David Kwon, University of California, Davis

Dissolved oxygen (DO) is a critical property defining the viability of pelagic habitat in marine ecosystems. Previous studies using CalCOFI’s historical DO dataset documented a substantial subsurface decline in the California Current System (CCS) since the 1980s. An iconic manifestation of this trend is shoaling of the hypoxic boundary (60 µmol/kg), a threshold below which aerobic life can be stressed. This shoaling contributes to habitat compression and increases the likelihood that hypoxic waters are upwelled into nearshore environments. Here, we examined updated CalCOFI observations (1984-2021) from the core domain (Lines 76.7 to 93.3) to assess changes over the past decade, a period marked by major climate-driven oceanographic events. After a domain-wide rise to peak shoaling from 2005-2015, we identified a subsequent deepening of the hypoxic boundary between 2015 and 2021 in inshore regions, mirrored by simultaneous DO increases at 200m depth. Regression modeling of select stations indicates that this deepening represents a sustained >10-year trend, with hypoxic boundary depths returning to levels comparable to the late-1990s by 2021. We hypothesize that this pattern represents a low-frequency modulation superimposed on the long-term deoxygenation trend in the CCS, suggesting that regional deoxygenation under climate change may include interannual periods of mitigation or amplification. Although the mechanisms driving this low-frequency variability remain uncertain, we suggest that changes in southern source water properties or transport may be a key driver. Regardless of cause, the existence of a recent mitigation of hypoxic boundary shoaling could have significant ecological consequences with implications for the management of ecologically and economically important species that are affected by hypoxia-driven habitat loss.

Evan Howard, University of Washington

I present observations from a 15-year time series (2010 – 2025) of high-frequency ocean carbon measurements, hydrographic observations, and derived ocean acidification tracers, including aragonite saturation state collected from the CCE2 buoy West-Southwest of Point Conception (CalCOFI Line 80 Station 55). This site is part of the Pacific Marine Environmental Laboratory’s globally distributed moored carbon observatories. Using this data, I examine the time scales, magnitudes, and event characteristics of ocean acidification in the southern California Current Ecosystem. These data are publicly available and complement the CalCOFI time series for exploring the linkages between coastal biogeochemical stressors and biological responses in the changing coastal ocean.

Christina Frieder, Southern California Coastal Water Research Project

The vast majority of OAH observations and models are for chemical data only – like oxygen, pH, or calculated saturation state of aragonite. Despite the (relative) vastness of chemical data, there is limited translation of how OAH matters for biology. Biological translation of chemical data is critical to interpret ecosystem condition. However, there are just a few biological indicators of OAH that have been applied to a subset of California’s OAH data. The result is under-representation of marine habitats and taxa in OAH assessments. Here, we will discuss opportunities to co-leverage CalCOFI’s biological observations with ROMS-BEC model scenarios to address key OAH questions like – What are the dominant scales of OAH variability? Is there evidence that single species or assemblages of zooplankton relate to OAH gradients? Are there threshold metrics or mechanistic frameworks to explain observed outcomes? These types of studies have the potential to augment biological interpretation of OAH along California’s coast.

María Blanco Orta, Center for Scientific Research and Higher Education of Ensenada, Baja California

Phytoplankton represents the base of marine food webs, therefore, fluctuations in its biomass and community structure regulate the population dynamics and trophic interactions of higher consumers in the California Current System. In this study, we estimate the phytoplankton community responses to environmental variation, measured as temperature, salinity, density, and inorganic nutrients, from Todos Santos Bay, Baja California, Mexico. We quantified changes in biomass, size structure, and functional composition through pigments analysis to identify the physical and chemical drivers shaping phytoplankton variability across spatial and temporal scales. Water samples were collected along a longitudinal transect of six stations over three years: 2022-2024. Nutrient concentrations and pigments were measured with a segmented flow analyzer and a high-performance liquid chromatography, respectively. Our results reveal high variability in community structure, with overall microphytoplankton dominance (> 80 %) associated with high salinity, low temperature and nutrient availability. In contrast, nano- and picophytoplankton ( ̴ 40 %) increased their abundance under warm conditions of low nutrients availability, accompanied by higher concentrations of photoprotective pigments, indicating a physiological response to environmental stress. These findings identified consistent patterns of phytoplankton variability and their main drivers, providing insights into how climate-driven changes may alter bottom-up-regulations, and energy transfer efficiency in the Baja California transition zone. 

