Effects of mussel (Perna canaliculus) biodeposit decomposition on benthic respiration and nutrient fluxes

Suspension-feeding bivalves increase the quantity and quality of sedimenting organic matter through the production of faeces and pseudofaeces that are remineralised in coastal sediments and thus increase sediment oxygen demand and nutrient regeneration. Bivalves are intensively cultivated worldwide; however, no bivalve biodeposit decay rates are available to parameterise models describing the environmental effects of bivalve culture. We examined sediment biogeochemical changes as bivalve biodeposits age by incubating coastal sediments to which we added fresh mussel (Perna canaliculus) biodeposits and measured O₂ and nutrient fluxes as well as sediment characteristics over an 11-day period. Biodeposits elevated organic matter, chlorophyll a, phaeophytin a, organic carbon and nitrogen concentrations in the surface sediments. Sediment oxygen consumption (SOC) increased significantly (P=0.016) by ∼1.5 times to 1,010 μmol m⁻² h⁻¹ immediately after biodeposit addition and remained elevated compared to control cores without additions for the incubation period. This increase is in the range of observed in situ oxygen demand enhancements under mussel farms. To calculate a decay rate for biodeposits in sediments we fitted a first-order G model to the observed increase in SOC. The significant model fit (P=0.001, r ²=0.72) generated a decay rate of 0.16 day⁻¹ (P=0.033, SE=0.05) that corresponds to a half-life time of 4.3 day. This decay rate is 1–2 orders of magnitude higher than published decay rates of coastal sediments without organic enrichment but similar to rates of decaying zooplankton faecal pellets. NH₄⁺ release increased rapidly on the day of biodeposit addition (P=0.013) and reached a maximum of 144 μmol m⁻² h⁻¹ after 5 days which was 3.6 times higher compared to control cores. During this period NH₄⁺ release was significantly (P<0.001 to P=0.043) higher in the cores with biodeposit additions than in control cores.     

Hydrocarbon bioaccumulation from contaminated sediment by the deposit-feeding polychaeteAbarenicola pacifica

This study examines the role of the organic carbon content of sediment in aromatic hydrocarbon bioaccumulation and assesses the importance of two routes of hydrocarbon uptake: (1) the uptake of the particulate contaminant fraction from ingested sediment; (2) the uptake of the dissolved contaminant fraction from interstitial or overlying water. The lugwormAbarenicola pacifica was collected from San Juan Island, Washington, USA, in January 1989, and exposed to three sediments contaminated with [³H]benzo (a) pyrene (BaP). By manipulating the organic content of these sediments, it was possible to establish three treatments with similar BaP concentrations in the interstitial water, but differing in the amount of BaP in the bulk sediment. BaP bioaccumulation over the first few days of exposure was correlated with feeding rate, suggesting that ingested sediments were a source of BaP. The greatest body burden, however, was attained in those individuals held in sediments with the lowest organic carbon content and the lowest BaP concentration. Body burden at steady state was not correlated with either BaP concentrations in bulk sediment (dry weight or organic carbon-normalized bases) or the interstitial water. Increased organic matter decreased BaP bioavailability in a non-linear fashion. Bioaccumulation factors relative to water and organic content were relatively constant between 1 and 2% organic carbon in the sediment, but these same accumulation factors substantially underestimated body burden if applied to sandy sediments with little (0.3%) organic carbon.     

Chromium in intertidal sediments of the Clyde,UK: potential for remobilisation and bioaccumulation

Detailed surveys of intertidal sediments have been performed along the north and south shores of the Inner Clyde estuary, UK. Surface sediment data reveal significant spatial variation in Cr content and an association with major sediment characteristics and location within the estuary. Depth variation for Cr and other heavy metals cannot be explained by variation in major geochemical controls such as grain size and organic matter and highlights the impact of historical contamination on sediment quality. These elevated levels at depth may still have environmental impact through redox-reactivity, in association with iron and manganese. Sequential extraction of sediments and pore water analysis of Cr(VI) and Cr(III) provide detailed information on release potential from the sediments. The implication of Cr mobility for biota in the estuary has been assessed by the analysis of a common marine bivalve, Mytilus edulis (Blue Mussel) and a burrowing polychaete, Nereis diversicolor (rag worm) from a number of survey sites. Bioconcentration factors for Mytilus indicate that the weakly held portion of sediment Cr is available for uptake and in the case of Nereis, bioaccumulation appears to be inhibited by sediment organic matter.     

