Ruppia Maritima Research Articles

Assessment of Biodiversity and Blue Carbon in Mangroves, Sea grasses, Salt Marshes and Algae in Mannar, Northern Sri Lanka

Blue carbon is the carbon stored in coastal and marine ecosystems. Coastal ecosystems such as mangroves, tidal marshes, seagrass meadows and algae sequester and store more carbon per unit area than terrestrial forests and are now being recognised for their role in mitigating climate change. The objective of this study was to assess the biodiversity and carbon storage capacities in these ecosystems. The study was conducted in Vidathalathivu in Mannar, Kiranchi in Kilinochchi and Pooneryn. In mangroves, belt transects were taken from the shore towards the land. Nested circular plots having 7 m radius were established, large trees were sampled for diameter. Small trees (<3 cm dbh) were sampled in 2 m radius. Litter, pneumatophores and seedlings were sampled in plots of 30×30 cm area. Soil samples were taken at depths; 0-30 cm, 30-60 cm, 60-100 cm for the measurement of bulk density and carbon content. The biomass of the mangrove plants was measured using species specific allometric equations. In the salt marshes, 1×1 m plots were sampled. In the seagrass beds and algae, several 30×30 cm grids were sampled. In each plot, the species composition and the number of plants in each species were assessed. Samples of seagrasses and salt marsh vegetation were uprooted and taken to the laboratory for oven dry analysis. Three soil cores were taken using the soil auger which was inserted to a depth of 1 m in each ecosystem. The soil samples were taken from the core to represent the following depths; 0-30 and 30-60, 60-90. The data was analysed using MINITAB statistical software. The results showed natural mangroves in the study sites comprised of Avicennia marina, Ceriops tagal, Excoecaria agallocha, Luminetzera racemosa, Rhizophora murconata and Pemphis acidula. In sea grasses, Thalassima hemprichii, Cymodocea serrulate, Ruppia maritima and Syringodium isoiifolium were observed. Kappaphycus alvarezii and Eucheuma spinosum were the cultivated algae and Padina antillarum, Caulerpa racemosa, Ulva lactuca, Sargassum illifolium and Gelidium sp. were natural ones observed. Suaeda sp. and Salicornia sp. were the salt marsh species observed. The carbon content of these ecosystems were assessed. Keywords: Blue carbon, Mangroves, Seagrasses, Salt marshes, Algae, Carbon sequestration

Molecular phylogeny of Ruppia maritima L. from Chilika Lake, Odhisa using nuclear and plastid genes

Aim: The present study aims to confirm the molecular identification of Ruppia maritima L. from Chilika Lake, Odhisa using different molecular markers and find out the evolutionary lineage of Ruppia species. Methodology: For molecular identification, R. maritima was collected from Chilika Lake and the rbcL, matK, and ITS gene sequences were investigated and analyzed using BLAST to verify the gene fragment. Phylogenetic tree was constructed using MEGA X software following Neighbor joining (NJ) and Maximum parsimony (MP) methods. Results: The nucleotide (ITS) and plastid gene (rbcL and matK) sequences of Ruppia maritima were examined. The tree topology of R. maritima rbcL and matK gene sequences revealed a paraphyletic cluster at 99 and 100% bootstrap. The conserved region was high in matK (74.8%), followed by rbcL (45.2%) and ITS (19.1%) with seagrass and freshwater species. ITS had the most significant proportion of variable sites (79.7%), followed by rbcL (52.4%) and matK (25.2%). The ITS region showed less parsimonious-informative character (66.1) than rbcL and matK region. Interpretation: The study concludes that the R. maritima was identified through molecular markers, which was a closed lineage with seagrasses than freshwater species.

