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1. Reduced Oxygen Impairs Photobehavior in Marine Invertebrate Larvae

   https://doi.org/doi.org/10.1086/717565  

   McCormick, Lillian R.; Levin, Lisa A.; Oesch, Nicholas W. (January 2022, Biological bulletin)

   Organisms in coastal waters experience naturally high oxygen variability and steep oxygen gradients with depth, in addition to ocean deoxygenation. They often undergo diel vertical migration involving a change in irradiance that initiates a visual behavior. Retinal function has been shown to be highly sensitive to oxygen loss; here we assess whether visual behavior (photobehavior) in paralarvae of the squid Doryteuthis opalescens and the octopus Octopus bimaculatus is affected by low oxygen conditions, using a novel behavioral paradigm. Larvae showed an irradiance-dependent, descending photobehavior after extinction of the light stimulus, measured through the change in vertical position of larvae in the chamber. The magnitude of photobehavior was decreased as oxygen was reduced, and the response was entirely gone at <6.4 kPa partial pressure of oxygen (<74.7 mmol kg21 at 15.3 7C) in D. opalescens paralarvae. Oxygen also affected photobehavior in O. bimaculatus paralarvae. The mean vertical velocity of paralarvae was unaffected by exposure to reduced oxygen, indicating that oxygen deficits selectively affect vision prior to locomotion. These findings suggest that variable and declining oxygen conditions in coastal upwelling areas and elsewhere will impair photobehavior and likely affect the distribution, migration behavior, and survival of highly visual marine species. 

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2. Anoxic waters constrain the vertical distribution of fish developmental stages in an oxygen minimum zone

   https://doi.org/10.1002/lno.12594  

   Gutiérrez‐Bravo, Juan_Gerardo; Sánchez‐Velasco, Laura; Jiménez‐Rosenberg, Sylvia_Patricia_Adelheid; Altabet, Mark_A; Méndez‐Mendez, Sofia; Cambronero‐Solano, Sergio (June 2024, Limnology and Oceanography)

   Abstract In the Eastern Tropical North Pacific Oxygen Minimum Zone (ETNP‐OMZ), fish larvae undergo development amidst highly variable dissolved oxygen environments. As OMZs expand, understanding the implications of low‐oxygen environments on fish development becomes increasingly relevant for fisheries management and ecosystem modeling. Using horizontal zooplankton tows to track five oxygen levels (oxic [200 μmol/kg], hypoxic [100 μmol/kg] suboxic [10 μmol/kg], anoxic [<1 μmol/kg], and deep [10 μmol/kg at ~ 1000 m depth]), this study analyzed the three‐dimensional distribution of fish larvae and adults across the ETNP‐OMZ. Results revealed a wide midwater anoxic core, extending from Costa Rica to Baja California, that was almost devoid of fish larvae (< 1 larvae/1000 m³). Early larval stages primarily inhabited the oxic and hypoxic levels above the core, while postflexion and transformation stages occurred across a wider oxygen gradient, including the deep level below the anoxic core. Epipelagic species (e.g.,Auxissp.) were predominantly found in the surface oxic level, whereas coastal‐demersal species (e.g.,Bregmaceros bathymaster,Ophidionspp.) were prevalent in the hypoxic level above the core. Meso‐bathypelagic species (e.g.,Diogenichthys laternatus,Cyclothonespp.) were present throughout the study area, including below the anoxic core as transformation larvae and juveniles. These findings indicate that a vertical expansion of anoxic waters in OMZs could further constrain the habitat of epipelagic species, while also affecting the ontogenic vertical movements of meso‐bathypelagic species. 

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3. Departures from isotropy: the kinematics of a larval snail in response to food

   https://doi.org/10.1242/jeb.239178  

   DiBenedetto, Michelle H.; Meyer-Kaiser, Kirstin S.; Torjman, Brooke; Wheeler, Jeanette D.; Mullineaux, Lauren S. (January 2021, Journal of Experimental Biology)

   null (Ed.)

