@Sea - Migration Mystery 2

	MIGRATION MYSTERY 2 Netting Clues to Solve a Deep-sea Puzzle Mission Specs: When: September 10 - 20, 2006 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 on September 10th, a 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 Wecoma, operated by Oregon State University. This research is a continuation of research started last year on the visual adaptations of "ontogenetic" migrators. In the life history of ontogenetic migrators, young juveniles live in the upper 200 m of the water column, which is brightly lit compared to the darkness of species. Work will continue on the deep-sea mysid Gnathophausia ingens, which has 2 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 700m for adults 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? Last year Dr. Frank discovered that temperature has a significant effect on the temporal resolution of the eye of Gnathophausia ingens. Temporal resolution basically tells you how fast an eye can track moving objects, and is easiest to understand if you think about how a camera shutter works. For example, in order to photograph a bird flying without blurring the image, you need a really fast shutter speed, keeping the shutter open for only 1/100 s. This is akin to having an eye with a very high temporal resolution. However, in order to get an image, you need to take your picture in very bright sunlight, because the shutter is open for such a short period of time. This means that eyes with high temporal resolution are less sensitive to light. To take pictures in dim light, you need to leave the shutter open for much longer periods of time, which means that moving objects will be blurred, but at least you'll have an image. This means that eyes adapted for dim light environments, like the deep sea, should have low temporal resolution. Preliminary evidence (what scientists say when they need to do more experiments) indicates that temperature alone can turn a slower eye into a faster one. This means that the shallow living juveniles may be less sensitive to light (and better able to track prey and predators) than the deep living adults because the water is warmer in their environment. On the upcoming cruise, Dr. Frank hopes run experiments on both juveniles and adults at a number of temperatures, to confirm last year's observations. Experiments will also continue to determine whether juveniles and adults are sensitive to the same colors of light. On last year's cruise, graduate student Elizabeth Whitehill started a study of the structure of the eyes, and found that optics of the eyes of the juveniles suggest that they're adapted for bright light. This year, she hopes to collect both older juveniles and adults, to try to determine when the transition to the adult-type eyes occurs. In addition, animals will also be collected for Megan Porter and Tom Cronin, at University of Maryland, Baltimore County Campus, who couldn't participate on the cruise this year. They are trying to determine if there are differences in the visual pigments between the juveniles and adults. 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. Gnathophausia ingens, the focus of this work, is found there in particularly great abundance. The animals will be collected with a specially designed net called tucker trawl. This net has 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.