Proceedings of the International Joint Conference on Neural Networks, 2003., 2003
ABSTRACT Seagrasses are marine plants that provide many services such as primary productivity, fo... more ABSTRACT Seagrasses are marine plants that provide many services such as primary productivity, food web interactions, shelter, nutrient cycling and habitat stabilization that are essential to marine and estuarine ecosystems. Therefore, monitoring seagrass health is crucial for the existence of many marine aquatic plants and animals. The minimal light requirement of seagrasses is about 20-30% of the total light measured just below the surface. This is relatively high compared to terrestrial plants and phytoplankton, which underlines the importance of water transparency for these species. Hence, light penetration into estuarine waters is critical for seagrass survival. In this paper, an approach to estimate the light attenuation coefficient from water quality parameters using neural networks is proposed. The model is compared with linear regression models such as step-wise linear regression and linear least squares regression. The light attenuation model presented here can be used for monitoring water quality and thereby seagrass health.
2004 IEEE International Joint Conference on Neural Networks (IEEE Cat. No.04CH37541), 2004
... Monitoring Seagrass Health Habtom Ressom Lombardi Comprehensive Cancer Mohamad T. Musavi Wend... more ... Monitoring Seagrass Health Habtom Ressom Lombardi Comprehensive Cancer Mohamad T. Musavi Wendy Tweedale ... 343-348. DP Solamatine and KN Dulal, Model trees as an alternative to neural networks in rainfall-runoff modeling. Hydmlogieoi Sciences Journal. vol. ...
We assess seagrass status and trends by two methods: (1) seagrass mapping every 2 - 3 years since... more We assess seagrass status and trends by two methods: (1) seagrass mapping every 2 - 3 years since 1986, plus 1943, and (2) monitoring of 59 fixed transects twice a year since 1994. In 2005, there were 26,101 ha of seagrass between Ponce de Leon Inlet and Vero Beach, which is at least as much as the 1943 coverage. Trends based on mapping show an increase in coverage in 12 of the 18 segments from 1994 to 2005. Similarly, average extent of seagrass beds from shore to the deep edge (transect length) increased from 1996 to 1999, then leveled off through 2006. The hurricanes of 2004 did not alter these positive trends, but may have contributed to reduction in seagrass densitites in 2006 from Melbourne to Vero Beach.
The Mosquito Lagoon (ML) contains one of the more extensive seagrass coverages in the Indian Rive... more The Mosquito Lagoon (ML) contains one of the more extensive seagrass coverages in the Indian River Lagoon (IRL) system, Florida. Most of this seagrass is confined to the vast shallow flats of the southern ML, where watershed development is minimal and seagrass coverage has remained relatively stable over time (1992-2003 coverages show only 8 to 12% loss since 1943). Despite such apparently favorable conditions, seagrass in the southern ML falls short of attaining its established seagrass deep-edge depth target of 1.3 m, and receives only a fair rating based on seagrass condition metrics. Although water quality in the southern ML is generally good from the standpoint of chlorophyll, color, and nutrients, water clarity conditions (turbidity, light attenuation) are less favorable. Empirical regression models used to develop external (watershed) pollutant loading targets based on seagrass deep-edge condition do not work well for ML. Internal factors (mainly light attenuation from resusp...
The spatial distribution of seagrass and algae communities can be difficult to determine in large... more The spatial distribution of seagrass and algae communities can be difficult to determine in large, shallow lagoon systems where high turbidity prevents the use of optical methods like aerial photography or satellite imagery. Further complications can arise when algae are not permanently attached to the substratum and drift with tides and currents. A study using acoustic seafloor discrimination was conducted in the Indian River Lagoon (Florida, USA) to determine the extent of drift algae and seagrass. Acoustic surveys using the QTC View V system based on 50 and 200 kHz transducers were conducted near Sebastian Inlet. Results indicate that areas of seagrass can be identified, and are mixed with a high abundance of drift algae. Nearest-neighbor extrapolation was used to fill in spaces between survey lines and thus obtain spatially cohesive maps. These maps were then ground-truthed using data from towed video and compared using confusion matrices, The maps showed a high level of agreeme...
