The zooplankton of the inshore waters of Dar es Salaam (Tanzania,S. E. Africa) with observations on reactions to artificial light

From 18th December, 1968 to 5th January, 1970, zooplankton samples were taken in darkness and using artificial light in selected areas of the Dar es Salaam coast (Tanzania, S. E. Africa). Surface sea temperature was measured on most occasions, salinity for the first 7 months only. The neritic waters of Dar es Salaam experience a warm period during January to March and a cool period during July to September. The annual salinity cycle is not known. Thirtysix dark and 17 light zooplankton samples were analysed; where possible, organisms were identified to species, others to generic or higher taxonomic level. The principal taxa and their mean percentage proportions (figures in parentheses) in the dark samples were: Calanoida (49. 1), Larvacea (11. 9), Corycaeus spp. (6.4), Cypridina sinuosa (5.6), Oithona spp. (4.8), caridean larvae (4.0), Sagitta spp. (3.8), Euterpina (2.1), Lucifer (1.2), Oncea (1.2), calyptopis larvae (1.0), Hydromedusae (1.0), Euconchoecia chierchiae (1.0), Creseis acicula (1.0), brachyuran zoeae (0.8), Ctenophora (0.5), Mysidacea (0.5), fish eggs (0.5), postlarval bivalves (0.5), postlarval gastropods (0.5), Cumacea (0.1), Gammaridea (0.1) and Hyperiidea (0.1). Evadne tergestina and Thalia democratica abound in waters at certain times of the year only and then virtually disappear. The remaining groups were numerically unimportant most of the time. Almost every major group showed an annual cycle of abundance; greater numbers were recorded either for the entire or part of the period February to August, compared to the period September to November. From the end of January to early August, 1969, the average numbers per haul of total zooplankton were about three times greater than for the period mid-August to mid-November. During February-March and July-August, several oceanic indicators were observed together in the neritic waters. Artificial light induced the following changes in night zooplankton: Mysidacea, Leptochela sp., Hyperiidea, Cypridina sinuosa, brachyuran megalopae and fish larvae were attracted towards artificial light and aggregated densely under the lamp; Calanoida, Corycaeus spp., Macrosetella, Microsetella and Euterpina avoided regions of strong illumination and aggregated in dim-lit areas; Lucifer, Creseis acicula and postlarval gastropods were more abundant in dim-lit samples compared to dark hauls; caridean larvae, brachyuran zoeae and larvaceans were less abundant in high-intensity light samples compared to dark hauls on the same nights.This work was performed at the Department of Zoology, University of Dar es Salaam, Tanzania, S.E. Africa.     

Community structure of the benthos in Scottish sea-lochs. III. Further studies on patchiness

Large-scale patchiness in the distribution of the benthic fauna was investigated in Loch Etive (Scottish west coast) by two series of van Veen grab hauls. Each series was taken along a traverse across the width of the loch, with sampling points about 100 m apart. One sample series was taken on sandy mud and the other, at a greater depth, on soft mud. Two approaches in data processing were applied: (1) The variance: mean ratio and the Morisita I tests for significant aggregation were applied to the species abundances in the sample series; (2) 3 measures of sample homogeneity, each involving the calculation of an index of faunal similarity, were applied to the separate samples. The results, however, could not show significant differences between the two series of samples. These findings were compared to results obtained from (a) a previous study, where differences in patchiness between areas were shown for a smaller scale of sampling design in Loch Etive and neighbouring areas, and to which the I method is also applied here; and (b) the results of applying the variance: mean ratio and I tests to data published by Holme (1953). The present results indicate greater aggregation at the present scale of sampling than for the previous, smaller scale of sampling, or for the comparable scale of Holme's sampling. The degree of concordance shown by the values of I for the circular-design sampling to the values of the 3 measures of patchiness applied previously, and to the means of the species abundances, was measured by Spearman's rank correlation coefficient. The results clearly demonstrated the I values, unlike the others measured, to be almost completely independent of the mean. It was concluded that, for comparing the pattern from benthic samples using standard-size bottom samplers, where the mean may vary widely between each set of samples, the I method is probably most useful.     

