Sediment organic matter and meiofauna community response to long-term fish-farm impact in the Ligurian Sea (Western Mediterranean)

Quantitative and qualitative changes in meiofauna community structure were investigated to assess the impact of a fish farm, which was operating continuously for 15 years (La Spezia Gulf, W Mediterranean). Sediment samples were collected in June, July, September, October 2000 and February 2001 for the analysis of phytopigments (chlorophyll-a and phaeopigments), the biochemical composition of organic matter (proteins, carbohydrates and lipids) and related to meiofaunal parameters.

Sediment organic matter reached extremely high concentrations beneath the fish cages when compared to the control. Particularly lipids, carbohydrates and chlorophyll-a were significantly higher in fish-farm sediments. On a long-term basis meiofauna displayed adaptations in sediments beneath the cages resulting in an increase of density. Organic impact on meiofaunal community structure was evident in terms of an increase of the nematodes to copepods (Ne/Co) and nauplius to copepods (Na/Co) ratios in fish farm sediments. Cumaceans and kinorhynchs were encountered in control sediments, but disappeared in fish-farm samples. These data suggest that meiofauna is a sensitive tool for evaluating the effects of organic enrichment in fish farm impacted areas.     

Effects of intensive mariculture on sediment biochemistry.

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.     

Meiofauna response to a dynamic river plume front

 The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g⁻¹ for chlorophyll a and 1.2 to 17.7 μg g⁻¹ for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g⁻¹). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541 ind. 10 cm⁻²) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector, the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath, their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages. Received: 30 November 1999 / Accepted: 24 May 2000     

Distribution quantitative de la méiofaune dans l'aire d'épandage de l'égout de Marseille

A quantitative analysis of meiofauna was carried out at ten sample stations distributed along a transect off Marseilles' (France) sewage outfall in November, 1981. The meiofauna was counted and average and total biomass of nematodes and copepods were calculated for each station. Comparison of data between stations or groups of stations was made using statistical tests. The results revealed three sectors in which effects of pollution on meiofauna differed: (1) A heavily polluted coastal zone (at a distance of 30 to 150 m from the outfall), relatively poor in meiofauna, which, however, was not completely absent-as were macrobenthic organisms; the meiofauna was composed mainly of nematodes and copepods, but acarians and naupliar larvae (probably copepods) were also numerous; the copepods were uncommonly large in size, and alone consituted most of the total benthic biomass in this zone. (2) An intermediate zone (400 to 1 150 m away from the coast), also polluted and much richer in meiofauna than the coastal zone; the meiofauna groups were more diversified, annelids (mainly polychaetes) increasing in number, while acarians became scarce and copepods decreased in size; at 400 m away from the outfall, where the sediment is strongly polluted, the nematode population consisted of large individuals which contributed greatly to the biomass; at 400 and 800 m, the distribution of both meiofauna and macrobenthos was heterogeneous; at 1 150 m away from the outfall, maximal meiofaunal densities were recorded, due primarily to an increase in nematode numbers; here, unlike all the stations nearer to the coast, total nematode biomass was greater than copepod biomass. (3) An off-shore zone (1.8 to 4 km distant from the coast), slightly polluted, where meiofauna densities were reduced and individuals decreased in size with increasing depth. Generally, an enrichment in the meiofauna was evident from the coastal to the intermediate zone. Enrichments induced by urban pollution have been recorded previously, but not, as in the present study, at a distance of 1 km away from the outfall, succeeding to a highly impoverished coastal zone. Thus, by supplying organic matter and nutrients, Marseilles' sewage can enrich sediments, but only to a certain distance away from the outfall, where the deleterious effects of pollutants are attenuated.     

Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes

The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex König meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology.     