Animal-sediment relations in Cape Cod Bay,Massachusetts II. Reworking by Molpadia oolitica (Holothuroidea)

Populations of Molpadia oolitica (Holothuroidea) were sampled over an area of 440 km² in Cape Cod Bay, Massachusetts, USA. This species occurs in silt-clay muds in densities of 2 to 6/m², and is limited to depths greater than 22 m where the highest annual temperature does not exceed 10°C. M. oolitica lives within the mud, with its anterior end located approximately 20 cm below the surface. This species ingests only fine-grained particles at depth in the sediment, and deposits uncompacted feces at the surface, producing a fecal mound around the anal opening. This reworking produces vertical sediment sorting, high sediment-water content, and topographic relief of the sea floor. The fecal cones of M. oolitica provide a relatively stable surface for settlement and growth of the suspension feeders Euchone incolor (polychaete), Aeginina longicornis (amphipod), and Thyasira gouldi (bivalve) Uncompacted feces, accumulated in depressions between the mounds, form an unstable substratum frequently resuspended by tidal flow. Suspension feeders are absent from intercone areas.Contribution No. 236 of the Systematics-Ecology Program, Marine Biological Laboratory, Woods Hole, Massachusetts, USA.     

Sinking rates of fecal pellets from gelatinous zooplankton (Salps,Pteropods, Doliolids)

Sinking rates were determined for fecal pellets produced by gelatinous zooplankton (salps, Salpa fusiformis and Pegea socia; pteropods, Corolla spectabilis; and doliolids, Dolioletta gegenbaurii) feeding in surface waters of the California Current. Pellets from the salps and pteropods sank at rates up to 2 700 and 1 800 m d^-1, respectively; such speeds exceed any yet recorded for zooplankton fecal pellets. Fecal pellets of salps were rich in organic material, with C:N ratios from 5.4 to 6.2, close to values for living plankton. The relation between volume and sinking rate indicates that salp and pteropod pellets are slightly less dense than those of pelagic Crustacea; moreover, pellet density varied between different collection dates, probably because of differences in composition. In contrast, doliolid pellets sank at rates up to 208 m d^-1, a rate much lower than would be expected from pellet size. Thus, density and sinking rates of pellets are much more variable in zooplankton than would be expected from studies of crustaceans alone. Moreover, the extraordinarily high sinking rates of fecal pellets of salps indicates that these tunicates may be disproportionately important in the flux of biogenic materials during periods when they form dense population blooms.     

Microbial activity and accumulation of organic matter in the burrow of the mud shrimp, <Emphasis Type="Italic">Upogebia major</Emphasis> (Crustacea: Thalassinidea)

Microbial activity and accumulation of organic matter in the burrow of the thalassinidean mud shrimp, Upogebia major, were studied on a tidal flat along the northern coast of Tokyo Bay, Japan. The burrow of U. major is Y-shaped with an upper U-shaped part plus a lower I-shaped part. Its lower part can extend to a depth of 2 m. In the present study, we compare electron transport system activity (ETSA), bacterial abundance and organic matter content [total organic carbon (TOC), total nitrogen (TN) and chlorophyll a (chl. a)] of the burrow wall sediment with the tidal flat surface and non-burrow sediments. We also compared the U- and I-shaped part in terms of these parameters. ETSA in the burrow wall was higher than at the tidal flat surface in the warmer season, and was always higher than at surrounding non-burrow sediments. Bacterial abundance in the burrow wall was higher than at the tidal flat surface and surrounding sediment. TOC and TN contents in the burrow wall were two to three times higher than those at the tidal flat surface and non-burrow sediments, regardless of season. However, there was no significant difference in chl. a content between burrow wall and tidal flat surface. These results suggest that organic enrichment of the burrow wall is a result of organic matter particles such as phytodebris accumulation along the burrow wall. For all parameters of the burrow walls, no statistical differences were found between the two parts. Present results indicate that U. major actively transports the water containing suspended organic particles not only through the U-part but also into the deeper I-part. These indicate that burrow of the mud shrimp provides a dynamic environment for microbial community in tidal flat sediment.     

