Global patterns of planktonic diversity are mainly determined by the dispersal of propagules with ocean currents. However, the role that abundance and body size play in determining spatial patterns of diversity remains unclear. Here we analyse spatial community structure - β-diversity - for several planktonic and nektonic organisms from prokaryotes to small mesopelagic fishes collected during the Malaspina 2010 Expedition. β-diversity was compared to surface ocean transit times derived from a global circulation model, revealing a significant negative relationship that is stronger than environmental differences. Estimated dispersal scales for different groups show a negative correlation with body size, where less abundant large-bodied communities have significantly shorter dispersal scales and larger species spatial turnover rates than more abundant small-bodied plankton. Our results confirm that the dispersal scale of planktonic and micro-nektonic organisms is determined by local abundance, which scales with body size, ultimately setting global spatial patterns of diversity.
We used suspensions of 0.2, 0.5, 0.75, 1, 2, 3 and 6 µm fluorescent beads in combination with analytical flow cytometry to determine the efficiency of retention by small (165 µm trunk length), medium (347 µm) and large (689 and 734 µm) Oikopleura dioica, and by large (585 µm) Fritillaria borealis. Large O. dioica and F. borealis were the most efficient at retaining the 2 µm beads, and small and medium O. dioica were most efficient for 1 µm beads. Large O. dioica and F. borealis showed efficiencies of ca. 15% for 0.2 µm, 33% for 0.5 µm, 58% for 0.75 µm beads, 66% for 1 µm beads and 88% for 2 µm beads. However, small O. dioica showed higher efficiencies, measuring ca. 10% for 0.2 µm, 43% for 0.5 µm, 72% for 0.75 µm beads, 87% for 1 µm beads and 93% for 2 µm beads. The combination of our measured appendicularian particle-retention efficiency spectra with typical particle size-distribution spectra in the ocean indicates that large and small appendicularians obtain 80% of their diet from particles smaller than 15 and 7 µm respectively, and that the smallest particles represent a significant part of their diet only when they strongly dominate the biomass size spectra. Comparison with data from the literature indicates that although the appendicularian:prey length ratio is extremely high, the appendicularian:prey body-carbon ratio (14 538:1) is within the reported range for mesozooplankton (1:1 to ca. 3 × 10 6 :1), and statistically undistinguishable from that of copepods (1603:
Different concentrations of 14 C radiolabeled cultures of the prymnesiophyte Isochrysis galbana (5.5 m in size), the prasinophyte Tetraselmis suecica (9.5 m), and the chlorophyte Chlorella sp. (3.5 m) were offered as food to groups of 2-5 Oikopleura dioica to determine the response of clearance (CR) and ingestion (IR) rates to food concentration (FC for the prey I. galbana, T. suecica, and Chlorella sp., respectively. The K m values are high and in two of three cases exceed the maximum concentration of ingestible particles found in the natural habitat, which suggests that O. dioica is adapted to high phytoplankton concentrations. In contrast with classical FR models, CR remained nearly constant for all concentrations. Particles cleared from suspension by O. dioica are ingested and transformed into fast-sinking fecal pellets at low FC, while they are mainly accumulated into slow to fast-sinking filter houses at high FC, which implies considerable shifts in the biogeochemical role of these animals with changing particle concentrations.
Marine Actinobacteria are emerging as an unexplored source for natural product discovery. Eighty-seven deep-sea coral reef invertebrates were collected during an oceanographic expedition at the submarine Avilés Canyon (Asturias, Spain) in a range of 1500 to 4700 m depth. From these, 18 cultivable bioactive Actinobacteria were isolated, mainly from corals, phylum Cnidaria, and some specimens of phyla Echinodermata, Porifera, Annelida, Arthropoda, Mollusca and Sipuncula. As determined by 16S rRNA sequencing and phylogenetic analyses, all isolates belong to the phylum Actinobacteria, mainly to the Streptomyces genus and also to Micromonospora, Pseudonocardia and Myceligenerans. Production of bioactive compounds of pharmacological interest was investigated by high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) techniques and subsequent database comparison. Results reveal that deep-sea isolated Actinobacteria display a wide repertoire of secondary metabolite production with a high chemical diversity. Most identified products (both diffusible and volatiles) are known by their contrasted antibiotic or antitumor activities. Bioassays with ethyl acetate extracts from isolates displayed strong antibiotic activities against a panel of important resistant clinical pathogens, including Gram-positive and Gram-negative bacteria, as well as fungi, all of them isolated at two main hospitals (HUCA and Cabueñes) from the same geographical region. The identity of the active extracts components of these producing Actinobacteria is currently being investigated, given its potential for the discovery of pharmaceuticals and other products of biotechnological interest.
Oikopleura dioica is an excellent model for studying food flow through the digestive system because of its transparency, non-motility and because fecal pellets move along the digestive system in an orderly sequence which can be easily timed. By observing fecal pellet circulation within the gut of healthy individuals, we have concluded that the average number of fecal pellets inside the gut of 0, dioica is 2.878 * 0.015 (mean r SE, n = 43). Thus, gut passage time (GPT, min) can be estimated from the time interval between successive fecal pellets (DI, min fecal pellet") as GPT = 2 878 DI. This establishes the basis for estimating GPT from simple fecal pellet production rate incubations, and is one way of determinating GPT without manipulating food concentration or quality, a major shortcoming of current techniques. In laboratory exper~ments, GPT of 0. diolca was independent of body size. At 15'C, GPT (min) decreased with increasing food concentration (FC, pg C I-') when the prymnesophyte Isochrysis galbana (4.5 I.lm in size), the prasinophyte Tetrasehis suecica (10 pm) or the chlorophyte Chlorella sp. (3 pm) were used as food, according to the power function GPT = 29.4 FC-0.245. There were no significant differences in GPT between algal types. The GPT of 0. dioica exhibited a Qlo of 0.687 over a temperature range of 10 to 20°C, independent of food concentration. Since the interaction between food concentration and temperature was not significant, GPT can be estimated as GPT = 51,67~-0 03761 FC-0 245
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