三沙湾盐田港养殖海域沉积物中的有机碳、氮和磷

于2012年8月(夏季)、11月(秋季)和2013年2月(冬季)、5月(春季)共4个航次对三沙湾盐田港养殖海域表层沉积物组成成分及其变化趋势进行调查分析,并采用单因子污染指数(Pi)对沉积物质量进行评价。结果表明不同功能区沉积物中有机氮(TN)、总磷(TP)和有机碳(OC)含量差异显著(P0.05),TN和TP含量4季变化范围分别是0.15~1.39 g/kg和0.11~1.08 g/kg,平均值分别为(0.89±0.36)g/kg和(0.56±0.26)g/kg。OC含量在1.00~14.71 g/kg之间,平均值为(8.26±3.78)g/kg。各站位沉积物中TN污染指数4季变化范围为0.25~2.53,4季超标率分别为67%、81%、80%和90%;各站位TP污染指数4季变化范围为0.18~2.63,4个季节超标率分别为35%、80%、40%和51%;各季节OC含量均未超标;OC/N原子比全年变化范围在8.4~10.3之间,平均值为8.9±0.6。较弱的水流交换条件和海水养殖,特别是海水网箱养殖,是造成沉积物污染的主要原因,开展多营养层次的综合养殖模式是促进盐田港海水养殖可持续发展的有效途径。     

Influence of prey abundance and abiotic factors on the long-term home-range and movement dynamics of spotted grunter Pomadasys commersonnii in an intermittently open estuary

Long-term home-range and movement dynamics of spotted grunter Pomadasys commersonnii and the distribution of their dominant prey, the sandprawn Callichirus kraussi, were investigated in the intermittently open East Kleinemonde Estuary, South Africa. In addition, the effects of fish length, diel cycle, season and other abiotic factors on home range and area use were examined. Nine adult spotted grunter (326–489?mm total length) were tagged with acoustic transmitters, and their movements were studied by manual tracking on six consecutive days and nights during each of five tracking sessions from March to November 2004. In addition, movement patterns were recorded by stationary data-logging receivers. Kernel home ranges (95% utilised distribution) varied in size (mean: 76 797?m²?, range: 26 296–165 321?m²), but were all located in the lower one-third of the 3.6 km-long estuary. There was no effect of season, the diel cycle or fish length on the home-range estimates. However, the distribution of prey corresponded with the home-range distribution of tagged fish. Although sandprawn distribution was highly variable within and among transects and depth classes, sandprawns were most abundant in the lower region of the estuary, which corresponded to the home-range distribution of spotted grunter. Spatial distribution of prey appears to be a dominant factor influencing home-range parameters of this species within an intermittently open estuary.     

Seasonally and spatially referenced estimates of recreational shore-angling effort,catch composition,catch rates and total catch in the Goukamma Marine Protected Area,South Africa

A roving creel survey of the recreational shore fishery along the 16.4-km coastline in the Goukamma Marine Protected Area on the south coast of South Africa was conducted from 2009 to 2011. Some 838 patrols were stratified equally among months, areas and years, but intentionally biased towards weekends. Angler densities at Buffalo Bay and Groenvlei were 0.59 and 0.28 anglers km?1, respectively. Weekend densities were double to quadruple weekday densities and fishing during winter was more popular than during summer. Area, habitat and distance to access points explained variation in angler densities. Shannon–Wiener diversity in catches declined from 2.18 in an earlier (1993–2002) survey to 1.79. Although the order of species abundance in the catches remained largely unchanged, blacktail Diplodus capensis dominance increased to 57.3% by number, at the expense of galjoen Dichistius capensis. Habitat explained 27% of the variance in catch composition. The catch per unit effort (CPUE) for the top nine species ranged from 0.19 to 6.35 fish 100-h?1. The CPUE of all species, except spotted grunter Pomadasys commersonnii, declined. Blacktail and galjoen CPUE declined by 17% and 77%, respectively. The total catch estimate was 2 986 fish y?1. Transgressions of size limits were common. The results suggest that the fishery is overexploited and that catch rates are declining.     

Coralligenous habitat in the northern Adriatic Sea: an overview

The rocky outcrops irregularly scattered in the sandy‐muddy sea bed of the Northern Adriatic, formed by a base rock and a superimposed concretion of vegetal and animal organisms, are considered an infralittoral coralligenous habitat, according to the most recent definition. In the last four decades, research has mainly concentrated on their geology because of the question of the origin of the base rock – very similar to beachrock – which has only recently been attributed to sedimentary cementation induced by methane seeps. Studies on their macrobenthic assemblages have also been published recently, but true comparisons among them are difficult because they mostly refer only to a few selected phyla or to short‐term observations. Very few papers deal with the whole of the animal and plant communities, including all taxonomic groups and the most important environmental variables. On the basis of the literature data concerning several outcrops in the Gulf of Venice, we suggest that the Adriatic reefs differ slightly from the classic deeper coralligenous assemblages around the Mediterranean coast because they have smaller concretions of algae builders. We also suggest that the Northern Adriatic coralligenous reefs are younger than the other reefs occurring in the Mediterranean Sea.     

