Ecosystem Status Report for the Northeast Large Marine Ecosystem
9. Ecosystem Services
Ecosystem services are the benefits humans derive from different aspects of ecosystem structure and function. These can be partitioned into (1) Provisioning Services, (2) Supporting Services, (3) Regulating Services and (4) Cultural Services. Ecosystem-based management is intended to ensure the sustainable flow of these services that are so vital to human well-being.
Ocean-related industries provide over $50 billion to the GDP in the Northeast (National Ocean Economics Program [NOEP] data available at http://www.oceaneconomics.org/Market). and are therefore important elements of the fabric of coastal economies in the region.
In the following, we provide an overview to some of the critically important ecosystem services now being tracked in the Northeast. In subsequent sections, we describe the threats and impacts to the sustainable delivery of these services and some of the resulting impacts on human communities of impaired ecosystem structure and function.
9.1 Provisioning Services
Provisioning services of current or potential importance for the Northeast Continental Shelf include production of seafood from capture fisheries and aquaculture, energy from renewable (wind and tides) and non-renewable (oil, gas) sources, natural products such as seaweeds used in pharmaceuticals, cosmetics and food products
The commercial fisheries of the NES LME have historically played a critical role in the economy of coastal communities throughout the region. Fishing has been called America’s First Industry and the lure of unexploited resources was a major catalyst in the exploration and colonization of eastern North America by European fishing nations. In the Gulf of Maine (GOM), the total biomass extracted peaked between the late 1970s and 1990s (Figure 9.1). However, the maximum annual removal of crustaceans occurred in 2012, driven primarily by landings of American lobster (Homarus americanus), and landings of pelagics are near the time series’ average. Crustacean landings in the Scotian Shelf are likewise at a series high, while mollusc landings are on par with the series average. Mollusc landings are also near long-run averages in Georges Bank. Although the landings composition has shifted dramatically, the total biomass removed from the Mid-Atlantic is very close to the series average [note that these estimates differ from previous Ecosystem Status Reports in using live weight rather than processed weight (e.g. scallop meat weight) to reflect more fully the biological dynamics of the systems]. The shift towards mollusc landings highlights the importance of Atlantic surf clams (Spisula solidissima), ocean quahogs (Arctica islandica), and Atlantic sea scallops (Placopecten magellanicus) to the Mid-Atlantic, while crustacean landings in this Ecosystem Production Unit are composed primarily of blue crab (Callinectes sapidus). Notwithstanding the above, recent landings are by and large substantially below historical levels.
Providing food is an important dimension of the recreational fishing experience, as reflected in the magnitude of the catch taken for consumption. It is however also an aesthetic pursuit and must also be considered as an important Cultural Service as well. Here we focus on recreational catch statistics.
The downward trend in recreational fishing effort and landings noted in the 2011 ESR has continued over the last few years (Figure 9.2). Attributing the trend to a single cause is problematic, as recreational fisheries are a complex amalgam of for-profit party and charter vessels together with private boat and shore fishing more purely characterized as leisure and/or subsistence (Steinback et al. 2009) activities. The recent recession, lethargic economic recovery, and an increase in real fuel prices likely explain a portion of the recent trend, as individuals slow expenditures on recreational activities or substitute less expensive leisure activities for fishing (Gentner 2008). The recreational fishery also depends on many of the same depleted fish stocks as some of the most contracted commercial fisheries in the Northeast, and these depletions likely account for a portion of the longer trends in landings observed.
Marine aquaculture, or mariculture, conducted in coastal and estuarine waters in the Northeast region, is a growing industry. The value of harvests from aquaculture – primarily oysters and clams, region wide, and salmon in Maine ($161M) – is ranked third in dollar value after scallops and lobsters and exceeds the collective value of all groundfish landings ($80M). It is difficult to inventory the full spatial and economic extent of commercial aquaculture in the Northeast region because of inconsistent reporting among states. Regional production of Atlantic salmon in Maine in 2010 was estimated at $74M dollars (Figure 9.3) and was conducted on approximately 250 ha (600 acres) (see http://www.maine.gov/dmr/aquaculture/). Shellfish aquaculture is conducted on approximately 61 thousand ha (150,000 acres) from Maine through Virginia, with annual production of about 349 million hard clams (Mercenaria mercenaria) and 100 million oysters (Crassostrea virginica) (pers. comm. R. Rheault, 2012; Figure 9.4). This represents an estimated annual value of about US $98 million dollars (Figure 9.4). Steady growth in East Coast oyster culture has led to a doubling of production in the last five years. Presently, there are over 1000 farms and 28 bivalve hatcheries in the region. Growth in leased acreage and production is projected for the shellfish aquaculture industry.
