Responses of marine fouling communities to sewage abatement in Kaneohe Bay,Oahu, Hawaii

The development of marine fouling communities was followed as part of a sewage abatement study in Kaneohe Bay (Oahu, Hawaii). Panels immersed near the outfall during sewage discharge were dominated by dense mats of blue-green algae and diatoms. This mat was significantly lighter at this station when sewage did not flow into the bay, and it never developed on panels within the same sector of the bay but away from the influence of the outfall. Taxonomic diversity, and the frequency of filamentous algae and the serpulidHydroides elegans were reduced near the outfall during discharge. It is suggested that this reduction in diversity and abundance of certain key foulers is due to competitive exclusion by the dense blue-green and diatom mats, and is not a direct effect of the sewage effluent.     

Impact of sewage on the distribution,abundance and community structure of rocky intertidal macro-organisms

The biological effects of a low-volume domestic sewage discharge were studied near Wilson Cove, San Clemente Island, California (USA), from February to June, 1972. There were fewer species and less cover near the outfall (7 macro-invertebrates, 17.6%; 13 macrophytes, 91.7%) than in nearby “unpolluted” control areas (9 macroinvertebrates, 9.2%; 30 macrophytes, 103.4%). The outfall biota was less diverse than that of the controls, as shown by 5 different diversity indices. A great reduction in community stratification (spatial heterogeneity) and, hence, community complexity occurred near the outfall; this reduction in stratification was primarilly due to the absence of Egregia laevigata, Halidrys dioica, Sargassum agardhianum and Phyllospadix torreyi. These were replaced in the mid-intertidal near the outfall by a low turf of blue-green algae, Ulva californica, Gelidium pusillum and small Pterocladia capillacea, and in the lower intertidal by Serpulorbis squamigerus covered with Corallina officinalis Var. chilensis. A statistically-based determination of assemblages or groups of organisms (i.e., cluster analysis) revealed 3 discrete outfall and 3 discrete control area groups; 3 assemblages contained samples from both areas. The distributional patterns of these groups indicate that near the outfall the degree of dilution of discharged sewage is more important in regulating zonation than is tidal height. The enhancement of the suspension feeder Serpulorbis squamigerus and the omnivores Ligia occidentalis, Pachygrapsus crassipes and Anthopleura elegantissima in the outer fringe of the outfall plume hypothetically is due to their ability to utilize sewage as a food source. A critical effect of the outfall may be to decrease environmental stability thereby favoring rapid-colonizers and more sewage-tolerant organisms. The outfall macrophytes were characterized by relatively higher net primary productivities, smaller growth forms, simpler and shorter life histories, and most were components of early successional stages.     

Sewage discharges in oceanic islands: effects and recovery of eulittoral macrofauna assemblages

Sewage discharges are among the most common anthropogenic stressors on rocky shores. However, studies on benthic invertebrates’ responses to sewage pollution on insular assemblages are rare. In order to fulfil this gap, (i) the effects of sewage pollution and (ii) the recovery capacity of eulittoral insular assemblages were examined. The study was conducted on Terceira Island (Azorean Archipelago, Portugal), in four distinct areas: one impacted area (outfall in operation), one post-impacted area (decommissioned outfall) and two undisturbed reference areas. Results showed that the abundance of the dominant species changed between reference and impacted areas. More specifically, the abundance of limpets Patella candei, and barnacles Chthamalus stellatus decreased, while the abundance of littorinids Tectarius striatus and Melarhaphe neritoides increased near the sewage discharges. Seventeen months after removal of the outfall, limpet and barnacle populations had partially recovered, but littorinid populations had still not fully recovered. This study confirms the negative effects of sewage discharges on eulittoral assemblages, and provides information on the resilience of benthic species following the cessation of sewage disposal.     

