Macrobenthic Assemblages Research Articles

Spatial distribution and assemblage structure of macrobenthos in a tidal creek in relation to industrial activities

The impact of petrochemical special economic zone activities on the health status of Jafari Creek was studied by assessing the changes in macroinvertebrate assemblages in nine sites during September 2006–January 2008. The relationship between spatial pattern of macroinvertebrate assemblages and ambient factors (i.e. water temperature, salinity, pH, dissolved oxygen, sediment grain size distribution, sediment organic content, heavy metals contents) was measured. Background enrichment indices, contamination factor and contamination degree, were used to assess the health status in the study area based on nickel, lead, cadmium and mercury contents of the sediments. The macrobenthic communities had a low diversity and were dominated by opportunistic taxa. The BIO-ENV analysis identified salinity, dissolved oxygen, pH and silt/clay content of sediments as the major environmental variables influencing the infaunal pattern. This suggests that management should attempt to ensure minimal disturbance to environmental variables underlying the spatial variation in macroinvertebrate assemblages. Background enrichment indices showed that the health of Jafari Creek has declined over time due to the constant discharge of heavy metals to the Creek system. These indices also identified a significant degree of pollution in the study area. The decrease in the ecological potential of Jafari Creek was best highlighted by the alteration in macrobenthic assemblages.

Impacts of maintenance channel dredging in a northern Adriatic coastal lagoon. II: Effects on macrobenthic assemblages in channels and ponds

Coastal lagoons are ephemeral habitats whose conservation requires human intervention, such as maintenance dredging of inner channels. Dredging can reduce the abundance of benthic species due to the removal of individuals with the sediment, modify sediment properties, and resuspend fine sediment, nutrients and pollutants, which can lead to eutrophication, hypoxic events and increasing toxicity. Both direct effects in the dredged channel and possible indirect effects in surrounding shallow areas could be expected. This study assesses the effects of the channel maintenance dredging, performed between October 2004 and August 2005, on the invertebrate assemblages both in channels and adjacent ponds in the northern Adriatic coastal lagoon of Pialassa Baiona. The lagoon is affected by eutrophication, chemical and thermal pollution from wastewater treatment and power plants. Three impacted sites were located in the dredged channel and three in the adjacent interconnected shallow water ponds, while three non-impacted sites were located in a channel and in a pond far from the dredged area. Replicate samples were collected from each site one time before and one time after the dredging operations. Despite the extent of the intervention, effects of the dredging on macrobenthic assemblages were detected only within the dredged channel, while in the surrounding ponds no clear and unequivocal effects were found. In particular the dredging could have promoted the increase of the abundance of the polychaete Streblospio shrubsolii in the southern and central parts of the dredged channel and the increase in abundance of the amphipod Corophium insidiosum in the northern side, compared to the controls. Instead, species diversity was reduced in the central and northern parts of the dredged channel. These effects on the macrobenthic invertebrate assemblages could be related to the observed changes of sediment characteristics, contamination and toxicity. Overall, direct effects on benthic assemblages in the dredged channels were more detectable than the possible secondary effects in the surrounding shallow ponds, where the higher spatial heterogeneity can mask any relevant effects.

Diversity and composition of macrobenthic community associated with sandy shoals of the Louisiana continental shelf

Along the Louisiana, USA continental shelf, sandy shoals are shallow, possibly oxygen-rich “islands” surrounded by deeper muddy deposits prone to hypoxia. Shoals also contain significant quantities of fine sand that may be mined in the future for coastal restoration. The ecological role of shoals remains poorly understood and we hypothesized that shoals provide critical habitat for benthic invertebrates. Using Ship Shoal as a model system, we assessed the diversity and structure of macrobenthic assemblages and how community structure varies with season and environmental parameters. High biomass (averaging 26.7 g m−2) and high diversity (161 species) of macrobenthos was found in 2006. Polychaetes (45%—72 species) and crustaceans comprised most of the species (28%—46 species); spionids and amphipods dominated the polychaete and crustacean groups respectively, both in terms of number of species and abundances. Sharp decreases in diversity, abundance and biomass occurred from spring to autumn. Species diversity and total abundance significantly increased with decreasing sediment grain size and increasing bottom water dissolved oxygen. Across seasons, mole crabs Albunea paretii and amphioxus Branchiostoma floridae typified the community and contributed most of the biomass. The polychaetes Nephtys simoni, Neanthes micromma, Dispio uncinata, Mediomastus californiensis and Magelona sp. A, the amphipod Acanthohautorius sp. A and the burrowing shrimp Ogyrides alphaerostris also contributed to variation in community composition. Cluster analyses quantified seasonal variation, mainly based on sharp decreases in abundance, as well as spatial differences in species composition oriented along both east–west and north–south gradients. Variation in benthic assemblages was correlated with water depth and sediment characteristics (mean grain size and percentage of gravel-sized shell debris). We conclude that Ship Shoal is an unrecognized biodiversity hotspot and a hypoxia refuge compared to the immediate surrounding area where the benthic community is affected by seasonal hypoxia events and we discuss how sand-mining may influence this community.

