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Recruit survival of Cymodocea nodosa along a depth gradient

Publication . Paulo, Diogo; Manent, Pablo; Barrio, Juan M.; Serrão, Ester; Alberto, Filipe

Clonal plants can reproduce sexually and clonally, expressing different proportions of these different life histories in distinctive environments. In seagrass meadows, light attenuation hinders marine plant colonization in deeper areas of its vertical distribution. Therefore it is expected that the fluorescence maximum quantum yield of seedlings will be higher at deep limits of the meadow relative to shallower depths. We hypothesized that seagrass seedlings experience higher mortality in deeper areas of the meadows than at shallower levels. Our objective was to test survival of seagrass seedlings along a depth gradient in meadows of Cymodocea nodosa in the Canary Islands. Seedlings germinated in laboratory conditions, were transplanted to a natural meadow at three water depths: shallow (5 m), medium (8 m) and deep (12 m). Transplanted seedlings were monitored by measuring maximum quantum yield, leaf length, number of leaves per shoot and survival. Our data suggest that light does not hinder survival of seedlings along the depth gradient of the meadow. Before establishing clonal growth, seedlings in deeper areas had higher survival rates than those in shallow areas. Even though seeds are present at shallow depths and sexual allocation is high, sexual contribution can be lower than expected due to seedling loss.

2016Journal article

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Effects of disturbance and stress on the reproductive modes of marine plants

Publication . Paulo, Diogo Filipe da Silva Gonçalves Soares; Serrão, Ester; Alberto, Filipe

Seagrass populations are declining worldwide due to human activities and rapid climate changes. Marine plants achieve population growth by a combination of sexual and clonal reproduction, and their relative contribution to population life history is poorly studied. Seagrasses are limited by light at the lower depth limit of distribution and by hydrodynamic action at the upper limit. Literature suggests a differentiated demography and genetic structure along the depth gradient, from higher contribution of sexual reproduction at shallower depths to a progressively larger contribution of clonal propagation deeper. In the first chapter we found that along a depth gradient more Cymodocea nodosa seedlings where lost at shallow depths than at deeper levels. The hypothesis of a differentiated reproductive balance along the depth gradient was tested in the second chapter, by analysing the demography and genetic structure of seagrass meadows along depth gradients. The results showed a heterogeneous pattern of genotypic richness and clonal structure, likely influenced by local acclimation and stochasticity. In the third chapter, the re-colonization strategies after perturbation along a C. nodosa meadow were investigated. Initially recolonization was mainly clonal, but after winter the study areas had loss biomass and only few shoots remained. Though the areas did not fully recover, genotypic richness increased along time in the perturbed areas, demonstrating the relevance of sexual reproduction at any depth level. In the fourth chapter, a Zostera marina meadow that disappeared after extreme perturbation was studied. Previous to its disappearance, the meadow was known to be genetically rich. Sexual reproduction, via seed bank, played a crucial role in its recovery. In a later stage, clonal growth was essential for colonization and spread. In the fifth chapter, seagrass transplants initiated via clonal propagation were tested in an area where 10 ha of seagrass were loss due to continued impacts. The result was the selection of the most successful species, donor population and time of the year to attempt future transplants. Furthermore, it is likely that larger initial transplant areas are able to surpass the required threshold to achieve vegetated stability, allowing for long term persistence. The challenges of seagrass restoration highlight the urgent need to protect seagrass meadows worldwide.

2019-01-14Doctoral thesis

Open access