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1.
The littoral zone of Chesapeake Bay contains a mosaic of shallow vegetated and nonvegetated habitats with biotic components that are sensitive to changes in biological and physical driving factors. Static and dynamic modelling frameworks provide an integrative way to study complex hydrodynamic and biogeochemical processes in linked estuarine habitats. In this study we describe a spatial simulation model developed and calibrated relative to a specific littoral zone, estuarine ecosystem. The model consisted of four distinct habitats that contained phytoplankton, sediment microalgae, Zostera marina (eelgrass), and Spartina alterniflora. There was tidal exchange of phytoplankton, particulate and dissolved organic carbon and dissolved inorganic nitrogen between the littoral zone ecosystem and the offshore channel. Physical exchange and biogeochemical transformations within the habitats determined water column concentrations in each habitat. Predicted subtidal water column concentrations and Z. marina and S. alterniflora biomass were within the variability of validation data and the predicted annual rates of net primary production were similar to measured rates. Phytoplankton accounted for 17%, sediment microalgae 46%, the Z. marina community 24% and S. alterniflora 13% of the annual littoral zone primary production. The linked habitat model provided insights into producer, habitat and ecosystem carbon and nitrogen properties that might not have been evident with stand-alone models. Although it was an intra-ecosystem sink for particulate carbon, the seagrass habitat was a DOC source and responsible for over 30% of the littoral zone carbon and nitrogen primary production. The model predicted that the Goodwin Islands littoral zone was a sink of channel derived POC, but a source of DOC to the surrounding estuary. The framework created in this study of estuarine ecosystem dynamics is applicable to many different aquatic systems over a range of spatial and temporal scales.  相似文献   

2.
The ecology and diversity of the shallow soft‐bottom areas adjacent to coral reefs are still poorly known. To date, the few studies conducted in these habitats dealing with macroinvertebrate fauna have focused on their abundance spatial patterns at high taxonomic levels. Thus, some aspects important to evaluate the importance and vulnerability of these habitats, such as species diversity or the degree of habitat specialization, have often been overlooked. In this study we compared the crustacean assemblages present in four different habitats at Magoodhoo Island coral reef lagoon (Maldives): coral rubble, sandy areas and two different seagrass species (Thalassia hemprichii and Cymodocea sp.). Forty‐two different crustacean species belonging to 30 families and four orders were found. ‘Site’ was a significant factor in all of the statistical analyses, indicating that tropical soft‐bottom habitats can be highly heterogeneous, even at a spatial scale between tens and hundreds of meters. Although traditionally it has been considered that seagrass beds host greater species diversity and abundance of organisms than adjacent unvegetated habitats, no differences in the univariate measures of fauna (abundance of organisms, number of species and Shannon diversity) were observed among habitats. However, sandy areas, coral rubble and seagrass beds exhibited different species composition of crustacean communities. The percentage of taxa considered as potential habitat specialists was 27% and the number of species exclusively occurring in one habitat was especially high in seagrass beds. Thus, degradation of this vegetated habitat would result in a great loss of biodiversity in tropical shallow soft‐bottom habitats.  相似文献   

3.
In the tropics and sub-tropics, estuarine environments with mangrove and seagrass habitats provide important structures and resources for diverse communities of benthic organisms. However, temperate estuarine habitats, especially in mangrove areas, may differ significantly in their community associations and interactions. The community composition of benthic macro-fauna was investigated within temperate Matapouri Estuary, northern New Zealand. The density and distribution of fauna were sampled within six distinctive habitats (mangrove stands, pneumatophore zones, Zostera beds, channels, banks, and sand flats), within four sampling events between December 2002 and September 2003. Each type of habitat was replicated seven times within different locations in the estuary. Counts of all infauna and epifauna within four replicate cores were recorded from each habitat and location. Multidimensional scaling plots were used to identify differences in structure and composition of assemblages among habitats and locations within each sampling event. Results from these benthic samples indicate that Matapouri Estuary has a high overall biodiversity, with distinctive faunal assemblages found within different habitats, and some seasonal variations also apparent. In terms of both number of individuals and taxa per unit area, seagrass beds had the highest numbers and mangrove areas had the lowest numbers, with all other habitats in between. Some locations were found to support a high diversity of organisms across habitats, while other locations had high densities of a few species only. Several physical and biological differences between tropical/sub-tropical and New Zealand's temperate mangrove habitats are put forth as potential reasons for the lower density and diversity of the benthic component observed herein. Further ongoing studies aim to elucidate the structure and interactions within food webs in this estuarine ecosystem.  相似文献   

