The vertical distribution of plankton is described for 3 stations representative of stratified. frontal and vertically mixed regions of the western English Channel in summer. All components of organic carbon, representing dissolved and particulate organic carbon, phytoplankton, bacteria. protozoans, micro-and meso-zooplankton, were estimated independently. Major differences were found In the abundance and species composition of the phytoplankton, and in the relative proportions of different groups of heterotrophs. In the frontal region the phytoplankton (26.5 g C m-2) was composed of an essentially monospecific, surface population of the dinoflagellate Gj~odinium aureolum; by contrast, under well-stratified cond~tions small naked flagellates (0.42 g C m-2) forming a sub-surface chlorophyll maximum were dominant, and the tidally mixed waters were characterised by diatoms (7.91 g C m-'). At each station the estimated standing stock of heterotrophs was between 2.3 and 3.2 g C m-' , 10 to 30 % of which consisted of bacteria. Hence the phytoplankton was the dominant compartment in the frontal and mixed regions, whereas the zooplankton biomass considerably exceeded that of the phytoplankton in the well-stratified water. The ecological implications of these carbon distribution patterns are discussed.
Urcmema sp. of ca 12 X 5 p m and Euplotes sp. ca 20 X 10 pm were isolated from surface waters of the English Channel. The rapidly motile Uronerna sp. has a relative growth rate of 3.32 d-' and responds rapidly to the presence of bacterial food with a doubling time of only 5.01 h. Its mortality rate is 0.327 d-' and mortality time is therefore short at 50.9 h once the bacterial food resource has become h i t i n g. Uronema sp. therefore appears to be adapted to exploit transitory patches when bacterial prey abundance exceeds a concentration of ca 6 X 106 cells ml-'. In contrast, Euplotes sp. had a slower relative growth rate of 1.31 d-' and a doubling time of ca. 12.7 h, implying a slower response to peaks in bacterial food supply. The mortality rate of 0.023 d-' is considerably lower than In Uronema and mortality time is as much as 723 h. This suggests that, relative to Uronerna, the slower moving Euplotes has a more persistent strategy w h c h under the conditions of our experiment favours a stable e q u h b n u m wlth its food supply. Grazing activities of these 2 ciliates have an important influence on abundance and size-class structure of their bacterial prey. In the presence of both Uronema and Euplotes, there is some evidence of an initial removal of large rods and squat rods, followed by removal of the smaller cocci before the initial population of bacteria is consumed. This is followed by the appearance of a secondary bactenal assemblage which is associated only with the development of the grazlng chates and is dominated by small thin rods. Gross growth efficiency of Uronema and Euplotes is ca 27 and 19 '10 respectively. Hence as much as 73 to 81 % of the carbon ingested with the bactenal food is dissipated through respiration and excretion. Should this occur in natural euphotic waters this process may supplement the DOM release by primary producers. Extracellular DOM production by the ciliates may therefore be of major significance in the maintenance of the secondary population of bacteria, and emphasizes the close interdependence of ciliate predators and bacterial prey in rnicroheterotrophic food webs.
Detritus from the dinoflagellates Scrippsiella (= Peridinurn) trochoidea and Isochrysis galbana and from the diatoms Skeletonema costaturn, Thalassiosira angstii and Chaetoceros tricornuturn incubated at 10 "C in seawater is colonised by a succession of micro-organisms. Primary microbial decomposers in the incubation experiments were bacterial rods and cocci which reached a peak standing stock carbon of 1.86 f 0.76 % of the carbon supplied to the incubation media by the third day of incubation. The bacteria were subsequently replaced by flagellates which attained a mean peak biomass of 12.5 f 3.58 % of the bacterial biomass by Day 6 before declining. Synchronous measurement of the utilisation of dissolved and particulate components from the incubation media shows that there is a well-defined initial sequence of aggregation of particulate matter to form bacterioparticulate complexes, much as have been recorded for natural waters. During this phase, carbon is mainly utilised from the dissolved component of phytoplankton cell debris, whilst the more refractory components including particulate debris is used more slowly. The dissolved organic component comprises a mean of 34 24 % of the total carbon in the debris and has a 50 % utilisation time of only 1.56 d (37.44 h), whereas the particulate component comprises 65 76 % of the total carbon and has a 50 % utilisation time of as much as 11.56 d (277.4 h). Bacterial carbon conversion efficiency (bacterial carbon/detrital carbon used X 100) during the initial phases of colonisation is 9.8 Sb -a value similar to that recorded for bacterial conversion of dissolved components of macrophyte debris. The results suggest that the carbon conversion budget for the decomposition of phytoplankton cell debris is 100 g carbon yielding 4 -644 g of bacterial carbon. This value for incorporation of carbon into bacteria from phytoplankton cell debris is much lower than might be anticipated from the absorption efficiency of selected labile components released in small quantities by living phytoplankton. The carbon conversion budget for whole phytoplankton debris thus suggests that as much as 30.8 % of the carbon is mineralised and returned to the environment within 3 d by the bacteria which initially colonise the material, whereas the more refractory 64.4 %, comprising carbon in the particulate components of the cell debris, is mineralised within approximately 11 d by bacteria characteristically associated with the decomposition phase of a phytoplankton bloom.
