Diatom composition and biomass variability in nearshore waters of Maxwell Bay, Antarctica, during the 1992/1993 austral summer

 Diatom composition and biomass were investigated in the nearshore water (<30 m in depth) of Maxwell Bay, Antarctica during the 1992/1993 austral summer. Epiphytic or epilithic diatoms such as Fragilaria striatula, Achnanthes brevipes var. angustata and Licmophora spp. dominated the water column microalgal populations. Within the bay, diatom biomass in surface water was several times higher at the nearshore (2.4–14 μg C l^-1) than at the offshore stations (>100 m) (1.2–3.2 μg C l^-1) with a dramatic decrease towards the bay mouth. Benthic forms accounted for >90% of diatom carbon in all nearshore stations, while in the offshore stations planktonic forms such as Thalassiosira antarctica predominated (50–>90%). Microscopic examination revealed that many of these diatoms have become detached from a variety of macroalgae growing in the intertidal and shallow subtidal bottoms. Epiphytic diatoms persistently dominated during a 19-day period in the water column at a fixed nearshore station, and the biomass of these diatoms fluctuated from 0.86 to 53 μg C l^-1. A positive correlation between diatom biomass and wind speed strongly suggests that wind-driven resuspension of benthic forms is the major mechanism increasing diatom biomass in the water column. Received: 28 April 1995/Accepted: 1 April 1996     

Die Weichbodenfauna vor der Elbemündung unter dem Einfluß der Klärschlammverklappung

Macrobenthic fauna and sediment structure were studied at 6 stations from June 1979 to April 1981. The investigations were carried out in the outer estuary of the River Elbe at depths of 15–38 m near a sewage sludge dumping site. The sediment near this area consisted of a high portion of silt. Usually, very few species and small numbers of individuals were found near that dumping ground. During summer 1980, a mass development ofAbra alba and several polychaete species caused an increase in species number which broke down during the following winter. The mass development observed in the study area was apparently not directly caused by the sludge dumping itself, but reflects the natural variability of the community structure. The number of species recorded was significantly correlated with a grain size fraction>31 μm, especially in summer. The seasonal and spatial fluctuation of the benthic community could be well documented by the abundance per species (N/S index). The Shannon-Wiener-Index (H′) and eveness (J) were also useful indicators of community variability. The log-normal distribution did not show the seasonal and the spatial differences of the stations. Possible reasons are discussed. The biomass at the stations near the dumping area was less except during the mass development ofA. alba. The average individual weight (B/N) was shown to be a good indicator of population fluctuations; polychaete biomass was positively correlated to a grain size fraction≦6 μm, that of molluscs to a grain size fraction>31 μm.      

Ringed and bearded seal densities in the eastern Chukchi Sea, 1999–2000

Aerial surveys were conducted in 1999 and 2000 to estimate the densities of ringed (Phoca hispida) and bearded (Erignathus barbatus) seals in the eastern Chukchi Sea. Survey lines were focused mainly on the coastal zone within 37 km of the shoreline, with additional lines flown 148–185 km offshore to assess how densities of seals changed as a function of distance from shore. Satellite-linked time-depth recorders were attached to ringed seals in both years to evaluate the time spent basking on the ice surface. Haulout patterns indicated that ringed seals transitioned to basking behavior in late May and early June, and that the largest proportion of seals (60–68%) was hauled out between 0830 and 1530 local solar time. Ringed seals were relatively common in nearshore fast ice and pack ice, with lower densities in offshore pack ice. The average density of ringed seals was 1.91 seals km⁻² in 1999 (range 0.37–16.32) and 1.62 seals km⁻² in 2000 (range 0.42–19.4), with the highest densities of ringed seals found in coastal waters south of Kivalina and near Kotzebue Sound. The estimated abundance of ringed seals for the entire study area was similar in 1999 (252,488 seals, SE=47,204) and 2000 (208,857 seals, SE=25,502). Bearded seals were generally more common in offshore pack ice, with the exception of high bearded seal numbers observed near the shore south of Kivalina. Bearded seal densities were not adjusted for haulout behavior, and therefore, abundance was not estimated. Unadjusted average bearded seal density was 0.07 seals km⁻² in 1999 (range 0.011–0.393) and 0.14 seals km⁻² in 2000 (range 0.009–0.652). Levels of primary productivity, benthic biomass, and fast ice distribution may influence the distributions of ringed and bearded seals in the Chukchi Sea. Information on movement and haulout behavior of ringed and bearded seals would be very useful for designing future surveys.     

