Unusual abundance of macrobenthos and biological invasions in the Chukchi Sea

The data from the expedition of the program RUSALCA conducted in 2004 showed unexpectedly high quantitative indices of macrobenthos in the southeastern Chukchi Sea. Extensive areas of the bottom northwest of the Bering Strait were dominated by the bivalve Macoma calcarea. The greatest biomass of benthos in Macoma-dominated areas was 4232 g/m² with an average of 1382 g/m² for the investigated region. Such a high biomass of soft-bottom communities, which is extremely uncommon even in the temperature regions of the oceans, is reported for the Arctic for the first time. The long-term existence (more than 70 years) of highly productive benthic communities dominated by Macoma calcarea in one and the same area of the Chukchi Sea can most likely be attributed to gyres, which constantly arise in the region northwest of the Bering Strait. These cyclonic gyres carry nutrient-rich bottom water to the surface and hinder larval transport away from mother populations. They also keep and concentrate major food sources of benthos (live and dead phyto-and zooplankton and fecal pellets) over the benthic community locations. Most likely, a significant proportion of the primary production in the southeastern Chukchi Sea is used by benthos within the investigated Macoma community. Findings of three relatively large warm-water Pacific species near Point Hope in the Chukchi Sea are probably indicative of the progressive climate warming during the last century.     

Colonisation patterns and vertical movements of stream invertebrates in the interstitial zone: a case study in the Apennines, NW Italy

We examined vertical migration and colonisation patterns of stream macroinvertebrates within the substratum of an Apennine creek in NW Italy. Macrobenthos was sampled at three depths in the streambed (0–5, 5–10, 10–15 cm) by means of artificial baskets filled with natural substratum. We placed 42 traps (5×5×15 cm), i.e. 21 top-opened (T-traps) and 21 bottom-opened (B-traps), each composed of three overlapping baskets (high-H, medium-M and low-L), to evaluate differences in the vertical movements. We also collected Surber samples to compare interstitial assemblages with streambed communities. The multilevel traps yielded 42 taxa, compared with 60 taxa in the natural riverbed. Interstitial traps were rapidly colonised; both taxa richness and organism number increased during the 42-day study period. We found active migration in both vertical directions, but there were more invertebrates in the top-opened traps than in the bottom-opened traps. In the T-traps the most colonised baskets were those placed at the H level, while in the B-traps the L level baskets were more rapidly colonised. The interstitial assemblages differed markedly from the streambed communities in both composition and functional organisation, with more collector-gatherers and predators in the interstitial zone and more filterers and scrapers in the natural riverbed. In Apennine lotic systems, the interstitial zone is an important habitat for stream macrobenthos, although it may not be used by all species.     

Three millennia of human and sea turtle interactions in Remote Oceania

Sea turtles are one of the largest vertebrates in the shallow water ecosystems of Remote Oceania, occurring in both sea grass pastures and on coral reefs. Their functional roles, however, over ecological and evolutionary times scales are not well known, in part because their numbers have been so drastically reduced. Ethnographic and archaeological data is analysed to assess long-term patterns of human–sea turtle interactions (mainly green and hawksbill) prior to western contact and the magnitude of turtle losses in this region. From the ethnographic data two large-scale patterns emerge, societies where turtle capture and consumption was controlled by chiefs and priests versus those where control over turtle was more flexible and consumption more egalitarian. Broadly the distinction is between societies on high (volcanic and raised coral) islands versus atolls, but the critical variables are the ratio of land to shallow marine environments, combined with the availability of refugia. Archaeological evidence further highlights differences in the rate and magnitude of turtle losses across these two island types, with high islands suffering both large and rapid declines while those on atolls are less marked. These long-term historical patterns help explain the ethnographic endpoints, with areas that experienced greater losses apparently developing more restrictive social controls over time. Finally, if current turtle migration patterns held in the past, with annual movements between western foraging grounds and eastern nesting beaches, then intensive harvesting from 2,800 Before Present in West Polynesia probably affected turtle abundance and coral reef ecology in East Polynesia well before the actual arrival of human settlers, the latter a process that most likely began 1,400 years later.     

