ISSN / EISSN : 1864-7782 / 1864-7790
Published by: Inter-Research Science Center (10.3354)
Total articles ≅ 750
Latest articles in this journal
Aquatic Biology, Volume 30, pp 119-132; https://doi.org/10.3354/ab00746
The combination of lower diet quality and increased metabolic rates is assumed to cause cascading effects on organismic C cycling. Future changes in CO2 levels or terrestrial nutrient discharges in marine ecosystems can lead to increased phytoplankton C:N ratios relative to consumer C:N ratios, lowering the quality of the food source. In this study, we compared the single and interactive effects of diet quality and temperature on the feeding behavior and C and N intake and release of a common and abundant intertidal mixotrophic protist, the foraminifer Haynesina germanica. Two batches of artificially produced and dual isotope-labeled (13C/15N) chlorophyte detritus with different C:N ratios (5.6 and 7.1) were fed to the foraminifer at 3 different temperatures (15, 20, 25°C). We observed a strong interactive effect of temperature and diet. A very strong increase in feeding rates was observed at 20°C for the low-quality food source. Respiration rates of carbon derived from the low-quality diet (C:N ratio of 7.1) were lower than those of the high-quality diets and increased at 25°C. This indicates that a high C content of the diet might be of advantage in calcifying mixotrophs, since respired excess C could be advantageous for test calcification. Additionally, respired excess C could be a useful resource of CO2 for kleptoplast photosynthesis and functionality in the mixotrophic lifestyle of H. germanica. Further, the observed effects of diet and temperature could impact nutrient fluxes in the habitat of H. germanica, possibly leading to food-web shifts in the future.
Aquatic Biology, Volume 30, pp 101-112; https://doi.org/10.3354/ab00744
Sound is the most effective means of communication in marine and freshwater ecosystems. However, no data about acoustic emissions from non-malacostracan crustaceans are currently available, so their ability to produce sounds is unknown. For the first time, this study investigated the sound produced by 2 tadpole shrimp species, Triops cancriformis and Lepidurus lubbocki. L. lubbocki individuals were collected from a natural temporary pond in Sicily (Italy), whereas T. cancriformis individuals were obtained from eggs contained in sediment from a rock pool in Sardinia (Italy). In the laboratory, experimental tanks with the animals (one species at a time) were acoustically monitored. Both species produced high-frequency, wideband pulses distinguishable by their sound pressure level, which was higher in L. lubbocki (146 dB) than in T. cancriformis (130 dB), and by their first and second peak frequencies, which were higher in L. lubbocki (65 and 86 kHz) than in T. cancriformis (63 and 71 kHz). The energy distributions in the power density spectra showed different shapes, as revealed by the 3 dB bandwidth and centre frequency. The pulse durations were 88 and 97 µs in L. lubbocki and T. cancriformis, respectively. L. lubbocki presented a higher emission rate than T. cancriformis and a marked circadian pattern, with a higher abundance of sounds during the night. This study reports the first evidence of sound emissions from non-malacostracan crustaceans and reveals the high potential of passive acoustic monitoring to detect the presence, abundance, and life cycle of these elusive keystone species of temporary water bodies.
Aquatic Biology, Volume 30, pp 85-99; https://doi.org/10.3354/ab00743
The Asian shore crab Hemigrapsus takanoi, native to the northwest Pacific Ocean, was recently discovered in Kiel Fjord (southwestern Baltic Sea). In laboratory experiments, we tested the salinity tolerance of H. takanoi across 8 levels (0 to 35) and across 3 life history stages (larvae, juveniles and adults) to assess its potential to invade the brackish Baltic Sea. Larval development at different salinities was monitored from hatching to the megalopa stage, while survival and feeding of juveniles and adults were assessed over 17 d. Larvae of H. takanoi were able to complete their development to megalopa at salinities ≥ 20 and the time needed after hatch to reach this stage did not differ between salinities of 20, 25, 30 and 35. At a salinity of 15, larvae still reached the last zoea stage (zoea V), but development to the megalopa stage was not completed. All juveniles and adults survived at salinities from 5 to 35. Feeding rates of juveniles increased with increasing salinity across the entire salinity range. However, feeding rates of adults reached their maximum between salinities of 15 and 35. Our results indicate that both juveniles and adults of H. takanoi are euryhaline and can tolerate a wide range of salinities, at least for the time period tested (2 wk). However, larval development was impaired at salinities lower than 20, which may prevent the spread of H. takanoi into the Baltic Proper.
Aquatic Biology, Volume 30, pp 59-68; https://doi.org/10.3354/ab00741
This paper presents a novel approach to the long-term recording of electrocardiogram (ECG) signals in prawns, including a 3-lead electrode, a lightweight external wires assembly, a waterproof electrode-wire junction, and a standardized implanting procedure. The proposed low-cost device is easily constructed, even by untrained undergraduate students, using common laboratory materials. Consistent ECG recordings were obtained over a period of 72 h in experiments on 6 freely moving prawns (Macrobrachium rosenbergii). A subsequent experiment conducted continuously for 38 d revealed that despite gradual attenuation the ECG signals could still be identified (signal-to-noise ratio ≥3). The prawns survived implantation and later underwent natural molting, whereupon the electrode was successfully re-implanted. The proposed electrode is a valuable tool by which to gain insight into the long-term physiological state of crustaceans.
