Skagerrak^ Kattegat^ Belts, and Baltic Sea 



In the Skagerrak considerable biolixminescence may be observed in 

 the early spring. Observers on board the MV LAKSA reported a display 

 off southern Norway in April 19^3 which was determined to have been 

 caused by luminous dinoflagellates. Pleurobrachia , a luminescent 

 ctenophore, is very abundant in the Skagerrak in May. Numbers of this 

 small transparent organism appear much like beads of green light when 

 viewed in the water. This ctenophore is especially prevalent inside 

 Oslo Fjord in the spring. Shoals of luminescent medusae may be en- 

 countered in the various fiords and inlets along the southwest coast 

 of Sweden dinging the summer. Sheet-type bioluminescence has been ob- 

 served in the various extensions of Oslo Fjord in August. Also, heavy- 

 concentrations of luminous dinoflagellates are common in this fiord 

 diiring late summer. Euphausiids and copepods often create displays of 

 some intensity within the Skagerrak during late spring and summer. 



Extensive displays of light are not common in the Kattegat, Qresund, 

 and the Belts. Some large concentrations of the tiny tunicate 

 Appendicularia are responsible for green luminescence in coastal waters 

 of the island of Laeso and along the Danish coast. Ctenophores cause 

 bioluminescence inside Limfjord and Mariagerf jord. Noctiluca attains 

 maximum abundance in the Belts and Kiel Bay in Ifey and June. Lumines- 

 cence is very intense diuring August in the various bays around Kiel, 

 whereas in the open sea some distance from the coast it becomes in- 

 tense in September and October. Michaelis (183O) observed that the 

 blooming of Ceratium was most pronounced during windless, warm summer 

 days leading to some rather strong sheet-type displays in Kiel Bay. 

 Wintertime luminescence is rare, although sea light has been observed 

 under the ice at Kiel. 



Very little bioluminescence occurs in the Baltic Sea. Tarasov 

 (1956) has indicated that some bioliiminescence may be observed diiring 

 July and August in the western and central Baltic. Large numbers of 

 Pleurobrachia develop along the south coast of Finland in summer and 

 autumn and are probably responsible for some glowing-ball displays in 

 the Gulf of Finland. No significant bioluminescence has been reported 

 from the Gulf of Bothnia. The extremely low salinity would seem to pre- 

 clude the development of large numbers of luminous organisms. 



SOUTHERN NCRTH ATLARTIC AED SOUTH ATLAJJTIC OCEANS (FIGURES 2 and 3) 



The percentages of total observations between 20 N and the Tropic 

 of Capricorn for three-month periods are as follows: 



January through March 27'^ 



April through June 22^ 



July through September 29^ 



October through December 22^ 



15 



