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USGS2011

Estimating site occupancy rates for aquatic plants using spatial sub-sampling designs when detection probabilities are less than one

Estimation of site occupancy rates when detection probabilities are <1 is well established in wildlife science. Data from multiple visits to a sample of sites are used to estimate detection probabilities and the proportion of sites occupied by focal species. In this article we describe how site occupancy methods can be applied to estimate occupancy rates of plants and other sessile organisms. We illustrate this approach and the pitfalls of ignoring incomplete detection using spatial data for 2 aquatic vascular plants collected under the Upper Mississippi River's Long Term Resource Monitoring Program (LTRMP). Site occupancy models considered include: a naïve model that ignores incomplete detection, a simple site occupancy model assuming a constant occupancy rate and a constant probability of detection across sites, several models that allow site occupancy rates and probabilities of detection to vary with habitat characteristics, and mixture models that allow for unexplained variation in detection probabilities. We used information theoretic methods to rank competing models and bootstrapping to evaluate the goodness-of-fit of the final models. Results of our analysis confirm that ignoring incomplete detection can result in biased estimates of occupancy rates. Estimates of site occupancy rates for 2 aquatic plant species were 19–36% higher compared to naive estimates that ignored probabilities of detection <1. Simulations indicate that final models have little bias when 50 or more sites are sampled, and little gains in precision could be expected for sample sizes >300. We recommend applying site occupancy methods for monitoring presence of aquatic species.

Aquatic Botany↗

USGS2012

Will inundation and salinity levels associated with projected sea level rise reduce the survival, growth, and reproductive capacity of Sarcocornia pacifica (pickleweed)?

In the San Francisco Bay Estuary, CA, USA, sea level rise (SLR) is projected to increase by 1.4 m during the next 90 years resulting in increased inundation and salt water intrusion up-estuary. Since inundation and salinity are critical factors that drive vegetation structure and composition in coastal wetlands, we asked whether inundation and salinity levels associated with SLR would reduce the survival, growth, and reproductive capacity of a dominant halophyte, Sarcocornia pacifica (pickleweed). We conducted a 4 × 4 factorial greenhouse experiment to examine the effects of a range of inundation periods (25, 50, 75, and 100%) and water salinities (0, 10, 20, 30 psu) on individual S. pacifica adults and seedlings. We found that inundation and salinity treatments affected the height of adults and seedlings combined. When examined separately, adult height was negatively affected by inundation ≥75%, while seedling height was affected by the interaction of both inundation and salinity. Adult belowground biomass was negatively affected by complete inundation. Seedling aboveground biomass decreased 46% at the highest salinity (30 psu) and belowground biomass decreased at salinities ≥20 psu. Adult flower production was not affected by treatments but was reduced by 38% at 30 psu salinity for seedlings. While adult survival was 99%, seedling survival was 56% with greatest mortality at low (25%) inundation, possibly because their roots were more susceptible to desiccation. Vegetation structure of the marsh platform comprised of S. pacifica adults will be susceptible to greater inundation rates associated with SLR. Our results suggest that adults may grow less tall, thus altering the vegetation structure and likely the tidal marsh wildlife that rely on these habitats.

Aquatic Botany↗

USGS2013

Environmental clustering of lakes to evaluate performance of a macrophyte index of biotic integrity

Proper classification of sites is critical for the use of biological indices that can distinguish between natural and human-induced variation in biological response. The macrophyte-based index of biotic integrity was developed to assess the condition of Minnesota lakes in relation to anthropogenic stressors, but macrophyte community composition varies naturally across the state. The goal of the study was to identify environmental characteristics that naturally influence macrophyte index response and establish a preliminary lake classification scheme for biological assessment (bioassessment). Using a comprehensive set of environmental variables, we identified similar groups of lakes by clustering using flexible beta classification. Variance partitioning analysis of IBI response indicated that evaluating similar lake clusters could improve the ability of the macrophyte index to identify community change to anthropogenic stressors, although lake groups did not fully account for the natural variation in macrophyte composition. Diagnostic capabilities of the index could be improved when evaluating lakes with similar environmental characteristics, suggesting the index has potential for accurate bioassessment provided comparable groups of lakes are evaluated.

