Figure 5. Conceptual illustration of a normalized biomass 

size spectrum (numbers of organisms plotted against weight 

classes) in an unperturbed (left panel) and perturbed (right 

panel) ecosystem. In a perturbed ecosystem, abundance 

of small, undesirable phytoplankton (A) may increase while 

abundance and size of large organisms (fish) may decline (B). 

As a result, the slope of the disturbed biomass size spectrum 

becomes steeper and other statistical properties (e.g., levels of 

abundance) may shift.

3) BIOMASS SIZE SPECTRA AS AN INDICATOR OF

ECOSYSTEM STATE

A biomass size spectrum (BSS) depicts the abundance 

and distribution of organisms by size classes in an 

ecosystem. In aquatic ecosystems, the biomass (i.e., 

aggregate weight) of organisms at each level in the 

food chain from microscopic phytoplankton to the 

largest vertebrate animals is nearly equal. Because 

biomass is near equal, numbers of small organisms 

greatly exceed numbers of large organisms. Sizespecifi c predation (big organisms eat smaller ones) in 

aquatic communities maintains the observed biomass 

size structure and has led to methods for evaluation of 

biomass-size relationships to characterize the structure 

and state of ecosystems. To derive BSS, data from 

monitoring programs on organism abundances must 

be aggregated into size categories. BSS models can 

serve as ecological indicators because properties of 

BSS respond to natural or human-induced stressors. 

ACE INC scientists at the University of Maryland are 

evaluating BSS as an indicator of ecosystem state in 

Chesapeake Bay. 

Jung, S. and E.D.Houde. 2005. Fish Biomass Size Spectra in Chesapeake 

Bay. Estuaries 28(2): 226-240.

 

Ecological Indicator: Changes in the slope or other statistical properties of the 

normalized BSS relative to reference standards or historical benchmarks is an indicator 

of changes in the abundance and biomass of the suite of organisms in an aquatic 

ecosystem.

Ecological Effect/Impact: Changes in the slope of the normalized BSS can be 

indicative of changes in the biological community structure, productivity, food-chain 

effi ciency, predator-prey relationships, and effects of environmental variability, fi shing, 

nutrient loading, and habitat change. BSS of stressed ecosystems often have steep 

negative slopes. For example, in heavily fi shed ecosystems larger fi sh may be reduced 

in number and biomass. Or, in highly eutrophic ecosystems with excess nutrient 

loading, blooms of microscopic phytoplankton can greatly increase the abundance 

and biomass of small organisms, leading to stressful conditions such as hypoxia and 

mortality of larger organisms (e.g., crabs, fi sh). 

Environmental Application: BSS can be used by managers to describe long-term 

effects of stress or the success of restoration efforts in estuaries impacted by human 

activities. BSS can be applied to a broad suite of aquatic biological communities, 

not only to selected organisms, and thus can indicate how whole ecosystems are 

responding to either deteriorating conditions or remediation efforts in resource 

management (e.g., better fi sheries management, habitat restoration, improved water 

quality). Periodic monitoring of sizes and abundances of organisms is required to 

apply BSS as an indicator. 

Unperturbed ecosystem Perturbed ecosystem

Biomass Size Spectra as Indicators of Ecosystem Status 

theoretical slope = -1.0 steeper slope

A

B

Log Abundance

Log Weight Class Log Weight Class

Illustration courtesy of William J. Connelly

University of Maryland Center for Environmental Science
Ecological Effect/Impact: Changes in phytoplankton community composition are important 

indicators of estuarine and coastal ecological condition and health because phytoplankton plays a major 

role in primary production, eutrophication (including harmful algal blooms), nutrient cycling, water 

quality, and food web dynamics. 

Environmental Application: Phytoplankton community composition can serve as an early warning 

signal of toxic or hypoxia-generating algal blooms. It has proven useful and applicable for evaluating 

ecosystem and regional responses to environmental stressors, including increased nutrient loads, 

changes in hydrologic characteristics, and climatic disturbances such as hurricanes and droughts. 

