Marina Seedlings Research Articles

Combined impact of water column oxygen and temperature on internal oxygen status and growth of Zostera marina seedlings and adult shoots

Eelgrass (Zostera marina L.) occasionally experiences severe die-offs during warm summer periods with variable water column oxygen partial pressures (pO2). Eelgrass is known to be very intolerant to tissue anoxia with reduced growth and increasing mortality after ≤12h anoxia in the dark at temperatures of ≥25°C. In the present study we experimentally examine the impact of combined water column oxygen and temperature on oxygen dynamics in leaf meristems of seedlings and adult shoots to better understand how stressful environmental conditions affect eelgrass oxygen dynamics and subsequent growth and mortality. There was a strong interaction between water column oxygen and temperature on meristem pO2 implying that eelgrass is rather resistant to unfavorable oxygen conditions in winter but becomes increasingly vulnerable in summer, especially at high temperatures. At 25°C meristems became anoxic at a water column pO2 of 12kPa corresponding to 60% of air saturation, and leaf growth was negatively affected after 24h exposure to water column pO2 below 7kPa. Temperature had in itself a substantial impact on meristem pO2 both in light and in the dark as a result of increasing tissue respiration. Seedlings were less prone to meristem anoxia than adult shoots suggesting that seedlings would better tolerate unfavorable combinations of water column oxygen conditions and temperature. The results suggest that eelgrass die-offs will occur more frequently in eutrophied coastal areas with the more frequent periods of unusually high temperatures expected in the future as a result of global warming.

Tolerance and response of Zostera marina seedlings to hydrogen sulfide

Populations of Zostera marina L., the common seagrass of Pacific Northwest shallow marine environments, has undergone local extinction in coastal embayment's where it has traditionally existed. Because the habitat created by these plants is important for near-shore productivity and biodiversity, declining populations and local extinctions can have serious ecosystem consequences. One possibility for the failures of population increase and re-colonization of embayment's with complete loss is an increase in sediment H2S. We designed experiments to test the influence of various H2S concentrations on Z. marina seedlings. To do this we immersed seedlings in five different concentrations of H2S (68μM, 204μM, 680μM, 2.04mM and 6.8mM) in 2010, and three additional concentrations (400μM, 500μM and 800μM) in 2011. Treated seedlings were consistently killed above 680μM. In addition, high doses (680μM, 800μM, 2.04mM and 6.8mM) of H2S caused depression of photosynthetic output, as well as causing Photosystem II to become inactive whereas Photosystem I remained active. At low doses of H2S (68μM) it appears that photosynthesis increases. Our observations also suggest that this plant may adapt to lethal H2S concentrations if subjected to multiple, but gradually increasing sub-lethal H2S concentrations. These results suggest that Z. marina seedlings are consistently killed at concentrations of hydrogen sulfide found in localities that have experienced declines and local extinctions, and ultimately can be used to explain the lack of re-colonization in these sites.

Differential responses of the mangrove Avicennia marina to salinity and abscisic acid.

Salinisation of the soil can cause plant water deficits, ion and nutrient imbalances and toxic reactions. The halophyte, Avicennia marina (Forssk.) Vierh., is a mangrove that tolerates a wide range of soil salinities. In order to understand how salinity affects plant growth and functioning and how salinity responses are influenced by the water deficit signalling hormone abscisic acid (ABA) we grew A. marina seedlings under two non-growth limiting salinities: 60% seawater and 90% seawater and with and without exogenously supplied ABA. We measured growth, photosynthesis, sap flow, aquaporin gene expression, hydraulic anatomy and nutrient status as well as sap ABA concentrations. ABA addition resulted in a drought phenotype (reduced sap flow, transpiration rates and photosynthesis and increased water use efficiency and aquaporin expression). In contrast, growth in high salinity did not lead to responses that are typical for water deficits, but rather, could be characterised as drought avoidance strategies (no reduction in sap flow, transpiration rates and photosynthesis and reduced aquaporin expression). Tissue nutrient concentrations were higher in seedlings grown at high salinities. We did not find evidence for a role for ABA in the mangrove salinity response, suggesting ABA is not produced directly in response to high concentrations of NaCl ions.

