Community structure and diets of fishes associated with pelagic Sargassum and open-water habitats off North Carolina

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Tara L. Casazza (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Steve Ross

Abstract: The community structure and diets of fishes inhabiting Sargassum and open water lacking Sargassum were examined off North Carolina during annual summer or fall cruises, 1999-2003. Significantly more individual fishes (n= 18,799), representing at least 80 species, were collected in samples containing Sargassum, compared to 60 species (n=2706 individuals) collected in open water. The majority of fishes collected in both habitats were juveniles, and Stephanolepis hispidus dominated both communities. Regardless of sampling time (day or night), Sargassum habitat yielded significantly higher numbers of individuals and species compared with open water collections. Overall, fishes collected in Sargassum neuston net tows were significantly larger than fishes collected in open water neuston tows. A significant positive linear relationship existed between numbers of fishes and Sargassum quantity. Underwater video recordings indicated a layering structure of fishes among and below the algae, with smaller fishes being more tightly associated with the algae than larger fishes. Additional observations from underwater video recordings included schooling behaviors of filefish, dolphinfish and jacks, and fish-jellyfish associations. The diets of the dominant fish species collected from Sargassum habitat were compared to the diets of the same species collected from open water, the diets of fishes collected during the day were compared to the diets of fishes collected at night within and across habitats, and the diets of each fish species across different size ranges were compared. Fishes collected from Sargassum consumed a higher diversity and volume of prey compared with fishes collected from open water. Fishes collected from Sargassum habitat had fewer empty stomachs than fishes collected from open water. Overall, fishes collected from Sargassum primarily consumed fishes that are closely associated with the algae (e.g., balistids, carangids, monacanthids) and endemic shrimps (Latruetes fucorum and Leander tenuicornis). In contrast, open-water fishes primarily consumed copepods and fishes from the family Exocoetidae. Comparisons between the diets of Sargassum-associated fishes and fishes collected from open water indicated several species fed similarly in both habitats. Fishes belong to one or more of three trophic groups: zooplanktivores, crustacean feeders or piscivores. Overall, fishes collected from Sargassum and open-water habitats primarily fed during the day. It appears Sargassum habitat enhances early survival of pelagic fishes by providing protection and concentrating prey resources in an otherwise nutrient poor area of the western North Atlantic Ocean. Efforts should be made to protect this unique pelagic habitat because these fishes are very closely tied to Sargasssum and may not be able to survive without Sargassum.

Additional Information

A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Fishes--Effect of habitat modification on--North Carolina, Fishes--Food--North Carolina, Marine algae, Sargassum, Sargassum--Food
Marine algae
Fishes -- Effect of habitat modification on -- North Carolina
Fishes -- Food -- North Carolina
Sargassum -- Food

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