ForImmediateRelease:MonthDD,YearContact:MattGlasenapp,AnnabelleLeahy,MarieSpychala,YageWang www.sea.edu

EelLarvaeDistributionShowsGeographicTrendswithinWesternNorthAtlantic

June13,2017,WoodsHole,MA

Scientists from the Sea Education Association found that eel larvae, known as leptocephali, follow geographic family distribution trends, and that their nightly migration may be affected by moon illumination. Family Distribution

Of the 180 samples morphologically identified, 32% were from the Nemichthyidae family and 28% from the Congridae family. Samples from the Anguillidae, Xenocongridae, Derichthyidae, Moringuidae, Muraenidae,

Ophichthidae, and Serrivomeridae families were also collected. The Antilles Current and South Sargasso Sea regions were notably more diverse compared to the North Sargasso Sea. “It was really exciting to look at the lepto samples in the South Sargasso and Antilles Current regions. In those nets there were a lot of interesting families that aren’t commonly seen,” said Marie Spychala, one of four scientists on the research team. Also notable was the significant decline in total samples caught compared to numbers seen in previous studies conducted in the same area.

Data Collection

In 5-week long study conducted in the Sargasso Sea aboard the research vessel SSV Corwith Cramer, the scientists collected samples from nightly net tows at surface, 50 meter, and 100 meter depths throughout three main regions: the Antilles Current, the South Sargasso Sea, and the North Sargasso Sea. The vessel followed a cruise track from the Bahamas, to Bermuda, ending in New York.

Vertical Migration

Because light intensity has often been identified as a confounding factor in leptocephali research, family abundance at different depths was also analyzed in relation to moon illumination. Eel larvae, like many other small marine organisms, migrate great distances vertically through the water column, traveling up to the surface at night and returning to the depths during the day. Research has shown that moonlight may affect migrating behaviors, but there are few studies on the

© Solvin Zankl

© Solvin Zankl

subject. In the future, more research will be needed to determine true correlation, but some promising evidence was found in support of these hypotheses. Number of eel larvae found at the surface generally decreased as moon illumination, while the opposite trend occurred at depth. These patterns make sense in the context of known eel migration behavior, as we would expect individuals to not migrate to the surface from greater depths when illumination is highest.

Genetic Analysis The most common species collected

throughout the voyage was Ariosoma balearicum, from the Congridae family. It was previously hypothesized that Ariosoma balearicum had two separate breeding sub-populations. Further molecular work was conducted on the cruise in order to assess these claims as well as to offer insight into possible factors that could be contributing to this diversification. The two unique subpopulations were distinguished by the number of myomeres, the vertical muscle bands visible only under microscope. After counting the myomeres of the cruise samples, there

was a clear distinction between two groups, one with a high myomere count (>126) and one

with a low count (<126). Despite these morphological differences, results of genetic analysis did not show a correlation between myomere counts and genetic variation. This was comparable to the results of previous studies from SEA cruises, however, this evidence refutes past study on these populations of leptocephali, confirming the need for future study in eel larvae genetics.

Sargasso Sea Conservation Eels and eel larvae are underrepresented in marine research, so the further study of eel larvae will provide

clues to the interactions or isolation between populations or species. As threats to certain species of eels and their habitats grow, it will become increasingly important to study both eels and eel larvae to understand the dynamics of the Sargasso Sea for future conservation for both the ecosystem and the eels. AboutSeaEducationAssociation/SEASemester®SeaEducationAssociation(SEA)isaninternationallyrecognizedleaderinundergraduateoceaneducation.Fornearly45yearsandmorethanonemillionnauticalmilessailed,SEAhaseducatedstudentsabouttheworld’soceansthroughitsBostonUniversityaccreditedstudyabroadprogram,SEASemester.SEA/SEASemesterisbasedonCapeCodintheoceanographicresearchcommunityofWoodsHole,Massachusettsandhastworesearchvessels:theSSVCorwithCramer,operatingintheAtlanticOcean,andtheSSVRobertC.Seamans,operatinginthePacific.

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© Solvin Zankl