A primary obstacle in the expansion of aquaculture is the complexity of the permitting process. Numerous and in some cases overlapping permits are required to culture food in federal waters, and obtaining them typically takes a huge investment over several years. The first permit for aquaculture in federal waters was approved in southern California for a blue mussel production effort (http://www.catalinasearanch.com/Catalinasearanch.com/Home.html). Mussels have been cultured successfully near the Isles of Shoals in New Hampshire state waters, and permits are pending for a mussel production operation in federal waters (Maney et al. 2013).
Mariculture is emerging as means of meeting increasing demand for secure food production and for other ecosystem services, such as the removal of excess nutrients from eutrophied estuaries (reviewed by Rose et al. 2014). The economic benefits of this industry are of great importance to coastal communities. For these reasons, bivalve aquaculture is seen as an important component of healthy coastal ecosystems.
Commercial harvesting of seaweed is practiced in Maine which currently supports four large rockweed companies. Rockweed harvests are principally used in pharmaceutical products, nutritional supplements, cosmetics, fertilizers, animal feed and horticultural additives. In addition, some smaller operations harvest and market edible seaweeds and for use in clambakes and shipping/packing. A kelp aquaculture business is now in operation in Casco Bay and some experimental kelp aquaculture projects being conducted at mussel farms. The total number of seaweed harvester licenses/year of all types is currently approximately 120 licenses.
The number of licensed rockweed harvesters in Maine climbed from 29 to 59 between 2004 and 2012, when harvesters gathered about 14 million pounds of rockweed. Rockweed, which clings to rocks in the intertidal zone, sells for only 3 cents a pound at the dock. But the harvest was worth $20 million after it was processed for use in a range of products (Figure 9.5). Note that in 2001, harvester reporting was voluntary, and not until 2008 did mandatory dealer reporting begin.
Interest in the development of offshore renewable energy sources as part of an overall national strategy for energy independence has dramatically changed the seascape for ocean use patterns in the United States. Significantly, it has also generated considerable interest in development of comprehensive marine spatial planning to deal with competing uses of ocean space. National assessments of the energy production potential for offshore wind resources in the U.S. indicate that up to 20% of the electricity needs of coastal states could be met (MMS 2009). Current technologies and engineering constraints restrict consideration to water depths less than 30m. Prospects for floating installations and other approaches however are currently under active investigation to remove these constraints.
The first offshore windfarm (the Cape Windproject; see Figure 9.6) in the United States was proposed in 2001. The Cape Windproject has passed several levels of regulatory review (Rodgers and Olmsted 2010) and test towers are now slated for installation. The proposal entails placement of 130 wind turbines distributed over approximately 7,500 ha in federal waters off Massachusetts (see also http://offshorewinddc.org/).
Other renewable marine energy sources under consideration include wave, ocean current, and tidal energy. Options for harvesting these untapped resources are in varying but still nascent degrees of development in the United States. High tidal amplitudes in the Gulf of Maine in proximity to the Bay of Fundy have focused interest in potential tidal power installations in the Gulf of Maine. In Cobscook Bay, ME, the first grid-connected ocean energy project in the nation has recently begun operation using tidal energy (Figure 9.6). A 5 MW pilot installation, (the Muskeget Tidal Energy Project) is currently in development off the coast of Martha’s Vineyard, MA (Figure 9.6).
The ocean is a critical resource for supporting domestic waterborne commerce and international transportation and trade. The Maritime Administration within the U.S. Department of Transportation deals with waterborne transportation, working to promote the use of the 29,000 nautical miles comprising America’s Marine Highway System. Additionally, the administration works to further incorporate these waterways into the greater U.S. transportation system.
The NES LME is a significant corridor for marine transportation, encompassing several of the nation’s most heavily trafficked ports. In 2011, four of the top ten U.S. ports (based on the cumulative number of vessel calls across all vessel types) were located in the NES LME. In 2011 the top 10 U.S. ports accounted for 56% of oceangoing vessel calls, while North Atlantic ports accounted for 15.8% of all U.S. port calls.
