Dynamics of lipid and fatty acid composition of shallow-water corals under thermal stress: an experimental approach

Coral bleaching induces changes in lipid and fatty acid composition that result in low lipid content, reducing the likelihood of coral survival. Species-specific differences in the metabolism of lipid reserves may contribute to the differential resistance of corals under acute heat exposures. Here, we examined the dynamics of lipids and fatty acid abundance in corals subjected to short-term heat stress. The stony corals Acropora intermedia, Montipora digitata, and the soft coral Sinularia capitalis all showed a 60–75% decline in both storage and structural lipids. However, S. capitalis and M. digitata exhibited no significant change in the percentages of structural lipids (i.e., polar lipids and sterols) until they had lost 90–95% of their endosymbionts, whereas A. intermedia showed a rapid decline in structural lipids after a 50% loss of symbionts. After a 90–95% loss of symbionts under heat stress, all three corals showed a relative depletion of polyunsaturated fatty acids that had symbiont biomarkers, suggesting that polyunsaturated fatty acids were translocated from the symbiont to the coral host tissue.     

Energy allocation strategy of skipjack tuna Katsuwonus pelamis during their reproductive cycle

The lipid composition of somatic and reproductive tissues was determined for female skipjack tuna Katsuwonus pelamis caught in the western Indian Ocean between latitude 10° N and 20° S and longitude 40° and 70° E. The highest total lipid (TL) contents were in the liver and gonads, with white muscle levels approximately three‐fold lower. Three lipid classes dominated: triacylglycerols (TAG), sterol esters and wax esters (SE‐WE) and phospholipids (PL). Collectively, these accounted for between 70 and 80% of TLs. Changes in lipid concentrations were evaluated over the maturation cycle. Immature fish had the lowest gonad and liver TL levels; concentrations of TL, TAG, SE‐WE and PL accumulated from immature to mature (spawning‐capable) phase, reflecting sustained vitellogenic activity of the liver and a transfer of lipids to developing oocytes from the onset of vitellogenesis. Gonado‐somatic and hepato‐somatic indices were positively correlated with each other and positively related to TL in the gonads and liver. Fulton's condition index and lipid concentrations in muscle did not vary significantly over the maturation cycle; fat content in the main storage tissues was undepleted as the ovary developed. Hence, K. pelamis apparently supports reproduction directly from food intake over the breeding season. In the gonads, reserve lipids (SE‐WE and TAG) and sterols were related to batch fecundity but this was not the case for somatic and hepatic tissues. These results suggest that K. pelamis utilizes an income breeding strategy.     

Lipid characterization of Pleuragramma antarcticum (Nothoteniidae) larvae off East Antarctica (139°E–145.10°E) during summer

Pleuragramma antarcticum (Antarctic silverfish) larvae are a key component of the neritic assemblages in the Antarctic coastal waters and can be considered as an indicator of the future changes that may occur in this area. Lipid class and fatty acid composition was studied to assess the nutritional status and evaluate the type of dominant trophic interactions of P. antarcticum larvae collected between Terre Adélie and the Mertz Glacier Tongue (139°E–145.10°E) during summer 2007. P. antarcticum larvae exhibit moderate lipid levels (11.9–15.0% dry weight). Lipid class analyses showed a similar pattern over the study area consisting mainly of polar lipids (61–75% of total lipids). During their first summer, larvae started to accumulate small amount of lipid reserves in the form of triacylglycerols (10–16% of total lipids). Polar lipids were dominated by phosphatidylcholine (55–59%) followed by phosphatidylethanolamine (19–21%). Fatty acid signature of triacylglycerols indicates (1) a dominance of copepod of the Oithona type in the trophic pattern of P. antarcticum larvae and (2) a significant contribution of phytoplankton. In the same way, the analysis of gut content shows that 70% of larvae fed on various assemblages of phytoplankton and zooplankton (mainly copepods) and 30% of larvae fed exclusively on phytoplankton. Although a carnivorous diet is commonly described, our results suggest that P. antarcticum larvae showed an opportunistic feeding strategy (i.e. high degree of omnivory) and that dietary energy seems to be mainly directed towards fast growth rather than energy storage for periods of starvation.     

