2010 SOUTHEASTERN NATURALIST 9(3):477–486 Submersed Aquatic Vegetation of the Jean Lafitte National Historical Park and Preserve Michael A. Poirrier1,*, Kathy Burt-Utley1, John F. Utley1, and Elizabeth A. Spalding1 Abstract - The Barataria Preserve unit of Jean Lafitte National Historical Park and Preserve is located in wetlands of the upper Barataria-Terrebonne estuary near New Orleans, LA and subject to perturbations that affect aquatic resources. A study of submersed aquatic vegetation (SAV) was conducted to determine community composition, distribution, and abundance. Seven native species—Cabomba caroliniana, Ceratophyllum demersum, Heteranthera dubia, Najas guadalupensis, Potamogeton pusillus, Vallisneria americana, and Zannichellia palustris—and three exotic species—Egeria densa, Hydrilla verticillata, and Myriophyllum spicatum—were present. The highly invasive, exotic, floating fern Salvinia molesta was also present. The Preserve is affected by a coastal restoration project designed to return Mississippi River flow to the upper Barataria Estuary. Preserve SAV did not conform to the general estuarine management paradigm of decline and loss with nutrient introductions. Instead, freshwater dominated the Preserve, and sufficient light was present to support robust SAV growth in ponds, canals, and Lake Cataouatche. Native and exotic species formed large surface mats that clogged waterways. Vallisneria americana may be decreasing due to the increase in nuisance SAV and floating plants. This study is the first of its kind for any wetland habitat in the states of the Northern Gulf Coast and therefore will be an important baseline to future studies both generally and specifically for the Preserve as Louisiana’s coastal wetland waterways experience change brought on by the general coastal wetland loss from sea level rise and efforts to restore the wetlands. Introduction Submersed aquatic vegetation (SAV) refers to rooted, vascular, flowering plants that live and grow below the water surface (Cronk and Fennessy 2001). These submersed macrophytes perform a multitude of ecological functions including providing habitat and food for estuarine animals, decreasing wave energy, increasing sedimentation, and stabilizing sediments (Cronk and Fennessy 2001, Hemminga and Duarte 2000, Ward et al. 1984). SAV is very sensitive to slight changes in salinity, turbidity, and nutrient levels, and its distribution and abundance are good indicators of subtidal environmental quality (Davis and Brinson 1980, Dennison et al. 1993). Loss of SAV can have direct effects on fish and wildlife resources and estuarine landscape dynamics. Despite the ecological importance of SAV, little is known about community composition or environmental factors that control SAV distribution and abundance in coastal Louisiana. A study of submersed aquatic 1Department of Biological Sciences, University of New Orleans, 2000 Lakeshore Drive, New Orleans, LA 70148. *Corresponding author - mpoirrie@uno.edu. 478 Southeastern Naturalist Vol. 9, No. 3 vegetation in the Barataria Preserve of Jean Lafitte National Historical Park and Preserve (JELA; henceforth the Preserve) was conducted to provide information on community composition, distribution, and abundance (Poirrier et al. 2009). The need to protect representative natural communities in the Preserve was identified in the Resource Management Plan (JELA 1997). The 7446- hectare Preserve is in the northeast portion of the 0.6 millionha Barataria-Terrebonne estuarine system, approximately 15 km south of New Orleans in Jefferson Parish, LA (Fig.1). Waters within the Preserve generally range from fresh to slightly brackish (Swarzenski et al. 2004). Sources of brackish water include Bayou Barataria and Lakes Salvador and Cataouatche. Sources of freshwater include local rainfall, drainage from wetlands, agricultural land, and urban areas, and a coastal restoration diversion. Since 2002, Mississippi River water enters northern Lake Cataouatche during openings of the Davis Pond Diversion. It is capable of transferring 10,650 cubic feet/second (cfs) of water from the Mississippi River into waterways adjacent to the Preserve (USACE 2000). Flow from the diversion occurs during high-water periods in the River during the first half of the year, and a minimum flow of about 1000 cfs is maintained year-round. Nutrients are generally present in these freshwater sources causing a north–south gradient of decreasing nutrient levels along the Bayou Segnette Waterway and shorelines of Lake Cataouatche and Salvador. In coastal Louisiana, salinity is the primary factor controlling SAV community structure, and light intensity at suitable depths determines abundance (Cho and Poirrier 2005). A diverse SAV community occurs in freshwater, and some freshwater species extend into low-salinity brackish water (3–5 ppt), but at salinities ranging from 5 to 20 ppt, only Myriophyllum spicatum L. (Eurasian