Competition and coexistence in a rare Northeastern Pacific multispecies seagrass bed

Seagrass meadows with more than two species co-occurring at a small scale are unusual in temperate regions, and such multispecies seagrass beds are undocumented in the Northeastern Pacific. Seagrasses in multispecies beds may coexist through trait differentiation in body size, life history types and phenology, especially when competitive exclusion is interrupted by environmental variability. Here, we survey and manipulate a multispecies seagrass meadow in Willapa Bay, Washington (USA), containing Zostera marina, Zostera japonica and Ruppia maritima; our 13-month survey is the first formal documentation of multispecies seagrass bed occurrence in the Northeastern Pacific. Z. japonica, a non-native species, reached an end-of-summer biomass that was an order of magnitude greater than either native seagrass. To test competition, we experimentally removed Z. japonica and found competition occurred disproportionately on the smaller R maritima relative to larger Z. marina. R. maritima germinated later and senesced earlier than the two Zostera species, and the removal of Z. japonica positively affected R. maritima biomass, supporting previous studies that R. maritima is an opportunistic species. In addition to species-specific phenology and body size, all species presented annual life histories and thus began each annual cycle under high resource availability, such as light, space and nutrients, which may contribute to coexistence.

Sensitivity of Photosynthesis to Warming in Two Similar Species of the Aquatic Angiosperm Ruppia from Tropical and Temperate Habitats

Climate change-related events, such as marine heatwaves, are increasing seawater temperatures, thereby putting pressure on marine biota. The cosmopolitan distribution and significant contribution to marine primary production by the genus Ruppia makes them interesting organisms to study thermal tolerance and local adaptation. In this study, we investigated the photosynthetic responses in Ruppia to the predicted future warming in two contrasting bioregions, temperate Sweden and tropical Thailand. Through DNA barcoding, specimens were determined to Ruppia cirrhosa for Sweden and Ruppia maritima for Thailand. Photosynthetic responses were assessed using pulse amplitude-modulated fluorometry, firstly in short time incubations at 18, 23, 28, and 33 °C in the Swedish set-up and 28, 33, 38, and 43 °C in the Thai set-up. Subsequent experiments were conducted to compare the short time effects to longer, five-day incubations in 28 °C for Swedish plants and 40 °C for Thai plants. Swedish R. cirrhosa displayed minor response, while Thai R. maritima was more sensitive to both direct and prolonged temperature stress with a drastic decrease in the photosynthetic parameters leading to mortality. The results indicate that in predicted warming scenarios, Swedish R. cirrhosa may sustain an efficient photosynthesis and potentially outcompete more heat-sensitive species. However, populations of the similar R. maritima in tropical environments may suffer a decline as their productivity will be highly reduced.

Dataset on the isotopic (ẟ13C, ẟ15N) and elemental (C, N) composition of estuarine primary producers in the subtropical Southwestern Atlantic coast

Benthic and pelagic primary producers had their isotopic (ẟ13C, ẟ15N) and elemental (C, N) composition monitored in the Patos Lagoons estuary, in southern Brazil. The present dataset comprises temporal data obtained through seasonal samplings of C3 (Scirpus spp.) and C4 (Spartina densiflora) salt marsh plants, ephemerous bloom-forming drift macroalgae (Ulvophyceae), the widgeon grass Ruppia maritima, particulate (POM) and sedimentary (SOM) organic matter in shallow waters (< 2m) of a subtropical estuary from austral summer 2010 to autumn 2016. POM and SOM were collected as proxies of phytoplankton and microphytobenthos, respectively. Salt marsh plants were randomly sampled (N = 126) at a regularly flooded low marsh area, whereas submerged drift macroalgae (N = 29) and Ruppia plants (N = 14) were collected in adjacent mudflats. POM was collected (N = 33) by filtering water samples using glass fiber filter. SOM was obtained (N = 35) by removing superficial sediment. In laboratory, samples were processed and further analyzed for total organic carbon (TOC), total nitrogen (TN) and carbon (13C/12C) and nitrogen (15N/14N) stable isotopes ratios. With a total of 237 samples analyzed, this dataset provides key information on the isotopic and elemental composition of distinct estuarine primary producers and sources of particulate organic matter (POM and SOM) and their temporal variability in a highly variable aquatic environment. Such knowledge may add to ecological studies investigating food webs, biogeochemical cycles and sources tracking in coastal systems.