Historically, the top five trafficked ports of the NES LME have included the ports of Baltimore, Boston, Philadelphia, New York, and Virginia. Of these locations, New York ports have consistently received significantly higher vessel calls than all other ports from 2002 – 2012. Annual vessel calls at the five highest trafficked ports in the NES LME are shown in Figure 9.7.
Automatic Identification Systems (AIS) are automated tracking systems used on ships and by vessel traffic services for identifying and locating vessels for all vessels operating in international waters with gross tonnage (GT) of 300 or more tons, and all passenger ships regardless of size. Figure 9.7 illustrates the 2011 vessel traffic density for all vessels carrying AIS transponders for the NES LME. Figures 9.8 – 9.12 provides similar images for selected major ports with the scale is reduced to a specific waterbody in each subregion. Track lines are filtered to emphasize the most heavily trafficked areas using a high to low density scale.
9.2 Supporting and Regulatory Services
Supporting Services are vital to ecosystem structure and function. Supporting Services include factors such as habitat, primary production, and nutrient cycling. Regulating Services include climate regulation, carbon sequestration, filtration and detoxification, nutrient regulation, and shoreline stabilization. Many ecosystem components provide a constellation of services. For example, phytoplankton provide most (~95%) of the primary production in the sea but also synthesize and emit dimethyl sulfate, a compound that plays an important role in regulating climate climate through its effect on backscattering solar radiation and in cloud formation. In estuaries, bays, and other nearshore environments, macroalgae and vascular plants such as seagrasses provide habitat for other organisms and also are important primary producers. Biogenic habitats such as oyster reefs provide structural complexity and shelter for a broad spectrum of fish and invertebrate species as well economically important food resources and filtration services with important implications for water quality.
We describe the role of phytoplankton as the dominant form of primary producers on the Northeast U.S. Continental Shelf in Section 4.1. In this section we focus on habitats of different types with respect to supporting and regulating services.
Coastal wetlands provide a multitude of ecosystem services. Coastal wetlands provide important habitat for juvenile fish which sustain coastal fisheries dependent on nursery areas for recruitment. Additionally, these important habitats provide feeding grounds and shelter for many animals thus playing an important role in coastal food webs. These habitats also play an important role along coastal shorelines, helping to lessen the impacts of coastal erosion, providing flood protection, improving water quality, providing opportunities for coastal recreation, and acting as sinks for carbon sequestration (Carter 1997, Murray et al. 2001).
Despite their importance to coastal wildlife, coastal economies, and human health and safety, these areas are under significant pressure from both natural and anthropogenic sources. Anthropogenic stressors such as siltation, nutrient uploading, and dredging and filling for development attack coastal wetlands from the landward side, while natural forces such as climate change and sea-level rise affect them from the sea (Dahl and Stedman 2013). As coastal populations and the demand for coastal resources continue to grow, these pressures are likely to increase as well. As such, there have been numerous studies to examine both anthropogenic and natural causes of coastal wetlands loss, as well as coastal wetlands and shoreline restoration efforts.
Historical estimates of overall wetland loss for the Northeastern United States indicate that approximately 45% of combined freshwater and coastal wetlands were lost during the period 1790~1985 (Mitsch and Gosselink 2000). The estimated loss in total wetland area ranged from 9-74% for the states of Maine to North Carolina. Further estimates for coastal wetlands alone from Maine to New York for the period 1906-1978 suggest a loss rate of approximately 50% during this time period (Figure 9.13; Gosselink and Baumann 1980). The sharpest decline occurred during 1922-1956 in response to extensive public work projects undertaken during the Great Depression, construction related to defense installations during the Second World War, and the post-war housing boom (Gosselink and Baumann 1980). Overall, the historical loss in potential buffering capacity against rising CO2 levels in the atmosphere and protection against storm surge other coastal hazards, and pollution is significant.
More recent estimates of loss of wetland habitats are available through the NOAA Coastal Change Analysis Program (C-CAP) for the period 1996-2010. The estimates are presented in terms of change during each of three time blocks: 1996-2001, 2001-2006, and 2006-2010 and for the entire time period
Total coastal wetlands coverage for the GOM subregion remained relatively stable over the entire time period with an estimated increase of just of 0.62% in total coverage.
