Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients

Regional Genetic Structure in the Aquatic Macrophyte Ruppia cirrhosa Suggests Dispersal by Waterbirds

The evolutionary history of the genus Ruppia has been shaped by hybridization, polyploidisation and vicariance that have resulted in a problematic taxonomy. Recent studies provided insight into species circumscription, organelle takeover by hybridization, and revealed the importance of verifying species identification to avoid distorting effects of mixing different species, when estimating population connectivity. In the present study, we use microsatellite markers to determine population diversity and connectivity patterns in Ruppia cirrhosa including two spatial scales: (1) from the Atlantic Iberian coastline in Portugal to the Siculo-Tunisian Strait in Sicily and (2) within the Iberian Peninsula comprising the Atlantic-Mediterranean transition. The higher diversity in the Mediterranean Sea suggests that populations have had longer persistence there, suggesting a possible origin and/or refugial area for the species. The high genotypic diversities highlight the importance of sexual reproduction for survival and maintenance of populations. Results revealed a regional population structure matching a continent-island model, with strong genetic isolation and low gene flow between populations. This population structure could be maintained by waterbirds, acting as occasional dispersal vectors. This information elucidates ecological strategies of brackish plant species in coastal lagoons, suggesting mechanisms used by this species to colonize new isolated habitats and dominate brackish aquatic macrophyte systems, yet maintaining strong genetic structure suggestive of very low dispersal.Fundacao para a Cincia e Tecnologia (FCT, Portugal) [PTDC/MAR/119363/2010, BIODIVERSA/0004/2015, UID/Multi/04326/2013]Pew FoundationSENECA FoundationMurcia Government, Spain [11881/PI/09]FCT Investigator Programme-Career Development [IF/00998/2014]Spanish Ministry of Education [AP2008-01209]European Community [00399/2012]info:eu-repo/semantics/publishedVersio

Biomass loss and nutrient redistribution in an Indonesian Thalassia hemprichii seagrass bed following seasonal low tide exposure during daylight

The intertidal reef flat of Barang Lompo Island, Indonesia, is exposed to air for several hours per day on the days around spring tides. The time of exposure shows a seasonal pattern. In the period January-June, the reef flat only runs dry at night, whereas in the period July-December, exposure only occurs during daylight. During the low tide daylight exposure period of July-December 1993, the leaf and rhizome biomasses (g m(-2)) declined significantly by 61 and 37%, respectively. Total rhizome length remained unchanged. C- and P-concentrations (% of dry weight) of leaves showed no change, while the leaf N- concentration increased by 25%. C-, N- and P-contents of leaves showed a decline that was strongly correlated to leaf biomass decline. In the rhizomes, C-concentration declined by 8%, but the N- and P-concentrations increased by 111 and 25%, respectively. Rhizome C-content (g m(-2)) declined (43%), N- content increased (46%) and P-content did not change. Total C- and P-contents of the summed biomass of leaves and rhizomes declined by 46 and 34%, respectively, but N-content showed no change. Ammonium and phosphate concentrations in the water column and pore water phosphate were not significantly different during daylight exposure compared to during nocturnal exposure. Ammonium concentration in the pore water, however, was 1.6 times higher during daylight exposure. Results show that during a period of frequent daylight exposure, the nutrient status in the intertidal Thalassia hemprichii seagrass bed changed considerably. Despite biomass reduction, the total nitrogen content in leaves and rhizomes together was constant, which was achieved by an enhanced nitrogen accumulation in the rhizomes. Two theories possibly responsible for the stable sum of the total leaf and rhizome nitrogen content are discussed. The first theory describes the seagrass bed as a relatively closed system with respect to nutrient cycles: detached leaf fragments remain trapped within the meadow. The second theory postulates that the loss of part of the photosynthesising canopy due to daylight exposure has a series of consequences for microbial N-transformation processes in the sediment, which indirectly affects the plants' nitrogen status. This study shows that Thalassia hemprichii, covering the reef flat of an intertidal tropical offshore coral island, which is often considered as a nutrient-poor environment, is rather resilient to a significant canopy die-off and concomitant nutrient losses. [KEYWORDS: daylight exposure; seagrass; biomass redistribution; nutrient contents; Thalassia hemprichii; Indonesia South sulawesi indonesia; banks ex konig; cymodocea-nodosa; syringodium filiforme; terrigenous sediments; zostera capricorni; halodule-wrightii; leaf growth; testudinum; carbonate

New evidence for habitat specific selection in Wadden Sea Zostera marina populations revealed by genome scanning using SNP and microsatellite markers