Genetic structure of the subtidal red alga Delisea pulchra

We used random amplified polymorphic DNA (RAPDs) to examine small-scale spatial genetic structure in the red alga Delisea pulchra (Greville) Montagne at two locations near Sydney, Australia. We examined genetic structure among plants at four spatial scales ranging from 2 km apart down to <50 cm apart between locations, among sites within locations, among quadrats within sites, and among plants within quadrats. Haploid stages of D. pulchra were absent from the populations studied, suggesting that they are maintained through asexual reproduction of diploid plants. Consistent with this, we found that 19 RAPD phenotypes scored in this study had multiple individuals, indicating the presence of clones in these populations. However, there were no RAPD phenotypes common to two locations separated by only 2 km. Analysis of molecular variance revealed that strong genetic differences occurred between plants from these two locations, with 46.3% of the total genetic variation occurring at this scale, most probably reflecting limited gene flow. Within each location, <25% of the genetic variation was attributable to differences among sites or quadrats, indicating gene flow at those smaller scales. Most of the variation within each location occurred at the smallest spatial scale, among plants within 0.25 m² quadrats. Nonetheless, some pairwise genetic distances (φST) between sites or quadrats within locations were large, indicating some genetic divergence on smaller scales. Genetic distance was independent of spatial distance within both locations, suggesting that fine-scale differences within locations were most probably caused by variation in fine-scale patterns of water movement or fine-scale natural selection. We assessed the impact of one potential selective agent, grazing sea urchins, on the fine-scale genetic structure of D. pulchra. There was no evidence that grazing by sea urchins affected the genetic structure of D. pulchra. In combination with demographic data, our results indicated that local populations of D. pulchra within locations were relatively open and that fine-scale genetic structure was probably constrained by gene flow. At the larger scale however, strong genetic differentiation indicated little gene flow between locations and restricted dispersal of spores. Received: 22 April 1999 / Accepted: 29 November 1999     

Remarques sur la structuration des populations zooplanctoniques dans la zone de l'émissaire de Marseille-Cortiou

The impact of a polluted water-layer on zooplanktonic populations was studied in the sewage discharge zone at Marseille-Cortiou throughout 1977 and a modification of specific diversity was observed: diversity was instable near the outfall, but increased slightly and became more stable further away in non-polluted stations. The population composition did not seem to change. Species rank varied slightly and the number of species increased with increasing distance from the outfall. Specific dominance remained relatively unchanged, and essentially consisted of only 5 species: Clausocalanus acuicornis, Evadne spinifera, Oithona helgolandica, Temora stylifera and Centropages typicus. The population structure, as illustrated by Frontier diagrams, was higher during or just preceding winter. Population organisation was the same close to or far away from the outfall, although the total population counts and number of species were smaller at the most polluted stations. The taxons exhibiting the largest decreases in density were: euphausids, nauplii, larvae of various brachyurans and gastropods, fish eggs, the pteropod Cavolinia inflexa, the copepod Calanus minor and several Coryceidae. The greatest disturbance of the population structure at all stations was observed during the summer. The composition of the zooplanktonic population seems to depend much more on seasonal factors than on the level of pollution. In was not possible to distinguish a cluster of species which were sufficiently dominant to be considered as really characteristic; perhaps the rather high exposure of the sewage site to winds and waves prevents the formation of a local facies.     

Preponderance of a few diatom species among the highly diverse microphytoplankton assemblages in the Bay of Bengal

The microphytoplankton assemblages were studied from water samples collected at eight discrete depths in the top 120 m at five central (open ocean) and four western (shelf/slope region) locations in the Bay of Bengal. The Bay is a low-productive warm pool regime with poor inorganic nutrient inputs to its intensely stratified surface layer despite the very large riverine influx. In addition, the prolonged cloud cover has an adverse effect on the top 25–40 m, on primary production, chlorophyll concentration and phytoplankton assemblages. Microphytoplankton were the most abundant in the northern area of the Bay. A total of 153 phytoplankton species were identified during this study. The most abundant species (at least 1,800 individual cells belonging to a given species or ≥2% of the total counts of identified specimens) during this study were: Thalassiothrix longissima, Thalassiothrix fauenfeldii, Rhizosolenia styliformis, Nitzschia angularis, Thalassionema nitzschioides, Coscinodiscus radiatus, Chaetoceros eibenii, Skeletonema costatum, Coscinodiscus concinnus and Chaetoceros coarctatus. Similarly, there were 20 moderately abundant (≥0.5 but <2%) species. Thirty-three of the least abundant species (<0.5%) occurred at one station. Diatom species, T. fauenfeldii and T. longissima were ubiquitous in the study area. The exclusive occurrence of S. costatum in the northernmost stations suggests that it proliferates only in the low-salinity regions with adequate silica from the land inputs. Abundance of pennate diatoms was higher in the open Bay compared to that of centric diatoms in the more productive northern locations and the western Bay. There appears to be a basic difference between near shore flora and offshore flora. This first analysis of phytoplankton assemblages from the offshore Bay suggests that while there is predominance of only a few species, the Bay harbors very diverse diatom communities that seem to be syntrophic, non-competitive and co-habiting in the generally low nutrient, stratified surface waters.     

