Current Conditions of the Northeast U.S. Shelf Ecosystem: Spring 2022 Update

Introduction

Current Conditions is a biannual report on ecosystem and fisheries data for the Northeast U.S. continental shelf ecosystem. The report includes measurements of temperature and salinity indicators of seasonal warming and cooling patterns. We derive indicators describing phytoplankton distribution and blooms from satellite remote sensing data. Northeast Fisheries Science Center bottom trawl surveys provide upper trophic level indicators of fish and macroinvertebrate habitat and distribution dynamics.

Note that some data elements usually reported in Current Conditions are not available for this report, as some of our surveys did not occur as planned. This would include bottom temperature, surface and bottom salinity, and modeling data related to fish distribution and habitat.

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Summary

• During the last half of 2021, sea surface temperatures in the Northeast U.S. Shelf Ecosystem continued to be above average following a shift in thermal conditions that began around 2010. For some data series, temperature was at its highest level measured.
• Fall phytoplankton blooms were generally below average with the exception of Georges Bank, which had a large late-season bloom.
• The fall thermal transition continues to shift to progressively later in the year, raising concern over the timing of production cycles in the food web.

Temperature

Daily Sea Surface Temperature for the Last Half of the Year

Daily sea surface temperatures were at or generally above average conditions during the last half of 2021. The Georges Bank, Gulf of Maine, and Scotian Shelf ecoregions had the largest departures from average conditions where mid-summer temperatures were approximately 3°C above the average. In the Middle Atlantic Bight ecoregion, temperatures fluctuated around one standard deviation above the mean. In all areas, temperatures tended to moderate toward the mean by the end of the year.

Sea Surface Temperature Trends for the Last Half of the Year

Sea surface temperatures for the last half of 2021 continued at high levels in all ecoregions. On Georges Bank, this temperature data series was at its highest level in the time series in 2021, whereas in other segments of the ecosystem, it was among the highest temperature. The linear trends in all the ecoregions appear to be significant.

Sea Surface Temperature Distribution for the Last Half of the Year

The distribution of sea surface temperature by ecoregion was generally above normal, with the highest temperature anomalies observed in October. There were some negative anomalies observed in the Mid-Atlantic Bight in July. Some of the highest anomalies were associated with the southern flank of Georges Bank, an effect related to recent movement of Gulf Stream position.

Trends in Variability of Sea Surface Temperature for the Last Half of the Year

Sea surface temperature variability (the standard deviation) for the last half of 2021 increased in the coastal boundary ecoregions. The increase in variability appears to be significant in the Gulf of Maine but not significant in the other areas. There were no clear-cut patterns in any change points in variability between areas.

Long-term Trends of Sea Surface Temperature for the Last Half Year

The long-term temperature time series is derived from the Extended Reconstructed Sea Surface Temperature dataset. It provides a low-resolution depiction of sea surface temperature on the Northeast Shelf since the 1850s. The data is based on historical shipboard measures and augmented with other data in recent years. The temperature for the last half of 2021 was the highest temperature in this particular time series.

Fall Thermal Transition Day

Phenology is the climate’s influence on the timing between plant and animal production cycles. Many marine organisms time their reproductive cycles to make best use of seasonal phytoplankton blooms, like the spring and fall blooms. In turn, temperature plays a role in the development of blooms. Identifying the initiation date of the fall transition temperature, which varies by region, can help determine the physical forcing on fall transition events. The fall thermal transition date was relatively constant from 1982 to approximately 2008 for the Northeast Shelf ecoregions. A change point appears in the northern areas around 2008, when the fall transition date advanced approximately two weeks. The trend to earlier fall transition dates appears significant in all the Northeast Shelf ecoregions.

Chlorophyll Concentration

Weekly Chlorophyll for the Last Half of the Year

Chlorophyll concentration was generally below average during the last half of 2021, with the exception of Georges Bank, where there appears to have been significant late-season bloom activity.

Chlorophyll Concentration Trends for the Last Half of the Year

Average chlorophyll concentrations during the last half of the year appears to have decreased in recent years in all ecoregions. The most dramatic decline appears to have occurred in the Middle Atlantic Bight and Georges Bank areas. It is noteworthy that we have identified a change point in chlorophyll concentration in all areas within the last decade or so.

Fish Distribution from Autumn Survey Data

The species of the Northeast Shelf ecosystem have shown changes in distribution over recent decades. Individual species have shifted distribution due to a number of reasons and these shifts can be characterized in a number of different ways. Three metrics that have been used to characterize distribution on the Northeast Shelf:

• Position in the ecosystem along an axis oriented from the southwest to the northeast referred to as the “along shelf distance”
• Depth
• Distance from the coastline

Along shelf distances range from 0 to 1360 km, which relates to positions along the axis from the origin in southwest to northeast. Depth ranges from 0 to 260 m, which relates to depth of occurrence. Distance to the coast ranges from 0 to 110 km. These indices are based on 48 of the most abundant taxa. Along-shelf distance has increased over time, reflecting a shift in species distribution to the Northeast. The 2021 distance was the longest in the time series. Depth of occurrence has also increased over time, reflecting a great use of deeper habitats. There is no significant trend in distance to the coastline. The map position of the center of gravity for these species was at its most extreme northeastern position in 2021, east of Nantucket Island, in contrast to the first point in the time series 1968, which was well to the south and west.