КОНСПЕКТ ВЫСШИХ ВОДНЫХ РАСТЕНИЙ ОМСКОЙ ОБЛАСТИ

The article presents the results of generalizing the factual material on the diversity of hydromacrophytes from the divisions Marchantiophyta, Bryophyta and Magnoliophyta in the territory of the Omsk region. For each species the geographical frequency of occurrence in natural zones, the group of halobility and trophicity are indicated. For the region 176 species of higher hydromacrophytes have been identified. The division Magnoliophyta is distinguished by the greatest species diversity, which includes 116 species (65.9% of all higher hydromacrophytes), the division Bryophyta accounts for 49 species (27.9%), Marchantiophyta – 7 (4.0%), the divisions Equisetophyta and Polypodiophyta include only 2 species each (1.1%). Currently in the region 24 species of higher hydromacrophytes are included in the number of protected species with an established category of protection or as species that need special attention to their state and natural environment. In total, the following moss species are known from several habitats: Riccia fluitans, R. frostii, R. rhenana, Ricciocarpos natans, Fissidens adianthoides, Paludella squarrosa and vascular plants: Ceratophyllum platyacanthum subsp. oryzetorum, Elatine hydropiper, Veronica beccabunga, Najas marina, Sagittaria trifolia, Potamogeton rutilus, including brackish Ruppia maritima, Althenia orientalis, Zannichellia palustris var. repens.

Succession pattern and phylotype analysis of microphytobenthic communities in a simulated oil spill seagrass mesocosm experiment

Microphytobenthic communities play a significant role in nutrient modulation, sediment stabilization, and primary production in seagrass beds, which provide various ecosystem services. We hypothesized that microphytobenthic communities in sediments of chronically oil-exposed seagrass beds will exhibit increased resiliency to stressors associated with oil exposure as opposed to seagrass beds never exposed to oil spills. We prepared 14-liter seawater mesocosms, each containing a submersed macrophyte Ruppia maritima collected from the Chandeleur Islands, Louisiana, and Estero Bay, Florida. Mesocosms were initially exposed to 50% water-accommodated oil fractions (WAF) and subsequently diluted by 50% with daily artificial seawater exchanges over 8 days to simulate tidal dilution. High-throughput amplicon sequencing based on 23S rRNA gene targeting cyanobacteria and chloroplasts of eukaryotic microphytobenthos was conducted to assess the impact of oiling on microphytobenthic communities with additional assessment via microscopy. High-throughput sequencing in combination with traditional microscopic analysis provided a robust examination in which both methods roughly complemented each other. Distinct succession patterns were detected in benthic algal communities of chronically oil-exposed (Louisiana) versus unexposed (Florida) seagrass bed sediments. The impact of oiling in microphytobenthos across all samples showed that benthic diatoms dominated all algal communities with sample percentages ranging from 42 to 97%, followed by cyanobacteria (2 to 50%). It is noteworthy that drastic changes in microphytobenthic community structure in terms of the larger taxonomic level were not observed, rather change occurred at the phylotype level. These results were also confirmed by microscopy. Similarity percentages (SIMPER) analysis identified seven phylotypes (Cyanobacteria, Bacillariophyceae, and Mediophyceae) in the Louisiana samples and one phylotype (Bacillariophyceae) in the Florida samples that increased in relative sequence abundance after oil exposure. The detailed phylotype analysis identifying sentinel microphytobenthic indicators provides a base for future research on benthic microalgae response to ecosystem disturbance.

