Digestion in a subtidal population of Mercenaria mercenaria (Bivalvia)

The digestive processes of Mercenaria mercenaria (Linn.) were studied in a natural subtidal population. Hourly sampling of 4 to 5 quahogs was conducted over one 25 h period in August, 1978, at Woods Hole, Ma., USA. Crystalline style length did not vary significantly with time, tide, particulate C, N or suspended material in the water. Changes in secretory activity of the style sac epithelium were not evident from histological sections. Based on cellular morphological differences, digestive tubules were individually classified into one of 4 categories, indicative of the state of intracellular digestion within the digestive cells. All 4 tubule types were present in individuals from each sample hour, signifying that intracellular digestion occurs continually within the digestive gland. A 3 h time lag is evident between times of peak C, N or suspended materials and apparent peak levels of absorptive (Type II) tubules.Contribution No. 76 Marine Science Institute, Northeastern University; Nahant, MA 01908, USA     

Digestive rhythms in the mussel Mytilus edulis

Mytilus edulis L., collected from a mid-tide level on the shore, showed rhythmic changes in mantle fluid pH, crystalline style pH, style length and total protein, and in the amylase activity in the digestive gland. These changes were correlated with the changes in tidal height. Style size may be related to extracellular digestion in the stomach. Style size and amylase content of the style were not significantly correlated with each other. The changes in amylase activity in the digestive gland confirmed the existence of a tidal rhythm for intracellular digestion in M. edulis.     

R-cells and the digestive cycle in Penaeus semisulcatus (Crustacea: Decapoda)

Shrimp, Penaeus semisulcatus, were collected from Kuwaiti waters in 1980, and the R-cells in the hepatopancreas were observed during the digestive cycle. During the first 12 h they absorb soluble material from the lumen of the gland and, subsequently, they take-up soluble and particulate material from the haemolymph. Within the cytoplasm, apical and basal systems of smooth endoplasmic reticulum are concerned with these processes. Pinocytosis only occurs at the basal cell membrane. The absorbed material is stored as lipid and glycogen, and copper, sulphur and other elements are accumulated in a large dense vacuole. These activities are integrated with those of the other cell types to effect the assimilation of food in the hepatopancreas. A scheme is proposed which accounts for the main processes of digestion. The hepatopancreas governs the duration of the digestive cycle, which takes at least 24 h. Observations on the nature of intracellular storage and waste products could be used to assess the dietary requirements of artificially reared shrimp.     

Co-ordinated rhythms of digestion,absorption and excretion in Mytilus edulis (Bivalvia: Mollusca)

Sequential alternation of extracellular digestion in the stomach and intracellular digestion in the diverticula appears widespread among bivalves. The present study documents some physiological consequences of such processes in Mytilus edulis L. collected during 1981 from Whitsand Bay, Cornwall, England. Pronounced temporal fluctuations in faecal deposition are described that relate, in terms of amplitude and period, to both sinusoidal rhythmicity established for ammonia excretion and changes in the morphology of digestive tubules. Although at least partially synchronised among replicate groups of mussels, these cycles bore no consistent relationship with exogenous influences. Hourly fluctuation in the net absorption efficiency for nitrogen, as evidenced by the mean percentage ±2 SE, measured over 24 h sampling periods, was considerable (16.0±53.7, 49.3±10.9 and 52.8±6.6 for mussels acclimated in March, June and October, respectively). This variation in absorption derived from an inverse relationship between the percentage nitrogen within faeces and the rate of faecal egestion. Accordingly, peaks of faecal deposition presumably represented the pulsed remnants of intracellular digestion. Co-ordinated rhythms of digestion, absorption and excretion were thus evident in M. edulis. These processes displayed seasonally dependent periodicities of approximately 8, 3 and 4 h in March, June and October, respectively. It was concluded that, at least for M. edulis, this previously unquantified rhythmicity of physiological processes warrants careful consideration during assays commonly undertaken in the complication of nutrient and energy budgets.     

