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1. Reduced Oxygen Impairs Photobehavior in Marine Invertebrate Larvae

   https://doi.org/10.1086/717565  

   McCormick, Lillian R. ; Levin, Lisa A. ; Oesch, Nicholas W. ( October 2022 , The 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 umol kg-1 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. Effects of hypoxia on the behavior and physiology of kelp forest fishes

   https://doi.org/10.1111/gcb.15076  

   Mattiasen, Evan G. ; Kashef, Neosha S. ; Stafford, David M. ; Logan, Cheryl A. ; Sogard, Susan M. ; Bjorkstedt, Eric P. ; Hamilton, Scott L. ( April 2020 , Global Change Biology)

   Forecasts from climate models and oceanographic observations indicate increasing deoxygenation in the global oceans and an elevated frequency and intensity of hypoxic events in the coastal zone, which have the potential to affect marine biodiversity and fisheries. Exposure to low dissolved oxygen (DO) conditions may have deleterious effects on early life stages in fishes. This study aims to identify thresholds to hypoxia while testing behavioral and physiological responses of two congeneric species of kelp forest fish to four DO levels, ranging from normoxic to hypoxic (8.7, 6.0, 4.1, and 2.2 mg O₂/L). Behavioral tests identified changes in exploratory behavior and turning bias (lateralization), whereas physiological tests focused on determining changes in hypoxia tolerance (pCrit), ventilation rates, and metabolic rates, with impacts on the resulting capacity for aerobic activity. Our findings indicated that copper rockfish (Sebastes caurinus) and blue rockfish (Sebastes mystinus) express sensitivity to hypoxia; however, the strength of the response differed between species. Copper rockfish exhibited reduced absolute lateralization and increased escape time at the lowest DO levels, whereas behavioral metrics for blue rockfish did not vary with oxygen level. Both species exhibited decreases in aerobic scope (as a function of reduced maximum metabolic rate) and increases in ventilation rates to compensate for decreasing oxygen levels. Blue rockfish had a lower pCrit and stronger acclimation response compared to copper rockfish. The differences expressed by each species suggest that acclimatization to changing ocean conditions may vary, even among related species that recruit to the same kelp forest habitat, leading to winners and losers under future ocean conditions. Exposure to hypoxia can decrease individual physiological fitness through metabolic and aerobic depression and changes to anti‐predator behavior, with implications for the outcome of ecological interactions and the management of fish stocks in the face of climate change.

    

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3. Climate Change Will Fragment Florida Stone Crab Communities

   https://doi.org/10.3389/fmars.2022.839767  

   Alaerts, Lauranne ; Dobbelaere, Thomas ; Gravinese, Philip M. ; Hanert, Emmanuel ( July 2022 , Frontiers in Marine Science)

   Many marine species have been shown to be threatened by both ocean acidification and ocean warming which are reducing survival, altering behavior, and posing limits on physiology, especially during earlier life stages. The commercially important Florida stone crab, Menippe mercenaria , is one species that is affected by reduced seawater pH and elevated seawater temperatures. In this study, we determined the impacts of reduced pH and elevated temperature on the distribution of the stone crab larvae along the West Florida Shelf. To understand the dispersion of the larvae, we coupled the multi-scale ocean model SLIM with a larval dispersal model. We then conducted a connectivity study and evaluated the impacts of climate stressors by looking at four different scenarios which included models that represented the dispersion of stone crab larvae under: 1) present day conditions as modelled by SLIM for the temperature and NEMO-PISCES for the pH, 2) SSP1-2.6 scenario (-0.037 reduction in pH and +0.5°C compared to present-day conditions), 3) SSP2-4.5 scenario(-0.15 reduction in pH and +1.5°C) and 4) SSP5-8.5 scenario (-0.375 reduction in pH and +3.5°C). Our results show a clear impact of these climate change stressors on larval dispersal and on the subsequent stone crab distribution. Our results indicate that future climate change could result in stone crabs moving north or into deeper waters. We also observed an increase in the number of larvae settling in deeper waters (defined as the non-fishing zone in this study with depths exceeding 30 m) that are not typically part of the commercial fishing zone. The distance travelled by larvae, however, is likely to decrease, resulting in an increase of self-recruitment and decrease of the size of the sub-populations. A shift of the spawning period, to earlier in the spring, is also likely to occur. Our results suggest that habitats in the non-fishing zone cannot serve as a significant source of larvae for the habitats in the fishing zone (defined as water depth< 30 m) since there is very little exchange (< 5% of all exchanges) between the two zones. These results indicate that the stone crab populations in Florida may be susceptible to community fragmentation and that the management of the fishery should consider the potential impacts of future climate change scenarios. 

