Stable carbon isotope evidence for coupling between sedimentary bacteria and seagrasses in a sub-tropical lagoon

• Published in: Marine ecology. Progress series (Halstenbek) 2003-06, Vol.255, p.15-25
• Main Authors: Jones, W. Brian, Cifuentes, Luis A., Kaldy, James E.
• Format: Article
• Language: English
• Subjects: Algae; Animal and plant ecology; Animal, plant and microbial ecology; Bacteria; Biological and medical sciences; Brackish water ecosystems; Carbon; Carbon isotopes; Fatty acids; Fundamental and applied biological sciences. Psychology; Habitats; Lipids; Macrophytes; Marine; Microalgae; Sea water ecosystems; Sediments; Synecology; Thalassia testudinum
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps255015

We measured stable carbon isotope ratios (δ13C) in phospholipid fatty acids (PLFAs) to identify the primary carbon source utilized by sedimentary bacteria in Lower Laguna Madre, Texas, which is a seagrass dominated lagoon. Comparisons were made between 3 differing habitat types consisting of a bare area, a transitional area, and a vegetated area. Using PLFA concentrations, we estimated that bacterial abundance was significantly higher in the vegetated habitat compared with bare or transitional habitats. SeagrassThalassia testudinumabove-ground tissues averaged –10.8 ± 0.3‰ and benthic microalgae, based on 20:5Δ3 PLFA, averaged –20.5 ± 0.6‰. The δ13C of total organic carbon (TO13C) from all habitats and depths were within ±2‰ ofT. testudinumabove-ground tissues, suggesting that the majority of sedimentary organic carbon originated from this source. The δ13C of the ubiquitous 16:0 PLFA indicated more complexity in surface vegetated sediments and at depth (ca. 19 cm) in bare and transitional habitats. In turn, the δ13C of branched, iso- and anteiso-15:0 (i&a15:0) PLFAs found only in bacteria were within ±3‰ of TO13C in all habitats and at all depths. Our work confirmed coupling between sedimentary bacteria and seagrasses occurs in oligotrophic systems with few allochthonous inputs.