Detritus-Bacteria-Meiofauna interactions in a seagrass bed (Posidonia oceanica) of the NW Mediterranean

The biochemical composition of the sediment organic matter, and bacterial and meiofaunal dynamics, were monitored over an annual cycle in aPosidonia oceanica bed of the NW Mediterranean to test the response of the meiofauna assemblage to fluctuations in food availability. Primary production cycles of the seagrass and its epiphytes were responsible for relatively high (compared to other Mediterranean systems) standing stocks of organic carbon in sediments (from 1.98 to 6.16 mg Cg−1 sediment dry weight). The biopolymeric fraction of the organic matter (measured as lipids, carbohydrates, and proteins) accounted for only a small fraction (18%) of the total sedimentary organic carbon. About 25% of the biopolymeric fraction was of microphytobenthic origin. Sedimentary organic carbon was mostly refractory (56 to 84%) and probably largely not utilizable for benthic consumers. The biopolymeric fraction of the organic matter was characterized by high carbohydrate concentrations (from 0.27 to 5.31 mg g−1 sediment dry weight in the top 2 cm) and a very low protein content (from 0.07 to 0.80 mg g−1 sediment dry weight), which may be a limiting factor for heterotrophic metabolism in seagrass sediments. RNA and DNA concentrations of the Sediments varied significantly during the year. High RNA and DNA values occurred during the microphytobenthic bloom and in correspondence with peaks of bacterial abundance. Bacteria accounted for a small fraction of the total organic carbon (0.65%) and of the biopolymeric organic carbon (4.64%), whilst microphytobenthos accounted for 3.79% of total organic carbon and for 25.08% of the biopolymeric carbon. Bacterial abundance (from 0.8 to 5.8 × 108 g−1 sediment dry weight) responded significantly to seasonal changes of organic matter content and composition and was significantly correlated with carbohydrate concentrations. Bacteria might be, in the seagrass system, an important N storage for higher trophic levels as il accounted for 25% of the easily soluble protein. pool and contributed significantly to the total DNA pool (on average 12%). Total meiofaunal density ranged from 236 to 1858 ind. 10 cm−2 and was significantly related, with a time lag, to changes in bacterial standing stocks indicating that microbes might represent an important resource. Bacterial abundance and biomass were also significantly related to nematode abundance. These results indicate that bacteria may play a key role in the benthic trophic

[1]  R. Danovaro,et al.  Possible Use of Rna:Dna Ratio for Detecting Oil Induced Disturbance: A Field Report , 1995 .

[2]  R. Fichez.  Composition and fate of organic matter in submarine cave sediments : implications for the biogeochemical cycle of organic carbon , 1991 .

[3]  P. Montagna.  Sampling design and enumeration statistics for bacteria extracted from marine sediments. , 1982, Applied and environmental microbiology.

[4]  E. Hartree,et al.  Determination of protein: a modification of the Lowry method that gives a linear photometric response. , 1972, Analytical biochemistry.

[5]  W. J. Dyer,et al.  A rapid method of total lipid extraction and purification. , 1959, Canadian journal of biochemistry and physiology.

[6]  F. Azam,et al.  Protein content and protein synthesis rates of planktonic marine bacteria , 1989 .

[7]  D. Alongi.  Microbial-meiofaunal interrelationships in some tropical intertidal sediments , 1988 .

[8]  J. Soyer.  Mediterranean Sea Meiobenthos , 1985 .

[9]  M. Palmer,et al.  Phytal meiofauna from the rocky intertidal at Murrells Inlet, South Carolina , 1983 .

[10]  John C. Fry,et al.  2 Direct Methods and Biomass Estimation , 1990 .

[11]  M. O. Hall,et al.  Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes , 1993 .

[12]  P. Montagna.  In situ measurement of meiobenthic grazing rates on sediment bacteria and edaphic diatoms , 1984 .

[13]  G. Hicks.  Distribution and behaviour of meiofaunal copepods inside and outside seagrass beds , 1986 .

[14]  J. Ott.  Growth and Production in Posidonia Oceanica (L.) Delile , 1980 .

[15]  R. Danovaro,et al.  A three-year time series of elemental and biochemical composition of organic matter in subtidal sandy sediments of the Ligurian Sea (northwestern Mediterranean) , 1995 .

[16]  S. Findlay,et al.  Nitrogen Source for a Detritivore: Detritus Substrate Versus Associated Microbes , 1982, Science.

[17]  P. Montagna,et al.  The relationship between abundances of meiofauna and their suspected microbial food (diatoms and bacteria) , 1983 .

[18]  R. Danovaro,et al.  Seasonal and inter-annual variation of bacteria in a seagrass bed of the Mediterranean Sea : relationship with labile organic compounds and other environmental factors , 1995 .

[19]  D. Rice.  The Detritus Nitrogen Problem: New Observations and Perspectives from Organic Geochemistry , 1982 .

[20]  R. Danovaro,et al.  Labile organic matter and microbial biomasses in deep-sea sediments (Eastern Mediterranean Sea) , 1993 .

[21]  G. Févotte,et al.  DNA content of the sediment in relation to self-purification in streams polluted by organic wastes: With 2 figures and 1 table in the text , 1981 .