Together with the North Carolina Department of Environment and Natural Resources, researchers at 

the University of North Carolina at Chapel Hill’s Institute of Marine Sciences are using diagnostic 

pigment (e.g., chlorophyll a) concentration as the criteria for meeting allowable total maximum daily 

(nutrient) loads (TMDLs). In addition, diagnostic photopigments are used to determine phytoplankton 

community changes in response to hydrological variability, including hurricanes and droughts. Results 

from North Carolina’s Neuse River Estuary/Pamlico Sound system show that when conditions 

“freshen” in response to hurricanes and fl ooding, fast growing, low salinity-adapted chlorophytes 

(green algae) become dominant (Fig. 2). Conversely, when drought conditions prevail, slower-growing 

dinofl agellates prevail in wintertime and cyanobacteria (blue-green algae) prevail in summertime (Fig. 

2). Cyanobacteria can be especially dominant when a moderate to wet spring is followed by summer 

drought conditions. This sequence of events introduces high nutrient loads, followed by a reduction 

in fl ow and fl ushing, and subsequent retention of the nutrients; an ideal scenario for cyanobacterial 

blooms. Aside form impacting water quality, such hydrologic and nutrient-driven changes have 

Figure 2. Contribution of some key phytoplankton taxonomic groups (chlorophytes, cyanobacteria and 

dinoflagellates) to total chlorophyll a concentrations in the Neuse River Estuary, NC. The dates of landfall of the 

seven major hurricanes that have significantly affected flow and nutrient enrichment since mid-1996 are shown.

Hurricanes
Ecological Effect/Impact: Changes in phytoplankton community composition are important 

indicators of estuarine and coastal ecological condition and health because phytoplankton plays a major 

role in primary production, eutrophication (including harmful algal blooms), nutrient cycling, water 

quality, and food web dynamics. 

Environmental Application: Phytoplankton community composition can serve as an early warning 

signal of toxic or hypoxia-generating algal blooms. It has proven useful and applicable for evaluating 

ecosystem and regional responses to environmental stressors, including increased nutrient loads, 

changes in hydrologic characteristics, and climatic disturbances such as hurricanes and droughts. 

Together with the North Carolina Department of Environment and Natural Resources, researchers at 

the University of North Carolina at Chapel Hill’s Institute of Marine Sciences are using diagnostic 

pigment (e.g., chlorophyll a) concentration as the criteria for meeting allowable total maximum daily 

(nutrient) loads (TMDLs). In addition, diagnostic photopigments are used to determine phytoplankton 

community changes in response to hydrological variability, including hurricanes and droughts. Results 

from North Carolina’s Neuse River Estuary/Pamlico Sound system show that when conditions 

“freshen” in response to hurricanes and fl ooding, fast growing, low salinity-adapted chlorophytes 

(green algae) become dominant (Fig. 2). Conversely, when drought conditions prevail, slower-growing 

dinofl agellates prevail in wintertime and cyanobacteria (blue-green algae) prevail in summertime (Fig. 

2). Cyanobacteria can be especially dominant when a moderate to wet spring is followed by summer 

drought conditions. This sequence of events introduces high nutrient loads, followed by a reduction 

in fl ow and fl ushing, and subsequent retention of the nutrients; an ideal scenario for cyanobacterial 

blooms. Aside form impacting water quality, such hydrologic and nutrient-driven changes have 

Figure 2. Contribution of some key phytoplankton taxonomic groups (chlorophytes, cyanobacteria and 

dinoflagellates) to total chlorophyll a concentrations in the Neuse River Estuary, NC. The dates of landfall of the 

seven major hurricanes that have significantly affected flow and nutrient enrichment since mid-1996 are shown.

Hurricanes
Ecological Effect/Impact: Changes in phytoplankton community composition are important 

indicators of estuarine and coastal ecological condition and health because phytoplankton plays a major 

role in primary production, eutrophication (including harmful algal blooms), nutrient cycling, water 

quality, and food web dynamics. 

Environmental Application: Phytoplankton community composition can serve as an early warning 

signal of toxic or hypoxia-generating algal blooms. It has proven useful and applicable for evaluating 

ecosystem and regional responses to environmental stressors, including increased nutrient loads, 

changes in hydrologic characteristics, and climatic disturbances such as hurricanes and droughts. 

