cam- 

 eron, but the life of the jetties on the passes of 

 the Mississippi Delta has not been studied. The 

 biota of the Texas jetties has been discussed by 

 Whitten, Rosene, and Hedgpeth (1950) who de- 

 scribe the intertidal community of these jetties 

 as consisting principally of three species of 

 barnacles, a pulmonate limpet, a littorine, a 

 species of Brachidontes , and various less numerous 

 elements. Plants, an essential component of such 

 communities, were not studied. This community 

 was built up by colonization from nearby bottom 

 habitats and possibly sargassum since construction 

 of the jetties six or seven decades ago. Two motile 

 artliropods, the isopod, Ligia exotica, and the al- 

 most cosmopolitan crab, Pachygrapsus transversus, 

 are among the most characteristic and obvious 

 members of this community. 



Zonation is well-marked on the jetties, although 

 the zones are narrow and vary somewhat with the 

 season. At Port Aransas the average low-water 

 line is marked by a belt of the brown algae, 

 Padina vickersae, which extends down to extreme 

 low water, 8 to 12 inches lower. Above the 

 Padina belt is another narrow zone characteris- 

 tically occupied by various red algae, especially 

 Gelidium, Bryocladia, and the like, topped by a 

 still narrower band of Ulva. In these algal zones 

 are found such snails as Thais and Cantharus, and 

 in the Padina zone are found the purple urchin, 

 Arhacia punctulata, and the anemone, Bunodosoma 

 cavernata. Between the top of the narrow Ulva 

 belt and the maximum concentration of barnacles 

 {Chthamalus fragilis) at about 2.5 to 3 feet above 

 mean low water, there is a sparse scattering of 

 barnacles. Above the barnacles are found the 

 small, black littorine, Littorina ziczac, and the 

 pulmonate limpet, Siphonaria pectinata. 



There are, in summary, three principal zones on 

 the jetty rocks and walls: an upper zone, charac- 

 terized by the littorines and barnacles, a middle 

 algal zone occupied by greens and reds, and the 

 lower Padina zone. This pattern is associated 

 with the average tidal levels for most of the year. 



