Integrative Oceanography Division

Diet data are critical for describing predator resource use and partitioning among competitors. However, time series needed to properly assess variability in resource use and partitioning are limited, especially in pelagic (open ocean) ecosystems where predators and prey make broad use of horizontal and vertical habitats. We examined a diet time series spanning two decades (1998-2018) consisting of 2749 stomachs from 10 pelagic predators in the southern California Current Ecosystem (SCCE): albacore tuna (Thunnus alalunga), Pacific bluefin tuna (Thunnus orientalis), swordfish (Xiphias gladius), blue shark (Prionace glauca), shortfin mako (Isurus oxyrinchus), common thresher shark (Alopias vulpinus), bigeye thresher shark (Alopias superciliosus), short-beaked common dolphin (Delphinus delphis), long-beaked common dolphin (Delphinus capensis) and northern right whale dolphin (Lissodelphis borealis). We quantified feeding habits with respect to prey taxonomy, length, vertical habitat and horizontal habitat. From 1998 to 2015, each predator exhibited diet variability but maintained consistent resource partitioning with the other predators. Across years, the diets of predators feeding mostly on shallow-living prey (<200 m) were more variable than those feeding on deeper-dwelling prey (>200 m). Following an increase in the abundance of northern anchovy (Engraulis mordax) in the SCCE starting in 2015, the ecological niches of Pacific bluefin tuna and swordfish converged. During 2016-2018, both predators fed more heavily on northern anchovy and other prey that occupy shallow nearshore habitats. We show that pelagic predators can maintain resource partitioning under a wide range of conditions. However, we also observe that drastic changes in resource availability can alter the degree of niche partitioning among competitors, providing new perspectives on the flexibility of predator niches. As climate change continues to alter food webs, understanding how predators forage will be essential for anticipating changes to pelagic ecosystem structure and services.

The transition from day to night brings sweeping change to both environments and the organisms within them. Diel shifts in gene expression have been documented across all domains of life but remain understudied in microbial communities, particularly those in extreme environments where small changes may have rippling effects on resource availability. In hypersaline environments, many prominent taxa are photoheterotrophs that rely on organic carbon for growth but can also generate significant ATP via light-powered rhodopsins. Previous research demonstrated a significant response to light intensity shifts in the model halophile Halobacterium salinarum, but these cycles have rarely been explored in situ. Here, we examined genome-resolved differential expression in a hypersaline saltern (water activity (aw) ≅ 0.83, total dissolved solids = 250.7 g L-1) throughout a 24-h period. We found increased transcription of genes related to phototrophy and anabolic metabolic processes during the day, while genes related to aerobic respiration and oxidative stress were upregulated at night. Substantiating these results with a chemostat culture of the environmentally abundant halophilic bacterium Salinibacter ruber revealed similar transcriptional upregulation of genes associated with aerobic respiration under dark conditions. These results describe the potential for light-driven changes in oxygen use across both a natural hypersaline environment and a pure culture.

Changing environmental conditions are leading to shifts in the timing of seasonal events globally. In the ocean, environmental cues affecting larval fish (ichthyoplankton) abundance may not be synchronized with factors optimizing larval and juvenile survival, making the study of ichthyoplankton phenology in the context of a changing environment critical. In the southern California Current Ecosystem (CCE), a major eastern boundary current upwelling system, significant long-term shifts in larval fish phenology have been previously observed. To assess the stability of these estimates and extend them to the northern CCE, we evaluated multidecadal trends in ichthyoplankton abundance for 57 species from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) and 25 species from the Newport Hydrographic Line (NH Line). We show that on average, larval fish phenology in the southern CCE has continued to advance with an estimated rate of -0.18 ± 0.05 day year^-1 from 1951 to 2022, while phenology in the northern CCE has advanced at a rate of -0.48 ± 0.26 day year^-1 from 1996 to 2023. Thirty-nine percent of species showed significant advancing phenology, 12% exhibited delayed phenology, and 49% showed no long-term linear change. A comparison analysis showed that species in these groups had similar rates of change between the two locations for the 1997-2017 period. Phenological shifts in the southern CCE tracked changes in the phenology of upper ocean temperature, zooplankton, and upwelling. These variables poorly explained shifts in the northern CCE, where short-term effects of the El Niño-Southern Oscillation and the 2014-2016 marine heatwave on ichthyoplankton phenology were observed for some species. This research highlights regional variability and continuing phenological shifts in one of the world's most productive marine ecosystems.

Changing environmental conditions are leading to shifts in the timing of seasonal events globally. In the ocean, environmental cues affecting larval fish (ichthyoplankton) abundance may not be synchronized with factors optimizing larval and juvenile survival, making the study of ichthyoplankton phenology in the context of a changing environment critical. In the southern California Current Ecosystem (CCE), a major eastern boundary current upwelling system, significant long-term shifts in larval fish phenology have been previously observed. To assess the stability of these estimates and extend them to the northern CCE, we evaluated multidecadal trends in ichthyoplankton abundance for 57 species from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) and 25 species from the Newport Hydrographic Line (NH Line). We show that on average, larval fish phenology in the southern CCE has continued to advance with an estimated rate of -0.18 ± 0.05 day year-1 from 1951 to 2022, while phenology in the northern CCE has advanced at a rate of -0.48 ± 0.26 day year-1 from 1996 to 2023. Thirty-nine percent of species showed significant advancing phenology, 12% exhibited delayed phenology, and 49% showed no long-term linear change. A comparison analysis showed that species in these groups had similar rates of change between the two locations for the 1997-2017 period. Phenological shifts in the southern CCE tracked changes in the phenology of upper ocean temperature, zooplankton, and upwelling. These variables poorly explained shifts in the northern CCE, where short-term effects of the El Niño-Southern Oscillation and the 2014-2016 marine heatwave on ichthyoplankton phenology were observed for some species. This research highlights regional variability and continuing phenological shifts in one of the worlds most productive marine ecosystems.

