Sublittoral soft bottom communities and diversity of Mejillones Bay in northern Chile (Humboldt Current upwelling system)

The macrozoobenthos of Mejillones Bay (23°S; Humboldt Current) was quantitatively investigated over a 7-year period from austral summer 1995/1996 to winter 2002. About 78 van Veen grab samples taken at six stations (5, 10, 20 m depth) provided the basis for the analysis of the distribution of 60 species and 28 families of benthic invertebrates, as well as of their abundance and biomass. Mean abundance (2,119 individuals m^?2) was in the same order compared to a previous investigation; mean biomass (966 g formalin wet mass m^?2), however, exceeded prior estimations mainly due to the dominance of the bivalve Aulacomya ater. About 43% of the taxa inhabited the complete depth range. Mean taxonomic Shannon diversity (H′, Log e) was 1.54 ± 0.58 with a maximum at 20 m (1.95 ± 0.33); evenness increased with depth. The fauna was numerically dominated by carnivorous gastropods, polychaetes and crustaceans (48%). About 15% of the species were suspensivorous, 13% sedimentivorous, 11% detritivorous, 7% omnivorous and 6% herbivorous. Cluster analyses showed a significant difference between the shallow and the deeper stations. Gammarid amphipods and the polychaete family Nephtyidae characterized the 5-m-zone, the molluscs Aulacomya ater, Mitrella unifasciata and gammarids the intermediate zone, while the gastropod Nassarius gayi and the polychaete family Nereidae were most prominent at the deeper stations. The communities of the three depth zones did not appear to be limited by hypoxia during non-El Niño conditions. Therefore, no typical change in community structure occurred during El Niño 1997–1998, in contrast to what was observed for deeper faunal assemblages and hypoxic bays elsewhere in the coastal Humboldt Current system.     

The benthic foraminiferal communities of the northern Adriatic continental shelf

Off the Po Delta in the northern Adriatic, three different foraminiferal associations were identified in the fraction >0.125 mm of 25 sediment samples. The first association concerns sample stations between depths of 5 and 13.5 m in the shallow, nutrient-rich belt and is characterised by dominant Ammonia beccarii. The second occupies the 29.5–38.5-m-deep, nutrient-rich zone of clay-rich sediment, where inputs from the Po are concentrated, and is dominated by Nonionella opima. The third association, in the 21–46-m-deep and nutrient-poor zone, is dominated by Textularia agglutinans. The same distribution of communities was obtained using total associations (living and dead specimens) and biocenosis (stained individuals). The good correspondence with the foraminiferal distributions described in the past indicates that, in spite of the occurrence of anoxic and dysoxic events, the environmental state in the northern Adriatic may be considered stable.     

Summer fish communities in northern Gulf of Mexico estuaries: Indices of ecological condition

We used fish community data from trawl samples collected from >100 estuaries, bayous, and coastal lagoons of the Louisianan Biogeographic Province (Gulf of Mexico) to develop indicators of large-scale ecological condition. One data set, from which we derived reference values for fish community indicators, was based on bottom trawl samples collected from 367 randomly located sites during the summers of 1992–1994. A second trawl data set with similar geographic scope from 2000 to 2004 was used to test the robustness of the indicators derived from the reference data set to new data. We constructed a fish community index (FCI) from three basic indicators: number of species per trawl, total abundance per trawl, and an index of trophic balance among three common feeding guilds. The FCI was not correlated with salinity over a range from freshwater to marine and hypersaline conditions (0–52 psu). Direct correlations between the index and environmental variables generally were weak, although some were significant (p < 0.05). The FCI was negatively correlated with water clarity (secchi depth), water column depth, and sediment toxicity; correlations of the FCI with pH, sediment organic carbon, and sediment silt + clay content were positive. There was a hyperbolic relationship between dissolved oxygen and maximum values of the index, and no significant correlation with watershed land cover at the whole-estuary or estuary-complex scale. Values of all indicators increased between the two time periods. The FCI is a broad indicator of ecological condition for estuaries within the Louisianan Province, with data aggregated at scales ranging from large estuaries to the entire region. Sample density was insufficient to judge performance of the indicators or index at smaller scales.     