ABSTRACT Differentiation between benthic habitats, particularly seagrass and macroalgae, using sa... more ABSTRACT Differentiation between benthic habitats, particularly seagrass and macroalgae, using satellite data is complicated because of water column effects plus the presence of chlorophyll-a in both seagrass and algae that result in similar spectral patterns. Hyperspectral imager for the coastal ocean data over the Indian River Lagoon, Florida, USA, was used to develop two benthic classification models, SlopeRED and SlopeNIR. Their performance was compared with iterative self-organizing data analysis technique and spectral angle mapping classification methods. The slope models provided greater overall accuracies (63–64%) and were able to distinguish between seagrass and macroalgae substrates more accurately compared to the results obtained using the other classifications methods.
During the spring of 2011 an unprecedented "Super" algal bloom formed in the Indian River Lagoon ... more During the spring of 2011 an unprecedented "Super" algal bloom formed in the Indian River Lagoon (IRL), with Chlorophyll a (Chl a) concentrations over eight times the historical mean in some areas and lasted for seven months across the IRL. The European Space Agency's MEdium Resolution Imaging Spectrometer (MERIS) platform provided multispectral data at 665 and 708 nm, which was used to quantify the phytoplankton Chl a by fluorescence while minimizing the effects of other water column constituents. The three objectives were to: (1) calibrate and validate two Chl a algorithms using all available MERIS data of the IRL from 2002 to 2012; (2) determine the accuracy of the algorithms estimation of Chl a before, during, and after the 2011 super bloom; and (3) map the 2011 algal bloom using the Chl a algorithm that was proven to be effective in other similar estuaries. The chosen algorithm, Normalized Difference Chlorophyll Index (NDCI), was positively correlated with the in-situ measurements, with an R 2 value of 0.798. While there was a significant (62.9 ± 25%) underestimation of Chl a using MERIS NDCI, the underestimation appears to be consistent across the data and mostly in the estimations of lower concentrations, suggesting that a qualitative or ratio analysis is still valid. Analysis of the application of the NDCI processed MERIS data provided additional insights that the in-situ
Between August 14 and September 26, 2004, four tropical weather systems (Charley, Frances, Ivan, ... more Between August 14 and September 26, 2004, four tropical weather systems (Charley, Frances, Ivan, and Jeanne) affected the central Indian River Lagoon (IRL). The central IRL received a prodigious amount of rainfall for the 2 mo, between 72 and 83 cm, which is a once-in-50-yr rainfall event. High stream discharges were generated that, combined with wind-suspended sediments, significantly reduced salinities and water transparency. In September, salinities among central IRL segments dropped from 30 psu or more to # 15 psu, color increased from a low of 10 pcu to $ 100 pcu, and turbidity increased from # 3 NTU up to 14 NTU. Evidence of the hurricanes' physical effects on seagrasses (burial, no scour) was limited to just one of the more than 25 sites inspected. Within 2 to 3 mo following the hurricane period, most parameters related to water transparency returned to or showed improvement over their prehurricane (February-July 2004) levels. Unseasonably low salinities (,20 psu) and moderately high color (.20 pcu) were observed through spring 2005, largely attributable to a relatively long residence time and a wetter-than-average spring season in 2005. By the end of the study period (July 2006), the central IRL generally showed a continuation of two opposite seagrass trends-an increase in depthlimit coverage but a decline in coverage density-that began before 2004. Also, within a limited reach of the central IRL, there was a temporary shift in species composition in summer 2005 (Ruppia maritima increased as Halodule wrightii decreased). It is likely that the persistently low salinities (not color) in 2004-2005 affected the species composition and coverage density. This study reveals that seagrasses are resilient to the acute effects of hurricanes and underscores the need to reduce chronic, anthropogenic effects on seagrasses.
The Journal of Arts Management, Law, and Society, 1998
... Lori Morris holds a Ph.D. in sociology from Northwestern University. ... The following source... more ... Lori Morris holds a Ph.D. in sociology from Northwestern University. ... The following sources were used for Philadelphia: the Greater Philadelphia Cultural Alliance Directory, organizational lists from Philadelphia Dance Alliance, Performing Arts League of Philadelphia, Meet the ...
