Polychaete Capitella Capitata Research Articles

Deciphering macrobenthic biological traits in response to long-term eutrophication in Xiangshan Bay, China

As an emerging global issue in coastal marine ecosystems, eutrophication may lead to profound ecological consequences or disasters. Six locations in Xiangshan Bay were sampled during 2012–2022 along the eutrophication gradient from the innermost bay with the most eutrophication to the outer bay with the least eutrophication. A trait-based method was adopted to explore the ecological effects of eutrophication on macrobenthic communities. The results showed that the community composition is mostly characterized by deposit feeders and predators with small (1–3 cm) and large (> 10 cm) body sizes, classified as indifferent and tolerant species (AMBI ecological groups), deposit feeders and predators (feeding mode), and a preference for a free living lifestyle. The RLQ and fourth-corner analyses further confirmed that there was a negative correlation between the abundance of small macrobenthic organisms (< 1 cm) and nitrate concentration. Phosphorus was a crucial influencing factor for macrobenthic spatial patterns and was strongly affected by the activities of deposit feeders and the decomposition of macrobenthos. Due to mass organic deposition resulting from increased primary production, long-term eutrophication had led to an increase in the proportion of detritus feeders. In addition, the significant negative correlation between the concentration of dissolved oxygen and first-order opportunistic species represented by the polychaete Capitella capitata indicated tolerance to hypoxia. The macrobenthic community in Xiangshan Bay had been negatively affected but maintains considerable stability in functional diversity and functional redundancy under the influence of long-term eutrophication.

Using the Capitella complex to investigate the effects of sympatric cryptic species distinction on ecological and monitoring studies in coastal areas

The polychaete Capitella capitata is historically one of the most commonly used indicators of organic enrichment in marine benthic environments. However, this taxon has been used to refer to several cryptic species with distinct environmental tolerances, which may compromise ecological assessment and monitoring programs. In this study, we aimed to (1) assess the overlap and patterns of dominance in the spatial and temporal distribution and response to environmental variability of different species of the C. capitata complex in an urbanized coastal area and (2) investigate how the taxonomic resolution (species vs genera) could affect the observed patterns (i.e., whether the acknowledgement of cryptic species may affect the outcome of ecological assessments). Eight sampling campaigns were carried out from September 2011 to September 2013 in a heavily anthropized tidal flat in Southeastern Brazil. Four species of the complex were identified. Capitella nonatoi was the most abundant (~80% of the total abundance). Overall, the four species of Capitella showed high overlap in spatial distribution, especially between the most abundant ones. At community level, taxonomic resolution did not influence the perceived relationships with environmental and spatial variables, a result likely driven by the dominance of C. nonatoi and relatively high spatial overlap among species. The assemblage was influenced mainly by chlorophyll a and hydrocarbons, corroborating the indicator status of the taxa. At species level, however, individual response to environmental variability differed, suggesting that species may have distinct requirements. Thus, the use of a particular taxonomic resolution in ecological studies depends on the questions to be addressed. The recognition of cryptic diversity may be important for biodiversity assessments and studies at the population level (i.e., dynamics, behavior). Although further studies are needed to corroborate the observed patterns of dominance at larger scales, for community-level assessments, our results suggest that identifying Capitella to species level may not be needed for local ecological monitoring.

Environmental and Benthic Community Patterns of the Shallow Hydrothermal Area of Secca Delle Fumose (Baia, Naples, Italy)

The occurrence of hydrothermal vent ecosystems at Secca delle Fumose, Pozzuoli Bay (Gulf of Naples), represented an opportunity to study the benthic assemblages under the thermal stress of hydrothermal emissions in a very shallow environment (9 – 14 m water depth). In autumn 2016, the macrobenthic community was sampled by scuba divers at four sites located in the Baia Underwater Archaeological Park. Two sites were characterized by vent emissions (one with white bacterial mat scattered on the bottom and one with a yellow substrate around a geyser opening) and two at about 100 m away, used as control. Sediment and interstitial water environmental variables were measured to determine their influence on the structure of macrobenthic assemblages. A total of 1,954 macrofaunal individuals was found, characterized by great differences in abundance and species richness among sites. This pattern was correlated to the dominance of a particular set of variables that drastically change in a very small spatial scale, from one site to another. The control sites, characterized by the highest percentage of gravel in the sediments (19.67±2.6%) and normal level of major ions such as Ca2+, K+ and Mg2+ in the interstitial waters, showed the highest values of sinecological indices. The “white” hydrothermal site exhibited the lowest species richness, abundance and species diversity, influenced by low pH values (~7.6), high temperatures (~37.53°C) and by the highest total organic carbon content (TOC 34.78%) in the sediment. The “yellow” hydrothermal site, with sediment TOC equal to 30.03% and interstitial sulphide ions measuring 130.58 ppm, showed higher values of sinecological indices than those recorded at the “white” site. Therefore, taxonomic analysis revealed a high turnover between control and vents sites. This highlights the preference for hydrothermal vents by a few resistant species, such as the gastropod Tritia cuvierii and the polychaete Capitella capitata, confirming the role of the latter species as opportunistic in extreme environments like Secca delle Fumose.

