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1.
The Mediterranean endemic Cladocora caespitosa (Linnaeus, 1767) is a colonial scleractinian coral belonging to the family Faviidae and the only zooxanthellate coral from Mediterranean whose colonies may fuse in reef‐like structures (hermatypic). Recent surveys are focused on three locations where banks occur in the Adriatic Sea (Croatia): near Prvi? Island in the northern Adriatic, near Pag Island in the central Adriatic and in Veliko jezero (Mljet National Park) in the southern Adriatic. The C. caespitosa bank in Veliko jezero covers an area more than 650 m2 and is thus the largest bank of C. caespitosa found to date. The strong sea currents, which occur as a result of tidal exchange in the channel, appear to favour the growth of the bank. The goal of the study was to present the influence of major environmental factors upon the build‐up process of the coral bank. Biometrical parameters in the C. caespitosa colonies like diameter of the calyces, polyp ash free dry weight (AFDW), corallite linear growth rate and index of sphericity were investigated and compared from these three locations. The morphology of coral banks from the Adriatic Sea and the disposition of the biometrical values are affected by the sea currents, temperature and sedimentation.  相似文献   

2.
During a research cruise carried out in April 2010, aimed at updating the knowledge on the biodiversity of the Santa Maria di Leuca (SML) cold‐water coral province (Mediterranean Sea), a facies of the sea pen Kophobelemnon stelliferum (Muller, 1776) was found on mud‐dominated bottoms. This finding represents a new species and a new habitat record from the SML coral province as well as a new bathyal facies in the whole Central Mediterranean Sea. The colonies were collected using an epi‐benthic sledge, at depths between 400 and 470 m. A significant positive relationship between polyp number and colony length was detected. Density of the colonies ranged from 0.003 to 0.038 N·m?2. Differences and affinities between Mediterranean and Atlantic occurrences of K. stelliferum are discussed.  相似文献   

3.
Benthic oxygen uptake, sulphate reduction and benthic bacterial production were measured at two contrasting locations in the southern North Sea: the shallow and turbulent Broad Fourteens area in the Southern Bight, and the deeper Oyster Grounds, a deposition area, where thermohaline stratification occurs during summer. Oxygen uptake and sulphate reduction showed a clear seasonal pattern in the Broad Fourteens area, indicating a supply of carbon to the benthic system that is closely related to the standing stock of carbon in the water column. This close benthic-pelagic coupling is probably due to the influence of the tide in this part of the North Sea, which keeps the water column permanently mixed. At the Oyster Grounds, no seasonal pattern was observed. Peaks in oxygen uptake and sulphate reduction were found in winter. Irregularly occurring events, such as storms and fishery-related activities, are likely to affect the benthic mineralization patterns in this area. Annual benthic carbon mineralization rates estimated from oxygen uptake rates were 44 gC·m−2 at the Broad Fourteens, and 131 gC·m−2 at the Oyster Grounds, of which 26 and 28%, respectively, could be attributed to sulphate reduction (assuming an annual sulphide reoxidation rate of 100%). Although sulphate reduction rates in the southern North Sea are higher than previously suggested, aerobic respiration is the most important pathway for benthic carbon mineralization at the stations visited. Production rates of benthic bacterial carbon measured with labelled leucine were much higher than carbon mineralization rates based on oxygen uptake or sulphate reduction. This may either imply a very high bacterial carbon conversion efficiency, or point to shortcomings in the accuracy of the techniques. A critical evaluation of the techniques is recommended.  相似文献   