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4. Larval cross‐shore transport estimated from internal waves with a background flow: The effects of larval vertical position and depth regulation

   https://doi.org/10.1002/lno.11632  

   Garwood, Jessica C. ; Lucas, Andrew J. ; Naughton, Perry ; Roberts, Paul L. D. ; Jaffe, Jules S. ; deGelleke, Laura ; Franks, Peter J. S. ( October 2020 , Limnology and Oceanography)

   Cross‐shore velocities in the coastal ocean typically vary with depth. The direction and magnitude of transport experienced by meroplanktonic larvae will therefore be influenced by their vertical position. To quantify how swimming behavior and vertical position in internal waves influence larval cross‐shore transport in the shallow (~ 20 m), stratified coastal waters off Southern California, we deployed swarms of novel, subsurface larval mimics, the Mini‐Autonomous Underwater Explorers (M‐AUEs). The M‐AUEs were programmed to maintain a specified depth, and were deployed near a mooring. Transport of the M‐AUEs was predominantly onshore, with average velocities up to 14 cm s⁻¹. To put the M‐AUE deployments into a broader context, we simulated > 500 individual high‐frequency internal waves observed at the mooring over a 14‐d deployment; in each internal wave, we released both depth‐keeping and passive virtual larvae every meter in the vertical. After the waves' passage, depth‐keeping virtual larvae were usually found closer to shore than passive larvae released at the same depth. Near the top of the water column (3–5‐m depth), ~ 20% of internal waves enhanced onshore transport of depth‐keeping virtual larvae by ≥ 50 m, whereas only 1% of waves gave similar enhancements to passive larvae. Our observations and simulations showed that depth‐keeping behavior in high‐frequency internal waves resulted in enhanced onshore transport at the top of the water column, and reduced offshore dispersal at the bottom, compared to being passive. Thus, even weak depth‐keeping may allow larvae to reach nearshore adult habitats more reliably than drifting passively.

    

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5. Marine heat waves, climate change, and failed spawning by coastal invertebrates

   https://doi.org/10.1002/lno.11331  

   Shanks, Alan L. ; Rasmuson, Leif K. ; Valley, Jenna R. ; Jarvis, Marley A. ; Salant, Carly ; Sutherland, David A. ; Lamont, Eleanor I. ; Hainey, MacKenna A. H. ; Emlet, Richard B. ( October 2019 , Limnology and Oceanography)

   To investigate the timing and intensity of winter spawning by coastal invertebrates, we enumerated embryos in plankton samples collected in daily time series from January to March of 2014 (79 d), 2015 (73 d), and 2016 (74 d). Samples were collected near the mouth of the Coos Bay estuary in Oregon. We enumerated several hundred different morphologically distinct types of embryos and larvae representing at least five phyla. Forty‐three embryo types were abundant enough (abundance > 500 over the time series) to enable statistical analysis. Twenty of these types were identified using genetic barcoding of which there were four nemerteans, four gastropods, four chitons, five polychaetes, and two echinoderms. In winter 2014, hydrographic conditions were similar to average historical values. Conditions in 2015 and 2016 were characterized by marine heat waves (MHWs). In 2015, the “warm blob”—anomalously warm water in the Northeastern Pacific—affected conditions and in 2016, there was a strong El Niño. In 2015 and 2016, winter spawning intensity was orders of magnitude lower than in 2014 and many taxa failed to spawn (11 and 24 in 2015 and 2016, respectively); spawning appears to have been adversely impacted by the MHWs. The MHW of 2015 has been attributed to anthropogenic global climate change while the 2016 El Niño may have been strengthened by climate change. The frequency, intensity, and duration of MHW are projected to increase dramatically with global warming, which may adversely affect reproduction and recruitment by numerous marine taxa.

    

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