Nursery-propagated plants from seed: a novel tool to improve the effectiveness and sustainability of seagrass restoration

The combined effect of planting density and sediment fertilization on survival, growth and physiology of eelgrass Zostera marina

We subjected shoots of eelgrass Zostera marina to different combinations of planting density [300 (control), 450, 600, 750, 900 shoots m^-2] and sediment fertilization [0 (control), 35, 70, 105, 140 g m^-2] for 6 weeks under controlled conditions. We measured eelgrass responses in terms of survivorship, growth, productivity, leaf pigmentation and carbohydrate concentrations. The ramet frequency of Z. marina reached 47.8 % when exposed to the combination of 600 shoots m^-2 and 70 g m^-2, which was 3.2 times higher than that of shoots under the control. Survival analysis combined with growth assessment suggested that the optimal ranges of planting density and sediment fertilization for the propagation of Z. marina shoots were 501 to 530 shoots m^-2 and 51 to 60 g m^-2, respectively. The promotion of survival and propagation of Z. marina that stemmed from planting density and sediment fertilization mainly depended on the increase of chlorophyll content and accumulation of non-structural carbohydrate. The total chlorophyll content of Z. marina leaves exposed to the combination of 600 shoots m^-2 and 70 g m^-2 was 2.1 times higher than that of shoots under the control. The results will provide data that could prove helpful in the development of efficient artificial propagation technology for Z. marina shoots.

An examination of seed germination and seedling growth of Zostera marina for planting-time selection in Rongcheng Bay, Shandong Peninsula, China

This study firstly quantified the responses of seeds of Zostera marina to different planting times (22 September, 5 October, 23 October, 7 November and 20 November in 2015) through a field seed-planting experiment over a two year period. The suitable seed planting time required by the seeds of Z. marina was evaluated. The seedling establishment rate of Z. marina subjected to different planting times ranged from 7% to 55%, with the higher values attained on the treatments of 22 September and 5 October. New plant patches from seed were fully developed and well maintained on the planting time of 22 September, 5 October and 23 October after 2 years following planting. The shoot density under the three treatments ranged from 62 shoots per replicate to 72 shoots per replicate with an average of 67 shoots per replicate in September 2017. According to the propagation assessment and growth analysis, we found that the planting time from mid-September to mid-October may be the optimal time to plant seeds of Z. marina in our experimental site. Our results demonstrate that seed planting time has an important effect on the effectiveness of eelgrass restoration and provide data that could prove helpful in the development of successful eelgrass restoration.

Rewilding the Sea with Domesticated Seagrass

It is well known that seagrass meadows sequester atmospheric carbon dioxide, protect coasts, provide nurseries for global fisheries, and enhance biodiversity. Large-scale restoration of lost seagrass meadows is urgently needed to revive these planetary ecosystem services, but sourcing donor material from natural meadows would further decline them. Therefore, we advocate the domestication and mariculture of seagrasses in order to produce the large quantities of seed needed for successful rewilding of the sea with seagrass meadows. We provide a roadmap for our proposed solution and show that 44% of seagrass species have promising reproductive traits for domestication and rewilding by seeds. The principle of partially domesticating species to enable subsequent large-scale rewilding may form a successful shortcut to restore threatened keystone species and their vital ecosystem services.

Substrate Type Influences the Structure of Epiphyte Communities and the Growth of Posidonia oceanica Seedlings