The methane seeps on the Pacific margin of Costa Rica support extensive animal diversity and offer insights into deep-sea biogeography. During five expeditions between 2009 and 2019, we conducted intensive faunal sampling via 63 submersible dives to 11 localities at depths of 300-3600 m. Based on these expeditions and published literature, we compiled voucher specimens, images, and 274 newly published DNA sequences to present a taxonomic inventory of macrofaunal and megafaunal diversity with a focus on invertebrates. In total 488 morphospecies were identified, representing the highest number of distinct morphospecies published from a single seep or vent region to date. Of these, 131 are described species, at least 58 are undescribed species, and the remainder include some degree of taxonomic uncertainty, likely representing additional undescribed species. Of the described species, 38 are known only from the Costa Rica seeps and their vicinity. Fifteen range extensions are also reported for species known from Mexico, the Galápagos seamounts, Chile, and the western Pacific; as well as 16 new depth records and three new seep records for species known to occur at vents or organic falls. No single evolutionary narrative explains the patterns of biodiversity at these seeps, as even morphologically indistinguishable species can show different biogeographic affinities, biogeographic ranges, or depth ranges. The value of careful molecular taxonomy and comprehensive specimen-based regional inventories is emphasized for biodiversity research and monitoring.

The Southern Ocean is rich in highly dynamic mesoscale eddies and substantially modulates global biogeochemical cycles. However, the overall surface and subsurface effects of eddies on the Southern Ocean biogeochemistry have not been quantified observationally at a large scale. Here, we co-locate eddies, identified in the Meta3.2DT satellite altimeter-based product, with biogeochemical Argo floats to determine the effects of eddies on the dissolved inorganic carbon (DIC), nitrate, and dissolved oxygen concentrations in the upper 1,500 m of the ice-free Southern Ocean, as well as the eddy effects on the carbon fluxes in this region. DIC and nitrate concentrations are lower in anticyclonic eddies (AEs) and increased in cyclonic eddies (CEs), while dissolved oxygen anomalies switch signs above (CEs: positive, AEs: negative) and below the mixed layer (CEs: negative, AEs: positive). We attribute these anomalies primarily to eddy pumping (isopycnal heave), as well as eddy trapping for oxygen. Maximum anomalies in all tracers occur at greater depths in the subduction zone north of the Antarctic Circumpolar Current (ACC) compared to the upwelling region in the ACC, reflecting differences in background vertical structures. Eddy effects on air-sea CO2 exchange have significant seasonal variability, with additional outgassing in CEs in fall (physical process) and additional oceanic uptake in AEs and CEs in spring (biological and physical process). Integrated over the Southern Ocean, AEs contribute ∼0.03± 0.01 Pg C yr-1 (7 ±2% ) to the Southern Ocean carbon uptake, and CEs offset this by ∼0.01± 0.01 Pg C yr-1 (2 ±2% ). These findings underscore the importance of considering eddy impacts in observing networks and climate models.

Globally, ocean dumping of chemical waste is a common method of disposal and relies on the assumption that dilution, diffusion, and dispersion at ocean scales will mitigate human exposure and ecosystem impacts. In southern California, extensive dumping of agrochemical waste, particularly chlorinated hydrocarbon contaminants such as DDT, via sewage outfalls and permitted offshore barging occurred for most of the last century. This study compiled a database of existing sediment and fish DDT measurements to examine how this unique legacy of regional ocean disposal translates into the contemporary contamination of the coastal ocean. We used spatiotemporal modeling to derive continuous estimates of sediment DDT contamination and show that the spatial signature of disposal (i.e., high loadings near historic dumping sites) is highly conserved in sediments. Moreover, we demonstrate that the proximity of fish to areas of high sediment loadings explained over half of the variation in fish DDT concentrations. The relationship between sediment and fish contamination was mediated by ecological predictors (e.g., species, trophic ecology, habitat use), and the relative influence of each predictor was context-dependent, with habitat exhibiting greater importance in heavily contaminated areas. Thus, despite more than half a century since the cessation of industrial dumping in the region, local ecosystem contamination continues to mirror the spatial legacy of dumping, suggesting that sediment can serve as a robust predictor of fish contamination, and general ecological characteristics offer a predictive framework for unmeasured species or locations.

Abstract: The current United Nations Decade of Ocean Science for Sustainable Development (2021–2030; hereafter, the Decade) offers a unique opportunity and framework to globally advance ocean science and policy. Achieving meaningful progress within the Decade requires collaboration and coordination across Decade Actions (Programs, Projects, and Centres). This coordination is particularly important for the deep ocean, which remains critically under‐sampled compared to other ecosystems. Despite the limited sampling, the deep ocean accounts for over 95% of Earth's habitable space, plays a crucial role in regulating the carbon cycle and global temperatures, and supports diverse ecosystems. To collectively advance deep‐ocean science, we gathered representatives from 20 Decade Actions that focus at least partially on the deep ocean. We identified five broad themes that aim to advance deep‐ocean science in alignment with the Decade's overarching 10 Challenges: natural capital and the blue economy, biodiversity, deep‐ocean observing, best practices in data sharing, and capacity building. Within each theme, we propose concrete objectives (termed Cohesive Asks) and milestones (Targets) for the deep‐ocean community. Developing these Cohesive Asks and Targets reflects a commitment to better coordination across deep‐ocean Decade Actions. We aim to build bridges across deep‐ocean disciplines, which encompass natural science, ocean observing, policy, and capacity development.