Improved growth performance of the mangrove Avicennia marina seedlings using a 1-aminocyclopropane-1-carboxylic acid deaminase-producing isolate of Pseudoalteromonas maricaloris

Out of 62 bacterial isolates obtained from the mangrove Avicenniamarina rhizosphere that grows along the Abu Dhabi coast, United Arab Emirates (UAE), an isolate of Pseudoalteromonas maricaloris (Wild type strain) (WT) produced relatively high levels of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in vitro. Application of this WT strain under greenhouse conditions to A. marina seedlings significantly (P < 0.05), reduced endogenous levels of ACC in the roots and shoots, and significantly (P < 0.05) increased the levels of in planta endogenous plant growth regulators (PGRs) including indole-3-acetic acid (IAA), indole-3-pyruvic acid (IPYA), putrescine (Put), spermidine (Spd) and spermine (Spm) in roots and shoots compared with control mangrove seedlings. WT application has also significantly (P < 0.05) increased photosynthetic pigment contents, photosynthetic carbon assimilation, plant water use efficiency and promoted mangrove seedlings growth characteristics including increased dry weight and length of roots and shoots, total leaf area and the number of the side branches compared with control mangrove seedlings. In comparison, an ACC deaminase non-producing mutant strain (NPM) failed to reduce endogenous levels of ACC in the roots and shoots and also failed to increase endogenous PGRs and photosynthetic pigments and did not promote seedling growth. Both WT and NPM strains were incapable of producing in vitro detectable levels of IAA, IPYA, Gibberellic acid (GA3), zeatin (Z), Put, Spd and Spm in the culture filtrates. This study demonstrated for the first time the ability of ACC deaminase-producing bacteria to promote mangrove growth under greenhouse conditions. P. maricaloris has potential as biological inoculants to promote the growth of mangrove seedlings in afforestation programs in nutrient impoverished sediments in hyper-saline coastal areas in the UAE.

The impact of the herbicide atrazine on growth and photosynthesis of seagrass, Zostera marina (L.), seedlings

The impact of the widely used herbicide atrazine on seedling growth and photosynthesis of eelgrass was determined. The long-term impact of the herbicide atrazine (1, 10 and 100μg/L) on growth of eelgrass Zostera marina (L.) seedlings, maintained in outdoor aquaria, was monitored over 4weeks. Exposure to 10μg/L atrazine resulted in significantly lower plant fresh weight and total chlorophyll concentration and up to 86.67% mortality at the 100μg/L concentration. Short-term photosynthetic stress on eelgrass seedlings was determined and compared with adult eelgrass using chlorophyll fluorescence. The effective quantum yield in eelgrass seedlings was significantly depressed at all atrazine concentrations (2, 4, 8, 16, 32 and 64μg/L) even within 2h and remained at a lower level than for adult plants for each concentration. These results indicate that atrazine presents a potential threat to seagrass seedling functioning and that the impact is much higher than for adult plants.

Vulnerability of Zostera marina seedlings to physical stress

Eelgrass coverage in Odense Fjord (Denmark) has declined by 90% since 1983, due to eutrophication and its associated pressures, and the state of low eelgrass coverage has remained sta- ble despite 10 to 15 yr of reduced nutrient loading and improved water quality. We hypothesize that the survival of eelgrass seedlings, and thus recolonization through reproductive dispersal, is nega- tively affected by physical disturbances. The 3 most likely physical mechanisms involved are uproot- ing or burial through drifting macroalgae, Arenicola marina sediment reworking and current-driven sediment resuspension. Our hypothesis was tested by field observations during the summer of 2009, when the mortality of seedlings was followed through time. The density of seedlings decreased dra- matically by 80% during the first month of observations, and no seedlings survived past August, cor- responding to an average seedling mortality of 1.5% d -1 . This was >3 times higher than the mortal- ity for seedlings protected from physical disturbance by enclosures (0.4% d -1 ), indicating that physical disturbance contributed to high seedling mortality. A significant correlation (p = 0.02) between macroalgal drift and seedling mortality suggested that ~40% of seedlings were lost due to the physical disturbance of drifting algae. In contrast, no correlations were found between A. marina reworking or resuspension and seedling mortality, despite a mobility of up to 400 cm 3 sediment m -2 d -1 by these mechanisms. Given the observed intensity of macroalgal drift, we speculate that this

Expression and characterization analysis of type 2 metallothionein from grey mangrove species ( Avicennia marina) in response to metal stress