Community responses to UV radiation. II. Effects of solar UVB on field-grown diatom assemblages of the Carribean

The effects of ambient solar UV on community productivity and structure were assessed during primary succession of benthic diatoms on artificial substrate in a coral reef of the Caribbean. Artificial substrates, partially enclosed by UV cutoff filters, were placed at a depth of 60 cm below surface. During the initial colonization stages, the assemblages exposed to the full solar spectrum had a mean productivity 43.4% lower than the assemblages exposed to PAR+UVA only. Some differences in species diversity of assemblages under the different UV treatments were also observed. Sensitive species to UVB exposure were Mastogloia angulata, M. ovata, M. paradoxa, Nitzschia longissima, Plagiogramma staurophorum, Rhopalodia musculus, and Surirella ovata. These UVB effects gradually diminished as succession proceeded; 5 to 6 weeks after the placement of the substrates in the water, no significant differences in productivity were observed between the different treatments, while after 6 weeks of growth, species diversity and evenness were higher, although not statistically significant, in the UVB-exposed assemblages. During the first 2 weeks of growth, the productivity under PAR+UVA was significantly lower than that under PAR only. Received: 12 July 1996 / Accepted: 20 November 1997     

Spatio-temporal patterns in the diversity of demersal fish communities off the south coast of South Africa

The diversity of ecological communities has been the focus of many studies. Because biodiversity provides several indicators used in an Ecosystem Approach to Fisheries (EAF) to track changes in fish communities, we investigated the spatial and temporal patterns in the diversity of some demersal fish communities subjected to varying fishing pressure. Depth and catch rate were the most important predictors in explaining changes in diversity followed by longitude and survey year. Diversity, as measured by the various indices except for taxonomic distinctness (∆*), initially declined with increasing depth to about a depth of 80 m, then increased to about 150 m after which it declined. Taxonomic distinctness index (∆*) showed an increase in the taxonomic heterogeneity of the demersal community below the 300-m isobath. Diversity remained relatively constant with increase in longitude to around 24°E (which has the lowest diversity) after which it increased. The assessment of the temporal trend in diversity indicates that survey year has a significant effect on all diversity indices except for ∆*. Diversity increased and dominance declined with time. This may be result of a decline in the abundance of dominant species or an increase in the abundance less dominant species, or a combination of both effects. Multivariate analysis of the set of diversity indices showed three groups of indices: those reflecting species richness (S, Margalef’s d), those measuring mainly taxonomic relatedness (∆*), and those balancing the richness and evenness components of diversity (J′, H′, λ, ∆, Hill’s N1, and Hill’s N2). The relationship between evenness, catch rate, and size was also investigated. Size classes with highest evenness were found to have lowest catch rate and vice versa. This highlights the need to consider the size and trophic level of species when linking diversity to the functioning of ecosystems.     