Saltmarsh plants, but not fertilizer, facilitate invertebrate recolonization after an oil spill

AbstractFoundation species contribute to the recovery of animal communities from disturbance by engineering, by improving habitat quality, and by regulating food availability. In a salt marsh impacted by the Deepwater Horizon oil spill, we tested the hypothesis that nutrient subsidies would enhance the positive effects of the foundation species Spartina alterniflora on the initial recolonization of benthic invertebrate communities (e.g., copepods, annelids, nematodes) by augmenting food (i.e., microalgae) availability. After two months, plantings of S. alterniflora significantly elevated the densities of the polychaete Capitella capitata, meiofauna‐sized annelids, and total macroinfauna over unplanted plots. After 7 months, the significant effect of plantings persisted for meiofauna‐sized annelids, but not for C. capitata and total macroinfauna. Plantings had no effect on copepods (including Nannopus palustris, the dominant species), nematodes, or microalgal biomass for either month. Nutrient additions did not influence any taxon, despite initial increases in benthic microalgal biomass after 2 months. We hypothesize that the structural effects of plants were important to early colonization, possibly by facilitating larval settlement or ameliorating temperature and desiccation stress. Our results emphasize the importance of re‐establishing foundation species in oil‐impacted sites to enhance recolonization of saltmarsh annelids, but suggest that recolonization is not promoted by the addition of nutrients.

A new view on the morphology and phylogeny of eugregarines suggested by the evidence from the gregarine Ancora sagittata (Leuckart, 1860) Labbé, 1899 (Apicomplexa: Eugregarinida).

BackgroundGregarines are a group of early branching Apicomplexa parasitizing invertebrate animals. Despite their wide distribution and relevance to the understanding the phylogenesis of apicomplexans, gregarines remain understudied: light microscopy data are insufficient for classification, and electron microscopy and molecular data are fragmentary and overlap only partially.MethodsScanning and transmission electron microscopy, PCR, DNA cloning and sequencing (Sanger and NGS), molecular phylogenetic analyses using ribosomal RNA genes (18S (SSU), 5.8S, and 28S (LSU) ribosomal DNAs (rDNAs)).Results and DiscussionWe present the results of an ultrastructural and molecular phylogenetic study on the marine gregarine Ancora sagittata from the polychaete Capitella capitata followed by evolutionary and taxonomic synthesis of the morphological and molecular phylogenetic evidence on eugregarines. The ultrastructure of Ancora sagittata generally corresponds to that of other eugregarines, but reveals some differences in epicytic folds (crests) and attachment apparatus to gregarines in the family Lecudinidae, where Ancora sagittata has been classified. Molecular phylogenetic trees based on SSU (18S) rDNA reveal several robust clades (superfamilies) of eugregarines, including Ancoroidea superfam. nov., which comprises two families (Ancoridae fam. nov. and Polyplicariidae) and branches separately from the Lecudinidae; thus, all representatives of Ancoroidea are here officially removed from the Lecudinidae. Analysis of sequence data also points to possible cryptic species within Ancora sagittata and the inclusion of numerous environmental sequences from anoxic habitats within the Ancoroidea. LSU (28S) rDNA phylogenies, unlike the analysis of SSU rDNA alone, recover a well-supported monophyly of the gregarines involved (eugregarines), although this conclusion is currently limited by sparse taxon sampling and the presence of fast-evolving sequences in some species. Comparative morphological analyses of gregarine teguments and attachment organelles lead us to revise their terminology. The terms “longitudinal folds” and “mucron” are restricted to archigregarines, whereas the terms “epicystic crests” and “epimerite” are proposed to describe the candidate synapomorphies of eugregarines, which, consequently, are considered as a monophyletic group. Abolishing the suborders Aseptata and Septata, incorporating neogregarines into the Eugregarinida, and treating the major molecular phylogenetic lineages of eugregarines as superfamilies appear as the best way of reconciling recent morphological and molecular evidence. Accordingly, the diagnosis of the order Eugregarinida Léger, 1900 is updated.

