Glenn R. Lopez

Ecology of Deposit-Feeding Animals in Marine Sediments

Deposit-feeding animals acquire food by swallowing large volumes of sediment. Possible food sources include organic debris and sediment-associated microbes. The relative importance of these classes of food is currelty an area of active research. The idea that microbes attached to sediment and detritus particles constitute the major food source for deposit feeders is being replaced by more complex models that incorporate interactions between animals and the food sources in the sedimentary matrix. Many deposit feeders appear to require both microbial and detrital foods. Deposit feeders display many adaptations appear to be cosistent with the energy maximization principle of optimal foraging theory, but rigorous testing of foraging models has proven to be difficult. Elucidation of deposit-feeding strategies may develop as optimal foraging theory is integrated with physiological energetics.

The effect of grazing by the detritivore Orchestia grillus on Spartina litter and its associated microbial community

SummaryOrchestia grillus efficiently feeds upon microorganisms attached to ingested Spartina alterniflora litter, but does not digest litter itself. Microorganisms respond to Orchestia grazing with increased metabolic activity, reflected in accelerated decomposition of the nitrogen fraction of litter and increased microbial biomass. Increased microbial activity may be partly a function of ammonia excretion and higher diffusion rate due to animal movement, but mainly it is a direct response to grazing. Microbial biomass increases with grazing because the pool of available nitrogen becomes larger. A model postulating interactions between Orchestria, Spartina litter and attached microorganisms is presented.

Ecology of Marine Deposit Feeders

1 Deposit Feeding and Coastal Oceanography.- 2 Examining Relationships Between Organic Carbon Flux and Deep-Sea Deposit Feeding.- 3 Early Diagenesis of Organic Matter and and the Nutritional Value of Sediment.- 4 The Nature and Determination of Non-Living Sedimentary Organic Matter as a Food Source for Deposit Feeders.- 5 Digestion Theory Applied to Deposit Feeding.- 6 Time-Dependent Absorption in Deposit Feeders.- 7 Radiotracer Methods for Determining Utilization of Sedimentary Organic Matter by Deposit Feeders.- 8 The Lnportance of Size-Dependent Processes in the Ecology of Deposit-Feeding Benthos.- 9 The Relationship Between Ingestion Rate of Deposit Feeders and Sediment Nutritional Value.- 10 Modeling Deposit Feeding.- 11 The Effects of Sediment Transport and Deposition on Infauna: Results Obtained in a Specially Designed Flume.- 12 Small-Scale Features of Marine Sediments and Their Importance to the Study of Deposit Feeding.- 13 On Some Mechanistic Approaches to the Study of Deposit Feeding in Polychaetes.- 14 Some Ecological Perspectives in the Study of the Nutrition of Deposit Feeders.

Relationship between subcellular cadmium distribution in prey and cadmium trophic transfer to a predator

We tested the hypothesis that exposure-related alterations in the subcellular Cd distribution in prey relate to changes in Cd absorption by a predator. Oligochaete worms,Limnodrilus hoffmeisteri were exposed for 1 wk or 6 wk to 0.5 μg Cd 1−1, 47 μg Cd 1−1, or 140 μg Cd 1−1 (including109Cd as a tracer) and relationships between oligochaete subcellular Cd distribution and Cd absorption by a predator, the grass shrimp (Palaemonetes pugio), were determined. Concentration and duration of Cd exposure had direct effects on oligochaete subcellular Cd distribution. Changes in oligochaete subcellular Cd distribution were characterized by increases in both the amount and proportion of Cd bound to the cytosolic fraction. The induction of Cd-binding proteins (e.g., metallothioneins) were suspected to be responsible for these changes. We found 1∶1 relationships between the amount and percentage of Cd in oligochaete cytosol and the amount and percentage of Cd adsorbed by shrimp. These results demonstrate that only metal bound to the soluble fraction of prey is available to higher trophic levels, and that factors influencing subcellular metal distribution in prey will directly alter metal trophic transfer to predators.