Spatial–temporal variability of epibenthic assemblages on subtidal biogenic reefs in the northern Adriatic Sea

Spatial distribution and temporal variation of epibenthic assemblages of coralligenous biogenic rocky outcrops occurring in the northern Adriatic Sea (45°04′–45°24′N; 12°23′–12°43′E) were investigated by photographic sampling from 2003 to 2006 at 12 randomly selected sites. The dominant reef-forming organisms were the encrusting calcareous algae (Lithophyllum stictaeforme, Lithothamnion minervae and Peyssonnelia polymorpha), while the main bioeroders were boring sponges (Cliona viridis, C. celata, C. thoosina, C. rhodensis, Piona vastifica) and the bivalve Gastrochaena dubia. Composition of the assemblages varied thorough years and among sites. Spatial heterogeneity, at local and regional scale, prevailed over temporal variation. This variability was related both to the geo-morphological features of the outcrops and to environmental variables. Sites clearly differed in the percent cover of reef builder and bioeroder species while only limited temporal variation within site was found. Some taxa revealed complex intra-site temporal trends. These results provide valuable information on the diversity and variability of epibenthic assemblages of the northern Adriatic coralligenous reefs, essential for the management and conservation of these unique biogenic habitats.     

Sewage nutrient enrichment and phytoplankton ecology along the central coast of Lebanon

The abundance and taxonomic diversity of phytoplankton has been studied in relation to sewage pollution (proximity to outfalls) south of Beirut, Lebanon. Surface-water samples were collected from a series of beach stations extending from the American University of Beirut to 20 km south from June, 1973 to July, 1974. Samples were preserved, concentrated by settling, and the concentration of each taxon of phytoplankton enumerated in an inverted microscope. Water samples from the vicinity of two major sewer outfalls (Carlton and Khalde sewers) showed very high concentrations of NH₄ ⁺, NO₂ ^-, NO₃ ^- and PO₄ ^-3, a greater total concentration of phytoplankton, and a lower taxonomic diversity than samples remote from outfalls. A considerable variation in the occurrence of species and dominance occurred along the pollution gradient. Blue-green algae and dinoflagellates were dominant in polluted waters, while diatoms dominated in cleaner water away from major sewage outflow. From the dominance and relative distribution of the taxa along the pollution gradient, certain taxa (Oscillatoria spp., Spirulina spp., Phormidium spp., Synochococcus custos and S. elongatus, Gymnodinium spp., and Prorocentrum spp.) emerge as indicator species of pollution. These changes correspond to a typical degradation of a complex community to a less mature state by the inflow of nutrient-rich sewage (eutrophication) along a coastal region about 10 km long.     

Etude comparée des teneurs en plutonium chez divers mollusques de quelques sites littoraux français

Plutonium contents of various species of molluscs sampled from several sites along the French coast were measured in order to reveal any distributional patterns of the plutonium levels. The influence of the La Hague nuclear fuel reprocessing plant was apparent in the immediate proximity of the waste-disposal outfall (Ecalgrain Bay), and to a lesser degree in an oyster farming center situated about 50 km east of the Bay of Ecalgrain (St. Vaast-la-Hougue). Plutonium concentrations in molluscs from the remaining sites were quite comparable to levels that have been measured in similar species subject only to plutonium derived from atmospheric fallout. All molluscs, except those from Ecalgrain Bay, displayed higher levels of plutonium in the shell than in the soft parts, a finding in agreement with similar studies which have been reported recently. However, those individuals sampled from the vicinity of the outfall consistently displayed shell: soft parts plutonium ratios of less than 1. This difference may reflect different physico-chemical forms of this isotope present at the different sampling stations. With the exception of Crepidula fornicata shell, the tissues of filter-feeding molluscs do not appear to concentrate plutonium above the level found in other types of molluscs.

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Avec la collaboration technique de G. Moisan.     