Deep dynamic pools of phosphorus in the sediment of a temperate lagoon with recurring blooms of diazotrophic cyanobacteria

AbstractThe storage and release of phosphorus by sediments can act as an important control on the formation of noxious blooms of cyanobacteria in lakes and estuaries. Here we studied the uptake and release of phosphorus associated with iron oxides within sediments of a lagoon system affected by recurring summer blooms of the cyanobacterium Nodularia spumigena. Using an ascorbate extraction, we observed deep pools of iron oxide associated phosphorus (P) at concentrations of ∼5 μmol g−1 dry sed to a depth of ∼20 cm. This pool rapidly decreased with the onset of water column anoxia, leading to an integrated release of ∼300 mmol of phosphorus m−2 of sediment over 3.5 months. Scaling this flux over the periodically anoxic area of the lake and over the period of an N. spumigena bloom (November–December 2011) gave a broad mass balance agreement with the increase in total phosphorus within the water column and exported from the lagoon. Over this period we estimated that P release from the sediment would have allowed ∼130–187 tonnes of nitrogen to be fixed which agrees with previous estimates of nitrogen fixation. Upon reoxygenation of the water column, a regeneration of the deep iron oxide associated phosphorus pool was observed. This deep dynamic pool of phosphorus was most likely mediated by the burrowing activity of the polychaete Capitella capitata which was observed at the study site. This study underscores the potential importance of sediments colonized by deeply irrigating fauna to become a significant source of phosphorus during water column anoxia.

Effects of organic effluents from a salmon farm on a fjord system. III. Linking deposition rates of organic matter and benthic productivity

The vertical flux of organic matter and infauna production, biomass and abundance at six stations along a gradient away from a salmon farm, located in a western Norwegian fjord at a depth of 230 m and which produced 2910 tonnes of fish in 19 months, was measured repeatedly during an entire on-growth cycle. The study showed that large increases in benthic secondary production can result from the loading of organic waste in nutrient-poor systems like fjords and a strong correlation between annual sedimentation rates of particulate organic matter (carbon and nitrogen) and annual benthic secondary production was found. At the stations that received the bulk of the waste matter (stations situated within 250 m from the mooring point of the farm) infauna production followed feeding regimes at the farm and in 2004 annual benthic secondary production was 40 g ash-free dry weight m − 2 , 50 times as high as the production 550 to 3000 m away from the farm. Production close to the farm was mainly due to the polychaete Heteromastus filiformis and the bivalve Abra nitida in periods with moderate loadings of organic matter, and by the polychaete Capitella capitata in periods with high loadings. The results of the study further indicate that the threshold for increased infauna production in this deep benthic ecosystem had been reached at an annual flux of 500 g C m − 2 and that continuous loadings at this magnitude over time might cause overloading of fish farm localities.

Interaction of Cd and Zn during uptake and loss in the polychaete Capitella capitata: Whole body and subcellular perspectives