Feeding deterrence properties of apo-fucoxanthinoids from marine diatoms. I. Chemical structures of apo-fucoxanthinoids produced by Phaeodactylum tricornutum

Methanol extracts of freshly harvested cells of the marine diatom Phaeodactylum tricornutum were found to produce a feeding deterrent effect in the copepod Tigriopus californicus. Bioassay guided fractionation of the methanol extracts led to the isolation of four compounds possessing feeding deterrent activity. The compounds were identified as apo-10-fucoxanthinal (1), apo-12-fucoxanthinal (2), apo-12-fucoxanthinal (3), and apo-13-fucoxanthinone (4) by detailed spectroscopic analysis and comparison with authentic compounds produced semi-synthetically from fucoxanthin. Compounds 1 to 4 exhibited feeding deterrent responses in T. californicus at concentrations of less than 20 ppm.     

Investigations of carotenoids in some fauna of the Adriatic Sea. III. Leander (Palaemon) serratus and Nephrops norvegicus (Crustacea: Decapoda)

Investigations have been carried out on the carotenoids in Leander (Palaemon) serratus (Pennant) and Nephrops norvegicus (L.) (Crustacea: Decapoda) from the Adriatic Sea. The presence of the carotenoids was determined by means of columnar and thin-layer chromatography. The following carotenoids were found: Leander serratus: -carotene, echinenone, isocryptoxanthin, cryptoxanthin, canthaxanthin, lutein, isozeaxanthin, zeaxanthin, astaxanthin, and astacene; Nephrops norvegicus: -carotene, lutein, zeaxanthin, astaxanthin, and astacene.     

Zooplankton of the Bristol Channel and Severn Estuary. The distribution of four copepods in relation to salinity

The seasonal variations in distribution and abundance of the common zooplankton species in the Bristol Channel and Severn Estuary were related to the salinity regimes observed over the period November 1973 to February 1975. The dominant constituents in all regions were the calanoid copepods, which reached maximum densities in July: approximately 100 times their winter levels. Four zooplankton assemblages were recognised using an objective classification program which computed similarity coefficients and used group-average sorting. The assemblages existed along the salinity gradient observed from the Severn Estuary to the Celtic Sea. The assemblages were classified as true estuarine, estuarine and marine, euryhaline marine and stenohaline marine and were characterized by the copepods Eurytemora affinis (Poppe) (<30S), Acartia bifilosa var. inermis (rose) (27 to 33.5S), Centropages hamatus (Lilljeborg) (31 to 35S) and Calanus helgolandicus (Claus) (>33S), respectively.     

Silicon and the ecology of marine plankton diatoms. II. Silicate-uptake kinetics in five diatom species

The variation of the rate of silicate uptake with varying silicate concentration in the medium was investigated in short-term experiments with the following marine diatom species:Skeletonema costatum, Thalassiosira pseudonana, T. decipiens, Ditylum brightwellii, andLicmophora sp. The uptake conformed to Michaelis-Menten kinetics only after a correction had been made for reactive silicate that apparently could not be utilized by the diatoms. The magnitude of this correction was in the range of 0.3 to 1.3 g-at Si/l. Mean values of the half-saturation constant of silicate uptake were calculated for the different species. The lowest value was found inS. costatum (0.80 g-at Si/l) and the highest inT. decipiens (3.37 g-at Si/l). Growth limitation by low silicate concentrations could be a cause of species succession in marine plankton-diatom blooms.     

Biosystematic studies of the red algal genus Eucheuma. I. Electrophoretic variation among Florida populations

Electrophoretic techniques were used to assess the degree of genetic differentiation among 4 species of the seaweed Eucheuma; E. isiforme, E. nudum, E. gelidium and E. acanthocladum. Nine Floridian populations were surveyed for 5 enzymes (14 loci), and compared using both phenotypic identity (I _p )and Nei's genetic identity (I) statistics. Results suggest there is a very high degree of genetic similarity between E. isiforme and E. nudum (=0.904), and between E. gelidium and E. acanthocladum (=0.857), but a very low degree of similarity between these two pairs of species (=0.372). These findings are in agreement with an earlier report which recommended the removal of E. gelidium and E. acanthocladum from the genus based on differences in reproductive anatomy. Greater genetic similarity was observed among the E. isiforme populations than among the E. nudum populations, the latter being ecologically more diverse and geographically or hydrographically more isolated. The proportion of polymorphic loci per population ranged from 0.25 to 0.36. Heterozygote deficiencies were observed at two acid phosphatase loci in offshore populations of E. nudum which showed a propensity for vegetative reproduction.     