Main lipid classes in some species of deep-sea corals in the Newfoundland and Labrador region (Northwest Atlantic Ocean)

Corals contain large quantities of lipids in their tissues; these lipids may be either structural or for storage. Little information is available about the lipid content of deep-sea corals, as well as ratios of main lipid classes. In this study, lipid percentages of 81 deep-sea specimens were measured and the presence of six major classes, including sterols (STEROLS), free fatty acids (FFA), triacylglycerols (TG), monoalkyldiacyl glycerol (MADAG), wax (WAX), and sterol esters (SE), was assessed. Deep-sea corals had fewer lipids than their shallow water counterparts. Decision-tree analysis revealed a link between coral groups and total lipid percentages, showing that species within the same group were characterized by similar lipid amounts. Depth did not seem to impact the total lipid percentages, suggesting that deep-sea corals adapt to the differential access to food by changing the proportion of lipid classes while maintaining equivalent lipid levels. In deep-sea species, similar to their shallow water counterparts, energy seems to be stored as neutral lipids (wax esters and triacylglycerols), with the notable difference that a high proportion of MADAG is present. These compounds are less rich in energy than TG. Depth trends were found for FFA, TG and SE with an increase in percentages after 800 m suggesting a potential need for storage due to decreased food availability. A subsequent decrease after 1,100 m was observed for FFA and TG but a more detailed investigation is warranted as the number of specimens acquired from these depths was less than 20. It is nonetheless a surprising result as increased storage is expected when food sources are sparse.     

Food sources and lipid retention of zooplankton in subarctic ponds

1. Subarctic ponds are seasonal aquatic habitats subject to short summers but often have surprisingly numerous planktonic consumers relative to phytoplankton productivity. Because subarctic ponds have low pelagic productivity but a high biomass of benthic algae, we hypothesised that benthic mats provide a complementary and important food source for the zooplankton. To test this, we used a combination of fatty acid and stable isotope analyses to evaluate the nutritional content of benthic and pelagic food and their contributions to the diets of crustacean zooplankton in 10 Finnish subarctic ponds. 2. Benthic mats and seston differed significantly in total lipids, with seston (62.5 μg mg^?1) having approximately eight times higher total lipid concentrations than benthic mats (7.0 μg mg^?1). Moreover, the two potential food sources differed in their lipid quality, with benthic organic matter completely lacking some nutritionally important polyunsaturated fatty acids (PUFA), most notably docosahexaenoic acid and arachidonic acid. 3. Zooplankton had higher PUFA concentrations (27–67 μg mg^?1) than either of the food sources (mean benthic mats: 1.2 μg mg^?1; mean seston: 9.9 μg mg^?1), indicating that zooplankton metabolically regulate their accumulation of PUFA. In addition, when each pond was evaluated independently, the zooplankton was consistently more ¹³C‐depleted (δ¹³C ?20 to ?33‰) than seston (?23 to ?29‰) or benthic (?15 to ?27‰) food sources. In three ponds, a subset of the zooplankton (Eudiaptomus graciloides, Bosmina sp., Daphnia sp. and Branchinecta paludosa) showed evidence of feeding on both benthic and planktonic resources, whereas in most (seven out of 10) ponds the zooplankton appeared to feed primarily on plankton. 4. Our results indicate that pelagic primary production was consistently the principal food resource of most metazoans. While benthic mats were highly productive, they did not appear to be a major food source for zooplankton. The pond zooplankton, faced by strong seasonal food limitation, acquires particular dietary elements selectively.     

Analysis of neutral lipid biosynthesis in Streptomyces avermitilis MA-4680 and characterization of an acyltransferase involved herein

