RECOVER MAP 3.1.4.7 Role of Marsh-Mangrove Interface Habitats as Aquatic Refuges for Wetland Fishes and other Aquatic Animals

Work conducted in 2008 will continue to establish baseline conditions for fish and macroinvertebrate communities in the mangrove creeks of Everglades National Park (ENP). This monitoring was begun in 2004, with the focus from 2004-2007 on testing methodologies and strategies for sampling fishes and macroinvertebrates in this difficult–to-sample mangrove habitat. Findings from the 2004-2007 work showed electrofishing catch per unit effort (CPUE) provided a reliable estimator of large-bodied fish abundance and species richness at salinities below 15 (Loftus and Rehage 2007, Rehage and Loftus 2007). For the smaller species, our data showed that minnow trap CPUE provides an adequate estimate of forage-fish and macroinvertebrate abundance in the mangrove prop-root microhabitat. Results also showed that there is significant biotic connectivity between freshwater marshes and the oligohaline/mesohaline mangrove habitats, particularly along the Shark Slough-Shark River ecotone. These data indicate that mangrove creeks serve as important dry-season habitat for a variety of freshwater taxa. As upstream marshes dry, fishes and decapods move into mangrove creeks. We hypothesize that the timing and spatial extent of this movement into creeks is affected by the pattern and timing of water recession in marshes, and the effects of this recession on salinity levels in the creeks. We suspect that animal movements into creeks results in a shift in energy flow from avian predators in the wetlands to piscine predators in the creeks. Ecotonal creeks are deep (> 1m), and prey that move into creeks become unavailable to many wading birds, instead serving as prey for freshwater, estuarine, and marine fish predators (along with alligators). In 2008, we continue to test these hypotheses. Sampling in FY08 will result in additional sampling events and increase replication, which should enhance our ability to detect changes in the fish and macroinvertebrate community in relation to changes in key ecological drivers, namely freshwater inflow and salinity. In particular, our objectives for 2008 include:
(1) Continue data collection begun in 2004 to provide pre-CERP baseline conditions for the fish and macroinvertebrate community inhabiting mangrove creeks;
(2) Relate patterns of variation in the fish and macroinvertebrate community of creeks to key hydrological and physiochemical variables;
(3) Continue to develop an integrated experimental design that will optimize effort and information utility, incorporating both spatial (across the landscape) and temporal (seasonal and interannual) variability;
(4) Continue to work with other PIs to integrate our results with theirs in testing the key hypotheses in MAP II.
II. Statement of work (abbreviated)
This MAP activity will enhance the ongoing biological monitoring in freshwater and estuarine regions of ENP by providing data from an infrequently sampled habitat that provides both a source and a sink for wetland forage fishes that are prey for wading birds. Relatively little is known about the fish community inhabiting mangrove creeks in ecotonal and estuarine regions of southwest Florida. Small-scale inventory studies in several creek systems showed a mixed assemblage of marine, estuarine, and freshwater fishes (Tabb and Manning 1961, Tabb et al. 1962, McPherson 1970, Odum 1971, Loftus and Kushlan 1987), but those studies are not recent and mostly provided inventory data. Without understanding the factors that control the survival and abundance of those fishes once they are confined to this dry-season habitat, it is impossible to predict the effects of CERP actions on this prey base in the future. Similarly, this activity also provides the only data for freshwater and estuarine fishes that support a valuable sport fishery in south Florida. Without these data on the effects of hydrology and salinity variation on patterns of fish abundance and diversity, the effects of CERP on those key fishery species will not be science-based.

2008年开展的本项工作将继续为大沼泽地国家公园（Everglades National Park，ENP）红树林溪沟中的鱼类与大型无脊椎动物（macroinvertebrate）群落建立基线条件。本监测项目于2004年启动，2004-2007年的工作重点为测试在该难采样红树林生境中开展鱼类与大型无脊椎动物采样的方法与策略。2004-2007年的研究结果显示，当盐度（salinities）低于15时，单位捕捞努力量渔获量（catch per unit effort，CPUE）的电捕鱼法（electrofishing）可可靠估算大型鱼类的丰度与物种丰富度（species richness）（Loftus与Rehage 2007，Rehage与Loftus 2007）。针对小型物种，我们的数据表明，小鱼笼（minnow trap）的单位捕捞努力量渔获量可充分估算红树林支柱根微生境（prop-root microhabitat）中的饵料鱼类（forage-fish）与大型无脊椎动物丰度。研究结果还显示，淡水沼泽（freshwater marshes）与寡盐/中盐度（oligohaline/mesohaline）红树林生境之间存在显著的生物连通性（biotic connectivity），尤其在鲨鱼沼泽-鲨鱼河生态交错带（ecotone）沿线。这些数据表明，红树林溪沟是多种淡水类群（taxa）重要的旱季栖息地（dry-season habitat）。随着上游沼泽干涸，鱼类与十足目动物（decapods）会迁移至红树林溪沟中。

我们提出假说：此类向溪沟的迁移时机与空间范围，受沼泽水位退落（water recession）模式与退落时机的影响，同时该退落过程也会影响溪沟内的盐度水平。我们推测，动物向溪沟的迁移会导致能量流动（energy flow）从湿地（wetlands）中的鸟类捕食者（avian predators）转向溪沟内的鱼类捕食者（piscine predators）。生态交错带溪沟水深超过1米，迁移进入溪沟的猎物将无法被多数涉禽（wading birds）获取，转而成为淡水、河口生境及海洋鱼类捕食者（以及短吻鳄（alligators））的食物。2008年，我们将继续验证上述假说。2008财年（Fiscal Year 08，FY08）的采样将增加采样频次与重复采样（replication）次数，从而提升我们检测鱼类与大型无脊椎动物群落变化的能力，该变化与关键生态驱动因子（ecological drivers）——即淡水输入（freshwater inflow）与盐度——的变化相关。2008年的研究目标具体包括：
(1) 延续2004年启动的数据收集工作，为栖息于红树林溪沟的鱼类与大型无脊椎动物群落提供大沼泽地综合恢复计划（Comprehensive Everglades Restoration Plan，CERP）实施前的基线条件；
(2) 将溪沟内鱼类与大型无脊椎动物群落的变异模式与关键水文及理化变量相关联；
(3) 继续优化整合实验设计，以提升采样效率与信息利用效率，同时纳入景观尺度的空间变异与季节、年际尺度的时间变异；
(4) 继续与其他首席研究员（Principal Investigators，PIs）合作，将本研究结果与他们的成果相结合，以验证MAP II中的关键假说。

二、 工作内容简述
本MAP II相关活动将为大沼泽地国家公园淡水与河口区域的长期生物监测提供补充数据——该难采样生境同时作为涉禽饵料鱼类的源与汇。目前对佛罗里达州西南部生态交错带与河口区域红树林溪沟内的鱼类群落所知甚少。此前在多个溪沟系统开展的小型调查研究显示，该区域存在海洋、河口与淡水鱼类的混合类群（Tabb与Manning 1961，Tabb等1962，McPherson 1970，Odum 1971，Loftus与Kushlan 1987），但这些研究年代久远且大多仅提供了物种名录数据。若无法明确控制这些鱼类在旱季栖息地内存活与丰度的影响因子，便无法预测大沼泽地综合恢复计划（CERP）未来对该猎物基础的影响。同样，本项目也为支撑佛罗里达州南部重要休闲渔业的淡水与河口鱼类提供了唯一的监测数据。若缺乏水文与盐度变化对鱼类丰度与多样性模式影响的相关数据，便无法基于科学依据评估CERP对这些关键渔业物种的影响。