Temporal changes of a macrobenthic assemblage in harsh lagoon sediments

An opportunistic macrobenthic assemblage was studied from 2001 to 2003 in a central area of the Cabras lagoon (western Sardinia, Italy), known to be affected by environmental disturbances (i.e. organic over-enrichment of sediments, and episodic events of hypoxia/anoxia and sulphide development). We identified recurrent seasonal changes in this macrobenthic assemblage, with a general impoverishment in summer and a recovery in winter/spring. The nereids Neanthes succinea and Hediste diversicolor were found to replace the spionid Polydora ciliata as the most dominant species in the summer for 3 consecutive years. Occasional, unsynchronized appearances of small-sized deposit feeders, such as Tubificidae, Capitella cf. capitata, chironomid larvae and Hydrobia spp., were observed in winter/spring. We suggest that these changes are driven by the interplay of environmental conditions (worse in summer) with numerous biotic factors. This includes different tolerance levels of taxa to low oxygen concentrations and sulphides, variability in larval supply and post-larval transport, as well as competition for space and food between and within different functional groups, and facilitation through animal bioturbation and sediment reoxidation. A conceptual model is proposed to demonstrate how environmental conditions and biotic interactions may control the benthic assemblage in such a harsh lagoon environment.

Macrobenthos community structure and trophic relationships within active and inactive Pacific hydrothermal sediments

Hydrothermal fluids passing through sediments create a habitat hypothesized to influence the community structure of infaunal macrobenthos. Here we characterize the density, biomass, species composition, diversity, distributions, lifestyle, and nutritional sources of macroinfauna in hydrothermal sediments in NE and SW Pacific settings, and draw comparisons in search of faunal attributes characteristic of this habitat. There is increasing likelihood that seafloor massive sulfide deposits, associated with active and inactive hydrothermal venting, will be mined commercially. This creates a growing imperative for a more thorough understanding of the structure, dynamics, and resilience of the associated sediment faunas, and has stimulated the research presented here. Macrobenthic assemblages were studied at Manus Basin (1430–1634 m, Papua New Guinea [PNG]) as a function of location (South Su vs. Solwara 1), and hydrothermal activity (active vs. inactive), and at Middle Valley (2406–2411 m, near Juan de Fuca Ridge) as a function of habitat (active clam bed, microbial mat, hot mud, inactive background sediment). The studies conducted in PNG formed part of the environmental impact assessment work for the Solwara 1 Project of Nautilus Minerals Niugini Limited. We hypothesized that hydrothermally active sites should support (a) higher densities and biomass, (b) greater dominance and lower diversity, (c) a higher fraction of deposit feeders, and (d) greater isotopic evidence for chemosynthetic food sources than inactive sites. Manus Basin macrofauna generally had low density (o1000 ind. m

Sediment segregation by biodiffusing bivalves

The selective processing of sediment fractions (sand and mud; >63 μm and ≤63 μm median grain size) by macrofauna was assessed using two size classes of inert, UV-fluorescent sediment fraction tracers (luminophores). The luminophores were applied to the sediment surface in 16 m 2 replicated plots, defaunated and control, and left to be reworked by infauna for 32 days. As the macrofaunal assemblage in the ambient sediment and the control plots was dominated by the common cockle Cerastoderma edule, this species was used in an additional mesocosm experiment. The diversity, abundance and biomass of the defaunated macrobenthic assemblage did not return to control values within the experimental period. Both erosion threshold and bed elevation increased in the defaunated plots as a response to the absence of macrofauna and an increase in microphytobenthos growth. In the absence of macrobenthos, we observed an accretion of 7 mm sediment, containing ca. 60% mud. Image analysis of the vertical distribution of the different luminophore size classes showed that the cockles preferentially mobilised fine material from the sediment, thereby rendering it less muddy and effectively increasing the sand:mud ratio. Luminophore profiles and budgets of the mesocosm experiment under “no waves–no current” conditions support the field data very well.

