Exotic Macrophyte Research Articles

A Comparison of Macroinvertebrate and Epiphyte Density and Diversity on Native and Exotic Complex Macrophytes in Three Vermont Lakes

Abstract Invasion of New England lakes by exotic macrophytes can alter trophic interactions if the invaders host macroinvertebrate and epiphyte communities different from those of the native species they replace. Macroinvertebrate density and diversity appears to increase with macrophyte complexity and epiphytic algae colonization, which are also positively correlated. Because of this confounding effect, we investigated native and exotic macrophyte species of similar complexity in order to answer the question: Does the exotic macrophyte Myriophyllum spicatum have lower epiphyte density and richness that results in lower macroinvertebrate density and diversity than those found on a native species of similar complexity? Using independent-sample t-tests, we investigated this question in mixed macrophyte stands of three Vermont lakes. Holding complexity constant, macroinvertebrate density and diversity was positively related with epiphyte density and richness (r 2 = 0.17 and 0.13, respectively). Generally, M....

Asexual propagations of introduced exotic macrophytes Elodea nuttallii, Myriophyllum aquaticum, and M. propinquum are improved by nutrient-rich sediments in China

An increasing number of recent studies indicate that multiple interacting factors can affect the invasion of plants. However, few studies have focused on asexual propagation and the interaction of propagation with environmental factors that regulate the invasive potential of introduced exotic species in aquatic habitats. This study was designed to investigate the differences in asexual propagation between introduced exotic and non-invasive native aquatic macrophytes in nutrient-poor and nutrient-rich sediments and to test the hypothesis that differences in asexual propagation (stem fragment production) and propagule establishment between introduced exotic and non-invasive native macrophytes are driven by sediment nutrient levels. Three exotic aquatic macrophytes (Elodea nuttallii, Myriophyllum aquaticum, and M. propinquum) recently introduced to China and their non-invasive native counterparts (Hydrillaverticillata, M. oguraense, and M. ussuriense) were used for comparison in nutrient-poor (TN 0.59 and TP 0.03 mg g−1) and nutrient-rich (TN 2.35 and TP 0.10 mg g−1) sediments. After 8 weeks of growth, the exotic species tended to produce more total biomass, branch biomass and apical shoots and have higher relative growth rate (RGR) than their native counterparts in nutrient-rich sediment. Rooting efficiency and root growth of exotic fragments were higher than that of native counterparts in nutrient-rich sediment, although the survival rates of fragments did not differ between native and exotic species. In addition, superior traits (rooting efficiency and root growth) of exotic species were also observed in nutrient-poor sediment, but to a lesser degree than in nutrient-rich sediment. These results suggest that asexual propagation of these three introduced exotic macrophytes is more effective in nutrient-rich sediment than in nutrient-poor sediment in China.

COMPARATIVE ANALYSIS OF EPIPHYTIC FORAMINIFERA IN SEDIMENTS COLONIZED BY SEAGRASS POSIDONIA OCEANICA AND INVASIVE MACROALGAE CAULERPA SPP.

Mediterranean shallow-water soft bottoms are characterized by extensive meadows of the endemic seagrass Posidonia oceanica (L.) Delile that support abundant benthic biota including numerous epiphytic foraminiferal taxa. The biomass of the epiphytic communities varies with the P. oceanica cycle, especially influencing those taxa with higher abundances in summer, when the foliar surface is maximum. During the past decades exotic macrophyte species have invaded habitats formerly dominated by P. oceanica . Two of these taxa are the green algae Caulerpa taxifolia (Vahl) Agardh, 1817 and C. racemosa (Forsskal) Agardh, 1873, that, along with the non-invasive C. prolifera (Forsskal) Lamouroux, 1809, produce defensive, secondary metabolites such as caulerpenyne that affects turnover rates of P. oceanica leaves. As a consequence of different architectural features of the algal substrate, replacement of P. oceanica by Caulerpa spp. results in the change from a complex three-dimensional, long duration substrate into a simpler, two-dimensional one with a shorter life span. Epiphytic foraminifers can be clustered into functional groups according to their shape, structure, behavior and life span. The foraminiferal dead assemblage includes a total of 110 species, that included 43 species in sediments colonized by P. oceanica , 82 species in sediments with C. prolifera , 78 in sediments invaded by C. taxifolia , and 55 in sediments invaded by C. racemosa . Taxonomic composition of all assemblages is similar, though differences occur in the relative abundance of each taxon. Sediments in P. oceanica meadows are characterized by flat, encrusting, long life-span species (e.g., Planorbulina mediterranensis d’Orbigny, 1826), whereas in Caulerpa spp. habitat, temporarily motile, shorter life-span taxa (e.g., Lobatula lobatula (Walker and Jacob, 1798) and Rosalina bradyi Cushman, 1915) tend to dominate. Multivariate analysis shows that only the thanathocoenosis of P. oceanica sediments is representative of the P. oceanica epiphytic foraminiferal assemblage ( Planorbulinatum medi-terranensae Colom, 1942). Hence, differences among the foraminiferal assemblages in sediments colonized by different phytal substrates occur prior to taphonomic and dissolution processes and may be applicable to paleoecological interpretations.