Investigations on epibenthic meiofauna I. Abundances on and repopulation of the tube-caps of Diopatra cuprea (Polychaeta: Onuphidae) in a subtropical system

Cryptic meiofauna populated the imbricate, shell-sediment matrix of the tube-caps produced by the polychaete Diopatra cuprea (Bose) in Tampa Bay, Florida, USA. Nematodes, copepods (adults and nauplii), polychaetes (adults and juveniles) and amphipods (adults and juveniles) were the most abundant taxa found on tube-caps. Meiofaunal densities on tube-caps were 4 to 19 times higher than equivalent volumes of sediment in cores taken adjacent to D. cuprea tubes. Recruitment onto tube structure occurred within 1 to 2 d after defaunated tube-caps were replanted into sediments in the field (February–November 1980). Repopulation of copepods (adults and nauplii) attained levels equal to or exceeding natural abundances on tube caps within 1 to 5 d; nematode recovery rates were inconsistent. Short-term experiments using a variety of defaunated tube treatments indicated that immigration onto above-sediment tube-caps proceeds via both water column and sediment pathways. Based on data on tube-cap longevity and construction as well as meiofaunal recruitment rates, we conclude that the generation of new tube-cap structure is exploited rapidly by meiofauna.     

Predation on meiofaunal and macrofaunal invertebrates by western sandpipers (Calidris mauri): evidence for dual foraging modes

Western sandpiper (Calidris mauri) predation was examined by concurrent experiments and direct observations of foraging behaviour on high intertidal mudflats of the Fraser River estuary, British Columbia. Western sandpipers foraged by either “pecking” on the surface (64% of observational time) or probing into sediment (29%). The first experiment (probe-mark method) consisted of collecting small-volume cores (21.2 cm³) of probed (experimental) and non-probed (control) sediment on the tidal flat, following a 22.5-min feeding period. The second experiment (exclosure method) involved deploying exclosures immediately prior to the feeding period and subsequent collection of cores from inside (control) and outside (experimental) the exclosures. Sediment cores were analysed for both macrofaunal and meiofaunal size fractions. Comparisons between macro- and meiofaunal invertebrate densities in experimental and control sediments revealed significant differences, attributed to shorebird predation, for both experiments. The probe-mark experiment detected the removal of large infaunal polychaetes (∼ 20 mm), while the exclosure experiment showed depletion of epifaunal harpacticoid copepods (0.063–0.5 mm). Predation on macrofaunal cumaceans was detected in both experiments. Invertebrates selected by western sandpipers neither fell within traditional infaunal size classifications (macro- vs. meiofauna; 500 μm delineation) nor corresponded to the highest densities of taxa. Rather, inference from experimental results and observations is that western sandpipers forage in two modes, by: (1) surface gleaning of epibenthic copepods and cumaceans in the macro- and meiofaunal size ranges and (2) selective probing for larger infauna, such as polychaetes. These findings were facilitated by the combination of methodologies employed. Received: 29 December 1999 / Accepted: 11 September 2000     

Detritus-Bacteria-Meiofauna interactions in a seagrass bed (Posidonia oceanica) of the NW Mediterranean

The biochemical composition of the sediment organic matter, and bacterial and meiofaunal dynamics, were monitored over an annual cycle in aPosidonia oceanica bed of the NW Mediterranean to test the response of the meiofauna assemblage to fluctuations in food availability. Primary production cycles of the seagrass and its epiphytes were responsible for relatively high (compared to other Mediterranean systems) standing stocks of organic carbon in sediments (from 1.98 to 6.16 mg Cg^–1 sediment dry weight). The biopolymeric fraction of the organic matter (measured as lipids, carbohydrates, and proteins) accounted for only a small fraction (18%) of the total sedimentary organic carbon. About 25% of the biopolymeric fraction was of microphytobenthic origin. Sedimentary organic carbon was mostly refractory (56 to 84%) and probably largely not utilizable for benthic consumers. The biopolymeric fraction of the organic matter was characterized by high carbohydrate concentrations (from 0.27 to 5.31 mg g^–1 sediment dry weight in the top 2 cm) and a very low protein content (from 0.07 to 0.80 mg g^–1 sediment dry weight), which may be a limiting factor for heterotrophic metabolism in seagrass sediments. RNA and DNA concentrations of the Sediments varied significantly during the year. High RNA and DNA values occurred during the microphytobenthic bloom and in correspondence with peaks of bacterial abundance. Bacteria accounted for a small fraction of the total organic carbon (0.65%) and of the biopolymeric organic carbon (4.64%), whilst microphytobenthos accounted for 3.79% of total organic carbon and for 25.08% of the biopolymeric carbon. Bacterial abundance (from 0.8 to 5.8 × 10⁸ g^–1 sediment dry weight) responded significantly to seasonal changes of organic matter content and composition and was significantly correlated with carbohydrate concentrations. Bacteria might be, in the seagrass system, an important N storage for higher trophic levels as il accounted for 25% of the easily soluble protein. pool and contributed significantly to the total DNA pool (on average 12%). Total meiofaunal density ranged from 236 to 1858 ind. 10 cm^–2 and was significantly related, with a time lag, to changes in bacterial standing stocks indicating that microbes might represent an important resource. Bacterial abundance and biomass were also significantly related to nematode abundance. These results indicate that bacteria may play a key role in the benthic trophic     