The use of a biotic index (Bentix) in assessing long-term effects of dumping coarse metalliferous waste on soft bottom benthic communities

The biotic index Bentix [Simboura, N., Zenetos, A., 2002. Benthic indicators to use in Ecological Quality classification of Mediterranean soft bottom marine ecosystems, including a new biotic index. Mediterr. Mar. Sci., 3 (2), 77–111] developed for the classification of ecological status of zoobenthic communities was tested in a Mediterranean coastal area (Aegean Sea, N. Evvoikos gulf, Greece) subject to coarse metalliferous waste discharge. The residues in the form of slag are the byproducts of the smelting procedure of a local ferronickel plant and are discharged in a permitted area 8 km from the shore. This practice adopted over the last 36 years has led to the formation of a thick underwater deposit of slag on the sea bottom. A decade of monitoring resulted to a long series of data on macrozoobenthos communities in the area. Application of the Bentix and other indices on the data has revealed the long-term impact of dumping on the benthic communities and the potential of the indices used to assess the community health. Among the indices tested, Bentix index succeeded in assessing the long-term trends of decline or recovery of the community health. The index proved efficient in detecting differences of the ecological status of the communities attributed to the transferring of the core of the dumping activity over the area studied, as validated by the geophysical data provided.     

Ecological status of some Finnish rivers evaluated using benthic diatom communities

The applicability of some diatom methods to quality assessment of differenttypes of Finnish rivers was compared using dominant taxa of diatomcommunities and nutrient level estimations using Trophic Diatom Index(TDI) and a new Phosphorus Diatom Equation (PDE) [Tot. P_calc (g l^-1) = 39 – 0.278 ol-% – 0.117 olme-% – 0.346me-% – 0.006 meeu-% + 1.193 eu-%; n = 97; r² = 0.742;SE = 17.4]. The overall quality estimations were done by Index ofPollution Sensitivity (IPS) and by Generic Diatom Index (GDI); limit valuesfor quality classes are proposed.     

Ecosystem services transcend boundaries: estuaries provide resource subsidies and influence functional diversity in coastal benthic communities

Background

Estuaries are highly productive ecosystems that can export organic matter to coastal seas (the ‘outwelling hypothesis’). However the role of this food resource subsidy on coastal ecosystem functioning has not been examined.

Methodology/Principal Findings

We investigated the influence of estuarine primary production as a resource subsidy and the influence of estuaries on biodiversity and ecosystem functioning in coastal mollusk-dominated sediment communities. Stable isotope values (δ¹³C, δ¹⁵N) demonstrated that estuarine primary production was exported to the adjacent coast and contributed to secondary production up to 4 km from the estuary mouth. Further, isotope signatures of suspension feeding bivalves on the adjacent coast (Dosinia subrosea) closely mirrored the isotope values of the dominant bivalves inside the estuaries (Austrovenus stutchburyi), indicating utilization of similar organic matter sources. However, the food subsidies varied between estuaries; with estuarine suspended particulate organic matter (SPOM) dominant at Tairua estuary, while seagrass and fringing vegetation detritus was proportionately more important at Whangapoua estuary, with lesser contributions of estuarine SPOM. Distance from the estuary mouth and the size and density of large bivalves (Dosinia spp.) had a significant influence on the composition of biological traits in the coastal macrobenthic communities, signaling the potential influence of these spatial subsidies on ecosystem functioning.

Conclusions/Significance

Our study demonstrated that the locations where ecosystem services like productivity are generated are not necessarily where the services are utilized. Further, we identified indirect positive effects of the nutrient subsidies on biodiversity (the estuarine subsidies influenced the bivalves, which in turn affected the diversity and functional trait composition of the coastal sediment macrofaunal communities). These findings highlight the importance of integrative ecosystem-based management that maintains the connectivity of estuarine and coastal ecosystems.     

Interactions in soft bottom benthic communities: Quantitative aspects of behaviour in the surface deposit feedersPygospio elegans (Polychaeta) andMacoma balthica (Bivalvia)

The surface deposit feeding speciesPygospio elegans andMacoma balthica are dominant members of many sandy bottom communities of northern boreal regions. The feeding mode of both species and the tube-building ofP. elegans are assumed to affect community structure by interactions with other species. The weight of tubes ofP. elegans varied between 2 and 13 g DW/100 cm² at the two stations investigated and during the year, which is equivalent to 230–1500 cm of tubes per 100 cm² of sediment surface. Sediment stability may be affected directly or indirectly by the amount of tubes present.M. balthica shows a linear relation between the maximum size of particles which can be inhaled and animal length. In Kiel Bay, particles>0.5 mm are out of the range of this species. In summer, the potential feeding area (PFA) of aP. elegans population at one station in Kiel Bay was 1.8 times the available surface area. The PFA of three different populations ofM. balthica in Kiel Bay exceeded the available surface area by factors of 2.6, 2.7, and 3.2. These findings indicate strong intra- and interspecific competition for food. Additionally, the feeding of both species may strongly affect the recruitment of benthic species via pelagic larvae. Experiments are proposed to evaluate the significance of the investigated behavioural aspects for community structure. AWI Publication No. 393     

