Colonization of meiobenthos in oil-contaminated subtidal sands in the lower Chesapeake Bay

In-situ manipulative experiments were conducted over a 3-month period (May–August 1980) to examine the rate at which meiobenthos colonizes oiled and untreated azoic fine sands at a shallow subtidal site in the lower York River, Virginia. Three concentrations of fresh Prudhoe Bay crude oil were added to sediments: 100, 2 500 and 10000 mg oil kg^-1 dry wt sediment. Untreated azoic and natural sediments served as controls. Within 16 d, meiofauna densities in all treatments were comparable to natural populations in surface oxidized sediments, but densities fluctuated greatly during the remainder of the sampling period. Nematodes slowly colonized the subsurface anoxic sediments below the redox potential discontinuity (RPD); some less common species did not significantly recover below the RPD in the two more heavily oiled treatments. Analysis of nematode community composition by reciprocal averaging ordination and numerical classification revealed generally lower abundances, but no distinct differences, in species composition in the oiled substrates as compared to untreated and natural community controls. Ordination of sequential samples suggested that the nematode species assemblages in the untreated controls fully recovered from these small-scale disturbances by 90 d. Life history characteritics and frequent tidal transport combine to make estuarine meiobenthos highly resilient following disturbance. Contrary to prior recolonization studies, a successional sequence was found for the colonizing nematodes which may be analogous to models of macrobenthic colonization (e.g. McCall, 1975). The comesomatid nematode Sabatieria pulchra, which is frequently dominant in polluted sediments, colonized relatively late in the experiment. Consequently, stress resistance and resilience may not be as coincident in meiofauna as in macrofauna because of differences in factors affecting their dispersal.     

Effects of physical disturbance on nematode communities in sand and mud: a microcosm experiment

A microcosm experiment was carried out to evaluate the effects of continuous and spasmodic physical disturbance of differing frequency on the structure of nematode communities of intertidal sand and mud. There was a marked, characteristic change in abundance and diversity for both sediment types. In the sand microcosms, the majority of univariate measures of community structure, including species diversity, were lowest in the sediments subjected to a high frequency of disturbance. For the mud microcosms, most univariate measures reached their highest values in the treatments with an intermediate frequency of disturbance and were lower in treatments subjected to both higher and lower frequencies. Multivariate ordinations for both nematode assemblages showed a clear separation of undisturbed controls and disturbed treatments, but only for the muddy sediment was there a graded change in community composition with increasing frequency of disturbance. These results confirmed our a priori expectation that nematode assemblages from mobile sandy sediments would be more resilient to physical disturbance than those from sheltered muds, and these observations are considered in the context of Connell's intermediate disturbance hypothesis. Received: 7 May 1997 / Accepted: 10 October 1997     

Ecological effects of dumping of dredged sediments; options for management

Dredging and dumping of dredged sediments in estuarine and coastal waters may lead to increased turbidity and enhanced sediment deposition at dump sites. This mainly affects primary production by phytoplankton, performance of visual predators (e.g. fish, birds), and growth and survival of benthic organisms. This paper combines a compilation of literature information and results of additional experimental studies on the effect of enhanced concentrations of suspended matter (SPM) on growth of bivalve molluscs, and on survival of macro- and meiozoobenthos after dumping of dredged sediments. Furthermore, it focuses on non-toxic dredged sediments only. Release of nutrients from dredged sediments did, so far, hardly influence estuarine phytoplankton production. Increased turbidity may affect dab as well as prey location by sandwich terns. Enhanced SPM-concentrations are unfavourable for young herring and smelt. Growth of filter-feeding bivalves may be impaired, especially at SPM-concentrations >250 mg/l. Estuarine nematodes can survive burial by 10 cm of dumped dredged sediment provided that its physical characteristics are similar to those of the original sediment. Sessile benthos organisms such as mussels and oysters can cope with sediment deposition of only 1–2 cm. Other macrozoobenthos can survive sediment deposition of 20–30 cm. Recovery of benthos at a dump site will occur if the interval between successive dumpings is sufficiently long. Options for management of dumping of dredged sediments are described, relating to different locations of dump sites in estuarine and coastal waters, to different seasons, and to the actual use (area and frequency) of dump sites.     