4.
Recurrent climate‐induced mass mortality episodes have been recorded in the Mediterranean Sea over the past 15 years, affecting rocky benthic communities. In this study, we provide for the first time a report on the annual mortality events of benthic sessile invertebrates occurring in the eastern part of the Adriatic Sea. Over the course of 14 consecutive years, we studied the sea temperature gradient to a depth of 40 m and found an abnormal summer warming trend and an increased frequency of above‐average temperatures. Mortality events were recorded in the summers of 10 observed years, in particular in 2009, when the highest mortality rates were recorded. Late in summer 2009, extensive mass mortality of sessile invertebrates was observed in the entire Eastern Adriatic Sea. We performed an analysis of selected target benthic species associated with mass mortality events with inter‐regional differences in hydrological and temperature conditions. We were able to characterize the mortality event by studying five areas covering the northern, central and southern regions of the Eastern Adriatic Sea. The degree of impact on each study area was quantified at 28 sites by estimating the proportion of affected target species. According to the obtained data, the northern sites (Cres area) were the least affected, whereas sites in the Central and Southern Adriatic [Tela??ica and Lastovo Nature Parks, Mljet National Park (NP)] displayed the highest impact. In summer 2009, sea surface temperatures reached values of 28 °C in the Cres area and 30 °C in Mljet NP. These thermal conditions were concomitant with moderate to severe mass mortalities of benthic populations. Mass mortality events reached depths of 45 m in most parts of the affected areas. Amongst studied species, the scleractinian coral and gorgonian populations suffered the most extensive damage during the mass mortality events.  相似文献   

5.
During the CINCS project (Pelagic–benthic Coupling IN the oligotrophic Cretan Sea—NE Mediterranean), a single mooring with two sediment traps (at 200 and 1515m water depth) and two current meters was deployed in the southern Cretan Sea margin at a depth of 1550 m. A second mooring deployed at the 500 m station was lost, as a result of fishing activities. The duration of the study was 12 months (November 1994 to November 1995) with sampling intervals of 15 or 16 days. The traps were retrieved, serviced and the sedimented material was collected every 6 months. In total, 48 samples were collected (24 from each trap) throughout the study period and fluxes of total particulate mass, opal, organic matter, carbonates, and lithogenic component were measured. Natural radionuclides (210Po and 210Pb) were determined for all trap samples. Total mass flux and the fluxes of four major constituents increased with depth, the total mass flux reaching values of nearly 550 mg m−2 d−1 at 1515 m and 187 mg m−2 d−1 at 200 m depth, following the same patterns observed in other experiments (ECOMARGE, SEEP-I, SEEP-II). The mean annual mass fluxes were 209 and 49.8 mg m−2 d−1 at the near bottom and near surface trap respectively. This suggests that lateral transport of particulate matter is of importance in the area. Total mass fluxes at the two depths were characterized by different seasonal fluctuations, although a general decreasing trend was observed from the I (winter) to the II (summer) deployment at both depths. This was mainly a result of reductions in aluminosilicate inputs during the summer dry period. At 200 m depth carbonates were more important during winter, because of a large carbonate input consisting mainly of coccoliths of Emiliania huxleyi, while during the summer decreased fluxes of carbonates and aluminosilicates resulted in a reduction of the mass flux. In contrast, at 1515 m depth the lithogenic component was the dominant component during the winter deployment, indicating a terrigenous input. During the summer period the decrease in mass flux was strongly effected by the decrease in aluminosilicates. There was a diminution in the organic carbon content with a concomitant increase in total mass flux, which, together with the almost negligible increase in the annual 210Pb activity with depth and the increase of 210Po activity with depth could be interpreted as indicating a contribution of resuspended material to the input at 1515 m. The complex mesoscale circulation of the Cretan Sea, consisting of a cyclone (east)–anticyclone (west) system, controls particle transfer in the area. This hydrodynamic system seems to move water masses towards the southern Cretan Sea margin, and consequently carry materials from the open sea to the upper slope and shelf.  相似文献   

