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• Secondary dispersal is an important process in seagrass meadows. • Microtopography could affect secondary seed dispersal distances. • A theory relating secondary dispersal with the microtopography is formulated. • The formulation is validated with computational fluid dynamics for two seagrasses. • These results can inform seed-based restoration to assess secondary dispersal. Motivated by observational and experimental evidence, a theoretical model is proposed to relate the secondary dispersal of seagrass seeds with the complexity of microtopography in natural environments. Complexity is encoded in terms of the Hurst exponent of a fractal description of the microtopographical geometry. The percentage of a seafloor transect where secondary dispersal of seagrass seeds occurs, is quantified in terms of the mainstream velocity, bottom complexity and properties of the seeds. Theoretical expressions are validated considering the cases of Zostera marina and Posidonia oceanica seeds and using computational fluid dynamics (CFD). A total of 200 CFD simulations with different bottom complexities and flow conditions, were done for each seagrass genus to validate the theoretical model. Numerical results agree with theoretical predictions. This finding provides a management tool to assess the degree of seed retention in seed-based restoration areas. [ABSTRACT FROM AUTHOR]

Seagrass meadows, through their large capacity to sequester and store organic carbon in their sediments, contribute to mitigate climatic change. However, these ecosystems have experienced large losses and degradation worldwide due to anthropogenic and natural impacts and they are among the most threatened ecosystems on Earth. When a meadow is impacted, the vegetation is partial- or completely lost, and the sediment is exposed to the atmosphere or water column, resulting in the erosion and remineralisation of the carbon stored. This paper addresses the effects of the construction of coastal infrastructures on sediment properties, organic carbon, and total nitrogen stocks of intertidal seagrass meadows, as well as the size of such stocks in relation to meadow establishing time (recently and old established meadows). Three intertidal seagrass meadows impacted by coastal constructions (with 0% seagrass cover at present) and three adjacent non-impacted old-established meadows (with 100% seagrass cover at present) were studied along with an area of bare sediment and two recent-established seagrass meadows. We observed that the non-impacted areas presented 3-fold higher percentage of mud and 1.5 times higher sedimentary organic carbon stock than impacted areas. Although the impacted area was relatively small (0.05–0.07 ha), coastal infrastructures caused a significant reduction of the sedimentary carbon stock, between 1.1 and 2.2 Mg OC, and a total loss of the carbon sequestration capacity of the impacted meadow. We also found that the organic carbon stock and total nitrogen stock of the recent-established meadow were 30% lower than those of the old-established ones, indicating that OC and TN accumulation within the meadows is a continuous process, which has important consequences for conservation and restoration actions. These results contribute to understanding the spatial variability of blue carbon and nitrogen stocks in coastal systems highly impacted by urban development. • Seagrass organic carbon (OC) stock was impacted by coastal infrastructures. • OC stocks at impacted areas were 1.5 times lower than at non-impacted areas. • Non-impacted areas presented 3-fold higher percentage of mud than impacted areas. • Recently established meadow presented 30% lower OC than the old-established ones. [ABSTRACT FROM AUTHOR]

Ecological analyses are aimed at characterizing the complexity of the structure of natural objects, yet their heterogeneity is hardly described by the Euclidean concepts. For such purpose, the fractal geometry can be best suited due to its ability in describing, with mathematical rigor, the inherent irregularity of nature. Fractal dimension provides indeed a measurement of the complexity of the analyzed object in terms of space occupation. In this study, we applied the fractal geometry to Posidonia oceanica in order to characterize the structural complexity of its meadows, which are widely recognized as one of the most important coastal ecosystems in the Mediterranean basin. For achieving our aim, we developed an ad hoc implementation of the Box-Counting algorithm based on the Moore neighborhood analysis. Our approach allowed to render the structural complexity of P. oceanica meadows spatially explicit, thus expressing an intrinsic ecological property. The fractal analysis suggested that the complexity of meadows structure is intimately connected with the ecological conditions of P. oceanica. In fact, meadows in living and mixed conditions showed a higher fractal dimension, suggesting a largely uniform and smooth structure. While the fractal dimension associated to the regressed ecological condition of P. oceanica meadows exhibited lower values, highlighting a more jagged and rough structure. Therefore, the fractal theory may prove useful to both fundamental and applied ecological research focusing on P. oceanica and its interactions with Mediterranean coastal ecosystems. In fact, the fractal analysis we performed could result in an effective and straightforward approach for assessing the condition of P. oceanica at large spatial scale, enhancing an integrated maritime spatial planning over the whole Mediterranean basin. • Posidonia oceanica meadows are paramount ecosystems in the Mediterranean basin. • The complexity of meadows structure is a crucial property of Posidonia oceanica. • Fractal geometry is capable of describing the inherent complexity of nature. • Fractal dimension resulted strictly related to the ecological condition of meadows. • Fractal analysis proved to be effective for the assessment of meadows condition. [ABSTRACT FROM AUTHOR]

