Comparison between amphipod assemblages associated with Caulerpa racemosa var. cylindracea and those of other Mediterranean habitats on soft substrate

The spread of the invasive alga Caulerpa racemosa var. cylindracea in shallow-water habitats can present different faunal assemblage composition. We compared the amphipod assemblages associated with C. racemosa and natural habitats found on shallow-water Mediterranean soft substrata. Four vegetated habitats were compared: C. racemosa, Caulerpa prolifera, Cymodocea nodosa and Posidonia oceanica with unvegetated substrata. Samples were collected during two sampling periods (September 2004 and March 2005). A total of 63 amphipod species were recorded. The results showed that the vegetated habitats sampled, including C. racemosa stands, supported a higher abundance and species richness of amphipods. Furthermore, the assemblage structure differed between the different habitats, while the abundance of some species was significantly different, depending on habitat. For example, Microdeutopus obtusatus was favoured by C. racemosa habitat; Ampelisca diadema was associated with C. prolifera beds; and Hyale schmidti was more abundant in P. oceanica meadows. Habitat invasion by C. racemosa can exert an important influence on biotic assemblages, modifying habitat structure and associated fauna.     

Functional changes due to invasive species: Food web shifts at shallow Posidonia oceanica seagrass beds colonized by the alien macroalga Caulerpa racemosa

Multiple stable isotope analyses were used to examine the trophic shifts at faunal assemblages within the invading macroalga Caulerpa racemosa in comparison to established communities of Posidonia oceanica seagrass meadows. Sampling of macrobenthic invertebrates and their potential food sources of algal mats and seagrass meadows in Mallorca (NW Mediterranean) showed differences in species composition of faunal and primary producers among seagrass and C. racemosa. Accordingly, changes in food web structure and trophic guilds were observed, not only at species level but also at community level. The carbon and nitrogen isotope signatures of herbivores, detritivores and deposit feeders confirmed that the seagrass provided a small contribution to the macrofaunal organisms. δ¹³C at the P. oceanica seagrass and at the C. racemosa assemblages differed, ranging from −6.19 to −21.20‰ and −2.67 to −31.41‰, respectively. δ¹⁵N at the Caulerpa mats was lower (ranging from 2.64 to 10.45‰) than that at the seagrass meadows (3.51–12. 94‰). Significant differences in isotopic signatures and trophic level among trophic guilds at P. oceanica and C. racemosa were found. N fractionation at trophic guild level considerable differed between seagrass and macroalgae mats, especially for detritivores, deposit feeders, and herbivores. Filter feeders slightly differed with a relatively lower N signal at the seagrass and CR values at community level and at trophic guild level were higher in the C. racemosa invaded habitats indicating an increase in diversity of basal resource pools. C. racemosa did seem to broaden the niche diversity of the P. oceanica meadows it colonised at the base of the food web, may be due to the establishment of a new basal resource. The extent of the effects of invasive species on ecosystem functioning is a fundamental issue in conservation ecology. The observed changes in invertebrate and macrophytic composition, stable isotope signatures of concomitant species and consequent trophic guild and niche breadth shifts at invaded Caulerpa beds increase our understanding of the seagrass systems.     

Physiological response of the sea urchin Paracentrotus lividus fed with the seagrass Posidonia oceanica and the alien algae Caulerpa racemosa and Lophocladia lallemandii

The aim was to determine the effects of alien algae feeding on biomarkers of oxidative stress in the sea urchin Paracentrotus lividus. Sea urchins were fed during three months with the native seagrass Posidonia oceanica, and the alien macroalgae Caulerpa racemosa and Lophocladia lallemandii and biochemical analysis were performed in the gonads. A control group was immediately processed after sampling from the sea. Antioxidant enzyme and glutathione S-transferase activities and GSH concentration were significantly higher in sea urchins fed with alien algae when compared with the control group and the one fed with P. oceanica group. This response was more intense in the group fed with L. lallemandii respect to the C. racemosa group. The concentration of MDA, protein carbonyl derivates and 8-OHdG reported no significant differences between treatments. In conclusion, the invasive algae C. racemosa and L. lallemandii induced an antioxidant response in P. lividus without evident oxidative damage.     