The robustness of ecological indicators to detect long-term changes in the macrobenthos of estuarine systems

Accurate and reliable benthic quality indicators are in great demand following the recent developments and the strict time schedule for implementing the European Water Framework Directive. The Mondego estuary has experienced a progressive deterioration during the 1990s, followed by a partial ecological recovery due to restoration measures in 1997/1998. We have used the estuary as a model system to test the performance and robustness of a set of ecological indicators in highlighting the changes in the ecological state of intertidal areas. Over a period of 17 years (1985–2002), we calculated Margalef, Shannon–Wiener, Berger–Parker, Taxonomic Distinctness measures, AZTI’s Marine Biotic Index, Infaunal Trophic Index, and Eco-Exergy based indices and tested differences across periods characterised by different anthropogenic disturbance. We combined temporal data within three periods: before, during and after disturbance, based on progressive information on the changes in the extended type of anthropogenic disturbance. Indices were then compared with biological and abiotic descriptors (macroalgae, macrophytes, benthic macrofauna, nutrients concentration, sediment grain size and total organic carbon). We found great disparity in the indicators ability to capture temporal changes, showing distinct performances at each site. At the Zostera noltii site, only Margalef, Total Taxonomic Distinctness and the thermodynamically based indices captured temporal changes, despite giving higher values during the disturbance period. At the bare sediment site, Taxonomic Distinctness, ITI, Shannon–Wiener, Berger–Parker, AMBI and the TBI were able to distinguish between periods, in agreement with the differences observed analysing the macrobenthic assemblages. Furthermore, Taxonomic Distinctness was not robust enough to detect any temporal or spatial change. We thus suggest further research to understand the behaviour of ecological indicators, in view of their crucial importance for the management and protection of marine coastal areas.

Differences in soft-sediment macrobenthic assemblages invaded by Caulerpa taxifolia compared to uninvaded habitats

Caulerpa taxifolia is a habitat-forming green alga that has invaded several temperate regions worldwide. Although C. taxifolia covers large areas of soft-sediment habitat, little is known about its effects on soft-sediment invertebrate assemblages. We compared soft-sediment macroinver- tebrate assemblages in 2 estuaries in southeastern Australia invaded by C. taxifolia to examine 2 main predictions: (1) areas covered with C. taxifolia will have different assemblages compared to unvegetated sediment because infauna are inhibited but epifauna are facilitated, and (2) areas with C. taxifolia will have different assemblages compared to those with native seagrasses (Halophila ovalis and Zostera capricorni) because infauna are inhibited but epifauna are not. Multidimensional scaling and ANOSIM showed differences in invertebrate assemblages between all habitats. In C. tax- ifolia, infauna were less abundant and epifauna were more abundant compared to unvegetated sed- iment. However, when compared to native seagrasses, epifauna in C. taxifolia were more abundant than in H. ovalis in one estuary but less abundant than in Z. capricorni in another estuary, while infauna in C. taxifolia were less abundant than in both seagrass species. The consistently low infau- nal abundance in C. taxifolia, irrespective of infaunal feeding mode, suggests C. taxifolia impacts infauna generally. Examination of environmental factors potentially responsible for the low abun- dance of infauna indicated that differences in redox potential (and associated chemical changes) may explain patterns in abundance of infauna among habitats. Our findings indicate that invasion by C. taxifolia causes important changes to soft-sediment macroinvertebrate assemblages and suggest that infauna may be particularly vulnerable to invasion because of changes to sediment chemistry.

