Abstract:
Twelve field collections containing juvenile fishes and macro invertebrates associated with Sargassum habitat (windrows/weedlines) in the north-central Gulf of Mexico (GOM) were taken during three research cruises (September and October 2010, January 2011) conducted within an area generally defined as north of Latitude 28oN and between Longitude 87o 30W and 90oW and, inclusive of the Deepwater Horizon (DWH) site. Collections were taken using neuston net gear (3.2 mm mesh) towed perpendicular (directly through) to Sargassum aggregations. Surface water temperature and salinity ranged 32.4 - 35.0 ppt. and 19.5 - 29.2oC, respectively, for the total number of collections. A total of 1,916 juvenile fishes was collected representing 27 species and 13 families, with Mugil curema, Trachurus lathami, Histrio histrio, Balistes capriscus and Stephanolepis hispidus numerically dominating the overall collection. Family Carangidae was represented by the greatest number of species (n = 8), followed by Balistidae and Monacanthidae, each with three species. The other fishes collected were members of families Centrolophidae, Phycidae, Kyphosidae, Lobotidae, Macroramphosidae, Pomacentridae, Scombridae and Syngnathidae. Recreationally and commercially important species were represented in the collections, including triggerfish, pompano and tripletail. The diversity, abundance and size (SL, mm) of fishes varied SOMEWHAT? among the three cruises, but three species (H. histrio, S. hispidus, and S. louisianae) were present in collections from each cruise. Mean size (SL, mm) of individual species collected in each of the three cruises did not differ substantially among the cruises, even though samples were collected seasonally (September, October 2010, and January 2011). Although the focus on this project was on juvenile fishes, 82,892 macro-invertebrates were collected, identified (to the lowest taxonomic level deemed possible) and enumerated. The invertebrates strongly dominated the overall collection numerically (98%), far outnumbering fishes in most individual collections. Nine families were represented in the total collection, and Latreutes fucorum, L. tenuicornis, Portunus sayi and L. parvulus accounted for 99.8% of invertebrates identifiable to species level and 90% of invertebrates collected overall. Although the primary objective of the project was to describe, assess and compare the diversity and abundance of juvenile fishes collected from visibly oil-impacted Sargassum with visibly non-impacted Sargassum, no visibly impacted Sargassum was encountered during any of the three sampling cruises. The relatively short duration of the field aspect of the study period allowed for fall and winter collections only. Fishes and invertebrates found in the collections were perhaps generally representative of seasonal fish and macro-invertebrate inhabitants of Sargassum in the northern GOM during fall and winter months or may have been representative of fish and macro-invertebrate Sargassum associates only for the specific times and locations of collections in September and October 2010 and January 2011 following the DWH event. This study documented that Sargassum habitat sampled in the north-central GOM during the months of September and October 2010 and January 2011 provided habitat for a multitude of young fishes. Understanding the structure and function of the Sargassum community and the role it plays as Essential Fish Habitat in supporting and sustaining the feeding and spawning requirements, survivorship, and distribution of larval and juvenile fishes in the GOM is paramount to expanding the knowledge of the recruitment of young fishes into GOM fisheries.