Distribution patterns of meiofauna associated with a sublittoral<Emphasis Type="Italic"> Laminaria</Emphasis> bed in the Cantabrian Sea (north-eastern Atlantic)

This study deals with meiofauna associated with a sublittoral population of the kelp Laminaria ochroleuca located on the northern coast of Spain. By sampling once a year over a 4-year period, we examined patterns of faunal distribution as a function of some environmental factors at the meso-scale level (depth, and exposure to waves and surge). We also examined the relationship between L. ochroleuca abundance (as dry weight biomass and number of plants per sampling quadrat) and abundance and diversity of meiofauna. Finally, we investigated patterns of within-plant distribution (algal frond vs. algal holdfast), using also the meiofauna of the adjacent bottom as a referent to estimate the level of "phytal dependence" of the meiofauna collected on L. ochroleuca. We found that the bulk of permanent meiofauna consisted of nematodes, copepods, mites, polychaetes, tanaids and ostracods, with copepods being predominant on the fronds of the alga and nematodes in the holdfasts. The temporary meiofauna consisted of juvenile amphipods, bivalves and gastropods, together with barnacle nauplii and cyprids. Abundance and major composition of meiofaunal taxa were unrelated to both depth and hydrodynamic exposure of the sampling quadrats. However, we detected significant qualitative and quantitative faunal differences as a function of microhabitat. All meiofaunal groups were more abundant in holdfast samples than in frond and bottom samples. The gross taxonomic composition of meiofauna in bottom samples was similar to that in holdfast samples, but substantially different from that of meiofauna associated with the fronds. The L. ochroleuca holdfasts, in which dense aggregations of meiofauna can occur, appear to function as ecotone between phytal and rocky-bottom microhabitats. All together, our results suggest that the distribution of meiofauna within the Laminaria bed is mostly affected by factors operating at the microhabitat level rather than the meso-scale level.Communicated by L. Hagerman, Helsingør     

Colonization and early succession on artificial hard substrata by meiofauna

An experiment was undertaken at Farol Island, Brazil, to examine colonization of bare aluminium surfaces by microbes and meiofauna. It was hypothesized that a primary source of meiofaunal colonists was sediment resuspended during upwelling events, two of which occurred during the experiment. Microbial biofilms formed on the experimental substrata within 1 day, and continued to develop throughout the experimental period. Among meiofaunal groups copepods also appeared on the first day, and nematodes on the second. Meiofaunal community structure developed in three main phases: an initial phase of 2 days, characterized by low abundances of copepods; a second phase during the first upwelling period characterized by higher abundances of copepods and also by turbellarians; and a third phase from day 13 onwards characterized by relatively stable abundances of a range of taxa including copepods, cirripedes, nematodes and ostracods. Nematode assemblages also developed in three phases, but with different timings coinciding with upwelling events: an initial phase, from the beginning of the experiment to day 9, characterized by few species and low (or no) abundances; a second phase following the first upwelling characterized by moderate abundances of Chromadorina, Chromadorella, Daptonema and Euchromadora sp. 3; a third phase following the second upwelling period (from day 26 onwards) in which Daptonema disappeared and the assemblage was characterized by moderate to high abundances of Euchromadora (species 1 and 2) and Chromadorella. Although shifts in nematode assemblage structure coincided with upwelling events no evidence was found for sediments being the primary source of colonizers on the aluminium substrata, in contrast to our hypothesis.     