The sensitivity and comparative simplicity of 15 N stable isotopic tracer techniques has been use... more The sensitivity and comparative simplicity of 15 N stable isotopic tracer techniques has been used to quantify rates of nitrification in aquatic systems. However, the most commonly used method for recovery of inorganic oxidized nitrogen compounds from aqueous samples, ...
Seagrasses have been considered one of the most critical marine habitat types of coastal and estu... more Seagrasses have been considered one of the most critical marine habitat types of coastal and estuarine ecosystems such as the Indian River Lagoon. They are an important part of biological productivity, nutrient cycling, habitat stabilization and species diversity and are the primary focus of restoration efforts in the Indian River Lagoon. The areal extent of seagrasses has declined within segments of the lagoon over the years. Light availability to seagrasses is a major criterion limiting their distribution. Decreased water clarity and resulting reduced light penetration have been cited as the major factors responsible for the decline in seagrasses in the lagoon. Hence, light is a critical factor for the survival of seagrass species. Light attenuation coefficient is an important parameter that indicates the light attenuated by the water column and can therefore be used as an indicator of seagrass vigor. A number of region-specific linear light attenuation models have been proposed in the literature. Though, in practice, linear light attenuation models have been commonly used, there is need for a flexible and robust model that incorporates the non-linearities present in coastal and estuarine environments. This paper presents a neural network based model to estimate light attenuation coefficient from water quality parameters and thereby indirectly monitor seagrass population in the Indian River Lagoon. The proposed neural network models were compared with linear regression models, step-wise linear regression models, model trees and support vector machines. The neural network models performed fairly better compared to the other models considered.
Journal of Experimental Marine Biology and Ecology, 2005
Three areas of the Indian River Lagoon, Florida (USA) were surveyed to show seasonal changes in t... more Three areas of the Indian River Lagoon, Florida (USA) were surveyed to show seasonal changes in the distribution and biomass of macroalgae and seagrass. Acoustic seafloor discrimination based on first and second echo returns of a 50 kHz and 200 kHz signal, and two different survey systems (QTCView and ECHOplus) were used. System verification in both the field and a controlled environment showed it was possible to distinguish acoustically between seagrass, sparse algae, and dense algae. Accuracy of distinction of three classes (algae, seagrass, bare substratum) was around 60%. Maps were produced by regridding the survey area to a regular grid and using a nearest-neighbor interpolation to provide filled polygons. Biomass was calculated by counting pixels assigned to substratum classes with known wet-weight biomass values (sparse algae 250 g m À 2 , dense algae 2000 g m À 2 , seagrass 100 g m À 2 ) that were measured in the field. In three study areas (Melbourne, Sebastian Inlet, and Cocoa Beach), a dependence of algal biomass on depth and season was observed. Seagrass most frequently occurred in water less than 1 m deep, and in November, seagrass beds tended to be covered by dense algae that also extended up-and downstream of shoals in the Lagoon. In March, the pattern was similar, with the exception that some areas of previously dense algae had started thinning into sparse algae. Macrophyte biomass was lowest in May in the Melbourne and Cocoa Beach study areas, with the opposite situation in the Sebastian Inlet study area. In May, seagrass areas were largely devoid of dense algae and most algae accumulations were sparse. In August, dense algae covered large areas of the deep Lagoon floor while shoals were largely free of algae or had only sparse cover. We suggest this summer pattern to reflect moribund algae being washed from the shallows to deeper channels and from there being removed from the lagoonal ecosystem either through tidal passages into the open ocean or by degradation and breakdown in situ. The differences 0022-0981/$ -see front matter D (B.M. Riegl). xxx -xxx www.elsevier.com/locate/jembe JEMBE-47730; No of Pages 16 DTD 5