Minnesota↗

USGS2014

Aquatic CAM photosynthesis: a brief history of its discovery

Aquatic CAM (Crassulacean Acid Metabolism) photosynthesis was discovered while investigating an unrelated biochemical pathway concerned with anaerobic metabolism. George Bowes was a significant contributor to this project early in its infancy. Not only did he provide me with some valuable perspectives on peer review rejections, but by working with his gas exchange system I was able to take our initial observations of diel fluctuations in malic acid to the next level, showing this aquatic plant exhibited dark CO2 uptake. CAM is universal in all aquatic species of the worldwide Lycophyta genus Isoetes and non-existent in terrestrial Isoetes. Outside of this genus aquatic CAM has a limited occurrence in three other families, including the Crassulaceae. This discovery led to fascinating adventures in the highlands of the Peruvian Andes in search of Stylites, a terrestrial relative of Isoetes. Stylites is a plant that is hermetically sealed from the atmosphere and obtains all of its carbon from terrestrial sources and recycles carbon through CAM. Considering the Mesozoic origin of Isoetes in shallow pools, coupled with the fact that aquatic Isoetes universally possess CAM, suggests the earliest evolution of CAM photosynthesis was most likely not in terrestrial plants.

Aquatic Botany↗

USGS2015

Responses to water depth and clipping of twenty−three plant species in an Indian monsoonal wetland

Responses of species to disturbances give insights into how species might respond to future wetland changes. In this study, species of monsoonal wetlands belonging to various functional types (graminoid and non−graminoid emergents, submersed aquatic, floating−leaved aquatic) varied in their growth responses to water depth and harvesting. We tested the effects of water depth (moist soil, flooded) and clipping (unclipped, and clipped) on the biomass and longevity of twenty−three dominant plant species of monsoonal wetlands in the Keoladeo National Park, India in a controlled experiment. With respect to total biomass and survival, six species responded positively to flooding and twelve species responded negatively to clipping. Responses to flooding and clipping, however, sometimes interacted. Individualistic responses of species to water levels and clipping regimes were apparent; species within a functional group did not always respond similarly. Therefore, detailed information on the individualistic responses of species may be needed to predict the vegetation composition of post−disturbance wetlands. In particular, as demands for fresh water increase around the world, studies of life history constraints and responses to hydrological changes will aid wetland managers in developing strategies to conserve biodiversity.

Keoladeo National Park↗

USGS2015

Nutrient-enhanced decomposition of plant biomass in a freshwater wetland

We studied soil decomposition in a Panicum hemitomon (Schultes)-dominated freshwater marsh located in southeastern Louisiana that was unambiguously changed by secondarily-treated municipal wastewater effluent. We used four approaches to evaluate how belowground biomass decomposition rates vary under different nutrient regimes in this marsh. The results of laboratory experiments demonstrated how nutrient enrichment enhanced the loss of soil or plant organic matter by 50%, and increased gas production. An experiment demonstrated that nitrogen, not phosphorus, limited decomposition. Cellulose decomposition at the field site was higher in the flowfield of the introduced secondarily treated sewage water, and the quality of the substrate (% N or % P) was directly related to the decomposition rates. We therefore rejected the null hypothesis that nutrient enrichment had no effect on the decomposition rates of these organic soils. In response to nutrient enrichment, plants respond through biomechanical or structural adaptations that alter the labile characteristics of plant tissue. These adaptations eventually change litter type and quality (where the marsh survives) as the % N content of plant tissue rises and is followed by even higher decomposition rates of the litter produced, creating a positive feedback loop. Marsh fragmentation will increase as a result. The assumptions and conditions underlying the use of unconstrained wastewater flow within natural wetlands, rather than controlled treatment within the confines of constructed wetlands, are revealed in the loss of previously sequestered carbon, habitat, public use, and other societal benefits.