6.
Samples were collected with a plankton net in the four seasonal cruises during 2006-2007 to study the seasonal variability of the zooplankton community in the southwest part of Huanghai Sea Cold Water Mass (HSCWM, Yellow Sea Cold Water Mass). The spatial and temporal variations of zooplankton species composition, biomass, abundance and biodiversity were examined. A total of 122 zooplankton species and 30 pelagic larvae were identified in the four cruises. Calanus sinicus and Aidanosagitta crassa were the most dominant species, and Themisto gaudichaudi and Euphausia pacifica were widely distributed in the HSCWM area. The spatial patterns of non-gelatinous zooplankton (removing the high water content groups) were similar to those of the total zooplankton biomass in autumn, but different significantly in the other three seasons. The seasonal means of zooplankton biomass in spring and summer were much higher than that in autumn and winter. The total zooplankton abundance averaged 283.5 ind./m~3 in spring (highest), 192.5 ind./m~3 in summer, 165.5 ind./m~3 in autumn and 65.9 ind./m~3 in winter (lowest), and the non-gelatinous groups contributed the most total abundance. Correlation analysis suggests that the non-gelatinous zooplankton biomass and abundance had a significant positive correlation in the whole year, but the relationship was insignificant between the total zooplankton biomass and abundance in spring and summer. The diversity index H of zooplankton community averaged 1.88 in this study, which was somewhat higher than historical results. Relatively low diversity in summer was related to the high dominance of Calanus sinicus, probably due to the strongest effect of the HSCWM in this season.  相似文献   

7.
This study had the objective of quantifying the variability in abundance, cell volume, morphology and C content of a natural bacterioplankton community in a coastal zone of the North Adriatic Sea during two periods (February and June) of two consequent years (1996 and 1997). We used epifluorescence microscopy with Acridine Orange staining procedures and a microphotographic technique. Low variability in bacterial abundance (range 0.3–3.1 × 105 cells ml?1) occurred between summer and winter periods. Conversely, the cell volume and the calculated carbon content changed greatly with warm and cold periods (ranges: 0.015–0.303 μm3 and 5.83–42.17 fg C cell?1, respectively). Elongated bacteria were dominant while coccoid cells prevailed only in February 1997. Biomass showed high variability (range 0.12–10.21 μg C l?1) whilst the abundance did not show noticeable differences among the sampling periods. As a consequence, quantification of bacterial biomass based solely on cell abundance must be considered with caution because the true biomass could depend on variability in cell volumes and morphotypes.  相似文献   

8.
Hydroids are important components of the communities of rocky bottom shallow coastal areas. The hydrozoan fauna of the Mediterranean Sea is probably one of most investigated in the world, with lots of faunistic and biogeographical studies. However, quantitative studies using the same sampling methodology and controlled sampling effort have been restricted to areas in the Western and Central Mediterranean. We compared hydroid assemblages in four areas of the Mediterranean Sea, from the Gulf of Cádiz to the South Adriatic Sea, following the same sampling and quantification methodology. Our analysis showed the dominant Atlantic character of the assemblages of the Gulf of Cádiz and the South Alboran Sea because of the influence of the inflowing Atlantic waters. Conversely, the hydroid assemblages of the North Alboran Sea were more similar to the assemblages in the Ligurian and in the South Adriatic, and with a number of species ranking between the observed in these two Mediterranean zones. Fourteen species were identified as making the most significant contributions to characterizing the Mediterranean hydroid species pool from a quantitative point of view. These taxa include species previously named as typical components of the Mediterranean hydroid fauna as well as those only recently recorded in the region (Eudendrium moulouyensis) and invaders such as Clytia hummelincki.  相似文献   

9.
The spatial pattern of the nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) (Linnaeus, 1758) and deep-water rose shrimp (Parapenaeus longirostris) (Lucas, 1846) was studied in the South Adriatic and North Ionian Seas (Eastern-Central Mediterranean) applying geostatistical techniques and data from time series trawl surveys conducted in the area. The analysed variables were: R (number of recruits/km2) and R/Tot (fraction of recruits on the total sampled population). The structural analysis showed a spatial pattern of both variables characterized by continuity on a small scale. Predictions of nursery area localization with probability of finding recruits at different threshold values were obtained through median indicator kriging. For the red mullet the nurseries were mainly identified in the South Adriatic Sea off the Gargano peninsula and between Molfetta and Monopoli within 50 m in depth. The main concentration of hake juveniles was found to be between 100 and 200 m in depth along the Gargano peninsula and between Otranto and Santa Maria di Leuca, where a nursery of deep-water rose shrimp was also detected. An overlapping depth, between 100 and 200 m, was identified for hake and deep-water rose shrimp nurseries. Protection of these areas through limitations of fishing pressure is discussed.  相似文献   