The intra-annual variability of soft-bottom macrobenthos abundance patterns in the North Channel of the Seine estuary

Temporal and spatial variability of the Abra alba–Pectinaria koreni and Macoma balthica communities was examined in the northern part of the Seine estuary (North Channel) over different space and time scales in order to assess the role that the hydrologic regime and/or anthropogenic influences play in defining benthic communities over time. Sediment in the North Channel displayed strong spatial and temporal variability, sustained by intense sediment transport episodes. Total macrobenthic abundances ranged widely on the course of the year and there was no evidence of a seasonal signal for the density fluctuations, whatever the spatial scale considered. The bio-sedimentary dynamics can be divided into two periods: the first corresponds to the high flow rate period (January–May) during which fauna is influenced by fine silt/clay deposition, and the second to the low flow rate period (June–December) during which sandy deposits prevail. Despite the absence of significant correlations between sediment composition and abundance, episodes of sediment transport seem to be an important structuring mechanism in the Seine estuary. As a consequence, the faunal composition varied throughout the year. The winter and spring fauna, characterised by species living on muddy fine-sands or muds, were enriched during the summer and autumn by species living in clean fine sand, such as Donax vittatus, Nephtys cirrosa or Spio decoratus, mainly represented by adult individuals. Secondary settlement of drifters may explain the rapid structuration of assemblages a few days after the sandy deposits. Our results suggest the importance of the bentho-pelagic coupling, primarily induced by the sedimentary instability, on the macrobenthic fauna dynamics. The intra-annual variability of assemblages at the mouth of the Seine river and the silted situation of the North Channel might simply be the result of the silting up and alteration of the inner estuary, generated by several decades of man-made modifications and natural processes.     

Long-term studies at a benthic station off the coast of Northumberland

Biannual sampling (March and September) has been carried out over the period 1972 to 1985 at a muddy sand station, 55 m depth, with fauna belonging to the deeper offshore edge of Petersen's Amphiura filiformis community.During the period 1974 to 1980 the community exhibited a high degree of persistence stability. This stability was lost between 1980 and 1983, with rising total numbers and biomass and changes in species ranking. There is some evidence of a downward reversal between 1984–85.Evidence suggests that the principal stabilising process is density dependent mortality mediated by competition in a food limited environment. The principal destabilising process appears to be periodic fluctuations in the organic flux to the bottom. A secondary destabilising process is clearly concerned with fluctuating winter temperature. In competitive terms, cold winters favour increased survival in the dominant species at the expense of the lesser ranked species. This process is, however, more ephemeral and subject to adjustment within the time scale of a year.     

A continuous study of the total drift of freshwater shrimps, Gammarus pulex, in a small stony stream in the English Lake District

1. The objective was to determine the major factors affecting the downstream dispersal (drift) of freshwater shrimps, Gammarus pulex. Sample replication and frequency are major problems in the quantification of drift. For the first time, these problems were avoided by sampling the whole stream continuously so that all the shrimps drifting downstream at the sampling point were caught in a net emptied at dusk and dawn in 1966, and every 3 days in 1967. 2. There was no consistent seasonal pattern in drift rates, but a high proportion of annual drift was taken in only a few samples. There was a nocturnal diel pattern of drift with peaks soon after dusk and just before dawn. A power function described the significant (P < 0.001) relationship between drift and flow, and was used to neutralise the dominant effects of flow by standardising total drift over 24 h, nocturnal drift and diurnal drift (drift per 50 m³). These were all significantly (P < 0.001) related to benthos density, but not to date, temperature, or length of the night or day. 3. The relationship between drift values and the independent variables, flow and benthos density, was well described (P < 0.001) by a multiple‐regression model. Adding temperature, date, and/or the length of the night or day did not improve model fit. Variations in flow and benthos density explained 94% of the variation in total drift over 24 h, 97% of the variation in nocturnal drift, but only 44% of the variation in diurnal drift. A power function described (P < 0.001) the relationship between total drift and the volume of water sampled over 3‐day periods in 1967. Flow explained 95% of this drift variation; it was unnecessary to add another variable such as benthos density. 4. The significance of this study is that it avoided the problems associated with the quantification of drift samples. Therefore, the conclusions are more robust than those of many previous studies. A high proportion of the annual drift losses would have been undetected by intermittent sampling. Temperature, season, night or day length had no significant effect on drift densities, and the relationship between drift and benthos densities was proportional, not density dependent. The nocturnal increase in drift could not be interpreted as an antipredator behaviour. The dominance of flow and benthos density was apparent but the quantitative relationships posed further questions, especially those related to drift distances at different velocities.     

