Influence of wave climate on architecture and landscape characteristics of Posidonia oceanica meadows

Seagrass meadow characteristics, including distribution, shape, size and within‐meadow architectural features, may be influenced by various physical factors, including hydrodynamic forces. However, such influences have hardly been assessed for meadows of the ecologically important and endemic Mediterranean seagrass Posidonia oceanica. The distribution of P. oceanica meadows at five sites in the Maltese Islands was mapped to a depth of c. 15 m using a combination of aerial photography and SCUBA diving surveys. Estimates of wind‐generated wave energy and energy attenuated by depth were computed using the hydrodynamic model WEMo (Wave Exposure Model). Metrics for P. oceanica landscape features were calculated using FRAGSTATS for replicate 2500 m² subsamples taken from the seagrass habitat maps in order to explore the influence of wave dynamics at the landscape scale. Data on within‐meadow architectural attributes were collected from five sites and analysed for relationships with wave energy. The results indicate that landscape and architectural features of P. oceanica meadows located within the 6–11 m depth range are significantly influenced by wave climate. Posidonia oceanica meadows tend to be patchier and have low overall cover, more complex patch shapes and reduced within‐patch architectural complexity along a wave exposure gradient from low to high energy. The findings from the present study provide new insight into the influence of hydrodynamic factors on the natural dynamism of P. oceanica meadow landscape and architecture, which has implications for the conservation and management of the habitat.     

Population dynamics of the seagrass Cymodocea nodosa in Ria Formosa lagoon following inlet artificial relocation

The population dynamics of the seagrass Cymodocea nodosa was investigated in three meadows differently affected by the artificial relocation of an inlet in the western sector of the Ria Formosa lagoon, southern Portugal. One meadow was subjected to increasing currents that caused erosion, another one was subjected to an initial episode of burial and a third meadow was undisturbed by the inlet opening. The hydrodynamic/sedimentary condition of meadows was assessed through comparative sediment analysis between the meadow and the adjacent unvegetated area.     

Population dynamics and production of the seagrass Zostera noltii in colonizing versus established meadows

The dynamics of the seagrass Zostera noltii in established and colonizing meadows were assessed in Ria Formosa lagoon, Southern Portugal. Shoot weight, above:belowground biomass ratio, flowering shoot density, meadow production, and biomass–density relationships were investigated. Results indicate that the species population dynamics differ clearly in different development stages of the meadows. The overall mean of flowering shoot density was five times higher in the colonizing (83 flowering shoots m⁻²) than in the established meadow (16 flowering shoots m⁻²), revealing a greater contribution of sexual reproduction during the species colonization process. The temporal variation of the biomass–density relationship in the colonizing meadow showed a cyclic seasonal trajectory, a wider range of data, and a simultaneous peak of biomass and density, suggesting no space limitations constraining the internal packing of shoots during the growing season. In the established meadow, density peaked before biomass in agreement to the dominant role of the clonal architecture of seagrasses in the configuration of closed meadows, suggesting the occurrence of self-thinning and/or regulation of ramet formation. Slope of the biomass–density relationships was similar in the established and colonizing meadows, generally suggesting similar nutritional conditions, regardless of their muddy and sandy sediments. Plants of the colonizing meadow invest mainly on the belowground fraction (above:belowground biomass ratio <1), as meadow expansion is mainly controlled by the elongation of horizontal rhizomes. The annual total production (1163 g C m⁻² year⁻¹) and the biomass turnover (34.8 year⁻¹) were also higher in this meadow, corroborating the high investment of the species during the meadow expansion. The faster biomass turnover of the colonizing meadow implies a more limited capacity to accumulate biomass, indicating a greater exportation of organic carbon and nutrients to the coastal area. The different biomass turnover rates suggest different trophic and structural roles of Z. noltii communities in established and colonizing meadows.     

底质类型对热带海草海菖蒲种子萌发和幼苗生长的影响

近几十年来,受到人类活动和气候变化的影响,全球海草床呈现退化趋势,海草床的恢复备受关注.其中,海草种子或幼苗移植由于其对供体海草床破坏和影响较小,并能保证海草的遗传多样性而备受重视.移植区的底质类型是决定海草种子或幼苗移植存活率的重要因子,然而,目前关于热带海草种子萌发和幼苗生长对不同底质类型响应的研究很有限.本研究以...     

