Fractal properties of spatial distribution of intertidal benthic communities

We studied the spatial distribution of intertidal macrozoobenthos, microphytobenthos (diatom algae) and sediments at scales from decimeters to kilometers using an index of spatial homogeneity, D _I. Sediments were found to be randomly distributed, making up a mosaic of silty and sandy sites. On the contrary, the estimated spatial variability of macrofauna within all the scales up to 5500 m depended upon neither extent (total area covered) nor grain (finest spatial resolution) but only their ratio. We treat this as evidence of statistical self-similarity (fractal property) of the pattern. For diatoms, spatial heterogeneity of community structure was also self-similar in the range from 0.25 to 75 m (within a single bight). At larger scales, microalgae showed a combination of patchy structure with pronounced gradient along the shoreline from brackish-water to marine flora. Thus, fractal properties of both groups became manifested at scales corresponding to their mean body size. The ranges of fractal patterns were approximately equal to 10³–10⁵ if measured in body size units. We suggest that fractal-like spatial structures may be a general feature of communities, and speculate on the nature of such patterns. Received: 16 February 1999 / Accepted: 30 December 1999     

Modelling spatial distribution of the Croatian marine benthic habitats

Within the framework of the 3-year project “Mapping the habitats of the Republic of Croatia” the marine benthic habitats of the entire Croatian maritory were mapped. The supralittoral and the mediolittoral were mapped as a function of the coastal lithology and the presumed levels of human impact (both in scale of 1:100,000). The infralittoral was mapped on the basis of spatial modelling (using neural networks as a modelling tool, data about habitats collected by fieldwork as the independent variable for training and testing the model, and the digital bathymetrical model, the distance from coast, the second spectral channel of Landsat ETM+ satellite image and the sea bottom sea temperature, salinity and current magnitude, as dependent variables). The circalittoral and the bathyal were mapped by overlapping and reinterpretation of the existing spatial databases (bathymetry and lithology) within the framework of the raster-GIS.     

Spring and autumn spatial distribution of zooplankton carbon requirement across the Mediterranean Sea

Zooplankton represents a key contributor to the ocean biological pump through its consumption of sinking and suspended carbon. A specific and highly sensitive method to evaluate zooplankton carbon requirement from the sinking flux is through the estimation of the activity of the electron transport system. The present study was carried out from samplings in 2006, and it was focused on the spatial 200–0?m zooplankton carbon demand across 24 sampling stations, along the Mediterranean Sea, from the island of Crete to the Strait of Gibraltar. Its potential day/night variability was evaluated. The zooplankton composition, abundance and biomass were investigated. The carbon demand per unit zooplankton biomass indicates geographical and diel differences among the sampling stations. A higher mean carbon demand was seen for the western Mediterranean with respect to the eastern Mediterranean, which can be justified through the observed ratio of gelatinous:crustacean taxa and the water temperatures recorded. Higher carbon demand was measured in samples collected during the dark hours. The relation to the presence and abundance of actively migrating euphausiids and copepods was discussed. A comparison with data from another of our study carried out in the same study area but in another seasonal period was done.     

Modelling spatial distribution of hard bottom benthic communities and their functional response to environmental parameters

In this study we analyzed and modelled spatial distribution of hard bottom benthic communities in the Lagoon of Venice, and used the model to derive functional response of these communities to changing environmental conditions.     