Ecological assessment criteria for restoring anadromous salmonid habitat in Pacific Northwest estuaries

Restoration of estuarine habitats is essential for the conservation and recovery of depressed Pacific salmon populations. However, assessing the functions of recently restored habitat poses a number of problems because of the transitory occurrence of salmonids in any one location. We propose assessment criteria and metrics that are based on the habitat’s capacity, opportunity, and realized function to enhance survivability of juvenile salmon. Because of the paucity of data relating capacity and opportunity attributes to realized function (e.g. growth, consumption rate, survival), there continues to be a need for manipulative experiments to assess the developmental status of restoration sites. Such a self-monitoring approach of letting the fish diagnose the ecological state of restoration would effectively address the small-scale, site-specific assessment goals and criteria, but ignores the larger-scale issues relating to the ability of diverse salmon species and life histories to occupy estuarine habitat landscapes. If coastal restoration is going to contribute the recovery of anadromous salmonid populations, a landscape perspective is fundamental to restoration planning, implementation, and particularly assessment.     

Baseline study of soft bottom benthic assemblages in the Bay of Santander (Gulf of Biscay)

The Bay of Santander constitutes one of the most important estuarine areas in northern Spain (Gulf of Biscay) which has been significantly stressed by sewage discharges. However, an improvement in the environmental quality of the bay is expected once the new sewer system comes into operation. The evaluation of such an evolution needs to be contrasted with the current situation, established in specific baseline studies. For this purpose, a field study was carried out on the soft bottom assemblages of the estuary in spring of 1998. At each station, the benthic fauna abundance, grain size, organic matter, carbon, nitrogen, phosphorus and heavy metals concentrations were analysed. The community structure and the physical and chemical characteristics of the sediment reflected the higher impacts both near the points of discharges and in the low water exchange zones, whereas those areas showing higher tidal flows presented an acceptable quality. High heavy metal concentrations for Cd, Hg, Pb and Zn indicated contamination of industrial sources in several areas of the Bay. This information allows to establish a reference situation in order to improve the design of a specific monitoring program for this area.     

Competitive hierarchies in marine benthic communities

Summary Patterns of competitive displacement by over-growth were examined in communities of sessile organisms in the low intertidal zone at three sites in Washington state and Alaska. Cruotose invertebrates and algae can be arranged into a hierarchy such that species of lower competitive rank rarely overgrow any higher ranking species. Erect and solitary species show a wide range of competitive abilities, but whether they fall into a strict hierarchy is unknown. Few of the solitary or erect species occupy substantial amounts of space in the communities examined.An approximate competitive hierarchy is well established in middle to high intertidal areas dominated by mussels, fleshy algae, and barncles, and has been an important concept in developing both an intuitive understanding and specific mathematical models of the dynamics of benthic marine communities. In particular, lower ranking species in such communities are thought to depend upon predation or chronic disturbance to the dominants to avoid competitive displacement. An alternative viewpoint, proposed on the basis of nonstransitive competitive relationships observed in cryptic encrusting communities on the undersides of coral plates, is that specific competitive loops or networks allow the coexistence of a number of competitors. Although the growth forms and higher taxa represented in the low intertidal bear some similarity to those in the cryptic coral reef community, there is little evidence of ecologically important competitive loops in the intertidal. A reanalysis of data from cryptic reef communities suggests that they also do not depart substantially from a competitive hierarchy, although there appear to be many more cases of local reversals in the outcome of competition. It is suggested that the ecological importance of departures from a strict hierarchy depends upon the competitive rankings of the participants, with departures involving competitively dominant species likely to contribute much more to community structure than those involving opportunistic species.     

Landscape assessment of tree communities in the northern karst region of Puerto Rico

The northern karst of Puerto Rico is a unique formation that contains one of the island’s largest remaining forested tracts. The region is under ever-increasing human pressure, but large portions of it are being considered for conservation. Forest classification of the region is at a coarse scale, such that it is considered one vegetation type. We asked whether there were distinct tree assemblages which would necessitate targeted conservation strategies to ensure their protection. We examined tree species and communities across the region at three different major topographic positions along mogotes, or haystack-shaped hills. We found distinct tree communities on hilltops and valleys, with significantly more non-native species in valleys and significantly more endemic species on hilltops and hillsides. At a landscape level, we identified at least four different communities within each topographic position. Two mogote top communities were separated geographically (west and south) within the region, while two others co-occurred in the east-central part of the region. Mogote side and valley communities were less distinct geographically. Temperature, elevation, and precipitation were important variables in separating some communities, suggesting that abiotic stress may play an important role in the distribution of some species. In contrast, the lack of geographic separations of other communities suggested that variables such as soil conditions, land use and biotic interactions such as dispersal limitation may also be important. Conservation planning strategies should target the south, west, and east-central areas that harbor distinct mogote top plant communities to ensure protection of the widest range of tree species and communities in the karst region.     

