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1.
Distribution and biomass of green algal mats were studied in marine shallow (0–1 m) soft-bottom areas on the Swedish west coast from 1994 to 1996, by combining aerial photography surveys with ground truth sampling. Filamentous green algae, dominated by species of the genera Cladophora and Enteromorpha, were generally present throughout the study area during July and August, and largely absent in late April and early May. These algae occurred at 60 to 90% of the locations investigated during the summer, and were estimated to cover between 30 and 50% of the total area of shallow soft bottoms of the Swedish Skagerrak archipelago. The distributional patterns were similar during the three years of the investigation and appeared unrelated to annual local nutrient inputs from point sources and river discharge. We postulate that the apparent lack of such a relationship is due to an altered state of nutrient dynamics throughout the archipelago. Mechanisms are likely to involve long-term, diffuse elevations in nutrient levels in coastal waters of the Skagerrak and the Kattegat over several decades leading to current eutrophic conditions, exceeding nutrient requirements for abundant filamentous algal growth. Patterns of algal abundance in our study were largely related to physical factors such as exposure to wind, waves and water exchange under conditions where nutrient loads among embayments seemed to be unlimited. Further, our results show that sediments covered by algal mats had higher carbon and nitrogen contents than unvegetated sediments. We hypothesise that sustained high nutrient loads, manifested in extensive biomass of filamentous algae during summer months, are re-mineralised via decay and sedimentation in the benthic realm. Hence, accumulated carbon and nutrients in the sediment could, in turn, constitute the basic pool for future algal mat production overlying soft bottoms in areas where tidal exchange is limited. 相似文献
2.
Canopy-forming algae occur across of range of energy environments (i.e., wave sheltered to exposed coasts) where disturbances are frequent (i.e., gap formation) and benthic patterns largely reflect variation in post-disturbance processes. Disturbances vary in extent (area affected) and intensity (degree of damage), and this may affect recolonisation at local scales. On an open oceanic coast, we tested whether habitat structure (patches of canopy algae) differed between heavy and relatively lighter wave exposure (sheltered vs. exposed sides of islands), and whether wave exposure affected the response of prominent habitat-formers to varying disturbance regimes (different sizes of partial and complete canopy removal). Observations of naturally occurring patterns showed sheltered coasts to be characterised by small patches of fucoids, whereas exposed coasts were characterised by large patches of kelp. Canopy-gaps were larger at exposed than sheltered coasts, and mixed canopies constituted > 24% of the subtidal rocky habitat independently of wave exposure. Experimental disturbances showed the local density of kelps to affect recovery through greater recruitment to partial clearings (80% canopy removal). Fucalean algae, on the other hand, mainly recruited into complete clearings (100% removal), but when their recruits were abundant, they also recruited into partial clearings. The covers of filamentous, turf-forming algae increased in all clearings, and more so at exposed than sheltered sites. Extent of disturbance had no detectable effect on recolonisation by canopy-forming algae across the scales examined (i.e., 1.5 m, 3 m diameter loss of canopy). Recolonisation varied among islands kilometres apart, and correlations (r > 0.85) between cover of canopies and cover of their recruits in clearings at the scale of sites, suggested that differences in propagule supply could account for variation in patterns of recolonisation at scales of kilometres. There was no evidence to suggest that the effect of disturbance depended on wave exposure within the range of exposures tested in this study (i.e. open coasts). We recognise that wave exposure can be fundamental to habitat structure of subtidal rocky coasts, but we suggest that its influence may be mediated by the biological setting (e.g., canopy composition). 相似文献
3.
The macrobenthic animal biomass of the intertidal area of the Sembilang peninsula of South Sumatra, Indonesia, has been studied in 2004. Each month (March–August) 21 core samples were taken at each of six sampling stations. Macrobenthic fauna were identified at the lowest taxonomical level possible and counted. Biomass was measured as ash-free dry mass (afdm). The average biomass over all stations and months was 3.62 g afdm m−2, the highest biomass (47.45 g afdm m−2) found at a station in one month was due to abundant occurrence of the bivalve Anadara granosa. Low biomass of macrobenthic fauna at Sembilang peninsula cannot easily be explained but is in line with low biomasses found elsewhere in the tropics. For that reason we analyzed a data set of 268 soft-bottom intertidal biomasses collected world-wide to look for a relationship with latitude. It was shown that average biomass of intertidal macrobenthic fauna in the tropics was significantly (p < 0.05) lower than that at non-tropical sites. A significant second-order relationship between biomass of macrobenthic fauna and latitude was established. 相似文献
4.
