Abstract
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.
Highlights
Seagrass meadows are undergoing worldwide decline due to rapid environmental changes prompted by human activities [1,2]
No specific permit was required for P. oceanica fruit and seed collection as we used only beachcast biological material
The progression of seedling anchorage on the bare rocky substrates was observed over the first 3 weeks of culture: the emergence and growth of the root system was coupled with the production of extensive root hairs on the lower part of the seed as well as in the piliferous zone of primary and adventitious roots
Summary
Seagrass meadows are undergoing worldwide decline due to rapid environmental changes prompted by human activities [1,2]. Over the past few decades, increasing efforts have been made to prevent further losses and to restore degraded habitats through active transplantation, with variable results being obtained depending on the species involved [3,4], methodologies applied and availability of suitable sites [5,6]. A major concern regarding the application of these methods at medium and large scales is the potential detrimental effects on donor beds due to the removal of large amounts of biological material [7]. This concern has increased the demand for more ecologically sustainable techniques that support degraded populations without negatively impacting healthy ones. This aim is relevant when working with large, slow-growing species, such as members of the genera Thalassia and Posidonia
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