Нова знахідка Pleurocladia lacustris А.Braun (Phaeophyсеае) у Дніпровському лимані Чорного моря (Україна)

In article reports a new find of Pleurocladia lacustris in Ukraine. The species grew in the brackish-water Dnieper Estuary (depth 0.2 m, salinity of estuary water was 4.68‰, temperature – 23 °С, pH – 7.9) P. lacustris is a filamentous benthic species, the cells of which are not calcified here, as in freshwater conditions, but are covered with a slimy sheath. It was found in fouling of bushes of green algae Cladophora glomerata (Linnaeus) Kützing and Ulva flexuosa Wulfen, as well as blue-green (Calothrix C.Agardh ex Bornet & Flahault and Oscillatoria sp.) on a concrete slab in July 2020. The thickets of Potamogeton perfoliatus L., Ruppia maritima L., and Stuckenia pectinata (L.) Börner predominated in the coastal area of the estuary. Color illustrations of the vegetative and generative organs of P. lacustris are presented, its diagnostic macroscopic and microscopic characteristics are shown, which turned out to be somewhat larger than the data of the determinants. The ecological characteristics of the algae habitat meet the known requirements. This rare species is known in about 50 localities in Europe, North America, Australia and Africa. In many countries P. lacustris is considered an endangered species and is included in the protected red lists.

Abiotic and Biotic Interactions Control Ruppia maritima Life History Development Within a Heterogeneous Coastal Landscape

Habitat-forming submerged aquatic vegetation (SAV) in estuaries increasingly depend on sexual recruitment from propagules for population sustainability under varying conditions from climate and human-induced changes. Seed recruitment requires successful transitions through multiple life history stages, but few studies have examined abiotic and interspecies interactions on multiple life stages in SAV. A series of field experiments in Florida Bay quantified impacts of abiotic (salinity, temperature, light, sediment nutrients) and biotic (interspecific SAV interactions) factors on seedlings, adult individuals (genets), and shoots (ramets) of the SAV Ruppia maritima. Five study sites were established at the Everglades-Florida Bay ecotone, where seed recruitment sustains R. maritima. Seedling survival was low (≤ 16%), and further reduced under low light, P-limitation and competition with the macroalga Chara hornemannii. Significantly high genet survival and vegetative and sexually reproductive shoot production (4400 m−2 and 300 m−2, respectively) were found at a site where nutrients (P) were sufficient, when C. hornemannii was absent and light levels were three-times higher during the dry season (~ 14000 lumens m−2; December–March) than any other time of year. At P-limited sites, vegetative shoot production occurred with adequate light (> 20,000 lumens m−2) at stable salinities (CV 0.5) where 30–45-day averages remained < 15. However, variable or elevated salinity delayed vegetative shoot production ~ 60 days, suggesting salinity stress limits asexual reproduction. Understanding how light and P-limitation, salinity stress, and competition controls R. maritima recruitment in the Everglades is essential to its management for restoration and climate change.

Isolation and identification of a novel allelochemical from Ruppia maritima extract against the cyanobacteria Microcystis aeruginosa

Because submerged plants have allelopathic inhibition against the cyanobacterial growth in the nature, the extracts of the submerged plants could be an environment-friendly and efficient alternative for controlling cyanobacterial bloom. A growth inhibitor of Microcystis aeruginosa was identified from the Ruppia maritima extracts by a two-step extraction. In the first step, Ruppia maritima was extracted by methanol, ethyl acetate and petroleum ether, respectively. The petroleum ether extract with the best algal inhibition effect (EC50=92.82 mg L−1) was further isolated, using column chromatography eluted with petroleum ether and ethyl acetate mixtures in volume ratios of 10:1, 7:1, 5:1, 3:1, 1:1 and 0:1 (v:v). Based on the GC–MS analysis results, 2,2’-methylenebis(6-tert-butyl-4-methyl-phenol) (AO 2246) was identified as the most effective compound with an EC50 of 7.80 mg L−1. The further bioassay experiments using Chlorella vulgaris and zebrafish indicated the cyanobacterial-specific allelopathic effect and low acute toxicity of AO 2246. The effect of AO2246 may be also long-acting in the natural environments, as the 28-day illumination of AO2246 had little influence on its cyanobacteria inhibition efficacy.