Hepatic mixed-function oxidases in California flatfishes are increased in contaminated environments and by oil and PCB ingestion

Hepatic mixed-function oxidases (MFOs) were measured in the bothid flatfishes Citharicthys sordidus and C. stigmaeus from relatively uncontaminated and from polluted coastal populations of California, USA, at various times of the year during 1979–1980 and in individuals fed crude oil and polychlorinated biphenyl-augmented food in the laboratory. For C. sordidus, aryl hydrocarbon hydroxylase (AHH) specific activity was generally highest around the Los Angeles County sewage outfall on the Palos Verdes Shelf, intermediate near the 7-mile Hyperion sewage outfall in Santa Monica Bay and around a petroleum seep in the Santa Barbara Channel, and lowest in relatively unpolluted Monterey Bay. For C. stigmaeus, which had about ten times less specific activity than the foregoing species, specimens from the Santa Barbara petroleum seep had significantly greater AHH specific activity than those from Monterey Bay. Fishes from contaminated environments also showed increases of microsomal proteins with molecular weights of 56, 54, 57 and 46×10³; moreover, the content of cytochrome P-450 was elevated in specimens of C. sordidus from such environments. Augmentation of food with seep oil or polychlorinated biphenyls (PCBs) induced significant increases in the specific activity of AHH and amounts of microsomal proteins in C. stigmaeus. Thus, these two species of flatfishes are good candidates for monitoring biologically meaningful levels of petroleum and polychlorinated biphenyls in contaminated environments. Moreover, the mixed function oxidase pattern in fish populations from the Santa Barbara petroleum seep is evidently a functional adaptation to chronic intake of petroleum hydrocarbons.     

Intra- and interannual variability in the larval fish assemblage off Gran Canaria (Canary Islands) over 2005–2007

The present study provides the longest and most intensive plankton and larval fish seasonal variability analysis in the Canary Islands and forms a basis for understanding life cycle scheduling and interactions among species, as well as the potential variability in transport processes of early life stages. Larval fish assemblages were studied weekly at Gran Canaria Island, Canary Islands, from January 2005 to June 2007, which represented two contrasting hydrological and biological periods. The former year was characterized by lower temperature and salinity that increased through 2006 and 2007. In contrast, chlorophyll concentration and mesozooplankton biomass decreased through the same period, especially when only the late winter bloom period was evaluated. However, ichthyoplankton abundance did not exhibit any clear pattern, as larger values were observed during 2006. The larval fish community of this oceanic island, located near the NW African upwelling, was composed of both neritic and oceanic taxa. Two families accounted for almost half of the collected larvae: Clupeidae (21.9%) and Myctophidae (20.5%). Although total larval concentration did not exhibit any seasonal peak linked to changes in zooplankton, the ichthyoplankton composition gradually changed during the year due to the high diversity and extended spawning periods of the fish species represented in samples. “Winter” and “summer” larval assemblages were identified, corresponding to the mixing and stratification periods of the water column, respectively. These assemblages were characterized by changes in the contribution of the most abundant annual taxa (Sardinella aurita, Cyclothone braueri, Ceratoscopelus spp. and Gobids) and by the presence of larvae of winter (Pagellus bogaraveo, Pomacentridae sp1) or summer spawners (Pomacentridae sp2, Trachinus draco, Arnoglossus thori, Tetraodontidae sp1). Upwelling filaments shed from the NW African coast reached the sampling area three times during this study, but changes in the local larval community were only detected in August 2005.     

Human trampling as short-term disturbance on intertidal mudflats: effects on macrofauna biodiversity and population dynamics of bivalves