Seagrass both disappeared and recovered within 4 yr in one region of northern Indian River Lagoon... more Seagrass both disappeared and recovered within 4 yr in one region of northern Indian River Lagoon (IRL). For the specific area referred to as Turnbull Bay, a relatively pristine area of the IRL, over 100 ha of seagrass completely disappeared from 1996 to 1997 and then recovered by 2000. Based on lagoon-wide mapping from aerial photographs taken every 2-3 years since 1986, coverage of seagrass in Turnbull Bay declined from 124 ha in 1989 to 34 ha by 1999 and increased to 58 ha in 2003. Bi-annual monitoring of fixed seagrass transects tells a more detailed story. Species composition along the Turnbull transect shifted from Halodule wrightii to Ruppia maritima beginning in 1995, and macroalgal abundance increased. By the summer of 1997, seagrass completely disappeared along the transect, as well as in most of the surrounding areas in Turnbull Bay; macroalgae covered much of the sediment surface. No significant water quality changes were detected. Light attenuation and suspended solid values did increase after the seagrass disappeared. Porewater sulfide concentrations, taken after all the grass was gone in 1997, were high (2,000 M), but did improve by 1998 (1,200 M). Seagrass recovery was rapid and occurred in the reverse sequence of species loss. Seedlings of R. maritima were the first colonizers, then patches of H. wrightii appeared. In 2000, Halophila engelmannii returned in the deeper water (Ͼ 0. . By the summer of 2000, the beds had completely recovered. We conclude that this demise was a natural event caused by a long-term buildup of seagrass biomass and a thick (10-15 cm) layer of organic detritus and ooze. We surmise that such a crash and subsequent recovery may be a natural cycle of decline and recovery within this semirestricted, poorly-flushed area. The frequency of this cycle remains uncertain.
Seagrass protection and restoration in Florida's Indian River Lagoon system (IRLS) is a mutual go... more Seagrass protection and restoration in Florida's Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs. These programs require the establishment of management targets indicative of seagrass recovery and health. We used three metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the IRLS's spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments. Our method consisted of two steps: mapping the union of seagrass coverages from all available mapping to delineate wherever seagrass had been mapped and determining the distribution of depth limits based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively. Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using a 10-yr record of light data (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) and the union coverage depth limit distributions from the most temporally stable seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 6 17% of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions, is 20 6 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 6 13%). Variation in depth limits and light requirements is probably due to factors other than light that influence the depth limit of seagrasses (e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data sets and can be applied to other estuaries where grass beds are routinely monitored and mapped.
Proceedings of the International Joint Conference on Neural Networks, 2003., 2003
ABSTRACT Seagrasses are marine plants that provide many services such as primary productivity, fo... more ABSTRACT Seagrasses are marine plants that provide many services such as primary productivity, food web interactions, shelter, nutrient cycling and habitat stabilization that are essential to marine and estuarine ecosystems. Therefore, monitoring seagrass health is crucial for the existence of many marine aquatic plants and animals. The minimal light requirement of seagrasses is about 20-30% of the total light measured just below the surface. This is relatively high compared to terrestrial plants and phytoplankton, which underlines the importance of water transparency for these species. Hence, light penetration into estuarine waters is critical for seagrass survival. In this paper, an approach to estimate the light attenuation coefficient from water quality parameters using neural networks is proposed. The model is compared with linear regression models such as step-wise linear regression and linear least squares regression. The light attenuation model presented here can be used for monitoring water quality and thereby seagrass health.
2004 IEEE International Joint Conference on Neural Networks (IEEE Cat. No.04CH37541), 2004
... Monitoring Seagrass Health Habtom Ressom Lombardi Comprehensive Cancer Mohamad T. Musavi Wend... more ... Monitoring Seagrass Health Habtom Ressom Lombardi Comprehensive Cancer Mohamad T. Musavi Wendy Tweedale ... 343-348. DP Solamatine and KN Dulal, Model trees as an alternative to neural networks in rainfall-runoff modeling. Hydmlogieoi Sciences Journal. vol. ...
We assess seagrass status and trends by two methods: (1) seagrass mapping every 2 - 3 years since... more We assess seagrass status and trends by two methods: (1) seagrass mapping every 2 - 3 years since 1986, plus 1943, and (2) monitoring of 59 fixed transects twice a year since 1994. In 2005, there were 26,101 ha of seagrass between Ponce de Leon Inlet and Vero Beach, which is at least as much as the 1943 coverage. Trends based on mapping show an increase in coverage in 12 of the 18 segments from 1994 to 2005. Similarly, average extent of seagrass beds from shore to the deep edge (transect length) increased from 1996 to 1999, then leveled off through 2006. The hurricanes of 2004 did not alter these positive trends, but may have contributed to reduction in seagrass densitites in 2006 from Melbourne to Vero Beach.