The physiology of lipid production in Streptomyces avermitilis MA-4680 with regard to the fatty acid composition of the accumulated lipids and their cellular distribution was analyzed. Cells were able to accumulate about ten to 30 lipid granules with diameters between 100 and 500 nm filling about 70–80% of the cell cytoplasm. Gas chromatography/mass spectrometry analyses of total cellular lipids and from isolated triacylglycerols (TAG) confirmed a similar fatty acid composition with a large portion of iso- and anteiso-methyl-branched fatty acids. De novo biosynthesis of wax esters (WE) appeared only during cocultivation on glucose and hexadecanol as carbon source. Homology alignments with the wax ester synthase/acyl-CoA:diacylglycerol acyltransferase (WS/DGAT; AtfA) from Acinetobacter baylyi strain ADP1 yielded one open reading frame in the genome databases of S. avermitilis MA-4680 referred to as SAV7256 with 25.3% homology. The highly conserved HHAxxDG active site motif found in AtfA, which is present in SAV7256, as well as the similar hydrophobicity profiles of AtfA and SAV7256 indicate a similar structure and function of both proteins. High acyl-CoA:diacylglycerol acyltransferase activity (DGAT; 143 pmol (mg min)⁻¹) but low wax ester synthase activity (WS; 1.3 pmol (mg min)⁻¹) were detected in crude extracts of S. avermitilis, which were consistent with the high TAG and negligible WE content of the cells. This indicates that TAG accumulation in S. avermitilis MA-4680 is mediated by the classical acyl-CoA-dependent DGAT pathway. Heterologous expression experiments in recombinant Escherichia coli BL21(DE3) demonstrated both WS and DGAT enzyme activity of SAV7256. Furthermore, substrate specificities of the acyltransferase SAV7256 will be discussed. Chlud Kaddor and Karolin Biermann contributed equally to this work.     

Effect of fasting on the composition of the fat body lipid of Dipetalogaster maximus, Triatoma infestans and Panstrongylus megistus (Hemiptera: Reduviidae)

Modifications in content and lipid composition induced by fasting were examined in fat bodies from adults of Triatominae, Dipetalogaster maximus, Triatoma infestans and Panstrongylus megistus. With fasting, total lipid stores dropped approximately 50% for T. infestans and more than 70% for P. megistus. Total lipids analyzed by thin layer chromatography and fractionated by column chromatography on Unisil showed triacylglycerols as the main component in the three species, although P. megistus showed high levels of diacylglycerols (31–46%). Cholesterol amounted to 8–15%. In diacylglycerol fractions, C_16:0, C_18:1 and C_18:0 fatty acids were detected; their ratio varied with species but it was not dependent on nutritional status. In triacylglycerol fractions C_18:1 fatty acid was the major component at different times (48–68%); the ratio of monounsaturated to saturated in this fraction was 1.3, 2.6 and 1.2 for D. maximus, T. infestans and P. megistus respectively. The remarkable drop in lipid stores without noticeable changes in their relative composition would suggest that all types of lipid are used at similar rates. The higher content of diacylglycerols in P. megistus may be associated with the better flight performance of this species. Accepted: 4 August 1998     

Identification and characterization of DGA2, an acyltransferase of the DGAT1 acyl-CoA:diacylglycerol acyltransferase family in the oleaginous yeast Yarrowia lipolytica. New insights into the storage lipid metabolism of oleaginous yeasts

Triacylglycerols (TAG) and steryl esters (SE) are the principal storage lipids in all eukaryotic cells. In yeasts, these storage lipids accumulate within special organelles known as lipid bodies (LB). In the lipid accumulation-oriented metabolism of the oleaginous yeast Yarrowia lipolytica, storage lipids are mostly found in the form of TAG, and only small amounts of SE accumulate. We report here the identification of a new DAG acyltransferase gene, DGA2, homologous to the ARE genes of Saccharomyces cerevisiae. This gene encodes a member of the type 1 acyl-CoA:diacylglycerol acyltransferase family (DGAT1), which has not previously been identified in yeasts, but is commonly found in mammals and plants. Unlike the Are proteins in S. cerevisiae, Dga2p makes a major contribution to TAG synthesis via an acyl-CoA-dependent mechanism and is not involved in SE synthesis. This enzyme appears to affect the size and morphology of LB, suggesting a direct role of storage lipid proteins in LB formation. We report that the Are1p of Y. lipolytica was essential for sterol esterification, as deletion of the encoding gene (ARE1) completely abolished SE synthesis. Unlike its homologs in yeasts, YlARE1 has no DAG acyltransferase activity. We also reconsider the role and function of all four acyltransferase enzymes involved in the final step of neutral lipid synthesis in this oleaginous yeast.     