Abundance and habitat use of juvenile sunfish among different macrophyte stands

Collingsworth, PD and Kohler, CC. 2010. Abundance and habitat use of juvenile sunfish among different macrophyte stands. Lake Reserv. Manage. 26:35-42. Juvenile Lepomis sunfish (< 75 mm total length, TL) density, plant stem density and invertebrate density were compared in the 3 most common habitats in the littoral zone of Cedar Lake, a Midwestern North American reservoir: nonvegetated areas, stands of the exotic macrophyte Eurasian watermilfoil (Myriophyllum spicatum) and stands of American pondweed (Potomogeton nodosus). Eurasian watermilfoil stands consistently had significantly higher stem density and invertebrate density than American pondweed stands. Juvenile sunfish densities were significantly higher in vegetated habitats than nonvegetated areas, but no significant differences were observed between the 2 vegetated habitats. Juvenile sunfish densities were initially higher in American pondweed stands than Eurasian watermilfoil stands, but fish density in American pondweed stands declined dramatically as water levels fell in autumn. Juvenile sunfish size structure was related to habitat type, with the smallest fish associated with Eurasian watermilfoil (38.2 mm TL), intermediate fish associated with American pondweed (43.1 mm TL), and the largest fish associated with nonvegetated habitats (51.2 mm TL). We suggest resource agencies should focus vegetation management efforts on eradicating Eurasian watermilfoil stands to provide foraging access for largemouth bass to improve their growth rate and reduce stunting of sunfish. However, management agencies must recognize that a healthy plant community below the depth of water level fluctuation may be the only source of cover for juvenile centrarchids during late summer in reservoirs prone to fluctuating water levels.

Using Macrophytes in Urban Stream Rehabilitation: A Cautionary Tale

Abstract Native macrophytes were transplanted into a small urban stream as part of a rehabilitation program, that also meandered the previously channeled stream, naturalized stream banks, and planted native riparian vegetation. Transplanted macrophytes minimized spread of introduced macrophytes and were viewed beneficially by residents, as was the stream rehabilitation. We transplanted the native macrophyte Myriophyllum triphyllum into five larger streams dominated by exotic macrophytes—some of which were weeded prior to transplanting—to see whether Myriophyllum could prevent regrowth of weeded plants. Transplanted Myriophyllum plants were washed away in two streams, reflecting high shear stresses there. Myriophyllum cover in the other streams decreased as weeded plants regrew. Our attempt at eliminating exotic macrophytes in patches in large streams was unsuccessful. Furthermore, council authorities weeded other experimental sections following complaints from residents of excess macrophyte growth. This problem highlighted conflicting multiple values placed on urban streams by managers and the public. A repeat survey of residents living near the original rehabilitated stream showed that many respondents were now critical of excessive plant growth—both in‐stream and riparian. A recurring comment made concerned the apparent lack of maintenance to the stream, giving it an untidy appearance. Difficulties with propagating and transplanting native macrophytes into larger streams, coupled with a negative perception of native vegetation (both in‐stream and riparian) if it looks unmanaged, suggest that planting macrophytes or riparian plants as part of urban stream rehabilitation programs may be more problematic than realized.