Changes in the feeding behavior of the deposit-feeding polychaete<Emphasis Type="Italic"> Laeonereis acuta</Emphasis> on soft sediments inhabited by burrowing crabs

In this paper, we evaluate the influence of the burrowing crab Chasmagnathus granulatus on the feeding behavior, body condition, burrowing activity, and fecal production of the deposit-feeding polychaete Laeonereis acuta. Previous results and ours show that, due to crab activity, sediment organic matter decreases with depth outside a crab bed, but there were no differences inside. Also, particle sizes were smaller inside the crab bed. Polychaetes showed better body condition inside the crab bed, suggesting higher energy gain. They fed on the surface more frequently outside the crab bed than inside. However, feeding rate was higher inside the crab bed, which is consistent with the larger weight and volume of fecal pellets found inside crab bed. In both areas, the bedload sediment transport was not similar to the sediment ingested by this polychaete. A 1-month exclusion/inclusion experiment performed outside and inside the crab bed showed that the body condition of polychaetes changed between areas but that this was not directly due to crab manipulation. Thus, our results suggest that the higher sediment quality inside a crab bed can positively affect the feeding behavior of the deposit-feeding polychaete L. acuta, increasing its feeding rate and consequently enhancing its body condition.Communicated by P.W. Sammarco, Chauvin     

Effects of mussel aquaculture on the nitrogen cycle and benthic communities in Kenepuru Sound,Marlborough Sounds,New Zealand

Nitrogen pools and transformations and benthic communities at a Perna canaliculus farm and a nearby reference site without direct influence of marine farming in Kenepuru Sound, New Zealand, were compared on four dates between September 1982 and May 1983. The organic nitrogen pool in the top 12 cm sediment was 7.4 to 10.8 mol m^-2 at the mussel farm and 6.1 to 8.9 mol m^-2 at the reference site. The nitrate and nitrite pools were similar in both sediments, but the ammonium pool in the mussel farm sediment was about twice as high as in the reference sediment. In January, the sediment ammonium concentrations ranged from 418 nmol cm^-3 (surface) to 149 nmol cm^-3 (12 cm depth) at the mussel farm and from 86 to 112 nmol cm^-3 at the reference site. The molar C:N ratio of the sediment organic matter was 6.2 to 7.2 at the mussel farm and 7.9 to 10.0 at the reference site. The molar N:P ratio of the sediment organic matter was 4.3 to 7.2 and 3.3 to 6.1 at mussel farm and reference site, respectively. The total nitrogen mineralisation rate in the top 12 cm sediment ranged from 21.7 to 37.1 mmol m^-2 d^-1 at the mussel farm and from 8.5 to 25.0 mmol m^-2 d^-1 at the reference site. Ammonium excretion by mussels was about 4.7% (January) and 7.4% (May) of the combined nitrogen mineralisation by mussels and sediment. The sediment-denitrification rate was 0.7 to 6.1 mmol m^-2 d^-1 at the mussel farm and 0.1 to 0.9 mmol m^-2 d^-1 at the reference site. In January, 76 and 93% of the nitrate reduced in the sediments were denitrified at the mussel farm and reference site, respectively. The denitrification rate on the mussel lines (determined on detritus-covered mussels) was twice the mussel farm sediment-denitrification rate and 10 times the reference sediment-denitrification rate. Total denitrification at the mussel farm was 21% higher than at the reference site. The loss of nitrogen through mussel harvest and denitrification was 68% higher at the mussel farm. The surface layers of both sediments contained about 75 mg m^-2 chlorophyll a. Sediment phaeophytin levels were 52 mg m^-2 at the reference site and 137 mg m^-2 at the mussel farm. While the benthic infauna of the mussel-farm sediment consisted only of polychaete worms, the reference sediment contained also bivalve molluscs, brittle stars and crustaceans.     