Spatial distribution of copper in relation to recreational boating in a California shallow-water basin

The overall effect of the number of boats on the copper (Cu) levels in the water column and sediment, along with their spatial variability within Shelter Island Yacht Basin (SIYB), San Diego Bay, California was examined. We identified a horizontal gradient of increasing dissolved Cu and Cu in sediment from outside to the head of SIYB which was coincident with the increasing number of boats. Spatial models of Cu distribution in water and sediment indicated the presence of ‘hotspots’ of Cu concentration. From outside to the head of SIYB, dissolved Cu ranged from 1.3 μ g L^?1 to 14.6 μ g L^?1 in surface water, and 2.0 μ g L^?1 to 10.2 μ g L^?1 in bottom water. Cu in sediment exceeded the Effect Range Low of 34 mg kg^?1 (i.e. where adverse effects to fauna may occur), with a peak concentration of 442 mg kg^?1 at the head of the basin. Free Cu⁺⁺ in surface water was several orders of magnitude higher than in sediment porewater. High-resolution data of Cu species together with probability maps presented in this paper will allow managers to easily visualise and localise areas of impaired quality and to prioritise which areas should be targeted to improve Cu-related conditions.     

Polychaete assemblages along a rocky shore on the South Adriatic coast (Mediterranean Sea): patterns of spatial distribution

This study reports on the distribution of polychaete assemblages along a depth gradient from 5 to 25 m, along a stretch of rocky coast near Otranto (South Adriatic sea, Italy). Three depths were sampled in May and November 2000. At each depth three sites (about 100 m apart) were sampled by scraping off three replicate quadrats of 20×20 cm. The experimental design enabled identification of across- and along-shore spatial patterns of variation of polychaete assemblages. A total of 4,168 specimens, belonging to 152 taxa were collected. Multivariate analysis showed that the polychaete assemblages differed significantly among depths with the clearest differences between the shallowest sites (5 m) and the deeper ones (15–25 m). A considerable source of variation among sites at each level of the shore was also exhibited by the analyses, with the greatest differences among sites within depths recorded at 5 m. The species most contributing to the differentiation of assemblages among depths and sites within each depth were identified. Some potential causes of the observed differences are hypothesized and discussed. The importance of quantitative observation to provide the context for studying the underlying ecological processes is also stressed.Communicated by R. Cattaneo-Vietti, Genova     

Temporal and spatial components of variability in benthic recruitment,a 5-year temperate example

Deployment of artificial substrata is a common method of investigating early community development and recruitment, but rarely are such experiments of long enough duration to include even year time scales. We placed replicate, machined-slate panels (15×15 cm) in the intertidal and at depths of 6 and 12 m at two sites of differing flow rate at Lough Hyne, SW Ireland. These were serially replaced every 30–60 days for a period of 5 years (1997–2002), except in the intertidal (2000–2002). The number and identity of all recruits were recorded. Recruitment varied over several orders of magnitude both on temporal and spatial scales. The greatest source of variability was between the intertidal (with few species or recruit numbers) and the subtidal zones (many species, some with thousands of recruits per panel per 30 days). Highest levels of recruitment occurred at the low-flow site (Labhra Cliff). Here, recruitment was dominated by the serpulid polychaete, Pomatoceros sp., reaching ~4000 individuals per panel per 30 days. Highest species richness occurred, however, at the high flow site (Whirlpool Cliff). At this site more colonial forms (e.g. bryozoans) settled. Season was found to be the dominant pattern explaining subtidal recruit and species number variability. Year, however, was the dominant temporal pattern explaining change in diversity (Shannon–Wiener H). In space, depth explained most variability of recruit numbers, whereas site explained more variation in species richness. Both these spatial factors contributed similarly to variability of diversity (H). Recruitment has long been known to vary considerably over large spatial scales, such as with latitude and isolation, but we that show changes of a similar magnitude in recruitment can occur across small spatial scales. Individual taxa showed varied temporal patterns of recruitment including continuous, regular seasonal fluctuations and irregular pulses in particular years.     