The Mosquito Lagoon (ML) contains one of the more extensive seagrass coverages in the Indian Rive... more The Mosquito Lagoon (ML) contains one of the more extensive seagrass coverages in the Indian River Lagoon (IRL) system, Florida. Most of this seagrass is confined to the vast shallow flats of the southern ML, where watershed development is minimal and seagrass coverage has remained relatively stable over time (1992-2003 coverages show only 8 to 12% loss since 1943). Despite such apparently favorable conditions, seagrass in the southern ML falls short of attaining its established seagrass deep-edge depth target of 1.3 m, and receives only a fair rating based on seagrass condition metrics. Although water quality in the southern ML is generally good from the standpoint of chlorophyll, color, and nutrients, water clarity conditions (turbidity, light attenuation) are less favorable. Empirical regression models used to develop external (watershed) pollutant loading targets based on seagrass deep-edge condition do not work well for ML. Internal factors (mainly light attenuation from resusp...
The spatial distribution of seagrass and algae communities can be difficult to determine in large... more The spatial distribution of seagrass and algae communities can be difficult to determine in large, shallow lagoon systems where high turbidity prevents the use of optical methods like aerial photography or satellite imagery. Further complications can arise when algae are not permanently attached to the substratum and drift with tides and currents. A study using acoustic seafloor discrimination was conducted in the Indian River Lagoon (Florida, USA) to determine the extent of drift algae and seagrass. Acoustic surveys using the QTC View V system based on 50 and 200 kHz transducers were conducted near Sebastian Inlet. Results indicate that areas of seagrass can be identified, and are mixed with a high abundance of drift algae. Nearest-neighbor extrapolation was used to fill in spaces between survey lines and thus obtain spatially cohesive maps. These maps were then ground-truthed using data from towed video and compared using confusion matrices, The maps showed a high level of agreeme...
ABSTRACT Differentiation between benthic habitats, particularly seagrass and macroalgae, using sa... more ABSTRACT Differentiation between benthic habitats, particularly seagrass and macroalgae, using satellite data is complicated because of water column effects plus the presence of chlorophyll-a in both seagrass and algae that result in similar spectral patterns. Hyperspectral imager for the coastal ocean data over the Indian River Lagoon, Florida, USA, was used to develop two benthic classification models, SlopeRED and SlopeNIR. Their performance was compared with iterative self-organizing data analysis technique and spectral angle mapping classification methods. The slope models provided greater overall accuracies (63–64%) and were able to distinguish between seagrass and macroalgae substrates more accurately compared to the results obtained using the other classifications methods.
During the spring of 2011 an unprecedented "Super" algal bloom formed in the Indian River Lagoon ... more During the spring of 2011 an unprecedented "Super" algal bloom formed in the Indian River Lagoon (IRL), with Chlorophyll a (Chl a) concentrations over eight times the historical mean in some areas and lasted for seven months across the IRL. The European Space Agency's MEdium Resolution Imaging Spectrometer (MERIS) platform provided multispectral data at 665 and 708 nm, which was used to quantify the phytoplankton Chl a by fluorescence while minimizing the effects of other water column constituents. The three objectives were to: (1) calibrate and validate two Chl a algorithms using all available MERIS data of the IRL from 2002 to 2012; (2) determine the accuracy of the algorithms estimation of Chl a before, during, and after the 2011 super bloom; and (3) map the 2011 algal bloom using the Chl a algorithm that was proven to be effective in other similar estuaries. The chosen algorithm, Normalized Difference Chlorophyll Index (NDCI), was positively correlated with the in-situ measurements, with an R 2 value of 0.798. While there was a significant (62.9 ± 25%) underestimation of Chl a using MERIS NDCI, the underestimation appears to be consistent across the data and mostly in the estimations of lower concentrations, suggesting that a qualitative or ratio analysis is still valid. Analysis of the application of the NDCI processed MERIS data provided additional insights that the in-situ