Shannon Dolan, Scripps Institution of Oceanography

Submarine basins within the Southern California Bight (SCB) create a heterogeneous mosaic of hydrographic conditions that structure bathypelagic prey fields and influence the foraging ecology of deep-diving predators such as Ziphius cavirostris. To resolve fine-scale, deep-sea temporal variability within the broader CalCOFI sampling grid, three long-term Eulerian moorings were deployed from 2017 to 2023 in distinct SCB submarine basins. Each mooring was equipped with environmental sensors, a hydrophone, and a 70 kHz echosounder, providing continuous, high-resolution measurements of temperature, salinity, dissolved oxygen, prey acoustic backscatter, and beaked whale acoustic presence. Across sites, hydrographic variability was small yet ecologically significant, with temperature and salinity differing by less than 0.7°C and 0.06 g kg⁻¹, respectively. Despite this narrow range, each basin maintained a distinct hydrographic signature associated with basin-specific prey assemblages reflected in acoustic backscatter. Complementary eDNA data indicated taxonomic variability among basins, suggesting that even small variations in water mass properties can structure prey communities at depth. In addition, the moorings recorded episodic flushing events that introduced colder, saltier, and more oxygenated waters, resulting in basin-specific redistribution of prey. Integrating continuous moored observations with the spatially extensive CalCOFI grid underscores the importance of high temporal resolution, site-specific measurements for understanding ephemeral predator–prey dynamics in highly dynamic deep pelagic ecosystems.

Jaime Gómez-Gutiérrez, Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional

Over the past three decades, the epipelagic ecosystem of the Gulf of California has undergone persistent warming, which is hypothesized to have reduced zooplankton abundance and altered community composition. These changes in the food web are considered potential drivers of recent population decline in several megafauna species. We tested the hypothesis that zooplankton volume and euphausiid abundance, two indicators of zooplankton standing stock, have significantly decreased between 1957 and 2019 by comparing three sampling periods: 1957 (reference year), 1978–1988, and 1997–2019. Our analysis identified diel cycles and seasonal temperature variation (cold vs warm seasons) as the primary modes of variability influencing zooplankton volume and euphausiid abundance. Generalized additive models showed that peak values for both variables occurred under neutral ENSO conditions and intermediate temperatures. Quantile regression models and density distribution curves across the three sampling periods revealed no significant long-term decrease in nighttime zooplankton volume or euphausiid abundance. These findings suggest long-term stability despite sustained increases in sea surface temperature, indicating that the base of the trophic web has either remained stable or experienced declines too subtle to detect in response to regional warming in the Gulf of California.

Michael Montgomery, University of California, Santa Barbara

In its nearly eighty-year history, CalCOFI has featured many talks about the extreme warm-water events we now call marine heatwaves, often documenting warm-water species found outside their typical ranges and demonstrating a correlation with the elevated temperatures. For most of the species involved, however, we still lack a species-specific, physical explanation of how and why they extend their ranges during the heatwaves. Here I add a new and timely case study to this longstanding conversation: the purple swimming crab, Euphylax dovii, whose pelagic adult habits make it a likely indicator of ocean currents, acting in concert with warming, that transport species to new places. Based on the published literature, community observations on iNaturalist and elsewhere, and an extensive survey of museum specimens, many housed at the site of this conference, this talk offers an up-to-date view of the purple swimming crab’s range dynamics in relation to marine heatwaves and regional physical oceanography. In particular, Euphylax dovii’s occasional mass invasions of offshore islands and the coastal zones of Chile, Peru, and Mexico’s Gulf of Tehuantepec indicate a complex interplay of life-history and surface currents that results in the crab tracking the onset of El Niño events in some regions, lagging it in others—including southern California—and leading it, by short intervals, in others. Such an idiosyncratic, boom-or-bust dispersal pattern has far-reaching implications, as the crabs’ presence substantially impacts coastal fisheries and pelagic and shelf ecosystems, and may aid in forecasting El Niño. Indeed, the recent and apparently ongoing influx of masses of purple swimming crabs to southern Ecuador and the Galapagos Islands, the latter for only the third time in a century, suggests, as models predict, that 2026 is shaping up to be a year of significant change in the Eastern Tropical Pacific.