Microbial associations in sponges. III. Ultrastructure of the in situ associations in coral reef sponges

Symbiotic cyanobacteria are associated with marine sponges in three ways: the majority are free-living in the mesohyl; large aggregates occur in cyanocytes (specialized, vacuolated archeocytes); and few are present in digestive vacuoles. The cyanobacteria in Jaspis stellifera and Neofibularia irata are morphologically similar to those described in Mediterranean sponges, whereas those in Pericharax heteroraphis are different. The freeliving bacterial populations are morphologically similar, although the number of bacteria varies between the species. The fourth sponge Ircinia wistarii contains a mixed bacterial population unlike those in the other sponges. Sponge digestion of microbial associates is rare and not considered to contribute significant nutrients.     

Chemical aspects of mass spawning in corals. I. Sperm-attractant molecules in the eggs of the scleractinian coral Montipora digitata

This paper provides the first evidence for sperm chemotaxis in the Scleractinia. Montipora digitata Dana, 1845 (Scleractinia: Coelenterata) is a hermaphroditic coral which reproduces bi-annually, releasing egg-sperm bundles during the mass spawning at Magnetic Island (19°10S; 146°52E) in late spring-early summer, and autumn each year. The buoyant egg-sperm bundles float to the surface where they break apart, releasing eggs and sperm into the ocean. Fertilisation occurs after 30 min. Unfertilized eggs were collected, washed free of sperm, and freeze-dried. The eggs were extracted with dichloromethane, fractionated by chromatography on silica gel, and the fractions assayed for their ability to attract M. digitata sperm. The active fraction was further fractionated by high-performance liquid chromatography, resulting in the isolation of three highly unsaturated fatty alcohols: (1) dodeca-2,4-diynol; (2) tetradec-13-ene-2,4-diynol; (3) (14Z)-heptadeca-14,16-diene-2,4-diynol. Of these three compounds, only Compound 1 attracted sperm of M. digitata. Synthetic Compound 1, produced from simple precursors by known reactions, possessed sperm-attracting activity comparable to the naturally derived attractant. Preliminary experiments suggest that the natural mixture of Compounds 1, 2 and 3 in the ratio 1:4:9 is more effective in attracting sperm from M. digitata than sperm from other Montipora species. Sperm attractants may act to reduce the incidence of hybridisation between different species of Montipora.     

Effects of salinity and temperature on Corophium volutator and C. arenarium (Crustacea: Amphipoda), with particular reference to distribution

The responses of the post-embryonic stages of Corophium volutator (Pallas) and C. arenarium Crawford to the combined effects of salinity and temperature show that gravid females have a wider tolerance than nongravid adult females which in turn are more tolerant than adult males. C. volutator is more tolerant of low salinity (2 to 10) than C. arenarium, but the latter is more tolerant of salinities above 45. The embryos of C. volutator develop normally and hatch at lower salinities and temperatures than those of C. arenarium, in which successful development was recorded at higher temperatures. Females undergoing a pre-copulatory moult failed to lay eggs below salinities of 3 (C. volutator) and 10 (C. arenarium), but in both species the lowest salinity at which all females moulted and laid eggs was 20. The results are discussed in relation to the distribution of both species.     

Biremis blandi (Polychaeta: Terebellidae), new genus,new species,caught by D.S.R.V. “Alvin” in the Tongue of the Ocean,new providence,Bahamas

Biremis, n. gen., characterized by an enlarged cephalic lobe, achaetous thoracic segments, and abdominal bilobed uncinigerous pinnules, lacks eyes and branchiae and is, thus, grouped with the subfamily Polycirrinae of the Terebellidae. Biremis blandi, n. sp., has prominent longitudinal muscular ventral ridges, lacking ventral glandular scutes. The avicular uncini, arranged in a single row on each lobe of each abdominal pinnule, are very similar to those of Polycirrus. The new species, collected from D.S.R.V. Alvin, was observed resting on and swimming over the sloping walls of the Tongue of the Ocean (25° N; 77°35 W), at 600 m depth. Its ability to swim may be a requirement for survival on an unstable substratum.Contribution No. 2891 from the Woods Hole Oceanographic Institution.     