The effect of physical disturbance in the form of trampling on the benthic environment of an intertidal mudflat was investigated. Intense trampling was created as unintended side-effect by benthic ecologists during field experiments in spring and summer 2005, when a mid-shore area of 25 × 25 m was visited twice per month by on average five researchers for a period of 8 months. At the putatively-impacted location (I) (25 × 25 m) and two nearby control locations (Cs) (25 × 25 m each), three sites (4 × 4 m) were randomly selected and at each site, three plots (50 × 50 cm) were sampled after 18 and 40 days from the end of the disturbance. Multivariate and univariate asymmetrical analyses tested for changes in the macrofaunal assemblage, biomass of microphytobenthos and various sediment properties (grain-size, water content, NH₄ and NO₃ concentrations in the pore water) between the two control locations (Cs) and the putatively-impacted location (I). There were no detectable changes in the sediment properties and microphytobenthos biomass, but variability at small scale was observed. Microphytobenthos and NH₄ were correlated at I to the number of footprints, as estimated by the percentage cover of physical depressions. This indicated that trampling could have an impact at small scales, but more investigation is needed. Trampling, instead, clearly modified the abundance and population dynamics of the clam Macoma balthica (L.) and the cockle Cerastoderma edule (L.). There was a negative impact on adults of both species, probably because footsteps directly killed or buried the animals, provoking asphyxia. Conversely, trampling indirectly enhanced recruitment rate of M. balthica, while small-sized C. edule did not react to the trampling. It was likely that small animals could recover more quickly because trampling occurred during the growing season and there was a continuous supply of larvae and juveniles. In addition, trampling might have weakened negative adult-juvenile interactions between adult cockles and juvenile M. balthica, thus facilitating the recruitment. Our findings indicated that human trampling is a relevant source of disturbance for the conservation and management of mudflats. During the growing season recovery can be fast, but in the long-term it might lead towards the dominance of M. balthica to the cost of C. edule, thereby affecting ecosystem functioning.     

Protection from fishing alters the species composition of fish assemblages in a temperate-tropical transition zone

Closure of areas to fishing is expected to result in an increase in the abundance of targeted species; however, changes to populations of species not targeted by fishermen will depend upon their role in the ecosystem and their relationship with targeted species. The effects of protection on targeted and non-targeted reef fish species at the Houtman Abrolhos Islands, Western Australia were studied using baited remote underwater stereo–video cameras. Video images were collected from shallow (8–12 m) and deep (22–26 m) reef sites inside a Marine Protected Area (MPA) at each of three island groups and from three replicate fished locations at each of these groups that span a temperate-tropical transition area. The MPAs were established in 1994 and vary in size from 13.72 km² at the Pelsaert group in the south to 22.29 km² at the Easter group to 27.44 km² at the Wallabi group in the north. The relative abundances of 137 fish species from 42 families were recorded. Large differences in fish assemblage structure existed between MPA and fished locations, and also between shallow and deep regions. Targeted fish species Plectropomus leopardus, Lethrinus miniatus, Lethrinus nebulosus, Pagrus auratus and Glaucosoma hebraicum were more abundant inside MPAs than in areas open to fishing. Their abundance inside MPAs was between 1.13 and 8 times greater than their abundance at fished locations. For non-targeted fish species many were more abundant in areas open to fishing, e.g. Coris auricularis, Thalassoma lutescens, Thalassoma lunare, Dascyllus trimaculatus, however others were conversely more abundant inside MPAs, e.g. Gymnothorax spp, Kyphosus sydneyanus, Scarus microhinos, Chromis westaustralis, Chaetodon spp. This study demonstrates that the removal of abundant targeted species from an ecosystem by fishing can indirectly impact non-fished species and alter the trophic structure of fish assemblages. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Spatial patterns and temporal succession in soft-bottom macroinvertebrate assemblages surrounding an ocean outfall on the southern San Diego shelf: relation to anthropogenic and natural events

Spatial patterns and temporal succession in soft-bottom macroinvertebrate assemblages are described for an area of the southern San Diego shelf which is influenced by both anthropogenic and natural events. The study transect covered 19 km along the 60 m-depth contour and spanned the terminus of the Point Loma wastewater outfall (32°40N; 117°17W). Ordination and classification analyses revealed that eight major benthic assemblages occurred in the study area from 1986–1990. These analyses further indicated that: (1) the impact of wastewater discharge on the benthos was asymmetric about the outfall, and (2) primary and secondary impact zones existed within the outfall footprint. The primary impact extended only 0.5 km south, but usually up to 1 km north, of the point of discharge, reflecting the prevailing northerly flow of currents along the San Diego coast. Stations within the primary impact zone usually supported similar faunal assemblages at any point in time. A lessened, or secondary, impact was apparent at stations 1 to 2 km south and 2 km north of the outfall. The two stations 9 km to the north appeared to be outside the outfall footprint. Assemblages in the three zones did not differ greatly in species composition, but did differ with respect to organismal density, relative abundances (dominance hierarchy) of component species, and temporal persistence. Biostimulation of the benthos, manifest as increased species richness and organismal abundance, was apparent in the primary impact zone from 1986–1988, although dominance was relatively low. Dominance increased at these sites during 1989 and 1990 due to large increases in populations of a few small species, such as the polychaete Myriochele sp. M and the ostracod Euphilomedes carcharodonta. Biomass was slightly elevated in the primary impact zone during 1986–1987; however, this trend was not sustained. Communities within the outfall footprint were much less persistent over time than those beyond it. The observed shifts in benthic assemblages within the outfall footprint corresponded to natural oceanographic cycles (i.e., the transition from El Niño to La Niña conditions) and anthropogenic changes (i.e., changes in wastewater output). These observations suggest that the Point Loma outfall has a localized effect on the stability of infaunal communities. Possible destabilization mechanisms are explored. Finally, comparisons with pre-discharge data taken during 1956–1957 revealed that about half of the species present prior to construction of the outfall were still common in 1990, after 27 yr of wastewater discharge, although large increases in species diversity and abundance seem to have occurred at all stations.     

