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1.
Seasonal dynamics of Zostera noltii was studied during 1984 in Arcachon Bay, France. In this Bay, Z. noltii colonizes 70 km2, i.e. approximately 50% of the total area, while Z. marina occupies only 4 km2. Densities and length of vegetative and generative shoots and above-ground and below-ground biomasses were monitored in four meadows which differed according to their location in the Bay, tidal level and sediment composition. Three of these meadows were homogeneous, well-established beds whilst the fourth was under colonization and patchy. Shoot densities and maximal below-ground biomass were lower in the inner silty seagrass bed than in the sandy meadows located in the centre of the Bay. Maximal above-ground biomasses were similar in the two population types. In the well-established beds, vegetative shoot densities, above-ground and below-ground biomasses showed a unimodal pattern with minima in winter (4000 to 9000 shoots·m−2, 40 to 80 g DW·m−2, and 40 to 60 g DW·m−2, respectively) and maxima in summer (11000 to 22000 shoots·m−2, 110 to 150 g DW·m−2, and 140 to 200 g DW·m−2, respectively). Reproductive shoots were observed from the beginning of June until the end of September, except in the colonizing bed where they persisted until December. Furthermore, in the latter, maximal reproductive shoot density was higher (2600 shoots·m−2) than in the established beds (650 to 960 shoots·m−2). The total production of Z. noltii in Arcachon Bay was estimated to approximately 35.6·106 kg DW·y−1 (19.4·106 kg DW·y−1 for above-ground parts and 16.2·106 kg DW·y−1 for below-ground parts).  相似文献   

2.
Leaf growth, biomass and production of Cymodocea nodosa were measured from October 2006 to September 2007 in Monastir Bay (Tunisia). Shoot density showed a clear seasonal pattern, increasing during spring and summer and decreasing during fall and winter. Monthly mean shoot density ranged between 633 ± 48 and 704 ± 48 shoots?m?2. The monthly average total biomass ranged between 560 ± 37 and 646 ± 32 g dry weight (DW)?m?2. Total biomass varied significantly among stations and sampling times but did not show seasonal variation. Leaf plastochrone intervals varied seasonally, with an annual average of 28–30 days. Leaf productivity was highest in August (2.61 g DW?m?2?day?1) and lowest in February (0.35 g DW?m?2?day?1). Annual belowground primary production varied from 263 to 311 g DW?m?2?year?1. Annual leaf production was approximately equal for all the stations (from 264 to 289 g DW?m?2?year?1). Variability in water temperature, air temperature and salinity explained the annual variability in biological characteristics. Changes in belowground and total biomass were not correlated with seasonal variability in the environmental parameters monitored. Additionally, a literature review was conducted of C. nodosa features at other Mediterranean sites, encompassing 30 studies from 1985 to 2014.  相似文献   

3.
The vesicomyid Calyptogena kilmeri is one of the most abundant bivalves inhabiting chemosynthetic environments shallower than c. 1500 m along central California. We estimated the population size structure, biomass, rates of individual growth, somatic production, and mortality for C. kilmeri, based on sampling of seep habitats and tag–recapture studies at chemosynthetic communities in Monterey Bay, California. The composite growth rate of C. kilmeri over all sites was relatively high (K = 0.25), reaching c. 80% of asymptotic length (104.7 mm) in 6.6 years. The density of C. kilmeri was estimated as 938.5 ind. m−2 and biomass density varied from 704 to 2059 g ash free dry mass (AFDM) m−2. Somatic production was also high (294–297 g·AFDM·m−2 year−1), and production/biomass ratios for C. kilmeri varied from 0.14 to 0.42 among sites, related to variation in size–frequency distributions among sites. Instantaneous mortality rates estimated from size distributions ranged from 0.17 to 0.24 year−1. Growth and somatic production by C. kilmeri are in the range reported for chemosynthetic bivalves from hydrothermal vent and seep habitats, as well as photosynthetic‐based assemblages of inshore or intertidal bivalves, and greatly exceed rates reported for heterotrophic deep‐sea benthos.  相似文献   

4.
The relationship between flowering and growth performance of Posidonia oceanica (L.) Delile in meadows distributed along the south‐eastern coast of Sicily (Italy) was investigated by means of a statistical model (generalized linear mixed model) combined with the lepidochronological analysis. Over a 28‐year period, 67 floral stalk remains were observed. The highest flowering index was recorded in lepidochronological year 1998 (10.1%) and the Inflorescence Frequency per age showed a clear decrease corresponding to 15‐year‐old shoots. The sexual reproductive event had positive effects on rhizome elongation (cm year?1) and leaf production (no. leaves year?1) in the same flowering year, whilst no effect on the rhizome production (mg year?1) was observed. Rhizome growth variables showed significant negative lagged responses in the two years following flowering. On the whole, we calculated that the effect exerted by flowering, in terms of loss on rhizome elongation and production, was about 27% and 38%, respectively. Although it has been demonstrated that recovery from the stress induced by sexual reproduction is limited to the two years after flowering, the magnitude of the reproductive cost may become quite considerable especially in comparison with the whole lifespan of individual shoots.  相似文献   