10.
The dynamics of benthic primary production and community respiration in a shallow oligotrophic, marine lagoon (Fællestrand, Denmark) was followed for 1·5 years. The shape of the annual primary production cycle was explained primarily by seasonal changes in temperature (r2 = 0·67-0·72) and daylength (r2 = 0·63), whereas temperature almost explained all variation in benthic community respiration (r2 = 0·83-0·87). On a daily basis the benthic system was autotrophic during spring and summer supplied by 'new' and 'regenerated' nitrogen and predominantly heterotrophic during fall and winter caused by light and nutrient limitation. The linear depth-relationship between porewater alkalinity and ammonium indicated that the C:N ratio of mineralized organic matter is low in spring and summer (3-6) and high in fall and winter (9-16). This is inversely related to net primary production and thus the input of labile, nitrogen-rich algal cells. Accordingly, mineralization occurred predominantly in the upper 2-5 cm of the sediment. The pool of reactive material (microalgal cells) was estimated to account for 12% of total organic carbon in the upper 3 cm, and had an average turnover time of less than 1 month in summer. Assimilation of organic carbon by benthic animals was equivalent to about 30% of the annual gross primary production. Grazing reduced chlorophyll a concentration in the sediment during summer and spring to values 30-40% lower than in winter, but maintained a 3-4 times higher specific microalgal productivity. The rapid turnover of organic carbon and nitrogen, and important role of benthic microalgae showed that the benthic community in this oligotrophic lagoon is of a very dynamic nature.  相似文献   

11.
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12.
Phytoplankton communities, production rates and chlorophyll levels, together with zooplankton communities and biomass, were studied in relation to the hydrological properties in the euphotic zone (upper 100 m) in the Cretan Sea and the Straits of the Cretan Arc. The data were collected during four seasonal cruises undertaken from March 1994 to January 1995.The area studied is characterised by low nutrient concentrations, low 14C fixation rates, and impoverished phytoplankton and zooplankton standing stocks. Seasonal fluctuations in phytoplankton densities, chlorophyll standing stock and phytoplankton production are significant; maxima occur in spring and winter and minima in summer and autumn. Zooplankton also shows a clear seasonal pattern, with highest abundances occurring in autumn–winter, and smallest populations in spring–summer. During summer and early autumn, the phytoplankton distribution is determined by the vertical structure of the water column.Concentrations of all nutrients are very low in the surface waters, but increase at the deep chlorophyll maximum (DCM) layer, which ranges in depth from about 75–100 m. Chlorophyll-a concentrations in the DCM vary from 0.22–0.49 mg m−3, whilst the surface values range from 0.03–0.06 mg m−3. Maxima of phytoplankton, in terms of cell populations, are also encountered at average depths of 50–75 m, and do not always coincide with chlorophyll maxima. Primary production peaks usually occur within the upper layers of the euphotic zone.There is a seasonal succession of phytoplankton and zooplankton species. Diatoms and ‘others’ (comprising mainly cryptophytes and rhodophytes) dominate in winter and spring and are replaced by dinoflagellates in summer and coccolithophores in autumn. Copepods always dominate the mesozooplankton assemblages, contributing approximately 70% of total mesozooplankton abundance, and chaetognaths are the second most abundant group.  相似文献   