Diel vertical migration and feeding of chaetognaths in coastal waters of the eastern Mediterranean

This study investigates the diel vertical distribution and the diet of the most important chaetognath species found in the 0–50 m surface layer of a coastal area in the eastern Mediterranean during a 24-hour period in July 2004. Among the recorded chaetognaths, Sagitta enflata was the most abundant species (41.6%), followed by S. minima (32.5%) and S. serratodentata (20.8%). Those three species exhibited a “twilight migration” pattern, with only small differences among them. Vertical separation was found between S. enflata and S. minima. Both species preyed mainly on cladocerans, although copepods were the most abundant group in the zooplankton assemblage. The chaetognath species followed partially the diel vertical migration of their prey. S. enflata showed high feeding intensity at different times in both day and night, while S. minima fed more intensively at midday (12:00) and at dusk (20:00), and S. serratodentata in the morning (08:00). It seems that in order to coexist in an area of low productivity the chaetognath species follow the basic ecological rules of space, time and food-type separation, in order to reduce the inter- and intra-specific competition. The high preference of S. minima and especially of S. enflata for the cladocerans made them probably the most important predators of cladocerans during summer.     

Regional and seasonal variability of zooplankton collected using sediment traps in the southeastern Beaufort Sea, Canadian Arctic

Time-series sediment traps were deployed at six mooring sites in the southeastern Beaufort Sea from October 2003 to August 2004 during the cruise of the Canadian research vessel Amundsen within the framework of the Canadian Arctic Shelf Exchange Study (CASES). Trap-collected zooplankton (TCZ) at around 200 m water depth was dominated by copepods accounting for 74–93% of the total abundance throughout the year with increase in abundance at all sites during the fall. Seven distinct TCZ groups were identified through cluster analysis. Two marked seasonal shifts in TCZ composition from late fall to early winter and from spring to early summer were revealed at five sites at 200 m depth. The zooplankton was dominated by Oncaea spp., pteropods, and copepod nauplii in the late fall cluster and in the winter cluster, and by copepod nauplii in the summer cluster. A significant change in water temperature, salinity, and sea ice concentration was observed only with the spring–summer shift. The cluster analysis also revealed that TCZ composition at 200 m at a station located in the Cape Bathurst Polynya was markedly different from those at other sites through the study period by being characterized by the dominance of various copepodite stages of Metridia longa. This was probably due to a less prolonged period of sea ice cover, which provides favorable food conditions for the zooplankton community.     

Spatio-temporal variations of the zooplankton abundance and composition in a West African tropical coastal lagoon (Grand-Lahou,Côte d’Ivoire)

Zooplankton constitutes a sensitive tool for monitoring environmental changes in coastal lagoons; however, the available information on zooplankton communities is not sufficient to optimize their rational management. The relationships between zooplankton distribution and environmental factors were studied in a tropical lagoon to test whether the indicator properties of zooplankton assemblages could be used to monitor water quality, in a context of expected eutrophication provoked by an increasing anthropogenic activity. Twenty-one (21) stations were sampled monthly from January to December 2004. The community was composed of 65 taxa including Copepoda, Rotifera, and Cladocera. Copepoda was the most abundant group (81% of total numbers). The main zooplankton species were Oithona brevicornis, Acartia clausi, and Brachionus plicatilis. The highest zooplankton abundance (171–175 ind. l⁻¹) was recorded during the long, dry season (February–April) and the lowest (40–45 ind. l⁻¹) during the rainy and the flood periods (June–July). At a spatial level, the lowest abundance was observed in the estuarine zone. During the dry seasons (December–April and August–September), marine zooplankton taxa were abundant near the channel of Grand-Lahou, and brackish water taxa dominated in the other sites. Multivariate analyses (Co-inertia) showed that the composition of zooplanktonic communities and their spatio-temporal variations were mainly controlled by salinity variations closely linked to the climatic and hydrological context. The role of the trophic state on zooplankton communities could not be clearly evidenced. Our results and a comparison with previous studies in the neighboring, highly polluted Ebrié Lagoon suggest that the ratio between Oithona and Acartia abundance could be used as biological indicator for the water quality. Handling editor: S. I. Dodson     

The density of odontocete integument depends on blubber lipid composition and temperature