Water-milfoil) and Ruppia maritima L. (Widgeon-grass) occur (Hester et al. 2005, Stutzenbaker 1999). Salinity tolerance is affected by rate of salinity change, nutrients, and available light. Plants can generally tolerate higher salinities when values are stable and other conditions are optimum for maintenance and growth (French and Moore 2003). Submersed aquatics have true roots that absorb nutrients from sediment, which allows them to grow in nutrient-poor waters. However, with eutrophication, SAV is generally replaced by algae due to overgrowth of epiphytes on SAV and dense phytoplankton which shade SAV (Harlin 1995). The minimal depth that SAV can occur is controlled by low-water events that expose plants to lethal drying and damaging waves (Cho and Poirrier 2005). Wave energy in shallow water can also uproot plants and suspend sediments, which increase turbidity to levels that limit growth. Maximum depth of SAV occurrence is controlled by decreasing light with increasing depth. Previous general vegetation surveys conducted in the Preserve included White et al. (1983), Michot (1984), Michot and Doyle (1999), Swarzenski et al. (2004), and Nolfo-Clements (2006). These studies focused on marsh habitats, and most did not cover the entire Preserve. The following SAV species were reported: Cabomba caroliniana A. Gray (Fanwort, Carolina 2010 M.A. Poirrier, K. Burt-Utley, J.F. Utley, and E.A. Spalding 479 Fanwort); Ceratophyllum demersum L. (Coontail, Coon’s tail, Hornwort); Heteranthera dubia (Jacq.) MacM. (Water Star-grass, Grassleaf Mud Plaintain); Hydrilla verticillata (L.f.) Royle (Water Thyme); Myriophyllum spicatum; Najas guadalupensis (Spreng.) Magnus (Common Water Nymph, Southern Water Nymph); and Vallisneria americana Michx. (Water-celery, Tape-grass, Freshwater Eel Grass, American Eel Grass). Perturbations to the Preserve include habitat degradation from urban development, exotic species, marsh management, and oil and gas mining (JELA 1997). There is also concern about possible effects of the Davis Pond Mississippi River Diversion. While generally considered a solution to wetland loss, this diversion could harm SAV. Increases in nutrient levels and turbidity due to suspended silts, clays and phytoplankton can decrease light available for photosynthesis, increase the growth of algal epiphytes on SAV leaves, and restrict SAV growth. Invasive non-native SAV may become established under these conditions. The objectives of this study were to determine: the relative abundance and distribution of native, exotic, and nuisance SAV; the habitats where they occur; and factors associated with their distribution and abundance. Methods Aquatic habitats throughout the Preserve were surveyed from June 2006 through April 2008. Methods included observations of surface growth from a boat and raking the bottom to locate vegetation not visible at the surface. Lakes, canals, bayous, and ponds were sampled from a shallow draft boat with a garden rake. Marsh and swamp sites accessible by air boat and boardwalks were also examined. Familiar species were identified and photographed in the field. Unfamiliar species were identified in the laboratory. Representative specimens of each species were examined in the laboratory, and voucher specimens prepared. Nomenclature followed the Integrated Taxonomic Information System (USDA 2009). Voucher specimens were deposited in The University of Southern Mississippi herbarium. The ecological importance of the species within communities of underwater plants is generally not easy to quantify, especially from surface observations in the diverse types of habitats within an ecosystem such as that of the Preserve. Estimation of coverage over bottom plots was impossible. Quantification was made using relative abundance of each species based mainly upon proportion of presence/absence at the sites, i.e., rank order. We also estimated the size of rooted beds of canopy-forming species and included this information in our ranking. Data were obtained from 146 representative sites (Fig. 1), a large number of sites across all habitats in the Preserve. Our rank order values generally agreed with site abundance and distribution in the Preserve. We measured the maximum depth at which SAV occurred, photosynthetically active radiation, and Secchi disc transparency to obtain information on how light reduction with depth affected SAV abundance. Salinity (ppt) was also 480 Southeastern Naturalist Vol. 9, No. 3 determined using a YSI 85 S-C-T, DO meter. Secchi disc transparency (ft) and depth (ft) were determined using a weighted Secchi disc. Photosynthetically active radiation was measured with a Li-Cor quantum sensor and photometer. Results and Discussion Seven native species were found—Cabomba caroliniana; Ceratophyllum demersum; Heteranthera dubia; Najas guadalupensis; Potamogeton pusillus L. (Baby Pondweed, Small Pondweed); Vallisneria americana; and Zannichellia palustris L. (Horned