Epiphytes colonizing adult seagrasses highly contribute to seagrass ecosystem functioning and plant growth. Yet, little information exists on epiphytic communities developing on seagrass seedlings. Moreover, for some species our knowledge about seedling performance is limited to early establishment phases, and the role of substrate type in affecting their growth is still unclear. These are considerable knowledge gaps, as seedlings play an important role in meadow expansion and recovery from disturbance. In this study, seedlings of Posidonia oceanica, a keystone species of the Mediterranean, were grown in a shallow (1.5 m deep) coastal area along the Tuscany coast (Italy). After five years of growth (July 2009), seedlings were collected and, through multivariate analysis, we examined whether the epiphytic communities of leaves (both internal and external side) and rhizomes, as well as the growth characteristics differed between rock and sand substrate. The epiphytic communities of seedlings largely reflected those found on adult shoots. Epiphyte cover was similar between the two leaf sides, and it was higher on seedlings grown on rock than on sand, with encrusting algae dominating the community. No differences in epiphyte cover and community structure on rhizomes were found between substrates. Seedling growth characteristics did not differ between substrates, apart from the number of standing leaves being higher on rock than on sand. No correlation was found among epiphyte communities and seedling growth variables (i.e., leaf area, maximum leaf length, number of leaves, total number of leaves produced, rhizome length, total biomass, and root to shoot biomass ratio). Results indicate that epiphytes successfully colonize P. oceanica seedlings, and the surrounding micro-environment (i.e., substrate type) can influence the leaf epiphytic community. This study provides new valuable insights on the biological interactions occurring in seagrass ecosystems and highlights the need for better understanding the effects of seedling epiphytes and substrate on the formation of new meadows.

Microbial communities of polyhydroxyalkanoate (PHA)-based biodegradable composites plastisphere and of surrounding environmental matrix: a comparison between marine (seabed) and coastal sediments (dune sand) over a long-time scale

Most researches on the plastisphere in coastal environments deal with plastics floating in seawater. Comparatively smaller attention has been devoted to the plastisphere of plastics buried in marine sediments, and very little is known on that of plastics on coastal sand dunes. Yet, limited information is available on the impact of plastics, especially biodegradable plastics, on microbial organisms in their surroundings. Nevertheless, a large amount of plastics sink on the seabed or is deposited on beach-dune systems. We investigated the succession of plastisphere microbial community on two biodegradable composites based on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and seagrass fibres (PHBV/PO), buried in seabed and dune sediments over a 27 months period in mesocosm. PHBV is regarded as a valuable alternative to conventional plastics and PHBV/PO has recently been designed for applications in coastal habitat restoration. We also examined the degradation rate and impact of these plastics on the microbial communities of surrounding sediments. Microbial communities of the surface of PHBV and PHBV/PO in seabed and dune sand differ from those of surrounding sediments, displaying a lower richness. Plastics colonization occurs largely from bacteria present in surrounding sediments, although the contribution from the water column bacterial pool could be not negligible for plastics in the seabed. No significant differences were detected between the communities of the two plastics and no significant impact of plastics on microbial community of the surrounding sediments was detected. The exceptional long duration of this study allowed to gain information on the succession of a plastisphere community over a previously unexplored time scale. Succession appears highly dynamic in dune sand even after two years, while the community structure in seabed seems to reach stability after one year. These findings highlight the importance of performing long-term studies when trying to characterize composition and dynamics of plastisphere bacterial communities.

Plastics and sedimentation foster the spread of a non-native macroalga in seagrass meadows

Plastics are found in marine environments worldwide, and their effects on macrophytes (seagrasses and macroalgae) colonizing sandy bottoms are still poorly known. Seagrass meadows are valuable but declining ecosystems due to local and global-change related stressors, including sediment disturbance and introduced macroalgae. Understanding whether plastics pose a further threat to seagrasses is critically important. In two simultaneous additive experiments performed in an aquaculture tank, we examined the individual and combined effects of macroplastics (non-biodegradable high-density polyethylene and biodegradable starch-based) and sedimentation (no and repeated sedimentation) on the performance (in terms of biomass and architectural variables) of a native Mediterranean seagrass (Cymodocea nodosa) and an introduced macroalga (Caulerpa cylindracea), and on the intensity of their interactions. Macroplastics were still present in sediments after 18 months. Cymodocea nodosa produced a greater biomass and longer horizontal rhizome internodes forming clones with more spaced shoots probably to escape from plastics. Plastics prevented C. nodosa to react to sedimentation by increasing vertical rhizome growth. Under C. cylindracea invasion, C. nodosa allocated more biomass to roots, particularly to fine roots. In the presence of C. nodosa, C. cylindracea performance was reduced. High-density polyethylene (HDPE) plastic and sedimentation shifted species interactions from competitive to neutral. These results suggest that both HDPE and biodegradable starch-based macroplastics, if deposited on marine bottoms, could make seagrasses vulnerable to sedimentation and reduce plant cover within meadows. HDPE plastic and sedimentation could contribute to the decline of seagrass habitats by facilitating the spread of non-native macroalgae within meadows. Overall, the study highlights the urgent need to implement more effective post-marketing management actions to prevent a further entering of plastics in natural environments in the future, as well as to establish to conservation measures specifically tailored to protect seagrass habitats from plastic pollution.