Occurrence of tetrodotoxin in the starfishes Astropecten polyacanthus and A. scoparius in the Seto Inland Sea

Two starfishes, togemomijigai Astropecten polyacanthus and momijigai A. scoparius were collected from the Seto Inland Sea in October 1983 through November 1984, and assayed for toxicity by the standard method for tetrodotoxin (TTX). Most of the 54 A. polyacanthus specimens assayed were toxic, with the highest toxicity score being 520 mouse units (MU) g^-1. All seven A. scoparius were toxic, with the highest score being 46 MU g^-1. The toxin from A. polyacanthus was purified by a method which consisted mainly of activated charcoal treatment, and chromatography on CM-Sephadex C-25 and Bio-Rex 70 columns. The purified starfish toxin showed a specific toxicity of 4 700 MU mg^-1, a value which was almost comparable to that of authentic TTX. From the thin-layer chromatographic and electrophoretic behavior, along with ¹H-NMR spectrum, A. polyacanthus toxin was identified as TTX.     

Investigations of carotenoids in some fauna of the Adriatic Sea. I. Verongia aerophoba (Porifera: Spongiidae)

Investigations have been carried out on the carotenoids in Verongia aerophoba (Schmidt) (Porifera: Spongiidae) from the Adriatic Sea. The presence of the carotenoids -carotene, -carotene, isozeaxanthin, lutein (ester and free), zeaxanthin, violaxanthin, neoxanthin, astaxanthin and astacene was determined by means of columnar and thin-layer chromatography.     

Does displacement of spawning time occur in the sibling species Cerastoderma edule and C. lamarcki?

The spawning cycles of the sibling species Cerastoderma edule (L.) and C. lamarcki (Reeve) were studied in allopatric and sympatric Danish populations from 1978–1980. The results do not support earlier findings of reproductive character displacement in sympatric populations of the two species. New records of hybrid formation and intermediate forms are presented and discussed.     

Digestive carbohydrases from the hepatopancreas of two Antarctic euphausiid species (Euphausia superba and E. crystallorophias)

The hepatopancreatic extracts of Euphausia superba Dana and E. crystallorophias Holt and Tattersall collected from the Antarctic. Ocean during January 1985, are most effective in hydrolysing substrates containing (13)--glucosidic linkages. Three enzymes appear to be involved in the depolymerization of (13)--D-glucans in the euphausiid diet: (1) an exo-(13)--D-glucanase, (2) an endo-(13)--D-glucanase and (3) a -D-glucosidase. The glucanases have a pH optimum of 5.4, a temperature optimum of 50°C and are optimally extracted in bistripropane buffer, pH 7.2. Levels of (13)-D-glucanase in laboratory-cultured E. superba are inversely affected by food availability, and activities double after starvation for 12 d. The increase is due mainly to higher activities of exo-acting glucanases. -Amylase and endo-(14)--D-glucanase (cellulase) activity are also present in the extracts in addition to glycosidase activity against a range of p-nitrophenyl substrates (-and -D-glocose, - and -D-galactose, -D-xylose, - and -D-mannose). Digestive activity against several acidic polysaccharides, including the acidic mucilage polysaccharide of the ice diatom Stauroneis amphioxys, is minimal and is not induced when the polysaccharide is present in the diet of E. superba. These results indicate that some, but not all, components of the algal material in the euphausiid diet can be hydrolyzed and assimilated.     

Two sibling species of Tisbe (Copepoda,Harpacticoida): Tisbe reluctans and T. persimilis n. sp. Research on their morphology and population dynamics

Two new forms of the copepod genus Tisbe, one of which was found in the Lagoon of Venice near Chioggia (Italy), and the other in the port of Malta, have been studied. Although showing a striking resemblance in morphology, all attempts to cross representatives of the 2 populations have failed. They may, therefore, be considered as sibling species. Even on closer study, no qualitative structural differences between them were found. However, careful analysis of some biometrical traits revealed significant differences. A certain differentiation of another kind emerges from the comparison of the life-cycle and population dynamics. Under standard laboratory conditions the following main parameters have been considered: (1) survival; (2) mean and minimum generation time, T; (3) net reproduction rate, R ₀; (4) intrinsic rate of natural increase, r _m. The significance of the findings is discussed.     