Current patterns in McMurdo Sound,Antarctica and their relationship to local biotic communities

Summary Current speed and direction measurements collected during summer (January–February) and sping (November–December) of 1984 indicated that currents in McMurdo Sound, Antarctica were dominated by oscillatory flow associated with diurnal tidal components (O1, K1, P1). Net flow was southward in the eastern Sound, mixed in the central Sound, and northward in the western Sound. Short term observations (<5 days) from nearshore stations indicated a similar but more sluggish pattern of tidal and mean flow. Hydrographic data collected during the same period indicated a similar pattern of cold water with low chlorophyll a content flowing northward from under the Ross Ice Shelf in the western Sound and denser, slightly warmer water with higher chlorophyll a content flowing southward in the eastern Sound. Previous studies have shown that productivity is higher in the eastern Sound than in the west, apparently due to the circulation pattern. The western Sound consists of waters from beneath the Ross Ice Shelf which have a lower phytoplankton standing stock than eastern Sound waters which enter from the north. More sluggish current speeds in the western Sound result in even lower particle fluxes past benthic consumers. Finally, more persistent ice cover in the west further inhibits in situ primary productivity.     

Population dynamics, distribution, and growth rate of tilapia (Oreochromis mossambicus) in the Salton Sea, California, with notes on bairdiella (Bairdiella icistia) and orangemouth corvina (Cynoscion xanthulus)

The Salton Sea is a highly saline lake that has long supported sportfishery and large populations of fish-eating birds. A study was initiated in 1999 to assess the status of orangemouth corvina (Cynoscion xanthulus), bairdiella (Bairdiella icistia) and tilapia (Oreochromis mossambicus × O. urolepis). Multimesh (50 × 2 m) gillnets were set at nine stations in 1999, ten stations in 2000 and six stations in 2002. These stations were sampled every two months in 1999, every three months in 2000 and once in 2002. O. mossambicus was the most abundant of the four species, with a maximum mean catch per unit effort (CPUE) 13.8 kg net⁻¹ h⁻¹ or 29.9 fish net⁻¹ h⁻¹ being observed at the river mouth stations in August 1999. From spring to summer, tilapia CPUE increased at nearshore and river mouth stations and decreased at pelagic stations, apparently reflecting migration away from midlake areas in response to anoxia or hypoxia caused by periodic springtime overturn events in deep waters. Tilapia catches in nearshore, river mouth and pelagic habitats were 83 and 60% males in 1999 and 2000, respectively. Tilapia catches in rivers in August 1999 averaged only 6% male. During 1999–2000, the tilapia population consisted essentially of only the 1995 and 2000 year classes. Harsh conditions at the Salton Sea have led to erratic reproduction and survival rates and unstable age structures for its resident fishes. Massive parasite infestations of fry and physiological stressors such as anoxia, high sulfide levels, high salinity and high and low temperatures are potential causes of the irregular recruitment and periodic dieoffs of tilapia. The abundance of all fish species declined over the years of study. Between 1999 and 2002, the late summer mean CPUEs for tilapia, bairdiella and orangemouth corvina at four nearshore stations dropped from 16 fish to 0.02 fish, from 4.7 fish net to 0.23 fish, and from 0.08 fish to 0.02 fish, respectively. During 2000–2003, parallel declines occurred in estimated numbers of adult fish involved in mass mortality events at the Sea. The boom-and-bust dynamics of tilapia and other fish populations in the Sea have major consequences for fish-eating bird populations, for other components of the ecosystem, and for the recreational value of the lake. Guest Editor: John M. Melack Saline Waters and their Biota     

Composition and succession of dinoflagellates and chrysophytes in the upper fast ice of Davis Station, East Antarctica

Little is known of the wider Antarctic distribution of the upper fast ice community now comprehensively described from McMurdo Sound. We determined the fast ice protist community at Davis Station, East Antarctica and compared it with that of McMurdo Sound. As at McMurdo Sound, Davis fast ice is characterised by extreme and transitory salinities (96–2.5 psu) and temperatures (−4.5 to −0.1°C) during the spring/summer transition. Both communities are dominated by Polarella glacialis (an autotrophic dinoflagellate), chrysophytes and their life cycle stages. Furthermore, the physical parameters of brine temperature and salinity at which these successions occurred approximated those of McMurdo Sound. The high degree of similarity between the communities from the geographically disparate locations indicates that this community type has a circum-Antarctic distribution. Confirming the areal extent and seasonality of this community type will assist in future predictions of sea ice productivity.     