The benthic ecology of river estuaries entering the Severn Estuary

The fauna of the Rivers Avon, Usk and Wye was similar to that for soft sediment in the Severn Estuary. It was dominated by Nereis diversicolor, Corophium volutator, Aiacoma balthica and oligochaetes. Maximum densities of Corophium and Macoma were higher than in the main estuary, while that of Nereis was similar. Distributions of dominant species showed gradients along river length and across river profile. These are discussed.     

Species size distributions in Arctic benthic communities

In most subtidal soft-sediment faunal assemblages there is a trough in the species size distribution separating the macrofauna and meiofauna. To examine the hypothesis that this may be maintained by the avoidance of competition between macrofaunal adults and settling larvae, samples were taken from around Svalbard, an area where most macrofaunal species have either lecithotrophic or direct development. At three contrasting sites, bimodality of the species size spectrum was conserved. However, it is proposed that the adult-larval interaction hypothesis should not be rejected as low endemism in the fauna of the study area suggests its species size spectrum probably reflects evolutionary processes outside rather than within the Arctic. Received: 13 May 1996/Accepted: 26 July 1996     

Species size distributions in marine benthic communities

Summary Species body size distributions from eight temperate benthic communities show a highly conservative pattern with two separate lognormal distributions, corresponding to the traditional categories of meiofauna and macrofauna. The meiofaunal mode occurs at a dry body weight of 0.64 g and the macrofaunal mode at 3.2 mg, with a trough between them at 45 g. It is suggested that there is a particular body size at which meiofaunal life-history and feeding traits can be optimised, and another for macrofaunal traits. As size departs in either direction (larger or smaller) from these optima, fewer species of the same size are able to co-exist. The split occurs at 45 g because many life history and feeding characteristics switch more or less abruptly at about this body size, compromise traits being either non-viable or disadvantageous. Meiofauna and macrofauna therefore comprise two separate evolutionary units each with an internally coherent set of biological characteristics.The expression of this conservative pattern is modified by water depth: the proportion of macrofauna species increases from intertidal situations to deeper water, and it is suggested that mechanisms of resource partitioning and diversity maintainence in the meiofauna and macrofauna are affected differentially by sediment disturbance. Salinity does not affect this proportionality, and so does not differentially affect mechanisms for maintaining species diversity in any particular size category of animals. Meiofauna species size distributions may be modified in sandy sediments because of physical impositions on interstitial or burrowing lifestyles.Brief discussion of some implications of these observations includes speculations on the larval ecology of macrofauna, on gigantism in Antarctic invertebrates, and on the benthic Sheldon spectrum.     

Benthic macrofaunal communities in intermittent estuaries during a drought: Comparisons with permanently open estuaries

Drought conditions have prevailed in many areas of NSW since 2002. On the mid-north coast, below-average rainfall resulted in reduced riverine flows and the extended closure of intermittent estuaries within the Solitary Islands Marine Park. Patterns of structure of benthic infaunal communities were evaluated at the height of the drought to determine if they differed between closed, intermittent estuaries and permanently open estuaries within the region. Replicate van Veen grab samples were taken in the upper, mid- and lower reaches of six intermittent and three permanently open estuaries and sieved to retain the macrofauna. A range of physico-chemical measures was also taken at each sampling time. Multivariate analyses of assemblage data revealed a significant difference between the structure of the two estuary types and also among estuaries within each type. Differences between estuary types were attributable to small differences in the abundance of a number of taxa but also to the absence of the amphipod Urohaustorius metungi from most of the intermittent estuaries. In contrast, these small amphipods dominated communities in the lower reaches of the permanently open estuaries. Physico-chemical variables were highly variable among estuaries and were not strongly correlated with assemblage patterns. Correlations with catchment size were the strongest and, as most of the intermittent estuaries in the region are smaller than the permanently open estuaries, this confounds the interpretation of assemblage patterns in this preliminary study. In order to differentiate between the effects of catchment size and entrance status, the same estuaries need to be resurveyed during periods when at least some of the intermittent estuaries are open.     