Variance estimate and taxonomic resolution: An analysis of macrobenthic spatial patterns at different scales in a Western Mediterranean coastal lagoon

The effects of taxonomic resolution on the variance estimates of macrobenthic assemblages were studied at four spatial scales in a Mediterranean coastal lagoon. The assemblages exhibited significant differences at all the investigated scales; however, spatial variability was mainly associated with the smallest and the largest scales. The decrease of taxonomic resolution (from species to family) was not related to a decrease of the overall variability and similar estimates of variance components were obtained using species and family resolution levels. The ordination models derived from species and family abundances were very similar both in terms of location and dispersion effect, while further aggregation to the class level began to alter the observed spatial patterns. In future studies aimed at assessing changes in the lagoon, resources derived from the cost reductions achieved using family level could be employed to plan more frequent surveys and/or to adopt complex spatial sampling designs with a high number of replicates.

Effects of mariculture on macrobenthic assemblages in a western mediterranean site

The effects of solid organic wastes from a marine fish farm on sediment was tested using macrobenthic fauna as biological indicators. Impact on benthic fauna was evaluated in the vicinity of a fish farm in the Tyrrhenian Sea (Western Mediterranean) between July 2001 and October 2002. Changes in benthic community structure were investigated using multivariate, distributional and univariate analyses (diversity indices, AMBI and M-AMBI). The results showed sharp disturbance of assemblages under the cages and no effects in the area more than 25 m from the cages. Sediment alterations were related to an increase in farmed biomass and its wastes, as well as to low current speed that allowed accumulation of organic matter on the sea floor. It was possible to follow the ecological succession from slightly altered assemblages to heavily polluted ones in the very short period of a single fish fattening cycle (15 months).

새만금 4호 방조제 연결 후 군산갯벌 대형저서동물군집 변화

With the reduction of tidal currents by the closing of the Saemangeun 4th dyke, sedimentary environments on the Gunsan tidal flat, the nearest inner flat from the 4th dyke, has been severely changed, which might affect macrobenthic assemblages on the habitats. In order to investigate changes in macrobenthic community structure on Gunsan tidal flat, field surveys were seasonally conducted at seven stations from April 2002 to November, 2005. Sedimentary facies on the study area were shifted into muddominant facies. The fine sediment has been greatly deposited on the tidal flat with accumulation of organic materials after closing the water passage of 4th dyke section. These drastic variations in environments gave rise to change in macrobenthic community structure. Since the closure of the 4th dyke, the number of species of macrobenthos has gradually decreased. And the filter feeders and sand-favored species such as Urothoe convexa, Macrophthalmus dilatatus, Umbonium thomasi, and Mactra veneriformis have been replaced by the deposit feeders such as Macrophthalmus japonicus and Ilyoplax pingi. MDS ordination based on Bray-Curtis similarity from forth-root transformed species abundance data showed that the macrobenthic communities have passed through three succession stages from 2002 to 2005. During the third stage of 2005 opportunistic species such as Prionospio japonica, Heteromastus filiformis and Sinocorophium sinensis increased in population on the tidal flat.

Comparative study based on sediment characteristics and macrobenthic communities in two Italian lagoons

The aims of this study were to analyse sediment characteristics and macrobenthic assemblages in two very close Italian coastal lagoons (Lesina and Varano) and to assess the different behaviour between the two basins and the relationship between sediment matrix and benthic organisms within and between the two lagoons. The comparative study was performed in July 2007 at 13 sampling sites in Lesina lagoon and 15 sites in Varano basin for sediment grain size, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and macrobenthic structure analyses. Both lagoons were generally dominated by fine-grained sediments (clay and silt components). The average contents of TOC and TN measured in Lesina was higher than in Varano (3.31% vs 2.52% for TOC and 5,200 microg.g(-1) vs 3,713 microg.g(-1) for TN); in contrast, the TP was lower (540 microg.g(-1) vs 620 microg.g(-1)). Based on macrobenthic community patterns, the central zone in Varano lagoon and the eastern area in Lesina lagoon were characterised by the lowest abundance (168.7 ind.m(-2) and 503.2 ind.m(-2), respectively) and by the lowest number of species, as highlighted by the diversity indices (Shannon-Wiener, H' range was 0.47-1.45 for Lesina and 0.00-1.68 for Varano; Margalef species richness, d range was 0.00-1.67 for Lesina lagoon and 0.00-2.38 for Varano basin). Ordination diagrams suggested an influence of marine and freshwater inputs on the sediment distribution in Varano lagoon and on macrobenthic assemblages in Lesina lagoon.