Seasonal variability in the recruitment of macrofouling community in Kudankulam waters, east coast of India 总被引：2，自引：0，他引：2
The seasonal variability in fouling community recruitment on submerged artificial substratum was studied in Kudankulam coastal water, Gulf of Mannar, East coast of India for a period of two years, from May 2003 to April 2005. The results indicated that the fouling community recruitment occurred throughout the year with varying intensities. Barnacles, ascidians, polychaetes, bivalves and seaweeds were the major fouling groups observed from the test panels. Maximum fouling biomass of 9.17 g dm−2 was observed during August 2004 and a minimum value of 0.233 g dm−2 in February 2004. The biomass build-up on test panels was relatively high during the premonsoon season and low during the postmonsoon months. The number of barnacles settled on the panels varied from 1 to 4460 no. dm−2. The maximum percentage of the ascidian coverage (72%) on test panels was observed during March 2005. In general, July–December was the period of intense recruitment for barnacles and March–May was the period for ascidians. 相似文献
5.
Estimation of the leeway drift of small craft 总被引：1，自引：0，他引：1
Small craft (<6·4 m) leeway is determined as a function of the wind speed in the range of 5–20 knots (3·6–10·3 m/sec). Leeway is calculated relative to the surface current by measurement of the separation distance of the small craft from a dyed patch of surface water at sea, using time-sequenced aerial photography. Leeway increases linearly with wind speed for small craft equipped with or without a sea anchor in the wind range studied. Leeway for small craft without sea anchor can be calculated from the equation UL = 0.07 UW + 0.04 where UW is the wind speed at 2 m elevation. Leeway for small craft drifted off the be calculated from the equation ULD = 0·05 UW − 0·12. The small craft drifted off the downwind direction in about 80% of the experiments. The drift angle is variable and difficult to predict. 相似文献
6.
We describe an investigation into the reactivity of dissolved organic carbon (DOC), produced from marine algae, to conventional persulphate and ultraviolet (UV) oxidation methods. Marine algae were grown in batch culture in the presence of 14C bicarbonate and filtered samples of the phytoplankton dissolved organic carbon (PDOC) were oxidized with persulphate and UV techniques. The amount of fixed label found in solution after the oxidation procedures was compared with the initial amount of labelled DOC. Marine algae examined in this way included: the diatoms, Chaetoceros gracilis, Skeletonema costatum, Phaeodactylum tricornutum; the flagellate, Isochrysis galbana; and the cyanobacterium, Synechococcus strain DC2. It was found that 5–18% of the DOC produced by these phytoplankton resisted persulphate oxidation. Samples were also measured for their resistance to UV oxidation by an autoanalyzer method. It was found that 15–27% of these samples resisted UV oxidation. However, 95% of PDOC was oxidized after exposure for 6 h to high intensity UV irradiation using a variable exposure time system. P. tricornutum and Synechococcus PDOC samples were ultrafiltered into low molecular weight (< 10 000 Da) and colloidal (> 10 000 Da) size fractions. Both species produced mainly (> 68%) low molecular weight material. Slightly greater resistance to persulphate oxidation was generally found for the colloidal Synechococcus PDOC (15–22%) than for the low molecular weight material (14–17%). However, the opposite was found for the P. tricornutum PDOC which generally showed less resistance for the colloidal fraction (5–12%) than for the low molecular weight fraction (10–15%).Experiments were also conducted to determine the effects of short-term (days) and long-term (months) ageing of PDOC solutions in the presence of microbial populations from coastal seawater. Long-term ageing decreased the amount of PDOC that resisted oxidation in all cases. However, the fraction of PDOC resisting persulphate oxidation increased by small amounts over a short-term experiment. Increased resistance was attributed to preferential degradation of biologically and chemically labile components of PDOC by bacteria.The percentages of phytoplankton-produced (and microbially aged) DOC found in this study to resist UV or persulphate oxidation were low (5–27%), compared with those values (50–65%) reported for DOC in surface seawater on the basis of recent high temperature catalytic oxidation analyses. 相似文献
7.
Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m−2) is similar to phytoplankton production (6–10 g C m−2). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m−2 yr−1. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m−2 yr−1 is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m−2 yr−1 of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m−2 yr−1 was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters. 相似文献
8.