Multiple trophic resources for a chemoautotrophic community at a cold water brine seep at the base of the Florida Escarpment

The biological community that surrounds the hypersaline cold water brine seeps at the base of the Florida Escarpment is dominated by two macrofaunal species: an undescribed bivalve of the family Mytilidac and a vestimentiferan worm, Escarpia laminata. These animals are apparently supported by the chemoautotrophic fixation of carbon via bacterial endosymbionts. Water column and sediment data indicate that high levels of both sulfide and methane are present in surface sediments around the animals but absent from overlying waters. Stable isotopic analyses of pore water indicate that there are two sources of sulfide: the first is geothermal sulfide carried in groundwater leaching from the base of the escarpment, and the second is microbial sulfide produced in situ. The vestimentiferan E. laminata, and the mytilid bivalve (seep mussel) live contiguously but rely on different substrates for chemoautotrophy. Enzyme assays, patterns of elemental sulfur storage and stable isotopic analyses indicate that E. laminata relies on sulfide oxidation and the seep mussel on methane oxidation for growth.     

Zooplankton feeding ecology: contents of fecal pellets of the copepods Temora turbinata and T. stylifera from continental shelf and slope waters near the mouth of the Mississippi River

In-situ feeding habits of the copepods Temora turbinata and T. stylifera were investigated by scanning electron microscope examination of fecal pellets, the contents of which reflected copepod gut contents upon capture. Pellet contents were compared with assemblages of available phytoplankton in the water column at the times of zooplankton sampling. Samples were collected in continental shelf and slope waters of the Gulf of Mexico near the mouth of the Mississippi River. Both species ingested a wide size range and taxonomic array of phytoplankters, and to a lesser extent, other crustaceans. Fecal pellets contained primarily the remains of the phytoplankters that were most abundant in the water at times of collection. There was considerable overlap in the food items ingested by adult females of both copepod species, or two stages of T. turbinata copepodites. Thus, T. turbinata and T. stylifera are omnivores, but primarily opportunistic herbivores.     

La nutrition d'echinodermes abyssaux I. Alimentation des holothuries

In deep waters, deposit-feeding holothurians represent a high percentage of the total abyssal biomass and play an important ecological role in sediment modification. The feeding of these organisms, which inhabit a nutritively poor environment, has been studied by means of analyses of intestinal contents. Four abundant species: Psychropotes longicauda Theel, Paroriza pallens (Koehler), Benthogone rosea Koehler and Molpadia blakei (Theel), collected between 2000 and 4500 m in the Bay of Biscay during three cruises organized by CNEXO-COB, were chosen for this study. The morphological characteristics of the ingested alimentary particles are described and the results of analyses of the organic matter in the guts reported. The species studied do not exhibit a strict alimentary diet; 16 types of presumably nutritive particles were distinguished in the foregut. The nutritional sources for these holothurians mainly consist of organo-mineral aggregates, faecal matter and organic incrustations on mineral particles. Selection is for those detritus particles which are richest in bio-available compounds; a negative selection for living organisms is apparent. The finest fraction of the sediment (which is also the richest in organic matter) is also ingested. The concentrations of organic carbon and nitrogen in the sediment found in the foreguts are about 4 times and 6 times greater, respectively, than the concentrations in the environmental sediment. During passage through the intestines, assimilation of organic carbon and nitrogen is 15 and 22%, respectively; assimilation is maximal in the ascending intestine loop.

