Effects of Sediment Fertilization and Burial on Cymodocea nodosa Transplants; Implications for Seagrass Restoration Under a Changing Climate

Abstract

Sediment fertilization is recommended for improving seagrass restoration efforts, but few studies have evaluated the efficacy of such practice. Increasing storm frequency due to global change could lead to greater sediment mobilization. Understanding how this alteration will interact with fertilization to affect transplants is essential for future restoration planning. We examined the individual and combined effects of nutrients (ambient vs. repeated addition) and burial (control vs. increased frequency and intensity) on the performance and biomass partitioning of transplants of the seagrass Cymodocea nodosa at two sites within a north‐western Mediterranean meadow. Fertilization stimulated the production of shoots, total biomass, and branching. Burial increased leaf sheath length in one site while reduced shoot number, leaf number, leaf sheath length, total biomass, net shoot gain, and root‐to‐shoot ratio in the other site. Regardless of the site, fertilization and burial interaction reduced the length of vertical internodes and horizontal rhizomes, and the net shoot gain. Our research demonstrates that sediment fertilization ensures rapid colonization of restoration sites, providing C. nodosa plants up to eight times larger than controls in one growing season. However, it also indicates that interaction of increased burial and nutrients reduced the gain in terms of vegetative expansion and depressed vertical growth, making plants more vulnerable to subsequent disturbances. Therefore, seagrass restoration practitioners should account for changes in sediment elevation at transplanting sites when planning restoration programs and carefully evaluate the opportunity of applying fertilizers in sites subjected to greater sediment accumulation to avoid failure.

Seagrass Sensitivity to Collapse Along a Hydrodynamic Gradient: Evidence from a Pristine Subtropical Intertidal Ecosystem

“…In areas of low water velocity and high sediment deposition, seagrass seems to invest more in their light-harvesting compartment, the leaves. These results are in agreement with reported observational and experimental findings along intertidal gradients elsewhere (Marbà and Duarte 1995;others 2000, 2006;Cabaço and Santos 2007;Hovey and others 2012;Balestri and Lardicci 2014).…”

“…It has been suggested that seagrass leaf %N and %P contents are indicators of nutrient limitation (Duarte 1990) and nutrient loading (Govers and others 2014b). Biomass allocation (Herbert and Fourqurean 2009; Armitage and others 2011), as well as leaf and rhizomes internode lengths (Marbà and Duarte 1995;Peralta and others 2000;Cabaço and Santos 2007;Balestri and Lardicci 2014), has been associated with nutrient availability and sediment dynamics. Leaf isotopic ratios (d 13 C and d 15 N), on the other hand, have been proven to be powerful tracers for the sources of nutrients in the system (Lepoint and others 2004).…”

Root Hair Adhesion in Posidonia oceanica (L.) Delile Seedlings: A Numerical Modelling Approach

“…These initiatives have raised concerns in relation to their environmental sustainability (Balestri et al, 2019) and also because their large-scale application has rarely achieved high success rates (van Katwijk et al, 2016). To reduce the environmental impact on donor meadows, an approach known as "nursery seagrass" has been proposed which involves the propagation of plants from seeds reared in aquaculture facilities (Balestri and Lardicci, 2012;Balestri and Lardicci, 2014;Balestri et al, 2015). Research has recently focused on finding a suitable and low-impact way to fix germinated plants to the substrate (Alagna et al, 2019b).…”

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

“…Therefore, the application of fertilizers in transplanted areas has been proposed to minimize nutrient limitation and enhance the survival and growth of the seedlings at the initial stages of development. A number of fertilization experiments have shown that the addition of nitrogen and phosphorus to seagrass meadows stimulates shoot biomass and growth of C. nodosa ( Pérez et al, 1991 , 1994 ; Kenworthy and Fonseca, 1992 ; Balestri et al, 2010 ; Balestri and Lardicci, 2014 ), P. australis and P. sinuosa ( Hovey et al, 2012 ), and seedlings of Zostera marina ( Tanner and Parham, 2010 ) but not in seedlings of P. australis ( Statton et al, 2014 ). Nutrient additions to seagrass meadows have usually been made through the application of fertilizers with either balanced or unbalanced nutrient formulations.…”