[22]  V. Zachleder.  Optimization of nucleic acids assay in green and blue-green algae: extraction procedures and the light-activated diphenylamine reaction for DNA , 1984 .

[23]  C.J.F. ter Braak,et al.  CANOCO - a FORTRAN program for canonical community ordination by [partial] [etrended] [canonical] correspondence analysis, principal components analysis and redundancy analysis (version 2.1) , 1988 .

[24]  B. Velimirov,et al.  Bacterial growth rates and productivity within a seagrass system: seasonal variations in a Posidoma oceanica bed , 1993 .

[25]  B. Velimirov.  Organic Matter Derived from a Seagrass Meadow: Origin, Properties, and Quality of Particles , 1987 .

[26]  R. Garrels,et al.  What does percent organic carbon in sediments measure? , 1985 .

[27]  R. Rosenberg,et al.  Benthic macro- and meiofauna in the Gulf of Bothnia (Northern Baltic) , 1984 .

[28]  S. Y. Newell,et al.  Frequency of Dividing Cells as an Estimator of Bacterial Productivity , 1981, Applied and environmental microbiology.

[29]  D. B. Weinstein,et al.  Simple charring method for determination of lipids. , 1966, Journal of lipid research.

[30]  B. Velimirov,et al.  Seasonal changes in specific growth rates, production and biomass of a bacterial community in the water column above a Mediterranean seagrass system , 1992 .

[31]  R. Danovaro,et al.  Seasonal changes of benthic bacteria in a seagrass bed (Posidonia oceanica) of the Ligurian Sea in relation to origin, composition and fate of the sediment organic matter , 1994 .

[32]  L. Meyer-Reil,et al.  Uptake of Organic Matter by Meiofauna Organisms and Interrelationships with Bacteria , 1980 .

[33]  J. B. Lewis,et al.  Leaf epifauna of the seagrass Thalassia testudinum , 1982 .

[34]  F. James Rohlf,et al.  Biometry: The Principles and Practice of Statistics in Biological Research , 1969 .

[35]  V. N. Jonge,et al.  Fluctuations in the Organic Carbon to Chlorophyll a Ratios for Estuarine Benthic Diatom Populations , 1980 .

[36]  Proximate Constituents, Biomass, and Energy in Posidonia oceanica (Potamogetonaceae) , 1989 .

[37]  M. O. Hall,et al.  Response of small motile epifauna to complexity of epiphytic algae on seagrass blades , 1988 .

[38]  P. Montagna,et al.  Temporal variability and the relationship between benthic meiofaunal and microbial populations of a natural coastal petroleum seep , 1987 .

[39]  D. Delille,et al.  Temporal Variations of Benthic Bacterial Microflora on the Northwestern Mediterranean Continental Shelf and Slope , 1990 .

[40]  F. Smith,et al.  COLORIMETRIC METHOD FOR DETER-MINATION OF SUGAR AND RELATED SUBSTANCE , 1956 .

[41]  J. Hedges,et al.  Carbon and nitrogen determinations of carbonate‐containing solids1 , 1984 .

[42]  K. Tenore.  Organic nitrogen and caloric content of detritus III. Effect on growth of a deposit-feeding polychaete, Capitella capitata , 1983 .

[43]  C. Heip,et al.  The ecology of marine nematodes , 1985 .

[44]  B. Velimirov.  DOC dynamics in a Mediterranean seagrass system , 1986 .

[45]  S. Bell,et al.  Meiofauna from seagrass habitats: A review and prospectus for future research , 1984 .

[46]  L. Mayer.  The Nature and Determination of Non‐Living Sedimentary Organic Matter as a Food Source for Deposit Feeders , 1989 .

[47]  E. Laws,et al.  DNA:ATP RATIOS IN MARINE MICROALGAE AND BACTERIA: IMPLICATIONS FOR GROWTH RATE ESTIMATES BASED ON RATES OF DNA SYNTHESIS 1 , 1995 .

[48]  R. Newell,et al.  The Contribution Of Bacteria And Detritus To Carbon And Nitrogen Flow In A Benthic Community , 1983 .

[49]  P. Montagna,et al.  Partitioning radiolabeled thymidine uptake by bacteria and meiofauna using metabolic blocks and poisons in benthic feeding studies , 1988 .

[50]  P. Hatcher,et al.  IMPROVED TECHNIQUE FOR ANALYSIS OF CARBOHYDRATES IN SEDIMENTS1 , 1972 .

[51]  S. Bell,et al.  Diel Patterns of Active Vertical Migration in Seagrass Meiofauna , 1986 .

[52]  R. Novak.  Spatial and seasonal distribution of the meiofauna in the seagrass posidonia oceanica , 1982 .

[53]  W. Kenworthy,et al.  Production and decomposition of the roots and rhizomes of seagrasses, Zostera marina and Thallassia testudinum, in temperate and subtropical marine ecosystems , 1984 .

[54]  A. Palumbo,et al.  Size of Suspended Bacterial Cells and Association of Heterotrophic Activity with Size Fractions of Particles in Estuarine and Coastal Waters , 1984, Applied and environmental microbiology.

[55]  J. Ott.  Adaptive Strategies at the Ecosystem Level: Examples from Two Benthic Marine Systems , 1981 .