Louisiana↗

USGS2017

Ecology of the macrophyte Podostemum ceratophyllum Michx. (Hornleaf riverweed), a widespread foundation species of eastern North American rivers

Podostemum ceratophyllum , commonly called Hornleaf Riverweed, occurs in mid-order montane and piedmont rivers of eastern North America, where the plant grows submerged and attached to rocks and stable substrates in swift, aerated water. Multiple studies, mostly conducted in the southern portions of the plant’s range, have shown that Podostemum can variously influence benthic communities in flowing waters. However, a synthetic review of the biology and ecology of the plant is needed to inform conservation, particularly because P. ceratophyllum is reported to be in decline in much of its range, for mostly unknown reasons. We have thus summarized the literature showing that Podostemum provides substantial habitat for invertebrates and fish, may be consumed by invertebrates, turtles, and other vertebrates, removes and sequesters dissolved elements (i.e., nitrogen, phosphorus, calcium, zinc, etc.) from the water column, and contributes organic matter to the detrital pool. Podostemum may be tolerant to some forms of pollution but appears vulnerable to sedimentation, epiphytic over-growth, and hydrologic changes that result in desiccation, and possibly increased herbivory pressure. Much remains unknown about Podostemum , including aspects of morphological variation, seed dispersal, and tolerance to changes in temperature and water chemistry. Nonetheless, Podostemum may be considered a foundation species, whose loss from eastern North American rivers is likely to affect higher trophic levels and ecosystem processes.

Aquatic Botany↗

USGS2018

Submerged aquatic vegetation mapping in coastal Louisiana through development of a spatial likelihood occurrence (SLOO) model

Determining the spatial distribution of coastal foundation species is essential to accurately determine restoration goals, predict the ecological effects of climate change, and develop habitat management strategies. Mapping the distribution of submerged aquatic vegetation (SAV) species assemblages, which provide important habitat resource and ecological services in Louisiana, has been difficult due to the dynamic nature of SAV occurrence and the limited water clarity across much of the coast. Species distribution models (SDMs) link ecological conditions species occurrence across landscapes, and can predict the distribution of species across un-sampled or hard to sample areas and support the development of habitat maps. To predict SAV distribution in coastal Louisiana, a SDM was developed and projected across the landscape to create a spatial likelihood of occurrence (SLOO) model describing the probability of SAV presence in aquatic habitats. SAV presence and absence data were examined from over 500 field observations in relation to physical and hydrologic variables, including exposure, turbidity, water level, and salinity. A binary logistic regression model (p < 0.0001) identified three significant predictors of SAV presence: mean winter salinity, exposure, and turbidity. As each of these variables increased, the probability of SAV presence in the summer growing season decreased. The spatial application of this SDM helps to predict the likelihood of occurrence across the coastal landscape, creating a valuable tool to describe un-sampled SAV habitat and estimate future changes in habitat availability.

Louisiana↗

USGS2019

Cryptic introduction of water chestnut (Trapa) in the northeastern United States

Trapa natans , characterized by four-horned fruits, has been recognized as an introduced species in the northeastern United States since the 1920′s. However, in 2014 a two-horned morphotype of Trapa was discovered in the Potomac River in Virginia. As such, we hypothesize the two-horned variety represents a cryptic introduction of a Trapa taxon distinct from the four-horned T. natans previously identified in North America. We tested this hypothesis by genotyping 129 amplified fragment length polymorphism loci for 304 Trapa individuals collected from across the Northeast US and several populations from Asia and Africa. The two-horned and four-horned morphotypes in the northeastern US were found to be genetically and morphologically distinct. The two-horned Trapa taxon was most genetically and morphologically similar to samples from Taiwan identified as T. bispinosa Roxb. var iinumai Nakano. The four-horned Trapa taxon previously identified as T. natans was most genetically and morphologically similar to T. natans collected from Japan, but were genetically distinct. Therefore, it is likely that the US four-horned Trapa was introduced from somewhere outside of Japan, an unsampled area in Japan, or have genetically diverged since introduction. Distinguishing these two US Trapa taxa will be important for documenting spread and identifying new populations, and for further study on the timing and efficacy of physical, chemical, and biological control options. Our study also highlights the need for a comprehensive geographic survey of Trapa morphology and genetics to clarify the taxonomy.