Effects of long-term physical disturbance by commercial scallop fishing on subtidal epifaunal assemblages and habitats

 This paper examines spatial differences in the distribution of by-catch assemblages from the scallop [Pecten maximus (L.) and Aequipecten opercularis (L.)] fishing grounds in the North Irish Sea, during 1995. The sites examined have been exposed to differing known levels of fishing disturbance by scallop dredging, based on unusually high-resolution data extracted from fishermens' logbooks. Uni- and multi-variate techniques have been used on a production dataset (a value which incorporates both abundance and biomass figures), as well as abundance and biomass data individually. The original species list was reduced to higher taxonomic groupings in line with the theory that the latter is more appropriate for detecting anthropogenic change. Species diversity and richness, total number of species, and total number of individuals all decrease significantly with increasing fishing effort. Species dominance increases with effort. Total abundance, biomass and production, and the production of most of the major individual taxa investigated decrease significantly with increasing effort. Multivariate analysis reveals a significant relationship between fishing effort and by-catch assemblage structure. The taxa most responsible for the differences are the echinoids and cnidarians, but prosobranch molluscs and crustaceans also contribute to the differences. By-catch assemblage structure is more closely related to fishing effort than any other environmental parameter investigated, including depth and sediment type. We observed an approximately linear decrease in diversity with increasing fishing disturbance, and suggest this is primarily due to selective removal of sensitive species and, more importantly, habitat homogenisation. These results were interpreted in the light of ecological theories relating disturbance to community structure. The argument that invertebrate scavenger populations benefit from prolonged exposure to fishing disturbance was also examined, but no supporting evidence was found. Received: 29 January 2000 / Accepted: 31 May 2000     

Reproduction in the diadematoid sea urchin Centrostephanus rodgersii in contrasting habitats along the coast of New South Wales, Australia

Reproduction in the sea urchin Centrostephanus rodgersii was examined in two types of habitats (“barrens”, i.e. habitats characterised by the high crustose coralline algal cover typical of urchin-barren grounds, and by the absence of macroalgae; and “fringe”, i.e. habitats characterised by a high macroalgal biomass and few C. rodgersii) at four locations in New South Wales. The four locations: the Solitary Islands, Sydney, Ulladulla and Eden, span the distribution of C.␣rodgersii from the subtropics at its northern limit to temperate waters near its southern limit. Histology and estimates of gonad retrieval rate (GRR) from January 1994 to October 1995 indicated that reproduction was synchronous at all locations. An increase in the tempo of gametogenesis in May and onset of spawning in June at all locations is consistent with entrainment in response to exogenous factors. Over the range studied, C. rodgersii experienced relatively similar daylength cycles and contrasting sea-temperature cycles. Short days and lunar conditions coinciding with the solstice appear likely proximate cues for the onset of spawning. The major difference in reproduction among locations was in the duration of spawning. In the southern parts of its range breeding occurred over a 5 to 6 mo period, whereas at the Solitary Islands it lasted ≃1 mo. At most locations the GRRs were significantly higher in the fringe habitat than in the barrens habitat. The lower reproductive output of urchins in the barrens habitat was attributed to the food-poor conditions typical of this habitat. The developing fishery for C. rodgersii is likely to be most effective from March to early May. Urchins from barrens areas may not provide sufficient yield to warrant harvesting. Received: 29 October 1997 / Accepted: 18 May 1998     