Biokinetics of selected heavy metals and radionuclides in two marine macrophytes: the seagrass Posidonia oceanica and the alga Caulerpa taxifolia

Uptake and loss kinetics of Zn, Ag, Cd, ¹³⁴Cs, and ²⁴¹Am by shoots of the seagrass Posidonia oceanica and fronds of the green alga Caulerpa taxifolia were determined in controlled laboratory radiotracer experiments using low contaminant concentrations. The two species accumulated most of the elements efficiently. The only exceptions were ¹³⁴Cs in both P. oceanica and C. taxifolia and Cd in C. Taxifolia (concentration factors 6.4). Steady state in uptake was reached in C. taxifolia for each element except Ag. In P. oceanica, steady state was noted for the uptake of Ag and ¹³⁴Cs whereas Zn, Cd, and ²⁴¹Am were linearly accumulated during the course of the experiment (15 d). With respect to relative metal bioavailability, the different compartments of P. oceanica shoots were generally ranked in the order: leaf epiphytes > adult LEAVES = intermediate leaves > leaf sheaths. The long-lived component of the loss kinetics for each element in P. oceanica was characterized by a relatively short biological half-life (T_b1/2 28 d). However, observations for the individual compartments indicated that adult leaves had a high retention capacity for Ag and ¹³⁴Cs, with virtually 100% retained after 21 d in uncontaminated sea water. In C. taxifolia, the long-lived component of the loss kinetics for each element was characterized by a T_b1/2 value that was not significantly different from infinity, an observation which suggests that a substantial fraction of the metal or radionuclide incorporated during a contamination event would be irreversibly bound by this algal species.     

Differential herbivory of invasive algae by native fish in the Mediterranean Sea

The potential role of generalist herbivores to serve as a source of biotic resistance against algal invasion in marine ecosystems has been poorly examined. The present study investigates the capacity of Mediterranean herbivorous fishes to consume three of the most invasive seaweeds of the Western Mediterranean (Caulerpa racemosa, Lophocladia lallemandii and Womersleyella setacea) and examines vertical and temporal variations of such consumption. Our results show that although fish feed throughout the depth gradient examined (5–35 m), they concentrate in shallow waters, and can consume high amounts of C. racemosa. Such high ingestion of C. racemosa does not appear to be random, since this alga is consistently chosen when offered in pairs with several native species. Conversely, L. lallemandii and W. setacea are barely eaten by fish even though they can be very abundant in the field throughout the year. Our results suggest that fish could be an important controlling agent that has been overlooked in temperate marine invasions, and they may be able to provide certain resistance to C. racemosa invasion. In contrast, they are unlikely to exert any important control effects on L. lallemandii or W. setacea.     

Expansion of the macroalga Caulerpa racemosa and changes in softbottom macrofaunal assemblages in Moni Bay,Cyprus

The recent expansion of the Red Sea macroalga Caulerpa racemosa and its impact on the diversity and abundance of macrobenthos were examined and compared in the summers of 1992 and 1997, in Moni Bay, Cyprus. The phytobenthic community of the bay in 1992 was dominated by the seagrass Posidonia oceanica while, in 1997, the Lessepsian migrant C. racemosa became the most dominant, forming extensive mats. Changes in the vegetation system in Moni Bay have caused significant compositional changes in macrofaunal assemblages. A total of 178 individuals of 62 species are recorded. The composition of the macrofauna in 1992 was dominated by gastropods (44 %), crustaceans (22%), bivalves (17 %), polychaetes (11 %) and echinoderms (6 %). In 1997, the gastropods and crustaceans had decreased to 13 % and 16 % respectively, while, polychaetes had increased to 38 % becoming the most dominant taxon. Bivalves and echinoderms also increased to 22 % and 11 %, respectively, in 1997. The proliferative growth of C. racemosa imposed successional changes on the macrofaunal assemblages in Moni Bay, Cyprus, between 1992 and 1997. It remains to be tested whether the expansion of C. racemosa is related to the increase of water temperature associated with global warming or nutrient inputs or with the differences in the life history characteristics of this migrant vs. native algal species.     