Temporal trends and effects of diversity on occurrence of exotic macrophytes in a large reservoir

Two exotic invasive macrophyte species (the emergent Urochloa subquadripara - tenner-grass - and the submersed Hydrilla verticillata - hydrilla) were investigated in a large sub-tropical reservoir. We analyzed their occurrences over an extended period and tested the hypothesis that macrophyte richness decreases their invasibility. The alternative hypothesis that the occurrence of these exotics is affected by fetch and underwater radiation (important determinants of macrophyte assemblage composition in this reservoir) was also tested. Incidence data (presence/absence) was obtained over 9.5 years at 235 stations. Logistic regression was applied to test whether the likelihood of occurrence of these two species was affected by macrophyte richness, fetch or underwater radiation. Tenner-grass was recorded at a high frequency and quickly recovered from disturbances caused by water drawdown. In contrast, H. verticillata was first recorded in 3 sites in January 2007, but it spread quickly, reaching 30.5% of the sites 19 months later. The main channel of the Paraná River was the main source of propagules for this species. The likelihood of occurrence of tenner-grass was positively affected by macrophyte richness but negatively affected by fetch. Thus, wave disturbance is probably more important than diversity in preventing invasion by this species. Hydrilla, by contrast, was negatively affected by macrophyte richness and positively affected by fetch and underwater radiation. Although this result might indicate that macrophyte diversity prevents hydrilla invasion, this is probably not true because hydrilla colonized deeper sites where few species of plant exist. Resistance to disturbances caused by water drawdown (tenner-grass) and waves (hydrilla) as well as persistency of tenner-grass and fast spread of hydrilla make these exotic species a cause for concern because of their potential impacts on water uses and maintenance of diversity.

Epiphytic macroinvertebrate communities on Eurasian watermilfoil (Myriophyllum spicatum) and native milfoils Myriophyllum sibericum and Myriophyllum alterniflorum in eastern North America

Aquatic macrophytes play an important role in the survival and proliferation of invertebrates in freshwater ecosystems. Epiphytic invertebrate communities may be altered through the replacement of native macrophytes by exotic macrophytes, even when the macrophytes are close relatives and have similar morphology. We sampled an invasive exotic macrophyte, Eurasian watermilfoil ( Myriophyllum spicatum ), and native milfoils Myriophyllum sibericum and Myriophyllum alterniflorum in four bodies of water in southern Quebec and upstate New York during the summer of 2005. Within each waterbody, we compared the abundance, diversity, and community composition of epiphytic macroinvertebrates on exotic and native Myriophyllum. In general, both M. sibericum and M. alterniflorum had higher invertebrate diversity and higher invertebrate biomass and supported more gastropods than the exotic M. spicatum. In late summer, invertebrate density tended to be higher on M. sibericum than on M. spicatum, but lower on M. alterniflorum than on M. spicatum. Our results demonstrate that M. spicatum supports macroinvertebrate communities that may differ from those on structurally similar native macrophytes, although these differences vary across sites and sampling dates. Thus, the replacement of native milfoils by M. spicatum may have indirect effects on aquatic food webs.

An Experimental Simulation of an Exotic Aquatic Macrophyte Invasion and Its Influence on Foraging Behavior of Bluegill

ABSTRACT We investigated the hypothesis that a shift from a native aquatic plant bed to an exotic invasive Hydrilla verticillata (hydrilla) plant bed would alter spatial complexity and light transmittance and therefore alter Lepomis macrochirus (bluegill) foraging success. Experimental treatments included: (i) intermediate densities of native-mixed plants and (ii) 50% native—50% hydrilla, (iii) hydrilla, (iv) high density of hydrilla, and (v) no plants. Spatial complexity and light transmittance were influenced by increasing the homogeneity of hydrilla in vegetated aquatic habitat. In addition, bluegill foraging efficiency was affected negatively by increasing spatial complexity of a hydrilla dominated habitat. As a result bluegill searched faster, exhibited 60% more mean foraging bouts, and recognized 38% more food items in a native diverse habitat versus a hydrilla dominated habitat.