Experimental variation of near-bottom current speeds and its effects on depth distribution of sand-living meiofauna

Meiofauna are eroded from sediments and transported in the water column. To examine how meiofauna respond to erosive currents, in situ current speeds were altered on an intertidal sandflat located in Bogue Sound, North Carolina, USA in July 1982. Replicates of two different weir designs were erected. One design increased measured current speed and the other, a control, did not. The depth distributions of meiofauna in each treatment and from undisturbed sediment were compared. There were few differences among treatments in depth distribution of the most abundant taxa: nematodes, turbellarians, and ciliates (>37-m-long). However, a significant amount of sediment erosion (a mean of almost 0.5 cm in 2 h) occured in the increased flow treatment. Meiofauna responded to the loss of sediment with no discernable differences in depth distribution relative to the controls. There was some evidence that nematodes were less abundant and ciliates more abundant in the top 0.5 cm of the increased flow treatment. This may indicate that nematodes respond to fast surface current speeds by moving deeper into the sediments, while ciliates manage to remain near the surface even as sediment erodes. The entrainment of meiofauna may be passive but meiofauna clearly exert considerable behavioral influence over their susceptibility to entrainment.     

Detection of pollution effects on marine macrobenthos: further evaluation of the species abundance/biomass method

Further empirical data are presented to evaluate the method of detecting pollution-induced disturbance in marine benthic communities by a comparison of the distribution of numbers of individuals among species with the distribution of biomass among species. A suggested abbreviated name for the technique is the ABC method (abundance biomass comparison). Application of the technique to new data shows that it is a sensitive indicator of natural physical and biological disturbance as well as pollution-induced disturbance over both spatial and temporal scales. Changes in the configuration of ABC plots during ecological succession are the reverse of those resulting from increased pollution levels. The technique should also be applicable to intertidal sediments, where physical disturbance of the sediment by waves does not appear to preclude its utility.     

Studies on the sublittoral free-living nematodes of Liverpool Bay. II. Influence of sediment composition on the distribution of marine nematodes

Previous work has shown that the composition and diversity of nematode populations in Liverpool Bay (UK) are correlated with sediment granulometry, and possible reasons for this relationship are now discussed. Sediment granulometry and nematode size appear not to be directly related, but the range of nematode lengths is greater in the more heterogeneous sediments. Median particle diameter, sorting efficiency and silt/clay content are all considered to affect sediment uniformity, and an index including all three factors correlated significantly with both size diversity and species diversity. Study of the distribution of the various feeding types revealed that the relative and absolute abundances of epistratum feeders and non-selective deposit feeders correlated significantly with the sediment silt/clay content. It is concluded that sediment granulometry influences nematode distribution both directly in determining the size range of the populations (and hence, to some extent, the species diversity) and indirectly in determining, to a great extent, the type of food available. In addition, it was noted that nematodes with very ornate cuticular ornamentation tended to be associated with coarser, silt-free sediments, and it is suggested that this may be correlated both with their mode of locomotion and with the need for mechanical protection in unstable substrata.     

Polycyclic aromatic hydrocarbons in surface sediments held in experimental mesocosms

Sediment was collected from three locations along a pollution gradient in Narragansett Bay and transplanted to controlled mesocosms. Total hydrocarbons and eleven individual polycyclic aromatic hydrocarbons (PAHs) were measured in these sediments over a period of 394 days. Total hydrocarbon concentrations increased in the “relatively uncontaminated”; (Rhode Island Sound) sediment that was held in the mesocosms, but did not change in the two other sediments. The concentrations of four PAHs: naphthalene, 2‐methyl naphthalene, 1‐methyl naphthalene and biphenyl, decreased in the “contaminated”; (Providence River) sediment during the experiment and the calculated half‐lives for these compounds were 287, 353, 321 and 333 days, respectively.     

Colonisation process of vegetative fragments of <Emphasis Type="Italic">Posidonia oceanica</Emphasis> (L.) Delile on rubble mounds