Current status and checklist of seagrass in Sri Lanka

This work provides the revised and updated checklist of the seagrass in Sri Lanka based on primary and secondary information. It is indeed to be an update the list of Seagrass species in Sri Lanka prepared by Abeywickrama and Arulgnanam (1991), which now been nearly three decades back. More than forty (40) published pieces of literature, herbarium sheets in the National Herbarium and author’s personal observations since 2011 were reviewed. Sri Lanka belongs to the Indo-Pacific bioregion and 15 species have been recorded so far representing seven genera. They are Enhalus acoroides, Halophila beccarii , H. decipiens , H. ovalis , H. major , H. minor , H. ovata , H. stipulacea , Thalassia hemprichii , Cymodocea rotundata , C. serrulata , Halodule uninervis , H. pinifolia , Ruppia maritima , and Syringodium isoetifolium with the estimated extend to be 37,137 ha. Halophila beccarii considered as a rare species, and has only been recorded in patchily distributed with few localities in Sri Lanka. Lack of evidences to cross check the identification of H. minor (only recorded in Negombo Lagoon) and H. ovata is a main drawback. The composition and distribution of seagrasses along the coastal zone of Sri Lanka is yet to be established. Therefore, island wide comprehensive and genetic studies could be positively contributed to fulfil the data gaps in future.

Salt Marsh Pond Biogeochemistry Changes Hourly‐to‐Yearly but Does Not Scale With Dimensions or Geospatial Position

AbstractShallow ponds are expanding in many salt marshes with potential impacts on ecosystem functioning. Determining how pond characteristics change over time and scale with physical dimensions and other spatial predictors could facilitate incorporation of ponds into projections of ecosystem change. We evaluated scaling relationships across six differently sized ponds in three regions of the high marshes within the Plum Island Ecosystems‐Long Term Ecological Research site (MA, USA). We further characterized diel fluctuations in surface water chemistry in two ponds to understand short‐term processes that affect emergent properties (e.g., habitat suitability). Primary producers drove oxygen levels to supersaturation during the day, while nighttime respiration resulted in hypoxic to anoxic conditions. Diel swings in oxygen were mirrored by pH and resulted in successive shifts in redox‐sensitive metabolisms, as indicated by nitrate consumption at dusk followed by peaks in ammonium and then sulfide overnight. Abundances of macroalgae and Ruppia maritima correlated with whole‐pond oxygen metabolism rates, but not with surface area (SA), volume (V), or SA:V. Moreover, there were no clear patterns in primary producer abundances, surface water chemistry, or pond metabolism rates across marsh regions supplied by different tidal creeks or that differed in distance to upland borders or creekbanks. Comparisons with data from 2 years prior demonstrate that plant communities and biogeochemical processes are not in steady state. Factors contributing to variability between ponds and years are unclear but likely include infrequent tidal exchange. Temporal and spatial variability and the absence of scaling relationships complicate the integration of high marsh ponds into ecosystem biogeochemical models.

Hydrological Management for Submersed Aquatic Vegetation in South Carolina Coastal Impoundments