Coastal and estuarine habitat mapping, using LIDAR height and intensity and multi-spectral imagery

The airborne laser scanning LIDAR (LIght Detection And Ranging) provides high-resolution Digital Terrain Models (DTM) that have been applied recently to the characterization, quantification and monitoring of coastal environments. This study assesses the contribution of LIDAR altimetry and intensity data, topographically-derived features (slope and aspect), and multi-spectral imagery (three visible and a near-infrared band), to map coastal habitats in the Bidasoa estuary and its adjacent coastal area (Basque Country, northern Spain). The performance of high-resolution data sources was individually and jointly tested, with the maximum likelihood algorithm classifier in a rocky shore and a wetland zone; thus, including some of the most extended Cantabrian Sea littoral habitats, within the Bay of Biscay. The results show that reliability of coastal habitat classification was more enhanced with LIDAR-based DTM, compared with the other data sources: slope, aspect, intensity or near-infrared band. The addition of the DTM, to the three visible bands, produced gains of between 10% and 27% in the agreement measures, between the mapped and validation data (i.e. mean producer's and user's accuracy) for the two test sites. Raw LIDAR intensity images are only of limited value here, since they appeared heterogeneous and speckled. However, the enhanced Lee smoothing filter, applied to the LIDAR intensity, improved the overall accuracy measurements of the habitat classification, especially in the wetland zone; here, there were gains up to 7.9% in mean producer's and 11.6% in mean user's accuracy. This suggests that LIDAR can be useful for habitat mapping, when few data sources are available. The synergy between the LIDAR data, with multi-spectral bands, produced high accurate classifications (mean producer's accuracy: 92% for the 16 rocky habitats and 88% for the 11 wetland habitats). Fusion of the data enabled discrimination of intertidal communities, such as Corallina elongata, barnacles (Chthamalus spp.), and stands of Spartina alterniflora and Phragmites australis, which presented misclassification when conventional visible bands were used alone. All of these results were corroborated by the kappa coefficient of agreement. The high classification accuracy found here, selecting data sources, highlights the value of integrating LIDAR data with multi-spectral imagery for habitat mapping in the intertidal complex fringe.     

Inter-season and interannual variations in fish and macrocrustacean community structure on a eastern English Channel sandy beach: Influence of environmental factors

The intertidal zone of an exposed sandy beach on the French coast of the English Channel was sampled with a 1.5 m beam-trawl over five years (2000 and 2003–2006) at weekly intervals. The fish and macrocrustacean catches were analysed to determine the inter-season and interannual variation in community structure and relate these variations to changes in the major environmental variables. Only six species (plaice Pleuronectes platessa, common goby Pomatoschistus microps, sprat Sprattus sprattus, sand eel Ammodytes tobianus, brown shrimp Crangon crangon and shore crab Carcinus maenas) from the 27 species captured can be considered as dominant species of the intertidal zone, and they accounted for >90% of total numbers. Most individuals caught were young-of-the-year or juvenile. Analysis of similarities (ANOSIM) and similarities percentage (SIMPER) indicated that inter-season variability of community structure (mean average similarity = 47%) was more pronounced than interannual variability (mean average similarity = 65%). Canonical correspondence analysis (CCA) indicates that a substantial component (32.2%) of the measured inter-season variation in community structure can be explained by environmental factors (mainly water temperature). The main inter-season changes in the abundance and community structure were due to the variation of the six key species and reflect the different times of their recruitment. During the five years of the study, the structure of the fish and macrocrustacean spring community persisted from year to year, with the dominant species reappearing consistently even though their abundances fluctuated from year to year. This interannual variation probably reflects variable recruitment success influenced by physico-chemical conditions. In spite of the considerable interannual variation (40 times) in the spring bloom of the prymnesiophyte alga Phaeocystis globosa we found no effect of this bloom on either fish and macrocrustacean species densities or diversity index.     

Use of SPOT 5 and IKONOS imagery for mapping biocenoses in a Tunisian Coastal Lagoon (Mediterranean Sea)

Mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of Mediterranean lagoons. Fused images from two satellites, SPOT 5 and IKONOS, were tested as management tools for identifying specific ecosystems in the El Bibane lagoon, situated in southern Tunisia near the Libyan border. The objectives of this study were to provide a precise map of the entire El Bibane lagoon using fused images from SPOT 5 and to compare fused images from SPOT 5 and IKONOS over a test-area. After applying a supervised classification, pixels are automatically classified in four classes: low seagrass cover, high seagrass cover, superficial mobile sediments and deep mobile sediments. The maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon (essentially Cymodocea nodosa; 19 546 ha) and a large area of mobile sediments more or less parallel to the shore (3 697 ha). A direct comparison of overall accuracy between SPOT 5 over the entire area, SPOT 5 over the test-area and IKONOS over the test-area revealed that these tools provided accurate mapping of the lagoon environment (83.25%, 85.91% and 73.41% accuracy, respectively). The SPOT 5 images provided greater overall accuracy than the IKONOS image, but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment. Although IKONOS imagery provided lower overall accuracy than SPOT 5, it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account. The use of SPOT 5 and IKONOS fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the Mediterranean Sea.     