We investigated the geographical variations in abundance and biomass of the major taxonomic groups of micro- and net-zooplankton along a transect through Ise Bay, central Japan, and neighboring Pacific Ocean in February 1995. The results were used to estimate their secondary and tertiary production rates and assess their trophic roles in this eutrophic embayment in winter. Ise Bay nourished a much higher biomass of both micro- and net-zooplankton (mean: 3.79 and 13.9 mg C m–3, respectively) than the offshore area (mean: 0.76 and 4.47 mg C m–3, respectively). In the bay, tintinnid ciliates, naked ciliates and copepod nauplii accounted for, on average, 69, 18 and 13% of the microzooplankton biomass, respectively. Of net-zooplankton biomass, copepods (i.e. Acartia, Calanus, Centropages, Microsetella and Paracalanus) formed the majority (mean: 63%). Average secondary production rates of micro- and net-zooplankton in the bay were 1.19 and 1.87 mg C m–3d–1 (or 23.1 and 36.4 mg C m–2d–1), respectively, and average tertiary production rate of net-zooplankton was 0.75 mg C m–3d–1 (or 14.6 mg C m–2d–1). Available data approximated average phytoplankton primary production rate as 1000 mg C m–2d–1 during our study period. The transfer efficiency from primary production to zooplankton secondary production was 6.0%, and the efficiency from secondary production to tertiary production was 25%. The amount of food required to support the zooplankton secondary production corresponded to 18% of the phytoplankton primary production or only 1.7% of the phytoplankton biomass, demonstrating that the grazing impact of herbivorous zooplankton was minor in Ise Bay in winter. 相似文献
9.
Bacterial biomass and production rate were measured in the surface (0–100 m) and mesopelagic layers (100–1,000 m) in the subarctic Pacific and the Bering Sea between July–September, 1997. Depth profiles were determined at stations occupied in oceanic domains including the subarctic gyres (western, Bering Sea, and Gulf of Alaska) and a boundary region south of the gyres. In the surface layer (0–100 m), both bacterial biomass and production were generally high in the western and Bering Sea gyres, with the tendency of decrease toward east. This geographic pattern was consistent with the dominant regime of phytoplankton biomass at the time of our survey. A significant portion of variation in bacterial production was explained by the concentration of chlorophyll a (r
2 = 0.340, n = 60, P < 0.001) and, to the greater extent, by the concentration of semilabile total organic carbon (SL-TOC = TOC at a given depth—TOC at 1,000 m, r
2 = 0.488, n = 59, P < 0.0001). Temperature significantly improved the regression model: temperature and chlorophyll jointly explained 60% of variation in bacterial production. These results support the hypothesis that bacteiral growth is largely regulated by the combination of temperature and the supply of dissolved organic carbon in subarctic surface waters. In the mesopelagic layer (100–1,000 m), the geographic pattern of bacterial production was strikingly different from the surface phytoplankton distribution: the production was high in the boundary region where the phytoplankton biomass was lowest. Bacterial growth appeared to be largely controlled by the supply of organic carbon, as indicated by the strong dependency of bacterial production on SL-TOC (r
2 = 0.753, n = 75, P < 0.0001). The spatial uncoupling between surface phytoplankton and mesopelagic bacterial production suggests that the supply rate of labile dissolved organic carbon in the mesopelagic zone does not simply reflect the magnitude of the particulate organic carbon flux in the subarctic Pacific. 相似文献
10.
J. Ishizaka K. Harada K. Ishikawa H. Kiyosawa H. Furusawa Y. Watanabe H. Ishida K. Suzuki N. Handa M. Takahashi 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)
Size and taxonomic structure of plankton community carbon biomass for the 0.2–2000 μm equivalent spherical diameter range were determined at the equator at 175°E in September 1990–1993 and April 1994. Total biomass of the plankton community ranged from 1944 to 3448 mg C m−2. Phytoplankton, zooplankton and bacteria carbon biomasses were 604–1669 mg C m-2, 300–797 mg C m2, and 968–1200 mg C m-2, and the percentages were 31–54%, 15–26%, and 29–54%, respectively. Biomass of heterotrophic bacteria was always the largest fraction andProchlorococcus biomass was second. Heterotrophic and autotrophic flagellates and dinoflagellates in the nanoplankton size range and copepods (adults and copepodites) in the mesoplankton range were also high. Relatively small biomass was observed in the microplankton size range. The differences in integrated biomass of plankton community for El Nin˜o type oligotrophic conditions of September 1990–1993 and non-El Nifio type mesotrophic conditions of April 1994 were generally small compared with the interannual difference during 1990–1993. However, the percentage ofProchlorococcus in phytoplankton carbon biomass was larger in non-El Nin˜o year. Biomasses of cyanobacteria, diatom, dinoflagellates, nauplii of copepods, and crustaceans other than copepods were larger in the non-El Nin˜o year. Primary production increased significantly from El Nin˜o to non-El Nin˜o years. Carbon flow through the plankton food chain was estimated using the plankton carbon biomass data, primary production measurements, and published empirical relationships. 相似文献
11.