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Contribution Nr. 690 du Centre Océanologique de Bretagne     

Ingestion of bivalve larvae by<Emphasis Type="Italic"> Mytilus edulis</Emphasis>: experimental and field demonstrations of larviphagy in farmed blue mussels

Ingestion of bivalve larvae by Mytilus edulis was investigated. Laboratory experiments revealed that ~ 90% of bivalve larvae offered to mussels was ingested and apparently fully digested. The shell of the bivalve larvae offered no protection against digestive processes, resulting in high larval mortality once inside the stomach. Stomach content analysis (September 2001–January 2003) showed that bivalve larvae were ingested by farmed mussels year-round, with the exception of March 2002. Numbers of ingested larvae were highest in October 2001 and May 2002, which coincides with known spawning times of farmed mussels in Ireland. Mussels ingested a large size-range of bivalve larvae, suggesting that all stages of the bivalve life cycle are vulnerable to predation. It is suggested that adult bivalves routinely filter larvae from the surrounding water and that, given the high biomass of mussels present in mussel farms, filtration by adult bivalves significantly reduces numbers of bivalve larvae in nearby waters.Communicated by J.P. Thorpe, Port Erin     

Ingestion and assimilation of nitrogen from benthic sediments by three species of coral

We quantified the nitrogen and enzyme hydrolyzable amino acid (EHAA) concentrations of sediments prior to and after corals sloughed, ingested, and egested sediments layered onto their surfaces, for the three coral species Siderastrea siderea, Agaricia agaricites, and Porites astreoides in Jamaica. The percent nitrogen of the sediments egested by all three species was lower than in the sediments available to the corals. Additionally, the sediments sloughed (not ingested) by A. agaricites and P. astreoides were lower in percent nitrogen, while the sediments sloughed by S. siderea had the same percent nitrogen as that of the available sediments. The percent nitrogen of the sediments sloughed and egested by P. astreoides showed significant negative and positive relationships, respectively, to increasing sediment loads, while the percent nitrogen of the sediments sloughed and egested by both S. siderea and A. agaricites showed no relationship to sediment load. EHAA concentrations were not significantly different between the sloughed and available sediments but were significantly lower in the sediments egested by S. siderea and A. agaricites (EHAA concentrations were not measured for P. astreodies sediment fractions). Comparisons of the nitrogen and EHAA concentrations in the sloughed and egested sediments to what was available prior to coral processing show that maximum ingestion was between 0.1 and 0.2 µg N µg^–1 coral N cm^–2 and between 0.5 and 0.6 µg EHAA·cm^–2. Maximum assimilation efficiencies were estimated to be 30–60% of the available nitrogen. The data show that corals ingest and alter the nitrogen concentration of particles that land on their surfaces. The corals abilities to process these sediments, and the sediments possible contributions to coral nutrition, are discussed based on these results.Communicated by O. Kinne, Oldendorf/Luhe     

Feedbacks between bivalve density, flow, and suspended sediment concentration on patch stable states

We explore the role of biophysical feedbacks occurring at the patch scale (spatial scale of tens of meters) that influence bivalve physiological condition and affect patch stability by developing a numerical model for the pinnid bivalve, Atrina zelandica, in cohesive sediments. Simulated feedbacks involve bivalve density, flow conditions (assumed to be primarily influenced by local water depth and peak current speed), suspended sediment concentration (evaluated through a balance between background concentration, deposition, and erosion), and changes in the physiology of Atrina derived from empirical study. The model demonstrates that high bivalve density can lead to skimming flow and to a concomitant decrease in resuspension that will affect suspended sediment concentration over the patch directly feeding back on bivalve physiology. Consequently, for a given flow and background suspended sediment load, the stability of a patch directly depends on the size and density of bivalves in the patch. Although under a range of conditions patch stability is ensured independently of bivalve density, simulations clearly indicate that sudden changes in bivalve density or suspended sediment concentration can substantially affect patch structure and lead to different stable states. The model highlights the role of interactions between organisms, flow, and broader scale environmental conditions in providing a mechanistic explanation for the patchy occurrence of benthic suspension feeders.     