Sediment accumulation rates along the inner eastern Brazilian continental shelf

Box cores were collected close to river mouths along the eastern Brazilian shelf at water depths of 10–30 m. One core was taken from more than 1000 m depth at the shelf slope. ²¹⁰Pb and ²²⁶Ra activities were measured to establish sediment accumulation rates. Seven of the 10 cores exhibited an exponential decrease with depth of excess ²¹⁰Pb activities. The sediments from the sheltered Sudeste Channel off Caravelas revealed the highest sediment accumulation rate of 0.81 cm yr⁻¹. The sediments at the shelf slope seaward of the Rio Doce revealed the lowest accumulation rate of 0.13 cm yr⁻¹. Sediment accumulation rates increased towards the Caravelas Bank. Current patterns and the morphology of the seabed favor sediment deposition in this area.     

210Pb-derived sediment accumulation rates in the southwestern East Sea (Sea of Japan)

 Recent sediment accumulation rates are 18–230 mg cm^-2 yr^-1 (0.02–0.2 cm yr^-1) based on excess ²¹⁰Pb activity profiles in the southwestern part of the East Sea (Sea of Japan). Assuming no mixing beneath surface mixed layers, ²¹⁰Pb-derived sediment accumulation rates are 18–32 mg cm^-2 yr^-1 in the northern part of the Yamato Ridge and the Ulleung Basin, 29–136 mg cm^-2 yr^-1 in the Korea Plateau, and 230 mg cm^-2 yr^-1 in the southern shelf. These values generally agree with long-term sedimentation rates estimated from dated ash layers. Received: 6 October 1995 / Revision received: 31 May 1996     

Preferential settling of smectite on the Amazon continental shelf

Seventy-five surface and subsurface sediment samples collected on the Amazon continental shelf were analyzed by X-ray diffraction (XRD) in the grain-size fractions smaller than 2 μm. The groups of clay minerals thus identified were smectite, kaolinite, illite, and mixed-layer illite/smectite. Calculation of relative abundance shows a predominance of smectite (37%) in the whole area, followed by kaolinite (27%), illite (23%), and a small percentage of mixed-layer illite/smectite (12%). The distal, northwest region of the continental shelf is characterized by a high abundance of smectite (41%), high salinity values, and high sediment accumulation rates (10 cm year⁻¹), whereas the proximal region is characterized by a comparatively low abundance of smectite (30%), low salinity values, and low sediment accumulation rates (<1 cm year⁻¹). This trend of increasing abundance northwestwards documents a preferential settling of smectite in the distal and more saline regions of this estuarine system. Received: 17 September 1999 / Revision accepted: 17 January 2000     

The relationship between seagrass (Posidonia oceanica) decline and sulfide porewater concentration in carbonate sediments

In this study we test the hypothesized negative relationship between seagrass status and porewater hydrogen sulfide (H₂S) levels, through a comparative analysis within a range of seven Posidonia oceanica meadows growing over carbonate sediments in the NW Mediterranean Sea around Mallorca Island. The studied meadows range from meadows growing on sediments with very low sulfide porewater concentrations (4.6 μM) to those growing over higher sulfide conditions (33.5 μM). Organic matter content, sulfate reduction rates and sulfide porewater concentrations in the sediments were determined concurrently with the assessment of demographic plant dynamics (specific mortality and net population growth rates). Sulfide porewater concentration increased with increasing organic matter content in the sediment, while net population growth decreased significantly with low increases of sulfide concentrations. Our results confirm the previously suspected vulnerability of seagrass meadows growing on carbonate sediments to increased sulfide levels. An excess of 10 μmols H₂S L⁻¹ porewater is identified to already conduce P. oceanica meadows to decline, which this study identifies, particularly, as strongly sensitive to sulfides. The results reported here suggest that even moderate increases in organic carbon inputs may lead to enhancement of dissolved sulfides and may be an important factor for seagrass status in these iron-depleted carbonate sediments from the Mediterranean Sea.     