ABSTRACTWe conducted a field experiment to test effects of complete drawdown to dried substrates versus partial (shallow water, 0–10 cm) drawdown on widgeongrass (Ruppia maritima) and other native submersed aquatic vegetation (SAV) biomass (dry) in managed brackish tidal impoundments (hereafter, impoundments) in the Ashepoo, Combahee, and Edisto Rivers Basin, South Carolina, USA. We sampled SAV in 20 impoundments (complete drawdown, n = 8; partial drawdown, n = 12) during August 2016, November 2016, January 2017, and April 2017. We detected a drawdown effect on SAV biomass for August 2016 samples before Hurricane Matthew in October 2016, which subsequently confounded drawdown treatment effects. Mean SAV biomass in August 2016 was nearly 4 times greater in partially drawndown ( = 35.98 g/m2 ± 6.05 [SE]) than completely drawndown impoundments ( = 9.52 g/m2 ± 7.41). We suggest partial drawdowns to promote SAV biomass in coastal South Carolina and other south Atlantic brackish wetlands. We also encourage managers to conduct complete drawdowns periodically to reduce flocculent soils and organic matter and promote rooting by SAV. Our results may aid the Atlantic Coast Joint Venture of the North American Waterfowl Management Plan to estimate potential energetic carrying capacity of brackish impoundments in South Carolina and elsewhere as applicable for wintering ducks and American coots (Fulica americana), and to illustrate the effect of a hurricane that decreases SAV biomass in impounded wetlands. © 2020 The Wildlife Society.

Habitat diversity and type govern potential nitrogen loss by denitrification in coastal sediments and differences in ecosystem-level diversities of disparate N2O reducing communities.

ABSTRACTIn coastal sediments, excess nitrogen is removed primarily by denitrification. However, losses in habitat diversity may reduce the functional diversity of microbial communities that drive this important filter function. We examined how habitat type and habitat diversity affects denitrification and the abundance and diversity of denitrifying and N2O reducing communities in illuminated shallow-water sediments. In a mesocosm experiment, cores from four habitats were incubated in different combinations, representing ecosystems with different habitat diversities. We hypothesized that habitat diversity promotes the diversity of N2O reducing communities and genetic potential for denitrification, thereby influencing denitrification rates. We also hypothesized that this will depend on the identity of the habitats. Habitat diversity positively affected ecosystem-level diversity of clade II N2O reducing communities, however neither clade I nosZ communities nor denitrification activity were affected. The composition of N2O reducing communities was determined by habitat type, and functional gene abundances indicated that silty mud and sandy sediments had higher genetic potentials for denitrification and N2O reduction than cyanobacterial mat and Ruppia maritima meadow sediments. These results indicate that loss of habitat diversity and specific habitats could have negative impacts on denitrification and N2O reduction, which underpin the capacity for nitrogen removal in coastal ecosystems.

A profound view and discourse on the typification and status of three confused taxa: Ruppia maritima, R. spiralis and R. cirrhosa

AbstractTaxonomic difficulties have persisted within the genus Ruppia for a long time. We first unravel misconceptions as perceived on different continents and subsequently present a revised interpretation of the identity and typification of three European taxa at species level: Ruppia maritima L., Ruppia spiralis L. ex Dumortier, and Ruppia cirrhosa (Petagna) Grande. To do this, historical specimens, illustrations and original descriptions were studied. We supersede a previous choice of the figure of Buccaferrea maritima, foliis minus acutis Micheli (1729) as the lectotype of R. maritima and type species of the genus Ruppia owing to a serious conflict with the protologue. Based on a meticulous interpretation of protologues and figures in a historical context, we reject the recent view of assigning R. cirrhosa and its proposed lectotype (iconotype) as a homotypic synonym of R. maritima. We agree with an earlier lectotypification of R. spiralis, though for another reason than the above-mentioned abused homotypy. Consequently, R. cirrhosa is a synonym of neither R. maritima or R. spiralis, based on material from Petagna in the Herbarium of Naples designated as the holotype of R. cirrhosa. We argue for three species to be considered as fully independent taxa: R. maritima, R. spiralis and R. cirrhosa.