Metallothioneins (MTs) are a family of low-molecular-weight cysteine-rich proteins and are thought to play possible roles in metal metabolism or detoxification. To evaluate the roles of metallothioneins in metal homeostasis or tolerance in Avicennia marina, a real-time quantitative PCR protocol was developed to directly evaluate the expression of AmMT2 mRNA, when A. marina seedlings were exposed to different concentrations of zinc (Zn), copper (Cu) or lead (Pb) for 3 and 7 d. Real-time quantitative PCR results indicated that the regulation of AmMT2 mRNA expression by Zn, Cu and Pb was strongly dependent on concentration and time of exposure. A significant increase in the transcripts of AmMT2 gene was also found in response to Zn, Cu and Pb, at least under some experimental conditions. When AmMT2 was overexpressed in Escherichia coli BL21 as a carboxy-terminal extension of glutathione-S-transferase (GST), the transgenic bacteria showed an increased tolerance to Zn, Cu, Pb and Cd exposure as compared to control strains. Moreover, GST-AmMT2 was purified from E. coli cells grown in the presence of 400 μM Zn, Cu, Pb or Cd. The purified GST-AmMT2 fusion protein could bind higher levels of all four metals than GST alone. Taken together, these data support the hypothesis that AmMT2 may be involved in processes of metal homeostasis or tolerance in A. marina.

Responses of the mangroves Avicennia marina and Bruguiera gymnorrhiza to oil contamination

The effects of bunker fuel oil on morphological and physiological responses of Avicennia marina and Bruguiera gymnorrhiza were investigated in glasshouse and field experiments. In the glasshouse study, 15-month-old seedlings of A. marina were subjected to oiling or debarking treatments for 6 months. Oiling or debarking of a 5 cm ring of the basal portion of the stem, alone and in combination, reduced leaf CO 2 exchange by over 50% and resulted in the production of adventitious roots immediately above the debarked and/or oiled stem 8–12 weeks after the commencement of treatments. In the field study, sediment oiling at a single dose of 5 l m −2 of A. marina and B. gymnorrhiza trees reduced electron transport rate (ETR) through Photosystem II (PSII) and PSII quantum yield. Oiling also reduced the photochemical efficiency of PSII ( F v/ i m) in B. gymnorrhiza, but not in A. marina. After 15 weeks of oiling, adventitious roots developed at the base of the stem in A. marina, but not in B. gymnorrhiza. Naturally occurring A. marina seedlings with adventitious roots exhibited lower leaf CO 2 exchange rates, photochemical efficiency of PSII and leaf chlorophyll content than similar seedlings without these roots. These results indicate that bunker fuel oil adversely affects photosynthetic performance of A. marina and B. gymnorrhiza mangroves. A. marina responds to oiling by producing adventitious roots at the base of the stem. Adventitious root production at the base of the stem may be a useful biological indicator of oil or other toxic pollutants in A. marina.

Pyridine salvage and nicotinic acid conjugate synthesis in leaves of mangrove species

The metabolic fate of [carbonyl- 14C]nicotinamide was surveyed in leaf disks of seven mangrove species, Bruguiera gymnorrhiza, Rhizophora stylosa, Kandelia obovata, Sonneratia alba, Pemphis acidula, Lumnitzera racemosa and Avicennia marina, with and without 250 mM NaCl. Uptake of [ 14C]nicotinamide by leaf disks was stimulated by 250 mM NaCl in K. candel, R. stylosa, A. marina and L. racemosa. [Carbonyl- 14C]nicotinamide was converted to nicotinic acid and was utilised for the synthesis of nucleotides and nicotinic acid conjugates. Formation of nicotinic acid by the deaminase reaction was rapid; there was little accumulation of nicotinamide in the disks 3 h after administration. Radioactivity from [carbonyl- 14C]nicotinamide was incorporated into pyridine nucleotides (mainly NAD and NADP) in all mangrove leaves, and the rates varied from 2% (in L. racemosa) to 15% ( S. alba) of the total radioactivity taken up. NaCl generally reduced nicotinic acid salvage for NAD and NADP. In all mangrove leaf disks, the most heavily labelled compounds (up to 70% of total radioactivity) were trigonelline ( N-methylnicotinic acid) and/or nicotinic acid N-glucoside. Trigonelline was formed in all mangrove plants, but N-glucoside synthesis was found only in leaves of A. marina and K. obovata. In A. marina, incorporation of radioactivity into N-glucoside (51%) was much greater than incorporation into trigonelline (2%). In general, NaCl stimulates the synthesis of these pyridine conjugates. The rate of decarboxylation of nicotinic acid in roots of A. marina seedlings was much greater than for the corresponding reaction observed in leaves.