The availability of microorganisms attached to sediment particles as food for Hydrobia ventrosa Montagu (Gastropoda: Prosobranchia)

SummaryThe deposit-feeding prosobranch Hydrobia ventrosa Montagu feeds most rapidly upon sediment particles that pass through a 10 μm sieve. Ingestion rate decreases with particles 80–125 μm, then increases with larger particles, which are fed upon by scraping fine material from their surfaces. Hydrobia is capable of digesting diatoms and bacteria from sediment particles, but with generally lower efficiencies than reported when fed pure cultures. Digestion of microorganisms appears to be constrained by ability of the snail to detach cells from sediment particles; only those cells detached from sediment seem to be available for digestion. In contrast, the amphipod Corophium volutator is capable of utilizing most of the diatoms not digested by Hydrobia. For a given sediment, a constant number of microorganisms appear to be safe from digestion by H. ventrosa, and bacteria and microalgae over this amount constitutes the available food.

Bacterial abundance in relation to surface area and organic content of marine sediments

Based on direct measurements on surface sediments collected from an intertidal salt marsh, a positive relationship was demonstrated between bacterial abundance and specific surface area of sediment. While this relationship has been postulated previously, this is the first direct confirmation that it holds over a wide range of sediment types. A laboratory experiment was conducted to determine the effects of specific surface area, distribution of surface area, and organic loading on bacterial colonization. Model sediments included angular silica particles, kaolin, and spherical glass beads, used singly or in mixtures. Organic loading resulted in substantial enhancement of bacterial colonization. Distribution of surface area controlled by textural, shape, and sorting, had a complex effect, with glass bead sediments generally supporting better colonization than silica particles or kaolin. The effect of specific surface area was noted only in restricted comparisons of similarly shaped glass beads.

The effect of body size on digestive chemistry and absorption efficiencies of food and sediment-bound organic contaminants in Nereis succinea (Polychaeta)

Abstract We investigated the hypothesis that absorption efficiencies for organic matter (OM) and hydrophobic organic contaminants (HOC) correlate with body size in the deposit feeding polychaete Nereis succinea (Frey and Leuckart). Gut passage time (GPT) in N. succinea is approximately five to ten times shorter in juveniles than in adults. Since shorter GPT is likely to diminish the efficiency of intestinal digestion and solubilization, one would expect juvenile worms to have significantly diminished absorption efficiencies compared to adults. To test this hypothesis, we measured absorption efficiencies (AE) for radioactively labeled phytoplankton ( Pseudonitzschia sp.), sediment OM, and three sediment-bound hydrophobic organic contaminants (tetrachlorobiphenyl [TCBP], hexachlorobenzene [HCB] and benzo(a)pyrene [BaP]) over a gradient of body size spanning 10–110 mm. We furthermore measured gut pH and gut fluid surface tension (surfactancy) in relation to body size, to examine whether small worms might compensate for shorter GPT by having comparatively more aggressive gut conditions. Absorption efficiencies were measured in pulse-chase feeding experiments over 5–48 h. Live phytoplankton was absorbed with AEs of 55–95%, while bulk sediment OM was absorbed with AEs of only 5–18%. Sediment-bound TCBP, HCB and BaP were absorbed with AEs of 55–92%. AEs were commonly higher in larger worms, and linear and Ivlev-type regressions of AE onto body size explained more than 59% of the AE variance in any treatment. AEs for phytoplankton and OM correlated strongly with depuration time, i.e. the time until first detection of non-radioactive “chaser”-feces. In contrast, no time dependency of AE was detected for HOCs, albeit over a narrower range of depuration times. Gut fluid pH of N. succinea ranged between pH 5.8 and 7.7, and was on average slightly higher (closer to seawater pH) in larger individuals. Surface tension, measured as drop contact angle, was greatly diminished relative to seawater in all worms, with greatest differences found in large worms. In contrast to AE measurements, only 10–20% of the variance in gut surfactancy and pH data was explained by body size, suggesting that differences in gut chemistry (pH and surfactancy) play a subordinate role in explaining the higher AEs in adult worms. We conclude that gut chemistry is likely to set upper and lower limits on absorption efficiency of food and sediment-bound HOCs in N. succinea , while body size, and in the case of food uptake, differences in GPT, probably account for most of the variance within this range.

