Interplay of host morphology and symbiont microhabitat in coral aggregations

被引:46
作者
Helmuth, BST
Timmerman, BEH
Sebens, KP
机构
[1] Univ Washington, Dept Bot, Seattle, WA 98195 USA
[2] Univ Maryland, Dept Zool, College Pk, MD 20742 USA
[3] Univ Maryland, Ctr Environm & Estuarine Studies, Horn Point Environm Lab, Cambridge, MD 21613 USA
[4] Univ Washington, Dept Zool, Seattle, WA 98195 USA
关键词
D O I
10.1007/s002270050219
中图分类号
Q17 [水生生物学];
学科分类号
071004 ;
摘要
The Belizean reef coral Agaricia tenuifolia Dana forms aggregations in which rows of thin, upright blades line up behind each other. On average, the spacing between blades increases with depth and hence with decreasing ambient irradiance. We designed and built a small, inexpensive light meter and used it to quantify the effect of branch spacing on light levels within colonies at varying distances from branch tips. Concurrently, we measured photosynthetic pigment concentrations and population densities of symbiotic dinoflagellates (zooxanthellae) extracted from coral branches of colonies with tight (less than or equal to 3 cm) vs wide (greater than or equal to 6 cm) branch spacing, collected at 15 to 17 m and from colonies with tight branch spacing collected at 1 to 2 m. Light levels decreased significantly with tighter branch spacing and with distance from the branch tips. Total cellular pigment concentrations (chlorophylls a, c(2) and peridinin) as well as chlorophyll a:c(2) and chlorophyll a:peridinin ratios all increased significantly with distance from the branch tip, indicating very localized differences in photoacclimation within individual branches. Zooxanthellae from colonies with widely-spaced branches displayed significantly lower chlorophyll a:c(2) and chlorophyll a:peridinin ratios, and were present at significantly higher population densities than those from colonies with tightly-spaced branches collected at the same depth (15 m). Tightly-spaced colonies collected from shallow environments (1 to 2 m) displayed pigment ratios similar to those from widely-spaced colonies from deeper water (15 m), but maintained zooxanthellae populations at levels similar to those in tightly-branched colonies from deeper water. Thus, variation in colony morphology (branch spacing and distance from branch tip) can affect symbiont physiology in a manner comparable to an increase of over 15 m of water depth. These results show that a host's morphology can strongly determine the microhabitat of its symbionts over very small spatial scales, and that zooxanthellae can in turn display steep gradients in concordance with these altered physical conditions.
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页码:1 / 10
页数:10
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