Together with the North Carolina Department of Environment and Natural Resources, researchers at 

the University of North Carolina at Chapel Hill’s Institute of Marine Sciences are using diagnostic 

pigment (e.g., chlorophyll a) concentration as the criteria for meeting allowable total maximum daily 

(nutrient) loads (TMDLs). In addition, diagnostic photopigments are used to determine phytoplankton 

community changes in response to hydrological variability, including hurricanes and droughts. Results 

from North Carolina’s Neuse River Estuary/Pamlico Sound system show that when conditions 

“freshen” in response to hurricanes and fl ooding, fast growing, low salinity-adapted chlorophytes 

(green algae) become dominant (Fig. 2). Conversely, when drought conditions prevail, slower-growing 

dinofl agellates prevail in wintertime and cyanobacteria (blue-green algae) prevail in summertime (Fig. 

2). Cyanobacteria can be especially dominant when a moderate to wet spring is followed by summer 

drought conditions. This sequence of events introduces high nutrient loads, followed by a reduction 

in fl ow and fl ushing, and subsequent retention of the nutrients; an ideal scenario for cyanobacterial 

blooms. Aside form impacting water quality, such hydrologic and nutrient-driven changes have 

Figure 2. Contribution of some key phytoplankton taxonomic groups (chlorophytes, cyanobacteria and 

dinoflagellates) to total chlorophyll a concentrations in the Neuse River Estuary, NC. The dates of landfall of the 

seven major hurricanes that have significantly affected flow and nutrient enrichment since mid-1996 are shown.

Hurricanes
Figure 5. Conceptual illustration of a normalized biomass 

size spectrum (numbers of organisms plotted against weight 

classes) in an unperturbed (left panel) and perturbed (right 

panel) ecosystem. In a perturbed ecosystem, abundance 

of small, undesirable phytoplankton (A) may increase while 

abundance and size of large organisms (fish) may decline (B). 

As a result, the slope of the disturbed biomass size spectrum 

becomes steeper and other statistical properties (e.g., levels of 

abundance) may shift.

3) BIOMASS SIZE SPECTRA AS AN INDICATOR OF

ECOSYSTEM STATE

A biomass size spectrum (BSS) depicts the abundance 

and distribution of organisms by size classes in an 

ecosystem. In aquatic ecosystems, the biomass (i.e., 

aggregate weight) of organisms at each level in the 

food chain from microscopic phytoplankton to the 

largest vertebrate animals is nearly equal. Because 

biomass is near equal, numbers of small organisms 

greatly exceed numbers of large organisms. Sizespecifi c predation (big organisms eat smaller ones) in 

aquatic communities maintains the observed biomass 

size structure and has led to methods for evaluation of 

biomass-size relationships to characterize the structure 

and state of ecosystems. To derive BSS, data from 

monitoring programs on organism abundances must 

be aggregated into size categories. BSS models can 

serve as ecological indicators because properties of 

BSS respond to natural or human-induced stressors. 

ACE INC scientists at the University of Maryland are 

evaluating BSS as an indicator of ecosystem state in 

Chesapeake Bay. 

Jung, S. and E.D.Houde. 2005. Fish Biomass Size Spectra in Chesapeake 

Bay. Estuaries 28(2): 226-240.

 

Ecological Indicator: Changes in the slope or other statistical properties of the 

normalized BSS relative to reference standards or historical benchmarks is an indicator 

of changes in the abundance and biomass of the suite of organisms in an aquatic 

ecosystem.

Ecological Effect/Impact: Changes in the slope of the normalized BSS can be 

indicative of changes in the biological community structure, productivity, food-chain 

effi ciency, predator-prey relationships, and effects of environmental variability, fi shing, 

nutrient loading, and habitat change. BSS of stressed ecosystems often have steep 

negative slopes. For example, in heavily fi shed ecosystems larger fi sh may be reduced 

in number and biomass. Or, in highly eutrophic ecosystems with excess nutrient 

loading, blooms of microscopic phytoplankton can greatly increase the abundance 

and biomass of small organisms, leading to stressful conditions such as hypoxia and 

mortality of larger organisms (e.g., crabs, fi sh). 