In Southeast Asia, seagrass meadows are under threat through coastal development and increased pollution, but remain understudied. The dugong is a marine herbivore that is dependent on the availability of seagrass as a primary food source. In this study, we assess the patterns of co-occurrence between dugongs and seagrass. We hypothesize that the changing spatial patterns of dugong feeding are positively correlated to the seasonal variation in distribution and abundance of mixed species in subtidal tropical seagrass meadows. We documented seagrass cover and dugong feeding trails in the Sibu Archipelago meadow in Johor, Malaysia, across the monsoon seasons of 2016–2017 using an underwater towed video method. Moran's I and Getis-Ord G i * statistics were used to quantify the degree of clustering in feeding trails, feeding patch size, and to identify feeding hotspots and coldspots. This site has the single largest subtidal meadow in Peninsular Malaysia known to date, measuring 12.88 km2. The study captured a reduction in seagrass extent and coverage during the study. Feeding trail occurrence averaged three per image throughout the seasons, with the maximum number being 14 trails per image. Dugongs fed in a spatially clustered manner leaving two distinct feeding trail patterns: (1) a dispersed pattern when seagrass cover was high or low (76–100% and 0–25%) that resulted in larger patch sizes, and (2) a concentrated pattern in moderate seagrass cover (26–75%) that resulted in smaller patch size. Feeding hotspots and coldspots had significantly different seagrass cover, suggesting that dugongs foraged strategically within the meadow. Our results demonstrate that seagrass cover played a significant role in driving dugong feeding patterns and in creating feeding hotspots and coldspots in tropical subtidal meadows. • The largest seagrass meadow in Malaysia undergoes dramatic changes in cover and extent. • Underwater towed video method captures spatial patterns of dugong feeding. • Dugong feeding patterns in the subtidal meadow changes in response to seagrass cover. • Seagrass cover influences the locations of dugong feeding hotspots and coldspots. • Dugongs in the Sibu Archipelago consumed Halophila ovalis and Halodule uninervis. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative sampling in combination with classification of fish species into six major feeding guilds revealed the position and contribution of non-indigenous species (NIS) in the food web of Posidonia oceanica and sandy habitats in an area of the eastern Mediterranean. In P. oceanica beds and on sandy bottoms 10 and five species, respectively, were non-indigenous fish of Indo-Pacific origin. The proportional contribution of NIS individuals on P. oceanica beds was lower than that of sandy bottoms (12.7 vs. 20.4%) a pattern that also followed for biomass (13.6 vs. 23.4%), indicating that low diverse systems may be more liable to introductions than species-rich communities. The two habitats had similar fish feeding guilds, but the biomass contribution from NIS varied within each guild, indicating different degrees of impact on the available resources. This study showed that only few non-indigenous fish species contributed to the differences in biomass between habitats. No support could be found in postulating that taxonomic affiliation could predict invasion success. Size was considered highly important due to habitat shift of species with increased size. Two of the aspects considered in this study, the chance of establishing vs. the chance of being very dominant will depend upon competitive abilities strongly coupled to size and grounds for habitat shift. However, success of establishment will also depend on appropriate food resources in the recipient community as well as competitive abilities and level of competition in the food web within habitats. [Copyright &y& Elsevier]