Nereis diversicolor is generally considered to be a predator and deposit feeder, but have also been found to graze on benthic algae in shallow coastal areas. In this study we investigated the grazing effects on the development and growth of green algae, Ulva spp. Algal growth was studied in an experiment including two levels of sediment thickness; 100 mm sediment including macrofauna and 5 mm sediment without macrofauna, and three treatments of varying algal biomass; sediment with propagules, sediment with low algal biomass (120 g dry weight (dwt) m− 2) and sediment with high algal biomass (240 g dwt m− 2). In the 100 mm sediment, with a natural population of macrofauna, N. diversicolor was the dominating (60% of total biomass) species. After three weeks of experimentation the result showed that N. diversicolor was able to prevent initial algal growth, affect growth capacity and also partly reduce full-grown algal mats. The weight of N. diversicolor was significantly higher for polychaetes in treatments with algae added compared to non-algal treatments. There were also indications that a rich nutrient supply per algae biomass counteracted the grazing capacity of N. diversicolor. 相似文献
12.
Over the last thirty years, many shallow estuarine bays, located in Scandinavian sheltered coastal environments, have been subject to the increased dominance of opportunistic species of filamentous green algae, oxygen deficiency in bottom waters and the alteration of flora and fauna. Human-induced eutrophication has been held responsible for these recent changes, but from this study the importance of climatic factors emerges. This research is based on the analysis of sediment cores from 8 shallow areas (d < 50 cm) along the Bohuslän archipelago, Swedish west coast, and focuses on their recent (< 100 years) sedimentary evolution. Evidence of hydrodynamic change was observed in the sediments, where modern fining-upward sequences contrast with the expected coarsening upward model due to ongoing land uplift. Heavy metal concentrations from modern pollution and 14C dating of mollusk shells and eelgrass roots provided the age control, and allowed to place these changes within the last three decades. Data were compared with historical meteorological records (seasonal warming, modification of dominant winds and upwelling and reduction of sea-ice), and a clear connection emerged between the environmental changes and variations in the North Atlantic Ocean weather pattern. The increase of winter temperature and reduction of reworking winter sea-ice in these sheltered bays increased the storing of nutrients in the sediments and the turnover of organic matter, favoring the early growth stage of opportunistic algae in the most sheltered areas of the archipelago. This, together with human-induced modifications (overfishing and eutrophication), increased the possibility of opportunistic explosions, which in turn determined a reduced water exchange, the increased deposition of fine sediments and organic matter and evolving hypoxic conditions. 相似文献
13.
Michael R. Landry Susan L. Brown Yoshimi M. Rii Karen E. Selph Robert R. Bidigare Eun Jin Yang Melinda P. Simmons 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1348
As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80–100 m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0–40 m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50–60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70–90 m showed little evidence of growth rate enhancement and was principally defined by a 100-fold increase of large (>20-μm) diatoms and a shift from Prochlorococcus to diatom dominance (80%) of production. The intermediate layer of 50–60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal. 相似文献
14.
Erik Mrk Gustaf Lillieskld Sj Nils Kautsky Tim R. McClanahan 《Estuarine, Coastal and Shelf Science》2009,84(3):331-336
Top–down and bottom–up regulation in the form of grazing by herbivores and nutrient availability are important factors governing macroalgal communities in the coral reef ecosystem. Today, anthropogenic activities, such as over-harvesting of herbivorous fish and sea urchins and increased nutrient loading, are altering the interaction of these two structuring forces. The present study was conducted in Kenya and investigates the relative importance of herbivory and nutrient loading on macroalgal community dynamics, by looking at alterations in macroalgal functional groups, species diversity (H′) and biomass within experimental quadrats. The experiment was conducted in situ for 42 days during the dry season. Cages excluding large herbivorous fish and sea urchins were used in the study and nutrient addition was conducted using coated, slow-release fertilizer (nitrogen and phosphorous) at a site where herbivory is generally low and nutrient levels are relatively high for the region. Nutrient addition increased tissue nutrient content in the algae, and fertilized quadrats had 24% higher species diversity. Herbivore exclusion resulted in a 77% increase in algal biomass, mainly attributable to a >1000% increase in corticated forms. These results are in accordance with similar studies in other regions, but are unique in that they indicate that, even when prevailing nutrient levels are relatively high and herbivore pressure is relatively low, continued anthropogenic disturbance results in further ecological responses and increased reef degradation. 相似文献
15.
