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Trichodesmium in the western Gulf of Mexico: 15N 2 ‐fixation and natural abundance stable isotopic evidence
Author(s) -
Holl Carolyn M.,
Villareal Tracy A.,
Payne Christopher D.,
Clayton Tonya D.,
Hart Cassandra,
Montoya Joseph P.
Publication year - 2007
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2007.52.5.2249
Subject(s) - trichodesmium , trichome , cyanobacteria , nitrogen fixation , diazotroph , nitrogen , light intensity , abundance (ecology) , botany , biology , zoology , chemistry , ecology , physics , genetics , organic chemistry , bacteria , optics
Surface aggregations of the diazotrophic cyanobacterium Trichodesmium were encountered at nearly every station along a 300‐km transect in the northwestern Gulf of Mexico during July 2000. 15 N 2 ‐fixation rate measurements for all treatments and locations ranged from 1.3 X 10 −4 nmol N trichome −1 h −1 to 2.6 X 10 −2 nmol N trichome −1 h −1 , with a mean of 3.4 X 10 −3 ± 7.6 X 10 −4 nmol N trichome −1 h −1 (mean ± SE, n = 45). Trichodesmium C‐fixation, measured by the incorporation of 13 C, ranged from 1.3 X 10 −2 nmol C trichome −1 h −1 to 4.5 X 10 −1 nmol C trichome −1 h −1 , with a mean of 1.2 X 10 −1 ± 9.3 X 10 −2 nmol C trichome −1 h −1 (mean ± SE, n = 44). Both 15 N 2 ‐fixation and 13 C‐fixation rates attenuated with decreasing light intensity from a maximum at 50% surface intensity. Areal Trichodesmium 15 N 2 ‐fixation rates, based on a 10‐h N 2 ‐fixation day, enumerated vertical trichome abundance and corrected for estimated in situ light intensity ranged from 47.2 mmol N m −2 d −1 to 118.6 mmol N m −2 d −1 , with a mean of 84.5 ± 17.7 mmol N m −2 d −1 (mean ± SE, n = 4). The light natural abundance isotopic signatures of dissolved inorganic nitrogen, particulate nitrogen, and zooplankton nitrogen within these surface populations are consistent with our limited biological rate measurements and indicate that recently fixed N is moving into the food chain to promote secondary production in these nutrient‐impoverished waters. Although our sample size was relatively small, natural abundance isotope data indicate that as much as 60% of macrozooplankton C and N was derived from Trichodesmium in the oligotrophic regions of the Gulf of Mexico.