FISHERY BULLETIN: VOL. 72, NO. 2 



The present work constitutes a more detailed 

 survey on the siphonophores of the regions ad- 

 jacent to the above mentioned interoceanic canals. 

 These studies are based on the Siphonophorae 

 material (65 plankton samples) collected by Israel 

 in the eastern Mediterranean during 1967, 1968, 

 1969, and 18 plankton samples (Red Sea, 1969, 

 1970) corresponding to two locations in the Gulf 

 of Elat; and the 64 plankton samples from Scripps 

 Institution of Oceanography Expeditions (La 

 Creuse 1962, Bonacca 1963, Thomas Washing- 

 ton 1969) in the Caribbean and Pacific regions 

 adjacent to the Panama Canal. The Scripps 

 Institution collections covered larger regions than 

 the area in which the present studies are con- 

 centrated, and the total collections of the 

 mentioned expeditions have been analyzed and 

 the results included in Alvariiio (1968, 1971, 

 1972). 



The present studies chiefly concern with the 

 distribution and some ecological aspects of the 

 siphonophores. The subject is treated under two 

 parts: 1) distribution of siphonophores in the 

 eastern Mediterranean and the Red Sea, and 

 2) the siphonophores of the western part of the 

 Caribbean and the Central American Pacific. 



The pattern of distribution of the species is 

 presented. Tables with the distribution of the 

 species include also references on previous records 

 for the regions. 



Maximum density for most of the species off 

 Israel and around Cyprus can be attributed to 

 the high productivity of the region (Lakkis, 

 1971). 



The present study also indicates the Red Sea 

 includes fewer species than the Indian Ocean. 

 This factor may be related to the high salinity 

 and temperature of the Red Sea, as well as to 

 the shallowness of the sill at Bab el Mandeb. 



The incidence of both polygastric and eudoxid 

 forms in most of the samples shows breeding 

 is taking place in those regions, and that repro- 

 duction may be an uninterrupted process along 

 the year. 



A large number of species of siphonophores are 

 truly cosmopolitan, inhabiting the Arctic, Antarc- 

 tic, Indian, Pacific, and Atlantic Oceans, whereas 

 other species inhabit only the Atlantic, Pacific, 

 and Indian Oceans (Alvariho, 1971), and some 

 others are restricted to the Indian Ocean, adjacent 

 waters and the southeastern Asiatic regions, 

 while few are restricted to either the Atlantic 

 or the Indo-Pacific regions. 



Owing to the above mentioned biogeographic 

 considerations, particular emphasis in the dis- 

 tribution of the species should be dedicated to 

 the pairs of closely related species allopatric 

 in distribution. The pairs to be considered corres- 

 pond to the Panamanian region: Chelophyes 

 appendiculata-Ch. contorta (respectively related 

 to cold-temperate, and warm waters), Muggiaea 

 atlantica-M. kochi (inhabiting respectively the 

 neritic temperate and neritic warm waters), and 

 Lensia challengeri-L. fowleri (respectively Indo- 

 Pacific and Atlantic species). 



The evidence of a two way migration "via" the 

 Panama Canal, as shown by the distribution pre- 

 sented by several species at the regions adjacent 

 to the entrance to the Panama Canal, could be 

 active, by progression of the population along the 

 waterway, or passively transported in the ballast 

 waters or the waters used in the cooling system 

 of ships. Therefore, migrations could be also 

 greatly intensified or enhanced by passive 

 transport along the canal. 



METHODS 



The plankton samples here analyzed were not 

 collected in uniform manner. The plankton 

 collections from the eastern Mediterranean and 

 the Gulf of Elat were obtained with a standard 

 plankton net of the Villefranche type, as designed 

 and described by Working Party No. 2 (1968). 

 The net has a mouth internal diameter of 57 cm, 

 a total length of 261 cm, and 200-^( mesh. Vertical, 

 oblique, and horizontal tows were taken. The 

 vertical and oblique hauls in the eastern Mediter- 

 ranean and the Gulf of Elat reached from 200 m 

 to the surface, and the horizontal tows were 

 obtained at various depths in the upper 200 m at 

 a speed of 2-3 knots during 10 min. 



The material from the Scripps Institution col- 

 lections corresponds to 1-m net oblique hauls 

 taken from about 140 m to the surface, and at 

 less than 100 m or less than 50 m in shallow 

 waters; and the V2-m net oblique tows were 

 obtained from about 150 m to the surface and the 

 horizontal hauls at various depths between 50 

 and m. 



Each total plankton sample was analyzed for 

 siphonophores, and the number of specimens 

 determined for both polygastric and eudoxid 

 forms. However, owing to the diversity of the 

 collecting methods used, and the time span 



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