A mathematical model for the distribution and abundance of benthic algae in a Norwegian fjord

A mathematical model has been developed to study the distribution and abundance of benthic algae species in a Norwegian fjord. The main forcing functions are the physical factors which have well defined gradients in this area, but biotic interactions are also accounted for in the model.The distribution of algae along vertical transects in the intermediate fjord area has been simulated, and the observed distribution is reproduced fairly well. This indicates that the major factors determining the equilibrium elevation between intertidal and subtidal vegetations in this area are adequately represented in the model.Based on observations in a fjord branch with a high level of freshwater influx and polluted by heavy metals, assumptions are made of the combined influence of these contaminants on growth characteristics of the species considered. The resulting effects on community development and community patterns are simulated. For a certain level of contamination, the decrease in abundance, community development rate and species separation have been determined. It is also shown that the fluctuations in biomass during a year are more pronounced than under unaffected conditions.The relative importance of external growth regulating factors and self-shading is demonstrated for different degrees of community development, and we have indicated that this may be an important factor in the assessment of transient and long-term responses to “natural” and man-made influences on the shore-line vegetation.One of the main problems during model development was the formulation of the interaction function for factors influencing growth parameters. Several alternatives were examined.The differences between the most frequently used forms were small with respect to abundance and not very large with respect to possible changes in distribution. It was noted that even by including only the most limiting factor at each instant, (Liebig's form) a high percentage of the potentially limiting factors did actually limit growth during periods of the year.The model is intended as a working tool for the studies of changes in the shore-line vegetation caused by man-made interferences like heavy metal and oil pollution, and we believe that the results presented demonstrate that it can successfully be used for this purpose.     

Pigment composition and size distribution of phytoplankton in a confined Mediterranean salt marsh ecosystem

Pigment composition and size distribution of phytoplankton were analysed in a group of Mediterranean salt marshes, where hydrology is dominated by sudden inputs during sea storms, followed by long periods of confinement. These marshes are characterized by a low inorganic–organic nutrient ratio, and inorganic nitrogen is especially scarce due to denitrification. Nutrients were the main factor affecting phytoplankton biomass, while zooplankton grazing did not control either phytoplankton community composition, or their size distribution. The relative abundance of the different phytoplankton groups was analysed by correspondence analysis using the pigment composition measured by high-performance liquid chromatography (HPLC) and analysed with the CHEMTAX programme. In this analysis, phytoplankton pigment composition was correlated with two nutrient gradients. The first gradient was the ratio of nitrate–total nitrogen (TN), since the different phytoplankton groups were distributed according to their eco–physiological differences in nitrogen uptake. The second gradient was correlated with total nutrient loading. Biomass size distributions frequently showed a lack of intermediate sized nanophytoplankton (2.5–4 μm in diameter), and the importance of this lack of intermediate sizes correlated with dinoflagellate biomass. These results suggested that in confined environments, where nutrients are mainly in an organic form, dinoflagellates take advantage of their mixotrophy, by competing and grazing on smaller phytoplankters simultaneously.     

Fish feeding on mobile benthic invertebrates: influence of spatial variability in habitat associations

Patterns of habitat association and foraging were examined for a group of tropical goatfishes (family Mullidae) that feed on mobile benthic invertebrates at Lizard Island (Great Barrier Reef). All goatfish possess barbels that disturb the substratum during feeding. Foraging methods were examined for the six most common species and used in conjunction with data on habitat associations to estimate the distribution and potential impact on the benthic invertebrate assemblage of foraging-related disturbance. Particular species exhibited broad habitat associations which differed little over two surveys (January 1989, January 1990). All species showed different preferences for the substrata they foraged. Preferences for substrata exhibited by the most common reef-associated species, Parupeneus multifasciatus, differed among locations separated by 1 km, between sites 150 m apart, and between depths (shallow and deep). Habitat preferences changed with ontogeny. Based on their habitat associations and foraging preferences, species were divided into habitat generalists and specialists. Specialists associated primarily with soft sediments. Habitat generalists, such as P. multifasciatus and P. cyclostomus, are likely to have an impact on their mobile invertebrate prey that is localised, diffuse and transitory, making any experimental analysis difficult and expensive. Habitat specialists form a guild of fishes with complementary feeding modes that efficiently exploit soft sediments and are more amenable to experimental manipulation. Experiments designed to detect the impact of foraging by these fishes must be repeated at different locations and times and must account for depth differences in foraging pressure.     