Productivity of bacteria and microalgae and the effect of grazing by holothurians in sediments on a coral reef flat

Bacterial productivity in sandy sediments on reef flats at Lizard Island, Great Barrier Reef was determined from the rate of incorporation of tritiated thymidine into DNA. The study was conducted during January 1982 and July 1983. A small diurnal increase occurred in sediments having a dense population of microalgae. Bacterial production was 120 to 370 mg C m^-2 d^-1 in summer on reef flats, which was equivalent to 30–40% of primary production by benthic microalgae. In winter, rates of primary production by benthic microalgae and secondary production by bacteria were about one-half to one-fifth of those in summer. There was much variation in production, due to patchiness in the distribution of benthic microbes, especially microalgae. Doubling times for the bacteria in surface sediment were 1 to 2 d in summer and 4 to 16 d in winter on the reef flats. These high productivity values for bacteria indicated that a net input of organic matter to the sediment was needed to support the growth of bacteria. Sediment bacteria thus have a very important role in transforming organic matter on the reef flats. Grazing by Holothuria atra depressed both primary production and bacterial production. It was estimated that these holothurians ate about 10 to 40% of bacterial carbon produced each day in summer, and thus have an important role in the carbon cycle. Harpacticoid copepods were numerically important components of the benthic meiofaunal community and probably had a significant impact on bacterial density as grazers.     

Intertidal zonation and seasonality of meiobenthos in tropical mangrove estuaries

Intertidal zonation and seasonality of tropical meiobenthic communities were examined within five mangrove estuaries along the northeastern coast (Cape York peninsula) of Australia from May 1985 to January 1986. Partial correlation analysis revealed that environmental cues such as temperature and sediment granulometry were the most important factors regulating the zonation patterns of meiofauna. Seasonality was greatly influenced by monsoonal rains. During austral summer, prolonged monsoonal rains occurred along the coast north of 18°S latitude (Hinchinbrook Island), resulting in increased river discharge and scouring of surface silts and clays, organic matter and bacteria from most tidal sediments. Despite scouring, meiofaunal densities increased in the summer wet season, probably due to warmer temperatures and the high resilience of meiobenthos to sediment disturbance. In mangrove sediments not subjected to torrential rains (Hinchinbrook Island), meiofaunal densities were highest in austral autumn and winter (sediment temperature: 23 to 27°C) and lowest in austral spring and summer (28° to 40°C). Turbellarians were the dominant meiofaunal group, accounting for 58 to 67% of total faunal densities which generally decreased with elevation in all of the estuaries. Meiofauna in tropical Australian mangroves, as in other organic-rich muds and in coral reefs, appear to exert little impact on microbial standing stocks when intercorrelated variables are accounted for. The abundances of hard-bodied meiofauna were low compared with temperate communities, lending further support to Moore's (1972) contention that tropical intertidal communities are subjected to greater physical stress than their temperate counterparts.     

Energy flow model of an oxygen-deficient estuary on the Swedish west coast

The estuary Byfjord (Sweden) is characterized by high primary production, a well developed meiofauna compared to the macrofauna, high epifaunal biomass, a low number of herbivorous copepods and a small fish stock. A simplified energy flow model of the ecosystem of the fjord is given. The energy transfer is approximated to 15%. About one-fourth-300 (metric) tons of carbon — of the annual primary production is suggested to be directly consumed and to produce 5 tons of zooplankton carbon and 40 tons of epifaunal (mainly Mytilus edulis) carbon. About 500 tons of carbon from the detritus pool are probably utilized in animal production. This amount will produce 5 tons of zooplankton carbon, 6 tons of meiofaunal carbon, and 3 tons of carbon from the benthic macrofauna. Production of fish is estimated at 0.3 ton carbon per year. M. edulis seems to be the only food resource in the fjord worth harvesting by man.     