Estimated overall losses occured for the estuarine scrub/shrub (-2.6%) and estuarine emergent (-0.07%) subclasses during the 1999 – 2010 block. During this timeframe, an overall gain in total coverage was estimated for the unconsolidated shores subclass (+6.92%). Figure 9.14 provides a breakdown of subclass trends over each of the five year blocks during the study period, for the GOM.
Total coastal wetlands coverage decreased in the MAB subregion by an estimated 4,981 acres from 1996 – 2010. This represents a decrease of 0.61% in total coverage. Total wetland area remained relatively stable with 0.82% decline in total coverage during the entire time period. The largest losses were observed in the emergent wetland (-0.74%) and unconsolidated shore (-10.0%) subclasses during this time.
Overall losses for the estuarine emergent (-0.85%) and unconsolidated shore subclasses (-3.0%) were estimated during the entire time period, while an overall gain in total coverage for the estuarine scrub/shrub subclass (+28.06%) was recorded. Figure 9.15 provides a breakdown of subclass gains and losses over each of the five year blocks during the study period, for the MAB.
The value of submerged aquatic vegetation (SAV) to wildlife, coastal fisheries, conservation and management efforts is well documented. SAV serves as valuable habitat for diverse fish and invertebrate populations, and studies have shown higher abundance and productivity of these populations in areas containing SAV than neighboring unvegetated areas (Heck et al. 1995). SAV also plays a key role in sustaining waterfowl and is a crucial component to sediment and shoreline stabilization (Costello and Kenworthy 2011). SAV species are viewed as important indicator species due to their sensitivity to anthropogenic sources of pollution or perturbations (Kemp 1983), and international attention to SAV decline was first raised during the 1930's when a wide-spread die off of seagrass was observed in the North Atlantic. Decline is still prevalent today along highly populated coastlines around the world, as SAV communities face shifting environmental conditions and increasing anthropogenic perturbations. Light attenuation in the water column is a key component to SAV growth, therefore both natural and anthropogenic activities such as erosion, agricultural runoff, nutrient enrichment, dredging for waterway navigation, shellfishing, the building of recreational docks and piers, and the discharge of silt into the coastal waterbodies can all have limiting and or damaging effects. SAV inventories are conducted in coastal states to understand the cumulative impact and availability of these resources on biotic populations in estuarine and open waters. Due to its ephemeral nature, SAV coverage can vary significantly from one year to the next (Bortone et al. 1999). A comprehensive SAV database for Atlantic coast states currently does not exist, although NOAA, The Nature Conservancy, and other federal and state agencies, and non-profit organizations are actively involved in these efforts. The most consistently monitored sea grass beds in the Northeast are in Chesapeake Bay. Accordingly, here we will focus on trends in Chesapeake Bay.
The Chesapeake Bay Program has a long history of mapping SAV resources in the Bay and its tributaries, as well as in coastal bays, and represents the most extensive SAV database for the study area. SAV data dates back to 1971, with yearly mapping coverage classified as either: fully mapped; sparsely mapped; not fully mapped; or not mapped. The level of mapping varies annually based on aerial photo availability, water turbidity and other naturally occurring factors. Earlier years of the Program’s mapping inventories frequently do not have full mapping coverage of the Bay and its tributaries, however starting in 2002 the frequency with which the entire Bay is mapped increases significantly. Because of the discrepancy in mapped area, the overall trend for SAV coverage in the Chesapeake is inconclusive. Since 1990, the mean annual mapped SAV area is approximately 27,724 ha with a range of approximately 16,800 ha in annual coverage. The variability in coverage increases in later years, coinciding with the increased ability of the program to map all areas of the Bay and its tributaries. For example, between 1990 and 2000, mean annual mapped SAV area is approximately 26,580 ha with a range of approximately 5,340 ha compared to a mean of 28,770 ha and a range of 16,780 ha from 2001 – 2012. Prior to 2001, nine of eleven annual SAV calculations are depicted as “not fully mapped,” whereas eight of twelve annual calculations are fully mapped from 2001 – 2012. Based on analyses performed by the Chesapeake Bay program, notable changes in SAV distribution were measured between 2012 and 2011, where “SAV decreased 21% from 23,346 ha to 18,477 ha in regions mapped for both years” (Orth et al. 2013). Significant decreases are reported in baywide SAV coverage for the years 2011 and 2012, which are attributed to the effects of Hurricane Irene and Tropical Storm Lee that kept turbidity high in the Bay and deposited a large amount of sediment in the system. While these loses appear significant, the Chesapeake Bay Program also reports several resilient SAV beds, as well as areas that continue to increase in coverage over time (Orth et al. 2013). Figure 9.16 shows trends for annual mapped SAV resources in the Chesapeake Bay and its tributaries.