Long‐term changes in abundance and diversity of macrophyte and waterfowl populations in an estuary with exotic macrophytes and improving water quality

We assessed species‐specific coverage (km2) of a submerged aquatic vegetation (SAV) community in the fresh and upper oligohaline Potomac Estuary from 1985 to 2001 using a method combining field observations of species‐proportional coverage data with congruent remotely sensed coverage and density (percent canopy cover) data. Biomass (estimated by density‐weighted coverage) of individual species was calculated. Under improving water quality conditions, exotic SAV species did not displace native SAV; rather, the percent of natives increased over time. While coverage‐based diversity did fluctuate and increased, richness‐based community turnover rates were not significantly different from zero. SAV diversity was negatively related to nitrogen concentration. Differences in functional traits, such as reproductive potential, between the dominant native and exotic species may explain some interannual patterns in SAV. Biomass of native, as well as exotic, SAV species varied with factors affecting water column light attenuation. We also show a positive response by a higher trophic level, waterfowl, to SAV communities dominated by exotic SAV from 1959 to 2001.

A novel epiphytic cyanobacterium associated with reservoirs affected by avian vacuolar myelinopathy

Avian vacuolar myelinopathy (AVM) is a newly discovered bird disease, which is killing bald eagles ( Haliaeetus leucocephalus) and waterfowl in the southeastern United States. Surveys were conducted to investigate exotic macrophytes (e.g. Hydrilla verticillata) as a substrate for attachment by toxic cyanobacteria that may be associated with the incidence of AVM. While the specific cause of the disease has not been confirmed, one hypothesis is that birds ingest a neurotoxin produced by cyanobacteria epiphytic on macrophytes. A strong relationship was found between the field abundance of a specific undescribed epiphytic cyanobacterium and the incidence of AVM. The undescribed species is a filamentous, heterocystous, true branching cyanobacterium. Morphological characteristics place the cyanobacterium in section V, order Stigonematales. The 16S rRNA sequence identity was determined from environmental isolates of this unknown Stigonematalan species using DGGE (denaturing gradient gel electrophoresis). The 16S rRNA sequence data were aligned with additional cyanobacteria sequences to determine designations for probe development, to lay groundwork for its formal description and to advance understanding of the species’ phylogeny. Real-time PCR assays were developed for rapid, specific detection of the Stigonematales species from environmental samples. The genetic probe produced by this study will help test the hypothesized link between these cyanobacteria and AVM, and therefore help guide decisions on managing hydrilla and other invasive macrophytes in AVM-affected waters.

An experimental system to study ecophysiological responses of submerged macrophytes to temperature and light

An experimental growth system was devised to study the ecophysiological responses of submerged macrophytes to temperature and light. Using the system, a pilot study was conducted to compare responses to light of three representative species common to the littoral zone of Lake Biwa: Vallisneria asiatica Miki var. biwaensis Miki, which is endemic to Japan, Potamogeton maackianus A. Benn., a dominant submerged macrophyte in Lake Biwa, and Elodea nuttallii (Planch.) St. John, one of the most influential submerged exotic macrophytes naturalized in Japan. Different relative growth rate responses and other growth parameters among the species were observed. We ascertained the experimental system to be useful for the comparison of ecophysiological responses of submerged macrophytes.

Effects of the exotic macrophyte, para grass (Urochloa mutica), on benthic and epiphytic macroinvertebrates of a tropical floodplain

SUMMARY1. We examined the effect of the exotic macrophyte, para grass (Urochloa mutica), on benthic and epiphytic macroinvertebrates of a tropical floodplain in northern Australia. Macroinvertebrates were sampled from four grass communities: (1) para grass, (2) hymenachne (Hymenachne acutigluma), a native perennial; (3) rice (Oryza meridionalis), a native annual, and (4) areas where para grass had been sprayed with herbicide.2. Macroinvertebrate richness, abundance and community similarity showed very few differences among the grass communities, particularly in the epiphytic habitat. Benthic invertebrates showed some differences among grasses, with lower richness and abundance and different community structure associated with hymenachne. Herbicide control of para grass had no apparent effect on benthic invertebrates but reduced the abundance of epiphytic invertebrates in the short term.3. The results of this study indicate that para grass has very little impact on macroinvertebrate communities, despite the changes to macrophyte communities. This is probably because para grass has similar physical structure to the native grasses and because none of these grasses contribute directly to aquatic food webs. Control of para grass using herbicide has little impact on aquatic invertebrates. This suggests that predicting the impact of weed invasion in wetlands requires an understanding of both the functional properties of macrophytes and the habitat preferences of the macroinvertebrates.