A comparison of macrofaunal and meiofaunal distribution and standing stock across a rocky shore,with an estimate of their productivities

In 1984 and 1985 algal, macrofaunal and meiofaunal standing stocks were estimated on a exposed rocky shore along the west coast of False Bay, South Africa, using comparable, area-based sampling techniques. The shore supported a rich growth of algae, particularly in summer, when a maximum standing crop of 403 g m^-2 was recorded in the low shore. In winter, the largest component of macrofaunal biomass comprised the filter-feeding barnacle Tetraclita serrata, which attained 75 g m^-2 in the middle balanoid; but as a result of late recruitment and high mortality of this species, the summer shore was dominated by herbivorous gastropods, particularly Patella cochlear, which attained a maximum biomass of 66 g m^-2 on the low shore. Meiofaunal numbers and biomass were closely correlated to the distribution of algal turfs and associated trapped sediments. Numerically, the most important components of the meiofauna were nematodes and copepods, while the biomass was more evenly shared among foraminifera, minute gastropods, copepods and insect larvae. Numbers and biomass peaked in the lower balanoid during winter (1.9×10⁶ individuals, or 8.5 g m^-2). Macrofauna:meiofauna numbers and biomass ratios are presented for each zone and the distribution patterns discussed in relation to the conditons in each. Numerically, meiofauna exceed macrofauna by an overall ratio of 1:391, with values ranging from 1:556 in the lower balanoid to 1:18 in the Littorina zone. Macrofaunal biomass exceeds that of meiofauna in all zones by an overall ratio of 10:1, but values range from 2.1:1 in the upper balanoid to 48:1 in the middle balanoid. By incorporating turnover ratios extrapolated from the literature, mean annual productivity ratios have been calculated. These indicate that macrofauna account for 75% of total secondary production and meiofauna for 25%. Failure to incorporate meiofauna in analyses of energy flow on rocky shore ecosystems would thus lead to considerable errors. The possible trophic role of meiofauna in such systems is discussed.     

Predation on meiofauna by juvenile fish in a Western Mediterranean flatfish nursery ground

The authors investigated the gut contents of juveniles of three flatfish species (Buglossidium luteum, Arnoglossus thori and A. laterna) collected from Banyuls Bay, Western Mediterranean, from January 1981 through June 1982. Young solenettes, B. luteum, appear to be dependent on meiofauna, particularly harpacticoid copepods, as prey during their first year of benthic life. By comparison, the scaldfish, especially A. laterna, prey primarily upon peracarids from the beginning of their benthic life. Evidence of prey selection exists for the genera Photis (amphipod) and Longipedia (harpacticoid copepod). By regrouping these results with those of Bodiou and Villiers (1978/1979) on the goby Deltentosteus quadrimaculatus, and comparing them with other data from the literature, it appears that the impact of predation by juvenile fish is significant for some meiofaunal species, providing that they are actively selected by the predators, as is Longipedia scotti. Generally, however, predation impact on the meiofauna as a whole is weak.     

Mesoscale variability of organic matter composition in nw adriatic sediments

We investigated the spatial variability of sediment organic matter content and composition in three areas (A, B and C) of the Northwestern Adriatic Sea, subjected to a putative gradient of trophic state ( i.e. , increasing distance from the Po river outflow) in order to determine the appropriate sample size and replication. The analysis of the mesoscale variability was carried out comparing variability on the scale of meters ( i.e. among different deployments) with the variability observed on a scale of several kilometres ( i.e. among different sampling areas). Sediment samples, collected on April 1999, October 1999, April and October 2000, were analysed for chloropigment content (chlorophyll-a and phaeopygments) and protein, carbohydrate and lipid concentrations. Chloropigment, protein, carbohydrate and lipid concentrations were high, indicating that this system shares trophic conditions typical of highly productive environments. All organic matter components displayed a distribution independent from the increasing distance from the Po river outflow and a clear spatial variability, characterised by significant differences among different areas, but not among deployments. Carbohydrates were the biochemical compound displaying the highest spatial variability among the three areas. Chloropigment, protein, carbohydrate and lipid concentrations displayed also significant temporal changes. When spatial and temporal variability were compared, chlorophyll-a, phaeopigment and protein concentrations displayed a higher temporal than spatial variability. Conversely, for carbohydrates and lipids spatial and temporal variability was of the same order of magnitude. Organic matter composition displayed limited changes among areas, but a strong temporal variability. The results from the Adriatic sea suggest that analyses from sediments collected from a single deployment are sufficient for assessing organic matter concentration and composition over areas of several hundreds of square meters. However, for estimating organic matter composition over larger spatial scales ( i.e. miles) the identification of different sampling areas is needed.     