Signals from the benthos: Development and evaluation of a benthic index for the nearshore Gulf of Maine

We developed a benthic index for the nearshore Gulf of Maine to provide researchers and environmental managers a way to make spatial and year-to-year comparisons of benthic condition. The data set used included 248 stations sampled for physical, chemical, and biological variables by the National Coastal Assessment in 2000–2003. We used logistic regression with 49 candidate measures of benthic species diversity, pollution sensitivity-tolerance, and community composition to discriminate sites with high and low benthic environmental quality (BEQ). BEQ was based on the concentrations of metal and organic contaminants in the sediments, total organic carbon, sediment toxicity, and dissolved oxygen level of the bottom water. An analysis of similarity test showed that the community composition of low BEQ stations was significantly different (p < 0.001) from high BEQ stations. Ten of the 49 benthic metrics showed a strong ability to discriminate stations. We developed several candidate benthic indices and tested them with independent data from Massachusetts Bay and Casco Bay to help select and validate the best index. A model using the Shannon-Wiener diversity measure, Rosenberg's species pollution tolerance measure, and the percent capitellid polychaetes (or percent Capitella spp.) strongly discriminated stations, with an area under the receiver operating characteristic (ROC) curve of 0.82 and a classification accuracy of 80%. Signal detection theory (ROC curves and positive–negative predictive value curves) was used to evaluate the index and to predict how well an index developed for one geographic area might work in another area with a different prevalence of the degraded condition. We show how these techniques can also guide decisions by environmental managers about choosing thresholds and weighing costs and benefits of particular actions.     

Predicting habitat use and trophic interactions of Eurasian ruffe,round gobies,and zebra mussels in nearshore areas of the Great Lakes

The Laurentian Great Lakes have been subject to numerous introductions of nonindigenous species, including two recent benthic fish invaders, Eurasian ruffe (Gymnocephalus cernuus) and round gobies (Neogobius melanostomus), as well as the benthic bivalve, zebra mussel (Dreissena polymorpha). These three exotic species, or “exotic triad,” may impact nearshore benthic communities due to their locally high abundances and expanding distributions. Laboratory experiments were conducted to determine (1) whether ruffe and gobies may compete for habitat and invertebrate food in benthic environments, and (2) if zebra mussels can alter those competitive relationships by serving as an alternate food source for gobies. In laboratory mesocosms, both gobies and ruffe preferred cobble and macrophyte areas to open sand either when alone or in sympatry. In a 9-week goby–ruffe competition experiment simulating an invasion scenario with a limited food base, gobies grew faster than did ruffe, suggesting that gobies may be competitively superior at low resource levels. When zebra mussels were added in a short-term experiment, the presence or absence of mussels did not affect goby or ruffe growth, as few zebra mussels were consumed. This finding, along with other laboratory evidence, suggests that gobies may prefer soft-bodied invertebrate prey over zebra mussels. Studies of interactions among the “exotic triad”, combined with continued surveillance, may help Great Lakes fisheries managers to predict future population sizes and distributions of these invasive fish, evaluate their impacts on native food webs, and direct possible control measures to appropriate species.     

The distribution and abundance of soft-sediment macrobenthos around Casey Station, East Antarctica

Grab samples of shallow (5–35 m) marine benthic sediments and epi- and infaunal assemblages were taken from nearshore regions around Casey Station, Windmill Islands, East Antarctica. A hierarchical, spatially nested sampling design was used with locations (kilometres apart), sites (hundreds of metres apart) and plots (tens of metres). Two potentially impacted, polluted locations (adjacent to a sewage outfall and an old garbage tip) were compared with two control locations in an asymmetrical design. Significant differences in assemblages were found between locations and between sites within locations. Significant differences in the abundances of taxa at several taxonomic levels (species, family, order, phylum) were found at all three spatial scales. Significant differences were also detected between the polluted and control locations. Compared with other Antarctic locations, the assemblages were dominated by crustaceans (90–97% of individuals) and there was a paucity of polychaete fauna at the locations sampled. Accepted: 3 June 2000     