The interaction between Cd and Zn in aquatic organisms is known to be highly variable. The purpose of this study was to use a subcellular compartmentalization approach to examine Cd and Zn interactions in the deposit-feeding polychaete Capitella capitata (sp. I). Laboratory-reared C. capitata were co-exposed to Cd (background or 50 μg Cd l − 1 ) and Zn (background or 86 μg Zn l − 1 ) with 109Cd and 65Zn as radiotracers for 1 week. After the 1-week uptake period, subsets of worms were allowed to depurate accumulated metals for an additional 1 week. Worms from both phases (uptake and loss) were then subjected to subcellular fractionation to determine the compartmentalization of metals as metal-sensitive fractions [MSF — organelles and heat-denaturable proteins (HDP)] and biologically detoxified metals [BDM — heat-stable proteins (HSP) and metal-rich granules (MRG)]. Uptake and loss of Cd and Zn in C. capitata at the whole body level were similar at bkgd-Cd/bkgd-Zn, with worms depurating the majority of accumulated metal (∼ 75% Cd and ∼ 64% Zn). When exposure of Zn or Cd was increased (bkgd-Cd/86-Zn; bkgd-Zn/50-Cd), uptake of background levels of Cd or Zn, respectively, was suppressed by ∼ 50%. These accumulated metals, however, were retained during the loss phase resulting in ∼ 40–50% greater Cd and Zn whole body tissue burdens than those of bkgd-Cd/bkgd-Zn worms. Beyond exhibiting similar patterns of uptake and loss at the whole body level, Cd and Zn behaved similarly at the subcellular level. Under background levels (bkgd-Cd/bkgd-Zn), after uptake, worms partitioned a majority of Cd (∼ 65%) and Zn (∼ 55%) to the HSP and organelles fractions. The HDP and MRG fractions contained less than ∼ 6% of both metals. Following depuration, at bkgd-Cd/bkgd-Zn, Cd and Zn were lost from all subcellular fractions; loss from HSP was the greatest contributor to whole body loss. When exposed to elevated concentrations of Zn or Cd, the suppression in uptake of bkgd-Cd or bkgd-Zn observed in whole body uptake was largely due to suppressions in the storage of Cd and Zn to HSP. These results suggest that Cd–Zn interactions reduce partitioning of both Cd and Zn to HSP, indicating that metal-binding proteins such as metallothioneins play a key role in these interactions.

Differences in PAH tolerance between Capitella species: Underlying biochemical mechanisms

The polychaete Capitella capitata consists of a species complex within which differences in tolerance to toxicants have been observed. For example, it has been shown that Capitella sp. S is more sensitive (e.g., in terms of survival, growth and reproduction) to PAH and other stressors than the more opportunistic Capitella sp. I, which is able to take up and biotransform the PAH fluoranthene (Flu). In the present study, an investigation was performed to examine whether differences in tolerance between Capitella species sp. I and sp. S are due to differences in biotransformation, measured as the amount of Flu-metabolites produced by worms. We exposed both sibling species to sediment contaminated with 21 and 26 μg Flu/g dry weight sed for 10–15 days. We found that Capitella sp. I took up more Flu from the sediment than sp. S (346 μg Flu eq./g dry weight worm versus 219 μg Flu eq./g dry weight worm, respectively), but as sp. I was much more effective at biotransforming this PAH (62% versus 11%, respectively of total Flu), the net amounts of parent Flu accumulated by the two species were similar. We found significant differences in the subcellular distribution of Flu and its metabolites between sibling species, with sp. I accumulating mostly in the cytosol and sp. S accumulating mostly in the membrane fraction. A previous study by our group showed Flu to be genotoxic to sp. I upon biotransformation. In the present study, we found no detectable genotoxicity in sp. S following Flu exposure. Our results demonstrate that DNA damage is tightly coupled to biotransformation ability and that other aspects of PAH toxicity (e.g., membrane disruption) are more relevant than DNA damage for predicting tolerance differences between these species.

Heavy Metal Contents in Tissues of Dominant Species of the Benthos and in Bottom Sediments of Zolotoi Rog Bay, Sea of Japan

Data on heavy metal contents in polychaetes and free-living nematodes inhabiting the bottom sed- iments of Zolotoi Rog Bay near the port of Vladivostok are reported. Chronically high contents of heavy metals (Fe, Cu, Zn, and Cd) were found in the bottom sediments and in the infauna. The levels of some toxic elements in tissues of the polychaete Dorvillea (Schistomeringos) japonica inhabiting polluted sediments of Zolotoi Rog Bay were higher than in worms of this species from relatively clean areas of the Sea of Japan. Similar high con- centrations of Fe were found in the polychaete Capitella capitata and the nematode Oncholaimium ramosum. The highest concentrations of Fe, Zn, Cu, and Cd were found in tissues of the free-living nematode O. ramosum. Chronic heavy pollution of the bottom sediments leads to a decrease in the biodiversity of the infauna and to specific metal-tolerant communities.