Macroalgal assemblages of disturbed coastal detritic bottoms subject to invasive species

Characteristic flora and fauna that are highly sensitive to disturbances colonize coastal detritic bottoms in the Mediterranean Sea. In the present study, a comparison of the assemblage composition and colonization by invasive macroalgae was made between two coastal detritic macrophyte assemblages, one dominated by rhodoliths (free-living non-geniculate Corallinales) and the other dominated by fleshy algae, in an area that has been exposed to important levels of anthropogenic disturbance, mainly pollution (including changed sedimentation regimes) in the recent past (bay of Marseilles, France). In comparison with less strongly impacted Mediterranean regions, the macrophyte assemblages in the bay of Marseilles were characteristic in terms of species identity and richness of coastal detritic macrophyte assemblages. However, extremely low species abundance (cover) was observed. As far as invasive species were concerned, Caulerpa racemosa var. cylindracea was only abundant in the rhodolith assemblage whereas the two invasive Rhodophyta Asparagopsis armata and Womersleyella setacea were mainly found in the fleshy algae assemblage. The seasonality observed in the Rhodolith assemblage seemed to be related to the development of C. racemosa var. cylindracea and did not follow the typical pattern of other Mediterranean assemblages. This study represents the first study of coastal detritic assemblages invaded by C. racemosa var. cylindracea.     

Modelling formation of complex topography by the seagrass Posidonia oceanica

Posidonia oceanica is a slow growing seagrass species that extends via growing rhizomes that grow only centimetres both horizontally and vertically each year. Posidonia oceanica forms topographically complex biogenic reefs of dead rhizome and sediments that are up to 4 m in height that are called “matte”. This study investigates the role of slow horizontal and vertical growth of rhizomes in the formation of topographic complexity in P. oceanica matte using agent-based modelling. The simulated infilling of landscapes by P. oceanica was run over 600 iterations (years) for 10 random starts of 150 agents each. Initial infilling rates were very slow and P. oceanica had limited cover after a century of growth. Growth accelerated after 100 years but plateaued after 400 years such that after 600 years only two-thirds of the landscape was occupied by P. oceanica. The pattern of spread of agents was initially random in direction but after larger patches were formed spread was radial from these patches. The seagrass landscape was initially highly fragmented with many small separate patches made up of a few agents each, with a Landscape Division index close to 1. Between 300 and 600 years Landscape Division declined sharply to 0.42, indicating patches had coalesced into larger more continuous meadows forming a less fragmented landscape. Perimeter to area ratio of seagrass patches declined exponentially from >1 to approximately 0.2 over 600 years of simulation. The matte developed from growth of patches and its greatest height occurred in more continuously occupied cells of the grid. The topography of the reef that occupied two-thirds of the landscape after six centuries of growth could be described as a pattern of channels between reef plateaus elevated 1–2 m above channels. These results demonstrate that development in P. oceanica meadows of three-dimensional structure, in the formation of biogenic reefs, can be explained by, and is an emergent property of, slow horizontal and vertical rhizome growth rates combined with the time it takes for the accumulation of rhizomes in any region of the landscape. As such, the model provides a parsimonious explanation for the development of complex matte topography.     

Temporal and spatial variability in shallow- and deep-water populations of the invasive Caulerpa racemosa var. cylindracea in the Western Mediterranean

The invasive green alga Caulerpa racemosa var. cylindracea represents an important threat to the diversity of Mediterranean benthic coastal ecosystems by interfering with native species and modifying benthic assemblages. The present study deals, for the first time, with the temporal and spatial variability of the biomass and phenology of C. racemosa considering both deep- and shallow-water populations. Two sampling depths (30 and 10 m) were sampled at three different rocky bottom sites every 3 months in the Archipelago of Cabrera National Park (Western Mediterranean). All morphometric variables analysed showed a spatial variation and temporal patterns depending on depth. Between depths, C. racemosa biomass, stolon length, number of fronds and frond length were usually significantly higher at deep-water populations, suggesting that C. racemosa grows better in deep-waters. Deep- and shallow-water populations displayed a high temporal variation although no evidence of seasonal patterns was found, in contrast with what has been reported by other authors. The sources of this variability are still unknown but probably both physical factors and differential herbivory pressures display a key role.     