Aquatic Biology, Volume 30, pp 47-57; https://doi.org/10.3354/ab00740
In the present study, we have developed an efficient system for regenerating Posidonia oceanica via the storage of free cells at low temperature and the initiation of cell encapsulation. This system could help in solving problems related to the intractable nature of in vitro marine phanerogam regeneration. Free cells from enzyme digestion were preserved with glycerol and DMSO at different concentrations and stored at low temperature. Cell encapsulation was performed with sodium alginate and calcium chloride. First, results showed that optimum cell culture was obtained when the initial cell concentration was 104 cells ml-1. Cell scaling allowed exponential growth to produce 2268000 cells at 13 d. Second, treatment based on cell storage with 60% glycerol plus 1.3 M DMSO was a success. The preserved cells grew and produced 1.96 more cells than the initial cell concentration (104 cells ml-1). Third, the encapsulated cells (beads) showed a survival range of 84 to 100% over 4 yr. The divided beads released cells that developed embryos or free cells depending on the culture medium. Cell encapsulation was the only method that was successful to acclimatise the cells to salinity, store artificial material for sowing and obtain embryos. We concluded that encapsulated cells could be used as a starting material for the production of embryos in the regeneration of P. oceanica.
Aquatic Biology, Volume 30, pp 33-46; https://doi.org/10.3354/ab00739
Rockfish, which are well known for their site fidelity and homing ability, live sympatrically with many conspecifics. Conspecifics may be external drivers influencing rockfish movement, and rockfish may move cohesively while travelling. We tested whether rockfish formed a group when returning to their original habitat after artificial displacement and examined the routes they travelled to return home. A fine-scale multi-individual simultaneous positioning method was used to observe the movement trajectories of tagged fish. Our results showed that tagged fish, released in groups, returned to their original habitat (5 of 8 fish) but generally did not travel with other individuals. There was one exception in which 2 individuals moved together for ~100 s immediately after release. These 2 fish had no designated leader, alternating as leader and follower. Our hypothesis was partially corroborated by these rockfish possibly travelling cohesively. The returning fish tended to travel along the sea bottom and the coastline, independent of current; thus, they likely used visual cues, rather than olfactory or social cues, to return home.
Aquatic Biology, Volume 30, pp 19-31; https://doi.org/10.3354/ab00737
Freshwater fishes in the river and lake systems in the Himalayas and Tibetan Plateau are morphologically diverged but the evolutionary relationship of putative subspecies separated in these freshwater systems has not been explored. Snowtrout (Schizothorax spp.) are minnows (Cyprinidae) broadly distributed in Asia. Body shapes of 3 Lake Rara (northwest Nepal) endemics (S. macrophthalmus, S. nepalensis, S. raraensis) and 2 widely distributed riverine species (S. progastus, S. richardsonii) across 3 drainages in Nepal (i.e. Karnali, Gandaki, and Koshi Rivers) were studied using geometric morphometry. Data were derived from museum voucher specimens/tissues collected in 1984-1986 and 1996 (Lake Rara). Cartesian coordinates of 18 anatomical points (Type I landmarks) from 528 individuals were digitized; shape variation was then quantified with principal component analysis and visualized with thin-plate splines derived from a Procrustes analysis. Models of shape variation (i.e. taxonomy versus geography) were tested with a multivariate analysis of variance and a morphological distance matrix. Phylogeographic relationships were examined with a haplotype network (N = 115) derived from 1140 base pairs of the mitochondrial DNA cytochrome b gene, and selected GenBank sequences (N = 5). Koshi River snowtrout diverged morphologically from conspecifics, consistent with the phylogeographic data. In contrast, Gandaki and Karnali River snowtrout grouped by morphotype (up- versus downstream) irrespective of geographic origin, yet clustered separately within the haplotype network. Lake Rara snowtrout were morphologically but not genetically distinct, due to incomplete lineage sorting. Morphological and genetic variability in Schizothorax from Nepal represent a mosaic driven by isolation (= vicariance) and specialization (= adaptation), with taxonomy insufficiently reflecting diversity. Additional data are required to appropriately derive management and effective conservation plans.
Aquatic Biology, Volume 30, pp 1-18; https://doi.org/10.3354/ab00736
Aging Antarctic icefish is difficult because of their lack of scales and poorly calcified bones. Icefish ages must therefore be estimated from otoliths. We describe a method of reading daily micro-increments in connection with shape, size and mass analyses of the otoliths of the South Georgia icefish Pseudochaenichthys georgianus. Changes in otolith morphology and mass correlate with fish size and age group. The otolith micro-increment analysis is capable of establishing the age of an icefish by relating the daily micro-increment count to the life history of the fish. Micro-increment measurements and analyses are relatively simple to do by light and scanning electron microscopy and by using micro-densitometer and digitizing equipment. Drastic changes in the life history of an individual are reflected by measurable changes in its otolith micro-increment data as seen in our analyses of age groups 0-VI. The initial drastic change in daily micro-increment shapes and periodicities occur in connection with the hatching period of the icefish. The next drastic change in otolith shape and daily micro-increments occurs when ~7 cm long fish shift from pelagic to benthic habitats. As the fish age beyond group III, individual otolith variability lessens until they begin spawning. Our results indicate a single population of P. georgianus between the Antarctic Peninsula and South Georgia.
Aquatic Biology; https://doi.org/10.3354/ab00742
Aquatic Biology; https://doi.org/10.3354/ab00745