Invertebrate Zoology (IZ) research zoologist Jerry Harasewych has recently developed a special interest in glass bottles recovered from the sea floor. Several years ago, Jerry noticed that many such bottles contained tiny snail shells. It turns out, the bottles are home to small octopuses (e.g., Macrotritopus cf. defillipi) that capture and bring the shells back into the bottles to feed on their inhabitants, leaving the empty shells to accumulate in the bottle.
Jerry first observed this phenomenon on dives using the "Curasub" submersible off the coast of Curaçao. These dives were conducted as part of the Deep Reef Observation Project (DROP), which is a long-term collaboration between the Smithsonian and the Curaçao Sea Aquarium, owned by Adrian "Dutch" Schrier. Since discovering the peculiar shell-filled bottles, Jerry has started collecting them as a means of conveniently recovering large numbers of shells from difficult-to-sample deep sea locations.
According to Jerry, these shells are small—small enough to fit through the mouth of a glass soda bottle! That also means these shells are usually too small to see by eye through the curved windows of the submarine. Instead, "the octopus is finding them for us," says Jerry, appreciative of his new "collaborators." Depending on how long a given bottle has been submerged, it can contain empty shells from weeks, months, or even years of meals.
From a handful of bottles already analyzed in the lab, Jerry and his colleagues have discovered several new species of snail, some already published (such as Attenuiconus marileeae), others still in manuscript form. The team has also uncovered many significant extensions to the known distributions of other deepwater species. Of course, Jerry warns that this technique is not without limitations.
To begin with, almost all of the shells recovered from the bottles are simply that--shells. Their original snail inhabitants are long gone. In fact, Jerry has observed that most of these shells exhibit the telltale signs of subsequent habitation by hermit crabs. Pointing to the broken edge of a shell, Jerry states matter-of-factly, "no self-respecting snail would live in a shell like that."
Many of the shells have evidence of tube worms on their surfaces—or even in their openings. Some of the shells are from snail species known to burrow in the sediment, so the presence of tube worms and encrustations of animals that only grow on surfaces exposed above the sea floor indicates that the octopuses collecting these snail shells weren't eating snails at all, but hermit crabs.
Of course, each bottle can contain as many as one hundred snail shells. The full contents of a bottle must be sorted, cleaned, identified, catalogued, and imaged, in many cases using a scanning electron microscope because the distinctive features are so small. This work has benefited greatly from the energetic help and support of Marilee McNeilus, who has an extensive interest in mollusks. Marilee has not only participated in the dives using the Curasub, but she has also put in long hours sorting and processing the specimens. Rosemary Ginzberg has recently joined the effort, producing the scanning electron microscope images that will be added to the Electronic Museum ("EMu") records as the tiny shell specimens are catalogued and entered into the museum's collections.
The ultimate goal is to collect living specimens of many of the more rare species that have been discovered in the bottles, so that they can be used in anatomical and molecular studies. To aid this effort, prototypes of traps and substrate arrays are being designed and deployed in areas that have produced the most interesting finds.
Most of the bottles were sampled at depths of 400-1,000 feet, from an area off the southern coast of Curaçao near Willamstadt that has been used as a harbor since 1634. Bottles are not uncommon on the bottom in that area, the result of nearly four centuries of accumulation. Still, the vast majority are modern, with easily recognizable shapes and brand names.
Although the bottle technique is a great adjunct to sampling using submarines, it should, in theory, be applicable at most subtidal depths. Many biologists as well as hobbyist shell collectors are also SCUBA divers, and Jerry hopes to see the new technique expanded to snorkel and SCUBA depths. Jerry will be advocating this approach among friends and colleagues at various shell and SCUBA club meetings in the near future, and he expects preliminary reports of others recovering bottles to begin arriving within a year.