Twilley Robert R, Pozo Mireya, Garcia Victor H, Rivera-Monroy Victor H, Zambrano Ramon, Bodero Alejandro
Department of Biology, University of Southwestern Louisiana, Lafayette, LA 70504, USA Fax: 318 482 5834; e-mail:
School of Natural Sciences, University of Guayaquil, Guayaquil, Ecuador, , , , , , EC.
Oecologia. 1997 Jun;111(1):109-122. doi: 10.1007/s004420050214.
The hypothesis that rates of litter turnover in mangroves are controlled by local geophysical processes such as tides has been studied at sites with mostly small tides (<1 m) and minor crab consumption of leaf litter. Our study describes litter dynamics of three riverine mangrove sites (M1, M2, M3), inhabited by the mangrove crab Ucides occidentalis, located in a macrotidal (>3 m) river-dominated tropical estuary in Ecuador (2.5°S latitude). There were statistical effects of site and depth on soil salinities, but all mean salinities were <17 g kg. Daily rates of leaf litter fall were higher in the rainy compared to the dry season, although no seasonal effects were observed for other components of litter fall. Annual total litter fall rates were significantly different among sites at 10.64, 6.47, and 7.87 Mg ha year for M1, M2, and M3, respectively. There were significant site (M3 > M2 > M1) and season (rainy > dry) effects on leaf degradation, and both effects were related to differences in the initial nitrogen content of senescent leaves. Mean leaf litter standing crop among the sites ranged from 1.53 to 9.18 g m, but amounts were strongly seasonal with peak values during September in both years of our study (no significant year effect) at all three sites. Leaf turnover rates based on leaf fall estimates and litter standing crop were 10- to 20-fold higher than estimated from rates of leaf degradation, indicating the significant effect of leaf transport by tides and crabs. Field experiments demonstrated that the mangrove crab can remove daily additions of leaf material within 1 h at all three sites, except during August-October, when the crab is inactive on the forest floor. Even though there is seasonally elevated leaf accumulation on the forest floor during this time, leaf turnover rates are much higher than expected based on leaf degradation, demonstrating the importance of tidal export. This is the first description of how crabs influence litter dynamics in the New World tropics, and results are similar to higher rates of crab transport of leaf litter in the Old World tropics. Even in riverine mangroves with high geophysical energies, patterns of litter dynamics can be influenced by ecological processes such as crab transport.
关于红树林凋落物周转速率受潮汐等当地地球物理过程控制的假说，此前已在潮汐大多较小（<1米）且蟹类对落叶消耗较少的地点进行过研究。我们的研究描述了三个河口红树林地点（M1、M2、M3）的凋落物动态，这些地点位于厄瓜多尔（南纬2.5°）一个以河流为主的热带大潮汐（>3米）河口，栖息着西方招潮蟹（Ucides occidentalis）。地点和深度对土壤盐度有统计学影响，但所有平均盐度均<17克/千克。与旱季相比，雨季的落叶日速率更高，不过对于落叶的其他组成部分未观察到季节效应。M1、M2和M3三个地点的年总落叶速率分别为10.64、6.47和7.87公吨/公顷·年，差异显著。落叶降解存在显著的地点（M3>M2>M1）和季节（雨季>旱季）效应，且这两种效应均与衰老叶片的初始氮含量差异有关。各地点的平均落叶现存生物量在1.53至9.18克/平方米之间，但数量具有强烈的季节性，在我们研究的两年中，所有三个地点在9月均达到峰值（年份效应不显著）。基于落叶估计和落叶现存生物量得出的叶片周转速率比根据叶片降解速率估计的结果高10至20倍，表明潮汐和螃蟹对叶片运输的显著影响。野外实验表明，除了8月至10月螃蟹在林地不活动期间外，在所有三个地点，招潮蟹都能在1小时内清除每日添加的叶片材料。尽管在此期间林地的落叶积累在季节上有所增加，但叶片周转速率远高于基于叶片降解预期的速率，这表明潮汐输出的重要性。这是首次描述螃蟹如何影响新世界热带地区的凋落物动态，其结果与旧世界热带地区螃蟹对落叶的较高运输速率相似。即使在地球物理能量较高的河口红树林中，凋落物动态模式也可能受到螃蟹运输等生态过程的影响。