Abstract Deposits of the endemic Mediterranean seagrass, Posidonia oceanica , are usually found covering the fronts of sandy beaches. In Egypt, these deposits are thought of as waste and subjected to removal by heavy machinery. The current study provides the first report on the status and distribution of P. oceanica deposits along the Mediterranean Coast of Egypt, in addition to an assessment of trace elements (TE), organic carbon (OC), and nutrient contents of some of their banquettes. The results indicate that TE concentrations of P. oceanica litter and associated sediments and water are acceptable according to the international limits. The results also show that organic matter constituted >10% of P. oceanica litter dry weight, while OC constituted 1.9% similar to that reported for P. oceanica living tissue. A research strategy is needed to assess carbon stocks of P. oceanica meadows and their deposits along the Mediterranean coast of Egypt, in order to set strategies to mitigate climate change based on their carbon storage capacity. Local campaigns should be conducted to increase people's awareness of the importance of P. oceanica to the environment and consequently to their livelihood. • First report on the distribution of P. oceanica deposits in Egypt. • Data on the carbon stocks of P. oceanica meadows in the Mediterranean coast of Egypt is sparse. • Assessment of trace elements and nutrients content of some P. oceanica banquettes in Egypt. • Trace elements content of P. oceanica litter is acceptable according to the international limits. • Organic matter and organic carbon constituted of >10% and 1.9% of P. oceanica litter, resp. [ABSTRACT FROM AUTHOR]

Seagrass loss can be partially attributed to naturally- or anthropogenically-induced sediment dynamics that involve excessive burial or erosion processes. The main goal of this work was to develop a modelling approach for analysing bottom morphological changes on Sites of Community Importance (SCIs) characterized by the presence of Posidonia oceanica meadows. Sediment dynamics (settling fluxes) and composition (grain size and mineralogy) within the two SCIs of the Civitavecchia coastal zone (north-eastern Tyrrhenian, Italy) were investigated using sediment traps and bottom sediment samples. Moreover structural, morphological, and dynamic parameters of P. oceanica meadows were analyzed. The results showed high reliability in reproducing the settling fluxes of medium and coarser sands (the most abundant sediment fractions of the two SCIs) compared to the corresponding fluxes estimated with sediment traps. To further confirm the accuracy of the proposed approach, a significant relationship was shown to exist between bottom morphological changes reproduced by the numerical model and plant rhizome growth as measured by in-situ sampling; this relationship attests to the capacity of P. oceanica to withstand burial and erosion processes. The model allowed us to perform a high spatial resolution evaluation of erosion levels and deposition processes that occur within the two SCIs, providing a predictive and useful tool towards a more sustainable management and conservation strategy of P. oceanica meadows in coastal zones. • Numerical model was used to analyse the sediment dynamics on P. oceanica meadows. • Numerical results for sedimentation fluxes correlated with the experimental results. • The model explained the belowground morphology of P. oceanica. • The approach can be adopted as a predictive tool to support P. oceanica conservation. [ABSTRACT FROM AUTHOR]

Seagrass meadows are globally threatened by anthropogenic and natural pressures that cause habitat fragmentation and ecosystem degradation. Seagrass fragmentation is manidested by the loss of vegetation in gaps within a meadow. Depending on the degree of fragmentation, the ecological services provided by theseagrass meadows may be compromised. This study aims to understand the effect meadow fragmentation hason the shoot density of the canopy (large-scale or meadow-scale effect), as well as the effect the local gap size has on the shoot density at the edge of the gap (local-scale or gap-scale effect). In other woerd, determine whether the effects on the large scale can impact the local scales of the gap. This study demonstrates that the greater the gap area is, the lower the shoot density of the vegetation surrounding the gap. Moreover, the effect of fragmentation at the meadow-scale has been proved: the higher the fragmentation degree of the meadow is, the lower the shoot density is in the surrounding vegetation near the gap. Hence, the differences in shoot density at the edges of a gap are proven to be produced by both meadow fragmentation and gap characteristics. Image 1 • Meadows fragmentation impacts on the canopy density at both gap- and canopy-scales. • The larger the gap size the sparser the canopy density of the on-shore canopy nearby. • The higher the meadow fragmentation the sparser the canopy density at gap edges. [ABSTRACT FROM AUTHOR]