Effects of suction-dredging for cockles on non-target fauna in the Wadden Sea

Suction dredging for cockles removes large cockles from tidal flats and may also cause mortality of non-target fauna and make the habitat less suitable for some species. This study examines whether suction dredging for cockles on tidal flats of the Dutch Wadden Sea had affected densities of non-target fauna, directly after fishing and one year later. Densities of non-target fauna in two randomly chosen undredged locations were compared to densities at the surrounding heavily commercially dredged area. A significant negative effect of cockle dredging on densities of 0-group Macoma balthica was observed and this effect persisted one year after dredging. The dredged area appeared to be less suitable for settlement of mussels Mytilus edulis. No significant effects of dredging on the mudsnail Hydrobia ulvae and on 0 and 1-group C. edule were found. For the mobile young Macoma balthica it seems unlikely that the effect found after one year was still due to the mortality caused by dredging and this suggests that the habitat was less suitable as a consequence of dredging. Thus, even in the highly dynamic ecosystem of the Wadden Sea, effects of bottom disturbance by cockle dredging may persist after one year.     

Effects of current exposure on habitat preference of mobile 0-group epibenthos for intertidal seagrass beds (Zostera noltii) in the northern Wadden Sea

In the northern Wadden Sea, the extent of intertidal seagrass beds, their plant biomass and shoot density highly depends on local current regimes. This study deals with the role of intertidal Zostera noltii beds as nursery for mobile epibenthic macrofauna and the impact of seagrass bed characteristics on their abundance and distribution patterns. According to their exposure to the main tidal gullies, sampling sites were separated into exposed, semi-exposed and sheltered. Dominant species of crustaceans and demersal fish were studied in respect of their abundances within seagrass beds and adjacent unvegetated areas. Quantitative sampling was performed at day and night high tide using a portable drop trap. In general, species composition varied little between seagrass beds and bare sand. However, the presence of vegetation had a quantitative effect increasing individual numbers of common epifaunal species. Abundances of 0-group shore crabs (Carcinus maenas), common gobies (Pomatoschistus microps) and brown shrimps (Crangon crangon) were highest within sheltered seagrass beds. With decreasing plant density habitat preference of epibenthos changed on species level. By regulating the habitat complexity the currents regime is profoundly influencing the nursery function of intertidal seagrass beds in the Wadden Sea.     

Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

The aim of this study is to analyse the effects in space and time of relict sand-dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo-beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re-suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re-colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency.     

Diet and food preference of intertidal Astrostole scabra (Asteroidea: Forcipulata)

Dietary composition in Astrostole scabra was ascertained by regular sampling at four geographically separated locations on the Kaikoura coast between January 1976 and January 1977. A. scabra is a food generalist and scavenger with a diet composed mainly of molluscs and crustaceans belonging to more than 60 genera. The diet was dominated numerically by chitons and trochid molluscs. Several site‐specific differences in dietary composition were apparent. Only Ischnochiton maorianus was a numerically important prey species at all study sites. Dietary diversity and evenness were more or less constant and comparable both seasonally and geographically. The proportion of intertidal seastars feeding fluctuated during the study from a peak of 42% in January to 23.7% in June 1976. Prey species were consumed in proportions independent of their abundance. In the laboratory, A. scabra, free of ingestive conditioning, discriminated between different prey species and preferentially consumed I. maorianus. There were strong prey preferences at the specific, but not at the familial, level.     

A novel time-series station in the Wadden Sea (NW Germany): First results on continuous nutrient and methane measurements

In autumn 2002 a time-series station was installed in the tidal inlet between the Islands of Langeoog and Spiekeroog (Southern North Sea, NW Germany) to continuously measure physical, chemical, and meteorological parameters, even during extreme weather conditions (gale-force storms, drifting ice). Inside the pole of the station sensor tubes are installed in direction of the prevailing tidal currents. The tubes are equipped with hydrographic sensors (pressure, temperature, conductivity) and allow retrieval of water for nutrient analysis by automated instruments located inside the pole. Dissolved methane and the nutrients ammonia, nitrite, nitrate, phosphate, and silicate are measured at the station.     