Much damage for little advantage: Field studies and morphodynamic modelling highlight the environmental impact of an apparently minor coastal mismanagement

While coastal management activities have long been known to exert a strong influence on the health of marine ecosystems, neither scientists nor administrators have realized that small interventions may lead to disproportionately larger impacts. This study investigated the broad and long-lasting environmental consequences of the construction of an ill-planned, although small (only 12 m long) jetty for pleasure crafts on the hydrodynamic conditions and on the meadow of the seagrass Posidonia oceanica of an embayed cove in the Ligurian Sea (NW Mediterranean). There, P. oceanica used to develop on a high (>1.5 m) matte (a lignified terrace causing seafloor elevation) in which the leaves reach the surface and form a compact natural barrier to waves in front of the beach. Such a so-called ‘fringing reef’ of P. oceanica is today recognized of high ecological value and specific conservation efforts are required. The construction of the jetty implied the cutting of the matte, which directly destroyed part of the fringing reef. In addition, meadow mapping and sedimentological analyses coupled with morphodynamic modelling showed that the ecosystem of the whole cove had been greatly altered by the jetty. We used the geometric planform approach, a proper tool in the study of headland-controlled embayment, both to characterise the present situation of Prelo cove and to simulate the original one, before the jetty was built. In the long term, such a small jetty completely altered the configuration and the hydrodynamic conditions of the whole cove, splitting the original pocket beach into two smaller ones and creating strong rip-currents flowing seaward along the jetty. These rip-currents enhanced erosion of residual shallow portions of the meadow and further modified the sedimentary fluxes in shallow waters. A century after the construction of the jetty, an irreversible environmental damage has occurred, as the slow growing rate of P. oceanica implies that the high matte terrace and the fringing reef will hardly form again, even after the removal of the jetty. The lesson learnt from this study is that even such small, and therefore reputed intrinsically ‘innocent’, interventions on the coastal zone require accurate planning based on interdisciplinary studies to understand and respect the delicate interplay among morphological, hydrodynamic and ecological components.     

Persistence of biological invasion effects: Recovery of macroalgal assemblages after removal of Caulerpa racemosa var. cylindracea

The present study evaluated the capability of recovery of Mediterranean macroalgal assemblages on rocky bottom invaded by Caulerpa racemosa. A manipulative experiment was performed to compare the structure of native assemblages that: (a) were invaded by the alga, (b) were invaded, but where the invasive alga was removed, and (c) had never been invaded. Macroalgal assemblages differed significantly between areas invaded by C. racemosa and control areas. Moreover, one year after removal of the invader, the recovery of community was minimal. Overall, recovery consisted of a significant increase in species richness and cover of macroalgae, but cover of each vegetation layer (encrusting, turf and erect) did not vary significantly between cleared and Invaded plots through time. Results showed that the effects of the colonization persist after the removal of the alga and the process of recovery of the assemblages appears to be quite slow. This finding might be an important contribution to evaluate invasion costs and thus potentially useful for an effective addressing of control strategies.     

Size‐frequency distributions of Joania cordata and Argyrotheca cuneata (Brachiopoda: Megathyrididae) from the Central Tyrrhenian Sea

Size‐frequency distributions can support reliable inferences concerning population dynamics of brachiopods, but only a few data are available so far. In this study, length and width frequency distributions of dead specimens of the Recent brachiopods Joania cordata and Argyrotheca cuneata from the Marine Protected Area ‘Secche di Tor Paterno’, Central Tyrrhenian Sea, Italy (41°35′ N, 12°20′ E), are reported in order to add new data about size‐frequency distributions of brachiopods. The studied specimens came from death assemblages in the coralligenous substrate, in the Posidonia oceanica meadows, and in the sand channels. The observed patterns vary from left‐skewed (J. cordata) to right‐skewed (A. cuneata), indicating respectively a low and high mortality of smaller individuals. Significant differences between the coralligenous substrate and the P. oceanica meadow were observed for both species, revealing a variation among different habitats. All length and width distributions are clearly polymodal, but the biological meaning of the peaks is difficult to interpret, as the two species seem to have a 2‐year life span. A biometric analysis of shell sizes revealed that length and width are the most variable parameters during the growth of the animal.     