A modification of the 51Cr:'4C twin-labelling technique is described in which the food source is labelled with 14C but the 51Cr is enclosed in a polymeric resin membrane and presented as microspheres of a similar diameter to the food particles. This eliminates the major uptake of 5 1~r which is transferred to the ctenidia and palps of the suspension-feeding mussel Aulacomya ater(Mo1ina) from detritus labelled with 51Cr. The results suggest that although bacterial cultures based on isolates of kelp bacteria can be absorbed with an efficiency of 67 to 70 %, the debris itself is also absorbed with an efficiency of approximately 50 %. The kelp debris, which forms an important component of the particulate matter potentially available for consumers, may thus represent an important source of carbon for the filter feeding community adjacent to kelp beds. In contrast to the results obtained in other studies with artificial food sources, the data for kelp debris suggest that A. ateris able to maintain a positive scope for growth at the concentrations of suspended organic matter which occur under natural conditions in the kelp bed environment. INTROCUCTIONThe decomposition of detrital material and its subsequent utilisation by consumer organisms has been widely studied in marlne and freshwater habitats. Since many invertebrates apparently show only a weak ability to digest cellulose, xylan, alginic acid or other structural carbohydrates which make up the bulk of detrital material (Kristensen, 1972) it has been generally supposed that the carbon and, above all, the protein requirements of consumer organisms may be met by absorption of the microbial component of the ingested plant detritus (Newell, 1965(Newell, , 1979 Darnell, 1967a, b; Odum and De la 'Cruz, 1967;Hargrave, 1970a, b, 1971. Fenchel, 1972 De'la Cruz and Poe, 1975;Kofoed, 1975; Tenore, 1975;Moriarty, 1977).One of the difficulties in interpreting the significance of the microbiota in meeti.ng the nutritional requirements of consumer organisms is that the biomass of bacteria in the sediments may be too low to meet the estimated carbon or nitrogen requirements of the consumer organisms (Baker and Bradnam, 1976; O Inter-Research/Printed in F R. Germany Wetzel, 1977;Jensen and Siegismund, 1980). Tunnicliffe and Risk (1977), for example, calculated that the bivalve Macoma balthica could meet only 0.2 % of its nitrogen requirements from the microbial biomass in the sediments. Again, Cammen et al. (1978) and Cammen (1980a, b) have estimated that only 25 to 45 % of the carbon requirements of the deposit feeding polychaete Nereis succinea could be met by utilisation of microbial carbon.These results suggest that some of the carbon necessary to balance the energy budget may b e derived by direct utilisation of plant debris itself, a conclusion which is supported by studies on the relation between primary production and consumption requirements in kelp communities (Newel1 e t al., 1982). Other studies, however, suggest that beca.use microbial production is ...
Primary production by phytoplankton in a Benguela upwelling region off the west coast of the Cape Peninsula, South Africa, is almost equal to that within beds of the kelps Ecklonia maxima and Laminaria pallida. Total primary production of kelps, understorey algae and phytoplankton within a n idealised kelp bed of 10 nl average depth is 62,190 kJ yr-l, as compared to 54,037 kJ m-2 yr-' for the phytoplankton community in deeper water nearby. The overall energetic conversion from incident illumination is 1.7% within the kelp bed and 1.5% for phytoplankton in the nearby water column, suggesting that a net production efficiency of 1.5 to 1.7% may approach the maximum attainable by aquatic plants under conditions where nutrients are rarely limiting. The fauna is dominated by filter feeders, which are responsible for 72% of total animal standing stock (B), 77 % of total production (P), 9 4 % of respiration (R), 8 4 % of consumption (C) and 89% of faecal production (F). Independent estimates of primary production and energy requirements of consumers balance to within 8 %, lending confidence to the calculations. Suspended matter, the food of filter feeders, is comprised of macrophyte particles, animal faeces and phytoplankton in roughly equal proportions. Bacteria which utilise dissolved and particulate components of fragmented macrophytes and faeces may produce up to 6,403 kJ m-2 yr-', which is small energetically but belies their importance in protein enrichment of food and in nutrient cycling. The kelp community appears to depend primarily on rapid bacterial mineralisation of fragmented kelp and faeces to recycle the minerals necessary to sustain primary production, supplemented by bouts of upwelllng.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.