Rapid consumption of phytoplankton and ice algae by Arctic soft-sediment benthic communities: Evidence using natural and 13 C-labeled food materials

Reduction of sea ice in the Arctic may significantly alter the relative fluxes of phytoplankton and ice algae to the seafloor. To examine the response of Arctic benthic communities to changing food supplies, we incubated sediment cores collected from two sites (Smeerenburg Fjord, northwest Svalbard in May 2003 and Storfjord Trench, Barents Sea in May 2004) with controlled additions of natural phytoplankton and ice algal assemblages, and laboratory-cultured C-labeled ice algae (Nitzschia frigida, in 2004 only). We measured sediment respiration, pigments, lipid biomarkers, and compound-specific C signals over the course of incubations. Both communities responded rapidly to the addition of food materials: regardless of food type, concentrations of organic biomarkers (pigments and fatty acids) decreased to the levels of control cores within seven days. Although we found no evidence for selective ingestion of the different food types by macrofauna, fatty acids were differentially consumed. The enriched polyunsaturated fatty acids of the ice algae were preferentially utilized compared to saturated and monounsaturated fatty acids bound in ice algae. However, the saturated and monounsaturated fatty acids of phytoplankton (with depleted polyunsaturated fatty acids) are utilized more efficiently than those counterparts bound in ice algae. Bacterial activity was stimulated by food addition, indicated by the immediate increase of bacteria-specific fatty acids, but the direct assimilation of C-labeled carbon into bacterial biomass was limited. Our results imply that Arctic benthic communities can meet their energetic requirements by altering strategies to assimilate different components from variable food supplies.

THE ALLOMETRY OF DEPOSIT FEEDING IN CAPITELLA SPECIES I (POLYCHAETA:CAPITELLIDAE): THE ROLE OF TEMPERATURE AND PELLET WEIGHT IN THE CONTROL OF EGESTION

This study investigates the relationships between egestion rate, body size, and environmental temperature in the opportunistic marine polychaete Capitella species I. Measurements were made of (1) fecal pellet weight, (2) pellet production rate, and (3) pellet standing stock within the gut of live worms. Egestion rate experiments were conducted with worms ranging in size from 0.27 mm3 to 2.62 mm3 (approx. 1.0-15 mm in length). Pellet production rate measurements were made at 15°, 20°, and 25°C. Individual fecal pellet weight was related to worm body volume to the 0.70 power. Fecal pellet production rate in Capitella sp. I was independent of body size. The number of pellets maintained on average within the guts of larger animals is at least equal to that of smaller animals. Fecal pellet production rate increased exponentially with increasing temperature between 15°C and 25°C, with an overall Q10 ovalue of 2.49. Power functions relating changes in egestion rate (µg sediment h-1) and sizespecific egestion rat...

Potential carbon sources for the head-down deposit-feeding polychaete Heteromastus filiformis

In this study we investigated potential carbon sources for the capitellid polychaete, Heteromastusfiliformis. It is a head-down deposit feeder ingesting sediment from at least 15 cm below the sediment-water interface. This orientation appears to minimize the worm’s ability to acquire food and oxygen and maximize its exposure to sulfide. The food sources we examined were metabolically active bacteria, benthic algae, detritus and chemoautotrophic bacteria. Carbon retention efficiencies from metabolically active bacteria, benthic algae and detritus by H. jilifomis were 26%, 8% and 4% respectively. These values are relatively low compared to other deposit feeding species suggesting that H. jiliformis does not possess unique digestive capabilities. Rubisco (Ribulose bisphosphate carboxylase) assays were negative, which indicates an absence of symbiotic chemoautotrophic bacteria in tissue or absorbed carbon. Average 6 13C were -12.83 for worms and -20.70 for 15 cm sediment, which indicates that external gardening of chemoautotrophs is not a major carbon source for H. filiformis. Nevertheless, several experiments showed that this capitellid worm had an unusually high gross heterotrophic COZ uptake. We suggest that H. jiliformis utilizes both dissolved and particulate carbon sources stored within anoxic and sulfidic sediments that are not utilized by other deposit feeding organisms.