The American oyster (Crassostrea virginica) is the dominant reef-building organism in the Northeastern United States. Historical reports document the occurrence of extensive reef structures throughout the region and archeological evidence indicate the importance of oysters as a staple food item for native peoples along the coast (Kurlansky 2007). Laws enacted as early as 1658 in New York regulating fishing intensity on oyster reefs suggest that the vulnerability of these biogenic structures to destruction has long been recognized. The structural complexity of these reefs provides important habitat for a diverse assemblage of fish and invertebrate species. In addition to the supporting service provided by reef habitat, the filtering capacity of oysters provides a critically important regulating service in maintenance of water quality and clarity in estuaries and embayments. It has been estimated that the American oyster can filter up to 190 l (50 gallons) of water per day. Healthy oyster reefs also provide shoreline protection by attenuating wave action. Grabowski et al. (2012) document the high value of oyster reefs with respect to ecosystem services.
Loss of oyster reefs through destructive fishing practices (principally dredging, pollution and disease has resulted in large-scale changes in ecosystem structure in estuaries and bays. Estimates of the loss in the areal extent of oyster reefs and in biomass of oysters over the last century for a number of locations in the Northeast suggest that some oyster reef communities are now functionally extinct and most other locations for which estimates are available now support less than half of the extent and biomass estimates relative to @1885-1915 levels (zu Ermgassen et al. 2014).
Restoration efforts are now underway in many areas in the Northeast to rebuild oyster reef structures in recognition of their importance to food provisioning, supporting, and regulating services.
Deep corals are sessile animals that are important in certain deep sea benthic communities, providing structure for fish and invertebrates of higher trophic levels. Although there are no known coral reefs in the northeast U.S. waters, deep corals can be found from shallow waters to 6,000 m depth, and are most common at depths of 50‐1,000 m on hard substrate. The current status of deep coral populations is generally unknown because population trends are not available. However, concerns have been raised about the damage that mobile, bottom‐tending fishing gear, especially bottom trawls, may cause to these fragile, slow growing and low recruitment animals. Other potential threats to deep corals include offshore oil and gas drilling, wind farm or other alternative energy installations, as well as ocean acidification due to global warming. To help ensure the protection of deep corals, the New England Fishery Management Council led the development of a new Habitat Closed Area south of Georges Bank, which prohibits the use of bottom trawls and bottom gillnets in the area. Stony corals most often inhabit deep, rocky substrate and are often found on sea mounts and along the continental margin from the outer edges of Georges Bank south to Cape Hatteras (Figure 9.18). Most soft corals and sea fans are primarily deepwater species that occur at depths greater than 500 m in submarine canyons and on seamounts, although certain species occur throughout shelf waters to the continental slope (Figure 9.18). Sea pens are generally found on the continental slope between 200 and 4,300 m, although two species have been found at depths of less than 30 m off of the North Carolina shelf. Overall, deep corals likely provide important habitat, however more research is needed to determine population trends and ensure the conservation of these species.
Pelagic or water column habitats are defined in three-dimensional space by a range of water column properties such as temperature, salinity, and patterns of primary production (Christie and Regier 1988; Shackell et al. 2014). Surface water temperatures on the Northeast Shelf range over approximately 30°C, thus encompassing most of the temperatures found in the world’s oceans (Table 1). The water column can stratify with warm water at the surface and cool water at the bottom, which is considered a stable water column configuration. However, the water column can be inverted with cooler water at the surface. Salinities found on the shelf reflect the presence of oceanic water masses, but it is also common to find low salinity water associated with terrestrial sources. Chlorophyll concentration, which reflects the potential for biological productivity, can be so low that they are at detectable limits ranging upwards to the bloom levels associated with highly productive waters. The variability of these and other parameters creates a complex, dynamic matrix of habitats on the Shelf accommodating both resident and transient species. This section considers factors that create pelagic habitats including thermal regime, frontal boundaries, and upwelling events.