5.
Mud snails Hydrobia ulvae occupy different habitats in complex estuarine ecosystems. In order to determine if fatty acid profiles displayed by mud snails can be used to identify the habitat that they occupy within the same estuary, fatty acids of H. ulvae from one mudflat and one seagrass meadow in the Ria de Aveiro (Portugal) were analyzed and compared to those displayed by microphytobenthos (MPB), the green leaves (epiphyte-free) of Zostera noltii, as well as those exhibited by the epiphytic community colonizing this seagrass. MPB and epiphytic diatom-dominated samples displayed characteristic fatty acids, such as 16:1n-7 and 20:5n-3, while 18:2n-6 and 18:3n-3 were the dominant fatty acids in the green leaves of Z. noltii. Significant differences between the fatty acid profiles of H. ulvae specimens sampled in the mudflat and the seagrass meadow could be identified, with those from the mudflat displaying higher levels of fatty acids known to be characteristic of MPB. This result points towards the well known existence of grazing activity on MPB by mud snails. The fatty acid profiles displayed by H. ulvae inhabiting the seagrass meadows show no evidence of direct bioaccumulation of the two most abundant polyunsaturated fatty acids of Z. noltii (18:2n-6 and 18:3n-3) in the mud snails, which probably indicates that either these compounds can be metabolized to produce energy, used as precursors for the synthesis of essential fatty acids, or that the snails do not consume seagrass leaves at all. Moreover, the fatty acid profiles of mud snails inhabiting the seagrass meadows revealed the existence of substantial inputs from microalgae, suggesting that the epiphytic community colonizing the leaves of Z. noltii displays an important role on the diet of these organisms. This assumption is supported by the high levels of 20:5n-3 and 22:6n-3 recorded in mud snails sampled from seagrass meadows. In conclusion, fatty acid analyses of H. ulvae can be successfully used to identify the habitat occupied by these organisms within the same estuary (e.g. mudflats and seagrass meadows) and reveal the existence of contrasting dietary regimes.  相似文献   

6.
本文以印尼北苏拉威西东部的潟湖为对象，研究了热带海草床鱼类群落的种类组成和时空变化。研究发现当地鱼类的香农-威纳指数在1.57-3.69之间多样性相对较高。在科水平，天竺鲷科的丰度（8.27 ind./（100 m2））和生物量（28.49 g/（100 m2））最高。在物种水平，侧带天竺鲷（Apogon lateralis）的丰度最高，环纹圆天竺鲷（Sphaeramia orbicularis）的生物量最大。对于物种的空间变化，潟湖湖顶、湖中和湖口首先聚类在一起，这可能是由于基质类型引起的。干季和湿季的鱼类种类、丰度和生物量均比转换季高，这可能是由较强的季风造成的，强季风为鱼类提供了更适宜的环境和食物。93.1%的鱼类的最大体长小于它们的性成熟体长，暗示了海草床是很多鱼类的育幼场。因此，保护海草床对渔业和资源的可持续利用至关重要。  相似文献   

7.
The abiotic disturbance of urban wastewater discharge and its effects in the population structure, plant morphology, leaf nutrient content, epiphyte load and macroalgae abundance of Zostera noltii meadows were investigated in Ria Formosa coastal lagoon, southern Portugal using both univariate and multivariate analysis. Four sites were assessed, on a seasonal basis, along a gradient from a major Waste Water Treatment Works (WWTW) discharge to a main navigation channel. The wastewater discharge caused an evident environmental disturbance through the nutrient enrichment of the water and sediment, particularly of ammonium. Zostera noltii of the sites closest to the nutrient source showed higher leaf N content, clearly reflecting the nitrogen load. The anthropogenic nutrient enrichment resulted in higher biomass, and higher leaf and internode length, except for the meadow closest to the wastewater discharge (270 m). The high ammonium concentration (158–663 μM) in the water at this site resulted in the decrease of biomass, and both the leaf and internode length, suggesting a toxic effect on Z. noltii. The higher abundance of macroalgae and epiphytes found in the meadow closest to the nutrient source may also affect the species negatively. Shoot density was higher at the nutrient-undisturbed site. Two of the three abiotic processes revealed by Principal Component Analysis were clearly related to the WWTW discharge, a contrast between water column salinity and nutrient concentration and a sediment contrast between both porewater nutrients and temperature and redox potential. A multiple regression analysis showed that these abiotic processes had a significant effect on the biomass-density dynamics of meadows and on the overall size of Z. noltii plants, respectively. Results show that the wastewater discharge is an important source of environmental disturbance and nutrients availability in Ria Formosa lagoon affecting the population structure, morphology and N content of Z. noltii. This impact is spatially restricted to areas up to 600 m distant from the WWTW discharge, probably due to the high water renewal of the lagoon.  相似文献   

