Miguel Ángel Mateo

Variability in the carbon storage of seagrass habitats and its implications for global estimates of blue carbon ecosystem service.

The recent focus on carbon trading has intensified interest in ‘Blue Carbon’–carbon sequestered by coastal vegetated ecosystems, particularly seagrasses. Most information on seagrass carbon storage is derived from studies of a single species, Posidonia oceanica, from the Mediterranean Sea. We surveyed 17 Australian seagrass habitats to assess the variability in their sedimentary organic carbon (Corg) stocks. The habitats encompassed 10 species, in mono-specific or mixed meadows, depositional to exposed habitats and temperate to tropical habitats. There was an 18-fold difference in the Corg stock (1.09–20.14 mg Corg cm−3 for a temperate Posidonia sinuosa and a temperate, estuarine P. australis meadow, respectively). Integrated over the top 25 cm of sediment, this equated to an areal stock of 262–4833 g Corg m−2. For some species, there was an effect of water depth on the Corg stocks, with greater stocks in deeper sites; no differences were found among sub-tidal and inter-tidal habitats. The estimated carbon storage in Australian seagrass ecosystems, taking into account inter-habitat variability, was 155 Mt. At a 2014–15 fixed carbon price of A

The Posidonia oceanica marine sedimentary record: A Holocene archive of heavy metal pollution

25.40 t−1 and an estimated market price of

Influence of water depth on the carbon sequestration capacity of seagrasses

35 t−1 in 2020, the Corg stock in the top 25 cm of seagrass habitats has a potential value of

Millennial scale impact on the marine biogeochemical cycle of mercury from early mining on the Iberian Peninsula

AUD 3.9–5.4 bill. The estimates of annual Corg accumulation by Australian seagrasses ranged from 0.093 to 6.15 Mt, with a most probable estimate of 0.93 Mt y−1 (10.1 t. km−2 y−1). These estimates, while large, were one-third of those that would be calculated if inter-habitat variability in carbon stocks were not taken into account. We conclude that there is an urgent need for more information on the variability in seagrass carbon stock and accumulation rates, and the factors driving this variability, in order to improve global estimates of seagrass Blue Carbon storage.

Beach-Cast Cymodocea nodosa Along the Shore of a Semienclosed Bay: Sampling and Elements to Assess Its Ecological Implications

The study of a Posidonia oceanica mat (a peat-like marine sediment) core has provided a record of changes in heavy metal abundances (Fe, Mn, Ni, Cr, Cu, Pb, Cd, Zn, As and Al) since the Mid-Holocene (last 4470yr) in Portlligat Bay (NW Mediterranean). Metal contents were determined in P. oceanica. Both, the concentration records and the results of principal components analysis showed that metal pollution in the studied bay started ca. 2800yr BP and steadily increased until present. The increase in Fe, Cu, Pb, Cd, Zn and As concentrations since ca. 2800yr BP and in particular during Greek (ca. 2680-2465cal BP) and Roman (ca. 2150-1740cal BP) times shows an early anthropogenic pollution rise in the bay, which might be associated with large- and short-scale cultural and technological development. In the last ca. 1000yr the concentrations of heavy metals, mainly derived from anthropogenic activities, have significantly increased (e.g. from ~15 to 47μg g(-1) for Pb, ~23 to 95μg g(-1) for Zn and ~8 to 228μg g(-1) for As). Our study demonstrates for the first time the uniqueness of P. oceanica meadows as long-term archives of abundances, patterns, and trends of heavy metals during the Late Holocene in Mediterranean coastal ecosystems.

Reconstruction of centennial-scale fluxes of chemical elements in the Australian coastal environment using seagrass archives.

The actual estimates of carbon stocks beneath seagrass meadows worldwide are derived from few data, resulting in a tendency to generalize global carbon stocks from a very limited number of seagrass habitats. We surveyed Posidonia oceanica and Posidonia sinuosa meadows along depth-induced gradients of light availability to assess the variability in their sedimentary organic carbon (Corg) stocks and accretion rates. This study showed a fourfold decrease in Corg stocks from 2–4 m to 6–8 m depth P. sinuosa meadows (averaging 7.0 and 1.8 kg m−2, respectively; top meter of sediment) and a fourteenfold to sixteenfold decrease from shallow (2 m) to deep (32 m) P. oceanica meadows (200 and 19 kg m−2 average, respectively; top 2.7 m of sediment). The average Corg accretion rates in shallow P. sinuosa meadows were higher (10.5 g m−2 yr−1) than in deeper meadows (2.1 g m−2 yr−1). The reduction of sedimentary Corg stocks and accretion rates along depth-related gradients of light reduction suggests that irradiance, controlling plant productivity, meadow density, and sediment accretion rates, is a key environmental factor affecting Corg storage potential of seagrasses. The results obtained highlighted the exceptional carbon storage capacity of P. oceanica meadows at Balearic Islands (Spain), containing the highest areal Corg stocks of all seagrasses (estimated in up to 691–770 kg m−2 in 8–13 m thick deposits). Seagrass communities are experiencing worldwide decline, and reduced irradiance (following e.g., eutrophication or sediment regime alterations) will lead to photoacclimation responses (i.e., reduced plant productivity and shoot density), which may impact the carbon sequestration capacity of seagrasses.