Bulk density calibration for X-ray tomographic analyses of marine sediments

A calibration procedure is presented for generating bulk density profiles of intact marine sediment cores using X-ray computed tomography (CT). Developed using both artificial and natural marine sediment samples, the correlation is strong with an R ² value of 0.98. Similar experiments with carbonate sediments were also strongly linear, but offset from the terrigenous curve, illustrating the influence of sediment chemistry on scanner response. Comparison between newly computed densities for both sediment types with those from individually calibrated cores during our previous CT studies reveals good correspondence between the data sets. Received: 22 November 1998 / Revision received: 4 March 1999     

Sediment transport and morphodynamics of the Douro River estuary

A combination of dredging data, hydrographic surveys and numerical modelling has been used to assess morphological change and sediment transport in the Douro River estuary. The system is dominated by sand- and gravel-sized sediments and confined by resistant rock types. The evolution of the bed in the last 20 years has been strongly influenced by the opening of a navigation channel. According to the data available to date, the average maintenance dredging volume has been of the order of 0.4 × 10⁶ m³ year⁻¹. Comparisons of hydrographic surveys reveal a rate of volume loss of the same magnitude. Apparently, maintenance dredging mainly involves local material, transported into the channel from shallower areas of the estuary. The results of numerical modelling indicate that the sediment transport capacity due to tidal currents is very limited. River flood events increase the transport capacity by several orders of magnitude, thus playing a critical role in sediment redistribution and supply to the coast. The average sediment transport capacity is estimated to be of the order of 0.1 × 10⁶ m³ year⁻¹ in most of the estuary and 0.5 × 10⁶ m³ year⁻¹ at the inlet, with a large uncertainty. It is concluded that, if morphological stability is set as an environmental objective, the dredged material should not be removed from the system but rather be used to nourish the estuarine beaches and the barrier spit.     

Influence of food supply on the δ13C signature of mollusc shells: implications for palaeoenvironmental reconstitutions

Compared to oxygen isotopes, the carbon isotope composition of biogenic carbonates is less commonly used as proxy for palaeoenvironmental reconstructions because shell δ¹³C is derived from both dissolved inorganic (seawater) and organic carbon sources (food), and interactions between these two pools make it difficult to unambiguously identify any independent effect of either. The main purpose of this study was to demonstrate any direct impact of variable food supply on bivalve shell δ¹³C signatures, using low/high rations of a ¹³C-light mixed algal diet fed to 14-month-old (adult) cultured Japanese Crassostrea gigas under otherwise essentially identical in vitro conditions during 3 summer months (May, June and July 2003, seawater temperature means at 16, 18 and 20 °C respectively) in experimental tanks at the Argenton laboratory along the Brittany Atlantic coast of France. At a daily ration of 12% (versus 4%) oyster dry weight, the newly grown part of the shells (hinge region) showed significantly lower δ¹³C values, by 3.5‰ (high ration: mean of −5.8  ± 1.1‰, n = 10; low ration: mean of −2.3  ± 0.7‰, n = 6; ANOVA Scheffe’s test, p < 0.0001). This can be explained by an enhanced metabolic activity at higher food supply, raising ¹³C-depleted respiratory CO₂ in the extrapallial cavity. Based on these δ¹³C values and data extracted from the literature, and assuming no carbon isotope fractionation between food and shell, the proportion of shell metabolic carbon would be 26  ± 7 and 5  ± 5% for the high- and low-ration C. gigas shells respectively; with carbon isotope fractionation (arguably more realistic), the corresponding values would be 69  ± 14 and 24  ± 9%. Both groups of cultured shells exhibited lower δ¹³C values than did wild oysters from Marennes-Ol éron Bay in the study region, which is not inconsistent with an independent influence of diet type. Although there was no significant difference between the two food regimes in terms of δ¹⁸O shell values (means of 0.1  ± 0.3 and 0.4  ± 0.2‰ at high and low rations respectively, non-significant Scheffe’s test), a positive δ¹³C vs. δ¹⁸O relationship recorded at high rations supports the interpretation of a progressive temperature-mediated rise in metabolic activity fuelled by higher food supply (in this case reflecting increased energy investment in reproduction), in terms not only of δ¹³C (metabolic signal) but also of δ¹⁸O (seawater temperature signal). Overall, whole-shell δ¹⁸O trends faithfully recorded summer/winter variations in seawater temperature experienced by the 17-month-old cultured oysters.     

The influence of coastal dynamics on the upper limit of the Posidonia oceanica meadow

The recognized ecological importance of Posidonia oceanica, the most important seagrass of the Mediterranean Sea, makes it crucial to assess the state of health of its meadows, discriminating natural from anthropogenic impacts. In this paper, the hydrodynamic conditions at the upper limit of P. oceanica meadows along the Ligurian coast (NW Mediterranean Sea) were investigated. A relationship between the distance of the upper limit of the meadow from the shoreline and the morphodynamic domain of the beach (i.e. distinctive types of beach produced by the topography, wave climate and sediment composition) was found. A zonation of the state of the shallow portions of the meadows down the submerged beach profile was identified. Zone a, from the shoreline to the breaking limit, is naturally critical for the development of the meadow. Zone b, from the breaking limit to the closure depth, is subjected to natural and human impacts. Zone c, below the closure depth, is little influenced by coastal dynamics. This study quantifies for the first time how much the status of the shallow portions of P. oceanica meadows is dependent on coastal dynamics, which is important for their proper management.     