8.
《Journal of Sea Research》2009,61(4):255-263
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.  相似文献   

9.
The effect of self‐shading and competition for light in the seagrass Enhalus acoroides were investigated with a density reduction experiment in Haad Chao Mai National Park, Trang Province, Thailand. The study was carried out in a monospecific meadow with a natural density of 141.0 ± 8.7 shoots·m?2. The intent was to determine the response of E. acoroides beds to loss of shoots and thinning, which often occur during typhoons and severe storm activity. Permanent quadrats were manipulated by clipping the seagrass shoots to 140, 72, 36 and 16 shoots·m?2, to yield natural, 50%, 25% and 10% densities, respectively. Reducing shoot density in E. acoroides increased underwater light intensity below the canopy, generating increased leaf surface area and shoot weight. Seagrass leaf width, growth rate, and number of leaves per shoot also increased with greater light. The extent of flowering varied among treatments with no consistent trend. Our results demonstrate that increasing the available light to E. acoroides produces an increasing leaf size response as self‐shading in the bed is reduced.  相似文献   

10.
威海荣成桑沟湾海域海草床分布现状及其生态特征   总被引：1，自引：0，他引：1  
海草床是生物圈最高产的生态系统之一，在氮捕获、碳封存、水质净化及维持生物多样性等方面发挥关键作用。2016年8月通过对威海荣成桑沟湾海域的现场调查，发现分布总面积约为471.72 ha的海草床，种类为鳗草（Zostera marina）、红纤维虾形草（Phyllospadix iwatensis）、日本鳗草（Zostera japonica）和丛生鳗草（Zostera caespitosa），分布面积分别为395.33 ha、37.28 ha、32.74 ha和6.37 ha。鳗草分布范围较广，平均茎枝密度817.0±27.6 shoots/m2，平均生物量646.6±41.8 g DW/m2；红纤维虾形草主要分布于桑沟湾北部养殖池和南部楮岛海域，平均茎枝密度2 649.0±29.8 shoots/m2，平均生物量2 381.3±27.3 g DW/m2；日本鳗草主要分布于桑沟湾西部八亩地海域，平均茎枝密度506.0±26.2 shoots/m2，平均生物量118.3±12.5 g DW/m2；丛生鳗草主要分布于桑沟湾南部楮岛海域，其平均密度为513.0±17.9 shoots/m2，平均生物量为479.1±28.1 g DW/m2。结合历史资料，发现桑沟湾海域海草床严重退化，分析了海草床的退化原因并提出了相应的建议和对策，以期为海草资源及滨海生境修复提供参考。  相似文献   

11.
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.  相似文献   

12.
The seasonal plasticity of individual Zostera noltii architectural, reproductive and elemental content features, of plant epiphyte load and of meadow biomass–density relationships was investigated along a vertical intertidal gradient at Ria Formosa lagoon, southern Portugal. The vertical variability of the seagrass environment was evident in the sediment characteristics, which showed coarser grain size, less organic matter, lower N content and higher ammonium concentration in the low intertidal than in medium and high intertidal. A clear vertical differentiation in Z. noltii morphology was observed from longer and wider leaves, longer and wider internodes and shorter roots at low intertidal, to shorter and narrow leaves, shorter and narrower internodes and longer roots at high intertidal. The leaf size was negatively related to light availability and positively related to nutrient availability whereas the root size was negatively related to nutrient availability. The lower leaf N and P content found in low intertidal plants may reflect a dilution effect of the nutrients due to higher growth rates. Lower N content of low intertidal leaves supports previous findings that the nitrate reductase activity is lower in plants from this level. The higher epiphyte load observed in Z. noltii leaves of the low intertidal may be a consequence of the lower exposure period, but also of higher hydrodynamics that increase the availability of nutrients. No evidence of the influence of the intertidal level on the flowering shoot density was found. The cyclic temporal pattern of the biomass–density relationship was much wider at low and medium intertidal than at high intertidal. At low intertidal, the decline in shoot density during fall and winter was coincident with a biomass decrease and its increase in spring and summer coincided with the biomass increase. In medium and high intertidal, the biomass and density seasonal variations were decoupled. As a result, only at low intertidal there was a significant positive relationship between biomass and density. This suggests that Z. noltii population structure along the intertidal is regulated by different factors. Light is probably the most important factor regulating the population structure in the low intertidal, whereas desiccation is probably the main factor regulating the populations in upper intertidal. Zostera noltii showed a considerable plasticity at a physiological-, plant- and population-level along the intertidal zone, indicative of the species acclimation to the steep environmental gradient of this particular ecosystem.  相似文献   