Comparison of larval fish assemblages in three large estuarine systems, KwaZulu-Natal, South Africa

 The structure of the larval fish assemblages in three large estuarine systems on the KwaZulu-Natal coast of South Africa was examined using a combination of univariate, distributional and multivariate techniques. The database was comprised of a full annual set of larval fish samples taken from each estuarine system: Durban Harbour, Richards Bay Harbour and St Lucia Estuary. The mean monthly densities of each species in each system were used in the species matrix, and the mean monthly values of salinity, temperature and turbidity were used in the environmental matrix. The mean species diversity and evenness index were significantly higher in Durban Harbour (H′ = 1.03, J′ = 0.65) than in the other two systems. The cumulative dominance curve showed that St Lucia Estuary has a high dominance of a few species, with Richards Bay Harbour intermediate and Durban Harbour being the most diverse. Classification and MDS (multiple-dimensional scaling) analyses of larval fish densities in all three systems grouped together into three main clusters on the basis of system. The species similarity matrix (inverse analysis) clustered into five groups at the 25% similarity level. The MDS analysis of the same matrix showed that the groups separated out according to the degree of estuarine association of a species and hence habitat type. The species most responsible for system groupings were: Glossogobius callidus, Gilchristella aestuaria, Stolephorus holodon, Croilia mossambica and Gobiid 12. The “best fitting” of the environmental variables to explain the larval fish community patterns in each system was turbidity on its own (weighted Spearman's rank correlation, ρ_w = 0.55). The relationship of larval densities to environmental conditions was shown to be species-specific with estuarine species (e.g. G. callidus and G. aestuaria), having a strong positive correlation with temperature and turbidity but negative correlations with salinity. In summary, much longer term studies with more sites within each system are needed to assess whether the larval fish assemblages are stable or at an equilibrium (both spatially and temporally) and whether these assemblages are indicative of the relative “health” and nursery function of the system. Received: 28 April 1999 / Accepted: 30 May 2000     

Anthropogenic disturbance of deep-sea megabenthic assemblages: a study with remotely operated vehicles in the Faroe-Shetland Channel,NE Atlantic

The effects of local-scale anthropogenic disturbance from active drilling platforms on epibenthic megafaunal abundance, diversity and assemblage pattern were examined in two west of Shetland hydrocarbon fields at 420 and 508 m water depth. These areas were selected to include a range of disturbance regimes and contrasting faunal assemblages associated with different temperature regimes. Remotely operated vehicle (ROV) video provided high-resolution megafaunal abundance and diversity data, which were related to the extent of visible disturbance from drilling spoil. These data, in conjunction with a study deeper in the Faroe-Shetland Channel, have allowed comparison of the effects of disturbance on megabenthos across a range of sites. Disturbance to megafaunal assemblages was found to be high within 50 m of the source of drill spoil and in areas where spoil was clearly visible on the seabed, with depressed abundances (Foinaven 1,900 individuals ha⁻¹; Schiehallion 2,178 individuals ha⁻¹) and diversity (H′ = 1.75 Foinaven; 1.12 Schiehallion) as a result of smothering effects. These effects extended to around 100 m from the source of disturbance, although this was variable, particularly with current regime and nature of drilling activity. Further from the source of disturbance, megafaunal assemblages became more typical of the background area with increased diversity (H′ = 2.02 Foinaven; 1.77 Schiehallion) and abundance (Foinaven 16,484 individuals ha⁻¹; Schiehallion 5,477 individuals ha⁻¹). Visible effects on megafaunal assemblages as a result of seabed drilling were limited in extent although assemblage responses were complex, being controlled by differing effects to individual species often based on their motility.