Leaf production, shoot demography, and flowering of Thalassodendron ciliatum along the east African coast

exploitation of ore resources on the Iberian Peninsula. The chronology of Hg concentrations in the mat archive, together with other Hg pollution records from the Iberian Peninsula, suggests regional-scale Hg transport and deposition and shows earlier marine Hg pollution than elsewhere in Europe. Moreover, the mat also records a higher number of historic contamination phases, in comparison with other natural archives, probably due to the fact that the bioaccumulating capacity of P. oceanica magnify environmental changes in Hg concentrations. In this study, we demonstrate the uniqueness of P. oceanica meadows as a long-term archive recording trends in Hg abundance in the marine coastal environment, as well as its potential role in the Mediterranean as a long-term Hg sink.

Location and Associated Carbon Storage of Erosional Escarpments of Seagrass Posidonia Mats

Abstract Because sandy beaches are often totally devoid of primary producers, food webs based on autochthonous production are very rare. The accumulation of wrack along the shorelines has been shown to allow spatially subsidised food webs in these environments. A method for quantifying and describing the spatial distribution of beach-cast macrophyte material was developed based on line transects set up perpendicular to the shore. The method combined rapid visual techniques with measurements of detritus patch area, patch thickness, and patch distance from the shore. Average agreement between field observations and measurements was good: R2 = 0.93, p < 0.05, N = 53, with R2 ranging from 0.65 to 0.98. The method was used to quantify beach-cast Cymodocea nodosa leaf litter (dry weight, carbon, nitrogen, and phosphorus) along the 29 km shoreline of a semienclosed estuarine bay that is part of the delta arrow of an estuarine system (Alfacs Bay, Ebro River delta, Tarragona, Spain). The total amount of beach-cast leaf detritus varied from 0.07 to 3.02 kg dry wt m−1 of shoreline. The largest amounts of detritus accumulated on gentle slopes exposed to the dominant winds in the area. Total beach-cast leaf litter stocks in the bay amounted to 22.1 t dry wt, 7.1 t of carbon, 0.54 t of nitrogen, and 0.013 t of phosphorus. Export rates to the beach were estimated at 55.5 to 97.3 t y−1, which represented 4.1% to 7.4% of the C. nodosa leaf production in the bay and 5.8% to 10.3% of the total meadow leaf export.

A six thousand year record of climate and land-use change from Mediterranean seagrass mats

The study of a Posidonia australis sedimentary archive has provided a record of changes in element concentrations (Al, Fe, Mn, Pb, Zn, Cr, Cd, Co, As, Cu, Ni and S) over the last 3000 years in the Australian marine environment. Human-derived contamination in Oyster Harbor (SW Australia) started ~100 years ago (AD ~1900) and exponentially increased until present. This appears to be related to European colonization of Australia and the subsequent impact of human activities, namely mining, coal and metal production, and extensive agriculture. Two contamination periods of different magnitude have been identified: Expansion period (EXP, AD ~1900-1970) and Establishment period (EST, AD ~1970 to present). Enrichments of chemical elements with respect to baseline concentrations (in samples older than ~115 cal years BP) were found for all elements studied in both periods, except for Ni, As and S. The highest enrichment factors were obtained for the EST period (ranging from 1.3-fold increase in Cu to 7.2-fold in Zn concentrations) compared to the EXP period (1.1-fold increase for Cu and Cr to 2.4-fold increase for Pb). Zinc, Pb, Mn and Co concentrations during both periods were 2- to 7-fold higher than baseline levels. This study demonstrates the value of Posidonia mats as long-term archives of element concentrations and trends in coastal ecosystems. We also provide preliminary evidence on the potential for Posidonia meadows to act as significant long-term biogeochemical sinks of chemical elements.

Seagrass meadows provide 3D habitat for reef fish

Several characteristics of Thalassodendron ciliatum populations were evaluated along the coasts of Kenya and Zanzibar Island, with the aim to study spatial variability in this species. A reconstruction technique, using scars left by abscised leaves and flowers, was employed to determine leaf production, shoot demography, and flowering frequency. Eight subtidal sites in different back-reef lagoons were sampled along with a subtidal site that was not protected by a reef, a site with intertidal rack pools, and a subtidal site in a mangrove bay. Leaf- production rates were lowest for the population of the unprotected subtidal site and for the population from the intertidal rock pools (30 leaves per shoot per year). At these sites, leaf life-span was almost twice as long (94 days). Low leaf-formation rates seem to be compensated by long leaf life- spans to maintain similar numbers of standing leaves per shoot. Highest leaf-production rates were found at the mangrove-bay site (53 leaves per shoot per year). The mangrove-bay population showed internodal lengths of almost 7 mm and stem lengths of almost 90 cm. The stems were two- to four-fold longer than those at the other sites. A short leaf life-span of 51 days at the mangrove site indicates that the investment in stem growth occurs at the expense of leaf maintenance. Median ages of the populations varied almost four-fold from 0.5 to 1.8 years. All meadows showed shoot-recruitment rates that were either the same as or larger than shoot mortality rates, suggesting that the environmental quality in this region is still suitable for sustaining vigorous seagrass vegetation. Flowering frequencies were generally low and seedlings were not found. [KEYWORDS: seagrass; leaf production; demography; flowering; east Africa; Thalassodendron ciliatum Cymodocea-nodosa; reconstructive technique; seagrasses colonization; population-dynamics; den hartog; growth; pollination; amphibolis; biomass; lagoon]