Aquatic Botany↗

USGS2019

Effects of salinity and light on growth and interspecific interactions between Myriophyllum spicatum L. and Ruppia maritima L.

Submerged macrophyte habitats provide significant benefits to estuarine systems. In southeast Louisiana, Myriophyllum spicatum L. (milfoil) and Ruppia maritima L. (widgeongrass) are dominant species existing across fresh to brackish areas. Though frequently co-occurring across the range of salinity and light conditions, their individual responses to changing environmental conditions from restoration, weather and climate may determine overall species distribution, and biomass abundance. We compared milfoil and widgeongrass growth (i.e., biomass increase) across a range of salinity and light, in monoculture (salinity: 0, 5, 10, 15, 20; light: high ˜ 50% ambient; low ˜ 20% ambient), and in mixture (salinity: 0, 10, 20; light: high, low). In monoculture, milfoil growth was reduced at high salinity (20) versus low salinity (0), while biomass allocation differed significantly with greater allocation to shoots under high light, compared to low light. Widgeongrass was minimally affected by salinity, with reduced stem densities at high salinity compared to low salinity. In mixture, both species under-yielded compared to monoculture with milfoil reduced with high salinity and light, and low salinity and light; widgeongrass under-yielded with low salinity and high light, and mid salinity (10) and low light. These differences in species’ responses suggest that salinity and light contribute to the distribution of milfoil and widgeongrass, with higher salinities and light favoring widgeongrass growth, and lower light possibly decreasing both species’ growth, and ultimately, distribution. With continued changes occurring and predicted from both coastal restoration and climate change, understanding drivers of habitat forming species remains critical to inform future landscapes.

Aquatic Botany↗

USGS2020

Testing the interactive effects of flooding and salinity on tidal marsh plant productivity

Tidal wetlands support plant communities that facilitate carbon storage, accrete soil, and provide habitat for terrestrial and aquatic species. Climate change is likely to alter estuaries through sea-level rise and changing precipitation patterns, although the ecological responses are uncertain. We were interested in plant responses to physiological stress induced by elevated water salinity and flooding conditions, which may be more prevalent under climate change. . We used a greenhouse experiment and factorial flooding (1, 12, 24, and 48 % time) and salinity (0, 5, 15, 30 PSU) treatments to evaluate the productivity responses of three emergent herbaceous species ( Carex lyngbyei, Triglochin maritima, and Argentina pacifica ) common to tidal marshes of the Pacific Northwest, USA. We measured weekly changes in plant height and final above and belowground biomass for all species after 10 weeks. Increased salinity reduced final above and belowground biomass significantly in all three species, with A. pacifica responding the most, followed by C. lyngbyei and T. maritima . Increased flooding also reduced total biomass in A. pacifica and T. maritima . There was a significant response in C. lyngbyei aboveground biomass and A. pacifica height to the flooding-salinity interaction. These results indicate emergent plant community composition may change in response to novel climate conditions in estuaries, driven by distinct physiological tolerances to salinity and flooding, and highlight the importance of considering multiple climate drivers when projecting ecosystem change. This may be especially true for estuaries that currently have prolonged freshwater phases like those in the Pacific Northwest.