Macrobenthic communities in a tropical lagoon (Tahiti, French Polynesia, central Pacific)

Soft bottom communities were sampled quantitatively in Tahiti lagoon (French Polynesia) at 18 stations in five zones around the island over 1 year. In addition, various environmental parameters (silt/clay fractions, organic content, chlorophyll and phaeopigment content) were sampled at the same stations over 2 years. The temporal and spatial variabilities of the macrobenthic communities are described and related to these environmental parameters. Each zone ran from the fringing reef to the inner flat of the barrier reef. The macrofauna exhibited a high richness (392 taxa) with an average mean biomass of 1.8 g AFDW m⁻² (grams ash-free dry weight per square metre). These communities exhibited temporal but not seasonal fluctuations. The biomass of the macrofauna increased from the fringing to the barrier reefs, and the density of individuals was significantly higher on the fringing reefs. Ordination techniques highlighted four groups of stations characterised by distinctive species composition, density and biomass. The first group included stations located on the inner flat of the barrier reef and in the shallow lagoon area and was characterised by highly diverse communities dominated by polychaetes. The second group primarily included stations from the industrial and hotel zones. This group had the lowest diversity and was also dominated by polychaetes, especially the capitellid Dasybranchus sp. 1. The third group was dominated by gastropods and bivalves. The final group of stations was represented only by station 51, in zone 5, which was characterised by mobile soft sediments and wave action and was dominated by the decapod Hippa cf. pacifica. Presumably, these mobile sediments facilitate the development of this benthic community, which does not occur elsewhere in the lagoon. The diversity and biomass of these benthic communities are low compared with most other areas in the South Pacific. Accepted: 10 May 2000     

Sedimentation in McMurdo Sound, Antarctica: a disturbance mechanism for benthic invertebrates

A slumping event that occurred on permanent transect lines from 12- to 30- m depth located at Arrival Heights, McMurdo Sound, Antarctica in 1993, provided an opportunity to examine the effects of sediment-mediated disturbance on the benthic invertebrate fauna. The disturbance had a particularly significant impact on the soft coral Alcyonium paessleri, which resulted in 84% colony mortality downslope from the slump site compared to an average annual mortality rate of 14% on control transects. In contrast, anchor ice at the same site accounted for removal of 5% of the population in 1992. Laboratory experiments with A. paessleri colonies under conditions of periodic sediment resuspension indicate that the soft corals are susceptible to this form of disturbance. Our observations suggest they are capable of shedding fine silt in the laboratory, which might explain the presence of A. paessleri in soft-sediment sites around McMurdo Sound. However, scarring by larger gravel in laboratory assays was slow to heal and may account for much of the colony mortality we observed. Several invertebrate-barren rocky benthic regions in McMurdo Sound were suggestive of historical slumping events. Given the removal of the smaller grain size sediments from these areas – a typically slow process – it appears these communities are slow to recover. The long-term effects of sedimentation on the benthic communities are unknown, but the impact on A. paessleri, one of the most common and fastest growing species, suggests this disturbance mechanism could lead to significant restructuring of these communities. Received: 29 November 1996 / Accepted: 23 February 1997     

Effects of macrophyte growth forms on invertebrate communities in saline lakes of the Wyoming High Plains

In saline lakes, areal cover and both species and structural diversity of macrophytes often decline as salinity increases. To assess effects of the loss of certain macrophyte growth forms, we characterized benthic and epiphytic invertebrates in three growth forms (thin-stemmed emergents, erect aquatics, and low macroalgae) in oligosaline lakes (0.8–4.2 mS cm⁻¹) of the Wyoming High Plains, USA. We also measured the biomass and taxonomic composition of epiphytic and benthic invertebrates in two erect aquatics with very similar structure that are found in both oligosaline (Potamogeton pectinatus) and mesosaline (9.3–23.5 mS cm⁻¹) (Ruppia maritima) lakes. Although total biomass of epiphytic invertebrates varied among oligosaline lakes, the relative distribution of biomass among growth forms was similar. For epiphytic invertebrates, biomass per unit area of lake was lowest in emergents and equivalent in erect aquatics and low macroalgae; biomass per unit volume of macrophyte habitat was greatest in low macroalgae. For benthic invertebrates, biomass was less beneath low macroalgae than other growth forms. Taxonomic composition did not differ appreciably between growth forms for either benthic or epiphytic invertebrates, except that epiphytic gastropods were more abundant in erect aquatics. Total biomass of epiphytic and benthic invertebrates for the same growth form (erect aquatic) did not differ between oligosaline (Potamogeton pectinatus) and mesosaline (Ruppia maritima) lakes, but taxonomic composition did change. In the oligosaline to mesosaline range, direct toxic effects of salinity appeared important for some major taxa such as gastropods and amphipods. However, indirect effects of salinity, such as loss of macrophyte cover and typically higher nutrient levels at greater salinities, probably have larger impacts on total invertebrate biomass lake-wide.     