Harpacticoid copepod response to epiphyte load variations in Posidonia oceanica (L.) Delile meadows

We conducted a field experiment to assess the response of phytal harpacticoids to nutrient‐driven increases of epiphyte load in Posidonia oceanica meadows. First, we evaluated differences in species richness, diversity and assemblage structure of phytal harpacticoids in P. oceanica meadows with differing epiphyte loads. Secondly, we conducted a field experiment where epiphyte load was increased through an in situ addition of nutrients to the water column and evaluated the responses of the harpacticoid assemblages. We predicted that there would be changes in the harpacticoid assemblages as a result of nutrient‐driven increases of epiphyte load, and that these changes would be of a larger magnitude in meadows of low epiphyte load. Our results show that the harpacticoid fauna (>500 μm) present in P. oceanica meadows in the Bay of Palma comprised taxa which are considered phytal and other less abundant ones previously described as sediment dwellers or commensal on other invertebrate species. Nutrient addition had an overall significant effect on epiphyte biomass and on harpacticoid abundance, diversity and assemblage structure, possibly as a response to the increased resources and habitat complexity provided by epiphytes. The abundance of dominant species at each location was favoured by nutrient addition and in some cases correlated with epiphytic biomass, although never strongly. This may indicate that structural complexity or diversity of the epiphytic cover might be more important than the actual epiphytic biomass for the harpacticoid species investigated. More species‐specific studies are necessary to ascertain this and clarify the relationships between harpacticoids and epiphytes in seagrass meadows. To our knowledge, this is the first account of harpacticoid species associated with P. oceanica leaves and the epiphytic community they harbour in the Mediterranean Sea.     

Temporal and bathymetric variation of epiphyte cover and leaf biomass in a southern Posidonia oceanica (L.) meadow: the case of Mahdia coast,Tunisia

The aim of this research was to study spatial and temporal variation in epiphyte cover and leaf biomass of Posidonia oceanica in Eastern Tunisia. Sampling was conducted at four stations on the Mahdia coast during October and December 2010, and April and August 2011, which correspond respectively to autumn, winter, spring and summer in this area. Posidonia oceanica shoots were collected at two depths (5 and 10 m). Cover of macroinvertebrates and macroalgae was estimated on adult leaves. The results showed that leaf and epiphyte biomasses vary significantly according to sampling date, with the highest values recorded in August. We found a high diversity of epiphytic assemblages on the leaves of P. oceanica with clear qualitative and quantitative dominance of Rhodophyceae compared to other groups, followed by Phaeophyceae. Most epiphyte species on the leaves of P. oceanica in Eastern Tunisia are the same as those in other parts of the Mediterranean Sea. No bathymetrical variation in the epiphytic community was found in our study area, which can be explained by the high levels of water clarity in Mahdia.     

Effect of different substrata on rhizome growth,leaf biometry and shoot density of Posidonia oceanica

The effects of different substratum typologies on Posidonia oceanica growth and morphology were estimated in four Sicilian meadows using Generalized and Linear Mixed Models combined with retrodating and biometric analyses. Substratum exerted a multiple effect, resulting in different biometric features for P. oceanica shoots settled on rock from those growing on sand and matte. On rock, values for growth rate, leaf length and shoot surface were lower than those on other substrata, with 42%, 23% and 32% the highest degree of difference respectively. The present study may have interesting methodological consequences for the comprehensive understanding of the causative variables potentially affecting meadows features and their health status. The importance of substratum in the prediction of likely biometry changes in P. oceanica meadows, means that knowledge of substratum type should receive due attention in the future to derive reliable estimates of meadow status.     

Depth distribution of algal species on the deep insular fore reef at Lee Stocking Island,Bahamas

Deep-water benthic algal composition and cover were studied with a submersible on the deep fore reef of Lee Stocking Island, Bahamas, from 45 to 150 m. Algal cover decreased from 57% to 16% over this depth range. Although there was substantial overlap in depth distributions, different species or groups of species dominated benthic cover at different depths. Lobophora and Halimeda copiosa co-dominated the fore reef from 45 to 60 m. A Corallinales/Peyssonnelia group was abundant from 60 to 120 m. The Corallinales/Peyssonnelia group shared dominance with Ostreobium between 90 and 120 m. Ostreobium was the only alga observed below 150 m and remained abundant below 200 m. Movement of sand down the fore reef is recognized as having substantial influence on algal cover.     

