in the western Mediterranean occur from October through June. Sheet- 

 type displays predominate, with an occasional glowing-ball display. 

 Luminescent salps, pyrosomes, and medusae are responsible for many of 

 these displays. Pelagia noctiluca is especially plentiful in the sur- 

 face waters of the western Mediterranean. Salps often almost fill the 

 water; the organisms frequently form long chains and may emit long 

 lasting and rather intense light when disturbed. Noctiluca may be 

 present in great abundance, tinging the water red by day and luminescing 

 brightly by night. 



During one of the many cruises of the Norwegian research vessel 

 MICHAEL SARS in April I9O9, Murray (1912) noted that the sea surface 

 for several nautical miles in the Sea of Alboran was full of "phospho- 

 rescent" Noctiluca . The concentration was so great that the water was 

 like a "broth," and in the evening "the sea resembled a star-spangled 

 sky, and the wires following the vessel looked like gleaming stripes." 

 A more recent report from the SS EXANTHA in January 1951 bears out the 

 fact that strong sheet-type luminescence can be expected in this region. 

 The water was "phosphorescent" for several nautical miles along the 

 coast of southern Spain. The ship created a "liiminous sheet" so in- 

 tense that it was possible to read by the light emitted. The cause 

 of this luminescence was not ascertained; however, it was of the type 

 produced by dinoflagellates such as Noctiluca . Very intense biolumin- 

 escence has been observed di;iring the summer along the coast of Algeria. 



Luminous euphausiids are responsible for many spaxk-type displays 

 along the coast of southern Prance and northwestern Italy. During the 

 winter months these organisms may appear in large swarms, coloring the 

 water red. At night the light given off is sparkling and bluish white 

 in color, and when the organisms all light, the water takes on a "blue 

 radiance . " 



To the south, swarms of Noctiluca occur in the Bay of Naples in 

 August and September. Ehrenberg (1659)^ a German biologist, noted the 

 long luminescent walce created by these organisms as his boat traveled 

 through the water of the bay. He also noted that the fronds of a 

 common brown seaweed (Fucus) were covered by these tiny luminescent 

 forms, the fronds appearing to glitter when disturbed. Biolumi nescence 

 occurs most frequently during the spring and summer months in the Bay 

 of Naples. 



In the northern Adriatic Sea, biolumtnescent displays are observed 

 more often than in any other part of the Mediterranesn. The lumines- 

 cence observed in the coastal waters here is most pronounced from April 

 through September. In April and May water near the mouths of the Po 

 may become very luminescent; the development of Itjjninous organisms is 

 increased by the nutrients washed from land during the high springtime 

 runoff. At times bioluminescence may be produced by bacteria or proto- 

 zoa. Apparent bacterial luminescence usiially is found in fiordlike 

 inlets along the northern Yugoslavian coast, where much decomposition 

 and stagnation occur. 



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