Grantee Research Project Results
1999 Progress Report: Multiscale Assessment of the Population Status of Thalassia testudinum A New Approach to Ecosystem Assessment
EPA Grant Number: R825145Title: Multiscale Assessment of the Population Status of Thalassia testudinum A New Approach to Ecosystem Assessment
Investigators: Carlson, Paul R. , Moncreiff, Cynthia A. , Yarbro, Laura A. , Rose, Craig D. , Durako, Michael J. , Fourqurean, James W. , Blakesley, Barbara , McRae, Gil , Madley, Kevin , Randall, Todd
Current Investigators: Carlson, Paul R. , Durako, Michael J. , Fourqurean, James W. , McRae, Gil , Yarbro, Laura A. , Madley, Kevin , Rose, Craig D. , Moncreiff, Cynthia A. , Randall, Todd , Merello, Manuel
Institution: Florida Marine Research Institute , Florida International University , Oregon State University , University of Southern Mississippi , Florida Fish and Wildlife Conservation Commission , Gulf Coast Research Laboratory
Current Institution: Florida Marine Research Institute , Florida International University , Oregon State University , University of Southern Mississippi
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 1999
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $758,386
RFA: Ecological Assessment (1996) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems
Objective:
The primary goal of this project is to test the utility of demographic, morphological, physiological, and chemical characteristics of turtle grass (Thalassia testudinum) as indicators of chronic environmental stress on estuarine and nearshore ecosystems. We also are attempting to determine the most effective sampling design and scale for assessing the impact of natural and human impacts on seagrass beds. Turtle grass was selected for three reasons: (1) it is abundant along the Gulf coast; (2) it is particularly sensitive to stress because it has a large investment in non-photosynthetic tissue (roots and rhizomes); and (3) in estuaries like Tampa Bay, it has proven more vulnerable than other seagrass species to human impacts. On the basis of both our own prior research and seagrass literature, we have chosen demographic characteristics (population structure inferred from shoot age distribution), plant morphology (leaf width, length, shoot-specific leaf area, and leaf area index), and physiological parameters (rhizome carbohydrate levels, elemental (C:N:P) ratios, and stable isotope composition of turtle grass as potential stress indicators.
The project is a collaborative effort of scientists at the Florida Marine Research Institute, Florida International University, University of North Carolina at Wilmington, and the University of Southern Mississippi. The indicators are being tested at nine sites in the eastern Gulf of Mexico distributed between the Chandeleur Islands in Mississippi to Florida Bay at the southern tip of the Florida peninsula. The field sampling program at all nine sites uses three nested grids of tesselated hexagons. This spatially distributed, random-sampling design was first developed by the EPA Environmental Monitoring and Assessment Program (EMAP), and it provides the statistical advantages of random sampling and structured spatial coverage of sampling areas. At each site, we sample 30 stations at each of three (small-100 m2, medium-10,000 m2, and large-1,000,000 m2) spatial scales.
Progress Summary:
This project is in its fourth year. Initial funding arrived too late in 1996 for sampling during the summer-fall index period, so the first annual cycle of field sampling began in 1997. Field sampling has been conducted yearly since 1997, with the third, and final, samples collected in summer-fall 1999. Sample processing from each annual collection takes several months, so we anticipate completion of 1999 sample processing in late spring 2000.
In the first field season, sampling and analytical protocols were tested at five sites along the west coast of Florida. Seagrass cover and community structure were assessed visually in 0.25 m2 quadrants. Plant samples were collected for demographic analysis by reconstructive aging and for structural indices such as leaf width, length, shoot-specific leaf area, and leaf area index. Rhizome samples were collected for sugar and starch analysis, and leaf tissue was collected for elemental (C:N:P) ratio and stable isotope (del C-13, del N-15, and del S-34) analyses. In the second and third sampling seasons (summer-fall 1998 and 1999), nine sites were sampled using the same protocols. In 1998, additional water and sediment samples were collected from the 30 large-scale sampling points for each site. Water column turbidity and sediment porewater sulfide, porosity, loss on ignition, total nitrogen, and total phosphorous are being analyzed on these samples. At a project Principal Investigators meeting held at the Florida Marine Research Institute on March 15, 1999, we decided to measure epiphyte loads on all samples from the large-scale sample grid at each site in the 1999 field season.