Spatial and temporal patterns of seagrass habitat use by fishes at the Ryukyu Islands,Japan

To investigate whether or not regional–temporal patterns of seagrass habitat use by fishes existed at the Ryukyu Islands (southern Japan), visual surveys were conducted in seagrass beds and adjacent coral reefs in northern, central, and southern Ryukyu Islands, in November 2004, and May, August, and November 2005, the northern region having less extensive seagrass beds compared with the central and southern regions. During the study period, the seagrass beds were utilized primarily by 31 species, the densities of some of the latter differing significantly among regions. With the exception of Apogonidae and Holocentridae, all species were diurnal and could be divided into 6 groups based on seagrass habitat use patterns; (1) permanent residents A (10 species, e.g. Stethojulis strigiventer), juveniles and adults living in seagrass beds as well as other habitats; (2) permanent residents B (5 species, e.g. Calotomus spinidens), juveniles and adults living only or mainly in seagrass beds; (3) seasonal residents A (4 species, e.g. Cheilodipterus quinquelineatus), juveniles living in seagrass beds as well as other habitats; (4) seasonal residents B (6 species, e.g. Lethrinus atkinsoni), juveniles living only or mainly in seagrass beds; (5) transients (5 species, e.g. Parupeneus indicus), occurring in seagrass beds in the course of foraging over a variety of habitats; and (6) casual species (1 species, Acanthurus blochii), occurring only occasionally in seagrass beds. Regarding temporal differences, juvenile densities in each group were high in May and August compared with November in each region, whereas adult densities did not differ drastically in each month. For regional differences, juvenile and adult densities of permanent residents A and B were higher in the southern and central regions than in the northern region. Moreover, some seasonal residents showed possible ontogenetic habitat shift from seagrass beds to coral reefs in each region. These results indicated that seagrass habitat use patterns by fishes changed temporally and regionally and there may be habitat connectivity between seagrass beds and coral reefs via ontogenetic migration in the Ryukyu Islands.     

Influence of environmental and prey variables on low tide shorebird habitat use within the Robbins Passage wetlands,Northwest Tasmania

Shorebirds feed primarily on tidal flats, and their distribution over these flats is influenced by their prey and abiotic factors. These factors act by influencing the distribution and abundance of the prey, or the shorebirds ability to exploit it. The aims of this study were to investigate the low tide foraging distribution of shorebirds at four sites within the Robbins Passage wetlands, and the environmental and invertebrate factors that may influence their distribution. The greatest densities and number of shorebirds were found at Shipwreck Point and East Inlet. The shorebirds within-site distribution was also non-random, with the shorebirds present in greatest densities at the water's edge and low intertidal stratum, although this varied among species. Generally, on a small spatial scale, invertebrate diversity was positively correlated, and seagrass leaf mass was negatively correlated, with shorebird feeding density. On a large spatial scale, invertebrate biomass and seagrass root mass were positively correlated with shorebird feeding density. Invertebrate biomass and seagrass root mass explained 71% of the variance in total shorebird feeding density on the tidal flats. The variation in shorebird feeding density and diversity was therefore partly explained by invertebrate diversity and biomass, as well as the environmental factors seagrass roots and leaf mass and tidal flat area, although the strength of these relationships was influenced by the two different spatial scales of the study. The strength of the relationships between shorebird feeding density and the invertebrate and environmental variables was stronger on a large spatial scale. The presence of seagrass may have influenced shorebird-feeding density by affecting the invertebrate abundance and composition or the shorebirds ability to detect and capture their prey. The area of the tidal flat had opposing effects on the shorebird species. These results can be used to assist in the development of management plans for the Robbins Passage wetlands and the conservation of important shorebird areas.     

The onset of fish colonization in a coastal defence structure (Chioggia,Northern Adriatic Sea)

Coastal defence structures constitute the most extensive hard substrates of the Northwestern Adriatic Sea and are known to sustain rich benthic and nektonic communities. To appreciate the pattern of colonization, we studied the fish assemblage of a recently deployed breakwater. We compared observations from two years, the different sides (landward and seaward) of the barrier, and the two fringes, characterized by timing of work completion. The results indicate that colonization, still in process, follows different patterns among species. Benthic and necto-benthic species presented a striking increase in abundance and richness in the second year of colonization, while more mobile species did not evince any variation between years. Differences in mobility among species suggest that the latter group may have reached the breakwater from nearby artificial substrates, whereas the former colonized the new structure as recruits. In addition, fish assemblages differed between the two sides, likely due to variation in the environmental characteristics, and according to depth, reflecting species preferences.