Comparing biodiversity effects among ecosystem engineers of contrasting strength: macrofauna diversity in Zostera noltii and Spartina anglica vegetations

Whereas it is well known that ecosystem engineers can have a large influence on biodiversity, underlying mechanisms are still not fully clear. We try to enhance insight by comparing biodiversity effects of two neighboring intertidal, clonal, ecosystem engineering plant species that modify the physical environmental parameters in a similar way, but with a different magnitude. Macrobenthic assemblages were compared between meadows of the seagrass Zostera noltii, small patches (≤0.5 m Ø) and large areas (≫5 m Ø) of the emergent halophyte Spartina anglica and the surrounding bare tidal mudflat (control). Multivariate analyses revealed that the mudflat benthic assemblage and Zostera meadow assemblage showed highest similarities, whereas the Spartina marsh assemblage showed the highest dissimilarity with these two areas. Whereas the descriptive nature of our study limits interpretation of the data, some clear patterns were observed. For all vegetated areas, species diversity was lower compared to the unvegetated mudflat, and we observed a strong shift from endo- towards epibenthic species, suggesting that increased above-ground habitat complexity may be a main driving process in our system. As there were no clear patterns related to feeding types, food availability/productivity appeared to be of minor importance in structuring the benthic assemblages. Nevertheless, animals were in general smaller in vegetated areas. Patchiness had a distinct positive effect on biodiversity.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

Human activities threat seashore communities in many areas of the world and their impacts on coastal ecosystem are a matter of increasing concern. Present study describes the anthropogenic disturbances on the rocky shore community structure by comparing the benthic communities of disturbed and non-disturbed areas in Sri Lanka where rocky shores remain virtually untouched so far by experimental studies. Impacts of human disturbances; trampling, handling and exploitation on the community structure of rocky macro benthic assemblages were tested in high-, mid- and low-intertidal area by stratified sampling method at Rumassala marine sanctuary and adjacent two localities at either side of the marine sanctuary, Galle and Unawatuna. Univariate measures, log series model and multivariate techniques were used to discriminate the communities with respect to the disturbances. Proximity of study localities and indistinguishable physicochemical parameters of sea surface water (temperature, Salinity, conductivity, dissolved oxygen and pH) indicated that overall environment of the study area was relatively uniform and changes in community structure was due to human disturbances. Human disturbances documented as visitor censuses by transect walk method lead to categorize the Rumassala as non-disturbed, Unawatuna as disturbed with Galle being of moderately disturbance. Community abundance showed a decreasing trend along with increasing disturbances, albeit community biomass, due to opportunistic algae species, increased in parallel to disturbances. Computed Index of disturbance revealed that macrofauna was very sensitive to the disturbances and increased disturbances reduced their competitive pressure on macroalgae, leading to outstanding macroalgal growth. Macroalgal domination in disturbed communities contributed to lessen the heterotrophic dominance in Galle and Unawatuna. 96 macrobenthic taxa were encountered from the study and Species richness, Shannon and Fisher’s diversity index showed decreasing trend with increasing disturbances. Moreover, initial rising slope of species accumulation curves for three communities indicated that community evenness was low in disturbed communities. The community compositions from dominant conservative species to fast growing opportunistic species were well described by the log series model, showing left skewed distribution. The SIMPER analysis further confirmed that most biomass dominant species in stress status were the opportunistic species such as Valoniopsis pachynema, Gracilaria cassa and Padina boerggesenii. Providing strong support to the results highlighted from univariate measures and log series model, multivariate cluster analysis and nMDS plots completely separated three communities at ordinal scale. This separation was further confirmed by one-way ANOSIM test with significantly higher (2.9%) similarity of study sites within each community. Present study indicated that, allowing less time for recovery, human activities created press-type disturbance on macro-benthic assemblages, and subsequent changes in community structure could be attributed to less suitable substrata. Study proposed that ecological stress is the best measured by multiple methods, and results from different approaches provide the robustness necessary to judge the reliability of the conclusion. Present study strongly supports the growing concern that human activities impact on intertidal assemblages all over the world by changing community composition. Present finding is a contribution to the published literature that is scarcer from tropical rocky shores.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