Eelgrass Zostera marina is an ecosystem-engineering species of outstanding importance for coastal soft sediment habitats that lives in widely diverging habitats. Our first goal was to detect divergent selection and habitat adaptation at the molecular genetic level; hence, we compared three pairs of permanently submerged versus intertidal populations using genome scans, a genetic marker-based approach. Three different statistical approaches for outlier identification revealed divergent selection at 6 loci among 46 markers (6 SNPs, 29 EST microsatellites and 11 anonymous microsatellites). These outlier loci were repeatedly detected in parallel habitat comparisons, suggesting the influence of habitat-specific selection. A second goal was to test the consistency of the general genome scan approach by doubling the number of gene-linked microsatellites and adding single nucleotide polymorphism (SNP) loci, a novel marker type for seagrasses, compared to a previous study. Reassuringly, results with respect to selection were consistent among most marker loci. Functionally interesting marker loci were linked to genes involved in osmoregulation and water balance, suggesting different osmotic stress, and reproductive processes (seed maturation), pointing to different life history strategies. The identified outlier loci are valuable candidates for further investigation into the genetic basis of natural selection

Nutrient uptake by leaves and roots of the seagrass Thalassia hemprichii in the Spermonde Archipelago, Indonesia

The kinetics of ammonium and phosphate uptake by leaves and roots of the tropical seagrass Thalassia hemprichii were investigated in laboratory experiments. Uptake in leaves of plants from 3 different locations, covering the range from coastal to oceanic conditions in the region of investigation (Spermonde Archipelago, South Sulawesi, Indonesia), was compared. The leaves from all plant samples showed a clear capacity for both ammonium and phosphate uptake. This uptake could be described by Michaelis-Menten kinetics. v(max) ranged between 32 and 37 mu mol g(-1) leaf dry weight h(-1) for ammonium and between 2.2 and 3.2 mu mol g(-1) leaf dry weight h(-1) for phosphate. K-m ranged between 21 and 60 mu M for ammonium and between 7.7 and 15 mu M for phosphate. There was no significant site difference in uptake characteristics (v(max) and K-m) of ammonium and phosphate. Uptake of ammonium and phosphate by roots was investigated with plants from the intermediate location, Barang Lompo, using an approach which allowed only calculation of uptake rates at natural pore water concentrations. Uptake rates were 22 and 1.0 mu mol g(-1) root dry weight h(-1) for ammonium and phosphate, respectively Calculations suggest that at all 3 locations uptake of ammonium and phosphate by roots was probably limited by the diffusion of nutrients in the sediment rather than by their uptake capacity. Evidence was found that the availability of nutrients in the root zone relative to the leaf zone affects the uptake affinity of the leaves. The role of roots versus leaves in supplying plant nutrients is discussed. We concluded that even in the tropics, where water column nutrient concentrations are often very low, leaves clearly have a significant ability for ammonium or phosphate uptake and that in some situations nutrient uptake by the leaves may even be essential in meeting plant nutrient demands. [KEYWORDS: ammonium; phosphate; nutrient uptake kinetics; leaves; roots; seagrass; Thalassia hemprichii; Indonesia Zostera-marina-l; south sulawesi indonesia; phosphorus; epiphytes; release; phosphate; kinetics; biomass; nitrate; ammonia

Solar Radiation and Tidal Exposure as Environmental Drivers of Enhalus acoroides Dominated Seagrass Meadows

There is strong evidence of a global long-term decline in seagrass meadows that is widely attributed to anthropogenic activity. Yet in many regions, attributing these changes to actual activities is difficult, as there exists limited understanding of the natural processes that can influence these valuable ecosystem service providers. Being able to separate natural from anthropogenic causes of seagrass change is important for developing strategies that effectively mitigate and manage anthropogenic impacts on seagrass, and promote coastal ecosystems resilient to future environmental change. The present study investigated the influence of environmental and climate related factors on seagrass biomass in a large ≈250 ha meadow in tropical north east Australia. Annual monitoring of the intertidal Enhalus acoroides (L.f.) Royle seagrass meadow over eleven years revealed a declining trend in above-ground biomass (54% significant overall reduction from 2000 to 2010). Partial Least Squares Regression found this reduction to be significantly and negatively correlated with tidal exposure, and significantly and negatively correlated with the amount of solar radiation. This study documents how natural long-term tidal variability can influence long-term seagrass dynamics. Exposure to desiccation, high UV, and daytime temperature regimes are discussed as the likely mechanisms for the action of these factors in causing this decline. The results emphasise the importance of understanding and assessing natural environmentally-driven change when interpreting the results of seagrass monitoring programs

Conformational studies of peptides representing a segment of TM7 from H+-VO-ATPase in SDS micelles

The conformation of a transmembrane peptide, sMTM7, encompassing the cytoplasmic hemi-channel domain of the seventh transmembrane section of subunit a from V-ATPase from Saccharomyces cerevisiae solubilized in SDS solutions was studied by circular dichroism (CD) spectroscopy and fluorescence spectroscopy of the single tryptophan residue of this peptide. The results show that the peptide adopts an α-helical conformation or aggregated β-sheet depending on the peptide-to-SDS ratio used. The results are compared with published data about a longer version of the peptide (i.e., MTM7). It is concluded that the bulky, positively charged arginine residue located in the center of both peptides has a destabilizing effect on the helical conformation of the SDS-solubilized peptides, leading to β-sheet formation and subsequent aggregation