Cetacean integument serves many functional roles, including contribution to whole body buoyancy. The blubber of the integument of different cetacean species contains varying concentrations of triacylglycerols (TAG) and wax esters (WE); generally, these lipid classes have different densities. Integument can also experience a wide range of temperatures during a dive, so its density may change with depth. The goals of this study were to measure integument density and isolated blubber lipid density in three deep‐diving odontocete species (n = 3–4)—short‐finned pilot whales (Globicephala macrorhynchus), pygmy sperm whales (Kogia breviceps), and Gervais' beaked whales (Mesoplodon europeaus)—at different temperatures (6°C–35°C), and to relate these densities to lipid content and composition. Kogia and Mesoplodon integument and isolated lipids had high WE content (78.7–99.5 wt%) and were less dense (by 1.7%–9.3%) than those of Globicephala, which were composed predominately of TAG. Generally, densities increased as temperature decreased. Changes in integument densities mirrored those of isolated lipid densities, suggesting that blubber lipids are largely responsible for the buoyant properties of cetacean integument. These data demonstrate that the contribution of the integument to whole body density depends on lipid class and temperature, and therefore may provide useful, species‐specific correction factors for diving energetics models.     

Bioturbation as Driver of Zooplankton Recruitment,Biodiversity and Community Composition in Aquatic Ecosystems

In an experimental study we assessed if benthic bioturbating invertebrates affect the recruitment (hatching) of zooplankton from the sediment, and if this effect persists as differences in the zooplankton community in the water column, that is, if bioturbation quantitatively stimulates benthic–pelagic coupling. We investigated the effects of four different benthic invertebrates (Asellus aquaticus, Chironomus plumosus, Tubifex tubifex in the presence or absence of the predator Sialis lutaria). In total, 45 zooplankton taxa hatched from the sediment and the hatching success of some of these was dependent on the species identity of the bioturbating invertebrate. The predator Sialis reduced the abundance of all three invertebrate species, but tended to positively influence the zooplankton recruitment rates, possibly through increasing the activity of the bioturbating invertebrates. The most striking effect of bioturbation on the hatching and pelagic zooplankton community properties was that, on average, 11% more species hatched in the Asellus treatment than in any other treatment. This was also mirrored in the zooplankton water column community where, on average, 7% more species established a viable population in treatments with Asellus as bioturbator. In a complementary field survey, Asellus was more common in littoral than in profundal sediments. Because Asellus strongly affected recruitment of zooplankton in our experiment, we argue that bioturbation may partly explain why recruitment of resting stages of both phyto- and zooplankton is generally higher in littoral than in profundal areas.     

Hydrostatic pressure affects membrane and storage lipid compositions of the piezotolerant hydrocarbon‐degrading Marinobacter hydrocarbonoclasticus strain #5

A new piezotolerant alkane‐degrading bacterium (Marinobacter hydrocarbonoclasticus strain #5) was isolated from deep (3475 m) Mediterranean seawater and grown at atmospheric pressure (0.1 MPa) and at 35 MPa with hexadecane as sole source of carbon and energy. Modification of the hydrostatic pressure influenced neither the growth rate nor the amount of degraded hexadecane (≈ 90%) during 13 days of incubation. However, the lipid composition of the cells sharply differed under both pressure conditions. At 0.1 MPa, M. hydrocarbonoclasticus #5 biosynthesized large amounts (≈ 62% of the total cellular lipids) of hexadecane‐derived wax esters (WEs), which accumulated in the cells under the form of individual lipid bodies. Intracellular WEs were also synthesized at 35 MPa, but their proportion was half that at 0.1 MPa. This lower WE content at high pressure was balanced by an increase in the total cellular phospholipid content. The chemical composition of WEs formed under both pressure conditions also strongly differed. Saturated WEs were preferentially formed at 0.1 MPa whereas diunsaturated WEs dominated at 35 MPa. This increase of the unsaturation ratio of WEs resembled the one classically observed for bacterial membrane lipid homeostasis. Remarkably, the unsaturation ratio of membrane fatty acids of M. hydrocarbonoclasticus grown at 35 MPa was only slightly higher than at 0.1 MPa. Overall, the results suggest that intracellular WEs and phospholipids play complementary roles in the physiological adaptation of strain #5 to different hydrostatic pressures.     