Secondary production of Apedilum elachistum townes (Diptera: Chironomidae) in simulated reservoir wetlands

The chironomid fauna living on an exotic macrophyte, Eurasian water milfoil (Myriophyllum spicatum), was studied quantitatively for a year in experimental ponds constructed to simulate reservoir wetlands. A total of 10 species, 2 Orthocladiinae, 5 Chironominae, and 3 Tanypodinae, were recorded. Of these 10 chironomid species, Apedilum elachistum comprised 79% of all chironomid larvae collected on the plants. Annual production of A. elachistum was estimated by the size-frequency method to be 9.9 g dry mass/m2/yr for milfoil surface area, which is among the highest production estimates reported for a single species. Annual production/biomass was 79/yr. Laboratory-reared larvae required an average of 23 days at 15°, 16 days at 20°, and 11 days at 25 °C to complete their development from first instar to imago.

Plant architecture and epiphytic macroinvertebrate communities: the role of an exotic dissected macrophyte

AbstractThe abundance of epiphytic macroinvertebrates on aquatic macrophytes can be influenced by different plant architecture types. For example, dissected plants can provide epiphytic macroinvertebrates more substrate for foraging and more cover from predators than undissected plants. Large changes in macrophyte community composition have the potential to strongly influence whole-lake macroinvertebrate abundance if overall plant architecture changes. For example, when the exotic macrophyte Eurasian watermilfoil (Myriophyllum spicatum L., EWM), a dissected plant, invades a lake and becomes dominant, fundamental changes in lake-wide plant architecture occur. We conducted a 6-lake field study and a meta-analysis to examine whether macroinvertebrate density and biomass varies predictably with plant architecture and, if so, whether these relationships are evident at the whole-lake scale when EWM dominates the plant community. We found that higher macroinvertebrate densities and biomass per g of plant were as...

Effects of Macrophyte Bed Architecture on Largemouth Bass Foraging: Implications of Exotic Macrophyte Invasions

Invasive, canopy-forming macrophyte species such as Eurasian watermilfoil Myriophyllum spicatum and hydrilla Hydrilla verticillata are now widespread throughout North American lakes and reservoirs. However, their effects on economically and ecologically important species such as largemouth bass Micropterus salmoides are insufficiently understood. Canopy-forming exotic macrophytes typically displace structurally diverse native macrophytes. In aquaria, we tested whether exotic macrophyte canopies negatively affect age-0 largemouth bass foraging success compared with diverse macrophyte assemblages. In addition, we explored the relative effects of macrophyte density, and prey density of bluegills Lepomis macrochirus on largemouth bass foraging success. Bluegill prey density did not significantly affect largemouth bass foraging success. However, largemouth bass experienced shorter search times and greater attack and consumption rates in moderate plant density treatments (compared with dense) and diverse plant treatments (compared with canopy monocultures). Effects of macrophyte density and architecture (diverse versus canopy monoculture) on largemouth bass foraging success were similar in magnitude. Our results indicate that among lakes, the relative importance of macrophyte density and architecture to largemouth bass foraging will depend upon the extent to which each factor influences structural complexity.

A Sea Under Siege – Alien Species in the Mediterranean

Exotic macrophytes, invertebrates and fish are found in most coastal habitats in the Mediterranean Sea. The Mediterranean Sea has been subjected to introductions of non-indigenous species by ship traffic since the opening of interoceanic maritime routes five centuries ago. The Sea, a hub of shipping, is exceptionally susceptible to invaders that arrive in fouling communities or ballast. The Suez Canal has been the largest pathway for the entry of these species: more than 300 Erythrean species – principally molluscs, fish, decapod crustaceans, polychaetes and algae – have become established in the eastern Mediterranean, primarily along the Levantine coasts. Mariculture of nonindigenous shellfish predominates in the northern Mediterranean lagoonar environments. Unrestricted transport of commercially important exotic shellfish has resulted in numerous unintentional introductions of pathogens, parasites and pest species. Some invaders have outcompeted or replaced native species locally, severely reducing biodiversity; some other invaders are so abundant they are exploited commercially. The rate of these biotic invasions has increased in recent decades, and they collectively have significant ecological and economic impacts in the Mediterranean Sea.

