High metabolic rates in beach cast communities

Grey T. Coupland*, Carlos Duarte, Diana I. Walker

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


Metabolic hotspots at land-water interfaces are important in supporting biogeochemical processes. Here we confirm the generality of land-aquatic interfaces as biogeochemical hot spots by extending this concept to marine beach cast materials. In situ atmospheric pCO2, from a respiration chamber (10 cm in diameter and 20 cm high) inserted into wrack deposits, was determined using a high-precision (±1 ppm) non-dispersive infrared gas analyzer (EGM-4, PP-systems) at 1 minute recording intervals. The wrack deposits supported high metabolic activities, with CO2 fluxes averaging (±SE) 6.62 ± 0.88 μmol C m-2 s-1, compared to median value of 0.98 μmol C m-2 s-1 (mean 2.21 ± 1.25 μmol C m-2 s-1) for bare sand adjacent to deposits. Wrack metabolic rates ranged 40-fold across beaches, from a minimum of 0.57 ± 0.22 μmol C m-2 s-1 to a maximum of 20.8 ± 5.04 μmol C m-2 s-1, both derived from beaches with deposits dominated by Sargassum. Rates tended to increase significantly (F test, P < 0.05) from the shoreline to reach maximum rates at about 10 m from the shoreline, declining sharply further from the shoreline, and increased with increasing thickness of the deposits (maximum about 10 cm deep), declining for thicker deposits. Wrack differing in composition had similar metabolic rates, although deposits consisting of a mixture of seagrass and algae tended to show somewhat higher rates. Our results show a meter square of wrack deposit supports a metabolic rate equivalent to that supported by 3 m2 of living seagrass or macroalgal habitat. In wrack, the marine environment provides organic material and moisture and the land environment provides oxygen to render wrack ecosystems an efficient metabolic reactor. Intense wrack metabolism should also be conducive to organismal growth by supporting the development of a cryptic, but diverse wrack-based food web.

Original languageEnglish (US)
Pages (from-to)1341-1350
Number of pages10
Issue number8
StatePublished - Dec 1 2007


  • Beach wrack
  • Biogeochemical hot spots
  • Carbon dioxide
  • Land-water interface
  • Marine macrodetritus
  • Respiration

ASJC Scopus subject areas

  • Ecology


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