Seasonal correlations of elemental and ω3 PUFA composition of seston and dominant phytoplankton species in a eutrophic Siberian Reservoir

The elemental and fatty acid composition of seston was studied for 3 years, from May to October, in a small Reservoir. Under comparatively low C:P ratio, multivariate canonical analysis revealed no straightforward simple correlations between phosphorus and single ω3 PUFA species, but complex significant interaction between elemental composition (stoichiometry) of seston and total sestonic ω3 PUFA as a whole. Since sestonic C, P and N were found to originate mostly from phytoplankton, the contents of particulate elements and PUFA were attributed to single species in periods of their pronounced dominance. Phytoplankton species of genera of Stephanodiscus, Peridinium, Gomphosphaeria, Planktothrix and Anabaena in periods of their pronounced dominance had relatively constant species-specific elemental and PUFA composition. Phytoplankton species significantly differed in their elemental and PUFA composition, as well as in ratios of C:N, N:P, PUFA:P and partly C:P that indicate food quality for zooplankton. Hence, there were no phytoplankton species of clearly high or low nutritional value. All of phytoplankters, or at least detritus, that originated from them, may meet specific elemental and biochemical requirements of specific groups of zooplankton. Dividing phytoplankton on basis of their elemental and biochemical composition, i.e., nutrition quality, into large taxa (cyanobacteria, diatoms, etc.) appeared to be too coarse for assessing nutritional value for zooplankton.     

Near-bottom depletion of zooplankton over a coral reef II: relationships with zooplankton swimming ability

Intense predation by corals and associated fauna can generate vertical gradients of their zooplankton prey. The goal of this study was to characterize the small-scale distribution of zooplankton above the coral reef of Eilat, Israel. Four vertical arrays, each consisting five underwater pumps attached 0.5–3 m apart on a taut mooring, were deployed for 10 days at two sites over the reef slope. A distinct layer of depleted zooplankton was repeatedly found in the 1.5 m high benthic boundary layer. The gradient was sharpest for strong swimmers (copepods and polychaeta), intermediate for weak swimmers (nauplii, mollusks and appendicularia), and lacking for passive taxa (eggs and foraminifera). Spatio-temporal changes in the abundance of copepods and polychaetes were highly correlated, more so in the water aloft (Pearson r>0.9) than near the bottom (r>0.8). The spatio-temporal correlations between weak swimmers and between passive taxa were much weaker (r<0.8 and r<0.4, respectively). Flow and shear stress did not affect the distribution patterns. The correspondence between the zooplankton distribution and their swimming ability indicates that bottom avoidance contribute to the formation of depleted layer over the reef.     

Lipid class composition of bleached and recovering Porites compressa Dana, 1846 and Montipora capitata Dana, 1846 corals from Hawaii

Corals rely on stored reserves, especially lipids, to survive bleaching events. Lipid class composition reveals the lipid source, and provides evidence of metabolic changes (i.e., photoautotrophic or heterotrophic) during bleaching and recovery. Porites compressa Dana, 1846 and Montipora capitata Dana, 1846 corals were experimentally bleached in outdoor tanks with seawater temperature elevated to 30 °C (treatment corals). Additional control fragments were maintained in separate tanks at ambient temperatures (27 °C). After one month, all fragments were returned to the reef for 0, 1.5, 4, or 8 months. Lipid class composition was analyzed by Iatroscan (thin layer chromatography-flame ionization detection). In treatment P. compressa, triacylglycerol (TG) decreased at 0 and 1.5 months, phospholipid (PL) also decreased at 1.5 months, and both remained lower relative to controls along with wax esters (WE) after 8 months. Neither treatment nor control P. compressa had any detectable monoacylglycerol (MG) or diacylglycerol (DG). Overall, P. compressa first consumed available storage, then structural lipids, and all lipid classes remained low at the end of the study. In treatment M. capitata, TG and PL decreased, while MG increased relative to controls at 0 months. At 4 months, free fatty acid (FFA), sterol (ST), and PL in treatment M. capitata were two to ten times higher than controls. Treatment and control lipid class composition were not different from each other at 8 months. In contrast to P. compressa, M. capitata consumed some lipid classes and augmented others, probably due to sequential metabolism of storage lipids and increased heterotrophy. Overall, lipid class assimilation was more rapid in treatment M. capitata corals that switch between heterotrophy and photoautotrophy, than in treatment P. compressa corals that rely mostly on photoautotrophy.     

