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1. MOLLUSK FORENSICS IN ANTARCTICA: DO EPI- BENTHIC SCALLOPS EXHIBIT PREDATORY SHELL REPAIR?

   WALKER, S. ; BOWSER, S.S. ( June 2019 , PaleoBios)

   null (Ed.)

   One of the most fundamental changes predicted to occur under warming scenarios for Antarctica is the invasion of durophagous (shell-breaking or peeling) predators—like decapod crustaceans—which were last common in Antarctic waters during the warmer Eocene Period, over 30 million years ago. Since then, Antarctica’s shallow-water benthos developed Paleo- zoic (or deep-sea-like) ecosystems dominated by epi- benthic echinoderms. Despite the looming predatory carnage, little is known about how predators structure shallow subtidal communities in Antarctica, especially in regard to predation on shelled prey. We therefore need to have a baseline of shell repair—if it occurs— prior to the initial invasion of crabs. Here, we assess whether the shell of the Antarctic Scallop, Adamussium colbecki, living in the shallow subtidal under sea ice, records an ontogenetic history of shell repair. Shells of A. colbecki(n=623 valves; ~ 0.50 mm thick) were collected from shallow depths (6–24 m) within western McMurdo Sound, Ross Sea, from the coldest waters on Earth (-1.97 °C): Four sites in Explorers Cove (EC) with semi-permanent (decadal or more) sea ice and a Ferrar Glacier site (located ~30 km south of EC) with annual sea ice and icebergs. All sites were composed of fine sediments interspersed with glacial erratics that were more common at Ferrar than EC. Ju- venile (≤ 50 mm) and adult portions of the shells were examined under a dissecting scope for shell repair. Results indicate that repair did occur and was consistent with predatory damage: 1) valves had ste- reotypic damage patterns, both in style and spatial distribution; 2) there were five styles of repair rang- ing from typical crab-like (jagged) repair to elongate repair; 3) scallops living under ice scour regimes (Ferrar) did not have significantly different repair frequencies than those living under semi-permanent sea ice (EC sites); and 4) none of the shells had shell repair consistent with ice scour as described previ- ously for Laternula elliptica, an Antarctic burrowing bivalve. Frequency of repair varied between 0.04 and 0.26 for the five sites and depths (mean 0.10) and adults had the highest frequency of repair. The mean repair frequency is similar to infaunal Laternulafrom other semi-permanent sea ice sites in McMurdo Sound, but higher than those reported for epifaunal brachio- pods from the Antarctic Peninsula where ice scour does occur. We posit that shell repair can be used as an indicator of durophagy in Antarctica: The forensic agents are unexpectedly sea stars and possibly fish. In a warming world, this scallop may not survive long withboth an increase in ice scour and the putative ar- rival of shell-breaking crabs at ~1 °C. 

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2. Habitat analysis of the commercial tuna of the Eastern Tropical Pacific Ocean

   https://doi.org/10.1111/fog.12263  

   Hu, Chen ; Harrison, Daniel P. ; Hinton, Michael G. ; Siegrist, Zachary C. ; Kiefer, Dale A. ( April 2018 , Fisheries Oceanography)

   We have extracted information on the habitats of bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis) and yellowfin (Thunnus albacares) in the Eastern Tropical Pacific Ocean by matching the spatial‐temporal distribution of catch and effort of purse seine and longline fleets collected by the Inter‐American Tropical Tuna Commission with oceanographic conditions and subjecting the matched data to Quotient Analysis and General Additive Models (GAMs). These analyses yielded the following results. The habitats defined by theGAManalysis of young fish differ significantly between two periods, one before and one after the introduction of fish aggregation devices (FADs). This was not true for the older fish caught by longline. We speculate that these changes were caused by the extensive use ofFADs. Younger bigeye and yellowfin caught by the purse seine fleet have a different preference of environmental variables compared to older fish caught by longline. This is to be expected since tuna of different age groups have different sizes, metabolic capabilities and swimming skills. Moreover, as revealed byGAMs, the habitats of young fish differ between species to a much larger degree than those of older fish. Our results indicate the fundamental differences between fishing methods, targeted species, and operating region of the two fisheries. Specifically, young bigeye occupy equatorial waters farther from the coast and where the hypoxic layer is deeper, young skipjack occupy more productive waters associated with equatorial and coastal upwelling, and young yellowfin occupy broad areas where waters are underlain by a shallow hypoxic layer.

    

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3. Insights Into Changing Interglacial Conditions in Subarctic Canada From MIS 11 Through MIS 5e From Seasonally Resolved Speleothem Records

   https://doi.org/10.1029/2024GL108459  

   Batchelor, Cameron J. ; McGee, David ; Shakun, Jeremy D. ; Woodhead, Jon ; Jost, Adam B. ; Arnold, Sarah ; Horne, Greg ; Kinsley, Christopher W. ; Freudenburg‐Puricelli, Markey ( April 2024 , Geophysical Research Letters)

   High‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ¹⁸O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ¹⁸O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ¹⁸O and suggest low MIS 11 δ¹⁸O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them.

