MIGRATION MYSTERY
Netting Clues to Solve a Deep-sea Puzzle


Mission Specs:
When: June 1 - 11, 2005
Where: San Clemente Basin (off the coast of Southern California)
Who: Dr. Tammy Frank - HARBOR BRANCH Oceanographic - Visual Ecology Dept.
What: Visual Adaptations of Ontogenetic Migrators

Summary
Each day, the open ocean supports the world's largest migration as countless forms of sea life travel from deeper waters to the surface to feed there under the relative safety of darkness. An equally fascinating but far less understood migration that also takes place in the open ocean is driven not by light, but age.

Beginning June 1, an international team of scientists will journey to the San Clemente Basin off the Coast of Southern California to explore the common phenomenon known as "ontogenetic" migration, where many squid, fish, shrimp and other animals move deeper in the water column as they get older. Dr. Tammy Frank, head of Harbor Branch's visual ecology department will lead the expedition as chief scientist aboard the R/V New Horizon, operated by the Scripps Institution of Oceanography in La Jolla, California.

Frank's research will explore the visual adaptations of "ontogenetic" migrators. Young ontogenetic juveniles live in the upper 200 m of the water column, which is brightly lit compared to the darkness of deeper waters, while mature adults are found at 700-1000 m depth depending on species. Other scientists aboard, from universities in the U.S., Germany, and the UK, will be studying a variety of other topics ranging from how the internal clocks of deep-sea animals can function without benefit of regular daily light cycles to the physiology of squid and worms found in the region.

Almost nothing is known about how these two life history stages adapt to such dramatically different light environment. Is it a matter of possessing an eye that works in both bright and dim light, but isn't really optimal for either condition? Or are there mechanisms in place that allow for a dramatic restructuring of the migrator's eye from one that works very well in bright light to one that works very well in dim light?

The team will answer this question using a combination of physiological, molecular and histological (the microscopic study of tissue structure) techniques. This information is of great importance, as many of these ontogenetic migrators are major components of the oceanic food webs that support commercial fisheries. Understanding whether and how they adapt to different light environments is critical to predicting what effect a change in their light environment (such as a change in water clarity due to pollution) may have on their depth distribution patterns.

The San Clemente Basin, about 2,000 meters deep where the team will work, was chosen as the ideal location for the research because intense upwelling in this region, which brings nutrients up into the water column, fosters an abundance and diversity of midwater fish, shrimp and squid. Frank's work will focus on a crustacean called Gnathophausia ingens, which is found there in great abundance, has 3 distinct depth ranges based on age, and can live up to 8 years. This species has one of the largest known ontogenetic migrations--from 100m for juveniles to 900m for adults.

This expedition will be the scientists' first chance to use a new "mother tucker" trawl net. This net is twice the size of the "baby tucker" that Frank has used on previous cruises, with a 3 m x 4.25 m mouth opening (10 ft. x 14 ft.) that can be opened and closed by a timer to capture animals at specific depths. A specially designed closing end piece allows collection of animals in darkness, which prevents damage to their delicate eyes that would be caused by bright light at the surface. This is one of only a few nets in the country capable of retrieving live, deep-sea animals without blinding them. The net bars, release mechanism, and closing cod-end of the mother tucker were designed and constructed by HBOIs engineering department. Various forms of the tucker trawls have been used since the 1950s and are named after their inventor.

CRUISE PARTICIPANTS

This expedition is made possible by a grant from the National Science Foundation (NSF) Division of Integrative Biology and Neuroscience, which is providing science support, and Division of Ocean Sciences, which is providing the shiptime support. Additional support is provided by Harbor Branch Oceanographic Institution.



© 2005, Harbor Branch Oceanographic Institution