Occurrence of lysozyme in the common cockle Cerastoderma edule and the effect of the tidal cycle on lysozyme activity

In 1983 a sample of cockles [Cerastoderma edule (L.)] was removed from the mid-tide level at Booterstown Strand, County Dublin, Ireland at 2-h intervals, for a period of 24 h. The gills, mantle and visceral mass tissues contained significant levels of lysozyme, with the gills containing the highest, weight-specific levels. A tidal rhythm of lysozyme activity in the gills, mantle and visceral mass was inversely related to the tidal cycle. The data were best described by a tidal curve shifted-5 hours out of phase, with maximum and minimum levels of activity occurring one hour after low and high tides, respectively. In marine bivalves, lysozyme may be involved in the extracellular digestion and absorption of bacteria during low tide. In this context the present use of bivalves as biological indicators of bacterial pollution is discussed.Constribution No. 6282 from the Woods Hole Oceanographic Institution     

Light and electronmicroscopic studies of the acute and long-term toxic effects of N-nitrosodipropylamine and N-methylnitrosurea on the marine mussel Mytilus edulis

The acute (1) and long-term (2) toxic effects of N-nitrosodipropylamine (NDPA) and N-methylnitrosurea (NMU) were studied by light and electronmicroscopy following injection of the chemicals into the foot of the mussels Mytilus edulis (L.) (1) Mussels reveived one injection of NDPA at concentrations of 0.25, 0.5, 1.0, and 2.0 mg NDPA mussel^-1, and one injection of NMU at concentrations of 0.25, 0.5, 1.0, and 4.0 mg NMU mussel^-1. Within 12d, necrosis of the epithelial lining of the digestive diverticula took place, and the vesicular connective tissue in the digestive diverticula were heavily infiltrated by eosinophilic granular leucocytes. (2) Mussels received four weekly injections of 0.5 mg NDPA mussel^-1, and 0.5 mg NMU mussel^-1. NDPA-exposed mussels were examined for a period of 17 weeks, and NMU-exposed mussels were examined for a period of 24 weeks. Both chemicals produced progressive tissue damage, characterized by destruction of digestive tubules and ducts in the digestive diverticula. Destroyed tubules and ducts were replaced by collagenous scars, and granulocytomas were frequently seen.     

Juvenile growth of the polychaete Nereis virens feeding on a range of marine vascular and macroalgal plant sources

A laboratory experiment was conducted to examine variation of juvenile growth (% d^-1) of the polychaete Nereis virens (Sars) in relation to tidal flat plant species as food sources. We used vegetable materials (algae and vascular plants) which are carried along by tidal currents and are found abundantly at the upper tidal level. Juveniles (2-yr-old) markedly increased in wet weight with the algae Laminaria longicruris (weight-specific growth rate : 1.7% d^-1) and Enteromorpha intestinalis (: 1.6% d^-1) as food sources. A higher value of assimilation efficiency was observed for algal species (L. longicruris 55.1±7.9%; E. intestinalis 54.8±0.5%; Fucus vesiculosus 40.6%) than for marine vascular plants (Spartina alterniflora 26.8±10.9%; Zostera marina 1.4%). The digestion of marine vascular species lasts longer (19 to 38 h) than that of algal species. All these characteristics (growth, assimilation efficiency and duration of the digestive process) seem to correlate positively with lignin and cellulose concentrations in the plant structure.     

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.     

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.     

