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Duration of Temperature exposure controls growth of Zostera japonica: implications for zonation and colonization
Citation:
Kaldy, Jim, D. Shafer, AND D. Magoun. Duration of Temperature exposure controls growth of Zostera japonica: implications for zonation and colonization. JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY. Elsevier Science Ltd, New York, NY, 464:68-74, (2015).
Impact/Purpose:
Dr. James Kaldy from Western Ecology Division (WED), Dr. Deborah Shafer, US Army Engineer, Environmental Research and Development Center- Environmental Laboratory (ERDC-EL) and Dr. Dale Magoun, have concluded that the intertidal zonation patterns of non-native seagrass Z. japonica in North America are predominantly driven by temperature response. Increased duration of exposure to cold water temperatures (<10 °C) appears to limit expansion of the lower boundary of Z. japonica to the mid-intertidal; which effectively eliminates competitive interactions with the native seagrass Z. marina in most estuaries. The differential response to pulsed thermal regimes suggests that temperature is a primary control on zonation and that speculation that Z. japonica will outcompete and replace the native Z. marina may be unfounded. These conclusions are based on field and novel mesocosm experiments conducted using pulsed temperature treatments at the WED facility located on Yaquina Bay in Newport Oregon and represent an ongoing collaboration via an MOU between EPA and ERDC-EL.
Description:
At least two seagrass congeners in the genus Zostera are found along the Pacific Coast of North America: native Z. marina L. and the non-native Z. japonica Aschers. & Graebn. Efforts to understand the drivers behind the expanding colonization of Z. japonica have led to interest in the biology and ecology of this species. In most locations where they co-occur, these species exhibit a disjunct vertical zonation. We experimentally consider the influence of pulsed temperature effects on Z. japonica growth as a driver of vertical zonation. In mesocosm tanks seagrass planting units were cycled from ambient to treatment temperatures (8, 20, 32 °C) of variable duration (2, 6, 12, 24 h) each day for 10 d and then growth was assessed. Leaf elongation and growth rates exhibited strong, statistically significant relationships with increasing duration of exposure to 20 °C. Plants exposed to continuous 20 °C temperatures grew 2.5 times faster than plants exposed to 20 °C for 2 hours. Likewise, plants exposed to continuous 8 °C temperatures grew 2.5 times slower than plants at 8 °C for 2 hours. Plants exposed to 32 °C maintained fairly constant growth and elongation rates regardless of the duration of exposure. Field data indicate Z. japonica and Z. marina experience different thermal regimes in the same estuary. We suggest that intertidal zonation patterns of Z. japonica in North America are predominantly driven by seagrass temperature responses; increased duration of exposure to cold water temperatures appears to limit expansion of the Z. japonica bed lower boundary to the mid-intertidal. Additionally, we recognize characteristics that may be useful to identifying systems susceptible to colonization.