Inoculating rhizome-propagated Sporobolus pumilus with a native mycorrhizal fungus increases salt marsh plant growth and survival

Salt marshes are ecosystems of significant ecological importance for coastal stability and fundamental roles in marine ecosystems. Salt marshes are declining due to anthropogenic and natural causes including sea level rise. Coastal restoration efforts have increased worldwide, but many fail in long-term coastal stability. We used a naturally occurring arbuscular mycorrhizal fungus (AMF) to test whether survival and early growth of the salt marsh grass Sporobolus pumilus (formerly Spartina patens) improved under simulated salt marsh conditions. Using a tidal mesocosm bench, we grew inoculated plants with varying AMF treatments under simulated tidal regimes to determine if AMF could aid in establishment of healthy Sporobolus communities. Rhizome-derived S. pumilus had greater survival and grew faster than seed-derived plants. Plants inoculated with propagated AMF consistently outperformed both sterile and native sediment controls in terms of plant survival and growth. Use of rhizome-derived Sporobolus inoculated with propagated Funneliformis geosporum showed the most promise in producing successful plant populations for salt marsh restoration. This may be due to plant life stage and improved plant nutrient status, allowing rhizome-derived plants to grow more quickly than seed-derived plants. Using these plants in future large-scale restoration may increase re-establishment of salt marsh ecosystems.

The perfect microsite: How to maximize Posidonia oceanica seedling settlement success for restoration purposes using ecological knowledge

The use of sexual propagules to restore seagrass meadows has raised increasing attention in the last years as seed-based strategies avoid impacts on donor beds while preserving genetic diversity in restored populations. However, the availability of suitable microsites for seedling establishment at transplantation locations is crucial in order to achieve positive outcome of restoration actions. In this study we develop ad-hoc holders that act as optimal microsites for Posidonia oceanica seedling establishment. Holders are intended to be transferred in the field for restoration purposes after few months of indoor seedling culture. Seedling ability to self-anchor to rocky substrates via adhesive root hairs was exploited. We tested rocky holders with different designs in order to maximize seedling survival and settlement. The effect of the holder design on seedling anchorage performances was evaluated. Holders were provided with different topographical complexity and substrate slope. Topographical complexity significantly influenced settlement success, as seedlings did not attach to flat holders, while anchorage reached 100% on holders provided with complexity at seed and the root scales. Substrate slope did not affect the percentage of anchored seedlings, conversely it influenced root growth pattern and thus anchorage stability. This study shows how ecological knowledge of species' life history strategies and associated critical traits provides valuable hints to develop alternative approaches to seagrass restoration tailored to the biology of the system under study.

Use of bio-containers from seagrass wrack with nursery planting to improve the eco-sustainability of coastal habitat restoration

Traditional revegetation techniques employed to restore seagrass meadows and coastal dunes have recently been criticized for their impact on donor populations as well as for the installation of plant anchoring structures made of non-biodegradable or not natural materials in recipient habitats. To improve the ecological sustainability of restoration practices, a novel plantable biodegradable container made of beach-cast seagrass wrack and a bio-based polymer was produced. The long-term performance of two seagrasses, Cymodocea nodosa and Zostera noltei, and two dune plants, Euphorbia paralias and Thinopyrum junceum, grown in nurseries from seeds using the bio-container or a non-biodegradable container of equal size/form made of a conventional plastic (control) was also examined. In addition, the development of bio-container-raised C. nodosa plants in the field was compared to that of plants removed from control containers at the installation and anchored with a traditional system. The bio-container degraded slowly in seawater and in sand and lost its functionality after about three years. In nurseries, all the tested species grown in bio-containers performed as well as, or better than, those raised in non-biodegradable ones. Six months after transplanting into the field, 80% of the C. nodosa nursery-raised plants installed with their bio-container have colonized the surrounding substrate while most of those planted with the traditional system was lost. These results indicate that the new bio-container may support plant growth, and it may also provide protection and anchorage to plants in the field. The use of this bio-container in combination with nursery techniques could improve the environmental sustainability of coastal restoration interventions by providing large plant stocks from seed, thus reducing the impact of collection on donor populations. This approach would also limit the introduction of extraneous materials in recipient habitats and offer an opportunity for valorizing seagrass beach-cast material.

