THE BRYOZOA OF THE GULF OF MEXICO 



By Raymond C. Osburn. Allan Hancock Foundation, University of Southern California 



Brj'ozoans are abundant organisms everywhere 

 in the seas, from the polar regions to the tropics, 

 from the shore line to great depths, but with only 

 a few representatives in fresh water. The indi- 

 viduals are all small, rarely more than one milli- 

 meter in length, but their capacity for budding is 

 so great that they often produce colonies of con- 

 siderable size. With a few exceptions the colonies 

 are all attached, and most of them are encrusting. 

 Some species produce thick nodular masses by the 

 piling up of layer on layer, while still others grow 

 erect in branching bushy colonies to the height of 

 several inches. Within the Gulf, they are abun- 

 dant, encrusting shells, stones, dead corals and 

 corallines, algae, or anything else that may afford 

 attachment. The individuals are encased in hard 

 chitinous or calcareous walls, and they appear to 

 be of little importance in the food chain of other 

 animals, but their nuisance value in the fouling of 

 ship bottoms and buoys and the covering of 

 oyster beds to the exclusion of young oysters is of 

 considerable economic importance. The rate of 

 budding is so rapid that oyster shells used as 

 cultch on oyster beds may be completely covered 

 in a few weeks to the exclusion of oyster larvae. 



Apparently the first mention of Bryozoa from 

 the Gulf is the small list of 7 species by Count de 

 Pourtales in 1867. Pourtales then turned the 

 material obtained by him on the expeditions of the 

 U. S. Coast Survey, 1867 to 1869, over to the 

 Swedish zoologist Smitt for further study. The 

 area concerned was that about the Tortugas 

 Islands and the Straits of Florida, and Smitt re- 

 ported on 95 species, many of them new. In 1914, 

 Osburn discussed 83 species obtained by him in 

 shallow water around the Tortugas Islands, add- 

 ing 40 species to Smitt's list. In 1928, Canu and 

 Bassler reported on more than 40 dredgings made 

 by the U. S. Fisheries Steamer Albatross and added 

 36 more species, most of them new to the Bryozoa 

 of the Gulf. This makes a total of only about 170 

 species known from this great area, depending 



more or less on just where the boundary line is 

 drawn and also on the indefinite nature of some 

 of Smitt's records. 



From the neighboring West Indian and Carib- 

 bean waters. Busk (1884) listed 5 species from 

 near Puerto Rico, and in 1909, Levinsen men- 

 tioned a few species from the Virgin Islands. 

 Osburn (1927) reported on a small collection of 

 23 species taken by Dr. C. J. van der Horst at 

 Curagao Island; in 1940, on his own collection of 

 124 species from the southern shores of Puerto 

 Rico; and in 1947, on 107 species recovered by 

 the Allan Hancock Atlantic Expedition off the 

 southern shores of the Caribbean Sea. All of 

 these reports will be useful in the study of the 

 Bryozoa of the Gulf. The reports by Canu and 

 Bassler (1928) and Osburn (1940) contam de- 

 scriptions and references for all of the Gulf species. 



The Bryozoa of this region are strictly warm- 

 water species, many of them known to be circum- 

 tropical in distribution, and of the 170 species 

 recorded, 105 have a wide range in other seas. 

 Only 35 have not been recorded outside of the 

 Gulf, and some of these will undoubtedly be 

 found elsewhere. 



It might be supposed that the Gulf species 

 would show a close relationship to those of the 

 Pacific across the narrow region of Central Amer- 

 ica, but such is not the case. It is true that 93 of 

 the 170 Gulf species occur also in the eastern 

 Pacific, but nearly all of these are species of wide 

 distribution, and only 16 have been found only 

 in the Gulf and the near waters of the Pacific. 

 It would appear that most of the species have 

 been evolved since the waters of the Atlantic were 

 last closed oS from the Pacific. 



In the different groups of Bryozoa the numbers 

 of known species are as follows: 



Cyclostomata: 8 species recorded from within 

 the Gulf and 10 more from the adjoining West 

 Indian region ; many more undoubtedly occur. 



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