4.
Analysing the estuarine use patterns of juveniles of marine migrant fish species is vital for identifying important sites for juveniles as well as the basic environmental features that characterize these sites for different species. This is a key aspect towards understanding nursery function. Various estuarine systems along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria Formosa and Guadiana) were sampled during Spring and Summer 2005 and 2006. Juveniles of commercially important marine fish species Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax, predominantly 0-group individuals, were amongst the most abundant species and had distinct patterns of estuarine use as well as conspicuous associations with several environmental features. Juvenile occurrence and density varied amongst estuaries and sites within them, and differed with species. Sites with consistently high juvenile densities were identified as important juvenile sites (i.e. putative nursery grounds). Through generalized linear models (GLM), intra-estuarine variation in occurrence and density of each of the individual species was largely explained by environmental variables (temperature; salinity; depth; percentage of mud in the sediment; presence of seagrass; importance of intertidal areas; relative distance to estuary mouth; macrozoobenthos densities; and latitude). Decisive environmental factors defining important sites for juveniles varied depending on the system as a result of different environmental gradients, though there were common dominant features for each species regardless of the estuary considered. Analysed environmental variables in the GLM also accounted for inter-estuarine variation in species' occurrence and density. In several estuaries, the identified important juvenile sites were used by many of these species simultaneously and may be of increased value to both management and conservation. Overall, the variability in site features amongst estuaries highlighted the tolerance of these species to different available environmental conditions and provided fundamental information for future spatially explicit modelling of their distribution. This should ultimately enable the prediction of species response to habitat alterations.  相似文献   

5.
The spatial distribution, abundance, and assemblage structure of macrozoobenthos were examined at 45 stations in a brackish lagoon (Idoura Lagoon, Japan) to examine the animal–environmental relations in estuarine soft-bottom habitats. We found a total of 23 taxa; the polychaetes Heteromastus sp., Hediste spp., and Prionospio japonica and the isopod Cyathura muromiensis numerically dominated the community. Cluster analysis and one-way analysis of similarity (ANOSIM) identified seven groups of stations that had significantly different macrozoobenthic communities; these were subsequently consolidated into five habitat groups according to their association with environmental characteristics. Canonical correspondence analysis (CCA) showed that salinity, silt-clay content, and the oxidation–reduction potential (ORP) of the sediment strongly affected the macrozoobenthos distribution pattern in the lagoon, whereas other factors (e.g., relative elevation of the habitat and sediment organic content) had much weaker effects. Similarity percentages (SIMPER) procedures indicated that the polychaete Notomastus sp. and the bivalve Macoma contabulata were specific to habitats with low salinity and reduced mud, whereas the bivalve Nuttallia olivacea was specific to sandy bottoms. Heteromastus sp. and Hediste spp. achieved their highest densities in rather oxidized sediments. The acid-volatile sulfide (AVS) content in the sediment was suggested as another possible factor affecting macrozoobenthic density. Our results clearly demonstrate that macrozoobenthic assemblages in estuarine soft-bottoms have high spatial heterogeneity on a small scale (e.g., hundreds of meters) related to physical and chemical environmental changes. Our data also suggested the importance of sediment redox condition (e.g., ORP and AVS content) and sediment grain size as structuring factors in estuarine soft-bottom communities as well as the salinity in the habitat.  相似文献   

6.
Tropical shallow-water habitats such as mangroves and seagrass beds are widely acknowledged as important juvenile habitats for various coral reef fish species, most of which are commercially important to fisheries. Spatio-temporal variability in ontogenetic habitat use by fish among these tropical coastal ecosystems has rarely been investigated, yet there are sufficient reasons to believe that this plays an important role. In the present study, we test the spatio-temporal variability in patterns of ontogenetic habitat use by some mangrove/seagrass-associated coral reef fishes (Lethrinus harak, Lethrinus lentjan, Lutjanus fulviflamma and Siganus sutor). Abundances of these four species were investigated during two years in Tanzanian coastal waters, using underwater visual census in mangrove, seagrass, shallow and deep mudflat, and shallow and deep coral reef habitats. The study covered four distinct seasons of the year and was done at two spatially separated (>40 km) locations. Averaged across locations, seasons and years, juveniles (≤10 cm length) of the four study species had significantly higher relative densities in shallow-water (mangroves and seagrass beds) than in deep-water habitats (deep mudflats or coral reefs), whereas the opposite pattern was found for the adults (>15 cm). These findings suggest a strong and general pattern of ontogenetic habitat shifts from shallow- to deep-water habitats. However, specific habitat-use patterns of juveniles as well as adults differed significantly in time and space. Various species showed subtle to considerable flexibility in juvenile as well as adult habitat use across seasons, years, or at different locations. Furthermore, for some species the data suggest presence of ontogenetic habitat shifts at one location but lack thereof at the other location. In summary, ontogenetic habitat use needs to be considered at various spatial and temporal scales for the interpretation of habitat utilization by fish during different life stages. This is important for conservation and management of these habitats, as essential habitats or seasons may be ignored or over-emphasized with respect to their importance for fish during different parts of their life cycle.  相似文献   