Aquatic Botany↗

USGS2021

Biological and practical tradeoffs in planting techniques for submerged aquatic vegetation

Global loss of submerged aquatic vegetation (SAV) and associated ecosystem function has prompted an interest in SAV revegetation, particularly where underlying stressors such as nutrient enrichment are mitigated, yet natural recruitment remains low. Typically, SAV is hand-planted, but alternative reliable and practically scalable SAV planting techniques are needed. In mesocosms, we evaluated five planting techniques: 1) hand planting, anchoring using 2) fishing weights and 3) plaster blocks, and sediment-added methods using 4) peat pots and 5) burlap-wraps (“burritos”). Anchoring and sediment-added techniques were also field evaluated at four locations within a single lake. In mesocosms, all techniques effectively established two common North American SAV species, Vallisneria americana and Potamogeton illinoensis . Sediment-added techniques had species-specific benefits, e.g. burritos produced taller Vallisneria leaves, and greater Potamogeton biomass, while peat pots encouraged rapid Vallisneria shoot production. However, no treatment was universally beneficial across all growth metrics. In the field, all techniques were effective at two sites, but at two other sites, no techniques were successful. Results show that under favorable mesocosm and field conditions, all techniques promote establishment; however, subtle differences in technique-driven plant traits (height, density, nutrients) suggest that under specific environmental conditions, some techniques may be more favorable. Also, no technique offers practical advantages in every scenario, but each offers situation-specific advantages. Guidance emerging from this work is that all techniques are potentially effective, but small-scale tests in site-specific restoration scenarios, along with consideration of feasibility constraints, are recommended to inform large-scale plantings.

Aquatic Botany↗

USGS2021

Probabilities of detecting submersed aquatic vegetation species using a rake method may vary with biomass

Levels of submersed aquatic vegetation (SAV) are commonly assessed using a modified garden rake. However, the utility of the rake sampling method relative to methods that are typically viewed as more definitive (and expensive) such as snorkeling and coring remains a matter of debate. This study explores whether probabilities of species detections for four SAV species varied among sampling units in a rake-biomass study and, if so, whether such variation reflected variation in species abundance. Variation in detection probabilities, when unaddressed, may yield biased estimators of percent frequency of occurrence (“occupancy”) and of occurrence-habitat associations. Biomass-driven variation in detection probabilities is important because such variation may not be explainable using covariates typically measured when sampling using the rake method. This study found substantial among-unit variation in detection probabilities, with majorities of that variation on the logit or modeling scale being associated with biomass but not with the non-biomass covariates substrate type, water depth and day of study. The study closes by exploring sampling protocols and modeling methods that may yield improved SAV occupancy estimates.

Aquatic Botany↗

USGS2023

Genetic analysis of North American Phragmites australis guides management approaches

Phragmites australis subsp. australis is an invasive and ecologically detrimental plant in multiple regions of North America. Its co-occurrence with the native subspecies, and multiple instances of hybridization, has created the need to differentiate Phragmites subspecies or haplotypes so that management can be appropriately targeted to the invader. We compiled a review of current genetic discrimination methods among the three Phragmites subspecies inhabiting the United States and Canada, and discussed how each method can contribute to control of the introduced subspecies while preserving the two endemic subspecies. We also discussed various control tools and the implications of Phragmites genetics for implementation. The Phragmites subspecies endemic to North America have environmental or infrastructure significance (e.g., habitat sustainability, biodiversity, storm surge and erosion protection). Thus, faster and more accurate differentiation among the endemic and introduced subspecies is needed. Additionally, more in-depth genetic information on Phragmites subspecies could support better management decisions, as well as the development of improved control treatments. This review highlights technologies and approaches currently available for genetic identification, recently collected genomic, transcriptomic and proteomic information, and implications for biological control and herbicide treatments.

Aquatic Botany↗

USGS2000

Structure and composition of oligohaline marsh plant communities exposed to salinity pulses