Habitat characterization of Texas wild‐rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River, TX, USA

1. The habitat of Texas wild-rice (Zizania texana Hitchcock), known only from the spring-fed upper San Marcos River in Central Texas, was classified in terms of physical and chemical conditions, depth, current velocity, associated aquatic macrophytes, and substrate composition. 2. Randomly selected transects in sites with and without Texas wild-rice were evaluated during May, August and January 1994–1995. Physical and chemical conditions (temperature, dissolved oxygen, specific conductance, pH) were found to be nearly constant and uniform both among transect types and sampling dates. Chemical analysis of the substrate likewise showed few differences among transect types. Turbidity was found to be significantly different among transect types on only one sampling date (Kα0.05=0.60; p=0.009), but even non-significant levels of turbidity may present biologically significant impacts to wild-rice plants. 3. Differences in substrate particle size were highly significant (Kα0.05=0.71; p=0.001) with Texas wild-rice occupying sites having moderately coarse to coarse sandy soils (73%) compared with the moderately fine to fine clay soils found at non-rice sites (82%). However, no significant differences were found in organic matter content among rice and non-rice transects (=2.09 and 2.56%, respectively). 4. Texas wild-rice was found primarily in shallow areas of the river (<1 m) and at higher current velocities than those of non-rice sites (≥0.46 m s−1 and ≤0.22 m s−1, respectively). 5. Texas wild-rice appears to be more commonly associated with other native species rather than exotic species. Mean percentage composition of exotic macrophytes did not exceed 29% in areas where Texas wild-rice grew, but they accounted for nearly 47% of the composition in areas where rice did not grow. 6. The results of this study will allow for reliable and accurate identification of the remaining suitable habitat of Texas wild-rice in the San Marcos River for possible reintroduction and development of management plans. Copyright © 1999 John Wiley & Sons, Ltd.

Habitat characterization of Texas wild-rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River, TX, USA

1. The habitat of Texas wild-rice (Zizaniatexana Hitchcock), known only from the spring-fed upper San Marcos River in Central Texas, was classified in terms of physical and chemical conditions, depth, current velocity, associated aquatic macrophytes, and substrate composition. 2. Randomly selected transects in sites with and without Texas wild-rice were evaluated during May, August and January 1994–1995. Physical and chemical conditions (temperature, dissolved oxygen, specific conductance, pH) were found to be nearly constant and uniform both among transect types and sampling dates. Chemical analysis of the substrate likewise showed few differences among transect types. Turbidity was found to be significantly different among transect types on only one sampling date (Kα0.05=0.60; p=0.009), but even non-significant levels of turbidity may present biologically significant impacts to wild-rice plants. 3. Differences in substrate particle size were highly significant (Kα0.05=0.71; p=0.001) with Texas wild-rice occupying sites having moderately coarse to coarse sandy soils (73%) compared with the moderately fine to fine clay soils found at non-rice sites (82%). However, no significant differences were found in organic matter content among rice and non-rice transects (=2.09 and 2.56%, respectively). 4. Texas wild-rice was found primarily in shallow areas of the river (<1 m) and at higher current velocities than those of non-rice sites (≥0.46 m s−1 and ≤0.22 m s−1, respectively). 5. Texas wild-rice appears to be more commonly associated with other native species rather than exotic species. Mean percentage composition of exotic macrophytes did not exceed 29% in areas where Texas wild-rice grew, but they accounted for nearly 47% of the composition in areas where rice did not grow. 6. The results of this study will allow for reliable and accurate identification of the remaining suitable habitat of Texas wild-rice in the San Marcos River for possible reintroduction and development of management plans. Copyright © 1999 John Wiley & Sons, Ltd.