Broad-scale patterns of abundance of non-indigenous soft-bottom invertebrates in Denmark

Quantifying the broad-scale distribution and abundance of non-indigenous species (NIS) is necessary to provide accurate estimations on impacts of invasions, to prioritize research, and to guide national management. Sediment grab-sampling is a standardized method for monitoring marine benthos. In Denmark, ~45,000 grab-samples were collected from 1970 to 2005. Using these samples, we compared densities of NIS and native species among 27 broad spatio-temporal groupings. Eight known NIS and one ‘cryptogenic species’ (the polychaete Neanthes succinea) were found in the samples. Most were present in low abundance, but the bivalve Mya arenaria, likely introduced by the vikings from North America, was particularly abundant. M. arenaria was found in ca. 20% of all samples and was among the 10 most common species in all of Denmark. M. arenaria’s high abundance, high filtration capacity and importance in food-web interactions, suggest that this species has dramatically impacted shallow coastal ecosystems in Denmark. The polychaete Marenzelleria viridis, the gastropod Potamopyrgus antipodarum and N. succinea were also widespread and abundant, and they too are likely to have had broad-scale impacts. In conclusion, 28% of grab-samples collected in Denmark over 35 years were affected by some degree of NIS or cryptogenic species, suggesting that centuries of human-mediated transfer of organisms has had a profound impact on the ecology of soft-bottom systems in Denmark.     

The effect of long pools on the drift of macro-invertebrates in a mountain stream

Macro-invertebrate drift was measured entering and leaving two pools on the Middle Fork of the Cosumnes River, a third order California stream. Drift rates for Baetis spp., Chironomidae, Simulium spp., Capniidae and total drift were calculated. Significant differences in the numbers of organisms entering the two pools were found for Baetis, Chironomidae, and Capniidae. Comparisons of drift rates at the upstream and downstream ends of each pool showed that the abundance of Chironomidae, Simulium, Capniidae and total drift changed in different directions across the pools. The numbers of organisms leaving the two pools, however, were not significantly different for Baetis, Simulium, Capniidae and total drift. These findings lead us to hypothesize that long pools act as barriers, not filters, to stream macro-invertebrate drift. The composition of drift leaving the pools in this experiment appeared to be controlled by the composition of the benthic habitat at the tail of the pool and not by the composition of upstream drift entering the pools.     

The intertidal soft-bottom infaunal macrobenthos in three Basque estuaries (Gulf of Biscay): a feeding guild approach

Feeding types of the infaunal macrobenthos of the intertidal soft-bottom communities from the estuaries of La Arena, Plentzia and Gernika, along the Basque coast (Gulf of Biscay) were studied in relation to habitat conditions, characteristics of each estuary and seasonal variation. General feeding structure observed in La Arena estuary was different from the other estuaries: omnivores were dominant, both in number of species and individuals, while surface deposit-feeders were the main feeding group in Plentzia and Gernika both in the finest sediment communities and in the sandy ones. Subsurface deposit-feeders were abundant in Plentzia and Gernika but scarce in La Arena estuary. Feeding types were related to the environmental variables. Sandy sediment communities presented a more balanced proportion among different feeding types and showed higher values of feeding diversity; suspension-feeders and predators were abundant only in that communities. By estuaries, feeding diversity was higher in Gernika and lower in La Arena. Seasonal variation in feeding diversity was observed, explained by changes in density of certain feeding groups; a common pattern of variation was found in Gernika communities, with an increase in June and a decrease in September. Oscillation of this index in Plentzia and La Arena depended on the estuary and the different communities; nevertheless a decrease of feeding diversity in September was commonly observed. Finally, feeding structure observed in our estuaries was compared to those described in coastal areas with organic enriched sediments, in order to assess the degree of perturbation of the environment based on the relative dominance of a certain feeding type in the macrobenthos.     

Upstream-downstream movements of aquatic invertebrates in a Rocky Mountain stream

Simultaneous collections of drift and organisms moving either upstream or downstream in association with the substrate were made using a specially designed sampler. Samples were taken in a diel series along a transect across the study riffle of a Colorado foothills stream on six dates over an annual cycle. In addition to longitudinal movements, taxonomic composition and diel periodicity were evaluated. The insect-dominated fauna showed a net downstream displacement. Only the caddisflies Helicopsyche borealis and Hesperophylax occidentalis exhibited net upstream movement, primarily a result of low drift frequencies. The taxonomic composition of moving invertebrates differed from that of the benthos. Drift resembled downstream moving substrate-associated invertebrates in composition, but differed from that of the upstream directed fauna. Taxa collectively exhibited four types of diel patterns: 1) similar downstream (drift and substrate-associated movements) patterns, which generally differed from the upstream pattern; 2) similar benthic (upstream and downstream) patterns, which differed from that of drift; 3) aperiodic patterns; and 4) independent patterns for each type of directional movement. Analysis of size classes based on head capsule width for the mayfly Baetis tricaudatus showed significantly smaller size in stationary individuals compared with moving individuals in the population and revealed that nymphs moving during the day were smaller than those moving at night.     