    

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4. Stable isotopes of nitrate record effects of the 2015–2016 El Niño and diatom iron limitation on nitrogen cycling in the eastern North Pacific Ocean

   https://doi.org/10.1002/lno.12194  

   White, Margot E. ; Rafter, Patrick A. ; Stephens, Brandon M. ; Mazloff, Matthew R. ; Wankel, Scott D. ; Aluwihare, Lihini I. ( July 2022 , Limnology and Oceanography)

   In eastern boundary current systems, strong coastal upwelling brings deep, nutrient‐rich waters to the surface ocean, supporting a productive food web. The nitrate load in water masses that supply the region can be impacted by a variety of climate‐related processes that subsequently modulate primary productivity. In this study, two coastal upwelling regimes along central and southern California were sampled seasonally for nitrogen and oxygen stable isotopes of nitrate (i.e., nitrate isotopes) over several years (2010–2016) on 14 California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises. Seasonal, interannual, and spatial variations in euphotic zone nitrate isotopes were largely driven by the extent of nitrate utilization, sometimes linked to iron limitation of diatom productivity. Pronounced isotopic enrichment developed with the El Niño conditions in late 2015 and early 2016 which likely resulted from increased nitrate utilization linked to reduced nitrate supply to the euphotic zone. Differential enrichment of nitrogen and oxygen isotopes was observed in the surface ocean, suggesting that phytoplankton increased their reliance on locally nitrified (recycled) nitrate during warmer and more stratified periods. Overall, nitrate isotopes effectively differentiated important euphotic zone processes such as nitrate assimilation and nitrification, while archiving the influence of disparate controls such as iron limitation and climatic events through their effects on nitrate utilization and isotopic fractionation.

    

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5. Shaped by Their Environment: Variation in Blue Whale Morphology across Three Productive Coastal Ecosystems

   https://doi.org/10.1093/iob/obad039  

   Barlow, D. R. ; Bierlich, K. C. ; Oestreich, W. K. ; Chiang, G. ; Durban, J. W. ; Goldbogen, J. A. ; Johnston, D. W. ; Leslie, M. S. ; Moore, M. J. ; Ryan, J. P. ; et al ( November 2023 , Integrative Organismal Biology)

   Species ecology and life history patterns are often reflected in animal morphology. Blue whales are globally distributed, with distinct populations that feed in different productive coastal regions worldwide. Thus, they provide an opportunity to investigate how regional ecosystem characteristics may drive morphological differences within a species. Here, we compare physical and biological oceanography of three different blue whale foraging grounds: (1) Monterey Bay, California, USA; (2) the South Taranaki Bight (STB), Aotearoa New Zealand; and (3) the Corcovado Gulf, Chile. Additionally, we compare the morphology of blue whales from these regions using unoccupied aircraft imagery. Monterey Bay and the Corcovado Gulf are seasonally productive and support the migratory life history strategy of the Eastern North Pacific (ENP) and Chilean blue whale populations, respectively. In contrast, the New Zealand blue whale population remains in the less productive STB year-round. All three populations were indistinguishable in total body length. However, New Zealand blue whales were in significantly higher body condition despite lower regional productivity, potentially attributable to their non-migratory strategy that facilitates lower risk of spatiotemporal misalignment with more consistently available foraging opportunities. Alternatively, the migratory strategy of the ENP and Chilean populations may be successful when their presence on the foraging grounds temporally aligns with abundant prey availability. We document differences in skull and fluke morphology between populations, which may relate to different feeding behaviors adapted to region-specific prey and habitat characteristics. These morphological features may represent a trade-off between maneuverability for prey capture and efficient long-distance migration. As oceanographic patterns shift relative to long-term means under climate change, these blue whale populations may show different vulnerabilities due to differences in migratory phenology and feeding behavior between regions.

   Spanish abstract La ecología y patrones de historia de vida de las especies a menudo se reflejan en la morfología animal. Las ballenas azules están distribuidas globalmente, con poblaciones separadas que se alimentan en diferentes regiones costeras productivas de todo el mundo. Por lo tanto, brindan la oportunidad de investigar cómo las características regionales de los ecosistemas pueden impulsar diferencias morfológicas dentro de una especie. Aquí, comparamos la oceanografía física y biológica de tres zonas de alimentación diferentes de la ballena azul: (1) Bahía de Monterey, California, EE. UU., (2) Bahía del sur de Taranaki (BST), Nueva Zelanda, y (3) Golfo de Corcovado, Chile. Adicionalmente, comparamos la morfología de las ballenas azules de estas regiones utilizando imágenes de aeronaves no tripuladas. La Bahía de Monterey y el Golfo de Corcovado son estacionalmente productivos y apoyan la estrategia migratoria de la historia de vida de las poblaciones de ballena azul chilena y del Pacífico Norte Oriental (PNO), respectivamente. Por el contrario, la población de ballena azul de Nueva Zelanda permanece en la menos productiva BST durante todo el año. Las tres poblaciones eran indistinguibles en cuanto a la longitud corporal total. Sin embargo, las ballenas azules de Nueva Zelanda tenían una condición corporal significativamente mayor a pesar de una menor productividad regional, potencialmente atribuible a su estrategia no migratoria que facilita un menor riesgo de desalineación espaciotemporal con oportunidades de alimentación disponibles de manera más consistente. Alternativamente, la estrategia migratoria de las poblaciones de ballenas PNO y chilena puede tener éxito cuando su presencia en las zonas de alimentación se alinea temporalmente con la abundante disponibilidad de presas. Documentamos diferencias en la morfología del cráneo y la aleta caudal entre poblaciones, que pueden estar relacionadas con diferentes comportamientos de alimentación adaptados a las características de hábitat y presas específicas para cada región. Estas características morfológicas pueden representar una compensación entre la maniobrabilidad para la captura de presas y una migración eficiente a larga distancia. A medida que los patrones oceanográficos cambian en términos de mediano a largo plazo debido al cambio climático, estas poblaciones de ballenas azules pueden mostrar diferentes vulnerabilidades debido a diferencias en la fenología migratoria y el comportamiento de alimentación entre regiones.

    

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