The shallow-water macrobenthos of a northern New England estuary

In November 1973 the benthic macrofauna of two shallow-water areas in the lower Sheepscot River estuary (New England, USA) was quantitatively sampled. Numerical classification of the data, in both the normal and inverse modes, produced 4 site-groups and 7 species-groups. Each site-group was characterized by at least one of the species-groups. The fauna of the site-groups differed in several community parameters, particularly the patterns of dominance, but it was not possible to correlate these differences with any of the several extrinsic factors measured. A factor, or factors, related to water-column stability is the probable overriding ecological determinant of the observed community patterns. Comparisons with an earlier investigation in 1955 demonstrate dramatic changes in density, dominance and species composition.Contribution No. 78033 of the Bigelow Laboratory for Ocean Sciences.     

Flowering of the seagrass Posidonia oceanica in a north-western Mediterranean coastal area: temporal and spatial variations

Sexual reproduction in Posidonia oceanica (L.) Delile is likely to be highly variable both in space and time. However, there has been little effort to identify at what spatial scale variability exists in the distribution and abundance of reproductive shoots or the magnitude of these variations. Such information is important for elucidating several aspects of the reproductive strategy of this species. Here, by using a reconstructing technique, I estimated the rate at which flowering events occurred over the last decades in three P. oceanica meadows along the coastline of the north-western Mediterranean (Italy). Then, variation in inflorescence frequency (i.e. the percentage of shoots that flowered in a particular year of the total number of shoots present in the sample in that year) was examined on a hierarchy of spatial scales, ranging from a few metres to meadows separated by tens of kilometres over a 3-year period. Separate analyses were also conducted to examine the patterns of spatial variability of several plant characteristics (i.e. shoot age and density of vegetative shoots) that may influence the timing of flowering. In total, ten reconstructed flowering events were recorded during the period 1983–1999. Despite the similar climatic conditions experienced in the three meadows surveyed, no inflorescence scars were found in one meadow. In the other two meadows, the flowering rate fluctuated considerably from year to year (0–26%), and simultaneous flowerings were detected only in 3 years (1993, 1994 and 1995). The pattern of spatial variability in the inflorescence frequency varied among years. An investigation of the flowering events recorded along the north-western Mediterranean coast reveals that in the studied period flowering also occurred across a broad range of meadows. Therefore, flowering could be a far more widespread phenomenon in this sector of the Mediterranean basin than previously thought. Analysis of variance showed significant variation in 1993 at the mean inflorescence frequency on very small scales (metres to tens of metres), whereas variation was not found at any of the scales investigated in 1994 and 1995. Overall, variation in the inflorescence frequency within individual meadows (65–93%) was at least an order of magnitude greater than that among separate meadows (0.5–19%). Patterns of spatial variation in the plant characteristics examined did not reflect those of flowering. It may be hypothesised that internal rhythms of populations, in conjunction with changes in environmental conditions, which are consistent over relatively large spatial (kilometres), are involved in the control of flowering induction. Environmental heterogeneity (in terms of nutrient availability) on a very local scale (metres to tens of metres) and intrinsic factors might affect the distribution of reproductive shoots within P. oceanica meadows.Communicated by R. Cattaneo-Vietti, Genova     

Fine-scale distribution of juvenile Atlantic and Mediterranean loggerhead turtles (Caretta caretta) in the Mediterranean Sea