13.
A model was developed for Typha, to examine the effects of latitudinal changes in temperature and radiation on the partitioning of total biomass during the growing season into rhizomes, roots, flowering and vegetative shoots, and inflorescences.Regardless of initial rhizome biomass, both above and belowground biomasses converge on a equilibrium value, with the balance between total production and metabolic loss being latitude-specific. If aboveground biomass is harvested just once, then both above and belowground biomasses return to equilibrium values after several years. If the aboveground biomass is harvested annually, then both above and belowground biomasses converge on smaller equilibrium values, which are determined by the balance between the sum of production prior to harvesting and after harvesting, and the sum of annual metabolic losses and a loss due to harvesting.The model could be used in wetland management activities to predict the potential growth of Typha in given conditions as well as the responses of Typha stands to harvesting over a wide range of latitudes for times ranging from a season to several years.  相似文献   

14.
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.  相似文献   

15.
Although grazing is considered an essential process controlling epiphyte biomass on seagrass leaves, there is still a lack of fundamental knowledge about the species‐specific consumption rates of the most common grazers in Mediterranean meadows. This study experimentally assessed the effect of Posidonia oceanica‐associated gastropod grazing on early successional biofilm and the species‐specific relationship between biofilm consumption rates and biofilm biomass. Two biofilms on artificial substrata, both developed in situ (in a P. oceanica meadow), one under ambient conditions and the other under nutrient‐enriched conditions, were offered in aquaria assays to nine species of grazers found in P. oceanica meadows. Biofilm consumption rates and their association with biofilm biomass were assessed. It was found that: (i) there was a positive association between biofilm consumption and biofilm biomass up to 20 mg Chl a·m?2 for Bittium reticulatum, Gibbula ardens, Jujubinus exasperatus and Tricolia pullus; (ii) Alvania montagui, B. reticulatum and Jujubinus striatus showed the highest consumption rates and are thus expected to be amongst the leading consumers in early‐successional epiphytic communities; (iii) there was not an increase of consumption rate when a substratum colonized under nutrient‐enriched conditions was offered to any of the nine studied species. This study provides species‐specific consumption rates knowledge that is useful for the assessment of the strength of grazer–epiphyte interactions and trophic fluxes in P. oceanica meadows.  相似文献   

16.
The temporal dynamics of two seagrass species, Zostera marina and Z. japonica, were monitored monthly in Dadae Bay, Geoje Island, on the southern coast of Korea. Plant morphological characteristics, shoot density, biomass, leaf production, reproductive effort, and environmental characteristics were monitored from July 2001 to July 2002. Zostera japonica occurred in the intertidal zone and Z. marina occurred in the subtidal zone from 0.5 to 2.5 m below the mean low water level. Shoots and rhizomes were significantly larger in Z. marina than in Z. japonica, whereas the shoot density was greater in Z. japonica than in Z. marina. Despite differences in morphology and shoot density, biomass did not differ significantly between the species. Reproduction occurred from April to June in Z. marina and from May to July in Z. japonica. The proportion of reproductive shoots was approximately three times higher in Z. marina than in Z. japonica. Seasonal variation in the biomass of Z. japonica was caused by changes in both shoot size and density, whereas that of Z. marina was mainly caused by changes in shoot length. Leaf production in Z. marina and Z. japonica showed clear seasonal variation, and leaf production in Z. marina (2.6 ± 0.2 g DW·m−2·day−1) was higher than that in Z. japonica (1.7 ± 0.2 g DW·m−2·day−1). The mean plastochrone interval was not significantly different between the two species, whereas the leaf lifetime of Z. marina was longer (69 ± 7.8 days) than that of Z. japonica (59 ± 8.3 days). Our results indicated that seasonal leaf growth patterns in Z. japonica are correlated with irradiance and temperature, whereas those in Z. marina respond most to irradiance. Seasonal changes in irradiance appeared to control the temporal variation in above‐ground biomass in both species.  相似文献   