Disentangling exploitation of the intertidal grazer Phorcus sauciatus (Gastropoda: Trochidae) in an oceanic archipelago: Implications for conservation

Harvesting of intertidal grazers such as topshells is known to affect negatively the exploited populations by altering population structure and decreasing abundance. Phorcus sauciatus has a wide geographic distribution in the North‐eastern Atlantic Ocean and is subject to increasing levels of harvesting pressure due to the expansion of human population on coastal areas. The effect of proximity to human settlements and coastal accessibility on the size structure and abundance of P. sauciatus populations was examined in Madeira archipelago. Mean size, proportion of reproductive individuals, and abundance of this species were generally smaller in areas closer to human settlements and in more accessible coastal areas. Marine protected areas returned the highest mean sizes evidencing their effectiveness in preserving the size structure of this species. The results highlight the necessity to regulate the harvest of P. sauciatus in Madeira archipelago, as well as the implementation of management measures aiming at the sustainable exploitation and conservation of this species, exploited in this region since the early 15th century.     

Crustorhabditis chitwoodi sp. nov. (Nematoda: Rhabditidae): An intertidal species from the coast of New South Wales,Australia, with observations on its ecology and life history

A new species, Crustorhabditis chitwoodi, was discovered in nutrient agar plates inoculated with beach sand collected from an ocean beach in New South Wales, Australia. The three other known species of the genus have all been found as commensal inhabitants of ocypodid shore crabs. It is suggested that the sand inoculum was seeded with dauer larvae of the nematode that had been dispersed by scavenging crabs. The new species is distinguished from the three previously described species by possessing a smaller number of differently arranged bursal papillae, eight rather than 10. The species is amphimictic, oviparous, and produces abundant dauer larvae in culture, which can be sustained indefinitely on sea water nutrient agar in which it feeds on associated bacteria.     

Quantitative assessment of intertidal blue mussel (Mytilus edulis L.) stocks: combined methods of remote sensing, field investigation and sampling

The aim of this investigation was to develop appropriate methods for quantitative assessment of blue mussel beds. Combined methods of remote sensing, ground truth investigation and sampling in the field were applied to mature and young intertidal mussel beds. Three variables were measured to obtain reliable quantitative estimates of biomass and abundance: the total area covered by a bed; the cover, i.e. the area of mussel-covered patches in relation to the total mussel bed area; and the proportion, i.e. the area covered by mussels within the patches in relation to the total area of mussel patches. Cover and proportion of intertidal blue mussel beds were measured in the field by the transection method. Aerial photographs enabled the total area of the beds to be determined and large-scale surveys of mussel beds to be carried out synchronously. By examining large-scale aerial photographs it was possible also to determine the cover by remote sensing. The proportion could not be derived from aerial photographs, even from pictures at the largest scale tested during this investigation (scale 1:2500). By statistical methods it was estimated that 12 sub-samples (each covering 177 cm²) from mature beds, and 12 sub-samples (each covering 38 cm²) from young beds are needed to obtain reliable data on biomass and abundance.     

湛江东海岛潮间带沉积物硫化物(AVS)和重金属(SEM)及其生物毒效性评估(英文)

对湛江东海岛潮间带表层沉积物中酸可挥发性硫化物(AVS)和同步提取重金属(SEM)的含量及其分布进行了研究。研究表明,东海岛潮间带表层沉积物中AVS含量夏季平均为0.449μ mol/g,冬季为1.816μ mol/g,大多数站位AVS含量冬季高于夏季;AVS平均含量总体呈南、北区较高,东、西区较低的区域分布规律。潮区沉积物可提取重金属SEM总量夏季在0.56μ mol/g~4.60μ mol/g之间,冬季处于0.65μ mol/g~2.21μ mol/g之间;各重金属平均含量大小为ZnCrPbCuCd,其中Cd含量占SEM总量不到1%,Zn含量则在70%以上,SEMZn是控制着SEM分布的主要模式。联合利用(∑SEM/AVS)与(∑SEM-AVS)法和生物毒性阈值法综合评估重金属对沉积环境的影响,东海岛潮间带大部分区域沉积物中(∑SEM-AVS)处于0~5之间,重金属潜在生物毒性较强的区域为通明海区(7号站和8号站所在),具有较强潜在生物毒性的重金属为夏季通明海区的Zn。     

Short-term consequences of a benthic cyanobacterial bloom (Lyngbya majuscula Gomont) for fish and penaeid prawns in Moreton Bay (Queensland, Australia)