AbstractHuman activities threat seashore communities in many areas of the world and their impacts on coastal ecosystem are a matter of increasing concern. Present study describes the anthropogenic disturbances on the rocky shore community structure by comparing the benthic communities of disturbed and non-disturbed areas in Sri Lanka where rocky shores remain virtually untouched so far by experimental studies. Impacts of human disturbances; trampling, handling and exploitation on the community structure of rocky macro benthic assemblages were tested in high-, mid- and low-intertidal area by stratified sampling method at Rumassala marine sanctuary and adjacent two localities at either side of the marine sanctuary, Galle and Unawatuna. Univariate measures, log series model and multivariate techniques were used to discriminate the communities with respect to the disturbances. Proximity of study localities and indistinguishable physicochemical parameters of sea surface water (temperature, Salinity, conductivity, dissolved oxygen and pH) indicated that overall environment of the study area was relatively uniform and changes in community structure was due to human disturbances. Human disturbances documented as visitor censuses by transect walk method lead to categorize the Rumassala as non-disturbed, Unawatuna as disturbed with Galle being of moderately disturbance. Community abundance showed a decreasing trend along with increasing disturbances, albeit community biomass, due to opportunistic algae species, increased in parallel to disturbances. Computed Index of disturbance revealed that macrofauna was very sensitive to the disturbances and increased disturbances reduced their competitive pressure on macroalgae, leading to outstanding macroalgal growth. Macroalgal domination in disturbed communities contributed to lessen the heterotrophic dominance in Galle and Unawatuna. 96 macrobenthic taxa were encountered from the study and Species richness, Shannon and Fisher’s diversity index showed decreasing trend with increasing disturbances. Moreover, initial rising slope of species accumulation curves for three communities indicated that community evenness was low in disturbed communities. The community compositions from dominant conservative species to fast growing opportunistic species were well described by the log series model, showing left skewed distribution. The SIMPER analysis further confirmed that most biomass dominant species in stress status were the opportunistic species such as Valoniopsis pachynema, Gracilaria cassa and Padina boerggesenii. Providing strong support to the results highlighted from univariate measures and log series model, multivariate cluster analysis and nMDS plots completely separated three communities at ordinal scale. This separation was further confirmed by one-way ANOSIM test with significantly higher (2.9%) similarity of study sites within each community. Present study indicated that, allowing less time for recovery, human activities created press-type disturbance on macro-benthic assemblages, and subsequent changes in community structure could be attributed to less suitable substrata. Study proposed that ecological stress is the best measured by multiple methods, and results from different approaches provide the robustness necessary to judge the reliability of the conclusion. Present study strongly supports the growing concern that human activities impact on intertidal assemblages all over the world by changing community composition. Present finding is a contribution to the published literature that is scarcer from tropical rocky shores.

The macrobenthic community along a mercury contamination in a temperate estuarine system (Ria de Aveiro, Portugal)

Mercury is a widely distributed environmental pollutant and a toxic element to all living organisms. This study represents an attempt to evaluate its correlation with the macrobenthic community structure in a temperate estuarine system, the Ria de Aveiro (Portugal). The macrobenthic community structure showed significant differences along the mercury gradient. Overall, the increase of mercury contamination was associated with reduced total abundance, lower species richness, and dominance of tolerant taxa. The polychaetes Hediste diversicolor and Alkmaria romijni, and the isopod Cyathura carinata were associated with high levels of mercury in sediment, while the bivalves Scrobicularia plana, Cerastoderma edule and Abra alba showed higher density in lesser contaminated sites. Furthermore, highly contaminated sites showed substantially lower abundances of surface-deposit feeders and herbivores, and higher abundances of subsurface-deposit feeders and omnivores. Salinity was also a significant factor affecting the community, being responsible for seasonal variations in the macrobenthic assemblages.

Coralligenous habitat in the northern Adriatic Sea: an overview

AbstractThe rocky outcrops irregularly scattered in the sandy‐muddy sea bed of the Northern Adriatic, formed by a base rock and a superimposed concretion of vegetal and animal organisms, are considered an infralittoral coralligenous habitat, according to the most recent definition. In the last four decades, research has mainly concentrated on their geology because of the question of the origin of the base rock – very similar to beachrock – which has only recently been attributed to sedimentary cementation induced by methane seeps. Studies on their macrobenthic assemblages have also been published recently, but true comparisons among them are difficult because they mostly refer only to a few selected phyla or to short‐term observations. Very few papers deal with the whole of the animal and plant communities, including all taxonomic groups and the most important environmental variables. On the basis of the literature data concerning several outcrops in the Gulf of Venice, we suggest that the Adriatic reefs differ slightly from the classic deeper coralligenous assemblages around the Mediterranean coast because they have smaller concretions of algae builders. We also suggest that the Northern Adriatic coralligenous reefs are younger than the other reefs occurring in the Mediterranean Sea.