Loggerhead turtles nesting in the Mediterranean Sea exhibit remarkable genetic structuring. This paper tests the hypothesis that young loggerhead turtles from different rookeries do not distribute homogeneously among the major Mediterranean foraging grounds, due to a complex pattern of surface currents. We extracted long fragments of mitochondrial DNA from 275 stranded or bycaught juvenile turtles from six foraging grounds (Catalano-Balearic Sea, Algerian basin, Tyrrhenian Sea, Adriatic Sea, northern Ionian Sea and southern Levantine Sea). We used a Bayesian mixed-stock analysis to estimate the contributions from rookeries in the Mediterranean, the North-west Atlantic and Cape Verde to the studied foraging grounds. Differences were found in the relative contribution of juvenile turtles of Atlantic and Mediterranean origin to each foraging ground. A decreasing proportion of Atlantic juveniles was detected along the main surface current entering the Mediterranean, with a high prevalence of turtles from eastern Florida in the Algerian basin and lower numbers elsewhere. In regard to the turtles of Mediterranean origin, juveniles from Libya prevailed in central and western Mediterranean foraging grounds other than the Algerian basin. Conversely, the Adriatic Sea was characterised by a large presence of individuals from western Greece, while the southern Levantine Sea was inhabited by a heterogeneous mix of turtles from the eastern Mediterranean rookeries (Turkey, Lebanon and Israel). Overall, the distribution of juveniles may be related to surface circulation patterns in the Mediterranean and suggests that fisheries might have differential effects on each population depending on the overlap degree between foraging and fishing grounds.     

Littoral infauna of a West African estuary: An oil pollution baseline survey

Littoral infaunal density was recorded from December 1983 to October 1984 throughout the Bonny Estuary in the Niger delta, Nigeria, to provide a baseline for the monitoring of oil pollution. Results on the most abundant faunal elements, polychaetes and the fiddler crabUca tangeri L., are presented. In the upper reaches, polychaete density peaked in January — due to increases in the abundance of the principal species. In the lower reaches, euryhaline and stenohaline polychaetes exhibited maxima in April to July and lesser peaks earlier and later in the year. There were no wide fluctuations in the middle reaches, due to the lack of truly estuarine species — exceptU. tangeri which was most abundant between December and April. Features such as the salinity/substrate zones, faunistic components and reduction of species upstream, are typical of estuaries elsewhere. Others, including the low abundance of all species in the middle reaches, and the occurrence of species minimum far downstream of 5 S, are atypical, and pollution from the Okrika oil terminal, oil from outboard engines, and substrate disturbance by shipping, are suggested as causative factors.     

Control of the intertidal distribution of Gastroclonium coulteri in monterey bay,California, USA

Transplantation and selective removal experiments were carried out on Gastroclonium coulteri (Harvey) Kylin at Mussel Point, California, USA, between June, 1975 and May, 1979. Transplanted G. coulteri survived higher in the intetidal than the natural population, except during March and April when extreme low tides, and resultant severe desiccation, occurred during the daytime. Transplants survived, but did not grow, in low intertidal tidepools. Transplants to the shallow subtidal survived and increased in overall length. Transplants to the deeper subtidal zone died within 1 month. Transplants from the subtidal to the intertidal survived, but decreased in size. At the upper boundary of G. coulteri, removal of Gigartina papillata and Rhodoglossum affine resulted in a decrease in the percent cover of Gastroclonium coulteri. Presence of the other algae thus had a beneficial rather than competitive effect on G. coulteri. Removal of G. coulteri resulted in an increase in the percent cover of G. papillata and R. affine, demonstrating that the lower boundary of these two species is set by competition with G. coulteri. At the lower boundary of Gastroclonium coulteri, removal of Phyllospadix spp. or Prionitis lanceolata led to an increase in percent cover of G. coulteri. Removal of G. coulteri did not lead to an increase in percent cover of Phyllospadix spp. Thus, the lower boundary of G. coulteri is set by competition with Phyllospadix spp. or Prionitis lanceolata, but the upper boundary of Phyllospadix spp. is not set by competition with G. coulteri. The results support the hypothesis that upper boundaries tend to be set by physical factors (here, exposure at low tide), and lower boundaries tend to be set by biological factors (here, competition).     