This study examined the phenology and ecological consequences of a benthic filamentous cyanobacterial bloom (Lyngbya majuscula) in Deception Bay (Moreton Bay, Queensland, Australia). Bloom initiation occurred in mid December 1999 and expanded to encompass an 8 km² area by April 2000. Small fish and penaeid prawns (<25 cm total length) were quantitatively sampled through periods designated as before, during and after the bloom using a combination of pop-netting within mangroves and beam trawling over adjacent seagrass beds. Data on larger-bodied fish were compiled from daily fishing logs provided by local commercial fishers. Changes in dry mass of bloom material caught in nets and changes in water chemistry were also measured. Mean concentrations of ammonia-N in residual water within mangroves were several orders of magnitude higher in the affected area than in the control and dissolved oxygen was markedly lower in affected areas. Across the study area, mean density, live mass and number of species declined during the bloom, with fish assemblages using mangroves showing greater decline than assemblages using seagrasses. Response at the species level was highly variable; generally, epibenthic species showed a more sustained decline than demersals. Mean monthly fish catch was significantly lower in bloom than non-bloom years. This study has also demonstrated that throughout the bloom, the affected area continued to support a highly diverse and abundant fish and prawn assemblage, and probably maintained its function as an important nursery habitat for many species.     

Response of BITS (a benthic index based on taxonomic sufficiency) to water and sedimentary variables and comparison with other indices in three Adriatic lagoons

The European Water Framework Directive (WFD, 2000/60/EC) recommends the development of biotic indices for assessing the ecological quality status of water bodies. The Benthic Index based on Taxonomic Sufficiency (BITS) was specifically developed for lagoonal systems, according to the tolerant/opportunistic approach. Macrobenthic data, variables indicative of eutrophication and variables indicative of sedimentary organic matter quality were collected during 18 surveys carried out between 2004 and 2005 in three Adriatic coastal lagoons (Venice Lagoon, Sacca di Goro, Lesina Lagoon). The relationship between environmental variables and biotic indices (AMBI, BENTIX, BITS, BOPA and FINE) was tested using multivariate analyses. Indices based on species classification level appeared to relate better with the variables describing organic matter quality, whereas BITS, which is based on family classification level, seemed related to eutrophication indicative variables, such as sulphide, ammonium, dissolved oxygen and orthophosphate concentrations. The BITS approach reduces the costs associated with sorting and identification of organisms. Providing a rapid assessment of ecological quality, and producing an ecologically relevant classification, BITS seems a promising tool for monitoring programs of Adriatic lagoonal ecosystems. Its sensitivity in reflecting the field conditions elsewhere, however, remains to be assessed.     

Bottom-up and top-down controls of walleye pollock (Theragra chalcogramma) on the Eastern Bering Sea shelf

Control of walleye pollock (Theragra chalcogramma) recruitment in the Eastern Bering Sea involves complex interactions between bottom-up and top-down processes, although the mechanisms are poorly understood. We used statistical models to test the leading hypotheses linking recruitment variability to biotic and abiotic factors. Consistent with a “cold-pool hypothesis”, recruitment of pollock was significantly stronger if winters preceding the larval (age-0) and juvenile stages (age-1) were mild. However, our results did not support the proposed top-down mechanism (cannibalism) underlying this hypothesis. Several empirical relationships support an “oscillating control hypothesis”. As predicted by it, the effect of ice conditions on survival during the larval and early juvenile stages was modified by the abundance of adult pollock, implying stronger bottom-up control when adult abundance (hence cannibalism) was low. The proposed bottom-up mechanism predicts that the survival of pelagic-feeding walleye pollock (benthic-feeding yellowfin sole), should be higher during years with an early (late) ice retreat, which was confirmed by our analysis. Our results also provide additional evidence for a “larval transport hypothesis”, which states that cannibalism of larval and juvenile pollock is reduced in years when strong northward advection separates juveniles from cannibalistic adults.In addition to testing existing hypotheses, we identified new relationships between spawner-to-recruit survival rates of walleye pollock and several indicators of mixed layer dynamics during the spring and summer. Survival rates and recruitment were significantly reduced when larval or early juvenile stages experienced a delay in the (non-ice-associated) spring bloom as a result of stormy spring conditions, suggesting that the timing of the spring bloom is critical to both first-feeding larvae and age-1 juveniles. Furthermore, a dome-shaped relationship between pollock survival and summer wind mixing at the early juvenile stage is consistent with modeling and laboratory studies showing an increase in survival at low to moderate levels of wind mixing, but a decrease in feeding success at high levels of wind mixing.Top-down controls also regulate recruitment of walleye pollock. At least one-third of the variability in spawner-to-recruit survival could be accounted for by predation mortality at the early juvenile stage (age-1). Predation of juvenile pollock can be attributed largely to cannibalism, which varies with the abundance of adult pollock and with the availability of juveniles to adult predators. A simple index reflecting the spatial overlap between juvenile and adult pollock explained 30–50% of the overall variability in recruitment, similar to the variability explained by the best environmental predictors. Although environmental effects are difficult to separate from the effects of predation, we conclude that bottom-up and top-down processes are equally important in controlling the survival of pollock from spawning to recruitment at age 2. However, the magnitude of top-down control is itself modified by environmental factors that control the availability of juvenile pollock to adults (through impacts on spatial distribution) and the abundance of adult predators (through effects on productivity and carrying capacity).     