In situ measurements of the primary productivity of ice algae and phytoplankton were carried out in the fast ice area near Syowa Station (69°00S, 39°35E) during the austral spring and summer of 1983/84. Standing stock of ice algae reached a maximum of 45.1 mg chla m–2 in late October. Phytoplankton standing stock attained a value of 3.57 mg chla m–2 in mid-January. Primary production of ice algae in late October (7.64 mgC m–2 hr–1) was 14 times greater than that in mid-January (0.54 mgC m–2 hr–1). Production in the water column in mid-January (3.46 mgC m–2 hr–1) was 50 times greater than that in late October (0.07 mgC m–2 hr–1). These results indicate a substantial production by ice algae in the spring and by phytoplankton in the summer period. 相似文献
16.
Diet of Littoraria scabra, while vertically migrating on mangrove trees: Gut content, fatty acid, and stable isotope analyses 总被引：1，自引：1，他引：0
The snail, Littoraria scabra, is a dominant grazer on tropical mangrove trees, and may play an important role in the food web dynamics of these ecosystems. Its daily vertical migration to avoid tidal submersion results in exposure to varying food types and abundances. A comprehensive diet analysis – gut contents, fatty acid profiles, and stable isotopes (δ15N and δ13C) – was conducted on snails migrating along mangrove trees and snails maintained in non-tidal mesocosms at Nananu-i-ra, Fiji Islands. In addition, fatty acid profiles and stable isotope signatures were obtained from surface scrapings of mangrove roots, trunks, branches, and leaves. Results from this multi-technique study indicate that L. scabra is mainly a generalist herbivore, which easily shifts diets depending on food availability, and which also has the ability to ingest and assimilate zooplankton. Ingestion of greater quantities of diverse foods (i.e., microalgae, foliose/corticated macrophytes, filamentous algae, mangrove tissues, zooplankton) takes place in the bottom areas of mangrove trees (roots and trunks) during low tides, while top areas (branches and leaves) provide limited food resources for snails feeding during high tides. However, snails preferentially assimilate microalgae and bacteria, regardless of their feeding habitat (different areas within mangrove trees and non-tidal mesocosms). The daily vertical movements of this snail result in variable feeding times, ingestion of different food types and amounts, and different assimilations. These findings also suggest that organic matter derived from mangrove tissues may not be readily transferred to higher trophic levels through this grazing pathway. 相似文献
17.
Maud Cottet Xavier de Montaudouin Hugues Blanchet Pascal Lebleu 《Estuarine, Coastal and Shelf Science》2007,71(3-4):629-640
The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species.Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only.These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure. 相似文献
18.
Long‐term spatial dynamics in vegetated seascapes: fragmentation and habitat loss in a human‐impacted subtropical lagoon 
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下载免费PDF全文 Vegetated coastal seascapes exhibit dynamic spatial patterning, some of which is directly linked to human coastal activities. Human activities (e.g. coastal development) have modified freshwater flow to marine environments, resulting in significant changes to submerged aquatic vegetation (SAV) communities. Yet, very little is known about the spatially complex process of SAV habitat loss and fragmentation that affects ecosystem function. Using habitat mapping from aerial photography spanning 71 years (1938–2009) for Biscayne Bay (Florida, USA), we quantify both SAV habitat loss and fragmentation using a novel fragmentation index. To understand the influence of water management practices on SAV seascapes, habitat loss and fragmentation were compared between nearshore and offshore locations, as well as locations adjacent to and distant from canals that transport freshwater into the marine environment. Habitat loss and fragmentation were significantly higher along the shoreline compared with offshore seascapes. Nearshore habitats experienced a net loss of 3.31% of the total SAV mapped (2.57 km2) over the time series. While areas adjacent to canals had significantly higher SAV cover, they still experienced wide fluctuations in cover and fragmentation over time. All sites exhibited higher fragmentation in 2009 compared with 1938, with four sites exhibiting high fragmentation levels between the 1990s and 2000s. We demonstrate that freshwater inputs into coastal bays modify the amount of SAV and the fragmentation dynamics of SAV habitats. Spatial changes are greater close to shore and canals, indicating that these coastal developments have transformative impacts on vegetated habitats, with undetermined consequences for the provisioning of ecosystem goods and services. 相似文献
19.