Spatial intertidal distribution of bivalves and polychaetes in relation to environmental conditions in the Natori River estuary, Japan

This paper aims to reveal spatial variation in the abundance of infaunal bivalves and polychaetes at different spatial scales (station: 200–800 m intervals; plot: 5–20 m), and to reveal environmental variables affecting the spatial distribution of animals in the Natori River estuary, Japan. We found six bivalve species and eight polychaete species from 52 plots at 12 stations. Nuttallia olivacea and Heteromastus sp. were found to be the most abundant species of bivalves and polychaetes, respectively. Assemblage patterns of bivalves and polychaetes were classified into five distinct groups. Substrata (silt-clay contents), salinity, and relative elevation were the variables found to affect the infaunal assemblage patterns. Chlorophyll a was not a significant variable, but benthic animals were absent at sites with extremely low chlorophyll a conditions. Macrobenthic assemblage patterns were different not only between stations but often differed between plots at the same station, reflecting the complex assemblage structure of benthic invertebrates. Detailing such animal–environment relationship is essential in understanding the potential food supply for estuarine fishes.

Effects of regular and irregular temporal patterns of disturbance on biomass accrual and species composition of a subtidal hard-bottom assemblage

Assessing patterns of species distribution and abundance is important to understand the driving processes of, and predict future changes in, biodiversity. To this date, ecological studies have been mainly designed to investigate the effects of the mean magnitude of predictor variables, although ecological factors naturally vary in space and time. In a nine month long field experiment, we tested the effects of different temporal patterns (regular, lowly and highly irregular) in biomass removal (=disturbance event) on the diversity, species composition, and biomass accrual of macrobenthic assemblages grown on 15 × 15 cm2 PVC-panels. For each pattern of disturbance, disturbance events were timed at three sequences to control for possible confounding effects with recruitment patterns. Disturbance intensity was kept identical among treatments. Assemblages developed in the absence of disturbance for 3 months prior to a 150-day manipulation period, during which the biomass from 20% of the panel area was removed at each of ten disturbance events. Additional undisturbed settlement panels were deployed in the field to assess monthly recruitment rates and species succession over a one year period. Disturbance (i) reduced biomass and total species cover, (ii) changed species composition during the first half of the manipulation period significantly, and (iii) was without effect on species richness and evenness. Irregular disturbance regimes enhanced the abundance of the ascidian Ciona intestinalis, biomass accrual, and total species cover of assemblages relative to the regular disturbance regime, but had either no or only transient effects on diversity and species composition, respectively. Neither the degree of irregularity in disturbance nor the sequence of disturbance events affected any of the response variables significantly. Recruitment of species was strongly seasonal with almost only diatoms recruiting during winter, while recruitment was most intense during summer. Our results suggest that the temporal patterns of predictor variables might be of low explanatory power for the variance of responses in communities with seasonal recruitment patterns that are exposed to a high level of disturbance. Thus the need to include temporal patterns of predictor variables in experimental designs may depend on community dynamics and the characteristics of the process under investigation.

Effects of offshore platforms on soft-bottom macro-benthic assemblages: A case study in a Mediterranean gas field

The exploitation of fossil fuels in the Mediterranean Sea will likely lead to an increase in the number of offshore platforms, a recognized threat for marine biodiversity. To date, in this basin, few attempts have been made to assess the impact of offshore gas and oil platforms on the biodiversity of benthic assemblages. Here, we adopted a structured experimental design coupled with high taxonomic resolution to outline putative effects of gas platforms on soft-bottom macrofauna assemblages in the North Ionian Sea. The analysis was based on a total of 20,295 specimens of 405 taxa, almost entirely identified at species level. Multivariate and univariate analyses showed idiosyncratic patterns of assemblage change with increasing distance from the platforms. Potential reasons underlying such inconsistency are analyzed and the view that structured experimental monitoring is a crucial tool to quantify the extent and magnitude of potential threats and to provide sound baseline information on biodiversity patterns is supported.