Seasonal deposition processes and chronology of a varved Holocene lake sediment record from Chatyr Kol lake (Kyrgyz Republic)

Abstract. Microfacies analysis of a sediment record from Chatyr Kol lake (Kyrgyz Republic) reveals the presence of seasonal laminae (varves) from the sediment base dated at 11 619±603 BP (years Before Present) up to ∼360±40 BP. The Chatvd19 floating varve chronology relies on replicate varve counts on overlapping petrographic thin sections with an uncertainty of ±5 %. The uppermost non-varved interval was chronologically constrained by 210Pb and 137Cs gamma spectrometry and interpolation based on varve thickness measurements of adjacent varved intervals with an assumed maximum uncertainty of 10 %. Six varve types were distinguished, are described in detail, and show a changing predominance of clastic-organic, clastic-calcitic or clastic-aragonitic, calcitic-clastic, organic-clastic, and clastic-diatom varves throughout the Holocene. Variations in varve thickness and the number and composition of seasonal sublayers are attributed to (1) changes in the amount of summer or winter/spring precipitation affecting local runoff and erosion and/or to (2) evaporative conditions during summer. Radiocarbon dating of bulk organic matter, daphnia remains, aquatic plant remains, and Ruppia maritima seeds reveals reservoir ages with a clear decreasing trend up core from ∼6150 years in the early Holocene, to ∼3000 years in the mid-Holocene, to ∼1000 years and less in the late Holocene and modern times. In contrast, two radiocarbon dates from terrestrial plant remains are in good agreement with the varve-based chronology.

Rake Sampling to Estimate Biomass of Submersed Aquatic Vegetation in Coastal Wetlands

We evaluated two rake-enclosure sampling methods for estimating biomass of submersed aquatic vegetation (SAV) within managed tidal impoundments (MTIs) in the Ashepoo-Combahee-Edisto Rivers Basin, South Carolina. We collected SAV using a modified rake within 0.086 m2 cylindrical sampler (CS), a non-modified rake within 0.2-m2 quadrat (QS), and after raking, hand-collected remaining SAV within each enclosure (i.e., rake + hand = total SAV biomass). We used linear mixed models to evaluate rake sampling methods to estimate total (QS and CS) and species-specific SAV biomass (QS). The marginal coefficient of determination (R2) for both rake sampling methods was 0.95 for estimating total SAV biomass and model fitted values met our a priori acceptable level of precision (CV ≤ 15–20%). Furthermore, the QS-rake method explained 95% of the variation in total widgeongrass biomass (Ruppia maritima), 97% of dwarf spikerush biomass (Eleocharis parvula), and 97% of muskgrass (Chara spp.) biomass but model fitted values only met a priori precision for widgeongrass biomass. We conclude that our rake-SAV sampling estimates total SAV and widgeongrass biomass with little unexplained variation. Furthermore, abiotic variables had no significant effect when estimating SAV biomass. We suggest managers and researchers use our rake methods to estimate biomass of SAV in wetlands with similar species compositions, and resulting estimates may be used to estimate foraging carrying capacity for habitat conservation planning and management.

Using species distribution models to guide seagrass management

Seagrasses provide essential and global ecosystem services. However, due to natural and anthropogenic disturbance, seagrass meadows around the world have declined dramatically in recent decades. Researchers and managers have been calling for increased frequency and accuracy in the mapping of seagrass distributions to benefit seagrass conservation for over a decade, and we argue that a critical advancement in the management of seagrasses could come through increased and iterative model-based mapping of potential habitat as an accessory to seagrass monitoring. We further demonstrate how focus on errors of commission and omission during model interpretation could guide management activities, using the Texas Gulf Coast as a case study representing seagrass habitats worldwide. We used the species distribution modeling program Maxent to predict the location of suitable habitat for each seagrass species along the Texas Coast based on local current velocity, distance from boat launches (i.e., an index of human disturbance), nitrogen, light availability, salinity, and temperature. Models accurately predicted suitable habitat for all seagrass species, including Halodule wrightii (AUC = 0.830 ± 0.032), Thalassia testudinum (AUC = 0.901 ± 0.058), Syringodium filiforme (AUC = 0.911 ± 0.036), Halophila engelmannii (AUC = 0.865 ± 0.092), and Ruppia maritima (AUC = 0.868 ± 0.040). The relative importance of environmental factors differed between models. Distributions for H. wrightii and T. testudinum were most influenced by surface nitrate concentrations. S. filiforme, H. engelmannii, and R. maritima distributions were most influenced by benthic light availability. Human disturbances often lead to elevated nitrate concentrations and decreased benthic light availability, and our models generally predicted a lack of suitable habitat near sites characterized by abundant human development. We considered model errors of commission and omission for each species to identify candidate regions for seagrass transplantation and habitat restoration, respectively. Overall, we believe that the utility of the approach we have developed in the Texas Gulf Coast case study along extends beyond a single study site, and our methods will assist conservation of seagrass meadows worldwide.

