Structure of macrobenthic communities in relation to historical patterns of dredging in the Brisbane River estuary (original) (raw)
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Some Effects of Dredging on Populations of Macrobenthic Organisms
1974
Populations of epi- and infauna were studied from 10 mo before to 11 mo after a navigation channel was dredged through a small, shallow lagoon. A new sampler which penetrated 20·30 cm into the substratum was used. Current velocities and sedimentation patterns were changed due to an altered distribution of tidal currents, although flushing time was not appreciably altered. Values of certain particulate and dissolved nutrients changed after dredging, but no correlation was observed between animal populations and fluctuations in nutrients. Significant reductions in standing crop figures and species and specimen numbers occurred in both the bay and the dredged channel. Mercenaria mercenaria populations were reduced, but there was no evidence of mass mortality. Recovery of biomass in the channel was affected by sediment composition, but seasonal and sediment type variations were not significant in the bay as a whole. Goose Creek had a high predredging epi- and infaunal standing crop esti...
2001
The present work is part of an environmental assessment undertaken in the Sado estuary (Southern Channel and Mitrena Peninsula), western coast of Portugal, on February 1999 prior to maintenance dredging works. The macrofauna communities in the study area are generally rich and abundant. A single exception was found: a sampling site in the Mitrena area, with extreme impoverishment, probably related to sediment characteristics, i.e., fluid mud, unfavourable to the establishment of individuals. A comparative analysis of these macrofauna results to previous data from 1986 showed that this biological component had suffered no significant changes, especially as far as the most characteristic species. Although the Southern Channel had been dredged in 1995, no clear signs of such operation were apparent in the present survey.
Journal of Experimental Marine Biology and Ecology, 2006
The effects of dredging on the benthic communities in the Noosa River, a subtropical estuary in SE Queensland, Australia, were examined using a 'Beyond BACI' experimental design. Changes in the numbers and types of animals and characteristics of the sediments in response to dredging in the coarse sandy sediments near the mouth of the estuary were compared with those occurring naturally in two control regions. Samples were collected twice before and twice after the dredging operations, at multiple spatial scales, ranging from metres to kilometres. Significant effects from the dredging were detected on the abundance of some polychaetes and bivalves and two measures of diversity (numbers of polychaete families and total taxonomic richness). In addition, the dredging caused a significant increase in the diversity of sediment particle sizes found in the dredged region compared with elsewhere. Community composition in the dredged region was more similar to that in the control regions after dredging than before. Changes in the characteristics of the sedimentary environment as a result of the dredging appeared to lead to the benthic communities of the dredged region becoming more similar to those elsewhere in the estuary, so dredging in this system may have led to the loss or reduction in area of a specific type of habitat in the estuary with implications for overall patterns of biodiversity and ecosystem function.
Marine Pollution Bulletin, 2006
The long-term effects of marine aggregate dredging on near-shore benthic assemblages are still largely unknown, despite a global increase in demand for, and extraction of, marine aggregates. This study assessed the state of recovery of polychaete assemblages in Botany Bay, temperate NSW, Australia, at sites dredged for aggregate material more than 10 years previously. Sedimentary and faunal samples were collected from impact sites in Botany Bay, and from reference sites in nearby Pittwater estuary. This study was based on, and included data from, a study conducted by the Australian Museum at the same sites in the 2 years following cessation of dredging. Abundance, species richness and evenness of polychaetes, as well as overall polychaete assemblage structure, were compared between localities over time.
Marine Biology, 2006
Phylum-level meta-analysis was applied to 192 samples from a variety of dredgings disposal and relocation sites around the coast of England and Wales. No consistent relationship was found between the disturbance status of macrobenthic communities within disposal sites and the nature or amount of dredgings disposed. Differences between samples within and outside disposal sites were generally smaller than differences between different sites and various patterns of impact were detected. It is concluded that dredgings disposal has two contrasting impacts on benthic communities. One, associated with organic enrichment, leads to communities dominated by annelids and nematodes. The other, associated with intense physical disturbance, favours large motile or armoured forms, such as bivalve molluscs and crustaceans. These effects may act antagonistically, and in a phylum-level meta-analysis may cancel each other out. None of the samples examined from offshore disposal sites was grossly disturbed, in terms of the proportional contribution to production from different phyla, and overall most samples ranged from moderately disturbed to undisturbed. The ecological impacts associated with the intertidal placement of material (beneficial use schemes) were comparable to those observed for the conventional sea disposal sites.
Iheringia Serie Zoologia, 2023
The aim of the present study was to investigate the effect of dredging activities on the structure of the macrobenthic community of a port complex in São Luís do Maranhão (2°S, Brazil). Sampling was performed on four occasions: pre-dredging, dredging 1 (25% of the material dredged), dredging 2 (75% of the material dredged) and post-dredging. Total mean density was 430.8 ± 55.0 ind/m², with 147.76 ± 280.82 ind/m² at pre-dredging, 161.90 ± 285.67 ind/m² at dredging 1, 53.83 ± 72.15 ind/m² at dredging 2 and 67.29 ± 72.58 ind/m² after dredging, revealing a reduction during dredging 2. The most representative groups were Polychaeta, Oligochaeta, Crustacea and Mollusca. Lumbrineris sp. (Polychaeta) was present in all sampling periods and was the dominant species. Richness and Shannon diversity of the species were higher in the pre-dredging and post-dredging periods, with reductions during the dredging activities (dredging 1 and 2). Principal component analysis revealed a correlation with granulometry and heavy metals in the sediment. The dredging activities led to a reduction in the macrobenthic community. Moreover, post-dredging recovery was insufficient for the recovery of the community.