Seagrass colonise new areas via the dispersion of seeds or vegetative fragments. Independent of the manner of colonization, habitat requirements need to be met for the successful establishment of seagrasses. Here we report on the colonization process of Posidonia oceanica in a highly disturbed area: a gas pipeline trench at Capo Feto (SW Sicily, Italy). A trench dredged through a P. oceanica bed was back-filled with rubble added from dump barges leading to the formation of a series of rubble mounds on the seabed. Over time, these mounds became colonised with P. oceanica. I>. In order to understand the pattern of P. oceanica colonization, shoot density was quantified over 3 years (2001–2003) on different mound locations (crests, sides, valleys). Seagrass coalescence was observed only in valleys between mounds where shoot density averaged 133±50 shoots m⁻², while values for sides and crests were significantly lower (30.5±14 and 5.8±2.6 shoots m⁻², respectively). Although sediment accumulated on both crests and valleys, a significantly thicker sediment layer was recorded in the valleys (9.8±0.4 cm) than on crests (1.1±0.2). Plaster dissolution rate (an indicator of the hydrodynamic regime) tended to decrease from crests to valleys but even in the valleys, the currents were still higher than in the adjacent vegetated control location. This pattern was constant over time and depths. This is the first study to report on P. oceanica vegetative recruitment on artificial rubble after a disturbance event. It appears that the valleys between the rubble mounds are suitable for seagrass recruitment as sediment deposited between the rubble provides the necessary resources for plant settlement and growth. Once the seagrass patches are established, they may start a positive feedback of attenuation of currents, sediment accumulation and seagrass patch expansion.     

Type of disturbance and ecological history determine structural stability.

This study aims to reveal whether complexity, namely, community and trophic structure, of chronically stressed soil systems is at increased risk or remains stable when confronted with a subsequent disturbance. Therefore, we focused on a grassland with a history of four centuries of patchy contamination. Nematodes were used as model organisms because they are an abundant and trophically diverse group and representative of the soil food web and ecosystem complexity. In a field survey, a relationship between contaminants and community structures was established. Following, two groups of soil mesocosms from the field that differed in contamination level were exposed to different disturbance regimes, namely, to the contaminant zinc and a heat shock. The zinc treatment revealed that community structure is stable, irrespective of soil contamination levels. This implies that centuries of exposure to contamination led to adaptation of the soil nematode community irrespective of the patchy distribution of contaminants. In contrast, the heat shock had adverse effects on species richness in the highly contaminated soils only. The total nematode biomass was lower in the highly contaminated field samples; however, the biomass was not affected by zinc and heat treatments of the mesocosms. This means that density compensation occurred rapidly, i.e., tolerant species quickly replaced sensitive species. Our results support the hypothesis that the history of contamination and the type of disturbance determine the response of communities. Despite that ecosystems may be exposed for centuries to contamination and communities show adaptation, biodiversity in highly contaminated sites is at increased risk when exposed to a different disturbance regime. We discuss how the loss of higher trophic levels from the entire system, such as represented by carnivorous nematodes after the heat shock, accompanied by local biodiversity loss at highly contaminated sites, may result in detrimental effects on ecosystem functions.     

An ecophysiological study of some meiofauna species inhabiting a sandy beach at Bermuda

The dominant nematode and harpacticoid species inhabiting a sheltered beach at Bermuda were characterized by their vertical distribution in the sediment, by their tolerance of high temperature under oxic and anoxic conditions, and by their tolerance of extreme pH-values. In 4 species of nematodes the respiratory rate proved to be inversely proportional to the depth at which the species occurs, and directly proportional to the size of the buccal cavity. One species, the nematode Paramonhystera n.sp., is more temperature resistant at zero or near zero pO₂ than at atmospheric oxygen pressure; it is the first marine metazoan in which it can be shown that a specific biological process is favourably affected by anoxic conditions if compared with the situation at normal pO₂.Contribution No. 593, the Bermuda Biological Station     

Impacts of chronic trawling disturbance on meiofaunal communities

Bottom trawling causes chronic and widespread disturbance to the seabed in shelf seas. Meiofauna may be impacted directly or indirectly by this disturbance, since the passage of trawls causes immediate mortality or displacement, changes sediment structure and geochemistry and affects the abundance of predators or competitors. Since meiofauna make a significantly greater contribution to benthic production than the larger macrofauna, there are compelling reasons to assess their response to chronic trawling disturbance. In this study, we determined the effects of trawling disturbance, season, sediment type and depth on the structure and diversity of nematode communities. Our analyses were based on comparisons between nematode communities in three beam-trawl fishing areas in the central North Sea. These areas were trawled with mean frequencies of I (low disturbance), 4 (medium) and 6 (high) times year⁻¹ respectively. Our analyses showed that trawling had a significant impact on the composition of nematode assemblages. In two sampling seasons, the number of species, diversity and species richness of the community were significantly lower in the area subject to high levels of trawling disturbance than in the areas subject to low or medium levels of disturbance. However, levels of disturbance at the ‘low’ and ‘medium’ sites may have been insufficient to cause marked longterm changes in community structure. Many of the observed changes were consistent with responses to other forms of physical disturbance. The extent to which the observed changes in community structure reflect changes in the production of the nematode community remains unknown, although overall abundance was not significantly affected by trawling disturbance. Published online. 9 August 2002     