Biotic resistance and vegetative propagule pressure co-regulate the invasion success of a marine clonal macrophyte

Propagule pressure is considered a major driver of plant invasion success. Great propagule pressure would enable invasive species to colonize new areas overcoming the resistance of native species. Many highly invasive aquatic macrophytes regenerate from vegetative propagules, but few studies have experimentally investigated the importance of propagule pressure and biotic resistance, and their interaction, in determining invasion success. By manipulating both recipient habitat and the input of vegetative propagules of the invasive seaweed Caulerpa cylindracea in mesocosm, we examined whether higher propagule pressure would overcome the resistance of a native congeneric (Caulerpa prolifera) and influence its performance. With the native, C. cylindracea population frond number decreased irrespectively of pressure level. High propagule pressure did not increase stolon length and single plant size decreased due to the effects of intra- and interspecific competition. Native biomass decreased with increasing C. cylindracea propagule pressure. These results indicate that higher propagule pressure may fail in enhancing C. cylindracea invasion success in habitats colonized by the native species, and they suggest that biotic resistance and propagule pressure co-regulate the invasion process. These findings emphasize the need to preserve/restore native seaweed populations and may help to design effective management actions to prevent further C. cylindracea spread.

Light Is More Important Than Nutrient Ratios of Fertilization for Cymodocea nodosa Seedling Development

Restoration of seagrass beds through seedlings is an alternative to the transplantation of adult plants that reduces the impact over donor areas and increases the genetic variability of restored meadows. To improve the use of Cymodocea nodosa seedlings, obtained from seeds germinated in vitro, in restoration programs, we investigated the ammonium and phosphate uptake rates of seedlings, and the synergistic effects of light levels (20 and 200 μmol quanta m-2 s-1) and different nitrogen to phosphorus molar ratios (40 μM N:10 μM P, 25 μM N:25 μM P, and 10 μM N:40 μM P) on the photosynthetic activity and growth of seedlings. The nutrient content of seedlings was also compared to the seed nutrient reserves to assess the relative importance of external nutrient uptake for seedling development. Eighty two percent of the seeds germinated after 48 days at a mean rate of 1.5 seeds per day. All seedlings under all treatments survived and grew during the 4 weeks of the experiment. Seedlings of C. nodosa acquired ammonium and phosphate from the incubation media while still attached to the seed, at rates of about twice of adult plants. The relevance of external nutrient uptake was further highlighted by the observation that seedlings' tissues were richer in nitrogen and phosphorus than non-germinated seeds. The uptake of ammonium followed saturation kinetics with a half saturation constant of 32 μM whereas the uptake of phosphate increased linearly with nutrient concentration within the range tested (5 - 100 μM). Light was more important than the nutrient ratio of fertilization for the successful development of the young seedlings. The seedlings' photosynthetic and growth rates were about 20% higher in the high light treatment, whereas different nitrogen to phosphorus ratios did not significantly affect growth. The photosynthetic responses of the seedlings to changes in the light level and their capacity to use external nutrient sources showed that seedlings of C. nodosa have the ability to rapidly acclimate to the surrounding light and nutrient environment while still attached to the seeds. C. nodosa seedlings experiencing fertilization under low light levels showed slightly enhanced growth if nourished with a balanced formulation, whereas a slight increase in growth was also observed with unbalanced formulations under a higher light level. Our results highlight the importance of high light availability at the seedling restoration sites.