Marine Pollution Bulletin, 2011
A meta-analysis approach was used to assess the effect of dredging induced changes in sediment composition, under different conditions of natural physical disturbance, for the structure and function of marine benthic macrofaunal communities. Results showed the sensitivity of macrofaunal communities increased as both the proportion of gravel increased and the level of natural physical disturbance decreased. These findings may be explained by the close association of certain taxa with the gravel fraction, and the influence of natural physical disturbance which, as it increases, tends to restrict the colonisation by these species. We conclude that maintaining the gravel content of surface sediments after dredging and, where practicable, locating extraction sites in areas of higher natural disturbance will minimise the potential for long-term negative impacts on the macrofauna. Crown
The Port of Brisbane disturbance of the sedimentary environment at the mouth of the Brisbane River was assessed at the inner and outer river and in two periods following disturbance: 2 weeks (March) and 8 months (November) after dredging. Sediments in the inner river were dominated by silt, while in the outer river sediment were sandier. Total and organic carbon (TC and Corg) and total Kjeldahl nitrogen (TKN) were higher in the inner river, which could be an indication of higher organic loads. Ammonia (NH 4 -N) and nitrate (NO 3 -N) sediment profiles indicated suboxic conditions and denitrification in the inner river, as well as oxic conditions and nitrification at the outer river. Total meiofauna abundance and taxa composition was similar in both, the inner and outer river locations. For some individual taxa however, the suboxic sedimentary conditions in the inner river were adverse. Copepods, polychaetes and sipunculids abundance were lower in the inner river, and negatively correlated with fine sediments and high organic loads, and positively correlated with oxic conditions. Furthermore, the port strategic dredging operations had negative effects on the meiofauna of both locations. The abundance of most of the taxa in both the inner and outer river locations during March was lower at sites inside the dredged navigational channel than at the sites outside the channel. The meiofauna rapidly re-colonise the disturbed sediments as by November the abundances inside the channel considerably increased. The composition of the meiofaunal and nematode assemblage from different sites and months showed significant differences. The nematode assemblage at the mouth of the Brisbane River dominated by Sabatieria and Metalinhomoeus was characteristic of disturbed sediments. Résumé : Perturbation de la méiofaune et des caractéristiques biogéochimiques du sédiment en milieu portuaire à l'embouchure de la rivière de Brisbane, Australie orientale. La perturbation du sédiment, produite par l'activité du Port de Brisbane, a été mesurée dans et en dehors de l'embouchure de la rivière de Brisbane pendant deux périodes : 2 semaines (mars) et 8 mois (novembre) après l'activité de dragage. Les sédiments dans l'embouchure étaient très fins et dominés par le limon, dominés par des sables grossiers en dehors. Les taux de carbone total (TC), carbone organique (Corg) et azote (TKN) étaient plus élevés dans l'embouchure, ce qui indique un apport plus élevé de matière organique. Les profils d'ammoniaque et nitrate indiquaient des conditions hypoxiques dans l'embouchure avec de la dénitrification. En dehors cependant, ils indiquaient des conditions oxiques avec de la nitrification. La composition taxonomique et l'abondance totale
Marine Biology, 2006
Hydraulic dredging targeting the bivalve Chamelea gallina in the northern and central Adriatic Sea has been taking place for over 30 years. In the period 2000-2001, 73 commercial dredgers harvested the resource within the sandy coastal area of the Ancona Maritime District (central Adriatic Sea). Despite this, no study aimed at investigating the impact of the fishery on the macrobenthic community of the area has ever been carried out. Sampling was done at 6 monthly intervals in an attempt to relate the impact of hydraulic dredging to different levels of fishing intensity. Data regarding two depth strata (4-6; 7-10 m) were analysed separately by means of permutational multivariate analysis of variance. The results revealed an overall condition of moderate disturbance within the benthic community, especially so within the 4-6 m depth stratum. The response of the benthic community to varying intensities of fishing activity was rapid, occurring within 6 months. Differences in the response of benthic community to differing intensities of fishing activity were found between the two depth strata considered. Significant differences in multivariate location of the benthic community were revealed between the three disturbance levels in both depth strata. Differences in multivariate dispersion were detected above a threshold level of fishing intensity, only within the shallow community. Differences were found between depth strata relating to species diversity and evenness, with significant differences between levels of fishing intensity being evident only within the 4-6 m depth stratum. The results em-phasised that, even in a benthic community that is typical of a moderately disturbed environment, the effects of fishing on community structure were still discernible over and above the natural variation.