The response of two oligohaline marsh macrophyte communities to pulses of increased salinity was studied over a single growing season in a greenhouse experiment. The plant communities were allowed a recovery period in freshwater following the pulse events. The experimental treatments included: (1) salinity influx rate (rate of salinity increase from 0 to 12 gl-1); (2) duration of exposure to elevated salinity; and (3) water depth. The communities both included Sagittaria lancifolia L.; the codominant species were Eleocharis palustris (L.) Roemer and J.A. Schultes in community 1 and Schoenoplectus americanus (Pers.) Volk. ex Schinz and R. Keller in community 2. Effects of the treatments on sediment chemical characteristics (salinity, pH, redox potential, and sulfide and ammonium concentrations) and plant community attributes (aboveground and belowground biomass, stem density, leaf tissue nutrients, and species richness) were examined. The treatment effects often interacted to influence sediment and plant communities characteristics following recovery in fresh water. Salinity influx rate per se, however, had little effect on the abiotic or biotic response variables; significant influx effects were found when the 0 gl-1 (zero influx) treatment was compared to the 12 gl-1 treatments, regardless of the rate salinity was raised. A salinity level of 12 gl-1 had negative effects on plant community structure and composition; these effects were usually associated with 3 months of salinity exposure. Water depth often interacted with exposure duration, but increased water depth did independently decrease the values of some community response measures. Community 1 was affected more than community 2 in the most extreme salinity treatment (3 months exposure/15-cm water depth). Although species richness in both communities was reduced, structural changes were more dramatic in community 1. Biomass and stem density were reduced in community 1 overall and in both dominant species. Structural changes in community 2 consisted of reduced biomass and stem density in the community overall and in S. lancifolia; S. americanus was not affected by salinity. In this most extreme treatment, community 2 tended to change to a monospecific S. americanus stand while community 1 was reduced to a few surviving stems of secondary species. Our results suggest that vegetation recovery or establishment of new species following a temporary increase in soil water salinity will vary with exposure duration and water depth. (C) 2000 Elsevier Science B.V.

Aquatic Botany↗

USGS2001

Growth, biomass allocation and nutrient use efficiency in Cladium jamaicense and Typha domingensis as affected by phosphorus and oxygen availability

The effects of phosphorus (P) and oxygen availability on growth, biomass allocation and nutrient use efficiency in Cladium jamaicense Crantz and Typha domingensis Pers. were studied in a growth facility equipped with steady-state hydroponic rhizotrons. The treatments included four P concentrations (10, 40, 80 and 500 ??g I-1) and two oxygen concentration (8.0 and <0.5 mg O2 I-1) in the culture solutions. In Cladium, no clear relationship was found between P availability and growth rate (19-37 mg g-1 d-1), the above to below ground biomass ratio (A/B) (mean = 4.6), or nitrogen use efficiency (NUE) (mean = 72 g dry weight g-1 N). However, the ratio between root supported tissue (leaves, rhizomes and ramets) and root biomass (S/R) (5.6-8) increased with P availability. In contrast, the growth rate (48-89 mg g-1 d-1) and the biomass ratios A/B (2.4-6.1) and S/R (5.4-10.3) of Typha increased with P availability, while NUE (71-30 g dry weight g-1 N) decreased. The proportion of root laterals was similar in the two species, but Typha had thinner root laterals (diameter = 186 ??m) than Cladium (diameter = 438 ??m) indicating a larger root surface area in Typha. The two species had a similar P use efficiency (PUE) at 10 ??g PI-1 (mean = 1134 g dry weight g-1 P) and at 40 and 80 ??g PI-1 (mean = 482 dry weight g-1 P) but the N/P ratio indicated imbalances in nutrient uptake at a higher P concentration (40 ??g PI-1) in Typha than in Cladium (10 ??g PI-1). The two species had similar root specific P accumulation rate at the two lowest P levels, whereas Typha had 3-13-fold higher P uptake rates at the two highest P levels, indicating a higher nutrient uptake capacity in Typha. The experimental oxygen concentration in the rhizosphere had only limited effect on the growth of the two species and had little effect on biomass partitioning and nutrient use efficiency. The aerenchyma in these species was probably sufficient to maintain adequate root oxygenation under partially oxygen depleted conditions. Cladium had characteristics typical for plants from nutrient poor habitats, which included slow growth rate, low capacity for P uptake and relatively inflexible biomass partitioning in response to increased P availability. In contrast, Typha demonstrated a high degree of flexibility in growth, biomass partitioning, and nutrient accumulation to P availability, similar to species from nutrient rich habitats. Although the N/P ratio indicated that Typha was more nutrient stressed at the low P levels, Typha had a higher capacity for P uptake and was more competitive than Cladium at the applied P concentrations. ?? 2001 Elsevier Science B.V.