Novel Sustainable Composites Based on Poly(hydroxybutyrate-co-hydroxyvalerate) and Seagrass Beach-CAST Fibers: Performance and Degradability in Marine Environments

In order to produce sustainable, bio-based and highly biodegradable materials, composites based on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and fibers of Posidonia oceanica (PO), a dominant Mediterranean seagrass, were produced by simple melt mixing and characterized in terms of thermal stability, morphology and rheological/mechanical properties. In view of their potential application in marine environments, degradation of the developed composites was evaluated under simulated and real marine environmental conditions for 1 year. Using 10 wt % of acetyl tributyl citrate (ATBC) as a plasticizer, smooth processing was achieved for up to 30 wt % of PO fibers, despite the reduction of the melt fluidity observed with increasing fiber loading. The tensile modulus slightly increased (from 2 to 2.4 GPa) while the tensile strength and the elongation decreased (from 23.6 to 21.5 MPa and from 3.2 to 1.9%, respectively) by increasing the PO fiber content from 0 to 30 wt %. Interestingly, the impact resistance of the composites increased with the increasing of the PO content: the Charpy’s impact energy increased from 3.6 (without fiber) to 4.4 kJ/m² for the composite with 30 wt %. The results of the aerobic biodegradation under simulated marine conditions showed that the presence of PO fibers favored the physical disintegration of the composite increasing the biodegradation rate of the polymeric matrix: after 216 days, the composite with 20 wt % PO fibers showed a biodegradability of about 30% compared to 20% of the composite without fibers. Under real marine conditions, the specimens containing PO fibers showed higher weight losses and deterioration of tensile properties compared to those without fibers. Presumably, biodegradation occurred after colonization of the specimen, and the specimens with 20 wt % PO fibers showed well-developed biofilm consisting of bacteria and fungi on the surface after only 3 months of incubation in marine sediments, unlike the no-fiber specimens. Consequently, the persistence of an adequate mechanical performance for a relatively long period (1 year), due to a moderate rate of biodegradation in the marine environment, make the developed PHBV/PO composites particularly suitable for the production of relatively low-cost and biodegradable items which are usable in the sea and/or sand dunes, increasing the market opportunities for biopolymers such as PHBV and, at the same time, finding an eco-sustainable valorization for the PO fibrous residues accumulated in large quantities on Mediterranean beaches, which represents a problem for coastal municipalities.

Biodegradable plastic bags on the seafloor: A future threat for seagrass meadows?

Marine plastic litter is a global concern. Carrier bags manufactured from non-biodegradable polymers constitute a large component of this litter. Because of their adverse impact on marine life, non-biodegradable bags have recently been replaced by biodegradable ones. However, growing evidence shows that these latter are not readily degradable in marine sediments and can alter benthic assemblages. The potential impact of biodegradable bags on seagrasses inhabiting sandy bottoms, which are the most widespread and productive ecosystems of the coastal zones, has been ignored. Mesocosm experiments were conducted to assess the effect of a commercialized biodegradable bag on a common seagrass species of the Mediterranean, Cymodocea nodosa, both at the level of individual plant (clonal growth) and of plant community (plant-plant relationships), under three culture regimes (plant alone, in combination with a neighbour of the same species or of the co-existing seagrass Zostera noltei) simulating different natural conditions (bare substrate, monospecific meadows or mixed meadows). The bag behaviour in marine sediment and sediment physical/chemical variables were also examined. After six months of sediment exposure, the bag retained considerable mass (85% initial weight) and reduced sediment pore-water oxygen concentration and pH. In the presence of bag, C. nodosa root spread and vegetative recruitment increased compared to controls, both intra- and interspecific interactions shifted from neutral to competitive, and the growth form changed from guerrilla (loosely arranged group of widely spaced ramets) to phalanx form (compact structure of closed spaced ramets) but only with Z. noltei. These findings suggest that biodegradable bags altering sediment geochemistry could promote the spatial segregation of seagrass clones and influence species coexistence.

