The question reminds me of the story, possibly in Kingdom
of the Seashell, about people in the Maldives maintaining a
high standard of living by harvesting money cowries.
Putting a palm frond in the water would provide an
apparently good hiding place for the cowries, which would
then be easily gathered.  Any kind of plant would work as
long as it was large and study enough to sit on the seafloor
awhile and then be picked up with shells hiding on it.

    Dr. David Campbell
    Old Seashells
    46860 Hilton Dr #1113
    Lexington Park MD 20653 USA
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That is Uncle Joe, taken in the masonic regalia of a Grand
Exalted Periwinkle of the Mystic Order of Whelks-P.G.
Wodehouse, Romance at Droigate Spa