Browsing by Author "van Katwijk, Marieke M."
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- Biomechanical response of two fast-growing tropical seagrass species subjected to in situ shading and sediment fertilizationPublication . La Nafie, Yayu A.; de los Santos, Carmen B.; Brun, Fernando G.; Mashoreng, Supriadi; van Katwijk, Marieke M.; Bouma, Tjeerd J.Although seagrasses experience strong hydrodynamic forces, little is known about their biomechanical response in spite of the potential importance for their ecological success. We investigated how light reduction and sediment-nutrient enrichment affect biomechanical and morphological properties of two short-lived tropical seagrass species: Halophila ovalis and Halodule uninervis. A 50-day manipulative field experiment of shading and sediment-nutrient enrichment versus a natural population (control) showed that both shading and nutrient enrichment made the leaves of Halophila ovalis weaker (lower FTS) and more elastic (lower ET). As the absolute breakability of leaves (FMAX) was not affected by either of the treatments, this implies that these changes in strength and stiffness resulted from the increase in leaf dimensions under nutrient enrichment (i.e., longer, wider and thicker leaves) and shading conditions (i.e., thicker leaves). In contrast, the biomechanical properties of H. uninervis leaves were less responsive and only became more extensible under shading while their biomechanics did not change under sediment nutrient enrichment. This limited response of H. uninervis might be due to the lack of morphological response in this species since leaves only became longer under nutrient enrichment. When comparing both species across treatments under shading (after normalizing them with their controls), H. ovalis became significantly weaker compared to H. uninervis, and the latter became more extensible. Under nutrient enrichment, H. ovalis became significantly more elastic compared H. uninervis. Overall we found that (i) biomechanical properties can be affected by environmental conditions, (ii) the responses were species specific, and (iii) seagrass morphology (leaf thickness and width) affected by environmental conditions will influence seagrass biomechanical properties. Further experimental studies on seagrass biomechanics are needed as present understandings of the acclimation of these properties and the consequences for species functioning are only starting to emerge.
- Global analysis of seagrass restoration: the importance of large-scale plantingPublication . van Katwijk, Marieke M.; Thorhaug, Anitra; Marba, Nuria; Orth, Robert J.; Duarte, Carlos M.; Kendrick, Gary A.; Althuizen, Inge H. J.; Balestri, Elena; Bernard, Guillaume; Cambridge, Marion L.; Cunha, Alexandra; Durance, Cynthia; Giesen, Wim; Han, Qiuying; Hosokawa, Shinya; Kiswara, Wawan; Komatsu, Teruhisa; Lardicci, Claudio; Lee, Kun-Seop; Meinesz, Alexandre; Nakaoka, Masahiro; O'Brien, Katherine R.; Paling, Erik I.; Pickerell, Chris; Ransijn, Aryan M. A.; Verduin, Jennifer J.In coastal and estuarine systems, foundation species like seagrasses, mangroves, saltmarshes or corals provide important ecosystem services. Seagrasses are globally declining and their reintroduction has been shown to restore ecosystem functions. However, seagrass restoration is often challenging, given the dynamic and stressful environment that seagrasses often grow in. From our world-wide meta-analysis of seagrass restoration trials (1786 trials), we describe general features and best practice for seagrass restoration. We confirm that removal of threats is important prior to replanting. Reduced water quality (mainly eutrophication), and construction activities led to poorer restoration success than, for instance, dredging, local direct impact and natural causes. Proximity to and recovery of donor beds were positively correlated with trial performance. Planting techniques can influence restoration success. The meta-analysis shows that both trial survival and seagrass population growth rate in trials that survived are positively affected by the number of plants or seeds initially transplanted. This relationship between restoration scale and restoration success was not related to trial characteristics of the initial restoration. The majority of the seagrass restoration trials have been very small, which may explain the low overall trial survival rate (i.e. estimated 37%). Successful regrowth of the foundation seagrass species appears to require crossing a minimum threshold of reintroduced individuals. Our study provides the first global field evidence for the requirement of a critical mass for recovery, which may also hold for other foundation species showing strong positive feedback to a dynamic environment.Synthesis and applications. For effective restoration of seagrass foundation species in its typically dynamic, stressful environment, introduction of large numbers is seen to be beneficial and probably serves two purposes. First, a large-scale planting increases trial survival - large numbers ensure the spread of risks, which is needed to overcome high natural variability. Secondly, a large-scale trial increases population growth rate by enhancing self-sustaining feedback, which is generally found in foundation species in stressful environments such as seagrass beds. Thus, by careful site selection and applying appropriate techniques, spreading of risks and enhancing self-sustaining feedback in concert increase success of seagrass restoration.For effective restoration of seagrass foundation species in its typically dynamic, stressful environment, introduction of large numbers is seen to be beneficial and probably serves two purposes. First, a large-scale planting increases trial survival - large numbers ensure the spread of risks, which is needed to overcome high natural variability. Secondly, a large-scale trial increases population growth rate by enhancing self-sustaining feedback, which is generally found in foundation species in stressful environments such as seagrass beds. Thus, by careful site selection and applying appropriate techniques, spreading of risks and enhancing self-sustaining feedback in concert increase success of seagrass restoration.
- Waves and high nutrient loads jointly decrease survival and separately affect morphological and biomechanical properties in the seagrassZostera noltiiPublication . La Nafie, Yayu A.; de los Santos, Carmen B.; Brun, Fernando G.; van Katwijk, Marieke M.; Bouma, Tjeerd J.In an 8-week aquarium experiment, we investigated the interactive effects of waves (present vs. absent) and water-column nutrient level (high vs. low) on the survival, growth, morphology, and biomechanics of the seagrass, Zostera noltii. Survival was reduced when plants were exposed to both waves and high nutrient levels. Wave and nutrient interaction significantly reduced aboveground biomass and leaf lengths, whereas waves independently reduced growth rate, internode abundance, elongation, and appearance rates. Nutrient supply significantly reduced the strength of the leaves. Wave and nutrient interaction was the main driving force affecting survival and morphological properties of seagrass, whereas dynamical characteristics were independently affected by waves, and nutrient supply affected mainly biomechanical properties. In conclusion, this experiment revealed that the combination of exposure to waves and high nutrient levels was detrimental for Z. noltii, which indicates that this could be an important unexplored force involved in seagrass declines.