this reason, Haddock spent hundreds of hours using MBARI's remotely operated vehicles (ROVs) to observe siphonophores in their native habitat, thousands of meters below the sea surface. The siphonophore featured in Haddock's article (which is an unnamed species in the genus Erenna) lives at depths of 1,600 to 2,300 meters, where fish are few and far between. For this reason, Haddock was surprised to observe small fish in their guts. He found himself wondering how these jellies could capture enough fish to survive in their sparsely inhabited environment. Examining the siphonophores under the microscope, he discovered that interspersed among their stinging tentacles were thin rod-like structures. These "tentilla" were tipped with red, glowing blobs.

Several lines of evidence eventually led Haddock and his coauthors to the conclusion that these red blobs served as lures for small deep sea fish. Their first clue lay in the siphonophore's behavior. Jellies that use bioluminescence for self defense tend to have lights distributed all around their body, which flash brightly when disturbed (the "burglar alarm effect"). In contrast, the Erenna siphonophores kept their bioluminescence very localized and under tight control, suggesting that their lights had an entirely different function.

Continuing his microscope work, Haddock found more specific clues-the red, glowing blobs were shaped remarkably like the bodies of deep-sea copepods, a major food item for small deep-sea fish. Furthermore, the tentilla flicked back and forth repeatedly so that the glowing lures darted through the water just like swimming copepods. Finally, at least one siphonophore's digestive system contained both fish and lures, suggesting that the lures were ingested along with the fish.

Haddock sees these glowing lures as Erenna's way of adapting to a difficult environment. As he put it, "Most siphonophores set a big web of tentacles to catch animals that happen to swim by. But
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Contact: Kim Fulton-Bennett
kfb@mbari.org
831-775-1835
Monterey Bay Aquarium Research Institute
7-Jul-2005

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