global change

Anthropogenic global change is altering mean environmental conditions and the frequency of extreme events, creating potential chronic and acute environmental stress in many species. In aquatic ecosystems, this includes altered regimes of temperature, salinity, pH (i.e., ocean acidification), and oxygen, as well as exposure to biological and chemical pollution.

Broadly, our research group seeks to understand how and why organisms are affected by these environmental stressors, which is grounded in their (1) capability to find new suitable habitat (shifting in space and/or time), (2) phenotypic plasticity (the capacity to make biochemical adjustments and regain homeostasis under new conditions), (3) ability to mount rapid responses to acute stress, and (4) capacity for rapid genetic adaptation. Sublethal impacts also lead to indirect negative effects on fitness, such as reduced performance and species interactions (e.g., predation risk). However, some organisms have shown surprising capabilities to compensate within and across generations to persist in the face of strong environmental stressors.

We are particularly interested in understanding why impacts and resilience between species and populations seem to differ so drastically – or in other words: what mechanisms allow some animals to thrive in changing environments where others cannot? By deepening our understanding of the mechanisms that limit or facilitate persistence in the face of global change, we can not only forecast negative impacts on species of conservation concern and economic value, but also identify management strategies for promoting resilient populations and ecosystems.

Understanding ocean warming impacts on shrinking body sizes of California fishes


Reductions in body size of marine fishes linked to ocean warming have been reported across numerous ecosystem types and species. These smaller body sizes can in turn be linked to lower population biomass and reproductive output, which have serious potential implications for future fisheries yield projections, stock assessments, and ecosystem stability. The underlying mechanisms for this pattern largely remain untested, but one theory that has gained traction is that reduced body sizes result from constraints on gill size. However, this theory is strongly debated, and there has little empirical research to validate this hypothesis.

Led by postdoctoral researcher Joshua Lonthair and in collaboration with Drs. Nicholas Wegner (NOAA SWFSC) and Nann Fangue (UC Davis), we are using a combination of whole organism physiology metrics and biochemical assays to test the proposed mechanisms in a species of high value to California fisheries and ecosystems, the Pacific sardine (Sardinops sagax caerulea). Specifically, we are examining (1) if constraints on gill size and/or metabolism are the primary factors limiting growth in fish exposed to higher temperatures; (2) relationships of energetic demands and life history trade-offs (i.e., timing and investment in growth vs. reproduction) related to temperature and reduced body sizes; (3) the roles of phenotypic plasticity and local adaptation in shaping population level responses to ocean warming. Ultimately, through this research we aim to establish valid physiological mechanisms underlying current patterns that can be integrated into stock assessments and ecological models to predict climate change impacts on California fisheries yields and ecosystems under different management scenarios. This project is supported by California Sea Grant and the Ocean Protection Council.


Environmental change impacts on marine turtle demographics

Global change is affecting marine turtles in many ways, including potentially altering key demographic parameters that can strongly influence long-term population viability. One particular concern is that warming sand temperatures due to climate change is altering sex ratios, because (like many reptiles and fish), whether an individual becomes

Jamie photo (4)
Illustration by Erin Walsh

male or female depends on temperatures they are exposed to during early life (temperature dependent sex determination). In sea turtles, females are produced at higher incubation temperatures whereas males are produced at lower temperatures, but how that might lead to increases or decreases in abundance and long-term population persistence is not well understood. Other environmental changes are simultaneously affecting the habitat available and potentially breeding behaviors, such as the major reduction of green turtle nesting beach area in the Papahānaumokuākea Marine National Monument (PMNM) following a 2018 hurricane. However, marine turtles have persisted for millions of years through past climate shifts, and have complex life histories that might offer resilience in the face of these changes. We are combining genomic tools with complementary approaches to better understand marine turtle sex ratios and how their complex mating systems and other factors may affect their sensitivity or resilience to environmental change in several projects:

Photo Credit: NOAA Fisheries USFWS Permit #: TE-72088A-2

1) Hawaiian green turtles (Chelonia mydas) comprise a distinct population segment and use French Frigate Shoals (within PMNM) for their primary reproductive habitat. Led by ECo MS student Jamie Stoll and in collaboration with the Marine Turtle Biology and Assessment Program (NOAA PIFSC), we are using high-throughput genotyping approaches to conduct parentage analyses from samples collected over a five-year period (before and after the hurricane). These data will allow us to quantify the number of unique males and females contributing to viable offspring over time (breeding sex ratios), which will then be incorporated by PIFSC scientists into models of population viability under projected sand temperature and climate change scenarios. Want to learn more about Hawaiian green turtles and the amazing research NOAA MTBAP does? Check out the story of Mother Load: Part I & Part II!

2) We are very excited to soon begin a new project in collaboration with PROJECTO TAMAR and Drs. Mariana Fuentes (Florida State U.) and Will White (Oregon State U.) studying green sea turtle mating systems in Fernando de Noronha, Brazil. Supported by the National Science Foundation Division of Integrative and Organismal Systems, we will combine insights from state-of the art technologies in genomics, satellite telemetry, unmanned aerial vehicles and population modeling to understand how the complex reproductive behaviors of sea turtles could provide buffer against climate change. We have potential post-doctoral fellow and graduate student/technician opportunities on this project-if interested please get in contact:

We will soon be launching new global change research with the Headwaters to Oceans  & the Marine Global Change Ecology research groups and the MA Division of Marine Fisheries at the Gloucester Marine Laboratory. We also plan to have future global change projects in collaboration with the Northeast Climate Science Center, USFWS Richard Cronin Aquatic Resource Center & USGS Conte Anadromous Fish Leetown Science Center.

If you are interested in this work, please see our opportunities page! 

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