Comparison of fish assemblages associated with native and exotic submerged macrophytes in the Lake Pontchartrain estuary, USA

Since the exotic Eurasian milfoil Myriophyllum spicatum (L.) was first reported in the Lake Pontchartrain estuary in 1978, it has become established as a dominant species of submerged macrophyte, but its distribution and abundance have varied considerably. We compared fish assemblages among two native macrophytes, Vallisneria americana (Michx) and Ruppia maritima (L.), the exotic M. spicatum, and unvegetated substratum to determine if milfoil influenced assemblage structure and microhabitat use by common littoral fishes. We used a modified Wegener ring to quantitatively assess fish densities. In monthly sampling from March 1991 to January 1993, we collected 3564 fishes of 29 species, but four dominant species, rainwater killifish Lucania parva (Baird), naked goby Gobiosoma bosc (Lacepede), gulf pipefish Syngnathus scovelli (Evermann and Kendall), and clown goby Microgobius gulosus (Girard) accounted for over 87% of the fishes. Community diversity was highest in V. americana, intermediate in unvegetated areas, and lowest in R. maritima and M. spicatum. The patterns for evenness and richness differed from that of diversity among the four habitat types. Analyses of percent similarity and rank correlation of community structure showed no significant differences between M. spicatum and native macrophytes. The common fishes were significantly more abundant in vegetated areas than on adjacent unvegetated substratum, and total abundances were higher in M. spicatum and R. maritima than in V. americana. Only three fishes showed significant differences among macrophyte species: rainwater killifish and clown goby were more abundant in M. spicatum and R. maritima, and bay anchovy Anchoa mitchilli (Valenciennes) was more abundant in M. spicatum than in V. americana. Additionally, fish abundances were related to environmental variables in a factor analysis that resolved nine variables into four axes, characterized in order of importance as: a large-scale spatial (salinity) axis, a seasonal axis, a turbidity axis, and a plant surface area axis. The different patterns of fish species in environmental space revealed spatial and temporal differences in resource utilization. The exotic macrophyte M. spicatum may not have had a detectable influence on fish assemblages or abundances relative to the native macrophytes because high wave energy in the open system may prevent it from growing densely enough to strongly alter microhabitat characteristics.

Spatial and temporal patterns of sediment and nutrient accumulation in shallow lakes of the Upper St. Johns River Basin, Florida

We used paleolimnological methods to investigate spatial and temporal patterns of bulk sediment and nutrient (C, N, P) accumulation in Lakes Hell ‘n’ Blazes (A = 154 ha, zmax = 240 cm), Sawgrass (A = 195 ha, zmax = 157 cm) and Washington (A = 1766 ha, zmax = 322 cm), in the Upper St. Johns River Basin, Florida. The study was designed to evaluate long-term changes in sedimentation and nutrient storage in the basin, and was one component of a larger project addressing flood control, wetland restoration, and water quality improvement. These three study lakes are wide, shallow waterbodies in the upper reaches of the St. Johns River channel. Sediment mapping indicates soft, organic deposits are distributed uniformly throughout Lakes Hell ‘n’ Blazes and Sawgrass. In contrast, much of Lake Washington is characterized by sandy bottom, and organic sediment is largely restricted to the north end of the lake. Lakes Hell ‘n’ Blazes and Sawgrass are effective sediment traps because dense submersed macrophytes and their associated epiphytes reduce flow velocity, intercept suspended particles, and utilize dissolved nutrients. Abundant Hydrilla, combined with short fetch, prevents resuspension and downstream transport of sediments. Larger Lake Washington is probably wind-mixed and resuspended organic sediments are redeposited to downstream sites. 210Pb-dated sediment cores show that organic sediment accumulation began in all three lakes before 1900, but that bulk sediment and nutrient accumulation rates have generally increased since then. The increases are probably attributable, in part, to anthropogenic activities including 1) hydrologic modifications that reduced flow rates in the channel, 2) discharge of nutrient-rich waters from urban, agricultural and ranching areas, and, 3) introduction and periodic herbicide treatment of the exotic macrophytes Eichhornia and Hydrilla.