Pondweed)—as well as three exotic species—Egeria densa Planch. (Waterweed, Brazillian Elodea); Hydrilla verticillata; and Myriophyllum spicatum. These ten species are regarded as true SAV because they are rooted and have leaves that are always submersed. Three species that are similar to true SAV were also present: Myriophyllum aquaticum (Vell.) Verdc. (Parrot-feather), an exotic species with emergent leaves; Potamogeton epihydrus Rafinesque (Ribbon-leaf Pondweed), a native species with floating leaves; and Utricularia cf. radiata Small (Little Floating Bladderwort), a native, floating species. The presence of the exotic floating fern, Salvinia molesta D.S. Mitchell (Giant Salvinia) was also Figure 1. Map of the Jean Lafitte National Historical Park and Preserve showing its location in Louisiana and the 146 study sites. 2010 M.A. Poirrier, K. Burt-Utley, J.F. Utley, and E.A. Spalding 481 documented. This is the first record of Egeria densa, Potamogetom pusillus, Zannichelia palustris, and Salvinia molesta from the Preserve. Submersed vegetation was found in man-made canals, ponds, bayous, and estuarine lakes. True SAV is sensitive to desiccation and was absent from marshes and swamps because these shallow habitats are exposed to periodic drying. The distribution of different SAV species was directly influenced by salinity and the indirect effect of salinity reducing floating aquatics that shade SAV. Information about the distribution and ecology of individual species is summarized in Table 1 and further discussed in order of abundance below. General information about species was compiled from Godfrey and Wooten (1979, 1981), Flora of North America Editorial Committee (1993), and Stutzenbaker (1999). Ceratophyllum demersum, a native species, was found at 78 sites throughout the Preserve and occurred with all other SAV species found in this study and was previously reported in the Preserve. It lacks true roots, but has modified leaf branches that serve as anchoring “rhizoids”. Persistent growth produces large vegetative mats that are anchored to the bottom and cover quiet waters. However, plants are easily dislodged from the bottom and drift with currents. It is regarded as a freshwater species but was common in quiet tidal water at salinities ranging from 0.2 to 0.7 ppt. Najas guadalupensis is a native species and was found at 63 sites and ranked 2nd in relative SAV abundance. It occurred throughout and was previously reported in the Preserve. Although it is regarded as a freshwater species, it is known to tolerate stable salinities up to 3.5 ppt. Myriophyllum spicatum is a native of Europe, Asia, and North Africa that has rapidly spread throughout the US. It was found at 30 sites, ranked 3rd in relative SAV abundance, and was previously reported in the Preserve. It was more abundant in Bayou Segnette and waters west of Bayou Segnette Table 1. Summary of information on the submersed aquatic plants (SAV) of Jean Lafitte National Historical Park and Preserve including new species occurrence records, non-native and native species, relative abundance based on rank order of occurrence at study sites, species intolerant of salinity levels above 0.5 ppt (freshwater species), species tolerant of salinity levels 0.5 to 3.5 ppt (not salinity-limited), and species which form large nuisance canopies. First record Rank Fresh- Not from Non- order of water salinity Forms large Species Preserve native occurrence species limited canopies Cabomba caroliniana 8 X Ceratophyllum demersum 1 X X Egeria densa X X 9 X Heteranthera dubia 7 X Hydrilla verticulata X 4 X X Myriophyllum spicatum X 3 X X Najas guadalupensis 2 X X Potamogeton pusillus X 6 X Vallisneria americana 5 X Zannichellia palustrius X 10 X 482 Southeastern Naturalist Vol. 9, No. 3 than canals in the interior of the Preserve. It is generally regarded as an invasive, nuisance species because of excessive growth that displaces native vegetation and adversely affects habitat quality. However, it appears to have become naturalized and provides habitat for fish and invertebrates and food for waterfowl. It was found at salinities ranging from 0.2 to 0.5 ppt, and is known to tolerate stable salinities as high as 20 ppt. Hydrilla verticillata is native to Asia, Africa, and Australia. It has become established in the southeastern United States including Louisiana. It was found at 25 sites and ranked 4th in relative SAV abundance and was previously reported in the Preserve. It is generally regarded as a highly invasive species that can reproduce by fragments, stolons, seeds, turions, and tubers, but does provide habitat for invertebrates and fish, and its turions and tubers provide food for water fowl. It was more abundant in the northwestern areas of the Preserve. Competition from the more abundant species listed above may have restricted its growth. We found it in salinities ranging from 0.2–0.6 ppt, but it is known to tolerate periods of