1,721,176 research outputs found
A three-year time series of elemental and biochemical composition of organic matter in subtidal sandy sediments of the Ligurian Sea (northwestern Mediterranean).
Full text linkVariations in organic matter composition and microphytobenthic biomass were examined in the surface sandy sediments at a water depth of 10 m in the Gulf of Marconi (NW Mediterranean Sea) over a three year period. Seasonal changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter as well as Chi a were assessed in order to provide information about the origin and fate of sedimentary organic matter, the contribution of microphytobenthic biomass, seasonal and interannual variations of food quantity and quality, and factors related to food availability. Data obtained in this three-year study revealed that organic matter determined with a muffle furnace is clearly an overestimate of the organic content of the sediment and is thus of little significance for benthic ecologists studying community dynamics in relation to food availability. Labile organic matter, utilized to estimate the food potentially available for benthic consumers, accounted for only a small percentage (on average less than 10%) of total organic C. The highest labile fraction was observed in spring, whereas minima were recorded in winter. Analysis of elemental and biochemical composition of organic matter showed an inverse relationship between amount of organic matter and its potential availability to consumers; small quantities of high-quality organic matter were replaced by large quantities of refractory material. The labile portion was mostly microphytobenthic (65% of the labile carbon). Protein:carbohydrate ratios were low and confirmed the role of proteins as a potentially limiting factor for consumers. Significant differences in nutritional quality of the sediment organic matter were observed from year to year, changes due to the increase in specific labile compound content
Meiofaunal vertical zonation on hard-bottoms: comparison with soft-bottom meiofauna
Full text linkAn annual study on hard-substrate meiofaunal assemblages was carried out at 2 depths (2.5 and 8 m) along a vertical cliff of the Middle Adriatic (Mediterranean Sea) characterised by different macroalgal canopies and structural substrate complexities. The upper sampling area of the rocky cliff was covered by macroalgae, and its upper limit was characterised by the presence of a dense belt of Mytilus galloprovincialis. At 8 m depth, mussels were not present, the algal assemblage was less diversified, and phytal coverage decreased. Dynamics and community structure of meio-fauna-inhabiting hard substrates were compared with those of meiofauna collected from soft sediments at the cliff base (9 m depth). Meiofauna of hard and soft substrates displayed significant differences both in terms of density (7-fold higher in soft substrates) and assemblage structure. Meiofauna from rocky substrates were dominated by crustaceans (copepods, nauplii and amphipods), while soft sediments were largely dominated by nematodes (ca 90%). Significant temporal changes of meiofaunal density were observed on both hard and soft substrates, with higher densities in spring to summer and lowest abundance in winter, Despite a completely different algal assemblage and coverage at 2.5 and 8 m depths, hard substrates displayed very similar meiofaunal densities and community structure. Crustacean taxa were correlated with algal coverage, Polychaetes inhabiting hard substrates increased their relevance with depth, whilst amphipods, being significantly correlated with algal biomass, decreased. Nematodes were related with the structural complexity index, calculated on the basis of macroalgal geometric complexity and biomass, whereas copepod and nauplius densities were related with the total structural complexity (as a sum of the algal complexity). The results of the present study indicate that the nature of the substrate (hard vs soft) is the main factor responsible for the differences observed between hard- and soft-bottom meiofauna assemblages, whereas phytal coverage and substrate complexity influenced the structure of hard bottom meiofaunal assemblages. Finally, the analysis of spatial variability of meiofaunal assemblages indicates that hydrodynamic stress also played an important role in meiofaunal structure and distribution on hard substrates, especially at shallow depth
How many habitats are there in the sea (and where)?