The drift distances and time spent in the drift by freshwater shrimps, Gammarus pulex, in a small stony stream, and their implications for the interpretation of downstream dispersal

1. The objectives were (i) to determine experimentally and to model the relationship between mean water velocity and both the mean distance travelled, and the mean time spent, in the drift by freshwater shrimps, Gammarus pulex; (ii) to develop a drift distance–water velocity model from the experimental study, and validate it with field data; (iii) to examine the relationship between drift rate, water velocity and benthic density with the latter expressed as a mean value for the whole stream and a mean value corrected for the distance travelled in the drift. 2. In field experiments at 10 water velocities (0.032–0.962 m s^?1), the significant relationship between the mean drift distance and mean water velocity was described both by a power function (power, 0.96) and a linear relationship. The mean drift time was fairly constant at 8.3 s (95% CL ± 0.4). A simple model estimated the drift distance and time spent in the drift by different percentages of the drifting invertebrates. This model predicted correctly the positive relationship between drift rate and water velocity for field data over a year. 3. The relationship between drift rate per hour and the independent variables, water velocity and benthic density, was well described by a multiple‐regression model. Adding temperature and date did not improve model fit. Variations in water velocity and benthic density explained 96% of the variation in nocturnal drift rate (65% to velocity, 31% to benthic density), but only 40% of the variation in diurnal drift rate (29% to velocity, 11% to benthic density). Correcting benthic density for the drift distances did not improve model fit. 4. The significance of this study is that it developed models to predict drift distances and time, values being similar to those obtained in another, larger stream. It also illustrated the importance of spatial scale in the interpretation of drift by showing that when drift distances were taken into account, the impact of drift on the population was higher (4–10% lost day^?1) than when drift distances were ignored (usually < 3% lost day^?1), especially at a local level.     

The influence of density gradients on the transport of solutes in a deep estuary

This paper reports on an investigation into the lower Forth estuary where a combination of hydrody namic, dye and salinity measurement techniques have been employed to quantify the effects of temporally varying vertical and transverse density gradients on the diffusion and dispersion processes. It is concluded that the interaction of velocity shear and weak longitudinal salinity induced density gradient produces a complex and profound effect on estuarine solute mixing processes.     

Effect of meteorology and nutrient load on oxygen depletion in a Danish micro-tidal estuary

In a detailed analysis of oxygen saturation in a shallow Danish estuary it was possible to separate the effect of meteorological forcings (i.e. wind and solar radiation) and nutrient loads on oxygen depletion in bottom water. Regression analysis showed that oxygen saturation tied to nitrogen load rather than to phosphorus load. During summer periods of stratification the oxygen saturation could be attributed to the time elapsed after the onset of stratification and the accumulated nitrogen loading 10 month prior to measurement. Using a 10-year meteorological database and an empirical model it was calculated that a 25% reduction in nitrogen loading would reduce the number of days with severe oxygen depletion (i.e. <15% of saturation) by more than 50%.     

Substrate selection and seasonal variation in densities of invertebrates in stream pools of a tropical river

Spatial distribution and seasonal variation in densities of the invertebrates were investigated for a year in three stream pools of a South Indian river. The effects of season, substrate type and water depth on the distribution were analyzed. Substrate type and season influenced the invertebrate distribution the most. Leaf packs harboured most of the organisms followed by macro-algal substrate and sand. The lowest densities were observed on rocky substrates and in the water column. Rocky substrates in shallow water supported higher densities of total invertebrates than deeper areas. Chironomid larvae dominated all benthic substrates throughout the year. Of the 19 invertebrate taxa studied, 6 showed no seasonality in densities, and most of the rest showed their highest densities in the pre-monsoon period and lowest in the SW monsoon or post-monsoon periods. However, in two of the three pools, the densities of total invertebrates were highest during the post-monsoon period with secondary peaks in the pre-monsoon period.     