Lead stress in seedlings of Avicennia marina, a common mangrove species in South China, with and without cotyledons

The effects of lead (Pb; 0–1000 mg L −1) stress on the growth and biochemical responses of seedlings of Avicennia marina were examined, with and without cotyledons. After 50 days exposure to Pb, the growth of A. marina was not affected at low concentrations (0–50 mg L −1 Pb). Roots tolerated to high Pb concentrations, with a significant reduction in biomass only at 1000 mg L −1 Pb. In leaves and stems, 500 mg L −1 Pb already caused a significant decline in biomass (0.6-fold). Accumulation of Pb occurred mainly in roots, with some accumulation in cotyledons but very little in leaves. Pb concentrations in both roots and cotyledons were proportional to the Pb levels in the substrate ( y = 25.945 x − 4281, r 2 = 0.67, P = 0.001 for roots, and y = 0.249 x + 45.636, r 2 = 0.879, P < 0.001 for leaves). In treatments with 500 and 1000 mg L −1 Pb, nitrogen concentrations in cotyledons were higher, while the carbon to nitrogen ratios were significantly lower than in the control without Pb. The Pb levels had significant positive effects on sugar content, MDA concentration and POD activity in both roots and leaves, while the removal of cotyledons significantly decreased the POD activity and MDA content in roots A. marina seedlings according to the two-way multivariate analysis of variance test. The sugar content in the cotyledon of Pb-treated seedlings was significantly lower than that in the control (without Pb), suggesting that more carbohydrate reserves (e.g., sugar) stored in cotyledons had been mobilized to leaves and even roots under Pb treatment.

Leaf and stem anatomical responses to periodical waterlogging in simulated tidal floods in mangrove Avicennia marina seedlings

This study was aimed to evaluate anatomical responses to waterlogging of mangrove seedlings ( Avicennia marina (Forsk.) Vierh.) grown in experimentally simulated semidiurnal tides. The following treatments were used: 0, 2, 4, 6, 8, 10 and 12 h submergence period with two daily tidal cycles. With increasing waterlogging duration, the leaf thickness, mesophyll thickness, palisade parenchyma thickness, palisade–spongy ratio and hypodermis thickness decreased, but the mesophyll to leaf thickness ratio, stem and pith diameter, and cortex thickness increased. The tangential vessel diameter, vessel wall thickness in stem and leaf and fiber wall thickness in stem showed a similar tendency in response to waterlogging, remaining constant between 0 and 4 h waterlogging duration, but decreasing with more prolonged waterlogging. When the waterlogging duration exceeded 4 h, no sclerenchyma cells in leaves or gelatinous fibers in stems were observed. The response of these leaf and stem features indicated that water transport and mechanical support could remain relatively stable in the 0–4 h waterlogging duration, but they would be negatively influenced by longer flooding. Tissues for gas exchange were stimulated by waterlogging, while the functions of water storage, photosynthesis, mesophyll conductance were weakened with increasing waterlogging.

Differential effects of nitrogen and phosphorus enrichment on growth of dwarf Avicennia marina mangroves

The effects of N and P enrichment were investigated on growth and physiological responses of dwarf Avicennia marina mangroves in a hypersaline (58 ± 8 psu) field site in Richards Bay, South Africa. It was hypothesized that at high salinities mangroves allocate more resources to roots than shoots, and that nutrient enrichment with N and P will shift resource allocation to shoots and enhance growth and productivity. In unvegetated areas of the dwarf zone, 1-year-old A. marina seedlings were planted in pots and enriched bimonthly with N, P, N + P, or remained unfertilized (control-C), and growth and morphology of plants were monitored for 2 years. Enrichment with N and N + P shifted resource allocation to shoots from 38% to 55%, and increased dry biomass accumulation by over 500%, compared to the control treatment. In the N and N + P treatments, plant height, number of leaves, leaf chlorophyll content and photosynthesis increased by over 50%, 330%, 30% and 30%, respectively, compared to the C and P treatments. Enrichment with N and N + P increased N concentrations in roots by over 60% (from 1.0 ± 0.1% to 1.6 ± 0.2% of dry mass) and in shoots by over 100% (from 1.3 ± 0.1% to 2.7 ± 02% of dry mass). Plants enriched with P alone were similar to those of the control. This study has demonstrated that dwarf A. marina in Richards Bay is N limited, and that N enrichment shifts resource allocation from roots to shoots and increases growth and productivity.