   ABSTRACT The swimming behavior of invertebrate larvae can affect their dispersal, survival and settlement in the ocean. Modeling this behavior accurately poses unique challenges as behavior is controlled by both physiology and environmental cues. Some larvae use cilia to both swim and create feeding currents, resulting in potential trade-offs between the two functions. Food availability is naturally patchy and often occurs in shallow horizontal layers in the ocean. Also, larval swimming motions generally differ in the horizontal and vertical directions. In order to investigate behavioral response to food by ciliated larvae, we measured their behavioral anisotropy by quantifying deviations from a model based on isotropic diffusion. We hypothesized that larvae would increase horizontal swimming and decrease vertical swimming after encountering food, which could lead to aggregation at food layers. We considered Crepidula fornicata larvae, which are specifically of interest as they exhibit unsteady and variable swimming behaviors that are difficult to categorize. We tracked the larvae in still water with and without food, with a portion of the larvae starved beforehand. On average, larvae in the presence of food were observed higher in the water column, with higher swimming speeds and higher horizontal swimming velocities when compared with larvae without food. Starved larvae also exhibited higher vertical velocities in food, suggesting no aggregation behavior. Although most treatments showed strong anisotropy in larval behavior, we found that starved larvae without food exhibited approximately isotropic kinematics, indicating that behavioral anisotropy can vary with environmental history and conditions to enhance foraging success or mitigate food-poor environments. 

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4. Collective behavior emerges from genetically controlled simple behavioral motifs in zebrafish

   https://doi.org/10.1126/sciadv.abi7460  

   Harpaz, Roy; Aspiras, Ariel C.; Chambule, Sydney; Tseng, Sierra; Bind, Marie-Abèle; Engert, Florian; Fishman, Mark C.; Bahl, Armin (October 2021, Science Advances)

   It is not understood how changes in the genetic makeup of individuals alter the behavior of groups of animals. Here, we find that, even at early larval stages, zebrafish regulate their proximity and alignment with each other. Two simple visual responses, one that measures relative visual field occupancy and one that accounts for global visual motion, suffice to account for the group behavior that emerges. Mutations in genes known to affect social behavior in humans perturb these simple reflexes in individual larval zebrafish and change their emergent collective behaviors in the predicted fashion. Model simulations show that changes in these two responses in individual mutant animals predict well the distinctive collective patterns that emerge in a group. Hence, group behaviors reflect in part genetically defined primitive sensorimotor “motifs,” which are evident even in young larvae. 

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5. Ephemeral microbial responses to pulses of bioavailable carbon in oxic and anoxic salt marsh soils

   https://doi.org/10.1016/j.soilbio.2023.109157  

   Spivak, Amanda C.; Pinsonneault, Andrew J.; Hintz, Christopher; Brandes, Jay; Megonigal, J. Patrick (October 2023, Soil Biology and Biochemistry)

   Blagodatksaya, Evgenia (Ed.)

   Roots of salt marsh grasses contribute to soil building but also affect decomposition by releasing bioavailable carbon exudates and oxygen. Disentangling exudate and oxygen effects on decomposition is difficult in the field but essential for marsh carbon models and predicting the impacts of global change disturbances. We tested how pulsed, simulated exudates affect soil metabolism under oxic and anoxic conditions, and whether carbon and oxygen availability facilitate mineralization of existing organic matter (i.e., priming). We conducted a laboratory experiment in flow-through reactors, adding carbon pulses weekly for 84 days and then following starvation under low carbon conditions. Oxygen consumption and sulfide production were inhibited under anoxic and oxic conditions and slowed by 21±10% and 55±8%, respectively, between 1- and 5- days following exudate pulses. Respiration rates immediately following and between pulses increased over time, suggesting that microbes capitalize on and may acclimate to patchy resources. Starvation caused oxygen consumption and sulfide production to fall 28% and 78% in oxic and anoxic treatments. Smaller decreases in oxygen consumption following pulses could suggest greater access to secondary carbon sources and that sulfate reducers were more reliant on exudates. Soil organic carbon was not the likely secondary source because porewater dissolved inorganic carbon 13C values did not change during transit through the reactors, despite a ~26‰ difference between the supplied seawater and marsh soil. Interpretation of oxygen consumption rates is complicated by non-respiratory oxidation of reduced inorganic compounds and possibly significant lithoautotrophy. Exudate pulses elicited rapid and ephemeral respiratory responses, particularly under anoxia, but non-respiratory oxidation of reduced compounds obscured the impact of oxygen availability in our experimental system. Despite this, greater aerobic respiration rates suggest that oxygen availability has more potential to regulate carbon mineralization in coastal wetlands than root exudates. 

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