Identification and expression of two novel cytochrome P450 genes, belonging to CYP4 and a new CYP331 family, in the polychaete Capitella capitata sp.I

The polychaete Capitella capitata sp.I has a high capacity to metabolize polycyclic aromatic hydrocarbons (PAHs) which are among the most hazardous environmental pollutants with significant biological effects. In the present study, two novel cytochrome P450 (CYP) genes were identified in this species. One was named CYP331A1, the first member of a new family of CYP331, and the other CYP4AT1 is the first member of a new subfamily CYP4AT. Both of these genes are constitutively expressed in the worms and detectable by RT-PCR. The expression of CYP331A1 mRNA was observed to be more sensitive to PAH exposure than CYP4AT1, which indicated that CYP331A1 should play a more important role than CYP4AT1 in PAH metabolism in this species. Considering the importance of C. capitata sp.I in taking up PAH and other organic pollutants from contaminated marine sediments with the potential for subsequent food-chain transfer, our results are important for understanding the molecular basis of biotransformation and detoxification in this invertebrate, and also have evolutionary significance for understanding the diversity and history of the CYP superfamily.

Faunal structures associated with patches of mussels on East Asian coasts

Aggregations of mussels harbor a variety of associated animals and make it possible for diverse species to coexist at the shore. Species composition and diversity of the associated fauna are controlled by the position of mussel beds or patches, e.g. tidal level, age structure of mussels, quality of ambient water and by mussel species. When patches of mussels were surrounded by algal growth, a difference in the species composition of the associated fauna was recognized between the patches and algal mats. Mechanisms promoting coexistence are discussed. Biodeposit production by mussels may affect the environment both within the bed and the ambient waters. Reducing sediments showing low Eh values caused by the accumulation of biodeposits was observed in calm waters where the polychaete Capitella capitata, an indicator for organic enrichment, occurred both in the intertidal mussel bed and the subtidal sandy bottom communities. In a shallow subtidal sandy bottom of the Gulf of Thailand, where heavy bioturbation by the spatangoid urchin Brissus latecarinatus was occurring, small patches of the mussel Modiolus metcalfi increased species diversity and equitability in this habitat. Species composition was different between mussel patches and pure sandy bottoms.

Recovery of marine benthic habitats and fauna in a Swedish fjord following improved oxygen conditions

The Gullmarsfjord on the Swedish west coast has a sill at 40 m and a maximum depth of 118 m. The stagnant bottom water is usually renewed with oxygen-rich water each spring. In 1997 this did not occur, and the fauna was eliminated at depths below about 100 m and severely reduced between 80 and 100 m depth. In spring 1998, the whole fjord was re-oxygenated and the succession of the benthic fauna was studied at 5 stations over a 2 yr period. Simultaneously, the benthic habitat quality (BHQ) was assessed by analysing sediment redox conditions and faunal burrow structures in sediment profile images. Succession of the benthic fauna is described as increases in number of spe- cies, abundance and biomass. Conspicuous colonisers below 100 m depth were the polychaete Capitella capitata and the heart urchins Echinocardium cordatum and E. flavescens. Return to pre- oxygen stressed conditions was slowest at the deepest stations. By using a multivariate technique (multi-dimensional scaling) we show that the benthic communities at all depths more or less returned to the same faunal composition as during pre-disturbed conditions. The pioneering and mature ben- thic faunal Successional Stages I and III were predictable but not the intermediate Stage II. The path of recovery of the benthic community succession did not retrace the path of degradation. The sedi- mentary habitats and redox conditions were similarly restored over the 2 yr period as analysed by the BHQ index.

Benthic fauna of a shallow-water gaseohydrothermal vent area in the Aegean Sea (Milos, Greece)