High water-temperature tolerance in photosynthetic activity ofZostera marinaseedlings from Ise Bay, Mie Prefecture, central Japan

Photosynthetic activities of seedlings of Zostera marina were successively measured using a gas volumeter for 6 days at seven light (0–400 μmol photons/m2 per s) and 11 water temperature conditions (5–35°C). The seedlings were collected from mature plants (Ise Bay, central Japan), and stored and cultured in incubators accurately controlled at each test temperature. The maximum gross photosynthesis (P maxg) was recorded at an optimal water temperature of 29°C after 0 days. After 6 days, P maxg appeared at 25°C and most plants cultured at 29–30°C bleached and withered after the drastic increase of light compensation point (I c). On the contrary, at 5–28°C, the photosynthetic activities either changed little (5–25°C) or recovered after a temporal reduction (26–28°C); seedlings survived and looked healthy after being cultured for 6 days. The recovery was thought to be an acclimation to tolerate higher water temperature. As a result, the critical upper water temperature for Z. marina seedlings was proposed as 28°C. The temperature was consistent with the previously reported maximum water temperature in habitats around the southern boundary of Z. marina in the northern hemisphere.

Comparison of flooding-tolerance in four mangrove species in a diurnal tidal zone in the Beibu Gulf

The flood tolerance of four mangrove species, Aegiceras corniculatum (L.) Blanco (AC), Avicennia marina (Forsk.) Vierh. (Am), Bruguiera gymnorrhiza (L.) Savigny (Bg) and Rhizophora stylosa Griff. (Rs) was examined in a field trial conducted from August 2004 until August 2005 in a diurnal tidal zone in Yingluo Bay, Guangxi province, China. In a section of tidal flat, three replicate artificial platforms were constructed for seedling cultivation. Eight different tidal flat elevation (TFE) treatments were created on each platform. After one year of cultivation under the TFE treatments, the survival rate and growth parameters of seedlings were measured. Seedlings of A. corniculatum and A. marina seedlings survived all treatments. The survival rate of B. gymnorrhiza and R. stylosa seedlings, however, decreased sharply as the TFE fell; in any treatment, fewer B. gymnorrhiza seedlings survived than R. stylosa seedlings. Stem elongation in A. corniculatum and A. marina seedlings was significantly increased by lower TFEs. Lower TFE treatments also increased stem heights in B. gymnorrhiza and R. stylosa seedlings; however, growth was significantly higher as TFE increased. Leaf number, leaf conservation rate and leaf area per seedling changed relatively little among treatments in A. corniculatum and A. marina seedlings, while these three indexes in B. gymnorrhiza and R. stylosa seedlings all decreased dramatically with decreasing TFE. A. marina seedlings reached a higher neonatal biomass at lower TFE treatments, whereas A. corniculatum seedlings attained a higher biomass under moderate TFEs. In contrast, B. gymnorrhiza and R. stylosa seedlings accumulated more biomass in the higher TFEs habitats. Biomass partitioning among the components of both A. corniculatum and A. marina seedlings changed evenly; however, A. corniculatum accumulated more biomass in the leaf while A. marina accumulated more in the stem. The TFE treatments greatly influenced biomass partitioning in B. gymnorrhiza and R. stylosa seedlings, with a change from stem to leaf as the TFE increased. Generally speaking, the rank order of tolerance to flooding among these four mangrove species in the diurnal tidal zone was, from most to least tolerant, A. marina > A. corniculatum > R. stylosa > B. gymnorrhiza. This conclusion is consistent with the general pattern of natural mangrove species zonation along the Chinese coast in the Beibu Gulf. The critical tidal levels for afforestation with these four mangrove species are proposed.

Physiological responses of Avicennia marina seedlings to the phytotoxic effects of the water-soluble fraction of light Arabian crude oil