13.
《Progress in Oceanography》2007,72(2-3):214-232
Centropages typicus is one of the most common, abundant and best studied calanoid copepods in neritic waters of the Mediterranean Sea, which means it can provide useful information about the long-term dynamics of the Mediterranean epipelagic ecosystem. This paper presents the first comparative overview of the seasonal and long-term variability of C. typicus in different Mediterranean regions. This review is based on quantitative information from the published literature and novel data from five ongoing zooplankton time-series carried out in the Mallorca Island (Balearic Sea), the Bay of Villefranche (Ligurian Sea), the Gulf of Naples (Tyrrhenian Sea), the Gulf of Trieste (North Adriatic Sea), and the Saronikos Gulf (Aegean Sea). In most Mediterranean regions, C. typicus has a perennial occurrence, with peaks of abundance that reflect the succession of different generations. Throughout the Mediterranean, the annual cycle of C. typicus is characterized by minima in winter and major peaks in April–June, which is earlier than those observed in European Atlantic waters, where the peaks are more frequently recorded in summer and fall. In the regions investigated, the annual cycle shows remarkable similarities in terms of timing, but notable differences in the peak height; populations are far more abundant in coastal north-western regions and less abundant in the eastern basin. In the long-term, changes in C. typicus phenology observed in the Bay of Villefranche and in the Gulf of Naples are related to the North Atlantic Oscillation (NAO) index. In these two regions, the species responds to climate forcing similarly in terms of average seasonal patterns (bi-modal patterns in years of positive NAO, unimodal patterns in years of negative NAO) but oppositely in terms of quantity, indicating different influence of the NAO on the two regions. At decadal scales, C. typicus populations show high interannual variability with marked geographical differences. In some areas, the patterns are clearly characterized by alternate phases of higher and lower annual abundances, at higher frequency (mainly 1–2 years) in the Gulf of Naples, and lower frequency in the Saronikos Gulf (mainly 4–5 years) and in the Gulf of Trieste (mainly 5–6 years). Synchronous phases of increasing or decreasing abundance are discernable only for a few sites and short periods, for example from 1998 to 2000 in the Gulf of Naples, Gulf of Trieste and Saronikos Gulf. The regional differences observed in the long-term patterns of C. typicus populations suggest that the temporal dynamics of this species are significantly more affected by local conditions than by any possible common driving force acting at basin scale through teleconnections.  相似文献   

14.
Temporal variability and population structure of planktonic ostracods were investigated for the first time in the South Adriatic Sea during 1996. The maximal total ostracod abundance (1167 ind·100 m−3; 69% juveniles, 18% females and 13% males) was recorded in February. Thirteen species of marine planktonic ostracods were identified. Porroecia spinirostris and Archiconchoecia striata dominated the ostracod assemblage, accounting respectively for 62% and 18% of the total abundance. Their annual peaks were recorded during the cold season, which was the period of their intense reproduction, with favourable temperature conditions and lack of predators. The females surpassed the males in abundance in most species. The presence of the mesopelagic species indicated a strong influence of intermediate layer water masses from the Eastern Mediterranean Sea.  相似文献   

15.
We analyze a two-year time-series of chromophoric dissolved organic matter (CDOM) light absorption measurements in the upper 400 m of the water column at the BOUSSOLE site in the NW Mediterranean Sea. The seasonal dynamics of the CDOM light absorption coefficients at 440 nm (acdom(440)) is essentially characterized by (i) subsurface maxima forming in spring and progressively reinforcing throughout summer, (ii) impoverishment in the surface layer throughout summer and (iii) vertical homogeneity in winter. Seasonal variations of the spectral dependence of CDOM absorption, as described by the exponential slope value (Scdom), are characterized by highest values in summer and autumn at the surface and low values at the depths of acdom(440) subsurface maxima or just below them. Variations of acdom(440) are likely controlled by microbial digestion of phytoplankton cells, which leads to CDOM production, and by photochemical destruction (photobleaching), which leads to CDOM degradation. Photobleaching is also the main driver of Scdom variations. Consistently with previous observations, acdom(440) for a given chlorophyll a concentration is higher than expected from Case I waters bio-optical models. The total non-water light absorption budget shows that surface waters at the BOUSSOLE site are largely dominated by CDOM during all seasons but the algal bloom in March and April. These results improve the knowledge of CDOM absorption dynamics in the Mediterranean Sea, which is scarcely documented. In addition, they open the way to improved algorithms for the retrieval of CDOM absorption from field or satellite radiometric measurements.  相似文献   