|Table 1. Temperature|
Temperature is a key determinant of marine finfish and invertebrate habitats, owning in large part to the dominant effect temperature has on the physiology of organisms (McMahon and Hays 2006; Portner 2002). Because species have markedly different responses to temperature, variation in the thermal regime of an ecosystem has consequences for the assemblages of species found there (Attrill and Power 2002). Climate change is expected to impact the composition of fish assemblages and biodiversity over time (Cheung et al. 2009; Rijnsdorp et al. 2009) and of greater concern in context to the needs of society, these changes will likely alter patterns of fishery yields (Arnason 2012).
The US Northeast Shelf has warmed on the order of one degree centigrade over the past three decades. This warming has been characterized in a number of different ways and what has emerged is a complex picture of change in temperature that has not been uniform over seasons or sub-components of the ecosystem (Friedland et al. 2013). These nuanced differences in temporal and spatial change in thermal regime can be characterized by change in thermal habitat. In this case, thermal habitat is defined as the amount of the ocean surface that falls within a specified thermal range. As measured temperature increases, it would be natural to expect that the amount of warm water thermal habitat would also increase; this is the case for the Northeast Shelf as a whole and for the constituent production units of the ecosystem where trend analysis for 16-27°C thermal habitats indicates increasing trends in all segment of the ecosystem (Figure 9.19). Since the total amount of habitat is finite, it is also natural to expect that a concomitant decrease in colder water habitat would also occur, and we see that in the trends for 5-15°C habitats in all areas except for the northern part of the ecosystem or the Scotian Shelf production unit. However, cold water habitats have not declined in the ecosystem as seen by the absence of trends in the 1-4°C analyses. Since temperature of the Shelf ecosystem is determined by continental and oceanic effects, it would appear these forcing factors are working in a differential fashion that maintains cold water column habitats despite a warming of the ecosystem as a whole.
Thermal habitats have changed in size and so has the timing in which these habitats are formed and dissolved during the time course of the year. Warm water habitats, which have increased in size, have also increased in the duration during which they can be found. These habitats were only detected during a few days of the year in the Gulf of Maine and Scotian Shelf at the beginning of the time series compared to 60 and 30 days annually at the end of the time series, in their respective areas (Figure 9.20). In the southern production units, the warm water habitat duration has nearly doubled over the time series. Midrange thermal habitat duration has declined with the decline in habitat area, but where most production units showed a significant decline in habitat area, most units do not show a significant decline in habitat duration. Cold water habitat duration is without time series trend, so like habit area, the duration of cold water habitat has remained relatively constant each year. Taken together, the statistics on thermal habitat area and duration suggest an increasing role of warm water habitats as they are present for significant periods of time in all part of the Northeast Shelf ecosystem.
Oceanic fronts are boundaries between two distinct water masses with sharp gradients in temperature, salinity, light irradiance, hydrostatic pressure and/or other physical-chemical and biological factors (Belkin et al. 2014). A variety of fronts formed from vastly different physical processes, including water mass convergences, river outflows, tidal mixing and coastal upwelling, are present in the NES and can be detected in surface temperature and ocean color satellite remote sensing imagery (Belkin and O'Reilly 2009). At some fronts, vertical mixing and convergence increase the nutrient supply to the upper mixed layer and fuel primary production, creating foraging and biogeochemical cycling hotspots (Scales et al. 2014; Woodson and Litvin 2015). These unique habitats can affect every trophic level at varying life stages across a wide range of spatio-temporal scales (Belkin et al. 2014). For many species, specific life stages and behaviors, such as spawning, ontogenetic development, migration and feeding are associated with one or more frontal regions (Belkin et al. 2014).
In the NES, the sharp change of bathymetry at the shelf break results in the stable Shelf-Slope Front (SSF), which is a continuous shelf-break front running from Cape Hatteras, NC to the Tail of the Grand Banks (Figure 9.21) (Bisagni et al. 2009). The front separates cold, fresh shelf water from the warmer and more saline Slope Sea water (He et al. 2011). Primary production at the frontal region can be an order of magnitude greater than on either side of the front due to upwelling of nutrient rich deep waters up the continental slope (O'Reilly et al. 1987; Townsend et al. 2006). Plankton and small nekton are aggregated in the frontal zone and as a result, the shelf-edge front becomes an important foraging habitat for several fish species, marine mammals and sea birds (He et al. 2011; Scales et al. 2014; Waring et al. 2001).
