Article

Estuaries

, Volume 19, Issue 3, pp 740-750

Light requirements of seagrassesHalodule wrightii andSyringodium filiforme derived from the relationship between diffuse light attenuation and maximum depth distribution

  • W. Judson KenworthyAffiliated withBeaufort Laboratory Southeast Fisheries Science Center National Marine Fisheries Service, National Oceanic and Astmospheric Administration
  • , Mark S. FonsecaAffiliated withBeaufort Laboratory Southeast Fisheries Science Center National Marine Fisheries Service, National Oceanic and Astmospheric Administration

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Abstract

The correspondence between maximum depth of growth (Zmax) for two seagrases,Halodule wrightii andSyringodium filiforme, and the attenuation of diffuse photosynthetically active radiation (KdPAR) were evaluated over a 3.5-yr period in the southern Indian River Lagoon, Florida. The lower limit of seagrass depth distribution was controlled by light availability. Both species grew to the same maximum depth, indicating they have similar minimum light requirements. Based on average annual values of KdPAR, estimates of seagrass minimum light requirements ranged from 24% to 37% of the light just beneath the water surface (Io), much hgiehr than a photic zone for many phytoplankton and macroalgae (1–5% incident light). In less transparent waters of Hobe Sound, where turbidity (NTU) and color (Pt-Co) had their highest concentrations, minimum light requirements for growth were greatest. These results suggest that more sophisticated optical models are needed to identify specific water quality constituents affecting the light environment of seagrasses. Water quality criteria and standards needed to protect seagrasses from decreasing water transparency must be based on parameters that can be routinely measured and reasonably managed.