Spectral discrimination of coral reef benthic communities

Effective identification and mapping of coral reef benthic communities using high-spatial and -spectral resolution digital imaging spectrometry requires that the different communities are distinguishable by their spectral reflectance characteristics. In Kaneohe Bay, Oahu, Hawaii, USA, we collected in situ a total of 247 spectral reflectances of three coral species (Montipora capitata, Porites compressa, Porites lobata), five algal species (Dictyosphaeria cavernosa, Gracilaria salicornia, Halimeda sp., Porolithon sp., Sargassum echinocarpum) and three sand benthic communities (fine-grained carbonate sand, sand mixed with coral rubble, coral rubble). Major reflectance features were identified by peaks in fourth derivative reflectance spectra of coral (at 573, 604, 652, 675 nm), algae (at 556, 601, 649 nm) and sand (at 416, 448, 585, 652, 696 nm). Stepwise wavelength selection and linear discriminant function analysis revealed that spectral separation of the communities is possible with as few as four non-contiguous wavebands. These linear discriminant functions were applied to an airborne hyperspectral image of a patch reef in Kaneohe Bay. The results demonstrate the ability of spectral reflectance characteristics, determined in situ, to discriminate the three basic benthic community types: coral, algae and sand. Accepted: 12 January 2000     

Commensalism between a boring mytilid bivalve and a soft bottom coral in the Upper Eocene of northern Italy

The mytilid bivalveBotula cordata (Lamarck) from the Upper Eocene of the Venetian region, northern Italy, bored into live soft bottom corals, which reacted by forming a calcareous interseptal filling around the borehole. A chemical etching mechanism is inferred from the presence of “etch marks” on the borehole walls. The association with free-living corals capable of counteracting burial by sedimentation or accidental overturning enhanced the survival potential of the bivalve on the soft bottoms. Commensalism with soft bottom corals appears to have evolved convergently at least three times within the Mytilidae, but is unknown among other bivalves.     

Uncertain biotic and abiotic interactions in benthic communities

We analyze marine benthic communities at different sites in Skagerrak with the purpose of understanding the role of exogenous and endogenous factors in explaining the species' temporal dynamics. The previous finding that the dynamics of these species communities are mainly driven and synchronized by environmental (temperature) forcing was only weakly supported when analyzing single-species dynamics at five sites where four of the species were present every year. There was no consistent pattern in how the temperature affected the realized per capita growth rate, either across species at a given site, or among sites for a given species. Furthermore, there was no net-interaction from the community on a given species strong enough to give rise to second-order dynamics. However, when implementing a Multi Dimensional Scaling (MDS) analysis and incorporating all sampling sites and species -we found that the different communities clustered in relation to depth, hence, communities at the same depth were more "similar" than communities at different depth. Revealing the underlying interactions shaping these marine benthic communities is a challenge that calls for an array of various and complementary approaches.     

Ecological regime shifts in salinised wetland systems. II. Factors affecting the dominance of benthic microbial communities

This paper is the second in a pair investigating potential mechanisms for ecological regime change in salinising wetlands. The first paper in this series focused on the responses of the salt-tolerant submerged macrophyte community to salinity. In this second paper, we investigated some of the environmental conditions required for initiation and dominance of benthic microbial communities using a combination of experimental and observational data. Two experiments were carried out. One investigated the importance of prior establishment of benthic microbial communities on their ability to maintain prevalence over macrophyte colonisation (‘persistence’ experiment), while the other investigated hydrology and its effect on sediment perturbation, potential nutrient release and subsequent benthic microbial community establishment (‘flooding’ experiment). The ‘persistence’ experiment measured the biomass of benthic microbial communities and emergence of macrophytes from sediments kept either wet or dry for 4 weeks then flooded at a range of salinities. Benthic microbial biomass was similar across all of the salinities tested (15, 45 and 70 ppt), with a slight increase at higher salinities, suggesting that none of these limited benthic microbial community development. Pre-wetting of sediments usually increased benthic microbial community biomass and reduced macrophyte germination, but the latter was attributed to the presence of anoxic sediments rather than the increased benthic microbial community biomass. Germinating macrophytes emerged through benthic microbial communities or dense heterotrophic bacterial blooms, demonstrating that they could become dominant even when another community was already established. Field data supported these results, suggesting that the development of benthic microbial communities is not limited by salinity alone, but includes other factors, such as the water regime. In the ‘flooding’ experiment, the largest differences in nutrient concentrations ultimately lay between the pre-wet and pre-dry treatments (due to the greater release of nutrients and development of anoxia in the latter) rather than those subjected to fast versus slow flooding. In response to this, highest benthic microbial community biomass was in treatments with pre-wet sediment, corresponding with lower phytoplankton biomass.