Reproductive ecology and postpollination development in the hydrophilous monocot Ruppia maritima.

Water-pollination (hydrophily) is a rare but important pollination mechanism that has allowed angiosperms to colonize marine and aquatic habitats. Hydrophilous plants face unique reproductive challenges, and many have evolved characteristic pollen traits and pollination strategies that may have downstream consequences for pollen performance. However, little is known about reproductive development in the life history stage between pollination and fertilization (the progamic phase) in hydrophilous plants. The purpose of this study was to characterize reproductive ecology and postpollination development in water-pollinated Ruppia maritima L. Naturally pollinated inflorescences of R. maritima were collected from the field. Experimental pollinations using both putatively outcross and self pollen were conducted in the greenhouse and inflorescences were collected at appropriate intervals after pollination. Pollen reception, pollen germination, pollen tube growth, and carpel morphology were characterized. Ruppia maritima exhibits incomplete protogyny, allowing for delayed selfing. Pollen germinated within 15 min after pollination. The average shortest possible pollen tube pathway was 425 μm and pollen tubes first reached the ovule at 45 min after pollination. The mean adjusted pollen tube growth rate was 551 μm/h. Ruppia pollen is adapted for rapid pollen germination, which is likely advantageous in an aquatic habitat. Small effective pollen loads suggest that pollen competition intensity is low. Selection for traits such as a long period of stigma receptivity, fast pollen germination, and carpel morphology likely played a larger role in shaping postpollination reproductive development in Ruppia than evolution in pollen tube growth rates.

Does Ocean Acidification Benefit Seagrasses in a Mesohaline Environment? A Mesocosm Experiment in the Northern Gulf of Mexico

Ocean acidification is thought to benefit seagrasses because of increased carbon dioxide (CO2) availability for photosynthesis. However, in order to truly assess ecological responses, effects of ocean acidification need to be investigated in a variety of coastal environments. We tested the hypothesis that ocean acidification would benefit seagrasses in the northern Gulf of Mexico, where the seagrasses Halodule wrightii and Ruppia maritima coexist in a fluctuating environment. To evaluate if benefits of ocean acidification could alter seagrass bed composition, cores of H. wrightii and R. maritima were placed alone or in combination into aquaria and maintained in an outdoor mesocosm. Half of the aquaria were exposed to either ambient (mean pH of 8.1 ± 0.04 SD on total scale) or high CO2 (mean pH 7.7 ± 0.05 SD on total scale) conditions. After 54 days of experimental exposure, the δ13C values were significantly lower in seagrass tissue in the high CO2 condition. This integration of a different carbon source (either: preferential use of CO2, gas from cylinder, or both) indicates that plants were not solely relying on stored energy reserves for growth. Yet, after 41 to 54 days, seagrass morphology, biomass, photo-physiology, metabolism, and carbon and nitrogen content in the high CO2 condition did not differ from those at ambient. There was also no indication of differences in traits between the homospecific or heterospecific beds. Findings support two plausible conclusions: (1) these seagrasses rely heavily on bicarbonate use and growth will not be stimulated by near future acidification conditions or (2) the mesohaline environment limited the beneficial impacts of increased CO2 availability.