7.
The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km2 of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m− 2) than seagrass meadows (30.0 g AFDM m− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m− 2 and seagrass meadows 6.9 g AFDM m− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.  相似文献   

8.
The faunal communities of four intertidal habitats namely sand, mud, seagrass (Zostera noltii) and seagrass patches (mixSM) of a temperate coastal lagoon, Ria Formosa (southern Portugal), were sampled. A total of 47 species were taken in 428 bottomless drop sampler samples, with the highest number of species and the more commonly occurring species belonging to the Mollusca phylum. The dominance of these gastropod species underlines the importance of the grazing food chain in these habitats. Bittium reticulatum was the most abundant species, being especially abundant in the seagrass habitat. The most frequent and highest biomass species in the community was Carcinus maenas, a predator that makes use of the available resources and that is adapted to the highly variable intertidal environment. Pomatoschistus microps was the most abundant fish species, with highest densities in the mud habitat, which demonstrates an ability to occupy a low depth area. The seagrass habitat had the highest diversity, abundance and biomass, followed by the mixSM habitat and was different from all the others. Assemblages were highly influenced by the presence of vegetation, providing forage and refuge from predation. A well defined summer group was identified in all habitats. These results highlight the importance of seagrass beds and the idea that their decrease implies the decrease of lagoon production through the impoverishment of the trophic structure of the lagoon.  相似文献   

9.
Seagrass meadows across north-eastern Australia, survive a range of environmental conditions in coastal bays, reefs, estuarine and deepwater habitats through adaptation of a range of structural, morphological and physiological features. The aim of this study was to investigate the influence of spatial features (habitat type, site and depth) and photon flux on the photosynthetic performance of 11 tropical seagrass species. Pulse amplitude modulated (PAM) fluorometry was used to generate rapid light curves from which measures of maximal electron transport rate (ETRmax), photosynthetic efficiency (α), saturating irradiance (Ek) and effective quantum yield (ΔF/Fm′) were derived. The amount of light absorbed by leaves (absorption factor) was also determined for each population. In intertidal habitats many seagrass species exhibited typical sun-type responses with a close coupling of both ETRmax and Ek with photon flux. Photosynthetic performance ranged from minima in Thalassodendron ciliatum to maxima in Syringodium isoetifolium. The absence of a coupling between photosynthetic performance and photon flux in subtidal populations was most likely due to highly variable light climates and possible light attenuation, and hence the photo-biology of estuarine and deepwater seagrasses exhibited photosynthetic responses indicative of light limitation. In contrast seagrass species from shallow reef and coastal habitats for the most part exhibited light saturation characteristics. Of all the variables examined ETRmax, Ek and ΔF/Fm′ were most responsive to changing light climates and provide reliable physiological indicators of real-time photosynthetic performance of tropical seagrasses under different light conditions.  相似文献   

10.
The Kaipara Harbour in New Zealand is one of the largest estuarine systems in the world, containing significant areas of subtidal seagrass habitat (Zostera muelleri). Light availability at the maximum depth limit for Z. muelleri was measured at 2.10 (0.19 SEM) and 4.91 (0.53 SEM) mol photons m?2 d?1 during the winter and summer monitoring periods, respectively. The primary drivers of benthic light availability were found to be surface light availability, the timing of the low tide and water clarity. Core sampling analysis suggested that biomass of seagrass growing at the maximum depth limit was low, indicative of light limitation. The results of this study suggest that the subtidal distribution of seagrass in the Kaipara Harbour is light-limited and that reductions in water clarity due to changes in land use are likely to result in significant reductions in the extent and productivity of subtidal seagrass habitat.  相似文献   

11.
《Journal of Sea Research》2009,61(4):255-263
The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km2 of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m− 2) than seagrass meadows (30.0 g AFDM m− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m− 2 and seagrass meadows 6.9 g AFDM m− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.  相似文献   