How well do single samples reflect rotifer species diversity? A test based on interannual variation of rotifer communities in Big Bend National Park (Texas,USA)

Studies of rotifer community composition and dynamics often rely on limited sampling regimes. To determine how well species richness is reflected in these studies, we examined interannual variation of rotifer species richness and monogonont community structure from 10 aquatic systems comprising four habitat types—springs, rock pools (tinajas), former cattle tanks, and artificial ponds—in Big Bend National Park (Texas, USA). Planktonic, littoral, and benthic samples were collected from all sites at about the same date for each of five summers (2001–2005). Our survey yielded 15 monogonont families including 30 genera and 84 species. Two bdelloid taxa also were designated. Species richness varied widely among these four habitats: range, 1–32; mean (±1 SD), 11.2 ± 8.0. Total Species richness in the habitats also varied considerably: springs (54 taxa) > artificial ponds (35 taxa) > tinajas (19 taxa) > cattle tanks (15 taxa). Sessile species comprised ≈13% of the taxa in our samples. Species turnover indices (STI) of these systems indicate low overall relatedness: mean (±1 S.D.) = 85.2 ± 7.1%. The relative frequency of encounter of most taxa in the four systems was low, with 79 taxa (≈92%) having values ≤2.0%. Singleton rates were quite high, ranging from 46.7 to 71.4%, with an overall mean ≈65.1%. Most importantly, we found that both species richness and STI varied considerably among habitat type. Species richness varied by 2–10× between consecutive years and STI ranged from 64 to 89% over the entire study. Our results indicate that rotifer community composition fluctuates greatly over time, and that rotifer community structure may be more labile than is generally believed. Species richness and thus biodiversity may be dramatically underestimated using single sampling or short-term strategies that are often employed in studies of zooplankton community structure. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Composition,size, and biomass of zooplankton in large productive Florida lakes

Crustacean zooplankton data were compiled from long-term observational studies at seven large shallow Florida lakes, to determine whether there are general characteristics in regard to species composition, body size, and biomass. In particular, we examined whether patterns in body size and species richness fit empirical models developed by Stanley Dodson. The lakes included range in size from 125 to 1730 km² and encompass mesotrophic to hyper-eutrophic conditions. We found that zooplankton biomass was strongly dominated by one species of calanoid copepod—Arctodiaptomus dorsalis. Large daphnids were absent, and Cladocera assemblages were dominated by small taxa such as Ceriodaphnia, Chydorus, and Eubosmina. The total number of species of pelagic cladocerans (8–12) was consistent with Dodson’s predictions based on lake area. The average size of crustacean zooplankton in Florida lakes is small in comparison with temperate communities. A. dorsalis is the smallest calanoid copepod in North America, and the mean length of Cladocera (0.6 mm) is consistent with Dodson’s results that size decreases from temperate to tropical zones. Total biomass of crustacean zooplankton was very low, ratios of zooplankton to phytoplankton biomass (0.01–0.1) are among the lowest reported in the literature, and the zooplankton displayed short-lasting early spring peaks in biomass. Cladocera were almost entirely absent in spring and summer. Factors known to occur in Florida lakes, which appear to explain these characteristics of biomass, include intense fish predation and high summer water temperature.     

Effect of cell lipid composition on the formation of nonspecific antibiotic resistance in alkanotrophic rhodococci

The antibiotic resistance and lipid composition of rhodococci grown in rich organic media with gaseous or liquidn-alkanes were studied. Hydrocarbon-grown rhodococci exhibited an increased resistance to a wide range of antibiotics (aminoglycosides, linkosamides, macrolides, β-lactams, and aromatic compounds). The enhanced antibiotic resistance of rhodococci grown onn-alkanes correlated with an increased content of total cell lipids (up to 14–28%) and saturated straight-chain fatty acids (C_16:0, C_18:0, C_21:0) and was accompanied by the appearance of cardiolipin and phosphatidylglycerol in cells. These lipid compounds are supposed to promote the formation of nonspecific antibiotic resistance in rhodococci by decreasing the permeability of their cell envelope to antibiotics.