Gradients in biodiversity and macroalgal wrack decomposition rate across a macrotidal, ultradissipative sandy beach

The decomposition process of, and the meiobenthic and nematode colonization on, stranded macroalgae were studied along a macrotidal, ultradissipative sandy beach gradient at De Panne (Belgium). The horizontal patterns of macro- and meiofaunal densities and diversity in this beach have been well-documented. Defaunated Fucus detritus was buried in situ in litter bags, 10–15 cm under the sediment surface, at seven stations across the beach profile. Colonization by (meio)fauna and organic matter decomposition rates measured as carbon, nitrogen, phosphorus and dry weight loss, were studied after 10, 21 and 52 days of incubation. Algal detritus was colonized mainly by nematodes dominated by Rhabditidae, Sabatieria, Dorylaimoidea, Monhystera, Paracanthonchus and Daptonema. Organic matter weight loss was slowest at the higher and lower shore and fastest in the mid-shore, in line with the horizontal pattern of nematode diversity in the beach sediment. However, there was no consistent relationship between nematode diversity inside the litter bags and organic matter weight loss, prohibiting an unequivocal conclusion on whether the observed parallel between extant nematode diversity and organic matter decomposition rate indicates a causal relationship or follows from the fact that both are governed by the same set of physicochemical conditions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Life history of the nematode Theristus anoxybioticus from sublittoral muddy sediment at methane seepages in the northern Kattegat,Denmark

Field and laboratory studies from 1989 to 1994 of the nematode Theristus (Penzancia) anoxybioticus Jensen, 1995 inhabiting muddy sediment at methane seepages in the northern Kattegat, Denmark, have revealed a series of biological features of adults and juveniles not observed before in free-living marine nematodes. Reproductive adults were present in April and May only and inhabited the uppermost cm of sediment, while juveniles inhabited deep anoxic and sulphidic sediment layers during the remaining months of the year. This points to a downwards migration of newly hatched juveniles and an upwards migration during adulthood. Gut content analyses showed that adults feed mainly on benthic diatoms by swallowing whole cells while juveniles probably feed on bacteria; this differentiation in food clearly relates to the main bulk of potential food items in their respective microhabitats. The generation time is estimated to be one year, with a juvenile life span of about nine months, which is four to eight times longer than that found in related aerobic species of similar body size. Adults survived in oxic water but 50% died within 15 h in hypoxic water (5 to 6% atm sat), and all died within 12 h in anoxic water. Juveniles on the other hand died within 0.5 h in oxic water but survived anoxic water for at least 15 d. These results suggest that juveniles of T. anoxybioticus are adapted to an anaerobic life style.     

Population studies on benthic nematodes within a subtropical seagrass community

Examination of the benthic nematode fauna of the soft surface sediments of a turtle grass (Thalassia testudinum König) bed in Biscayne Bay (Miami, Florida) has revealed a high degree of homogeneity exemplified by the dominance of four species out of approximately 100 nematode taxa from the area. The dominant species, Metoncholaimus scissus, Theristus fistulatus, Spirinia parasitifera and Gomphionema typica, regularly comprised between 87 and 95% of the total number of nematodes present in samples collected during the winter and spring of 1966. T. fistulatus showed an abundance of 56% over the course of the study, i.e., 160 samples collected over a period of 14 months. Maximal peaks in population densities were noted and correlated with physiographic alterations in the environment. The M. scissus population declined concurrent with changes in the community; at the same time, with accumulation of sediment, the Terschellingia longicaudata population increased. Ratios of species, and especially shifts in the dominantforms present, with repeated collections, are extremely useful indicators of important biological and physical changes in a particular environment. Analysis of distributional data on dominant species in 64 samples from eight closely approximated positions showed that observed temporal and spatial variations were not significant statistically at the 5% level. It is concluded that erroneous observations can be made from ecological studies based on field data derived without proper replication or consideration of seasonal factors. The latter as well as intrinsic variability within the particular locality itself contribute to the basic faunistic composition of benthic communities.This work was supported by Grant 12482 from the National Institute of Health to the Institute of Marine Science, University of Miami, and is a contribution (No. 819) from the Institute of Marine Science and from the Nematology Section, Entomology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa.     