Recruitment and Patch Establishment by Seed in the Seagrass Posidonia oceanica: Importance and Conservation Implications

Seagrasses are declining globally, and deeper understanding is needed on the recruitment potential and distribution of new populations for many threatened species to support conservation planning in the face of climate change. Recruitment of Posidonia oceanica, a threatened seagrass endemic to the Mediterranean, has long been considered rare due to infrequent flowering, but mounting evidence demonstrates that the species is responding to a changing climate through greater reproductive effort. Due to the fragmentary information on recruit occurrence and distribution, little is known about reproductive success in the species and its contribution to persistence. We assembled P. oceanica recruitment data from published and unpublished sources, including our own, to examine the frequency and extent of recruitment events (establishment of seedlings in a site), seedling growth potential and habitat characteristics at recruitment sites. Results show that at least one recruitment event has occurred about every 3 years, and 18 localities were colonized at least one time since the first seedling record in 1986. Notably, consistently high seedling inputs were observed in four localities of the Western Mediterranean. Seedlings established mainly on unoccupied substrate areas along the coasts of islands, in sheltered sites and at shallower depths (<3 m) than the upper limit of adjacent P. oceanica meadows. Seedling establishment occurred more frequently on rocky than on sandy substrate, and rarely on dead "matte" or meadows of the seagrass Cymodocea nodosa. The chance of colonization success on rock was two times higher than on sand. Our 11 years of observations have allowed for the first time the documentation of the formation and development of patches by P. oceanica seed. These findings contradict the historical assumption that sexual recruitment is rare and usually unsuccessful for P. oceanica, and highlight the potential importance of recruitment for the long-term persistence and adaptation of the species to sea level rise predicted in the next century in the Mediterranean. Unfortunately, management actions have mainly focused on established meadows, ignoring the presence of recruits in outside areas. Therefore, it will be useful to identify and consider regeneration sites in designing future management strategies to improve seagrass conservation effectiveness.

New Bio-Composites Based on Polyhydroxyalkanoates and Posidonia oceanica Fibres for Applications in a Marine Environment

Bio-composites based on polyhydroxyalkanoates (PHAs) and fibres of Posidonia oceanica (PO) were investigated to assess their processability by extrusion, mechanical properties, and potential biodegradability in a natural marine environment. PHAs were successfully compounded with PO fibres up to 20 wt % while, at 30 wt % of fibres, the addition of 10 wt % of polyethylene glycol (PEG 400) was necessary to improve their processability. Thermal, rheological, mechanical, and morphological characterizations of the developed composites were conducted and the degradation of composite films in a natural marine habitat was evaluated in a mesocosm by weight loss measure during an incubation period of six months. The addition of PO fibres led to an increase in stiffness of the composites with tensile modulus values about 80% higher for composites with 30 wt % fibre (2.3 GPa) compared to unfilled material (1.24 GPa). Furthermore, the impact energy markedly increased with the addition of the PO fibres, from 1.63 (unfilled material) to 3.8 kJ/m² for the composites with 30 wt % PO. The rate of degradation was markedly influenced by seawater temperature and significantly promoted by the presence of PO fibres leading to the total degradation of the film with 30 wt % PO in less than six months. The obtained results showed that the developed composites can be suitable to manufacture items usable in marine environments, for example, in natural engineering interventions, and represent an interesting valorisation of the PO fibrous wastes accumulated in large amounts on coastal beaches.

The cost and feasibility of marine coastal restoration

Land-use change in the coastal zone has led to worldwide degradation of marine coastal ecosystems and a loss of the goods and services they provide. Restoration is the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed and is critical for habitats where natural recovery is hindered. Uncertainties about restoration cost and feasibility can impede decisions on whether, what, how, where, and how much to restore. Here, we perform a synthesis of 235 studies with 954 observations from restoration or rehabilitation projects of coral reefs, seagrass, mangroves, salt-marshes, and oyster reefs worldwide, and evaluate cost, survival of restored organisms, project duration, area, and techniques applied. Findings showed that while the median and average reported costs for restoration of one hectare of marine coastal habitat were around US$80000 (2010) and US$1600000 (2010), respectively, the real total costs (median) are likely to be two to four times higher. Coral reefs and seagrass were among the most expensive ecosystems to restore. Mangrove restoration projects were typically the largest and the least expensive per hectare. Most marine coastal restoration projects were conducted in Australia, Europe, and USA, while total restoration costs were significantly (up to 30 times) cheaper in countries with developing economies. Community- or volunteer-based marine restoration projects usually have lower costs. Median survival of restored marine and coastal organisms, often assessed only within the first one to two years after restoration, was highest for saltmarshes (64.8%) and coral reefs (64.5%) and lowest for seagrass (38.0%). However, success rates reported in the scientific literature could be biased towards publishing successes rather than failures. The majority of restoration projects were short-lived and seldom reported monitoring costs. Restoration success depended primarily on the ecosystem, site selection, and techniques applied rather than on money spent. We need enhanced investment in both improving restoration practices and large-scale restoration.

