Climate change is intensifying the effects of multiple interacting stressors on aquatic ecosystems worldwide. In the San Francisco Estuary, signals of climate change are apparent in the long-term monitoring record. Here we synthesize current and potential future climate change effects on three main ecosystems (floodplain, tidal marsh, and open water) in the upper estuary and two representative native fishes that commonly occur in these ecosystems: anadromous Chinook Salmon (Oncorhynchus tshawytscha) and estuarine resident Sacramento Splittail, (Pogonichthys macrolepidotus). Based on our review, we found that the estuary is experiencing shifting baseline environmental conditions, amplification of extremes, and restructuring of physical habitats and biological communities. We present priority topics for research and monitoring, and a conceptual model of how the estuary currently functions in relation to climate variables. In addition, we discuss four tools for management of climate change effects: regulatory, water infrastructure, habitat development, and biological measures. We conclude that adapting to climate change requires fundamental changes in management.
Phytoseiid mites are key predators in agricultural crops. However, not all species regulate pest populations below economic thresholds, and therefore knowledge of which species are associated with particular crops aids pest control recommendations. Surveys of 12 crops across six geographical regions of California demonstrated that phytoseiid species varied by crop and geographical location, with subtropical crops exhibiting the lowest species diversity and grape the greatest. The western predatory mite, Galendromus occidentalis , long cited as a dominant species in California crops, was not found to be the major species in most situations. Euseius stipulatus , a species introduced in the 1970s, was found in the surveyed crops in many areas of the state and appears to be displacing E. hibisci along the south coast.
Irrigation method has the potential to directly or indirectly influence populations of wild bee crop pollinators nesting and foraging in irrigated crop fields. The majority of wild bee species nest in the ground, and their nests may be susceptible to flooding. In addition, their pollination of crops can be influenced by nectar quality and quantity, which are related to water availability. To determine whether different irrigation methods affect crop pollinators, we compared the number of ground-nesting bees nesting and foraging in drip- and furrow-irrigated hybrid sunflower fields in the Sacramento Valley. We found that irrigation method did not impact wild bee nesting rates or foraging bee abundance or bee species richness. These findings suggest that changing from furrow irrigation to drip irrigation to conserve water likely will not alter hybrid sunflower crop pollination.
Largemouth Bass (Micropterus salmoides) were introduced into the Sacramento-San Joaquin Delta (the Delta) over 100 years ago. In the last 2 decades, the abundance of centrarchids (including Largemouth Bass) in the littoral zone has increased, while some native fish and fish that were previously abundant in the pelagic zone have declined. Largemouth Bass are now one of the most abundant piscivores in the Delta. Understanding the ecology of this top predator — including a comprehensive understanding of what prey are important in Largemouth Bass diets — is important to understanding how this species may affect the Delta fish community. To address this need, we conducted electrofishing surveys of Largemouth Bass at 33 sites every 2 months from 2008 to 2010, measuring fish fork lengths and collecting stomachs contents at each site. We characterized diets using Percent Index of Relative Importance for 3,004 Largemouth Bass, with samples that spanned all seasons. Amphipods dominated the diets of Largemouth Bass ≤175 mm FL year-round, with dipterans, odonates, and copepods and cladocerans representing other important diet items. Non-native red swamp crayfish (Procambarus clarkii) were the most important prey for Largemouth Bass >175 mm FL. Non-native centrarchids (including Largemouth Bass) and amphipods were important prey items as well. Prickly Sculpin (Cottus asper) were the most frequently consumed native fish. Other native fish and pelagic fish species rarely occurred in Largemouth Bass diets, and we discuss trends in how the frequency of co-occurrence of these fishes with Largemouth Bass in the electrofishing surveys was associated with their frequency in Largemouth Bass diets. The Largemouth Bass in the Delta appear to be sustained largely on a diet of other non-natives that reside in the littoral zone.
Ecosystems in the Sacramento–San Joaquin Delta are changing rapidly, as are ecosystems around the world. Extreme events are becoming more frequent and thresholds are likely to be crossed more often, creating greater uncertainty about future conditions. The accelerating speed of change means that ecological systems may not remain stable long enough for scientists to understand them, much less use their research findings to inform policy and management. Faced with these challenges, those involved in science, policy, and management must adapt and change and anticipate what the ecosystems may be like in the future. We highlight several ways of looking ahead—scenario analyses, horizon scanning, expert elicitation, and dynamic planning—and suggest that recent advances in distributional ecology, disturbance ecology, resilience thinking, and our increased understanding of coupled human–natural systems may provide fresh ways of thinking about more rapid change in the future. To accelerate forward-looking science, policy, and management in the Delta, we propose that the State of California create a Delta Science Visioning Process to fully and openly assess the challenges of more rapid change to science, policy, and management and propose appropriate solutions, through legislation, if needed.
Uncertainties in understanding ecosystems increase the risk that management will fail to achieve desired results. Adaptive management is a structured, iterative application of science-based knowledge to reduce uncertainties and build flexibility into decision-making. However, adaptive management is more easily planned than implemented, and it is only beginning to be applied in the California’s Sacramento–San Joaquin Delta. We draw from two assessments of adaptive management in the Delta and examples of its use elsewhere to suggest how the process can be facilitated. Although a highly structured adaptive-management process may not always be needed, several elements are essential. Adaptive management should begin by clearly identifying the problem, goals, and objectives; recognizing uncertainties; identifying decision points and alternative approaches; recognizing when adjustments are needed and having the flexibility to make them; and considering societal and political constraints. Model complexity should be matched to that of the system and management needs; experiments can help unravel causal relationships. Monitoring, analyses, and syntheses require comprehensive data-management systems. More frequent and organized communications among scientists, managers, stakeholders, and decision-makers are necessary. We propose the establishment of an “Adaptive Management Team” to coordinate efforts across the management spectrum of the Delta and to provide guidance and link individual projects to shared approaches and experiences. Reliable long-term support will be needed to assess results of management actions, adjust approaches where improvement is likely, and strive toward the legislated goals of enhancing the Delta ecosystem while also providing reliable water supplies to much of California, and doing both these things in a manner that protects values of the Delta as a place where people live and work.
Wildlife is increasingly forced to share space with humans, facing disturbances that operate across different spatial and temporal scales. The press-pulse framework, originally developed in the disturbance ecology literature, distinguishes between long-term sustained 'presses' and more acute 'pulses'. Because pulses occur during ongoing press conditions, their ecological effects depend on how they interact with that background, helping explain why certain disturbances result in transient, localized changes, while others lead to lasting, widespread impacts. Here, we expand this framework by applying it to regimes of human disturbances, and incorporating 'pauses' as a third category. Pulses and pauses (e.g. episodes of extreme weather, or drastic changes in human mobility) can substantially affect wildlife behaviour, yet their effects are often modulated by background 'press' conditions. We offer a conceptual framework for disentangling effects across space and time and highlight how plasticity in wildlife movement-particularly in terms of navigating risks and tracking resources-can lead to both adaptive and nonadaptive responses to human disturbances. This enables predictions about how shifts in animal movement can influence human wildlife interactions and conflict with humans under different scenarios. Applying the press-pulse-pause framework to movement ecology allows researchers to improve our understanding of how wildlife is affected by different disturbance regimes, advancing efforts to foster sustainable human-wildlife coexistence in an era of mounting pressures.