A link between biologically imported particulate organic nutrients and the detritus food web in reef communities

Previous work with planktivorous fishes has shown that they import particulate organic and inorganic material to reefs in the form of fecal pellets, which, in part, are deposited in crevices on the reef where these fishes shelter during their inactive period. Since these feces do not accumulate in fish shelters, we predicted that some of the feces could be rapidly consumed by reef detritivores. We examined the attractiveness of fish feces to potential reef detritivores by placing traps baited with planktivorous fish feces, along with unbaited control traps, in crevices on rocky reefs at Santa Catalina Island, California, USA, between June 1982 and November 1983, and on coral reefs at St. Croix, U.S. Virgin Islands, during June 1983. Significantly more animals (the majority being crustaceans) were trapped in the baited traps compared to the unbaited controls on both reefs. There was also a significant association between the presence of trapped animals and fish feces at Santa Catalina Island (p = 0.009); this association was not quite as strong in St. Croix (p = 0.069). The consumption by shrimp of feces marked with carmine particles and, in turn, the predation on these shrimp by a reef fish demonstrates the links between this type of imported particulate organic and inorganic material and the food web of the reef community.Please address all correspondence and requests for reprints to Dr. Miller at California State University, Long Beach     

Experimental field study of the effects of crude oil,drill cuttings and natural biodeposits on microphyto- and macrozoobenthic communities in a Mediterranean area

Effects of an experimental pollution by neogenous and fossil organic matter on microphyto- and macrozoobenthic communities were studied in situ over a 1 yr period (July 1989 to May 1990) in a shallow microtidal bay (Gulf of Fos, south coast of France). Three experimental enclosures of 1 m² non-defaunated sediments were covered with 1 cm of polluted defaunated sediments. The sediment in one enclosure contained natural biodeposits with a high organic matter content (BD), that in a second enclosure contained Arabian light crude oil (BAL), and the sediment in the third enclosure contained diesel oil-based cuttings (CUT). Pollution by contaminants did not prevent microphytobenthos from colouizing sediments. Population changes over time were quite similar in all enclosures, except in CUT, where a four times higher chlorophyll a content appeared to be related to a decreased number of grazers and consequently lower grazing rates of animals. Toxicity to the fauna was immediate in the case of BAL and occurred within 3 mo at CUT. Opportunistic species settled in all contaminated sediments; this occurred quite rapidly in BD and BAL which recovered within 3 mo to levels comparable with control sediments. In CUT, natural populations had not recovered after 1 yr, whereas a quasi-monospecific population of Capitella capitata was still present. During the first 3 mo, the oxygen demand of the sediment was higher in oil-contaminated sediments than in controls. On the whole, the changes in fluxes and organism assemblages in our weakly tidal area appear to be consistent with other findings in macrotidal seas.     

Transport of brine shrimps via the digestive system of migratory waders: dispersal probabilities depend on diet and season

Waterbirds are known to disperse invertebrate propagules that survive gut passage, but there is very little information about how the probability of dispersal changes at different times of the annual cycle when birds move in different directions, or how it is affected by changes in diet. We studied internal transport of brine shrimp Artemia cysts by migratory waders in the Odiel saltworks in south-west Spain. Viable cysts of parthenogenetic Artemia were abundant in the faeces and regurgitated pellets of redshank Tringa totanus, pellets of spotted redshank T. erythropus, and faeces of black-tailed godwit Limosa limosa during spring and/or autumn migrations in 2001–2002, but were not recorded during winter. Godwits did not produce pellets, and spotted redshank faeces were not sampled. Significant correlations between the number of cysts in a pellet or faecal sample and the proportion of that sample constituted by Artemia adults suggested that most cysts were ingested while in the ovisacs of gravid females. The proportion of cysts destroyed during digestion increased when accompanied by harder food items or grit, and when fewer cysts were ingested. The median number of intact cysts was higher in redshank faeces than in their pellets, but cysts extracted from pellets were more likely to hatch. A higher proportion of redshank pellets contained Artemia cysts in spring than in autumn, but more redshank migrated through the area in autumn. Significantly fewer cysts were recorded in redshank pellets in winter than in spring or autumn. Our results confirm that there is potential for long-distance dispersal of Artemia cysts via waders during both northwards (spring) and southwards (autumn) migrations.     