Stomatal behavior, growth performance and the accumulation of polynuclear aromatic hydrocarbons (PAHs) were evaluated in seedlings of the mangrove Avicennia marina (Forssk.) Vierh., treated with a water-soluble fraction (WSF) of Abu-Dhabi light Arabian crude oil through foliar spraying or soil application. Irregular stomatal behavior and weak stomatal control over transpiration were observed during the first 24 hours, where stomatal resistances of plants sprayed with 150 and 300 μg PAHs plant−1 were significantly lower than that of the control plants. After six weeks, all treated plants showed no significant difference in their relative growth rate (RGR) or in the net assimilation rate (NAR) compared with the control plants. Tri-aromatic hydrocarbons were the most accumulated in tissues of the treated plants. Penta- and hexa-aromatics, on the other hand, were undetectable in the WSF and consequently in the treated plants. A linear relationship was observed between the dose applied to plants and the amounts of tissue accumulated PAHs (r 2=0.515 for soil application and r 2=0.984 for foliar spray). In plants sprayed with 300 μg PAHs plant−1, the total PAHs accumulated were more than that accumulated in plants treated through soil application. These findings suggest that: aqueous extraction of crude oil tends to signify the percentage of the low molecular weight PAHs, e.g. naphthalene, to the total PAHs; disturbed stomatal behavior in the first day of the treatment may be due to the venting of the volatile low molecular weight aromatic hydrocarbons (e.g. benzene, toluene, and xylenes) through the stomata; and uptake of water-soluble hydrocarbons by plants is equally possible through both of the root system and the foliage. The ecological implications of these finding are discussed in relation to oil pollution of mangrove stands under field conditions.

Salt secretion and stomatal behaviour in Avicennia marina seedlings fumigated with the volatile fraction of light Arabian crude oil

Seedlings of the salt secreting mangrove Avicennia marina were exposed to fumes of the volatile fraction of light Arabian crude oil (VFCO) under controlled conditions. Rates of salt secretion were determined in leaves fumigated for 0, 3, and 6 h under four different salinity levels (10, 20, 30, and 40 ppt). Studying the effect of these fumigation periods on stomatal resistance and transpiration was restricted to one salinity level (20 ppt). Opposite to salinity, increasing the fumigation period significantly reduced both salt secretion and transpiration with a significant increase in the stomatal resistance to gas diffusion. During the first day of recovery from fumigation stress, different stomatal oscillation patterns were observed in the treated plants. The amplitude of the oscillations increased with the duration of fumigation, as did the time required for stomatal recovery. Seedlings fumigated for 3 h started to recover within 48 h, while full recovery in seedlings fumigated for 6 h required almost twice that period. The apparent recovery process was evident in the damping off of the amplitude of stomatal oscillations during the measurements period. Data presented herein show that the exposure of mangrove seedlings to VFCO disturbs the normal functions of two major structures in the leaves, i.e. the stomata and the salt glands. The ecophysiological significance of these results was discussed in relation to previous studies.

Responses of eelgrass Zostera marina seedlings to reduced light

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 223:133-141 (2001) - doi:10.3354/meps223133 Responses of eelgrass Zostera marina seedlings to reduced light Joanne C. Bintz1,*, Scott W. Nixon2 1Ocean Studies Board, National Academy of Sciences, 2101 Consitution Av. NW, HA 470, Washington, DC 2041, USA 2Graduate School of Oceanography, University of Rhode Island, PO Box 200, South Ferry Road, Narragansett, Rhode Island 02882, USA *E-mail: jbintz@nas.edu ABSTRACT: We subjected seedlings of Zostera marina L. to High (72%), Medium (23%), and Low (10%) daily irradiance (mean daily PAR of 24.4, 7.9, and 3.3 E m-2 d-1 respectively) over 12 wk. We measured plant response in terms of survivorship, lateral shoot production, morphology, growth rate, photosynthesis and respiration, and leaf pigment concentration. Decreasing the light available to eelgrass seedlings from 72 to 23% resulted in a reduction of lateral shoot formation, lower plant biomass, and longer and wider leaves. Shoot area, growth rate, and pigment concentrations remained similar. A reduction of incident light to 10% decreased survival to 74% and had a negative effect on shoot growth, size, and above- and belowground biomass. Pigment concentrations increased with respect to seedlings raised at medium light. In general, the responses of seedlings to reduced light are similar to those reported for mature Z. marina. Rapid expansion of seedling patches can only occur at irradiance levels greater than 7.9 E m-2 d-1. Morphological changes resulting from exposure to mean daily PAR levels of less than 8 E m-2 d-1 such as thinner leaves and low belowground biomass, have serious implications for decreased seedling survival in the field. KEY WORDS: Eelgrass · Seagrass seedlings · Light · Zostera marina · Shade adaptation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 223. Online publication date: November 28, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Salt Uptake and Excretion in the Mangrove, Avicennia marina(Forsk.) Vierh.