Vertical distribution and feeding patterns of midwater fish in the central equatorial Atlantic II. Sternoptychidae

The vertical distribution of seven sternoptychid species was examined from RMT 1+8 samples collected aboard R. V. Meteor in March-April 1979 and from Royal Research Ship R.R.S. Discovery in July 1974 in the central equatorial Atlantic. During daytime sternoptychids occupied depths between 200 and 1250 m, with Sternoptyx pseudobscura living deepest, centering between 800 and 900 m, and Argyropelecus sladeni most shallow, aggregating predominantly at 300 and 400 m. They are all considered limited or partial migrants, ascending only some 100 and 200 m towards the surface at night. Only A. sladeni was observed to enter the epipelagic zone (0 and 200 m).-Feeding patterns were investigated from stomach content analyses of Sternoptyx diaphana, S. pseudobscura, Argyropelecus sladeni and A. affinis. Additional stomach contents were analysed from samples of S. diaphana, A. hemigymnus and A. olfersi collected in June 1985 from F.R.V. Walther Herwig in the temperate NE Atlantic at 46°N, 17°W by means of the Engel Trawl. The food spectrum of the six species is generally described, and additional dietary evidence regarding calanoid copepod prey is provided for four of these taxa. All sternoptychid species investigated were planktivorous, feeding predominantly on copepods and ostracods, except for the largest size class, which preyed heavily on euphausiids and amphipods. The relationship of predator size towards prey type and prey size is analysed for both Sternoptyx species. Of these, S. pseudobscura in particular exhibits taxonomic selectivity towards polychaete prey. The diet of both species of Sternoptyx included a number of epipelagic or even neustonic calanoid copepod species which contributed more than 50% of the total copepod population by numbers. So far it is not known how the predators find access to prey organisms of the upper 200 m, as netfeeding is considered unlikely. Cyclopoid copepods of the genus Sapphirina were observed as dietary component particular of S. diaphana.     

Diurnal patterns in photosynthetic capacity and depth-dependent photosynthesis-irradiance relationships inSynechococcus spp. and larger phytoplankton in three water masses in the Northwest Atlantic Ocean

The photosynthetic characteristics of prokaryotic phycoerythrin-rich populations of cyanobacteriaSynechococcus spp. and larger eukaryotic algae were compared at a neritic frontal station (Pl), in a warm-core eddy (P2), and at Wilkinson's Basin (P3) during a cruise in the Northwest Atlantic Ocean in the summer of 1984.Synechococcus spp. numerically dominated the 0.6 to 1 m fraction, and to a lesser extent the 1 to 5 m size fractions, at most depths at all stations. At P2 and P3, all three size categories of phytoplankton (0.6 to 1 m, 1 to 5 m, and >5 m) exhibited similar depth-dependent chages in both the timing and amplitude of diurnal periodicities of chlorophyllbased and cell-based photosynthetic capacity. Midday maxima in photosynthesis were observed in the upper watercolumn which damped-out in all size fractions sampled just below the thermocline. For all size fractions sampled near the bottom of the euphotic zone, the highest photosynthetic capacity was observed at dawn. At all depths, theSynechococcus spp.-dominated size fractions had lower assimilation rates than larger phytoplankton size fractions. This observation takes exception with the view that there is an inverse size-dependency in algal photosynthesis. Results also indicated that the size-specific contribution to potential primary production in surface waters did not vary appreciably over the day. However, estimates of the percent contribution ofSynechococcus spp. to total primary productivity in surface waters at the neritic front were significantly higher when derived from short-term incubator measurements of photosynthetic capacity rather than from dawn-to-duskin situ measurements of carbon fixation. The discrepancy was not due to photoinhibitory effects on photosynthesis, but appeared to reflect increased selective grazing pressure onSynechococcus spp. in dawn-to-dusk samples. Low-light photoadaptation was evident in analyses of the depth-dependency ofP-I parameters (photosynthetic capacity,P _max; light-limited slope, alpha;P _max alpha,I _k ; light-intensity beyond which photoinhibition occurs,I _b ) of the > 0.6 m communities at all three stations and was attributable to stratification of the water column. There was a decrease in assimilation rates andI _k with depth that was associated with increases in light-limited rates of photosynthesis. No midday photoinhibition ofP _max orI _b was observed in any surface station. Marked photoinhibition was detected only in the chlorophyll maximum at the neritic front and below the surface mixed-layer at Wilkinson's Basin, where susceptibility to photoinhibition increased with the depth of the collected sample. The 0.6 to 1 m fraction always had lower light requirements for light-saturated photosynthesis than the > 5 m size fraction within the same sample. Saturation intensities for the 1 to 5 m and 0.6 to 1 m size fractions were more similar whenSynechococcus spp. abundances were high in the 1 to 5 m fraction. The > 5 m fraction appeared to be the prime contributor to photoinhibitory features displayed in mixed samples (> 0.6 m) taken from the chlorophyll maxima. InSynechococcus spp.-dominated 0.6 to 1 and 1 to 5 m size fractions, cellular chlorophylla content increased 50- to 100-fold with depth and could be related to increases in maximum daytime rates of cellularP _max at the base of the euphotic zone. Furthermore, the 0.6 to 1 m and > 5 m fractions sampled at the chlorophyll maximum in the warm-core eddy had lower light requirements for photosynthesis than comparable surface samples from the same station. Results suggest that photoadaptation in natural populations ofSynechococcus spp. is accomplished primarily by changing photosynthetic unit number, occuring in conjuction with other accommodations in the efficiency of photosynthetic light reactions.     