Zooplankton abundance and grazing at Davies Reef,Great Barrier Reef,Australia

Zooplankton abundance and grazing on autotrophic and heterotrophic particulate matter were measured along a transect across Davis Reef (18°5S; 147°39E) and in the back-reef lagoon over tidal and diel cycles during austral winter (August 1984). Zooplankton entering the reef from the surrounding shelf waters decreased in abundance over the reef flat, presumably because of predation. Within the reef lagoon, maximum daytime densities of pelagic copepods occurred during high water, suggesting an external input. At night, water-column zooplankton biomass increased by a factor of 2 to 3 due to the emergence of demersal reef zooplankton. Zooplankton grazing rates on heterotrophic particulate matter (bacteria + detritus and Protozoa) compared to phytoplankton were higher on the reef flat than on the fore-reef or lagoon. Within the lagoon, zooplankton grazing rates on heterotrophic material were maximum during high water, coincident with maximum tidal concentrations of particulate organic carbon. The combined demersal and pelagic zooplankton community were often able to crop 30% of the daily primary production by >2µm phytoplankton. However, >50% of phytoplankton biomass was in cells <2µm, presumably unavailable to these zooplankton. Our particulate production and ingestion measurements, together with zooplankton carbon demand extrapolated from respiration estimates, suggest that the zooplankton community of Davies Reef derives much of its nutrition from detritus.Joint contribution from the University of Maryland, Center for Environmental and Estuarine Studies (No. 2015), and the Microbial Ecology on a Coral Reef Workshop (MECOR No. 19)     

Determination of glyoxal and methylglyoxal in atmospheric particulate matter by 2,4-dinitrophenylhydrazine derivatisation

A simple and rapid method has been optimised to determine glyoxal and methylglyoxal in atmospheric particulate matter by extraction and derivatisation with 2,4-dinitrophenylhydrazine solutions. Minimal sample preparation was required by mixing a portion of filter charged with atmospheric particulate matter with 5?mL of a saturated solution of 2,4-dinitrophenylhydrazine (1.6?g?L^?1) in acetonitrile and acidified by H₂SO₄ (50?µL?L^?1). Chromatographic analyses were carried out 1?h after derivatisation solution was mixed. Finally, the proposed method was applied to quantify these dicarbonyls in atmospheric particulate matter samples, which were obtained as part of a large field study to characterise atmospheric aerosol from a rural area of Madrid. Glyoxal concentrations averaged 0.24?ng?m^?3, whereas mean values of methyl glyoxal were around 0.95?ng?m^?3. Methyl glyoxal levels showed a clear relationship with the particulate matter levels, whereas glyoxal data did not show such a correlation. This could indicate that both dicarbonyls come from different sources.     

Structural and functional peculiarities of the digestive system of Cucumaria frondosa (Echinodermata: Holothuroidea)

The fine structure of the intestinal epithelium of Cucumaria frondosa has been examined. The digestive cells possessed some specific ultrastructural peculiarities which testify to their participation in the transport of substances and in the processes of intracellular and cavitary digestion. The main units of the intestinal epithelium appear to be multifunctional digestive cells in which the phenomenon of compartmentalization among the organelles' groups, intended to carry out various functions, occurs. The heterogeneity of the structure of populations of the digestive cells is explained. Both primitive and progressive features of the structure of the digestive tract of C. frondosa are indicated.     

A Functional Approach to the Assessment of the Nutritional Value of Particulate Organic Matter

Organic matter lability can be determined with different approaches, based on the quantitative and qualitative estimate of its nutritional value. the C/N ratio and the particulate organic matter (as the sum of protein, carbohydrate and lipid bulks) vs total suspended matter (POM/TSM) deal with a quantitative assessment of the organic matter bulk, while other indices such as proteins/carbohydrates ratio (PRT/CHO) may give also qualitative information. Gordon (1970) proposed a functional approach, based on organic carbon decrease after enzymatic digestion. Coupling Gordon's approach with the evaluation of the main biochemical components (proteins, carbohydrates and lipids) contained in the particulate organic matter, a simple method to assess lability and nutritional value of organic substrates is proposed.

Water samples were collected at the surface and close to the bottom in a shallow coastal station (10 m depth) in the Marconi Gulf (Ligurian Sea, NW Mediterranean). the difference between “total labile” and “hydrolyzed labile” organic matter (respectively before and after enzymatic digestion) suggests a relevant presence of resuspended refractory materials vs about 60% of labile hydrolyzed organic matter, thus confirming the importance of a more qualitative approach to organic matter studies.     