17.
The Cape rock lobster Jasus lalandii is a major predator in the inshore Benguela system. The mean density and biomass at Oudekraal is 0,48 individuals ·m?2 or 49,75 g dry mass ·m?2. The main component of its diet is Aulacomya ater, the ribbed mussel, which has a mean biomass of 1,15 kg dry mass ·m?2. Daily consumption of carbon and nitrogen from this source reaches a maximum in summer and, when J. lalandii feed on mussels, 14,1 per cent of the flesh is lost to the environment as a result of "messy feeding". The absorption efficiency of ingested nitrogen is 86,2 per cent. Ammonia and urea excreted in the first 12 h after feeding represent 6,7 and 1,6 per cent respectively of the nitrogen ingested. Endogenous nitrogen excretion has a mean rate of 1,9 μg N·g (dry mass)?1·h?1 The range of estimates for combined figures of kelp and phytoplankton nitrogen requirements are 76,4 – 86,7 g N·m?2·year?1 J. lalandii returns 6,3 g N·m?2·year?1 to the system, accounting for 7,2 – 8,2 per cent of annual kelp and phytoplankton requirements. This could be of particular importance during downwelling when the supply of new nitrogen is limited.  相似文献   

18.
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.  相似文献   

19.
黄海镆铘岛海域海草床数量分布及其生态特征   总被引：1，自引：0，他引：1  
海草床是近海三大典型海洋生态系统之一,具有巨大的碳储备功能,并为众多海洋生物提供重要的栖息场所及食物来源,在维持近岸海洋生态系统平衡中发挥着重要的作用。2016年8月通过对黄海镆铘岛海域的现场调查,发现分布面积为272.84 ha的海草床主要种类为鳗草(Zostera marina)和红纤维虾形草(Phyllospadix iwatensis)。鳗草的分布面积约为177.23 ha,占总面积的65%,主要分布在镆铘岛沿岸的海参养殖池中,红纤维虾形草的分布面积约为95.61 ha,占总面积的35%,主要分布在沿岸的礁石上,呈明显的带状分布。鳗草的平均株高为(86.8±5.8)cm,平均植株密度和生物量分别为(364.0±14.2)株/m~2和(528.7±20.5)gDW/m~2;红纤维虾形草的平均株高为(112.8±3.8)cm,平均植株密度和生物量分别为(3087.0±35.4)株/m~2和(2320.0±26.6)gDW/m~2。红纤维虾形草的分布水深为(1.80±0.04)m,海草床的水体溶解氧含量较高,达到(10.4±0.1)mg/L,分布有鳗草的海参池塘的底质粒径为(4.6±0.1)mm。结合历史资料,发现该海域海草床退化现象十分严重,这除了受自然环境变化的影响外,与过度的人类活动干扰有关。并提出了海草床修复与保护的建议和对策,可为进一步研究与保护该区域海草床生态系统提供基础。  相似文献   

20.
《Marine Chemistry》2001,73(3-4):291-303
Oxygen and phosphate measurements from two sections across the Norwegian Atlantic Current, the Gimsøy-NW section from 67.5°N 9°E to 71.5°N 1°E and the Bjørnøya-W section along 74.5°N from 7 to 15°E, are used to estimate oxygen fluxes in the surface layer and between the atmosphere and the ocean. Vertical entrainment velocities of 0.9 m day−1 for the winter season and 0.1 m day−1 for the summer season are found and applied to the upper 300 m. The resulting oxygen fluxes to the surface layer driven by this vertical mixing are 0.58±0.05 and 0.27±0.02 mol O2 m−2 year−1 at the Gimsøy-NW and Bjørnøya-W sections, respectively. Oxygen fluxes to the surface layer due to phytoplankton production are 2.6 and 3.4 mol O2 m−2 year−1, which represent the net community production at the two sections. Estimated uncertainties in these numbers are ±15%. The surface water is a sink for atmospheric oxygen during fall and winter and a source during the productive season for both sections. On an annual basis there is a net uptake of oxygen from the atmosphere, 3.4±0.4 mol O2 m−2 year−1 at the Gimsøy-NW section and 4.9±0.5 mol O2 m−2 year−1 at the Bjørnøya-W. A decrease in temperature of 1°C to 1.5°C seen between the Gimsøy-NW section and the Bjørnøya-W section is the main reason for the increased atmospheric flux of oxygen at the latter section. An oxygen budget made for the area bounded by the two sections gives a net advective flux of oxygen out of the area of approximately 10 mol O2 m−2 year−1. The increased concentration of oxygen corresponding to the decrease in surface layer temperatures going northwards in the Norwegian Atlantic Current is mainly attributed to the air–sea oxygen exchange and phytoplankton production in this area.  相似文献   

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