12.
Caribbean spiny lobster (Panulirus argus) settle preferentially in macroalgal‐covered hard‐bottom habitat, but seagrass is more prevalent in Florida (United States) and the Caribbean, so even low settlement of lobsters within seagrass could contribute substantially to recruitment if post‐settlement survival and growth were high. We tested the role of seagrass and hard‐bottom habitats for P. argus recruitment in three ways. We first explored possible density‐dependent regulation of early benthic juvenile lobster survival within cages deployed in seagrass and hard‐bottom habitats. Second, we compared settlement and survival of P. argus in both habitats, by comparing the recovery of microwire‐tagged early benthic juveniles from patches of seagrass and hard‐bottom. Finally, we assessed the relative abundance of juvenile lobsters in each habitat by deploying artificial structures in seagrass sites and compared these data with data from similar deployments of artificial structures in hard‐bottom habitat in other years. More early benthic juvenile lobsters were recovered from cages placed in hard‐bottom than in seagrass, but mortality of the early benthic life stage was high in both habitats. In regional surveys, the mean number of lobsters recovered from artificial shelters deployed within seagrass was lower than in any year that we sampled hard‐bottom, indicating that fewer lobsters reside naturally in seagrass, particularly large juveniles >40 mm carapace length. The greater abundance (and likely survival) of juvenile P. argus that we observed in hard‐bottom habitat as opposed to seagrass, combined with previous studies demonstrating that postlarval P. argus are attracted to, settle in, and metamorphose more quickly in red macroalgae, confirm that macroalgae‐dominated hard‐bottom habitat appears to be the preferred and more optimal nursery for Caribbean spiny lobster.  相似文献   

13.
Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrates. The shore crab Carcinus maenas (Crustacea: Brachyura: Portunidae) inhabits a variety of coastal, estuarine and lagoon habitats. At low tide, habitat structural complexity may be most important for crabs in the intertidal, providing refuge from predation and desiccation. The quality of different vegetated and nonvegetated estuarine and rocky shore habitats in SW Portugal and SW England was evaluated for intertidal C. maenas populations. We estimated population density, size–structure, and potential growth (RNA/DNA ratios) to investigate habitat quality. Vegetated estuarine habitats supported higher crab densities, than nonvegetated estuarine and rocky shore habitats. Investigation of population size–structure revealed that all habitats seem important recruitment and nursery areas although estuarine habitats in SW Portugal appeared to support higher densities of new recruits than equivalent habitats in SW England. Significant variation was found in RNA/DNA ratios among habitats. Ratios were highest in the rocky shore suggesting a high quality habitat where growth potential is high. We speculate that competition from other top-predators (Pachygrapsus spp.) rather than low habitat quality may limit the occurrence of C. maenas in intertidal rocky shore habitats in SW Portugal. In estuarine environments RNA/DNA ratios were significantly higher in the vegetated than in the nonvegetated estuarine habitats in SW Portugal but not in SW England, suggesting geographic differences in the extent to which highly structure habitats represent high quality. Our results challenge the current paradigm that structured habitats are necessarily those of higher quality for C. maenas.  相似文献   

14.
The relationship between diet and feeding activity of intertidal crabs, and environmental cycles (tidal, daily and seasonal), habitat and level of the intertidal zone (high/low) was studied using Neohelice granulata (Brachyura, Varunidae) as a model. This is a semi‐terrestrial burrowing crab occupying different habitats in the Southwestern Atlantic coasts and estuaries from bare low intertidal mudflats to high intertidal salt marshes, and from fine, organic matter rich sediment to very coarse sediment with low content of organic matter. The study was carried out in two contrasting habitats of three sites with diverse sets of physical and biological conditions. Diet and feeding of adult N. granulata were indirectly studied through the proportion of food items and the presence/absence of food in crab stomachs, respectively. This species has a dual mode of feeding: predominantly herbivorous (live plants or plant litter in salt marshes) or deposit feeder (superficial sediment and detritus in mudflats), but the quantity and quality of ingested food varies among habitats and sites. A trend to omnivory (including algae and conspecifics) was detected in relation to low quality of resources. Feeding activity modulated by a complex interaction of factors varied according to spatial and/or temporal changes in some natural cycles. Males and non‐ovigerous females fed preferably after dark and during submersion periods, but also after emersion periods if mudflat sediment remained wet; salt marsh crab feeding is somewhat independent of light and tidal cycles. Ovigerous females almost never fed. Both diet and feeding activity of this crab seem to be flexible traits adapted to different combinations of physical and biological factors.  相似文献   

