Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Point Adams Research Station, Hammond, Oregon, United States of America.
Coastal Sciences Division, Pacific Northwest National Laboratory, Portland, Oregon, United States of America.
PLoS One. 2023 Mar 17;18(3):e0282655. doi: 10.1371/journal.pone.0282655. eCollection 2023.
Tidal freshwater wetlands linking terrestrial, riverine, and saline habitats are critical areas for material processing and exchange. Once historically widespread, herbaceous marsh and forested tidal freshwater wetlands especially are now highly degraded worldwide. Additionally, quantitative assessments of hydrology and material exchange from these systems are lacking compared to lotic and estuarine (saltmarsh) habitats. Here we investigate macroinvertebrate and energy export from tidal marsh and forested wetlands and consider potential benefits from this ecological process to endangered Pacific salmon in a large tidal freshwater system, the Columbia River (USA). Macroinvertebrate (salmon prey) concentration, water velocity, and discharge were measured at several wetland habitat types (forested swamp, emergent marsh, and restored marsh). We used these data to compute prey flux and transport metrics. Then, applying literature values to calculate prey energy equivalents and juvenile salmon metabolic requirements, we estimated the potential energy subsidy available to juvenile salmon. Numerically, larval stages of aquatic insects were the predominant type of prey exported from the wetlands, with Diptera chironomid fly abundance exceeding other groups. Energetically, however, non-chironomid dipterans and hemipteran prey comprised most of energy transport due to their higher energetic content (energy density × mean weight). We determined the prey energy transported from the sampled tidal channels was sufficient to meet energetic needs of tens to thousands of juvenile salmon per day, depending on prey production and hydrography. The prey taxonomic composition differed among organisms exiting forested swamp, emergent marsh, and restored marsh habitats with corresponding differences in energy transport, but all habitat types supported similar numbers of juvenile salmon. We conclude that macroinvertebrate prey exported from varied tidal freshwater wetlands likely provide significant benefits to juvenile salmon over a larger ecological footprint than the wetland area would suggest.
潮汐淡水湿地连接陆地、河流和咸水栖息地，是物质处理和交换的关键区域。曾经在历史上广泛分布的草本沼泽和森林潮汐淡水湿地，现在在全球范围内已经高度退化。此外，与溪流和河口（盐沼）栖息地相比，这些系统的水文和物质交换的定量评估是缺乏的。在这里，我们研究了潮汐沼泽和森林湿地的大型无脊椎动物和能量输出，并考虑了这一生态过程对大潮汐淡水系统——哥伦比亚河（美国）濒危太平洋鲑鱼的潜在益处。在几种湿地生境类型（森林沼泽、挺水沼泽和恢复沼泽）中测量了大型无脊椎动物（鲑鱼猎物）的浓度、水流速度和流量。我们使用这些数据来计算猎物通量和运输指标。然后，我们应用文献值来计算猎物的能量当量和幼鲑鱼的代谢需求，从而估计幼鲑鱼可用的潜在能量补助。从数值上看，水生昆虫的幼虫阶段是从湿地中输出的主要猎物类型，摇蚊科双翅目昆虫的丰度超过了其他群体。然而，从能量角度来看，非摇蚊双翅目和半翅目猎物由于其较高的能量含量（能量密度×平均重量），构成了大部分能量运输。我们确定从采样的潮汐通道中运输的猎物能量足以满足每天数十到数千尾幼鲑鱼的能量需求，具体取决于猎物的产量和水文学。从森林沼泽、挺水沼泽和恢复沼泽生境中出来的生物体的猎物分类组成不同，能量运输也存在相应的差异，但所有生境类型都支持相似数量的幼鲑鱼。我们的结论是，从不同的潮汐淡水湿地输出的大型无脊椎动物猎物可能为幼鲑鱼提供了显著的益处，其生态足迹比湿地面积所暗示的要大。