The benthic infauna and benthic respiration off the Banc d'Arguin (Mauritania,Northwest Africa)

In May 1988, a study was made of the benthic community structure and benthic respiratory activity along two transects across the Mauritanian shelf off Banc d'Arguin. The main emphasis of the present paper is put on the macrobenthos, but results of a gross analysis of the meibenthos are discussed as well. Macrofaunal and meiofaunal density showed no consistent decrease with distance from the shore. The composition of the macrofauna taxa appeared to be closely correlated with sediment parameters and less so with depth. The highest macrofaunal biomass was found at the northern edge of the Banc d'Arguin, and the lowest biomass along the outer shelf. The biomass levels on the shelf match the ones reported for the northern Cap Blanc area where, in contrast to the seasonal upwelling in the investigated area, upwelling takes place all year round.Benthic respiration rates on the offshore shelf were relatively high at the nearshore stations and low near the shelf break. Experimental evidence suggests that the low O₂ levels in the upwelling water covering part of shelf, inhibited benthic respiration. The high respiratory activity at some northern inshore stations coincided with the presence of oxygen-rich coastal water. In this area benthic respiration surpassed the level previously reported for the enriched Cap Blanc area. On the basis of our respiration data, an estimate is made of the total carbon demand of the benthic community on the shelf in May and this quantity is compared with the measurements of daily primary production.     

Distribution patterns of benthic microalgal standing stock at McMurdo Sound,Antarctica

Summary During the austral summer of 1975–76 and winter of 1977 benthic and water column chlorophyll a and phaeopigments were measured at several sites along the east and west sides of McMurdo Sound, Antarctica. Estimates of in situ primary productivity were made at some McMurdo Sound locations. Additionally, water column samples were collected at 5 stations in the Ross Sea during January, 1976. Standing stock data are analyzed to identify seasonal and spatial patterns. Variability in algal standing stock was related to ambient light levels and appeared to be mediated by ice and snow cover whereby the highest algal standing stock was present under high light conditions (low ice and snow cover, shallow water, summer). Differences in published benthic invertebrate densities appear to be closely allied to differences in benthic primary production, and less so to in situ planktonic ice microalgal production.     

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 patterns of benthic community development in an Arctic fjord (Kongsfjorden, Svalbard): results of a 24-year manipulation study

We investigated temporal patterns of recolonisation and disturbance in a benthic hard bottom community in high-arctic Kongsfjorden from 1980 to 2003 through annual photographic surveys. A manipulative sampling design was applied, where half of the study area (treatment areas) was cleared at the beginning of the study. Twenty-three different taxa and groups of benthic epifauna were found in the photographs. The benthic community structures of treatments and controls converged within the first decade, but significant differences prevailed until ≤13 years after the start of the study. We could distinguish between three different time intervals with increased inter-annual changes. While the observed differences during the first two intervals could be attributed to recolonisation and succession, the changes in interval 3 were mostly due to increased external forcing and characterised by low inter-group and high inter-annual differences. During this interval, brown algae (mainly Desmarestia) and the sea urchin Strongylocentrotus droebachiensis emerged in high densities, while sea anemone populations declined. Different recolonisation patterns for individual species were related to life span, rate of maturity, predators and larval settlement. We could not find a climax stage in the succession for the benthic community at Kvadehuken, presumably due to the constant level of disturbances at the site.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.     