15.
Surgeonfish and parrotfish play an important role in structuring the benthic communities of coral reefs. However, despite their importance, little is known about their distribution patterns in the north sector of the Mesoamerican Reef System. This study evaluated the distribution of these fish in 34 sites in four habitats (lagoon, front, slopes and terrace) along a depth gradient (c 0.5–20 m). These herbivorous fish were assessed by visual censuses. Species dominance was evaluated for each habitat using SIMPER analysis. Habitat characteristics data were collected to determine the relationship between habitat conditions and spatial variations in herbivorous fish (using abundance and biomass as a proxy) via redundancy analysis. The herbivorous fish assemblage had a low density (fish per 100 m2) and biomass (g·100 m?2) in comparison with assemblages in similar studies. In contrast, species richness was high compared with other studies in the Caribbean. Spatial variation of the abundance, biomass and size of herbivorous fish was strongly related to coral and seagrass cover, as well as to depth and rugosity. These four variables were critical in controlling the distribution patterns of the herbivorous fish assemblages. No associations were found between fish and macroalgae or any other benthic group. The present study indicates that the species richness of surgeonfish and parrotfish was not regionally affected by the dominance of macroalgae in the habitats studied. Seagrass beds and the coral reef matrix need to be preserved for the herbivorous fish assemblages to remain healthy and capable of controlling excess macroalgae growth.  相似文献   

16.
Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by variations in juvenile growth and survival. Condition indices are renowned proxies of juvenile nutritional status and growth rates and are valuable tools to assess habitat quality. Biochemical (RNA:DNA ratio) and morphometric (Fulton's condition factor K) condition indices were determined in juveniles of Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax collected in putative nursery areas of nine estuaries along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria Formosa and Guadiana) in the Spring and Summer of two consecutive years (2005 and 2006) with distinct climatic characteristics. Individual condition showed significant variation amongst species. The combined use of both condition indices highlighted the low correlation between them and that RNA:DNA had a higher sensitivity. RNA:DNA varied between years but overall the site relative patterns in condition were maintained from one year to the other. Higher RNA:DNA values were found in Spring than in Summer in most species. Intra-estuarine variation also occurred in several cases. Species specific trends in the variability of condition amongst estuaries were highlighted. Some estuaries had higher juvenile condition for more than one species but results did not reveal an identical trend for all species and sites, hindering the hypotheses of one estuarine nursery promoting superior growth for all present species. Significant correlations were found between condition indices, juvenile densities and environmental variables (water temperature, salinity and depth) in the estuarine nurseries. These influenced juvenile nutritional condition and growth, contributing to the variability in estuarine nursery habitat quality. Management and conservation wise, interest in multi-species approaches is reinforced as assessments based on a single species may not reflect the overall nursery habitat quality.  相似文献   

17.
Cold-seep environments and their associated symbiont-bearing megafaunal communities create islands of primary production for macro- and meiofauna in the otherwise monotonous and nutrient-poor deep-sea environment. To examine the spatial variation and distribution patterns of metazoan meiobenthos in different seepage-related habitats, samples were collected in two regions off Norway: several pockmarks associated with the Storegga Slide including the Nyegga pockmark area (730 m; 64°N), and the active, methane-venting Håkon Mosby Mud Volcano (HMMV) west of the Barents Sea (1280 m; 72°N). Based on sediment geochemistry and associated epifauna, three different habitat types were distinguished across the two regions: (1) reduced sediment with suboxic conditions, sometimes covered by bacterial mats, (2) sediment colonised by chemosynthetic, siboglinid tubeworms, and (3) sediment outside the influence of seepage and without a large chemosynthetic fauna. Meiofaunal communities varied strongly in terms of generic diversity and dominance among the different habitat types. Control sites and Siboglinidae polychaete fields both supported high nematode genus richness similar to normal deep-sea sediments, whereas the reduced sediments yielded a genus-poor nematode community dominated by one or two successful species. Meiofaunal densities in the different habitats were negatively correlated with macrobenthic densities. An extremely dense (>11,000 ind. 10 cm–2), mono-specific nematode population appeared to be restricted to the bacterial mats at HMMV. It consisted of a new cryptic species of the Halomonhystera disjuncta complex, which has been described from intertidal habitats in the North Sea. The reduced seep sediments at Nyegga did not yield H. disjuncta but were dominated by Terschellingia longicaudata, another cosmopolitan nematode species known to be abundant in organic-rich, oxygen-poor, shallow-water environments. These observations point to a past or recent connection between margins and shallow-water habitats.  相似文献   