Matrilineal evidence for genetic structure and Late Pleistocene demographic expansion of the Ornate goby Istigobius ornatus (Teleostei: Gobiidae) in the Persian Gulf and Oman Sea

The Persian Gulf and Oman Sea are characterized by an interesting paleoclimatic history and different ecological settings, and offer a unique study area to investigate the genetic structure of marine organisms including fishes. The Ornate goby Istigobius ornatus is widely distributed throughout the tropical Indo‐West Pacific including the Persian Gulf and Oman Sea. Here, we present the population structure, genetic diversity, and demographic history of four populations of I. ornatus from the latter two regions using the D‐loop marker of mitochondrial DNA. The results reveal a shallow genealogy, a star‐like haplotype network, significance of neutrality tests, and unimodal mismatch distribution. This is concordant with a recent demographic expansion of I. ornatus in the Persian Gulf and Oman Sea at about 63,000–14,000 years ago, which appears to be related to Late Pleistocene sea level fall and rise. The results of the pairwise Fst estimates imply high gene flow along the coast of the Persian Gulf, which is probably due to larval dispersion, whereas the Oman Sea population clearly differs from all Persian Gulf populations. The AMOVA result indicates that 7.74% of the variation is related to differences among ecoregions, while inter‐ and intra‐population differences explained ?3.20% and 95.47% of the variation, respectively. The haplotype network depicts two groups of haplotypes, most of them were specific to the Persian Gulf. No further evidence for geographic lineage substructuring was evident. The Mantel test result indicates that isolation by distance is not the main mechanism that promoted the genetic differentiation among the studied populations of I. ornatus. We suggest that cumulative effects of ecological and geographic barriers such as salinity, oceanographic conditions, and the presence of the Strait of Hormuz have shaped the genetic structure of I. ornatus in the Persian Gulf and Oman Sea.     

Sponges boring into precious corals: an overview with description of a new species of Alectona (Demospongiae, Alectonidae) and a worldwide identification key for the genus

Precious corals represent peculiar substrata for several species of boring sponges that exploit their carbonatic scleraxis, strongly decreasing their commercial value. Here we describe a new species of the genus Alectona from Japan recorded in a colony of Paracorallium japonicum (Kishinouye, 1903). The spicular complement of the new species consists of diactinal spicules covered by mushroom-like tubercles, often modified into styloid forms, and fusiform amphiasters with two or sometimes four verticils, each generally made up of six short tubercled rays. A complete survey of the literature on boring sponges recorded in precious corals in the Mediterranean Sea and Pacific Ocean indicates that the species of the family Alectonidae are the most strictly associated to this kind of substratum. Their world distribution, in fact, partially or totally overlap that of their coral hosts.     

The satellite reversion of dissolved organic carbon (DOC) based on the analysis of the mixing behavior of DOC and colored dissolved organic matter: the East China Sea as an example