The benthic community of shallow-water hydrothermal vents (10 m water depth) in a sandy bay on the south coast of Milos, Greece was studied. The macro- and meiofauna, as well as environmental factors such as temperature, salinity, sulfide concentration, grain size composition, ATP concentration, organic carbon, chlorophyll a and phaeopigments were evaluated. Samples were taken along transects from a seagrass meadow into a hydrothermally active area. Hydrothermally active spots were distinguished from the surrounding sediment by their black sediment coloration and an overlying white bacterial mat. For comparison, a control transect from a seagrass meadow into bare sand in a non-vent area in the same bay was studied. Overall, we found decreasing faunal diversity from the seagrass bed towards the hydrothermally active area. Along this gradient, four different zones could be distinguished. (a) The seagrass area had a relatively low diversity compared to the control stations, but much higher diversity than in the areas directly influenced by hydrothermal activity. (b) The border zone between the seagrass and the hydrothermal area, with moderate sulfide concentrations, pH values, seawater salinity and temperatures, was inhabited by an impoverished community dominated by the polychaete Capitella capitata, the nematodes Oncholaimus campylocercoides and Sabatieria sp., and an as yet undescribed chromadorid nematode (Chromadorina sp.). (c) The transition zone at the border of the hydrothermal area proper, with temperatures and sulfide concentrations higher than in the border zone, was characterized by high salinity (60‰) and low pH values. Along with the gastropod Cyclope neritea, single specimens of C. capitata and O. campylocercoides occurred. (d) The hydrothermal area proper, characterized by high sulfide concentrations, had high sediment temperatures and high salinities. The pH was as low as 6. Here, the gastropod Cyclope neritea was the only species occurring in considerable numbers. The gaseohydrothermal activity seems to largely exclude the surrounding fauna in a graded zonal pattern. The increasing hydrothermal stress entrains a change of the ambient biota towards a depauperate consortium of tolerant, opportunistic species, e.g. Capitella capitata (Polychaeta) and Oncholaimus campylocercoides (Nematoda). Although the hydrothermal area proper was characterized by a thick bacterial mat, the benthic community was characterized not by bacteria feeders but by scavenging species.

Relationship between acid volatile sulfide and the toxicity of zinc, lead and copper in marine sediments

AbstractIt has been proposed that acid volatile sulfide (AVS) is an important sediment phase for determining the toxicity of certain trace metals. By evaluating the ratio of the molar quantities of simultaneously extracted metal (SEM) to AVS, the toxicity of metals to organisms in contact with sediment can be predicted. This study examines the role of AVS in predicting the toxicity of zinc, lead, and copper in marine sediments.Sediment samples were titrated with zinc, lead, and copper and subsequently analyzed for SEM, pore‐water (PW) metal, and AVS retention. In most cases, metal was not detected in the pore waters until the AVS was exceeded, suggesting that AVS is an adequate measure of the metal‐binding capacity of a sediment. The [SEM]‐to‐[AVS] ratios were calculated and toxicities predicted for each spiking concentration where [SEM]/[AVS] &gt; 1. A 10‐d, flow‐through, acute bioassay using the marine poly‐chaete Capitella capitata was conducted to examine the prediction of toxicity from the metal titrations and the bioassay sediment chemistry data. In most cases, mortalities occurred as predicted. AVS and the [SEM]‐to‐[AVS] ratio proved useful as predictors of toxicity for zinc, lead, and perhaps copper. Another tool for predicting metal toxicity in sediments may be the [PW]/LC50 value; in every case where this ratio was &gt;1, mortalities occurred.

Occurrence and reproductive success of feminized males in the polychaete Capitella capitata (Species Type I)

Natural populations of the cosmopolitan polychaete species, Capitella capitata (Species Type I, Grassle and Grassle 1976) contain males, females and hermaphrodites. Hermaphroditic individuals arise through feminization of males when females are rare. The age-specific survivorships and fecundities of females and hermaphrodites were estimated. There were no significant differences between females and hermaphrodites in survivorship, number of offspring per brood, or percentage of aborted eggs per brood. Net reproductive rates were used to estimate fitness, and the relative fitness of a hermaphrodite as a female ranged from 0.09 to 0.31. The fitness differential was due to the difference in the number of broods that females and hermaphrodites produce. The effects of density, sex ratio, age and body size on the timing of the development of hermaphrodites in groups of siblings were also examined. Hermaphrodites appeared when females were rare or when densities were low. Hermaphrodites never developed in cohorts with larger males unless females were rare. These observations suggest that feminization of males occurs when some males are unable to gain access to females because of mate competition. Feminization does not appear to be correlated with a threshold in body size.