MESOSCALE VARIABILITY OF ORGANIC MATTER COMPOSITION IN NW ADRIATIC SEDIMENTS

We investigated the spatial variability of sediment organic matter content and composition in three areas (A, B and C) of the Northwestern Adriatic Sea, subjected to a putative gradient of trophic state ( i.e. , increasing distance from the Po river outflow) in order to determine the appropriate sample size and replication. The analysis of the mesoscale variability was carried out comparing variability on the scale of meters ( i.e. among different deployments) with the variability observed on a scale of several kilometres ( i.e. among different sampling areas). Sediment samples, collected on April 1999, October 1999, April and October 2000, were analysed for chloropigment content (chlorophyll-a and phaeopygments) and protein, carbohydrate and lipid concentrations. Chloropigment, protein, carbohydrate and lipid concentrations were high, indicating that this system shares trophic conditions typical of highly productive environments. All organic matter components displayed a distribution independent from the increasing distance from the Po river outflow and a clear spatial variability, characterised by significant differences among different areas, but not among deployments. Carbohydrates were the biochemical compound displaying the highest spatial variability among the three areas. Chloropigment, protein, carbohydrate and lipid concentrations displayed also significant temporal changes. When spatial and temporal variability were compared, chlorophyll-a, phaeopigment and protein concentrations displayed a higher temporal than spatial variability. Conversely, for carbohydrates and lipids spatial and temporal variability was of the same order of magnitude. Organic matter composition displayed limited changes among areas, but a strong temporal variability. The results from the Adriatic sea suggest that analyses from sediments collected from a single deployment are sufficient for assessing organic matter concentration and composition over areas of several hundreds of square meters. However, for estimating organic matter composition over larger spatial scales ( i.e. miles) the identification of different sampling areas is needed.     

A field colonization experiment with meiofauna and seagrass mimics: effect of time,distance and leaf surface area

From a conservation point of view, it is essential to know how fast an ecosystem can recover after physical disturbance. Meiofauna and especially harpacticoid copepods are abundant in seagrass beds and are therefore useful to study ecosystem recovery after disturbance. In the western Caribbean coast, a fragmented Thalassia testudinum seagrass bed was selected to conduct a colonization field experiment by means of plastic seagrass mimics. Meiofauna colonization, with special emphasis on harpacticoid copepods, was followed in relation to: (1) colonization time (2, 4, 6, 10, 14 and 21 days); (2) distance to source of colonizers (close and far series) and (3) leaf surface area to colonize (small, medium, large). Colonization was recorded after 2 days with average meiofauna densities of 480 ind/100 cm² (close) and 1350 ind/100 cm² (far) of leaf surface area, while on average 400 ind/100 cm² were collected from the natural seagrass plants. In this early phase, the meiofauna diversity was high, with on average 8 taxa. A longer period of colonization (21 days) showed an increased meiofaunal density and diversity (average density: 3220 ind/100 cm², 13 taxa). Increasing meiofauna colonization with time is probably related to the development of a biofilm making the leaf more attractive for meiofauna. The effect of distance was not so pronounced as that of time. Total absolute densities were highest in the far series (5 m away from natural seagrass patch), mainly because of nematode densities. Meiofauna diversity was lower in the far series than in the close series (at the border of the natural seagrass patch). A larger individual leaf surface area did not affect the overall meiofauna densities but had a significant positive effect on copepod densities. Larger surface areas promoted the presence of epiphytic copepod families such as Tegastidae and Dactylopusiidae. Overall, we found a rapid recovery of meiofauna in fragmented seagrass beds with primary colonizers (both nematodes and benthic opportunistic copepods) originating from the sediment and later colonizers as epiphytic copepods and their nauplii from the local seagrass regeneration pool.