Aquatic Botany↗

USGS2001

The importance of propagule establishment and physical factors in mangrove distributional patterns in a Costa Rican estuary

Establishment of Laguncularia racemosa , Avicennia germinans , and A . bicolor was measured along intertidal gradients (mud bank (MB), lower intertidal (LI), and upper intertidal (UI)) on point bars and islands in a Costa Rican tropical estuary. Successful establishment showed the following order — Laguncularia : LI (73%)>MB (52%)>UI (18%), with UI significantly lower than LI and MB; Avicennia spp.: LI (66%)>UI (51%)>MB (29%), with LI significantly higher than MB. Establishment of Laguncularia in UI was significantly lower than Avicennia spp. due to selective crab herbivory. After 25 days, 52% of Laguncularia propagules were eaten compared to 5% for Avicennia spp. Total mortality of Laguncularia propagules and seedlings was significantly higher than that of Avicennia spp. in all three zones. The hydrological regime affected propagule establishment under controlled mesocosm conditions. Four hydrological treatments included flooded according to tidal cycle (FT), no flooding (NF), continuous flooding (F), and flooded according to tidal cycle with propagules additionally buried (FTB). Laguncularia establishment under NF (93%) and F (84%) was significantly greater than under FT (63%). A. germinans establishment under NF (97%) was greater than under FT (69%). Laguncularia showed significantly higher establishment than A. germinans under F conditions. Laguncularia propagules sank soon after their radicles protruded (5–8 days), and subsequently established under water. A. germinans propagules floated during the 25-day experiment and never established. Propagule establishment under FTB was greater for Laguncularia than for Avicennia (11 and 1%, respectively). Height increase of established Laguncularia seedlings was significantly different among treatments: FT (5.2 mm per day)>NF (3.4 mm per day)>F (2.4 mm per day). Growth of established A. germinans seedlings did not differ between FT (4.8 mm per day) and NF (5.0 mm per day), but it was significantly higher than Laguncularia under NF. These results show that both genera can successfully establish on the lower intertidal zone when artificially retained. However, propagule buoyancy, availability, dispersal, and the effect of water movement on propagule anchoring limit Avicennia spp. establishment in this regularly flooded environment. In the upper intertidal zone, however, differential predation on Laguncularia propagules favors Avicennia spp. establishment and dominance.

Bebedero River, Gulf of Nicoya, Tempisque River↗

USGS2003

Annual variations of biomass and photosynthesis in Zostera marina at its southern end of distribution in the North Pacific

Density, biomass, morphology, phenology and photosynthetic characteristics of Zostera marina were related to continuous measurements of in situ irradiance, attenuation coefficient and temperature at three coastal lagoons in Baja California, Mexico. In situ irradiance was approximately two-fold lower at San Quintin Bay (SQ) than at Ojo de Liebre Lagoon (OL) and San Ignacio Lagoon (SI). As a consequence of the greater irradiance, plants at OL and SI were established 1 m deeper within the water column than those at SQ. At SQ, there was a four-fold variation in biomass of Z. marina caused by changes on shoot length and not shoot density, while at OL and SI biomass and shoot length did not fluctuate significantly throughout the year. Reproductive shoot density reached maximum values concomitantly with the greatest irradiance during spring-summer, however, the density was approximately three-fold greater at SQ than at the southern coastal lagoons. While irradiance levels were two-fold greater at the southern lagoons, in general, photosynthetic characteristics were similar among all three lagoons. The hours of light saturated photosynthesis, calculated from their photosynthetic characteristics and irradiance measurements, suggest that photosynthesis of shoots from OL and SI are saturated for more than 6 h per day throughout the year, while shoots from SQ are likely light limited during approximately 15% of the year. Consequently, an increase in attenuation coefficient values in the water column will likely decrease light availability to Z. marina plants at SQ, potentially decreasing their survival.

Aquatic Botany↗