increased salinity up to about 10 ppt. Vallisneria americana is a native species that occurs in fresh and brackish water habitats in southeastern Louisiana and was previously reported in the Preserve. It was found at 20 sites and ranked 5th in relative SAV abundance. It occurred in the Pipeline Canal between the Waterway and the Lower Kenta Canal, but was more abundant in lower Bayou Segnette from north of Bayou Villars to the Tarpaper Canal, where it was replaced by canopy-forming species and filamentous alga. It also occurred in protected areas along the shore of Bayou Bardeaux. Plants 1.7 m long were present in Lake Cataouatche. In the past, this large growth form was regarded as a separate species, V. neotropicalis. A concern is the possible reduction of V. americana from competition from more abundant mat-forming SAV, filamentous algae, and floating plants. The leaves of V. americana are tape or ribbon-like and it is well rooted. Unlike bushy species, V. americana does not form large surface mats. It appears to be more abundant where wave energy from wind, boat traffic, and tidal exchange limit the growth of other SAV. It provides habitat for invertebrates and fish and food for water fowl. Vegetative propagation is by buds from in-bottom rhizomes. New growth is from the base of the leaves which are more susceptible to shading after winter die-back or damage. We found it at salinities ranging from 0.3 to 0.5 ppt, but it grows well at salinities up to 5 ppt. Potamogeton pusillus is a native species that is common in fresh and slightly brackish waters in southeastern Louisiana. This is the first report of this species from the Preserve. It was found at 18 sites and ranked 6th in relative SAV abundance. It was found at salinities ranging from 0.2–0.7 ppt, but it is known to occur at salinities up to 3.5 ppt. It was more abundant in the interior canals. Although widespread, it does not form nuisance mats and is an important waterfowl forage plant. It appears to be an opportunistic species that is more abundant in late winter and early spring and decreases during the summer and fall. 2010 M.A. Poirrier, K. Burt-Utley, J.F. Utley, and E.A. Spalding 483 Heteranthera dubia occurs throughout North America and is a native species that has been previously reported in the Preserve. We found it at 14 sites, and it ranked 7th in relative SAV abundance. It was found at salinities ranging from 0.2 to 0.6 ppt, but has been reported at salinities up to 3.5 ppt. Although some large beds occurred in Lake Cataouatche, it did not occur at nuisance levels in the Preserve. It provides habitat for fish, invertebrates, and waterfowl and currently does not present a management concern. Cabomba caroliniana is a native freshwater species that occurs in eastern and central US. It is common in southeastern Louisiana and was previously reported in the Preserve. It was found at 13 interior sites east of Bayou Segnette and ranked 8th in relative SAV abundance. We found it at sites that had a salinity range of 0.3–0.4 ppt. It appears to be limited by salinities greater than 0.5 ppt. This restriction may explain its absence from western and southern areas of the Preserve. It did not produce large, nuisance colonies. Although it provides habitat for aquatic animals, it is not regarded as a food source for wildlife. Egeria densa is a South American native that has become widely naturalized in waters that include the Gulf States, but has not previously been reported in the Preserve. It was found at 4 sites and ranked 9th in relative SAV abundance. We found it at salinities ranging from 0.3 to 0.4 ppt. It was found in interior canals and ponds. Since it does not occur at salinities greater than 0.5, salinity tolerance appears to restrict its distribution. Dispersal is by plant fragmentation. Zannichellia palustris is a native species that occurs in fresh and tidal freshwaters in southeastern Louisiana. This is the first record of this species from the Preserve. We found it at one site in the interior of the preserve, and it ranked 10th in relative SAV abundance. Little is known about its ecology, but it is known to tolerate brackish water. Unpublished observations by Poirrier from other sites in southeastern Louisiana indicate that it behaves as an annual species with growth in late winter and spring and die-back during summer. This seasonal occurrence and competition from species that persist throughout the year may explain its limited distribution. Many species were abundant at nuisance levels. With the exception of V. americana, Preserve SAV was generally dominated by species with nearsurface terminal growth, which formed large surface mats that clogged waterways. This growth often included plants which were suspended near the water surface, but were not rooted. These thick mats were usually composed of C. demersum, N. guadalupensis, H. verticillata, M. spicatum, floating aquatics, and filamentous algae. These