Between August 14 and September 26, 2004, four tropical weather systems (Charley, Frances, Ivan, ... more Between August 14 and September 26, 2004, four tropical weather systems (Charley, Frances, Ivan, and Jeanne) affected the central Indian River Lagoon (IRL). The central IRL received a prodigious amount of rainfall for the 2 mo, between 72 and 83 cm, which is a once-in-50-yr rainfall event. High stream discharges were generated that, combined with wind-suspended sediments, significantly reduced salinities and water transparency. In September, salinities among central IRL segments dropped from 30 psu or more to # 15 psu, color increased from a low of 10 pcu to $ 100 pcu, and turbidity increased from # 3 NTU up to 14 NTU. Evidence of the hurricanes' physical effects on seagrasses (burial, no scour) was limited to just one of the more than 25 sites inspected. Within 2 to 3 mo following the hurricane period, most parameters related to water transparency returned to or showed improvement over their prehurricane (February-July 2004) levels. Unseasonably low salinities (,20 psu) and moderately high color (.20 pcu) were observed through spring 2005, largely attributable to a relatively long residence time and a wetter-than-average spring season in 2005. By the end of the study period (July 2006), the central IRL generally showed a continuation of two opposite seagrass trends-an increase in depthlimit coverage but a decline in coverage density-that began before 2004. Also, within a limited reach of the central IRL, there was a temporary shift in species composition in summer 2005 (Ruppia maritima increased as Halodule wrightii decreased). It is likely that the persistently low salinities (not color) in 2004-2005 affected the species composition and coverage density. This study reveals that seagrasses are resilient to the acute effects of hurricanes and underscores the need to reduce chronic, anthropogenic effects on seagrasses.
The Journal of Arts Management, Law, and Society, 1998
... Lori Morris holds a Ph.D. in sociology from Northwestern University. ... The following source... more ... Lori Morris holds a Ph.D. in sociology from Northwestern University. ... The following sources were used for Philadelphia: the Greater Philadelphia Cultural Alliance Directory, organizational lists from Philadelphia Dance Alliance, Performing Arts League of Philadelphia, Meet the ...
The sensitivity and comparative simplicity of 15 N stable isotopic tracer techniques has been use... more The sensitivity and comparative simplicity of 15 N stable isotopic tracer techniques has been used to quantify rates of nitrification in aquatic systems. However, the most commonly used method for recovery of inorganic oxidized nitrogen compounds from aqueous samples, ...
Seagrasses have been considered one of the most critical marine habitat types of coastal and estu... more Seagrasses have been considered one of the most critical marine habitat types of coastal and estuarine ecosystems such as the Indian River Lagoon. They are an important part of biological productivity, nutrient cycling, habitat stabilization and species diversity and are the primary focus of restoration efforts in the Indian River Lagoon. The areal extent of seagrasses has declined within segments of the lagoon over the years. Light availability to seagrasses is a major criterion limiting their distribution. Decreased water clarity and resulting reduced light penetration have been cited as the major factors responsible for the decline in seagrasses in the lagoon. Hence, light is a critical factor for the survival of seagrass species. Light attenuation coefficient is an important parameter that indicates the light attenuated by the water column and can therefore be used as an indicator of seagrass vigor. A number of region-specific linear light attenuation models have been proposed in the literature. Though, in practice, linear light attenuation models have been commonly used, there is need for a flexible and robust model that incorporates the non-linearities present in coastal and estuarine environments. This paper presents a neural network based model to estimate light attenuation coefficient from water quality parameters and thereby indirectly monitor seagrass population in the Indian River Lagoon. The proposed neural network models were compared with linear regression models, step-wise linear regression models, model trees and support vector machines. The neural network models performed fairly better compared to the other models considered.