Zooplankton community and hydrographical properties of the Neretva Channel (eastern Adriatic Sea)

Temporal and spatial variability of micro and mesozooplankton was studied in 1998 and 1999 at four stations in the Neretva Channel area influenced by the Neretva river and the open waters of the south Adriatic Sea. The area is orthophosphate limited, but an excessive accumulation of land derived nitrogen is prevented by phytoplankton uptake and the general circulation pattern. Microzooplankton was dominated by ciliates, with average abundances comparable to other Adriatic channel areas (122–543 ind. l⁻¹). Non-loricate ciliates (NLC) generally peaked in the warmer periods, but a winter increase was evident towards the inner part of the channel. Tintinnid abundances generally increased in autumn. A significant relationship with temperature was not recorded for either protozoan group. An inverse relationship between NLC and salinity might be indirectly caused by their preference for the food abundant surface layer. Mesozooplankton was dominated by copepods, with distinct summer maxima throughout the area and pronounced winter maxima of >10,000 ind. m⁻³ at the inner stations. The community was predominantly neritic but the open sea waters were important in structuring the mesozooplankton assemblage at all stations during the autumn–winter period. Although temperature regulated the seasonal dynamics of most metazoans and the species succession in the copepod community, small omnivorous copepods (Oncaea media complex, Oithona nana and Euterpina acutifrons) dominated regardless of the season. A trophic link between copepods and ciliates was evident in winter during low phytoplankton biomass.     

Early life-history dynamics of Caribbean coral species on artificial substratum: the importance of competition, growth and variation in life-history strategy

The development of a coral community was monitored for 6 years (1998–2004) on 46 m² of artificial settlement substrate in Curaçao, Netherlands Antilles. Growth and survival of recruits (n=1385) belonging to 16 different species were quantified in relation to characteristics of the benthic community developing around them. The early life history dynamics (i.e. growth rate, growth strategy and survival) of corals differed among species although these differences were small for species occupying similar habitats (i.e. underside versus topside of substratum). In contrast to recruit survival, juvenile growth rates were highly variable and unrelated to benthic community structure, at least at the scale of this study. Competing benthic organisms affected coral recruitment success through space preemption (mainly by macroalgae) or recruit overgrowth (mainly by sponges). The results highlight the small spatial scale (mm–cm) at which the processes responsible for recruitment success or failure occur and emphasize the need to include such small-scale observations in studies of coral early life-phase dynamics.     

Long-term changes in a benthic assemblage associated with artificial reefs

The aim of the study was to evaluate the long-term development of a hard bottom benthic assemblage over a period of 20 years in an area off the mouth of a large river. The artificial reef of Fregene was selected because benthic assemblage data were available for the period 1981–1992. This artificial reef is located in the mid Tyrrhenian Sea, 5 nautical miles north of the two mouths of the Tevere River (Latium, Italy) and 1.5 nautical miles offshore from Fregene (Rome, Italy). The artificial reef was deployed in March 1981 for fisheries enhancement in 10–14 m of water on a sandy-silty seabed. The Tevere River carries suspended materials and a heavy load of organics since it transports Rome’s effluent, resulting in the eutrophic state of area waters. Benthic sampling was conducted in 2001 by SCUBA diving; two standard surfaces of 400 cm² were scraped from the vertical walls of the same uppermost block in four different periods. All organisms were identified and counted. The methodology used is the same as that adopted in the previous periods, so that the 2001 data could be compared with past collected data. The benthic assemblage was analysed by cluster analysis using the Bray-Curtis index and clustered using the group average clustering algorithm. The SIMPER procedure was used to identify those taxa that characterize each station group identified by cluster analysis. Changes in benthic assemblages and hydrological trends of the Tevere River were investigated using the cumulative sum series method. The 20-year development of the benthic community, starting from the new substratum, is composed of different phases characterised by different benthic assemblages. In particular five different phases were distinguished: 1. Pioneer species recruitment (May 1981–June 1981); 2. Mytilus galloprovincialis (mussel) dominance (August 1981–November 1983); 3. M. galloprovincialis regression (July 1984–October 1985); 4. M. galloprovincialis absence (91–92); 5. Bryozoans bioconstruction dominance (2001). The dynamic succession of the observed benthic assemblages exhibited a good relation with the Tevere River flow. The Tevere River flow, and the subsequent sedimentation process, seems to have strongly influenced the benthic assemblage succession of the Fregene artificial reef. Guest editors: G. Relini & J. Ryland Biodiversity in Enclosed Seas and Artificial Marine Habitats