235 seedlings of Avicennia marina were grown for 12 months in nutrient solutions containing 0, 25, 50, 75, 100, 125 and 150% artificial seawater. The salt concentration in the various organs and salt excretion from the leaves were measured to examine the salt regulation in the seedlings. The water potential of various organs in relation to external media was measured concurrently with salt concentration in the seedlings to discuss the water potential adjustment. A. marina was found to absorb a great amount of sodium (Na+) and chloride (Cl-). The salt uptake increased with the increase of external salinity and reached to the ceiling level at around the normal external seawater. The salt concentrations in the seedlings were maintained at levels higher than those of external media. This contributed to produce water potential in the seedlings lower than that of external media. The salt excretion was found to be related positively with the salt concentration in leaves. It was concluded that A. marina seedlings equipped a workable mechanism of salinity regulation through absorption and excretion. And therefore it can survive in the high salinity environment.

Beyond BACI: experimental designs for detecting human environmental impacts on temporal variations in national populations: A. J. Underwood, Australian Journal of Marine & Freshwater Research, 42(5), 1991, pp 569–587

Seagrass global distribution has declined in the last decades due to many causes, and the implementation of recovery programmes as well as the development of new restoration techniques are needed. This work describes the development of an innovative restoration measure to enhance Zostera marina (eelgrass) seed germination and seedling survival in sediments inhabited by lugworms (Arenicola marina) and its validation in mesocosm experiments. The technique consists of placing 3 cm thick biodegradable coconut fibre mats (membrane) in the surface sediment to exclude the negative effects of sediment reworking (burial of seeds and destabilization/burial of seedlings). Two different flume mesocosm experiments were setup to test for: i) the effect of membranes on burial of Z. marina seeds; ii) the effect of membranes on survival and growth of Z. marina seedlings. The experiments were run for 8 and 10 weeks, respectively. Results show that the membrane was effectively preventing critical burial of Z. marina seeds as all seed mimics placed on the surface initially were recovered from 0 to 4 cm depth in the plots with membrane, while in the absence of the membrane, all seeds were buried to below the critical depth of 5–6 cm. The membrane also significantly enhanced the survival of Z. marina seedlings. The initial seedling density was in both cases 30/m2 and the final density was 26.0 ± 3.3/m2 with membrane versus 8.0 ± 1.6/m2 without membrane. This new marine restoration measure showed to be effective on the reduction of the physical stress imposed by sediment reworking lugworms on Z. marina recovery, as a membrane keeps seeds at optimal depth for germination and protects seedlings from burial and erosion. In comparison to other measures, this new restoration technique is a low-tech nature-based solution. The results clearly show that this restoration technique can support Z. marina recovery through seeds and seedling protection. In this way, this technique contributes to decrease Z. marina vulnerability and increase its natural recovery potential and stability.

Growth characteristics of Zostera marina seedlings under anaerobic conditions

Seeds of Zostera marina L. are capable of germinating in anaerobic (nitrogen-gassed) seawater (10%) and developing into seedlings with unusual morphology. The axial hypocotyl of seedlings grown in light and dark was characteristically elongated (mean in dark = 32 mm), but the pumule and adventitious roots remained rudimentary and embryonic in appearance. Aerobic seedlings by contrast exhibited little hypocotyl elongation (mean in dark = 5 mm), and plumule nad roots were well developed. The stalk-like blade of the cotyledon elongated in both aerobic and anaerobic cultures, but growth of the cotyledonary sheath surrounding the plumule was most marked in the presence of oxygen. When seedlings were grown anaerobically in the dark for 16 days and then transferred to aerobic-light conditions, elongation of the axial hypocotyl ceased instantly, but plumule and cotyledonary sheath growth was evident within 32 h, and by 96 h after transfer there was pronounced greening of the plumule leaves and swelling of the root primordia. Hypocotyl elongation of seedlings from seeds planted in sediment varied directly with planting depth. Elongation of the hypocotyl pushed the cotyledonary node with rudimentary plumule and root primordia up through the sediment to a position below the sediment surface where hypocotyl elongation stopped and plumule and root growth commenced. The cotyledonary blade which grew concomitantly with the axial hypocotyl continued to elongate after protruding from the sediment into the overlying water. Results from experiments in which the distal part of a seedling cotyledon was exposed to aerated water while the rest of the seedling was maintained in N 2-gassed water suggested that the cotyledon may function as a conduit for oxygen diffusion to the plumular region of the seedling.