Seasonal tidal mixing fronts on Georges Bank separate the well-mixed shallow portions of the bank from the deeper, thermally stratified northern flank of the bank (Ullman et al. 2003). Vigorous tidal mixing injects deep nutrient-rich shelf waters onto the northern flank of the bank, and advection distributes the nutrients in a clockwise flow to the southern flank creating a “donut” of primary production (Figure 9.21) (Hu et al. 2008; Townsend et al. 2006). In addition to the high rates of primary production feeding the ecosystem, the inner well-mixed zone of Georges Bank is considered to be a relatively large retention area for Atlantic herring, cod, haddock, hake, flounder and other commercially important species. Atlantic cod and haddock have peak spawning in the spring on northeastern Georges Bank, and their pelagic eggs and larvae are advected along the flank so that the highest concentrations of larvae are found between the Georges Bank tidal front at ~ 60 m isobaths and the Shelf-Slope front near the 100 m isobaths (Lough and Manning 2001).
Coastal upwelling is a physical dynamic in marine ecosystems that is known to be a primary driver of some of the most productive fisheries in the world. Coastal upwelling occurs when winds force surface ocean currents to the right (left) of the wind direction in the Northern (Southern) Hemisphere. This geophysical fluid dynamic is known as Ekman transport. Along coastlines, Ekman transport can move warm, nutrient-poor surface waters away from the coast that are then replaced by nutrient-rich and colder deep waters. These nutrient-rich deeper waters can stimulate massive phytoplankton blooms that ultimately support the entire marine ecosystem, including fish and fisheries.
Upwelling in coastal marine ecosystems is a predominant feature in eastern boundary current systems such as the California Current (U.S. Western Coast) and Benguela Current (African Southwestern Coast) because winds typically derive from the north (south) in the Northern (Southern) Hemisphere and thus surface waters can be pushed away from the coastlines. In western boundary systems like the U.S. NES, coastal upwelling is not as common because winds that typically derive from the north do not push water away from the coasts. Moreover, the U.S. NES has a broad shelf and thus its coastlines are more distant from deeper, off-shelf water intrusions than regions like the California coast that have a much narrower shelf. However, during the summer, winds shift from northerly to southerly in the U.S. NES causing coastal upwelling, predominately in the New Jersey coastline (Figure 9.22). Unique topographic variations associated with ancient river deltas along the coast of New Jersey force the upwelled water into an alongshore structure of recurrent upwelling centers (Glenn et al. 2004).
The source of the deeper cold, nutrient-rich water that upwells in the summer in coastal New Jersey is from the Middle-Atlantic Bight Cold Pool, an 8 oC or less bottom water body that is formed seasonally after each winter and remains below the thermocline in the summer every year (Figure 9.23). The shoreward position of the Cold Pool is variable and it is suggested that the position and strength of the Cold Pool may be the main driver of the strength and frequency of the summertime coastal upwelling events in coastal New Jersey (Glenn et al. 2004).
These episodic summertime upwelling events in coastal New Jersey can result in substantial phytoplankton blooms that are thought to predominately comprise dinoflagellates. In the summer of 2011, an anomalously large phytoplankton bloom occurred in coastal New Jersey in late July and early- to mid-August, just before Hurricane Irene struck the New Jersey shore on August 28th. Satellite measurements of surface temperature and surface chlorophyll show cooling of coastal ocean temperature in early July that was followed by an enormous phytoplankton bloom that started in July and persisted throughout August and part of September (Movie 9.1). On August 28th, the widespread sudden drop in surface ocean temperature was due to the rapid vertical mixing from Hurricane Irene (Movie 9.1).Coastal upwelling in the New Jersey coast has been associated with changes in the abundance and size of several species of larval fish (Able et al. 2010) and shellfish (Ma 2005) in the surf zone. These large, summer blooms could also be major contributors to vertical export flux (sinking organic matter) that fuels the benthic community of living marine resources in the New Jersey Shelf.