Sources and concentrations of vascular plant material in sediments of Buzzards Bay,Massachusetts, USA

Samples of surface sediment from Buzzards Bay and creek sediment from Great Sippewissett Marsh were analyzed for lignin and stable carbon isotope composition in 1984. The lack of change in composition of lignins in detritus of Spartina alterniflora over two years of decomposition and similar aldehyde/acid ratios of lignin oxidation products of plant and sediment samples indicated minimal diagenesis of lignins in sediments. Remains of non-woody angiosperm tissues made up the bulk of the vascular plant debris in Great Sippewissett Marsh and Buzzards Bay sediments. These plant remains were evenly distributed over the sampling area in Buzzards Bay. Based on model calculations, salt marshes potentially contributed a significant fraction of the total amount of vascular plant debris in coastal marine sediments. The bulk of the organic matter in Buzzards Bay sediments, however, was derived from phytoplankton; vascular plant remains made up only 5 to 7% of the total amount of organic carbon in these sediments.     

Inorganic and organic contaminants in sediments from an urban playa and associated toxicity among Hyalella azteca

Playa wetlands are important components of the Southern High Plains (USA) landscape as they are the major aquatic surface feature. Chemical contaminants associated with playas have been documented, particularly for grassland and agricultural watersheds, but not for playas in urban settings. The objectives of this study were to determine concentrations of inorganic and organic contaminants in sediments from an urban playa within the I-20 Wildlife Preserve and Jenna Welch Nature Study Center in Midland, TX, and evaluate toxicity of these sediments to Hyalella azteca. Concentrations of most trace elements were below sediment quality guidelines with exceptions of lead, cadmium, and arsenic. Concentrations of organic contaminants, particularly PAHs, DDT, DDE, and malathion, were above sediment quality guidelines at various locations within the playa. Decreased survival was observed among H. azteca exposed to sediment from a single location when compared those exposed to reference sediments. This location also produced maximum observed concentrations for five of seven trace elements, potentially due to its location at the lowest elevation within the playa. This study documented concentrations of contaminants in sediments of an urban playa associated with past and present land uses in its urban setting, including those from automotive emissions and historical pesticide use.     

Seasonal variations in the densities of fecal pellets produced by Oikopleura vanhoeffeni (C. Larvacea) and Calanus finmarchicus (C. Copepoda)

Two abundant macrozooplankters, Oikopleura vanhoeffeni (Lohmann) and Calanus finmarchicus (Gunnerus) were collected from the coastal waters off Newfoundland in different seasons during 1990–1991 and incubated in natural seawater to collect freshly egested, field produced, fecal pellets. The densities of fecal pellets from O. vanhoeffeni and C. finmarchicus were measured in an isosmotic density gradient. These are the first reported seasonal measurements of fecal pellet densities from two different types of macrozooplankters, O. vanhoeffeni, a larvacean, filter feeder and C. finmarchicus, a crustacean, suspension feeder. Pellet density ranges and medians were significantly different among seasons for both species, depending primarily on the type of phytoplankton ingested and its ability to be compacted. Winter O. vanhoeffeni and fall C. finmarchicus feces filled with nanoplankters and soft bodied organisms had less open space [packing index (% open area) = 3.5 and 4% for O. vanhoeffeni and C. finmarchicus, respectively] and were more dense (1.23 and 1.19 g cm^-3) than spring feces filled with diatoms (packing index = 15 and 23%, density = 1.13 and 1.11 gcm^-3). For copepods, these results contrast with previously published density values and with the predicted copepod fecal pellet density calculated, in the present study, using the conventional mass/volume relationship. Copepod spring and summer diatom-filled feces had a calculated density of 1.12 and 1.24 gcm^-3 vs a measured median density of 1.11 gcm^-3 for both spring and summer feces; the fall feces containing nanoplankters had a calculated density of 1.08 gcm^-3 vs a measured median density of 1.19 gcm^-3. Knowledge of the seasonal variations in fecal pellet densities is important for the development of flux models.