Seasonal prediction of bottom temperature on the Northeast U.S. Continental Shelf

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chen, Z., Kwon, Y.-O., Chen, K., Fratantoni, P., Gawarkiewicz, G., Joyce, T. M., Miller, T. J., Nye, J. A., Saba, V. S., & Stock, B. C. Seasonal prediction of bottom temperature on the Northeast U.S. Continental Shelf. Journal of Geophysical Research: Oceans, 126(5), (2021): e2021JC017187, https://doi.org/10.1029/2021JC017187.The Northeast U.S. shelf (NES) is an oceanographically dynamic marine ecosystem and supports some of the most valuable demersal fisheries in the world. A reliable prediction of NES environmental variables, particularly ocean bottom temperature, could lead to a significant improvement in demersal fisheries management. However, the current generation of climate model-based seasonal-to-interannual predictions exhibits limited prediction skill in this continental shelf environment. Here, we have developed a hierarchy of statistical seasonal predictions for NES bottom temperatures using an eddy-resolving ocean reanalysis data set. A simple, damped local persistence prediction model produces significant skill for lead times up to ∼5 months in the Mid-Atlantic Bight and up to ∼10 months in the Gulf of Maine, although the prediction skill varies notably by season. Considering temperature from a nearby or upstream (i.e., more poleward) region as an additional predictor generally improves prediction skill, presumably as a result of advective processes. Large-scale atmospheric and oceanic indices, such as Gulf Stream path indices (GSIs) and the North Atlantic Oscillation Index, are also tested as predictors for NES bottom temperatures. Only the GSI constructed from temperature observed at 200 m depth significantly improves the prediction skill relative to local persistence. However, the prediction skill from this GSI is not larger than that gained using models incorporating nearby or upstream shelf/slope temperatures. Based on these results, a simplified statistical model has been developed, which can be tailored to fisheries management for the NES.This work was supported by NOAA's Climate Program Office's Modeling, Analysis, Predictions, and Projections (MAPP) Program (NA17OAR4310111, NA19OAR4320074), and Climate Program Office's Climate Variability and Predictability (CVP) Program (NA20OAR4310482). We acknowledge our participation in MAPP's Marine Prediction Task Force

Seasonal Phytoplankton Blooms in the North Atlantic Linked to the Overwintering Strategies of Copepods

The North Atlantic Ocean contains diverse patterns of seasonal phytoplankton blooms with distinct internal dynamics. We analyzed blooms using remotely-sensed chlorophyll a concentration data and change point statistics. The first bloom of the year began during spring at low latitudes and later in summer at higher latitudes. In regions where spring blooms occurred at high frequency (i. e., proportion of years that a bloom was detected), there was a negative correlation between bloom timing and duration, indicating that early blooms last longer. In much of the Northeast Atlantic, bloom development extended over multiple seasons resulting in peak chlorophyll concentrations in summer. Spring bloom start day was found to be positively correlated with a spring phenology index and showed both positive and negative correlations to sea surface temperature and the North Atlantic Oscillation in different regions. Based on the characteristics of spring and summer blooms, the North Atlantic can be classified into two regions: a seasonal bloom region, with a well-defined bloom limited to a single season; and a multi-seasonal bloom region, with blooms extending over multiple seasons. These regions differed in the correlation between bloom start and duration with only the seasonal bloom region showing a significant, negative correlation. We tested the hypothesis that the near-surface springtime distribution of copepods that undergo diapause (Calanus finmarchicus, C. helgolandicus, C. glacialis, and C. hyperboreus) may contribute to the contrast in bloom development between the two regions. Peak near-surface spring abundance of the late stages of these Calanoid copepods was generally associated with areas having a well-defined seasonal bloom, implying a link between bloom shape and their abundance. We suggest that either grazing is a factor in shaping the seasonal bloom or bloom shape determines whether a habitat is conducive to diapause, while recognizing that both factors can re-enforce each other

Seasonal Phytoplankton Blooms in the North Atlantic Linked to the Overwintering Strategies of Copepods