Ingrid Ibarra Navarrete, Center for Scientific Research and Higher Education of Ensenada (CICESE)

El Niño-Southern Oscillation is a major driver of climatic variability in the California Current System, strongly influencing plankton biomass and community composition. These changes, in turn, influence the trophodynamics of the Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax), which are key species in pelagic food webs. These commercially and ecologically important species are planktivorous but exhibit different buccal morphologies, physiological tolerances, and prey preferences. We evaluated spatiotemporal differences in the trophic niche of S. sagax and E. mordax along Baja California by analyzing stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in bulk tissue during warm (2023) and cold (2024) conditions. In addition, amino acid-specific δ¹⁵N values were quantified to track baseline variation and estimate trophic positions. Spatial and temporal variation in the trophic niches and trophic position were observed across latitudes, suggesting differential foraging strategies and habitat use, despite both species being collected at the same sites. Isotopic niches for both species were larger during 2023 and smaller during 2024, suggesting a shift toward more generalist feeding under lower availability of optimal prey, and more specialized feeding when optimal prey were more abundant. The overlap between species for both years was moderate (36.7%), indicating niche partitioning. Amino acid δ¹⁵N values indicated slight interspecific different trophic positions, reflecting species-specific feeding in response to shifts in plankton community composition and biomass under contrasting warm and cold conditions.

Nick Wegner, Southwest Fisheries Science Center, NOAA Fisheries

In the eastern North Pacific, the oxygen minimum zone (OMZ) has shoaled in recent decades, potentially affecting the habitat and distribution of commercially important fish species such as rockfishes (genus Sebastes). Respirometry and behavioral experiments were used to determine the hypoxia sensitivities of two rockfish species that inhabit deep-water, rocky-reef habitat along the upper boundaries of the OMZ, but that exhibit contrasting movement patterns and habitat use: Cowcod (S. levis) are strongly benthic-oriented, while bocaccio (S. paucispinis) are more pelagic and active above the reef. These species thus serve as excellent models for examining the potential range in hypoxia sensitivity among rockfishes and similar species. Standard metabolic rate, critical oxygen threshold (Pcrit), and hypoxia-induced loss of equilibrium (LOE) were determined for each species at two seasonal and depth relevant temperatures (9 and 12°C). Additionally, a shuttle box system was used to determine the dissolved oxygen level eliciting a behavioral avoidance response. Results show that cowcod and bocaccio are both resilient to low-oxygen environments, though cowcod generally demonstrated greater tolerance to low oxygen levels and changes in temperature. In particular, cowcod tolerance to low oxygen ranks especially high among fishes and likely facilitates a sit-and-wait approach to episodic low-oxygen exposure, whereas more mobile bocaccio are more likely to behaviorally avoid hypoxia and seek favorable conditions. Our findings indicate that dissolved oxygen levels typical of depths occupied by bocaccio are nearing their critical metabolic limits. Thus, the shoaling of the OMZ is likely to push bocaccio and similar species into shallower habitats.

Gaelila McKaughan, Scripps Institute of Oceanography

In the past decade, CalCOFI has integrated environmental DNA (eDNA) methods for monitoring biodiversity in oceanic ecosystems through programs such as NCOG. While traditional ichthyoplankton tows on CalCOFI cruises have provided us with valuable insights to fish community composition on the coast of California, these methods are life-stage dependent as they only assess larvae. In this paper, we compare the species richness of bony fishes in historical CalCOFI net tow data to our eDNA water sampling efforts. In only two cruises, eDNA detected 23 fish species that have never been detected in CalCOFI ichthyoplankton net tows. Our study posits how eDNA can be used as a complementary tool to existing CalCOFI fish sampling methods to fill in gaps for fish that are rare, shy, and reside in our ecosystem at non-larval stages.