No full textCurrent policies of habitat conservation, recovery, and management are strongly biased in favour of
terrestrial systems, being poorly applicable to marine environments. A sound habitat classification, leading to
spatially explicit accounts on the distribution of marine habitats and communities, is a prerequisite to
identify conservation priorities, based on appropriate methods for assessing habitat sensitivity to human
disturbance, aimed at preventing habitat loss. The ten major European marine habitat classifications,
recognizing a total of 1121 marine habitats, have been here revised, and their major differences have been
formally tested in terms of multivariate dissimilarity. Mediterranean-based classifications resulted rather
uniform, their habitats forming a separate cluster from the rest of European ones; these differences might be
due to either distinct ecological features, or to divergences in the way habitats are classified. Either too vague
or too detailed classifications, leading to cumbersome appreciations of biodiversity at habitat level, fail to
provide proper tools for the conservation and management of marine environments. Different species
assemblages can inhabit the same habitat type, representing the well-know natural variability that, at large
scale, should not affect the appreciation of habitat distribution. Intra-habitat natural variability, in fact, causes
a misleading qualitative interpretation of small-scale biodiversity distribution. Mediterranean classifications
have been integrated and simplified by identifying habitats according to explicit criteria: level on the shore,
type of primary substrate, presence of bioconstructors, presence of habitat formers, presence of ecosystem
engineers. The motivating idea is to limit the current emphasis on spatial dominance as the only criteria for
the introduction of species, assemblages, and habitats in the lists, towards a clearer recognition of the
structural and functional role of biodiversity. The reduction of previous classifications to a list of 94
Mediterranean marine habitat types represents an initial attempt at providing a simple and flexible tool for
the evaluation of biodiversity at habitat level, leading to more feasible conservation measures, potentially
extendable at European scale.Current policies of habitat conservation, recovery, and management are strongly biased in favour of terrestrial systems, being poorly applicable to marine environments. A sound habitat classification, leading to spatially explicit accounts on the distribution of marine habitats and communities, is a prerequisite to identify conservation priorities, based on appropriate methods for assessing habitat sensitivity to human disturbance, aimed at preventing habitat loss. The ten major European marine habitat classifications, recognizing a total of 1121 marine habitats, have been here revised, and their major differences have been formally tested in terms of multivariate dissimilarity. Mediterranean-based classifications resulted rather uniform, their habitats forming a separate cluster from the rest of European ones; these differences might be due to either distinct ecological features, or to divergences in the way habitats are classified. Either too vague or too detailed classifications, leading to cumbersome appreciations of biodiversity at habitat level, fail to provide proper tools for the conservation and management of marine environments. Different species assemblages can inhabit the same habitat type, representing the well-know natural variability that, at large scale, should not affect the appreciation of habitat distribution. Intra-habitat natural variability, in fact, causes a misleading qualitative interpretation of small-scale biodiversity distribution. Mediterranean classifications have been integrated and simplified by identifying habitats according to explicit criteria: level on the shore, type of primary substrate, presence of bioconstructors, presence of habitat formers, presence of ecosystem engineers. The motivating idea is to limit the current emphasis on spatial dominance as the only criteria for the introduction of species, assemblages, and habitats in the lists, towards a clearer recognition of the structural and functional role of biodiversity. The reduction of previous classifications to a list of 94 Mediterranean marine habitat types represents an initial attempt at providing a simple and flexible tool for the evaluation of biodiversity at habitat level, leading to more feasible conservation measures, potentially extendable at European scale. (C) 2008 Elsevier B.V. All rights reserved
Human-driven impacts on marine habitats: a regional meta-analysis in the Mediterranean Sea
No full textHabitat destruction is one of the main threats to environmental integrity. Assessing the consequences
of human impacts is crucial both to predict and prevent structural and functional changes of habitats.
However, to date almost all studies on marine threats, from regional to global scales, have been
entirely qualitative and generally based on little more than expert opinion. We have developed a
meta-analytical approach to quantify overall effects of various stressors on different Mediterranean
habitat types and to compare the relative importance of different impacts across a range of habitats.
We first qualitatively reviewed and synthesized 366 experiments (either manipulative or correlative)
collected in the literature. After a selection procedure, we finally quantitatively meta-analyzed 158
experiments. We showed that fisheries (destructive or not), species invasion, aquaculture, sedimentation
increase, water degradation and urbanization have negative effects on Mediterranean habitats
and associated species assemblages. We also explored the overlap between the impacts identified
as important in the Mediterranean and those identified by experts as being important globally, highlighting
the inadequacies of relying on expert opinion alone. Finally, we drew attention to the critical
lack of empirical knowledge about marine systems in many areas of the Mediterranean, which
impedes the implementation of effective conservation measures. Our study is the first to synthesize
experimental analyses on human-driven impacts on marine habitats across such a broad geographic
scale
The effects of sewage discharge on shallow hard bottom sessile assemblage