Molluscan assemblages of seagrass-covered and bare intertidal flats on the Banc d'Arguin, Mauritania, in relation to characteristics of sediment and organic matter

The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km² of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m^− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m^− 2) than seagrass meadows (30.0 g AFDM m^− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m^− 2 and seagrass meadows 6.9 g AFDM m^− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.     

Geoacoustic and physical properties of carbonate sediments of the Lower Florida Keys

 Near-surface sediment geoacoustic and physical properties were measured from a variety of unconsolidated carbonate sediments in the Lower Florida Keys. Surficial values of compressional and shear speed correlate with sediment physical properties and near-surface acoustic reflectivity. Highest speeds (shear 125–150 m s^-1; compressional 1670–1725 m s^-1) are from sandy sediments near Rebecca Shoal and lowest speeds (shear 40–65 m s^-1; compressional 1520–1570 m s^-1) are found in soft, silty sediments which collect in sediment ponds in the Southeast Channel of the Dry Tortugas. High compressional wave attenuation is attributed to scattering of acoustic waves from heterogeneity caused by accumulation of abundant shell material and other impedance discontinuities rather than high intrinsic attenuation. Compared to siliciclastic sediments, carbonate sediment shear wave speed is high for comparable values of sediment physical properties. Sediment fabric, rather than changes due to the effects of biogeochemical processes, is responsible for these differences.     

Impact of fish farming facilities on Posidonia oceanica meadows: a review

The impact of fish farming facilities on Posidonia oceanica meadows was assessed from studies of intensive facilities carried out over the last few years. The disturbances caused by these fish farms were measured by means of both abiotic (light, sediment, interstitial water) and biotic variables (meadow density, leaf biometry, lepidochronology, primary production, epiphytes, reserve carbohydrates in the rhizomes), in function of increasing distance from cages and/or inside a geographically close reference site. The results showed significant degradation of these seagrass meadows in all the sectors investigated. When fish farming cages were placed above a P. oceanica bed, the meadow was severely degraded or disappeared and the sediment showed a strong increase in organic matter that could lead to anoxia phenomena. The irreversible impact of fish farming projects on P. oceanica meadows requires the application of the precautionary principle. Several recommendations (site selection, preliminary studies and monitoring over time) are suggested in order to enable piscicultural activities to be incorporated in a global process of Integrated Coastal Zone Management.     

Particulate organic carbon (POC) in surface sediments of the Baltic Sea

In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm^–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm^–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm^–3) and moderate POC concentrations (4–7 mg cm^–3). Furthermore, sediment mass accumulation rates (MAR), based on ²¹⁰Pb and ¹³⁷Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial rates. Overall, these vary between 14 and 35 g m^–2 year^–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor (morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon cycle in this large brackish-water marginal sea.     

Effects of organic matter input from a fish farming facility on a Posidonia oceanica meadow

In the Mediterranean, the development of aquaculture along the coasts appears as a source of disturbance to the littoral ecosystems, and in particular to Posidonia oceanica seagrass meadows. Although the impact of fish farms in Northern Europe has been studied over the last few years, the data are more scarce in the Mediterranean. Thus, a number of physico-chemical and biological parameters have been examined here in order to evaluate the impact of a fish farm in a littoral bay of Corsica. The following values that were recorded in the vicinity of the fish farm are much higher than those at the reference station: organic content of the sediment (24–21 versus 2%), nitrogen concentrations (ammonium: 19.5–8.4 versus 1.8 μM) and phosphorous levels in the pore water (orthophosphates: 5.2–1.3 versus 1.7 μM). The seagrass meadow vitality also seems to be affected in the vicinity of cages, with densities that drop from 466 (reference station) to 108 shoots m⁻² (20 m from cages). Total primary production also varies from 1070.6 to 87.9 g m⁻² year⁻¹. The main impact factors seem to be the input of organic matter originating from the cages and the high epiphyte biomass caused by the nutrient enrichment. The high level of organic matter and the presence of mud seem to alter the physico-chemical characteristics of the bottom sediment; moreover, the plant/epiphyte competition seems to lead to a leaf fragility and, more importantly, to a decrease in available light.     