Colonization and early succession on artificial hard substrata by meiofauna

An experiment was undertaken at Farol Island, Brazil, to examine colonization of bare aluminium surfaces by microbes and meiofauna. It was hypothesized that a primary source of meiofaunal colonists was sediment resuspended during upwelling events, two of which occurred during the experiment. Microbial biofilms formed on the experimental substrata within 1 day, and continued to develop throughout the experimental period. Among meiofaunal groups copepods also appeared on the first day, and nematodes on the second. Meiofaunal community structure developed in three main phases: an initial phase of 2 days, characterized by low abundances of copepods; a second phase during the first upwelling period characterized by higher abundances of copepods and also by turbellarians; and a third phase from day 13 onwards characterized by relatively stable abundances of a range of taxa including copepods, cirripedes, nematodes and ostracods. Nematode assemblages also developed in three phases, but with different timings coinciding with upwelling events: an initial phase, from the beginning of the experiment to day 9, characterized by few species and low (or no) abundances; a second phase following the first upwelling characterized by moderate abundances of Chromadorina, Chromadorella, Daptonema and Euchromadora sp. 3; a third phase following the second upwelling period (from day 26 onwards) in which Daptonema disappeared and the assemblage was characterized by moderate to high abundances of Euchromadora (species 1 and 2) and Chromadorella. Although shifts in nematode assemblage structure coincided with upwelling events no evidence was found for sediments being the primary source of colonizers on the aluminium substrata, in contrast to our hypothesis.     

Nematode assemblages from <Emphasis Type="Italic">Avicennia</Emphasis><Emphasis Type="Italic">marina</Emphasis> leaf litter in a temperate mangrove forest in south-eastern Australia

Meiofauna from Avicennia marina leaf litter in a temperate mangrove forest was enumerated, and the nematode assemblages compared on the bases of leaf colour (used as a guide to leaf age) and shore horizon where samples were collected. Twenty-one putative nematode species were collected from 48 leaf litter samples. Univariate analyses indicated that neither the colour of the leaf nor the shore horizon significantly affected abundance of nematodes. However, of the four (2Ƕ) treatment groups, rarefaction curves revealed highest diversity on brown leaves from under the shade of the tree canopy (H'=0.751ǂ.126 SE, n=17). Species diversity of leaf litter nematodes was lower in this temperate mangrove system than reported from tropical mangrove studies. ANOSIM tests confirmed a significant effect of shore horizon on nematode assemblages. The dominant feeding group among nematodes was non-selective deposit feeders (7/21 species, but 77% of all nematodes). Epigrowth grazers were represented by 8/21 species of nematodes, but only 19% of the total number. Excised leaves became skeletonised by about 15 weeks. Shorter temporal scales of life cycles of nematodes compared with leaf degradation, and the dynamic nature of epibiontic assemblages, probably explain the similar assemblage structure on yellow and brown leaves.     

Role of grapsid crabs, Parasesarma erythrodactyla, in entry of mangrove leaves into an estuarine food web: a mesocosm study

The influence of the crab Parasesarma erythrodactyla on the entry of the organic matter derived from Avicennia marina mangrove leaves in a sub-tropical mangrove ecosystem of southeast Queensland, Australia, was simulated using tidal mesocosms. Degradation of mangrove leaf organic matter was followed by analysing the fatty acid composition, carbon, and nitrogen isotopic signatures of the surface sediment and suspended particulate organic matter (SPOM) with and without the presence of crabs. Assimilation of mangrove organic matter by P. erythrodactyla was also assessed by stable isotope and fatty acid analyses in tissues and faeces. Results of the chemical tracer analyses question the adaptability of P. erythrodactyla to a diet comprised exclusively of mangrove leaves, and suggest that these organisms were dependent on additional food sources in their natural environment. Crab processing of senescent leaves significantly accelerated the transfer of mangrove organic matter to the surface sediments, as shown by a higher C/N ratio, a higher contribution of long-chain fatty acids and a more depleted C isotopic signature of sediment samples in the mesocosms with crabs compared to those without crabs.     