The effects of interaction of rate of food supply and population density on the bioenergetics of the opportunistic polychaete, Capitella capitata (type 1)1

Weight‐specific growth rates, population production, and trophic transfer efficiency (worm production/food supply) of different size classes of the polychaete Capitella capitata (type 1) were measured in the laboratory at 20°C under varying conditions of population density and rate of food supply (ration). A hyperbolic tangent function was fitted to the response of individual growth to unit nitrogen of food supply available per unit nitrogen biomass of worm (R : B̄). Maintenance ration, where growth = 0%, occurred at an R : B̄ = 0.08; i.e. a 0.08 g N daily ration of food was needed to maintain 1 g N biomass of C. capitata. Maximum daily individual growth rates of 21, 19, and 15% were predicted for small, medium, and large worms. The individual growth data were combined with long term‐population data collected at three food rations (50, 100, and 150 mg N m−2 d−1) to estimate long term population production. Changes in population density and the presence of meiofauna reduce the actual worm production for a given rate of food supply. Population production and trophic transfer efficiency changed dramatically as a function of rate of food supply, worm size, and biomass.

Laboratory studies of the effect of predation on production and the production:biomass ratio of the opportunistic polychaete Capitella capitata (Type I)

The effect of simulated predation upon the secondary production and P:B (production:biomass) ratio of the polychaete Capitella capitata (Type I) was estimated from laboratory studies. The first method (the maximum sustainable yield, MSY, method) summed net increases in biomass of each population over time with biomass exploited by predation. In the specific growth-rate method, experimentally determined specific-growth rates were applied to changes in size classes and standing stock over time, providing another estimate of production for comparison to the MSY method. Predation had a pronounced effect on the magnitude of production, standing stocks, and hence the P:B ratio causing a fourfold difference in P:B ratios between the controls (P:B=4.9) and the 23% wk-1 predation rate (P:B=19.6). Production reached a high of 87 g ash-free dry wt m-2 yr-1 in the highest predation treatment (23% wk-1). An estimate of the number of individuals recruited in each population showed that predation caused an increase in population turnover rate. Gross ecological efficiency (calories of food ingested by the predator/calories of food consumed by the prey) and food-chain efficiency (calories of prey ingested by the predator/calories of food supplied to the prey) were 7.4 and 5.8% respectively, for the 23% wk-1 predation treatment.

Effect of detritus supply on trophic relationships within experimental benthic food webs. I. Meiofauna-polychaete ( capitella capitata (Type I) Fabricius) interactions

In a long-term (40–55 wk) microcosm experiment, the presence of the polychaete Capitella capitata (Type I) Fabricius reduced population densities and trophic transfer efficiencies (detritivore production per amount of detritus supplied) of the nematode Diplolaimella chitwoodi Gerlach at high (150 mg N · m −2 · day −1) detritus ration and of the harpacticoid copepod Tisbe holothuriae Humes at low (50 mg N · m −2 · day −1) detritus supply. The rarer nematodes Theristus ostentator Wieser & Hopper and Paracyatholaimus pesavis Wieser & Hopper fed at depth on fungal hyphae attached to polychaete fecal pellets thereby minimizing contact with the other metazoa. In a series of short-term (4-day) growth experiments, the presence of either Diplolaimella chitwoodi or Tisbe holothuriae reduced daily weight-specific growth (g increase · g worm −1 · day −1) of Capitella capitata on separate diets of mixed cereal and red seaweed, Gracilaria foliifera (Harvey) Taylor, detritus. Both sets of experiments suggest that Capitella capitata competes for food with Diplolaimella chitwoodi and Tisbe holothuriae. Meiofauna-polychaete interactions were dependent, in part, upon the degree of similarity among species in food requirements and habitat preferences, and may incorporate a variety of regulatory mechanisms other than competition or predation.

Effects of predation and disturbance on the population growth and dynamics of the polychaete Capitella capitata (Type I)

Populations of the polychaete Capitella capitata (Type I) were cultured in the laboratory under constant conditions and subjected to two intensities of density-independent exploitation (12 and 23% of the population removed per week) over an 81- to 85-week period (September 1981 to May 1983). Density-independent exploitation reduced the amplitude of the oscillations but did not stabilize the populations. An additional pair of populations were cultured in a similar manner except that they were subjected to a daily physical disturbance of their sediment habitat. In these trays C. capitata established moderately stable low level populations in spite of the continuous disturbance of their habitat. The data suggest that C. capitata are unlikely to maintain an equilibrium population, except for short periods of time or when subjected to intense density-dependent effects. Exploitation by a predator may not stabilize its prey population unless the prey can respond in a density-dependent fashion to prey population growth.