An analysis of changes in the invertebrate community along a southern New Zealand montane stream

Changes in benthic community structure at four sites along a flood-prone montane stream continuum in the South Island of New Zealand were analysed using rank correlation (Kendall's Tau and Spearman's r_s) and a community similarity index (S_c) developed initially for stream pollution assessment. Species richness was highest in a forested headwater stream, which is attributed to its relatively greater physical stability and habitat heterogeneity. Community similarity decreased with distance apart, and pairs of open and forested sites showed the greatest similarity. Species composition and relative abundance along the continuum changed least in the numerically dominant Ephemeroptera and Plecoptera, groups in which several species had broad habitat requirements. In contrast, a number of dipteran and trichopteran species had more restricted distributions. The more specialised niche requirements of some species in these orders are attributed to their generally small size, their ability to spin silk, and their holometabolous development. Physical rather than biological factors appeared to limit the distributions of most invertebrates, and there was little evidence of ecological segregation by either food resource partitioning or differences in life history patterns amongst many closely related species. Theories that stream communities are well ordered entities maximising the efficiency of energy utilisation cannot realistically be applied to such unstable stream systems.     

Spatial Structure of the Insect Community of a Small Dimictic Lake in the Laurentians (Québec)

The distribution of merolimnic benthic insects was studied in Lake Cromwell, a small (9 ha) and shallow (max. depth 9 m) dimictic lake with a summer hypolimnetic warming on the Laurentian highlands of Québec. Communities were described from 22 sets of emergence data. Two hundred and twelve species were recognized of which 153 were Chironomidae (Diptera). Through clustering and ordination techniques, five communities were recognized: one in the flooded shrub zone along the shore, two littoral, one sublittoral and one profundal. Differences between the communities were more quantitative than qualitative. The majority of species inhabited the shore and littoral stations, and only the hardiest reached the deepest zone. There were few species characteristic of the profundal, none of them abundant. Discriminating, dominant, and characteristic species were determined for each community, as were the ubiquitous species. There is a general decrease in species richness, species diversity and population density, and a change in community structure along the depth gradient. A discontinuity at 1–2 m is related to a sharp increase in Chaoboridae in the deeper waters.     

Origin and trophic importance of detritus-evidence from stable isotopes in the benthos of a small,temperate estuary

Ratios of ¹³C/¹²C and ¹⁵N/¹⁴N were measured in dissolved inorganic carbon (DIC), marginal vegetation, benthic macrodetritus (diameter > 1 mm) and selected invertebrate consumers in the Gamtoos estuary, South Africa to: (1) trace the provenance of benthic detrital deposits, and (2) determine the extent to which three abundant species of macroinvertebrates utilise this resource. DIC was strongly depleted in ¹³C with average ¹³C values (–9.5±0.5) being typical of limnetic waters. Benthic detrital particles (¹³C–24.1±0.3) originated mainly from marginal vegetation (¹³C–25.7±0.3), but their slightly elevated carbon ratio suggests additional input from ¹³C-rich sources-possibly C₄ plants cultivated on the floodplain. Populations of the fossorial ghost shrimp Callianassa kraussi, the bentho-pelagic amphipod Grandidierella lignorum and the epifaunal crab Hymenosoma robiculare together account for 96% of total benthic biomass in the upper regions of this estuary. Marked differences in trophic niches were evident among these three consumer species. Ghost shrimp (¹³C –32.5±0.3) foraged by filter-feeding on fine suspended particulate organic matter (¹³C–31.2±0.5). Amphipods (¹³C–28.0±0.6) utilised some benthic detritus but fed mainly on suspended material. Only the relatively rare crabs (¹³C–23.8±1.5) appeared to utilise benthic detrital particles to any significant extent. In the benthic consumer community of the upper Gamtoos estuary, suspension feeders make up 98% of biomass and thus clearly dominate over deposit feeders. This can be traced to the low contribution of higher plants (c. 13%) to overall carbon production, and detritus originating from macrophytes is consequently relatively unimportant in supporting invertebrate secondary production in this particular system.     