Ontogenetic development of digestive enzyme activities in larval walleye pollock,Theragra chalcogramma

Activities of digestive enzymes trypsin, amylase and lipase in laboratory-reared walleye pollock, Theragra chalcogramma, were measured from hatching to Day 39 (just before notochord flexion) in 1993. All measurements were conducted individually or semi-individually (groups of two larvae of the same standard length). Close relationships between digestive enzyme activities and morphological development of digestive organs were observed. Activities of trypsin and lipase were low during the transition period from endogenous to exogenous energy. Amylase activity was constant with large variance during the same period. Specific enzyme activities of trypsin and amylase indicated high values with large variance during the early period. All three enzyme activities increased with age afterthe transition period, and the specific enzyme activities became constant. The existence of two types of lipase was suggested. One lipase showed a peak of specific activity at Day 4 and might be related to yolk-sac absorption. The activity of the other lipase increased with age after Day 14 and might be related to digestion of prey lipid. Our results suggest that digestive enzymes included in food organisms supplement larval pollock digestive enzymes.     

Characterisation of cysteine proteinase activities in the digestive tract of juvenile <Emphasis Type="Italic">Paragnathia formica</Emphasis> isopods,ectoparasites of estuarine fish

Juveniles of Paragnathia formica Hesse (Isopoda; Gnathiidae) are haematophagous ectoparasites, feeding on fish blood which supplies the nutrients for their development through growth and moulting, and the subsequent survival and reproduction of the free-living adults. Little is known of the mechanisms of digestion in juvenile gnathiids, and biochemical studies on the digestive tract of these interesting estuarine isopods have not been undertaken previously. Here, functionally active cathepsin-like cysteine proteinases are identified in the digestive system of juvenile praniza (fed) and zuphea (unfed) forms. The physiological pH of the digestive tract and the optimum proteolytic activities detected in praniza 3 homogenates using the cathepsin B/L, cathepsin B, and cathepsin H fluorogenic substrates, N-Carbobenzoxy-Phe-Arg-4-methoxy-2-naphthylamine (Z-phe-arg-MNA), N-Carbobenzoxy-Arg-Arg-4-methoxy-2-naphthylamine (Z-arg-arg-MNA) and Arg-4-methoxy-2-naphthylamine (H-arg-MNA), respectively, are in the acidic range (pH 5.8–6.7). Inhibition profiles against Z-phe-arg-MNA and Z-arg-arg-MNA using the cathepsin B inactivator urea, and cysteine proteinase inhibitors, support the presence of cathepsin L- and B-like enzymes. These proteolytic activities are 10–50 times higher in homogenates of praniza 3 compared with zuphea 3 forms. Histochemistry of praniza 3 sections reveals that the predominant enzyme activity towards Z-phe-arg-MNA is limited to the digestive glands during early and mid stages of digestion; later, this activity appears in the lining of the anterior hindgut. Moreover, activity towards Z-arg-arg-MNA is generally restricted to the digestive glands, and only occasionally present in the anterior hindgut. In conclusion, the digestive glands are the main site of cathepsin-like cysteine proteinase activities in P. formica juveniles; these enzymes appear to be important to the digestion of host fish blood enabling development through to the free-living adult.     

Comparison of the sedimentation of a diatom spring bloom and of a subsurface chlorophyll maximum

The seasonal pattern of sedimentation was determined over a 8-mo investigation period covering the productive season at a permanent station in the Southern Kattegat (Denmark) in 1990. The phytoplankton succession was characterised by a 4-mo long subsurface maximum associated with the pycnocline which was entirely dominated by the dinoflagellate Gyrodinium aureolum. The bulk sedimentation of organic matter took place during this period and accounted for >60% of the annual particulate organic carbon (POC) and particulate organic nitrogen (PON) sedimentation. The spring bloom period contributed 60% of the sedimentation of intact phytoplankton cells, but only 20% of the POC and PON sedimentation. A minor fraction of the sedimenting matter from the subsurface phytoplankton maximum consisted of intact phytoplankton (<20%), suggesting that the phytoplankton was processed by heterotrophs and that it was mainly products from this activity which contributed to thevertical flux of organic matter. The variation in oxygen concentration below the pycnocline coincided with the pattern of sedimentation with a delay of 3 to 6 wk.     