species did not dieback during winter due to the mild climate and protected waters of the Preserve. New spring growth continued from near-surface vegetation. In contrast, P. pusillus and Z. palustris behaved as annual species. In south Louisiana, they are generally present in late winter and spring, producing seeds and dying back during summer. The minimum depths of SAV occurrence ranged from near zero in protected interior canals and ponds, where abundant SAV generally extended 484 Southeastern Naturalist Vol. 9, No. 3 to the shoreline, to between 0.3 to 0.45 m in the lower Bayou Segnette Waterway, Lake Cataouatche, and Bayou Bardeaux, where wave energy from wind and boats in addition to higher water-level fluctuation contributed to near-shoreline stress. The minimum depths present in the Preserve are lower than those in estuarine water closer to the coast where stronger tides produce greater water-level fluctuations. Light availability was generally not a limiting factor for SAV growth in shallow canals and ponds where Secchi disc transparencies ranged from 0.4 to 1.2 m. Light did limit SAV growth to depths of 0.3 to 0.9 m on both banks of the Bayou Segnette Waterway, with Secchi disc transparencies ranging from 0.5 to 0.6 m. SAV did not occur at sites in upper Bayou Segnette and lower Bayou Barataria where Secchi disc visibilities were below 0.3 m. SAV was abundant in Lake Cataouatche and included H. dubia, N. guadalupensis, H. verticellata, M. spicatum, C. demersum, V. americana and P. pusillus. SAV was present at depths ranging from 0.3 to 1.7 m in Lake Cataouatche, and Secchi disc visibility there ranged from 0.3 m to being visible on the bottom at 1.7 m. SAV was absent from depths of 1.8 to 2.1 m in Lake Cataouatche. National Park Service staff and other local observers confirm that SAV abundance increased in Lake Cataouatche, Bayou Villars, and, in some years, northeastern Lake Salvador, as the operation of Davis Pond became more regular and volume increased from 2002 to the beginning of this study. The estuarine and marine management paradigm of SAV loss with nutrient introduction generally does not apply to freshwater submersed aquatics where nuisance growth often occurs with nutrient increases. The lowering of salinity to freshwater or near-freshwater levels and the movement of water through Davis Pond removing dissolved inorganic nutrients and binding them to particles which settle into the sediment are probable explanations for this increase. Freshwater ecosystems also support a diverse SAV community and numerous insect and amphibian epiphyte grazers that probably control algal overgrowth on SAV. Submersed vascular plants can out-compete algae when available nutrients are bound to sediments because they have true roots that can use sediment nutrients. Once established, SAV can decrease wave energy and increase water clarity to make habitats more suitable to persistent SAV growth. Invasive exotics may also promote SAV colonization and habitat modification to maintain SAV communities. Numerous floating plants occur in quiet Preserve canals and ponds (Nolfo-Clements 2006). They cover the water surface and through shading affect SAV abundance, distribution, and community structure. We found Salvinia molesta at 10 sites. This is the first record of this species from the Preserve. It is recognized as a noxious aquatic weed and listed on the Federal noxious weed list (USDA 2006). Based on studies by Divakaran et al. (1980), the USDA listed S. molesta as a “strictly” freshwater species. However, the lowest salinity level tested in their study was 7 ppt, which retarded growth and damaged plant tissue but did not result in mortality. Salvinia molesta was found in and around the lower Pipeline Canal and 2010 M.A. Poirrier, K. Burt-Utley, J.F. Utley, and E.A. Spalding 485 Bayou Segnette Waterway. Salinity ranged from 0.4 to 0.6 ppt and 1.2 ppt in nearby Lake Salvador, well below levels damaging to S. molesta. Unlike most other floating aquatics that are stressed by brackish water, S. molesta is not salinity-limited in the Preserve. In conclusion, the Preserve supports a diverse SAV community, and the Davis Pond Diversion seems to be increasing SAV abundance in most of the Preserve. Filamentous algae and native and exotic floating aquatics are also increasing but shade true SAV. This increased production could be regarded as a stage in wetland plant restoration or considered an unwanted shift in habitat type that interferes with recreational fishing and boating. A major concern is the spread of Salvinia molesta throughout the Preserve and the potential damage to SAV and general habitat quality for fish and wildlife. Vallisneria americana may be decreasing due to competition from floating aquatics and nuisance SAV. Acknowledgments This study was funded by the National Park Service, US Department of the Interior, PMIS #3862. 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