Response of benthic foraminifera to heavy metal contamination in marine sediments (Sicilian coasts,Mediterranean Sea)

To examine the suitability of benthic foraminifera and their test deformations as bioindicators of pollution in coastal marine environments, we studied foraminifera and metal concentrations in 72 marine sediment samples, collected from the inner shelf along the Sicilian coast (Gulfs of Palermo and Termini) and on the south-eastern coast of Lampedusa Island. These areas are characterised by different environmental conditions. On the basis of pollution sources and foraminiferal assemblages, we recognised different zones in the Gulf of Palermo. The most polluted zones showed high metal concentrations, and low diversity of benthic foraminifera with species typical of stressed environments. By contrast, the lowest polluted zones showed a high population density and the highest percentages of epiphytes. Epiphytes were abundant where a Posidonia oceanica meadow was present and decreased in the most polluted zones. Sediments of the Gulf of Termini and Lampedusa exhibited high percentages of benthic foraminifera typical of well-oxygenated waters and low concentrations of metals, with the exception of sites located near sewage outfalls and harbour areas. Furthermore, even though deformed tests are commonly known in natural stressed environmental conditions, this study shows that in the most polluted zones, benthic foraminifera were characterised by the highest percentages of deformed individuals.     

Effects of UVB radiation in a microbenthic community of a marine shallow-water sandy sediment

The role of ambient and enhanced ultraviolet-B radiation (UVB; 280 to 315 nm) in a natural sand-associated microbenthic community was studied in a 3-week experiment by incubating intact sediment cores from a shallow bay in an outdoor flow-through system with 27 aquaria. After sampling of initial cores, the remaining cores (one per aquarium) were given one of three treatments: no, ambient, and moderately enhanced UVB, and sampled, nine at a time, after 5, 12, and 19 d. The response of the community was studied by analysing algal and meiofaunal composition and biomass, chlorophyll a content, composition of pigments and fatty acids, and content of UV-absorbing compounds (state variables), as well as carbon fixation and allocation, and bacterial productivity (rate variables). Among rate variables, significant effects of UVB-treatments were found for carbon fixation and allocation, while bacterial productivity was not affected. For state variables, a significant response was observed for the composition of microalgae and fatty acids, and for chlorophyll a content. The effect of treatments was mainly observed as differences in development with time (two-way analysis of variance, treatment × time interaction). Towards the end of the experiment, the no-UVB treatment most often differed from one or both of the two treatments with UVB exposure, the latter showing lower values. There were marked successional changes in the community, irrespective of treatment. The microalgal community changed from being dominated by coccoid cyanobacteria and epipsammic diatoms to a dominance of epipelic diatoms and filamentous cyanobacteria. The pattern of carbon allocation, as well as an increased C/N ratio of the sediment, suggested limitation of growth, perhaps by nutrients, at the end of the experiment. This may possibly have acted synergistically with UVB exposure to create the treatment effects. The new knowledge gained from our experiment is that ambient UVB can exert a stress on the function of sand-associated microbenthic communities in shallow waters and that this effect coincides with structural differences in the community. More experiments in natural or semi-natural systems are needed to allow better prediction of microbenthic community-level responses to UVB. Received: 11 November 1997 / Accepted: 12 June 1998     

Spatial distribution of the infaunal benthic communities of the Ría de Muros,north-west Spain

Benthic samples were collected at 13 stations in the Ría de Muros, north-west Spain. There are three major communities: (1) in the southern and outer part of the ría, an Amphiura filiformis—Thyone fusus community, inhabiting sandy sediments with low organic content; (2) in the middle part of the ría, and Amphiura chiajei—Maldane glebifex community, inhabiting muddy sediments that are not anoxic (sulphide not detected); (3) in Muros Bay and the inner part of the ría, a Spiochaetopterus costarum community, inhabiting anoxic sediments with high organic content. Biomass is very high (up to 46.2 g ash-free dry wt) in the first two communities. In the Spiochaetopterus costarum community, biomass and diversity are much lower, probably because of oxygen deficiency.