The North Atlantic Ocean contains diverse patterns of seasonal phytoplankton blooms with distinct internal dynamics. We analyzed blooms using remotely-sensed chlorophyll a concentration data and change point statistics. The first bloom of the year began during spring at low latitudes and later in summer at higher latitudes. In regions where spring blooms occurred at high frequency (i. e., proportion of years that a bloom was detected), there was a negative correlation between bloom timing and duration, indicating that early blooms last longer. In much of the Northeast Atlantic, bloom development extended over multiple seasons resulting in peak chlorophyll concentrations in summer. Spring bloom start day was found to be positively correlated with a spring phenology index and showed both positive and negative correlations to sea surface temperature and the North Atlantic Oscillation in different regions. Based on the characteristics of spring and summer blooms, the North Atlantic can be classified into two regions: a seasonal bloom region, with a well-defined bloom limited to a single season; and a multi-seasonal bloom region, with blooms extending over multiple seasons. These regions differed in the correlation between bloom start and duration with only the seasonal bloom region showing a significant, negative correlation. We tested the hypothesis that the near-surface springtime distribution of copepods that undergo diapause (Calanus finmarchicus, C. helgolandicus, C. glacialis, and C. hyperboreus) may contribute to the contrast in bloom development between the two regions. Peak near-surface spring abundance of the late stages of these Calanoid copepods was generally associated with areas having a well-defined seasonal bloom, implying a link between bloom shape and their abundance. We suggest that either grazing is a factor in shaping the seasonal bloom or bloom shape determines whether a habitat is conducive to diapause, while recognizing that both factors can re-enforce each other

Detecting somatic growth trends for summer flounder (Paralichthys dentatus) using a state-space approach

In the past four decades, summer flounder abundance in the Northwest Atlantic shifted with no definitive explanation for this shift. Here, we extract patterns in population-level size variability from summer flounder mean length-at-age data from 1992 – 2015 using an autoregressive state-space modeling approach and annual fishing and oceanographic covariates. We found that summer flounder length-at-age varies annually, suggesting that productivity can vary annually due to variable sizes. We found that location and depth of the observed fish, exploitation, and the Gulf Stream appeared to influence the magnitude of length-at-age variation, whereby lengths-at-age were above the mean length at greater depth, northern latitudes, and during periods characterized by a northerly Gulf Stream position or higher fishing exploitation. These factors should be considered as indicators to track size and more accurately understand productivity as the summer flounder population changes and the fishery adapts in response. This study brings us closer to annual proxies for summer flounder length-at-age variation, an important tool for fisheries managers and stock-assessment scientists to more accurately predict fish stock abundances and productivity.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Overwintering survivorship and growth of young-of-the-year black sea bass Centropristis striata.

Overwintering conditions have long been known to affect fish survival and year-class strength as well as determine the poleward range limit of many temperate fishes. Despite this known importance, mechanisms controlling overwintering mortality are poorly understood and the tolerance of marine fishes to the combined effects of winter temperature, salinity, and size is rarely quantified. In recent years, higher abundances of the temperate Serranid, black sea bass Centropristis striata, have been observed at latitudes further north than their traditional range suggesting that warming water temperatures, particularly during winter, may be facilitating the establishment of a population at more northern latitudes. To examine overwintering survival of C. striata, the combined effects of temperature, salinity and body mass were quantified in laboratory experiments. We identified 6°C as the lower incipient lethal temperature for C. striata, below which fish cease feeding, lose weight rapidly and die within 32 days. A short cold exposure experiment indicated that temperatures below 5°C resulted in mortality events that continued even as the temperature increased slowly to 10°C, indicating that even short cold snaps can impact survival and recruitment in this species. Importantly, fish in lower salinity lived significantly longer than fish at higher salinity at both 3°C and 5°C, suggesting that osmoregulatory stress plays a role in overwintering mortality in this species. Size was not a critical factor in determining overwintering survival of young-of-the-year (YOY) C. striata. Overwintering survival of YOY C. striata can be effectively predicted as a function of temperature and salinity and their interaction with an accelerated failure model to project future range limits. Identifying temperature thresholds may be a tractable way to incorporate environmental factors into population models and stock assessment models in fishes

Evidence for ecosystem changes within a temperate lagoon following a hurricane-induced barrier island breach

The Great South Bay (GSB) is a shallow temperate lagoon in New York, USA, that has experienced a long-term decline in ecosystem maturity, defined as possessing increased complexity, stability, and resilience, dating back to the nineteenth century that is attributed to the loss of filter-feeding and upper trophic-level diversity and biomass. The observed decline is hypothesized to result from reduced connectivity to the Atlantic Ocean following installation of permanent inlets along the barrier island that reduce the probability of “rapid state” change through breaching. In October 2012, Hurricane Sandy created a breach in Fire Island that increased connectivity between GSB and the ocean, resulting in higher bay-wide salinity. We hypothesized that increased connectivity would result in a state change reminiscent of a mature system, characterized by higher nekton and mobile invertebrate species richness and diversity, and occurrence of migratory biomass. Otter trawl surveys were conducted throughout GSB from 2013 through 2015 and compared to a pre-breach survey conducted in 2007. An increase in species richness, diversity, and biomass in the 3 years following the breach and a difference in the dominant species collected between sampling periods was observed. Transition in the nekton and mobile invertebrate assemblage was also observed, whereby the assemblages in 2007 and 2015 differed from 2013 and 2014, with the greatest differentiation between the 2007 and 2015 assemblages, highlighting the influence of the breach rather than seasonal and/or inter-annual variation in driving these assemblages. This temporal trajectory of assemblage change clearly aligned with observed changes in salinity; however, this conclusion should be interpreted with caution given the lack of pre-breach survey replication. Nonetheless, our findings suggest that even a modest breach can cause detectible change in the community assembly in GSB. The expanded community diversity observed in GSB is suggestive of initial recovery of ecosystem maturity and underscores the importance of breaching as fundamental in maintaining lagoon ecosystems