Water chemistry variability in the lower intertidal zone [-2pt] of an estuary in the Seto Inland Sea,Japan: seasonal patterns of nutrients and particulate compounds

From April 1994 to April 1996, we carried out monthly surveys on the physical and chemical variability of ebbing water at two intertidal stations near the emerged tidal flat and surface water at a nearby subtidal station, in a tidal estuary of the Seto Inland Sea, Japan. The fresh water runoff was a major source of new nitrogen (nitrate+nitrite = –2.1 × salinity + 74.3, r ² = 0.76, p < 0.001, at the inner intertidal station). In contrast, the absence or weak correlation of ammonium, phosphate and silicate with salinity in ebbing water highlighted the importance of in situ biologically-mediated processes, including the excretory activity of intertidal dominant bivalves (Ruditapes philippinarum and Musculista senhousia) and primary producer nutrient uptake. Among suspended particulate matter (SPM), the negative correlation of Chl a with salinity (p< 0.001) suggested that an upper intertidal zone, where high microphytobenthic assemblages occur, may represent a considerable source of microalgal biomass. Whereas, a stronger correlation of POC with pheo-pigments (r ² 0.92) than with Chl a (r ² 0.44), a low fraction of living phyto-Carbon (ca. 5%) and a high pheo-pigment/Chl a ratio (ca. 3) indicated a high portion of refractory algal material and a close water–sediment coupling on the flat, in which abundant macrozoobenthos is likely to play an important role. In spite of the strong variability of this ecosystems, this study also demonstrated that highly significant seasonal patterns can be recognized in our study area. However, patterns varied depending on the different nutrient species, SPM and sites. In ebbing water, ammonium concentrations were significantly higher in the cold period (i.e. November–April: water temperature 10.0 ± 4.4 °C), when primary producer biomass decreases, while Chl a and pheo-pigment content were 4.3 and 4.8 higher in the warm period (May–October: water temperature 23.5 ± 4.2 °C), respectively. At the subtidal site, nutrients were 1.9 (silicate)–2.9 (phosphate) and SPM was 1.8 (POC)–2.1 (pheo-pigments) times higher in the warm period. On an annual basis, mean pheo-pigment and POC content was 12–25 times and 4–8 times higher on the intertidal zone than on the subtidal zone, respectively, while nutrient concentrations were within the same order of magnitude. Such a qualitative difference (i.e. nutrients vs. SPM) between sites suggests that particle deposition and/or removal is likely to occur along the estuary, resulting in a limited SPM content at the surface layer of the subtidal site, while nutrients are more directly transported into the surface layer of the subtidal zone by lower salinity water mass intrusion from the intertidal zone, most importantly during the warm period.     

Reproductive ecology of the freshwater red alga Batrachospermum boryanum Sirodot in a temperature headwater stream

The surface and hyporheic fauna of a second-order reach of a northern California Coast Range stream (Big Canyon Creek, Lake Co., CA, USA) was examined using substrate colonization samplers (i.e. hyporheic pots) during both the wet and dry seasons in the prevailing Mediterranean climate of the region. In terms of total number of macroinvertebrate taxa, the surface (0 cm to −5.0 cm within the stream substrate) level had higher richness than any level within the hyporheic (−5.1 cm to −15.0 cm, −15.1 cm to −25.0 cm, or −25.1 cm to −35.0 cm) from the beginning of the dry season (May) to the beginning of the wet season (October); during this period the surface was not subject to disturbance from wet-season storms. During the wet season, richness at the surface was similar to that observed at any of the three hyporheic levels examined. Macroinvertebrate density at the surface was substantially reduced during the wet season; however, mean surface densities always exceeded those found within the hyporheic zone (from 25% to 78% of total macroinvertebrate numbers were found at the surface). Seasonal fluctuations in abundance of total macroinvertebrates and density of many constituent populations were less within the hyporheic zone than at the surface. Apparently, early instars of abundant surface taxa do not penetrate the interstices, and substrate disturbance due to spates is less in deeper levels. Compared with many hyporheic faunas described from other temperate-zone sites, this hyporheic community shows reduced numerical dominance by the Chironomidae.     

Short term dynamics of the dominant annelids in a polyhaline temperate estuary

Weekly sampling over a two year period from a muddy sand bottom in the polyhaline York River, Virginia, U.S.A., clearly identified the pattern of recruitment and survival of the dominant annelid species. Three intermingled recruitment strategies and two survival patterns were observed, ranging from the classic opportunistic life style of mass recruitment over short time periods followed by mass mortality to prolonged recruitment with lower mortality. Qualitatively the annelid assemblage was very similar from year to year with most of the changes being quantitative. Oligochaetes, Tubificoides spp., were the most stable and characteristic members of the annelid assemblage.Contribution No. 1118 of the Virginia Institute of Marine Science