Project Timeline. We have requested, and EPA has approved a 1-year, no-cost extension for this project, extending it to September 30, 2000. Laboratory processing of the 1997 and 1998 samples is complete, and data analysis is proceeding. Processing of 1999 samples has begun and will be completed by late spring 2000. We will use spring and summer 2000 for comprehensive data analysis, and we anticipate final report submission on schedule.
Budget Status. Project spending is proceding on schedule. As of June 1999 (the end of the State of Florida fiscal year), the Florida Marine Research Institute has spent approximately $180,000 (73 percent) of the $248,000 budgeted for this site. Contracts to Co-Principal Investigators at University of North Carolina-Wilmington, Florida International University, and Gulf Coast Research Laboratory total $463,243, of which $310,898 (67 percent) has been spent.
Project Abstracts:
Durako MJ, Merello M, McRae G, Carlson PR. The University of North Carolina at Wilmington, Center for Marine Science Research, Wilmington, NC 28403; Florida Marine Research Institute, St. Petersburg, FL 33701
Scale-Based Variability in Thalassia testudinum Morphology and Demography Along the West Coast of Florida
Hierarchical sampling based on tesselated hexagons was used to examine spatial dependence among potential ecoindicators for the seagrass Thalassia testudinum at four Florida Gulf coast sites. Sampling grids consisted of three concentric 30-cell tesselations. The finest level of resolution was located nearest to suspected anthropogenic or natural perturbations. Sample stations were randomly located within each grid cell. A suite of morphometric and demographic characteristics were measured at each sample station. All characteristics varied significantly at the regional (among-site) scale. Within-site scale-based variability in shoot density was significant only at the Tampa Bay site. Sampling at this site was centered on a shallow area frequently traversed by small vessels. Samples from the small-scale sampling grid had significantly lower short-shoot densities, but similar apical densities to those of the large-scale grid, suggesting that the effect of vessel traffic is quite localized at this site and that Thalassia may exhibit a compensatory increase in branching in response to disturbances that reduce shoot densities. Shoot-specific characteristics such as the number of leaves short-shoot-1 and leaf width, exhibited the least spatially dependent variability within each of the four sites; the numbers of leaf scars shoot-1 exhibited the greatest spatial variability.
Rose CD, Fourqurean JW, Rutten LM, Department of Biology and SERP, Florida International University, Miami, FL 33199
Seagrass C:N:P?Investigating the Effects of Spatial Scale, Environmental Heterogeneity, Nutrient Sources, and Sampling Effort
We present results from several studies that were conducted in south Florida seagrass meadows concerning how leaf nitrogen and phosphorous in Thalassia testudinum varied with respect to spatial scale and environmental heterogeneity. In one study, we sampled Thalassia from five estuarine systems at three spatial scales. N:P varied from 3-75, indicating that some areas were either severely N or P limited. In estuaries associated with anthropogenic point-nutrient sources, C:N:P ratios were more dependent on spatial scale relative to more pristine sites. In another study, Thalassia was sampled throughout the Florida Keys National Marine Sanctuary (FKNMS). N:P ranged between 16-72; also suggesting N and P limitation. At one site within the FKNMS, we sampled within a permanently established 10x10 m2 plot. C:N varied between 17-26 and exhibited a highly heterogeneous spatial pattern with defined "neighborhoods" of low and high N availability?perhaps indicating the presence of nutrient microsites. Leaf N significantly varied with leaf mass (r = -.27), and both N and P were related to other population and environmental characteristics. These studies suggest that when we utilize seagrass leaf C:N:P ratios as a measure of seagrass nutrient availability we need to exercise caution due to the high degree of natural variability observed.
