The Sargasso Sea lies within and is probably responsible for the myth of
the Bermuda (Devil's) Triangle, a region of the western Atlantic which
covers about 440,000 sq. miles between the island of Bermuda, the coast
of southern Florida, and Puerto Rico.  It was first reported by
Christopher Columbus and regarded as uncanny and perilous by early
sailors.
 
Sargassum weed is a form of Brown Algae. The beds support many life
forms, but because the sea has weak currents, low precipitation and high
evaporation, the waters are saltier than those of other seas, making
them inhospitable to many species.
 
It is curious that freshwater eels (family Anguillidae) from Europe and
North American choose to spawn there.  After spawning there, the eels
die, leaving the free-floating eggs which take one year to reach North
American and three years to reach Europe.
 
If you are to find Janthina among the sargassum weed, then I would say
the hurricane season is the best time.  It is these storms that break
off parts of the weed and send them along the Gulf Stream.  Where we
lived in the panhandle of Florida, the invasions of Sargassum weed were
an annual occurence, much to the dismay of the tourist industry.  It
occured mostly in mid to late summer and early autumn.
 
Sylvia Edwards