Population distribution and structure of the free-living nematodes of Long Island Sound

The distribution and structure of nematode populations in 4 sedimentary environments (muds, muddy sands, fine sands and medium-coarse sands) in Long Island Sound were studied. Mean population densities were highest in muds and muddy sands. Cluster analysis suggested the presence of two basic faunistic units; a mud unit characterized by high species dominance, low species diversity and low species endemism, and a sand unit characterized by low species dominance, high species diversity and high species endemism. Species diversity in all habitats was a direct function of both species richness and equitability. Limited niche separation among deposit feeders, usually the dominant nematode trophic type in muddy sediments, is proposed as the cause for the high species dominance so often characteristic of shallow marine muds. The study afforded the opportunity to examine the quantitative and qualitative aspects of population structure in relation to environmental impact (as indicated by large differences in the heavy metal and organic carbon concentrations within each of the 4 sedimentary regimes). Within each sediment type no differences in population densities, species composition or species diversity of nematodes existed between heavily impacted and apparently non-impacted sediments, or between Long Island Sound and similar coastal regions. These findings cast doubt on (1) the use of heavy metal and organic carbon concentrations as indicators of environmental stress for marine nematodes; (2) the use of diversity indices alone as indicators of environmental deterioration; and (3) the usefulness of field monitoring studies alone for the assessment of pollution impact on marine nematodes.Contribution no. 100 from the Institute of Marine and Atmospheric Sciences, City College of New YorkCommunicated by M.R. Tripp, Newark     

Distribution quantitative de la méiofaune dans l'aire d'épandage de l'égout de Marseille

A quantitative analysis of meiofauna was carried out at ten sample stations distributed along a transect off Marseilles' (France) sewage outfall in November, 1981. The meiofauna was counted and average and total biomass of nematodes and copepods were calculated for each station. Comparison of data between stations or groups of stations was made using statistical tests. The results revealed three sectors in which effects of pollution on meiofauna differed: (1) A heavily polluted coastal zone (at a distance of 30 to 150 m from the outfall), relatively poor in meiofauna, which, however, was not completely absent-as were macrobenthic organisms; the meiofauna was composed mainly of nematodes and copepods, but acarians and naupliar larvae (probably copepods) were also numerous; the copepods were uncommonly large in size, and alone consituted most of the total benthic biomass in this zone. (2) An intermediate zone (400 to 1 150 m away from the coast), also polluted and much richer in meiofauna than the coastal zone; the meiofauna groups were more diversified, annelids (mainly polychaetes) increasing in number, while acarians became scarce and copepods decreased in size; at 400 m away from the outfall, where the sediment is strongly polluted, the nematode population consisted of large individuals which contributed greatly to the biomass; at 400 and 800 m, the distribution of both meiofauna and macrobenthos was heterogeneous; at 1 150 m away from the outfall, maximal meiofaunal densities were recorded, due primarily to an increase in nematode numbers; here, unlike all the stations nearer to the coast, total nematode biomass was greater than copepod biomass. (3) An off-shore zone (1.8 to 4 km distant from the coast), slightly polluted, where meiofauna densities were reduced and individuals decreased in size with increasing depth. Generally, an enrichment in the meiofauna was evident from the coastal to the intermediate zone. Enrichments induced by urban pollution have been recorded previously, but not, as in the present study, at a distance of 1 km away from the outfall, succeeding to a highly impoverished coastal zone. Thus, by supplying organic matter and nutrients, Marseilles' sewage can enrich sediments, but only to a certain distance away from the outfall, where the deleterious effects of pollutants are attenuated.     

Tube-worm-sediment relationships of Diopatra cuprea (Polychaeta: Onuphidae)

Diopatra cuprea (Bosc) builds a long, nearly vertical parchment tube in sediments, which is reinforced with bits of shell, sediment or debris. The tube can be divided on the basis of structure into reinforced sections built at or above the sediment surface, and unreinforced sections built below the sediment surface. If sediment accumulates faster than the worm can build reinforced tube, an unreinforced section results. When this occurs, D. cuprea builds reinforced tube at the new sediment surface, and then pulls it down into the substratum until it joins the next lower reinforced section, or until the worm can no longer overcome sediment resistance. In the latter case, the unreinforced section occurs between two reinforced sections. The tube cap is trimmed as sediment is eroded from around it. Selection for reinforcing materials occurs only in the transitional zone from unreinforced to reinforced tube. The exposed portion of the tube (the tube cap) extends from 1 to 6 cm above the sediment surface as an inverted J. The tube mouth is oriented perpendicularly to the direction of current flow. Tube maintenance continues at temperatures below feeding-response blockage (5° to 10°C), but ceases below about 1.8°C.