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Ecosystem Status Report for the Northeast Large Marine Ecosystem

Glossary

Driver: In the Driver-Pressure-State-Impact-Response sequence, a driver is generally a broad forcing factor that creates specific pressures on the ecosystem being studied.

Ecological Production Units (EPU): Subunits of the Northeast U.S. Continental Shelf Large Marine Ecosystem: Scotian Shelf, Gulf of Maine, Georges Bank, and Mid-Atlantic Bight. They were delineated through multivariate statistical analyses on physiographic and phytoplankton data sets. Each of these subunits may also have coastal and shelf break special consideration areas associated with them.

Impact: In the Driver-Pressure-State-Impact-Response sequence, an impact is the effect on humans of a changed state in the ecosystem being studied.

Indicator: In environmental or ecological terms, an indicator is a statistic that has been shown to be representative of a particular aspect of the environment. Indicators in an ecosystem can show overall trends, can point to potential areas needing management, or can help show the effects of current management. Examples we use are temperature, salinity, biomass of species and aggregated groups, etc. One analogy is the stock quote for a company which shows the ‘health’ of that company in general terms. Similarly the NASDAQ is an aggregate indicator of a number of stocks, which is often used as one of the indicators to determine the economic health of the United States.

Pressure: In the Driver-Pressure-State-Impact-Response sequence, specific pressures are created by the drivers. The pressures cause changes in state of one or more elements of the ecosystem being studied.

Principal Components Analysis (PCA): A commonly used statistical technique designed to take possibly correlated sets of variables and reduces it to a smaller set of uncorrelated variables, the principal components. Each principal component (PC) is a combination of all the initial variables into one number. In each principal component, some of the original variables are typically more important than others. The first principal component can be considered the most important as it explains most of the variance. The second PC explains the next most of the variance, etc.

Response: In the Driver-Pressure-State-Impact-Response sequence, a response is a change in management strategy based on changes in state of the ecosystem and impacts on humans.

Standardized Anomalies: In statistics, an anomaly is a measure of how far from the mean a given observation is. So, if the mean temperature over 10 years in a given oceanic region is 18.2 oC, and the temperature during one of the years was 16.2 oC, the anomaly would be -2.0. To make comparisons more meaningful, we use standardized anomalies which effectively convert all indicators to the same scale. A standardized anomaly is each anomaly divided by the standard deviation for a set of data. So a standardized anomaly of -2 in a temperature time series is as likely (or unlikely) to occur as a standardized anomaly of -2 in a salinity time series.

States: In the Driver-Pressure-State-Impact-Response sequence, a state is the current status or value of a given facet of the ecosystem being studied.

Thermohaline circulation: Also referred to as the ‘ocean conveyer belt’, (or more formally, the Meriodonal Overturning Circulation), the thermohaline circulation is that part of the global ocean circulation which is driven by density gradients, which are in turn caused by temperature and salinity differences in the ocean. In general, water flowing to the north through wind driven currents, such as the Gulf Stream, sinks near the North Pole due to the creation of ice, which increases the salinity in the underlying water while also making it cold. This water flows into the ocean basins, with the bulk of it rising (upwelling) in the Southern Ocean and North Pacific. This circulation permits mixing between the ocean basins, decreasing the differences between them.

Trophic Level (TL): The position an organism occupies in a food web. Primary producers such as phytoplankton occupy trophic level 1 (TL1). The TL number for each organism is the number of steps it is away from the start of the food web. So zooplankton which feeds on phytoplankton would be at TL2, herring which feeds on zooplankton would be at TL3, etc. Organisms are often assigned trophic levels in between whole numbers as they may eat prey which occupy two or more trophic levels.

Vessel Traffic Service (VTS): A marine traffic monitoring system established by harbour or port authorities, similar to air traffic control for aircraft. Typical VTS systems use radar, closed-circuit television (CCTV), VHF radiotelephony and automatic identification system to keep track of vessel movements and provide navigational safety in a limited geographical area.