18.
Whereas diel fish migration between mangrove and seagrass habitats has been recognized for decades, quantitative studies have focused mainly on diurnal patterns of fish distribution and abundance. In general, previous studies have shown that fish abundances decline with increasing distance from mangroves; however, evidence for such a pattern at night, when many fishes are actively feeding, is scarce. The present study is the first to report nocturnal fish abundances along a continuous distance gradient from mangroves across adjacent seagrass habitat (0–120 m). Here, we used nocturnal seine sampling to test the null hypothesis (based on diurnal studies and limited nocturnal work) that fish abundance would decrease with increasing distance from shoreline. We focused on species and life‐stage‐specific abundance patterns of Lutjanus griseus, Sphyraena barracuda, Archosargus rhomboidalis, and Haemulon sciurus. Results indicated that assemblage composition and structure differed significantly by season, likely influenced by temperature. However, within each season, the fish habitat use pattern at both the assemblage and species‐specific level generally failed to support our working null hypothesis. Species‐specific analyses revealed that, for most species and life‐stages examined, nocturnal abundance either did not change with distance or increased with distance from the mangrove‐seagrass ecotone. Our results suggest that analyses where taxa are grouped to report overall patterns may have the potential to overlook significant species‐ and stage‐specific variation. For fishes known to make nocturnal migrations, we recommend nocturnal sampling to determine habitat utilization patterns, especially when inferring nursery value of multiple habitats or when estimating fish production.  相似文献   

19.
Seagrass landscapes are coastal environments that support diverse and abundant faunal communities. This study investigated infaunal assemblage patterns in fragmented and continuous Zostera muelleri habitat in southeastern New Zealand. Intertidal macroinvertebrate assemblages were examined in fragmented seagrass habitat (containing discrete patches varying in size from 1 to 200 m2) and continuous meadows (>1000 m2), in a small and a large tidal inlet. Community indices differed between seagrass habitat types and the total number of taxa was significantly lower at fragmented seagrass sites in one of the inlets. The total number of individuals and diversity were significantly different between fragmented and continuous seagrass habitat in both inlets, but diversity values showed inconsistent patterns between inlets. Multivariate analysis confirmed that different seagrass habitat types support distinct macrofaunal assemblages in each inlet and position on the shore was identified as the single most important variable explaining dissimilarities in assemblage compositions. These findings confirm the influence of seagrass habitat size on infaunal assemblages and also highlight the importance of spatial position of seagrass habitat in intertidal areas.  相似文献   

20.
Seagrass beds have higher biomass, abundance, diversity and productivity of benthic organisms than unvegetated sediments. However, to date most studies have analysed only the macrofaunal component and ignored the abundant meiofauna present in seagrass meadows. This study was designed to test if meiobenthic communities, especially the free-living nematodes, differed between seagrass beds and unvegetated sediments. Sediment samples from beds of the eelgrass Zostera capricorni and nearby unvegetated sediments were collected in three estuaries along the coast of New South Wales, Australia. Results showed that sediments below the seagrass were finer, with a higher content of organic material and were less oxygenated than sediments without seagrass. Univariate measures of the fauna (i.e. abundance, diversity and taxa richness of total meiofauna and nematode assemblages) did not differ between vegetated and unvegetated sediments. However multivariate analysis of meiofaunal higher taxa showed significant differences between the two habitats, largely due to the presence and absence of certain taxa. Amphipods, tanaidacea, ostracods, hydrozoans and isopods occurred mainly in unvegetated sediments, while kinorhyncs, polychaetes, gastrotrichs and turbellarians were more abundant in vegetated sediments. Regarding the nematode assemblages, 32.4% of the species were restricted to Z. capricorni and 25% only occurred in unvegetated sediments, this suggests that each habitat is characterized by a particular suite of species. Epistrate feeding nematodes were more abundant in seagrass beds, and it is suggested that they graze on the microphytobenthos which accumulates underneath the seagrass. Most of the genera that characterized these estuarine unvegetated sediments are also commonly found on exposed sandy beaches. This may be explained by the fact that Australian estuaries have very little input of freshwater and experience marine conditions for most of the year. This study demonstrates that the seagrass and unvegetated sediments have discrete meiofaunal communities, with little overlap in species composition.  相似文献   

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