Journal of Experimental Marine Biology and Ecology, 2005
Three areas of the Indian River Lagoon, Florida (USA) were surveyed to show seasonal changes in t... more Three areas of the Indian River Lagoon, Florida (USA) were surveyed to show seasonal changes in the distribution and biomass of macroalgae and seagrass. Acoustic seafloor discrimination based on first and second echo returns of a 50 kHz and 200 kHz signal, and two different survey systems (QTCView and ECHOplus) were used. System verification in both the field and a controlled environment showed it was possible to distinguish acoustically between seagrass, sparse algae, and dense algae. Accuracy of distinction of three classes (algae, seagrass, bare substratum) was around 60%. Maps were produced by regridding the survey area to a regular grid and using a nearest-neighbor interpolation to provide filled polygons. Biomass was calculated by counting pixels assigned to substratum classes with known wet-weight biomass values (sparse algae 250 g m À 2 , dense algae 2000 g m À 2 , seagrass 100 g m À 2 ) that were measured in the field. In three study areas (Melbourne, Sebastian Inlet, and Cocoa Beach), a dependence of algal biomass on depth and season was observed. Seagrass most frequently occurred in water less than 1 m deep, and in November, seagrass beds tended to be covered by dense algae that also extended up-and downstream of shoals in the Lagoon. In March, the pattern was similar, with the exception that some areas of previously dense algae had started thinning into sparse algae. Macrophyte biomass was lowest in May in the Melbourne and Cocoa Beach study areas, with the opposite situation in the Sebastian Inlet study area. In May, seagrass areas were largely devoid of dense algae and most algae accumulations were sparse. In August, dense algae covered large areas of the deep Lagoon floor while shoals were largely free of algae or had only sparse cover. We suggest this summer pattern to reflect moribund algae being washed from the shallows to deeper channels and from there being removed from the lagoonal ecosystem either through tidal passages into the open ocean or by degradation and breakdown in situ. The differences 0022-0981/$ -see front matter D (B.M. Riegl). xxx -xxx www.elsevier.com/locate/jembe JEMBE-47730; No of Pages 16 DTD 5
Seagrass both disappeared and recovered within 4 yr in one region of northern Indian River Lagoon... more Seagrass both disappeared and recovered within 4 yr in one region of northern Indian River Lagoon (IRL). For the specific area referred to as Turnbull Bay, a relatively pristine area of the IRL, over 100 ha of seagrass completely disappeared from 1996 to 1997 and then recovered by 2000. Based on lagoon-wide mapping from aerial photographs taken every 2-3 years since 1986, coverage of seagrass in Turnbull Bay declined from 124 ha in 1989 to 34 ha by 1999 and increased to 58 ha in 2003. Bi-annual monitoring of fixed seagrass transects tells a more detailed story. Species composition along the Turnbull transect shifted from Halodule wrightii to Ruppia maritima beginning in 1995, and macroalgal abundance increased. By the summer of 1997, seagrass completely disappeared along the transect, as well as in most of the surrounding areas in Turnbull Bay; macroalgae covered much of the sediment surface. No significant water quality changes were detected. Light attenuation and suspended solid values did increase after the seagrass disappeared. Porewater sulfide concentrations, taken after all the grass was gone in 1997, were high (2,000 M), but did improve by 1998 (1,200 M). Seagrass recovery was rapid and occurred in the reverse sequence of species loss. Seedlings of R. maritima were the first colonizers, then patches of H. wrightii appeared. In 2000, Halophila engelmannii returned in the deeper water (Ͼ 0. . By the summer of 2000, the beds had completely recovered. We conclude that this demise was a natural event caused by a long-term buildup of seagrass biomass and a thick (10-15 cm) layer of organic detritus and ooze. We surmise that such a crash and subsequent recovery may be a natural cycle of decline and recovery within this semirestricted, poorly-flushed area. The frequency of this cycle remains uncertain.
Seagrass protection and restoration in Florida's Indian River Lagoon system (IRLS) is a mutual go... more Seagrass protection and restoration in Florida's Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs. These programs require the establishment of management targets indicative of seagrass recovery and health. We used three metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the IRLS's spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments. Our method consisted of two steps: mapping the union of seagrass coverages from all available mapping to delineate wherever seagrass had been mapped and determining the distribution of depth limits based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively. Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using a 10-yr record of light data (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) and the union coverage depth limit distributions from the most temporally stable seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 6 17% of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions, is 20 6 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 6 13%). Variation in depth limits and light requirements is probably due to factors other than light that influence the depth limit of seagrasses (e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data sets and can be applied to other estuaries where grass beds are routinely monitored and mapped.
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