The retrieval of dissolved organic carbon (DOC) distribution by remote sensing is mainly based on the empirical relationship of DOC concentration and colored dissolved organic matter (CDOM) concentration in many literatures. To investigate the nature of this relationship, the distributions and mixing behaviors of DOC and CDOM are reviewed in the world’s major estuaries and bays. It is found that, generally, the CDOM concentration is well correlated with the salinity in most estuaries, while DOC usually shows a nonconservative behavior which leads to a weak correlation between the DOC concentration and the CDOM concentration. To establish a good satellite reversion of the DOC concentration, the East China Sea(ECS) was taken as an example, and the mixing behavior of DOC and CDOM as well as the influence of biogeochemical processes were analyzed except for the physical mixing process with the data from late autumn (November, 2010) and winter (December, 2009) cruises. In the two ECS cruises, the CDOM concentration was found to be tightly correlated with the salinity, influenced little by the photochemical or biological processes. The data from the winter cruise show that DOC followed a conservative mixing along the salinity gradient, while in the late autumn cruise it was significantly affected by the biological activities, resulting in a poor correlation between the DOC and the CDOM. Accordingly, an improved DOC algorithm (CSDM) was proposed: when the biological influence was significant (Chl a greater than 0.8 μg/dm3 ), DOC was retrieved by the conservative and biological model, and if the conservative mixing was dominant (Chl a less than 0.8 μg/dm3 ), the direct DOC concentration and CDOM concentration relationship was used. Based on the proposed algorithm, a reasonable DOC distribution for the ECS from satellite was obtained in this study, and the proposed method can be applied to the other large river-dominant marginal sea.     

长江口与东海陆架泥质沉积动力过程与环境效应：长期数据采集需求

长江入海物质在东海内陆架水域形成了大规模泥质沉积区。内陆架泥区具有细颗粒沉积物和有机质的源/汇双重特征。长江口及邻近海域的泥质沉积过程 产物关系、泥质沉积在生态系统动力学中的作用、泥质沉积碳库增量潜力,是区域性沉积动力学的3个前沿问题,主要研究内容包括长江河口泥区未来演化趋势、泥区沉积物重力流形成条件和过程、泥区沉积物有机质含量与初级生产及低氧水层的关系、泥区消浪作用及其机制、颗粒态有机质衰减曲线(或曲线族)、颗粒态有机质碳库增量潜力等。其研究需要海洋观测站网在底部边界层、水层、新型数据上的支撑,以满足数据分辨率、连续性的要求。底部边界层连续观测将有助于重力流、泥区消浪作用、湍动影响下的沉积物起动曲线族等问题的解决。水层观测将有助于有机质衰减系数的研究,进而获得有机质埋藏率、浅层天然气、有机碳库增量等问题的答案。一些新型数据含有物源、沉积体特征和演化的大量信息,此类数据的获取将依赖于观测技术的突破。     

Intraspecific Interactions and Risk of Predation for Dyspanopeus sayi (Decapoda: Xanthidae) Living on Polychaete (Filograna implexa,Serpulidae) Colonies*

Abstract. Along the Atlantic coast of the United States, the mud crab Dyspanopeus sayi frequently occurs in crevices and depressions within aggregated calcareous tubes (termed “heads”) of the serpulid polychaete Filograna implexa. In New Jersey, U.S.A., waters, crab number was significantly correlated with the logarithm of worm tube colony volume. Laboratory experiments suggested that crabs compete for shelter within worm colonies. Additional laboratory experiments indicated that colony occupancy greatly decreased the risk of predation by blue crabs (Callinectes sapidus), and field tethering experiments also demonstrated that colony occupancy significantly decreased predation risk. Thus, the consequence of holding space on worm tube heads is a greatly increased probability of survival.     

Connectivity and stock composition of loggerhead turtles foraging on the North African continental shelf (Central Mediterranean): implications for conservation and management

The loggerhead turtle, Caretta caretta, is a highly migratory species with a complex life cycle that involves a series of ontogenetic habitat shifts and migrations. Understanding the links amongst nesting populations and foraging habitats is essential for the effective management of the species. Here we used mixed stock analysis to examine the natal origin of loggerhead turtles foraging on the North African continental shelf off Tunisia, one of the most important Mediterranean neritic habitats. An 815‐bp fragment of the mitochondrial DNA control region was sequenced from 107 individuals sampled from 2007 to 2009. No temporal variation in haplotype frequencies was detected. Juveniles (n = 87) and adults (n = 23) exhibited weak but significant genetic differentiation that resulted in different stock compositions. Libya was the main source population but the proportion of turtles from this rookery was higher in adults (median = 80%) than in juveniles (median = 35%). Western Greece was the second most important contributing population. Juvenile stock composition derived from mixed stock analysis and the estimates produced by numerical simulation of hatchling dispersion in the Mediterranean Sea were significantly correlated, supporting the recent theory that loggerheads imprint on possible future neritic habitats during the initial phase of their life. This association was not significant for adults, suggesting that other factors contribute to shaping their distribution. Overall, our results show that human activities on the South Tunisian continental shelf pose an immediate threat to the survival of the Libyan rookery.