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Estuaries and Coasts (2015) 38:558568 DOI 10.1007/s12237-014-9833-2
Seasonal Growth Responses of the Seagrass Zostera marina under Severely Diminished Light Conditions
Young Kyun Kim & Seung Hyeon Kim & Kun-Seop Lee
Received: 6 March 2013 /Revised: 25 April 2014 /Accepted: 13 May 2014 /Published online: 28 May 2014 # Coastal and Estuarine Research Federation 2014
Abstract Acute light attenuation events, such as those caused by red tide algal blooms or inflows of turbid plumes during monsoonal rains, are occurring with increased frequency in coastal waters. To explore seasonal growth responses of the seagrass Zostera marina to such severe light reduction events, we reduced radiation reaching Z. marina shoots by in situ shading with neutral density screens over 6-week periods in each of four seasons. Underwater photon flux densities (PFDs) in the shaded cages were reduced to 4.017.2 % of unshaded control values. Water temperatures ranged from8.2 C in the winter to 23.2 C in the summer over the experimental period. Under reduced light, the aboveground biomass of Z. marina usually decreased more rapidly than belowground biomass. By the end of each experiment, total biomass had decreased to ~10 % of the control biomass in the summer, fall, and winter periods but to ~50 % of controls during spring. Detrimental effects of light reduction on seagrass growth were most severe in summer and least severe in spring. Thus, Z. marina is more susceptible to the negative effects of light reduction when water temperatures are high. Since red tide algal bloom events and turbid plumes usually occur during high water temperature periods in summer, these light attenuation events are likely major drivers of observedZ. marina declines in coastal areas.
Keywords Growth . Light attenuation events . Light reduction . Redtide .Seagrass .Temperature . Zosteramarina
Introduction
Seagrasses can achieve high levels of production and are crucial components of coastal and estuarine ecosystems (McRoy and McMillan 1977). However, substantial declines in seagrass coverage have occurred throughout many parts of the world due to reduced water quality and increased turbidity (Moore et al. 1997, 2012; Orth et al. 2006; Waycott et al. 2009), which have been caused primarily by anthropogenic disturbances, such as dredging activities, resuspension of sediment, ship and barge traffic, pollution, and algal growth (Cambridge et al. 1986; Onuf...