Projected sea surface temperatures over the 21st century: Changes in the mean, variability and extremes for large marine ecosystem regions of Northern Oceans

Global climate models were used to assess changes in the mean, variability and extreme sea surface temperatures (SSTs) in northern oceans with a focus on large marine ecosystems (LMEs) adjacent to North America, Europe, and the Arctic Ocean. Results were obtained from 26 models in the Community Model Intercomparison Project Phase 5 (CMIP5) archive and 30 simulations from the National Center for Atmospheric Research Large Ensemble Community Project (CESM-LENS). All of the simulations used the observed greenhouse gas concentrations for 1976–2005 and the RCP8.5 “business as usual” scenario for greenhouse gases through the remainder of the 21st century. In general, differences between models are substantially larger than among the simulations in the CESM-LENS, indicating that the SST changes are more strongly affected by model formulation than internal climate variability. The annual SST trends over 1976–2099 in the 18 LMEs examined here are all positive ranging from 0.05 to 0.5°C decade–1. SST changes by the end of the 21st century are primarily due to a positive shift in the mean with only modest changes in the variability in most LMEs, resulting in a substantial increase in warm extremes and decrease in cold extremes. The shift in the mean is so large that in many regions SSTs during 2070–2099 will 'always' be warmer than the 'warmest' year during 1976–2005. The SST trends are generally stronger in summer than in winter, as greenhouse gas heating is integrated over a much shallower climatological mixed layer depth in summer than in winter, which amplifies the seasonal cycle of SST over the 21st century. In the Arctic, the mean SST and its variability increases substantially during summer, when it is ice free, but not during winter when a thin layer of ice reforms and SSTs remain near the freezing point

Fisheries Management in a Changing Climate Lessons from the 2012 Ocean Heat Wave in the Northwest Atlantic

Climate change became real for many Americans in 2012 when a record heat wave affected much of the United States, and Superstorm Sandy pounded the Northeast. At the same time, a less visible heat wave was occurring over a large portion of the Northwest Atlantic Ocean. Like the heat wave on land, the ocean heat wave affected coastal ecosystems and economies. Marine species responded to warmer temperatures by shifting their geographic distribution and seasonal cycles. Warm-water species moved northward, and some species undertook local migrations earlier in the season, both of which affected fisheries targeting those species. Extreme events are expected to become more common as climate change progresses (Tebaldi et al., 2006; Hansen et al., 2012). The 2012 Northwest Atlantic heat wave provides valuable insights into ways scientific information streams and fishery management frameworks may need to adapt to be effective as ocean temperatures warm and become more variable

Energetic consequences of resource use diversity in a marine carnivore

Understanding how intraspecific variation in the use of prey resources impacts energy metabolism has strong implications for predicting long-term fitness and is critical for predicting population-to-community level responses to environmental change. Here, we examine the energetic consequences of variable prey resource use in a widely distributed marine carnivore, juvenile sand tiger sharks (Carcharias taurus). We used carbon and nitrogen isotope analysis to identify three primary prey resource pools—demersal omnivores, pelagic forage, and benthic detritivores and estimated the proportional assimilation of each resource using Bayesian mixing models. We then quantified how the utilization of these resource pools impacted the concentrations of six plasma lipids and how this varied by ontogeny. Sharks exhibited variable reliance on two of three predominant prey resource pools: demersal omnivores and pelagic forage. Resource use variation was a strong predictor of energetic condition, whereby individuals more reliant upon pelagic forage exhibited higher blood plasma concentrations of very low-density lipoproteins, cholesterol, and triglycerides. These findings underscore how intraspecific variation in resource use may impact the energy metabolism of animals, and more broadly, that natural and anthropogenically driven fluctuations in prey resources could have longer term energetic consequences