Cultures of the pelagic cyanophytes Trichodesmium erythraeum and T. thiebautii in synthetic medium

Trials for determination of culture conditions for the marine cyanophytes of Trichodesmium erythraeum and T. thiebautii were made with use of a synthetic medium. The Aquil medium, either with or without combined nitrogen, brought about stable growth of the two strains, T. erythraeum and T. thiebautii. However, they failed to grow in an ASP₇ medium. The failure was found to be due to the toxic effect of Tris-aminomethane, the pH-buffer in this medium. Two important chemical conditions for the stable growth of Trichodesmium spp. were revealed. (1) Stable growth was supported by Ca²⁺ at high concentrations; in a concentration lower than 0.9 mM, cell-lysis promptly occurred, while the cells could grow without cell-lysis at Ca²⁺ concentrations higher than 7.5 mM even at a salinity as low as 19 S. Ca²⁺ is probably essential for the osmotic regulation in this organism. (2) Phosphate-toxicity at high concentrations was at least partly due to heavy metal(s) contaminating the reagent of inorganic phosphate. After treatment with a Chelex-100 column, phosphate concentration could be increased up to four times the previous concentrations without toxicity.     

Ultrastructure of the gonad and gametogenesis in the eastern oyster,Crassostrea virginica. II. Testis and spermatogenesis

The pelagic harpacticoid copepod, Macrosetella gracilis (A. Scott), is found in association with colonies of the nitrogen-fixing (diazotrophic), bloomforming cyanobacterium Trichodesmium spp. in tropical and subtropical waters. M. gracilis is one of the few direct grazers of these often toxic cyanobacteria. Experiments investigating NH ₊ ⁴ regeneration by M. gracilis were conducted in the Caribbean in September 1992 and the Coral Sea, Australia in November 1994. Rates of M. gracilis ingestion of Trichodesmium thiebautii labelled with ¹⁵N₂ measured in the eastern Caribbean indicated that M. gracilis could consume 33 to 45% of total T. thiebautii colony N d^-1 and >100% of new N fixed d^-1. We also measured the release of NH ₊ ⁴ by M. gracilis feeding on T. thiebautii, as well as by non-feeding copepods, using ¹⁵N isotope dilution methods. In non-feeding copepods, rates of NH ₊ ⁴ release increased as numbers of copepods were increased as both copepod numbers and food availability increased. In the presence of T. thiebautii colonies, M. gracilis had an average rate of NH ₊ ⁴ regeneration of 7.7±1.5 nmol N copepod^-1 h^-1 (±SE), which was significantly higher than when food was absent (1.9±0.7 nmol N copepod^-1 h^-1). Rates of M. gracilis excretion were relatively high based on excretion: ingestion ratios, which could be due to having a high-N food source readily available, to sloppy-feeding effects, or as a response to toxins in the cyanobacterium. Incubations of M. gracilis with and without T. erythraeum resulted in significant increases in [NH ₊ ⁴ ] as a function of copepod density only. Ammonium leakage from the cyanobacterium and/or microheterotroph associates was relatively low. M. gracilis, through excretion and possible mechanical breakage of cells while grazing, appears to provide a direct link between atmospherically derived new nitrogen and regenerated NH ₊ ⁴ in the oligotrophic systems where Trichodesmium spp. are abundant.