Moncreiff CA, Randall TA, Caldwell JD, McCall RK, Blackburn BR, Criss GA, The University of Southern Mississippi, Institute of Marine Sciences, Gulf Coast Research Laboratory, Ocean Springs, MS 39566-7000
Recovery of North Chandeleur Islands Seagrass Populations from the Effects of Hurricane Georges
Seagrass community disturbances associated with tropical storm events are related to strength and duration of individual storms, ranging from loss of seagrass blades, epiphytes, and associated flora and fauna to complete removal of seagrasses and substrate, depending on storm severity and proximity. Seagrasses located along the northwest shoreline of the Chandeleur Islands were affected by the passage of Hurricane Georges near the Chandeleur Islands in northeast Gulf of Mexico prior to landfall on September 28, 1998. This seagrass community, dominated by turtle grass (Thalassia testudinum), was subjected to storm surge in excess of 2 m for over 30 hours. The area had been sampled from August 12?14, 1998, as a component of an ongoing project. One of the metrics used, the Braun-Blanquet sampling technique, employs a nondestructive visual assessment of seagrasses coverage. These observations were repeated on November 5, 1998, to assess impacts of the passage of Hurricane Georges on the seagrass area under study, and will be repeated during August 1999. Patterns observed in the shifting of substrates, loss of drift algae, loss of seagrass coverage, and the spread of manatee grass (Syringodium filiforme) to previously nonvegetated sites will be analyzed to determine degree of recovery of this seagrass system.
Peterson BJ, Fourqurean JW, Department of Biological Sciences and Southeast Environmental Research Program, Florida International University, Miami, FL
Spatial Variability of Thalassia testudinum Population Growth Dynamics in South Florida
An examination of the population age structure of 131 spatially separated populations of Thalassia testudinum over the extent of the Florida Keys National Marine Sanctuary (FKNMS) over a 2-year period revealed significant spatial variation in short-shoot demographic characteristics and population dynamics. Shoot age was determined for 13,544 short shoots. Number of leaf scars on individual shoots were converted to shoot ages using observed seasonally variable leaf-emergence rates. The yearly mean plastochron interval was 34.4; 3.8 (d leaf-1), and the mean population age was approximately 3 years. A significant relationship between asexual reproductive output and gross recruitment (r2 = 0.15, p = 0.001) and mortality and gross recruitment (r2 = 0.72, p <0.001) existed. The greatest risk of mortality occurred in areas where gross recruitment was highest. The net population growth for T. testudinum within the boundaries of FKNMS was stable (mean = - 0.007 0.087 y-1). However, areas within FKNMS fluctuated between positive and negative net growth rates (-0.20 y-1 to 0.50 y-1). The power of such large-scale observations is the ability to identify areas of management concern and frame questions addressing the controlling mechanisms influencing these regions of fluctuating population growth.
Future Activities:
The remainder of the project will be spent processing and analyzing samples collected in the 1999 field season, data analysis and integration, and preparation of manuscripts and the final report. We currently are collecting as much historical water quality data from our sites as we can find. For example, to explore the spatial and temporal extent of ENSO-induced phytoplankton blooms, we are analyzing reflectance data from AVHRR imagery of the Florida West Coast for 1998 and 1999.Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
ecosystem, indicators, scaling, ecology, Gulf of Mexico, RFA, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, exploratory research environmental biology, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Ecosystem Protection, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, Gulf of Mexico, Ecological Indicators, risk assessment, aquatic, multi-scale biophysical models, Thalassia testudimum, ecosystem assessment, stressors, multiple spatial scales, Seston C:N:P ratio, disturbance based variable, estuarine ecosystems, aquatic ecosystems, assessment methods, population-based, spatial and temporal patterns, diseaseProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.