16.
Since the late 1980s, the small-sized non-commercial flatfish species solenette (Buglossidium luteum) and scaldfish (Arnoglossus laterna) have increased in abundance in the southern North Sea. Because these species are considered as possible competitors for prey of commercial flatfish, this study aimed at advancing knowledge of their feeding ecology.Between January 2009 and January 2010 stomach contents of solenette and scaldfish and benthic infauna were sampled seasonally in a study area in the German Bight. The objectives were to investigate the seasonal variability of feeding activity and diet composition of both flatfish species related to benthic prey availability.For both flatfish, the highest feeding activity was found in summer, at the same time that the highest prey densities occurred in the study area. A reduced feeding activity was observed during the winter of 2010, but not in the winter of 2009, probably related to higher 2009 water temperatures.In all seasons, diet composition of solenette was dominated by meiofauna, mainly harpacticoid copepods. Macrofauna prey species, namely juveniles of bivalves and echinoderms became important in spring. An increase in amphipods and cumaceans was found in the stomach contents during summer and autumn, simultaneously with their increased abundance in the benthic infauna. In contrast, polychaetes were rarely found in the diet, but dominated the infauna during all seasons.Diet composition of scaldfish was dominated by larger and mobile prey, and, during all seasons, was mainly comprised of crustaceans. Amphipods characterised the diet in both winters, while decapods such as Crangon spp. and Liocarcinus spp. were the dominant prey from spring to autumn. Additionally, juveniles of flatfish (Pleuronectids) and bivalves were found in the scaldfish diet in spring, replaced by cumaceans in summer. No dietary overlap between both flatfish species was found across seasons, indicating partitioning of prey resources between solenette and scaldfish. Their different feeding strategies and prey preferences, in turn were influenced by the seasonal variability of available prey.  相似文献   

17.
《Marine Chemistry》2001,75(4):1149
Spatial distribution and seasonal variability of surfactant activity (SA) of seawater were studied in the northern Adriatic Sea and compared to the temperature and salinity patterns in the 2-year period from February 1998 to January 2000, based on monthly surveys. Surface-active substances (SAS) were determined with alternating current voltammetry (in-phase mode) using o-nitrophenol as an electrochemical probe. A general characteristic of the SA seasonal variability for the northern Adriatic is the sinusoidal change of SA within the period of 1 year; similar behaviour was observed for the seasonal variations of temperature. Maximum SA values appeared during the summer period, while minimum SA values were measured in winter, during the period of well-mixed water layers and lower phytoplankton production. In May and October, the highest SA values were obtained in the upper seawater layer, which was ascribed to the influence of high inflow of nutrient-rich Po River freshwater. Riverine inputs indirectly favour autochthonous production processes, which result in increased concentration of organic matter (OM), particularly surface-active substances.  相似文献   

18.
We herein review the Adriatic opisthobranch fauna, provide an updated checklist of 223 species and assess their distribution at regional and country levels. New Adriatic records are provided for 67 opisthobranch taxa, adding three new records for the Italian coastline, five new records for Albania, eight for Croatia and 15 for Montenegro. The presence of Hermaea bifida (Montagu, 1815), Hermaea variopicta (Costa A., 1869) and Facelina annulicornis (Chamisso & Eysenhardt, 1821) is reported for the first time from anywhere in the Adriatic Sea. Including the new findings, our inventory includes 28 species from Albania, 163 from Croatia, 178 from the Italian coastline of the Adriatic, 41 from Montenegro and 74 from Slovenia. No records were available from Bosnia and Hercegovina. Ninety species (40.4%) are widespread, and were recorded from all three main divisions (Northern, Western and Eastern Adriatic), whilst 79 species (35.4%) were reported from only one of them. At sub‐division levels, the Albanian inventory is the most dissimilar to the other country/regional lists, presumably because of the lack of targeted field surveys. The highest similarity is observed amongst the Western Adriatic, Croatia and the Italian Ionian coastline. Seven alien, one possible alien and three cryptogenic opisthobranchs were reliably recorded from the Adriatic Sea. The first Mediterranean records of five species were in the Adriatic Sea, of which four species have not been found elsewhere in the Mediterranean. Shipping and aquaculture are the probable pathways for most of the alien species. A steady rate of one to two alien introductions per decade since the 1970s was evident. The Northern Adriatic coasts are the most affected by alien invasions, probably due to repeated local introductions along with shellfish transfers (oysters, mussels, Manila clams), and heavy maritime transport.  相似文献   