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.     

Evolution of Posidonia oceanica seagrass meadows and its implications for management

Results of the monitoring network of the Posidonia oceanica meadows in the Valencia region in Spain are analysed. For spatial comparison the whole data set has been analysed, however, for temporal trends we only selected stations that have been monitored at least 6 years in the period of 2002–2011 (26 stations in 13 localities).At the south of the studied area, meadows are larger, and they have higher density and covering than that in the Valencia Gulf, excluding Oropesa meadow. Monitoring of P. oceanica meadows in the Valencia region in Spain indicates that most of them are stationary or they are increasing their density and covering while no decline was observed in the studied meadows. These results indicate that there is not a general decline of P. oceanica meadows and that the decline of P. oceanica, when it has been observed in other studies, is produced by local causes that may be managed at the local level. This study also reflects the importance of long series of direct data to analyse trends in the population dynamics for slow-growing species.     

First evidence of a massive recruitment event in Posidonia oceanica: Spatial variation in first-year seedling abundance on a heterogeneous substrate

A recruitment event of Posidonia oceanica was recorded in the Gulf of Ventilegne (Corsica, Western Mediterranean) in June 2005. One-year seedlings (alive and dead) were found at shallow depth (2–3 m) on a mix of rock and sand substrates. Pattern in the distribution of seedlings was examined over spatial scales ranging from centimetres to hundreds of metres. We also examined (a) whether establishment was preferentially associated with a specific substrate type; (b) the relation between proportional mortality and the density of established seedlings; and (c) the growth characteristics of seedlings. The average density of seedlings varied from 19 to 189 seedlings m⁻², with a maximum of 480 seedlings m⁻². While significant variation was detected at the scale of area (i.e., tens of metres), no difference was found in abundance of seedlings at the scale of sites (i.e., hundreds of metres). Most of the overall variability was, however, at on the smallest scale examined (i.e., among sampling units tens of centimetres apart). No differences were also observed in the establishment probability and seedling abundance between sand and rock substrates. The fine scale analysis of spatial patterns on rock and sand substrates showed a clumped distribution of seedlings. These results indicated that the spatial distribution of seedlings was not random, but organized at small spatial scales within the study sites. Hydrodynamics and micro-scale bottom features appeared to account for such patterning. Proportional seedling mortality was highly variable (ranging from 0.3 to 0.8), and tended to increase with increasing settlement density. A total of 128,000 seedlings were recoded over the 1600 m² surface area investigated. Such event reflected conspicuous seed supply and particularly favourable local conditions. This finding contradicts the current statement of low recruitment ability of P. oceanica and indicates that the species can recruit both on consolidated and unconsolidated substrates, at least in the study area.     

Wave damping over artificial Posidonia oceanica meadow: A large-scale experimental study

An experimental study, conducted in the large wave flume of CIEM in Barcelona, is presented to evaluate the effects of Posidonia oceanica meadows on the wave height damping and on the wave induced velocities. The experiments were performed for irregular waves from intermediate to shallow waters with the dispersion parameter h/λ ranging from 0.09 to 0.29. Various configurations of the artificial P. oceanica meadow were tested for two stem density patterns (360 and 180 stems/m²) and for plant's height ranging from 1/3 to 1/2 of the water depth.The results for wave height attenuation are in good agreement with the analytical expressions found in literature, based on the assumption that the energy loss over the vegetated field is due to the drag forces. Based on this hypothesis, an empirical relationship for the drag coefficient related to the Reynolds number, Re, is proposed. The Reynolds number, calculated using the artificial P. oceanica leaf width as the length scale and the maximum orbital velocity over the meadow edge as the characteristic velocity scale, ranges from 1000 to 3500 and the drag coefficient C_d ranges from 0.75 to 2.0.The calculated wave heights, using the analytical expression from literature and the proposed relationship for the estimation of C_d, are in satisfactory agreement with those measured. Wave orbital velocities are shown to be significantly attenuated inside the meadow and just above the flume bed as indicated by the calculation of an attenuation parameter. Near the meadow edge, energy transfer is found in spectral wave velocities from the longer to the shorter wave period components. From the analysis it is shown that the submerged vegetation attenuates mostly longer waves.