Jean-Pascal Torrton Emma Rochelle-Newall Aymeric Jouon Vincent Faure Sverine Jacquet Pascal Douillet 《Estuarine, Coastal and Shelf Science》2007,74(4):766
Hydrodynamic modeling can be used to spatially characterize water renewal rates in coastal ecosystems. Using a hydrodynamic model implemented over the semi-enclosed Southwest coral lagoon of New Caledonia, a recent study computed the flushing lag as the minimum time required for a particle coming from outside the lagoon (open ocean) to reach a specific station [Jouon, A., Douillet, P., Ouillon, S., Fraunié, P., 2006. Calculations of hydrodynamic time parameters in a semi-opened coastal zone using a 3D hydrodynamic model. Continental Shelf Research 26, 1395–1415]. Local e-flushing time was calculated as the time requested to reach a local grid mesh concentration of 1/e from the precedent step. Here we present an attempt to connect physical forcing to biogeochemical functioning of this coastal ecosystem. An array of stations, located in the lagoonal channel as well as in several bays under anthropogenic influence, was sampled during three cruises. We then tested the statistical relationships between the distribution of flushing indices and those of biological and chemical variables. Among the variables tested, silicate, chlorophyll a and bacterial biomass production present the highest correlations with flushing indices. Correlations are higher with local e-flushing times than with flushing lags or the sum of these two indices. In the bays, these variables often deviate from the relationships determined in the main lagoon channel. In the three bays receiving significant riverine inputs, silicate is well above the regression line, whereas data from the bay receiving almost insignificant freshwater inputs generally fit the lagoon channel regressions. Moreover, in the three bays receiving important urban and industrial effluents, chlorophyll a and bacterial production of biomass generally display values exceeding the lagoon channel regression trends whereas in the bay under moderate anthropogenic influence values follow the regressions obtained in the lagoon channel. The South West lagoon of New Caledonia can hence be viewed as a coastal mesotrophic ecosystem that is flushed by oligotrophic oceanic waters which subsequently replace the lagoonal waters with water considerably impoverished in resources for microbial growth. This flushing was high enough during the periods of study to influence the distribution of phytoplankton biomass, bacterial production of biomass and silicate concentrations in the lagoon channel as well as in some of the bay areas. 相似文献
20.
Midsummer (1 August) population estimates of about 2 million O-group plaice (Pleuronectes platessa L.) were derived for sandy bays around the Firth of Forth in 1979–1980. This is an order of magnitude less than similar estimates made for the Clyde Sea Area in 1973–1974. Autumn population estimates of 0·4–1·0 million fish were comparable to estimates by the Ministry of Agriculture, Fisheries and Food for the area between the Scottish border and Flamborough Head (2·3 million for 1970 and 1973) which represented 4·8% (1973) to 5·3% (1970) of the total number of O-group fish on the English east coast.Largo Bay was the most important nursery area holding 25% of the total population. It is particularly well situated to receive newly metamorphosed plaice carried in water currents along the north side of the Forth from the spawning ground off Fife Ness. Plaice in the Forth are mainly distributed on fine to medium sandy beaches (186–480 μm), the mean number per haul in midsummer (D) being correlated with the median diameter (m.d. in μm) of the low water sediments by the equation: D=−45·7666+0·2327 m.d. (n=11,r=0·68,P<0·02 but>0·01).The shallow inshore water in sandy bays in the outer Firth was well mixed and more marine than estuarine (27·7–35·0‰). The correlation coefficient between fish density and water temperature was low, while that with salinity (S‰) was: D=6·1618+0·2238S (n=23,r=0·62,P<0·005).Regression analysis demonstrated that the relationship between the instantaneous mortality rate (Z) and the initial population density (Dp) was: Z×100=0·7480+0·0546dp (n=12,r=0·87,P<0·001).The mean mortality rate for the O-group plaice in the Forth nursery areas was 53% month−1. 相似文献