Assessing Posidonia oceanica seedling substrate preference: an experimental determination of seedling anchorage success in rocky vs. sandy substrates

In the last decades the growing awareness of the ecological importance of seagrass meadows has prompted increasing efforts to protect existing beds and restore degraded habitats. An in-depth knowledge of factors acting as major drivers of propagule settlement and recruitment is required in order to understand patterns of seagrass colonization and recovery and to inform appropriate management and conservation strategies. In this work Posidonia oceanica seedlings were reared for five months in a land-based culture facility under simulated natural hydrodynamic conditions to identify suitable substrates for seedling anchorage. Two main substrate features were investigated: firmness (i.e., sand vs. rock) and complexity (i.e., size of interstitial spaces between rocks). Seedlings were successfully grown in culture tanks, obtaining overall seedling survival of 93%. Anchorage was strongly influenced by substrate firmness and took place only on rocks, where it was as high as 89%. Anchorage occurred through adhesion by sticky root hairs. The minimum force required to dislodge plantlets attached to rocky substrates reached 23.830 N (equivalent to 2.43 kg), which would potentially allow many plantlets to overcome winter storms in the field. The ability of rocky substrates to retain seedlings increased with their complexity. The interstitial spaces between rocks provided appropriate microsites for seedling settlement, as seeds were successfully retained, and a suitable substrate for anchorage was available. In conclusion P. oceanica juveniles showed a clear-cut preference for hard substrates over the sandy one, due to the root system adhesive properties. In particular, firm and complex substrates allowed for propagule early and strong anchorage, enhancing persistence and establishment probabilities. Seedling substrate preference documented here leads to expect a more successful sexual recruitment on hard bottoms compared with soft ones. This feature could have influenced P. oceanica patterns of colonization in past and present time.

Salinity fluctuation of the brine discharge affects growth and survival of the seagrass Cymodocea nodosa

The increase of seawater desalination plants may affect seagrasses as a result of its hypersaline effluents. There are some studies on the salinity tolerance of seagrasses under controlled laboratory conditions, but few have been done in situ. To this end, Cymodocea nodosa shoots were placed during one month at four localities: two close to a brine discharge; and the other two not affected by the discharge, and this experiment was repeated four times. The results obtained showed a decrease in growth and an increased mortality at the localities affected by the brine discharge. An increase was detected in the percentage of horizontal shoots in respect to vertical shoots at the impacted localities. It is probably that not only the average salinity, but also the constant salinity fluctuations and slightly higher temperatures associated with the brine that may have caused physiological stress thus reducing C. nodosa growth and survival.

Restoring eelgrass (Zostera marina L.) habitats using a simple and effective transplanting technique

Eelgrass beds in coastal waters of China have declined substantially over the past 30 years. In this study, a simple new transplanting technique was developed for eelgrass (Zostera marina L.) restoration. To assist in anchoring single shoots, several rhizomes of rooted shoots were bound to a small elongate stone (50-150 g) with biodegradable thread (cotton or hemp), and then the bound packet was buried at an angle in the sediments at a depth of 2-4 cm. This stone anchoring method was used to transplant eelgrass in early November 2009 and late May 2010 in Huiquan Bay, Qingdao. The method led to high success. Three month survivorship of the transplanted shoots at the two transplant sites was >95%. From April 20 to November 19, 2012, the following characteristics of the 2009 and 2010 transplanted eelgrass beds were monitored: morphological changes, shoot density, shoot height, leaf biomass, and sediment particle size. Results showed that the sexual reproduction period of the planted eelgrass was from April to August, and vegetative reproduction reached its peak in autumn. Maximum shoot height and biomass were observed in June and July. After becoming established, the transplanted eelgrass beds were statistically equal to natural eelgrass beds nearby in terms of shoot height, biomass, and seasonal variations. This indicates that the transplant technique is effective for eelgrass restoration in coastal waters.