The tidal rhythm of extracellular digestion and the response to feeding in Ostrea edulis

Under natural conditions, on the shore, there is a tidal rhythm for changes in pH, length, and protein and amylase content of the crystalline style of Ostrea edulis L. When oysters were kept immersed and fed continuously for 2 weeks, in the laboratory, the rhythm of extracellular digestion was lost. Oysters were fed discontinuously for 2 weeks, in the laboratory, with a 6 h-on, 6 h-off feeding regime. During the feeding period, the changes in pH, size, and protein content of the style were similar to the changes observed in the field over the period of high tide. It is our hypothesis that the tidal rhythm of extracellular digestion in Ostrea is not endogenous, but is controlled by feeding activity.     

Distribution and retention of the copepodEurytemora affinis hirundoides in a turbid estuary

The spatial and temporal distribution of the copepodEurytemora affinis hirundoides (Nordquist, 1888) in the Gironde estuary, southwest France, was investigated in 1976, and between 1981 and 1983. The distribution pattern of the population bore a clear relationship to the patterns of water circulation and transport of particulate matter. Laboratory experiments suggested thatE. affinis hirundoides is incapable of autonomous displacement against the direction of general circulation and behaves as passive particles. A major problem faced by species living in estuaries is that of the maintenance of endemic populations. Some authors have suggested that behavioural responses may play an important role in minimising population losses. Our study indicated that hydrodynamic processes are sufficient to explain the distribution and retention ofE. affinis hirundoides, whose populations are retained in the estuary in the same manner as the suspended sediment. Since the outflow of particulate matter from the Gironde estuary to the sea is very sporadic, we hypothesize that most of the production ofE. affinis hirundoides remains within the estuary, and does not fertilize the continental shelf, at least not in the form of particulate organic matter.     

土壤中六六六在消化道中生物可给性的体外测定

采用体外消化实验模拟了4种有机质含量不同的土壤中六六六在胃和小肠中的释放,重点验证了消化释放出来的六六六在固态消化残渣上的吸着现象以及该现象对测定消化率的影响的研究假设.结果表明,固相吸着对测定消化率有非常显著的影响,这在有机质含量偏高的土壤中尤其明显.吸着影响可以用不同液固比实验设计配合非线性拟合方法加以校正.对有机碳含量分别为0.63%、1.08%、1.60%和2.87%的4种土壤,未经校正的总六六六消化率的均值与标准差分别为(16.7±2.8)%、(11.6±2.0)%、6.9%和(26.4±1.3)%,校正后则分别达到16.7%、16.5%、16.5%和59.7%.显然,除有机质含量很低的样品,未经校正的测定结果显著低估了消化道吸收风险.     

Tidal variations in the movement of organic carbon in New Jersey salt marshes

The movement of organic carbon was assessed by statistical and simulation modeling analyses in two marsh types in New Jersey;each marsh contained three water-drainage systems in which three tidal cycles were sampled in May and June 1973. Hourly water samples were obtained and filtered through a gelman Type A glass filter for separation into dissolved (DOC) and particulate (POC) organic carbon components of the total organic carbon (TOC). Simulation data showed that individual creeks and marshes functioned differently on the sampled tidal cycles in regard to net movement of water and organic carbon components. Organic carbon components exhibited similar tidal variations, with significantly lower concentrations at flood slack than at ebb slack. Mid-ebb concentrations were significantly higher than mid-flood concentrations for TOC and POC. Individual marshes showed significantly different concentrations in the latter segments of the tidal cycle for TOC's and POC's. Results indicate that individual creeks, marshes and tidal cycles are not representative of the total movement of organic carbon in estuaries.Paper of the Journal Series, New Jersey Agricultural Experiment Station, Cook College, rutgers—The state University of New Jersey, New Brunswick, New Jersey 08903, USA.