Environmental Application: BSS can be used by managers to describe long-term 

effects of stress or the success of restoration efforts in estuaries impacted by human 

activities. BSS can be applied to a broad suite of aquatic biological communities, 

not only to selected organisms, and thus can indicate how whole ecosystems are 

responding to either deteriorating conditions or remediation efforts in resource 

management (e.g., better fi sheries management, habitat restoration, improved water 

quality). Periodic monitoring of sizes and abundances of organisms is required to 

apply BSS as an indicator. 

Unperturbed ecosystem Perturbed ecosystem

Biomass Size Spectra as Indicators of Ecosystem Status 

theoretical slope = -1.0 steeper slope

A

B

Log Abundance

Log Weight Class Log Weight Class

Illustration courtesy of William J. Connelly

University of Maryland Center for Environmental Science
Figure 5. Conceptual illustration of a normalized biomass 

size spectrum (numbers of organisms plotted against weight 

classes) in an unperturbed (left panel) and perturbed (right 

panel) ecosystem. In a perturbed ecosystem, abundance 

of small, undesirable phytoplankton (A) may increase while 

abundance and size of large organisms (fish) may decline (B). 

As a result, the slope of the disturbed biomass size spectrum 

becomes steeper and other statistical properties (e.g., levels of 

abundance) may shift.

3) BIOMASS SIZE SPECTRA AS AN INDICATOR OF

ECOSYSTEM STATE

A biomass size spectrum (BSS) depicts the abundance 

and distribution of organisms by size classes in an 

ecosystem. In aquatic ecosystems, the biomass (i.e., 

aggregate weight) of organisms at each level in the 

food chain from microscopic phytoplankton to the 

largest vertebrate animals is nearly equal. Because 

biomass is near equal, numbers of small organisms 

greatly exceed numbers of large organisms. Sizespecifi c predation (big organisms eat smaller ones) in 

aquatic communities maintains the observed biomass 

size structure and has led to methods for evaluation of 

biomass-size relationships to characterize the structure 

and state of ecosystems. To derive BSS, data from 

monitoring programs on organism abundances must 

be aggregated into size categories. BSS models can 

serve as ecological indicators because properties of 

BSS respond to natural or human-induced stressors. 

ACE INC scientists at the University of Maryland are 

evaluating BSS as an indicator of ecosystem state in 

Chesapeake Bay. 

Jung, S. and E.D.Houde. 2005. Fish Biomass Size Spectra in Chesapeake 

Bay. Estuaries 28(2): 226-240.

 

Ecological Indicator: Changes in the slope or other statistical properties of the 

normalized BSS relative to reference standards or historical benchmarks is an indicator 

of changes in the abundance and biomass of the suite of organisms in an aquatic 

ecosystem.

Ecological Effect/Impact: Changes in the slope of the normalized BSS can be 

indicative of changes in the biological community structure, productivity, food-chain 

effi ciency, predator-prey relationships, and effects of environmental variability, fi shing, 

nutrient loading, and habitat change. BSS of stressed ecosystems often have steep 

negative slopes. For example, in heavily fi shed ecosystems larger fi sh may be reduced 

in number and biomass. Or, in highly eutrophic ecosystems with excess nutrient 

loading, blooms of microscopic phytoplankton can greatly increase the abundance 

and biomass of small organisms, leading to stressful conditions such as hypoxia and 

mortality of larger organisms (e.g., crabs, fi sh). 

Environmental Application: BSS can be used by managers to describe long-term 

effects of stress or the success of restoration efforts in estuaries impacted by human 

activities. BSS can be applied to a broad suite of aquatic biological communities, 

not only to selected organisms, and thus can indicate how whole ecosystems are 

responding to either deteriorating conditions or remediation efforts in resource 

management (e.g., better fi sheries management, habitat restoration, improved water 

quality). Periodic monitoring of sizes and abundances of organisms is required to 

apply BSS as an indicator. 

Unperturbed ecosystem Perturbed ecosystem

Biomass Size Spectra as Indicators of Ecosystem Status 

theoretical slope = -1.0 steeper slope

A

B

Log Abundance

Log Weight Class Log Weight Class

Illustration courtesy of William J. Connelly

University of Maryland Center for Environmental Science