228Ra, 226Ra, 224Ra and 223Ra in potential sources and sinks of land-derived material in the German Bight of the North Sea: implications for the use of radium as a tracer

Activities of the naturally occurring radium nuclides ²²⁸Ra, ²²⁶Ra, ²²⁴Ra and ²²³Ra were determined in waters of the open German Bight and adjacent nearshore areas in the North Sea, in order to explore the potential use of radium isotopes as natural tracers of land–ocean interaction in an environment characterised by extensive tidal flats, as well as riverine and groundwater influx. Data collected at various tidal phases from the Weser Estuary (²²⁸Ra: 46.3 ± 4.6; ²²⁶Ra: 17.1 ± 1.1; ²²⁴Ra: 26.1 ± 8.2 to 36.5 ± 6.1; ²²³Ra: 1.8 ± 0.1 to 4.0 ± 0.4), tidal flats near Sahlenburg (²²⁸Ra: 39.3 ± 3.8 to 46.0 ± 4.5; ²²⁶Ra: 15.5 ± 1.5 to 16.5 ± 1.7; ²²⁴Ra: 34.3 ± 2.2 to 85.3 ± 6.3; ²²³Ra: 3.6 ± 0.5 to 8.0 ± 1.2), freshwater seeps on tidal flats near Sahlenburg (²²⁸Ra: 42.1 ± 4.1; ²²⁶Ra: 21.3 ± 2.2; ²²⁴Ra: 5.1 ± 0.9; ²²³Ra: 2.6 ± 1.3) and also in permanently inundated parts of the North Sea (²²⁸Ra: 23.0 ± 2.3 to 28.2 ± 2.8; ²²⁶Ra: 8.2 ± 0.8 to 11.8 ± 1.2; ²²⁴Ra: 3.1 ± 1.0 to 10.1 ± 0.9; ²²³Ra: 0.1 ± 0.02 to 0.9 ± 0.05; units: disintegrations per minute per 100 kg water sample) reveal that, except for the fresh groundwater, the potential end-members of nearshore water mass mixing have quite similar radium signatures, excluding a simple discrimination between the sources. However, the decreasing activities of the short-lived ²²⁴Ra and ²²³Ra isotopes recorded towards the island of Helgoland in the central German Bight show a potential to constrain fluxes of land-derived material to the open North Sea. The largest source for all radium isotopes is generally found on the vast tidal flats and in the Weser Estuary. Future work could meaningfully combine this so-called radium quartet approach with investigations of radon activity. Indeed, preliminary data from a tidal flat site with fresh groundwater seepage reveal a ²²²Rn signal that is clearly lower in seawater.     

Late Pleistocene channel–levee development on Monterey submarine fan, central California

 Much of the modern upper (proximal) Monterey fan is a channel–levee complex, the Upper Turbidite Sequence (UTS), that was deeply eroded after the channel breached a volcanic ridge to reach a deeper base level. Ages of sediment samples collected with the ALVIN submersible from the deepest outcrop within the channel–levee system, 390 m below the adjacent western levee crest, indicate that the UTS deposits accumulated at ≥1 m ka^-1 during the last 500 ka. Neogene and Early Pleistocene sediment accumulation on the fan prior to the UTS was much slower (<0.03 m ka^-1), and underlying turbidite systems(?) had substantially different morphologic expression(s). Received: 10 February 1998 / Revision received: 6 July 1998     

Human influence on seagrass habitat fragmentation in NW Mediterranean Sea

Habitat fragmentation in meadows of Posidonia oceanica, the most important and abundant seagrass in the Mediterranean Sea, was investigated at a region-wide spatial scale using a synthetic ecological index, the Patchiness Index (PI). We tested the hypothesis that human impacts are the major factor responsible for habitat fragmentation in P. oceanica meadows contrasting fragmentation of meadows located in “anthropized” areas with that of meadows located in areas with low anthropization and considered as virtually “natural”. We also related fragmentation of meadow with the morphodynamic state of the submerged beach (i.e. distinctive types of beach produced by the topography, the wave climate and the sediment composition) in order to investigate the influence of one natural component on the seagrass meadow seascape. Results demonstrated that fragmentation in the P. oceanica meadows is strongly influenced by the human component, being lower in natural meadows than in anthropized ones, and that it is little influenced by the morphodynamic state of the coast. The use of landscape approaches to discriminate natural disturbance from human impacts that affect seagrass meadows is thus recommended for the proper management of coastal zones.