19.
Dissolved organic nitrogen (DON) dynamics in the North Sea was explored by means of long-term time series of nitrogen parameters from the Dutch national monitoring program. Generally, the data quality was good with little missing data points. Different imputation methods were used to verify the robustness of the patterns against these missing data. No long-term trends in DON concentrations were found over the sampling period (1995–2005). Inter-annual variability in the different time series showed both common and station-specific behavior. The stations could be divided into two regions, based on absolute concentrations and the dominant times scales of variability. Average DON concentrations were 11 μmol l−1 in the coastal region and 5 μmol l−1 in the open sea. Organic fractions of total dissolved nitrogen (TDN) averaged 38 and 71% in the coastal zone and open sea, respectively, but increased over time due to decreasing dissolved inorganic nitrogen (DIN) concentrations. In both regions intra-annual variability dominated over inter-annual variability, but DON variation in the open sea was markedly shifted towards shorter time scales relative to coastal stations. In the coastal zone a consistent seasonal DON cycle existed with high values in spring–summer and low values in autumn–winter. In the open sea seasonality was weak. A marked shift in the seasonality was found at the Dogger Bank, with DON accumulation towards summer and low values in winter prior to 1999, and accumulation in spring and decline throughout summer after 1999. This study clearly shows that DON is a dynamic actor in the North Sea and should be monitored systematically to enable us to understand fully the functioning of this ecosystem.  相似文献   

20.
This study describes changes in abundance of hyperbenthic zooplankton (including meroplankton) and benthic colonists at the seasonally hypoxic seabed of Saanich Inlet, British Columbia, Canada. We used the Victoria Experimental Network Under the Sea (VENUS) cabled observatory to measure water properties and to sample hyperbenthos with a sediment trap at 97 m from September 2008 to September 2009. Some faunal groups exhibited seasonal reproduction, and abundance peaked during their reproductive periods. These included larvae of the barnacle Balanus crenatus, and the crabs Petrolisthes eriomerus, Oregonia gracilis, and Lophopanopeus bellus bellus. Other groups were most abundant in spring and summer when food and oxygen levels were highest and temperature was lowest. These included cumaceans, the siphonophore Diphyes sp., the bryozoan Triticella pedicellata, and tintinnids. We also collected benthic colonists, predominantly bryozoans and polychaetes, on colonization plates deployed in spring/summer 2008, fall 2008/winter 2009, and spring/summer 2009. The total abundance of colonists and of bryozoans did not vary seasonally or with substrate complexity, whereas polychaetes were more numerous in spring/summer deployments and on a highly complex substrate. Taxon richness of colonists was higher in spring/summer 2008 than in fall 2008/winter 2009, whereas an anoxic episode in spring/summer 2009 reduced richness to similar values with that of fall 2008/winter 2009 levels. Substrate complexity had no effect on richness. Juvenile squat lobsters, digitally imaged in fall 2008/winter 2009, were most numerous when oxygen levels were lowest and potentially excluding larger predators. Our study illustrates how season, food availability, temperature, and oxygen can interact to shape community structure in a seasonally hypoxic habitat.  相似文献   

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