1,738 publications from this institution
Seagrass meadows often appear to the casual observer as static landscapes. However, seagrass meadows are subject to intense dynamics involving the continuous loss and replacement of shoots in the population, which, when in balance, maintain a dynamic equilibrium. Such apparent steady-state conditions can be maintained over extended time periods, leading to long-lived seagrass meadows, such as some Posidonia oceanica meadows, which possibly may persist for > 4000 years in the Mediterranean (e.g. Mateo et al., 1997), and Zostera marina meadows exceeding a millennium in age (Reusch et al., 1999).
The influence of lake morphometry on the growth of submerged macrophytes in response to sediment fertilization was studied at sites of varying bottom slope (steep to gentle), wave exposure (high to low), and depth (1.0 and 2.5 m) in Lake Memphremagog (Quebec–Vermont). The biomass increases were on average 2.1 times greater for fertilized plants than for the paired controls. The extent of the growth response was greatest at the 1.0-m sites. The smaller response at the 2.5-m sites was further decreased as exposure to waves increased. The smaller response at 2.5 m (depth of maximum biomass) suggests that factors such as light limitation, length of the growing season, and littoral slope, but not sediment nutrient levels, limit submerged biomass there. The importance of the physical factors appears to increase as the biomass increases. "Overwintering" plants showed greater response to fertilization than those growing from seeds. Overall, the extent of the growth response to sediment fertilization depends on the energy environment (i.e. depth, wave exposure, and slope) of the littoral. The influence of these physical factors explains previous difficulties in finding strong correlations between nutrient levels and the growth of submerged macrophytes.
Outline This chapter reviews coastal benthic communities with the aim of deriving a global estimate for respiration in these ecosystems. Reefs, mangroves, salt marshes, macroalgae, sea grasses, and unvegetated sediments dominate respiration in the coastal ocean. Estimates of coastal benthic respiration are not well constrained but converge on about 620 Tmol C a −1 . In coastal benthic ecosystems autotrophs and multicellular heterotrophs contribute significantly, and in some systems even dominate respiration unlike most other oceanic ecosystems in which bacteria dominate respiration.
Posidonia oceanica is a well-recognized source of dissolved organic matter (DOM) derived from exudation and leaching of seagrass leaves, but little is known about its impact on the chromophoric fraction of DOM (CDOM). In this study, we monitored for two years the optical properties of CDOM in two contrasting sites in the Mallorca Coast (Balearic Islands). One site was a rocky shore free of seagrass meadows, and the second site was characterized by the accumulation of non-living seagrass material in the form of banquettes. On average, the integrated color over the 250–600 nm range was almost 6-fold higher in the beach compared with the rocky shore. Furthermore, the shapes of the CDOM spectra in the two sites were also different. A short incubation experiment suggested that the spectral differences were due to leaching from P. oceanica leaf decomposition. Furthermore, occasionally the spectra of P. oceanica was distorted by a marked absorption increase at wavelength < 265 nm, presumably related to the release of hydrogen sulfide (HS−) associated with the anaerobic decomposition of seagrass leaves within the banquettes. Our results provide the first evidence that P. oceanica is a source of CDOM to the surrounding waters.
The relationship between dust deposition and surface water metal concentrations is poorly understood. Dissolution, solubility, and partitioning reactions of trace metals from dust particles are governed by complex chemical, biological, and physical processes occurring in the surface ocean. Despite that, the role of the sea surface microlayer (SML), a thin, but fundamental component modulating the air-sea exchange of materials has not been properly evaluated. Our study revealed that the SML of the Mediterranean Sea is enriched with bioactive trace metals (i.e., Cd, Co, Cu and Fe), ranging from 8 (for Cd) to 1000 (for Fe) times higher than the dissolved metal pool in the underlying water column. The highest enrichments were spatially correlated with the atmospheric deposition of mineral particles. Our mass balance results suggest that the SML in the Mediterranean Sea contains about 2 tonnes of Fe. However, we did not detect any trends between the concentrations of metals in SML with the subsurface water concentrations and biomass distributions. These findings suggest that future studies are needed to quantify the rate of metal exchange between the SML and the bioavailable pool and that the SML should be considered to better understand the effect of atmospheric inputs on the biogeochemistry of trace metals in the ocean.
Several studies have been carried out on heavy metal pollution in mangrove ecosystems. However, the role of mangroves in heavy metal remobilization is still relatively unknown. On one side, mangrove woody organs and soils sequester heavy metals for long time periods, but on the other hand, senescence of mangrove leaves may return these metals collected by roots to the upper layers of the soil. Here, we analyzed the concentration of chemical elements (Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, V and Zn) as a function of age in mangrove leaves to understand heavy metals retention by the plant and to quantify the amounts shed with senescing leaves. In addition, we estimated metal concentrations and stocks in mangrove soils. Our results revealed that the concentration of most metals increased with leaf age, resulting in the remobilization of metals stored in soil, thereby returning metals to the upper layers of the soil during senescence of mangrove leaves. Only Cu was reabsorbed prior to shedding of leaves, a mechanism similar to that described for nutrients in mangroves globally. These results provide key data to understand mangroves role in the dynamics of heavy metals.
As outlined in the first chapter, seagrasses are the only angiosperms that are adapted to a marine submerged existence. Basic requirements for growth are similar for terrestrial angiosperms and seagrasses alike. Life in the marine realm, however, implies exposure to environmental conditions that are considerably different in many respects from those in terrestrial habitats, imposing constraints on the availability of some resources, or calling for specific adaptations to acquire others. In this chapter we will focus on environmental resources imperative for growth in seagrasses, i.e. light, inorganic carbon and nutrients, and on the plant properties relevant to their acquisition and use.