No full textOn rocky shores, sewage discharges can modify natural distribution patterns Of sessile organisms. The impact of sewage On shallow hard substrate assemblages has been assessed along SW Apulian coast (lonian Sea Italy). providing it framework to evaluate the benefits of future sewage displacement to deeper waters. Four locations (three controls and One putatively impacted) were selected and three sites were chosen at each location. Each site was sampled by 10 replicate photographic records. Univariate analyses revealed that the outfall did not affect the spatial distribution of number of taxa, total cover and abundance of some dominant taxa (mostly algae. sponges and bryozoans). The outfall negatively influx seed the natural distribution pattern of filamentous green algae. whilst some algae (i.e. Gelidiales and Colpomenia sinuosa) were exclusively present at the impacted location. Multivariate analyses revealed that the outfall heavily modified the natural pattern of variability in the structure of the assemblage. (C) 2002 Elsevier Science Ltd. All rights reserved
Effects of intensive mariculture on sediment biochemistry
No full textABSTRACT. The exponential growth of off-shore mariculture that has occurred worldwide over the last 10 years has raised concern about the impact of the waste produced by this industry on the ecological integrity of the sea bottom. Investigations into this potential source of impact on the biochemistry of the sea floor have provided contrasting results, and no compelling explanations for these discrepancies have been provided to date. To quantify the impact of fish-farm activities on the biochemistry of sediments, we have investigated the quantity and biochemical composition of sediment organic matter in four different regions in the temperate–warm Mediterranean Sea: Akrotiri Bay (Cyprus), Sounion Bay (Greece), Pachino Bay (Italy), and the Gulf of Alicante (Spain). In these four study regions, the concentrations of phytopigments, proteins, carbohydrates, and lipids in the sediments were measured, comparing locations receiving wastes from fish farms to control locations in two different habitats: seagrass beds and soft nonvegetated substrates. Downward fluxes were also measured in all of the regions, up to 200 m from the fish farms, to assess the potential spatial extent of the impact. In all four regions, with the exception of seagrass sediments in Spain, the biochemistry of the sediments showed significant differences between the control and fish-farm locations. However, the variables explaining the differences observed varied among the regions and between habitats, suggesting idiosyncratic effects of fish-farm waste on the biochemistry of sediments. These are possibly related to differences in the local physicochemical variables that could explain a significant proportion of the differences seen between the control and fish-farm locations. Biodeposition derived from the fish farms decreased with increasing distance from the fish-farm cages, but with different patterns in the four regions. Our results indicate that quantitative and qualitative changes in the organic loads of the sediments that arise from intensive aquaculture are dependent upon the ecological context and are not predictable only on the basis of fish-farm attributes and hydrodynamic regimes. Therefore, the siting of fish farms should only be allowed after a case-by-case assessment of the ecological context of the region, especially in terms of the organic matter load and its biochemical composition
Incorporating change in marine spatial planning: A review
No full textMarine/maritime spatial planning (MSP) is intended as a process to apply an adaptive ecosystem-based approach
in order to manage the oceans towards the sustainable use of marine resources. Several policy documents and
research articles have identified the need for MSP to address change, intended as dynamic aspects from different
drivers. However, practical examples of MSP embracing change and dynamics are rare and the inclusion of
system dynamics, environmental variability and future change in MSP remains challenging. Here, we conceptualize
the multiple dimensions of change in MSP consisting in i) the dynamics of the marine and coastal
social-ecological system (SES), and ii) the dynamics of the planning process. This study depicts the current state
of scientific knowledge on incorporating change and dynamics in MSP through a systematic literature review.
Efforts to actually incorporate change in MSP are mainly limited to environmental dynamics, while social and
governance changes are rarely represented. Long-term temporal scales are only seldom considered, and climate
change effects rarely incorporated in methods and tools to support MSP. We propose a tier-approach to include
multiple response variables and scenario modeling to address socio-economic, environmental and governance
change and dynamics within MS
Life history traits of the bivalve Spisula subtruncata (da Costa) in the Ligurian Sea (northwestern Mediterranean): the contribution of the temporary meiofauna
No full textA population of Spisula subtruncata was studied in four different years (1983-1984; 1990-1993) on a shallow
sandy bottom in the Ligurian Sea. Throughout the studied period, the S. subtruncata population was characterised by wide
seasonal and interannual fluctuations both in abundance and biomass. Its life-cycle was normally annual, and there was an
almost complete disappearance of the bivalve during winter months. The population of Spisula subtruncata was characterised
by the dominance of juvenile forms and very few adults (maximum total length observed, 13 mm). Population size
varied according to recruitment success. In the 1 mm samples, Spisula was particularly abundant within the community during
the spring-summer period of 1991, with peaks of density and biomass of 1017 individuals m-2 (± 30.9 std) and 114.5 mg
AFDW m-2 in May. From January 1991 to February 1993 the juvenile density of the bivalve was measured in meiofaunal
samples. Juveniles were characterised by wide seasonal fluctuations, with density peaks in May (10,350 individuals m-2 ±
248 and 11,403 individuals m-2 ± 378, in 1991 and 1992, respectively). A mortality rate higher than 90% was estimated
(measured as the difference between the density peak of juveniles and the density of the following peak of adults).
Production was 0.58 (1983-84), 0.44 (1991-92) and 0.12 g m-2 yr-1 (1992-93). Considering also the contribution of temporary
meiofauna, secondary production raised up to 0.52 in 1991-1992; and to 0.18 g m-2 yr-1 in 1992-93. The year 1990 was
characterised by very low density so that no production value was estimated. A number of features are discussed: the variability
observed in the demographic structure of the bivalve with the latitudinal gradient; the relation between population
structure and production values; and the contribution of the smallest size classes to energy flow
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