Harnessing eDNA metabarcoding to investigate fish community composition and its seasonal changes in the Oslo fjord.

In the face of global ecosystem changes driven by anthropogenic activities, effective biomonitoring strategies are crucial for mitigating impacts on vulnerable aquatic habitats. Time series analysis underscores a great significance in understanding the dynamic nature of marine ecosystems, especially amidst climate change disrupting established seasonal patterns. Focusing on Norway's Oslo fjord, our research utilises eDNA-based monitoring for temporal analysis of aquatic biodiversity during a one year period, with bi-monthly sampling along a transect. To increase the robustness of the study, a taxonomic assignment comparing BLAST+ and SINTAX approaches was done. Utilising MiFish and Elas02 primer sets, our study detected 63 unique fish species, including several commercially important species. Our findings reveal a substantial increase in read abundance during specific migratory cycles, highlighting the efficacy of eDNA metabarcoding for fish composition characterization. Seasonal dynamics for certain species exhibit clear patterns, emphasising the method's utility in unravelling ecological complexities. eDNA metabarcoding emerges as a cost-effective tool with considerable potential for fish community monitoring for conservation purposes in dynamic marine environments like the Oslo fjord, contributing valuable insights for informed management strategies.

Embracing Their Prey at That Dark Hour: Common Cuttlefish (Sepia officinalis) Can Hunt in Nighttime Light Conditions.

Cuttlefish are highly efficient predators, which strongly rely on their anterior binocular visual field for hunting and prey capture. Their complex eyes possess adaptations for low light conditions. Recently, it was discovered that they display camouflaging behavior at night, perhaps to avoid detection by predators, or to increase their nighttime hunting success. This raises the question whether cuttlefish are capable of foraging during nighttime. In the present study, prey capture of the common cuttlefish (Sepia officinalis) was filmed with a high-speed video camera in different light conditions. Experiments were performed in daylight and with near-infrared light sources in two simulated nightlight conditions, as well as in darkness. The body of the common cuttlefish maintained a velocity of less than 0.1 m/s during prey capture, while the tentacles during the seizing phase reached velocities of up to 2.5 m/s and accelerations reached more than 450 m/s2 for single individuals. There was no significant difference between the day and nighttime trials, respectively. In complete darkness, the common cuttlefish was unable to catch any prey. Our results show that the common cuttlefish are capable of catching prey during day- and nighttime light conditions. The common cuttlefish employ similar sensory motor systems and prey capturing techniques during both day- and nighttime conditions.

Behavioural responses to infrasonic particle acceleration in cuttlefish.

Attacks by aquatic predators generate frontal water disturbances characterised by low-frequency gradients in pressure and particle motion. Low-frequency hearing is highly developed in cephalopods. Thus, we examined behavioural responses in juvenile cuttlefish to infrasonic accelerations mimicking main aspects of the hydrodynamic signals created by predators. In the experimental set-up, animals and their surrounding water moved as a unit to minimise lateral line activation and to allow examination of the contribution by the inner ear. Behavioural responses were tested in light versus darkness and after food deprivation following a 'simulated' hunting opportunity. At low acceleration levels, colour change threshold at 3, 5 and 9 Hz was 0.028, 0.038 and 0.035 m s-2, respectively. At higher stimulus levels, jet-propulsed escape responses thresholds in daylight were 0.043, 0.065 and 0.069 m s-2 at 3, 5 and 9 Hz, respectively, and not significantly different from the corresponding darkness thresholds of 0.043, 0.071 and 0.064 m s-2 In a simulated hunting mode, escape thresholds were significantly higher at 3 Hz (0.118 m s-2) but not at 9 Hz (0.134 m s-2). Escape responses were directional, and overall followed the direction of the initial particle acceleration, with mean escape angles from 313 to 33 deg for all three experiments. Thus, in the wild, particle acceleration might cause escape responses directed away from striking predators but towards suction-feeding predators. We suggest that cuttlefish jet-propulsed escape behaviour has evolved to be elicited by the early hydrodynamic disturbances generated during predator encounters, and that the inner ear plays an essential role in the acoustic escape responses.

Prophylactic treatment of jellyfish stings--a randomised trial.

BACKGROUND: Contact with jellyfish can cause skin irritation and manifestations. We wanted to investigate the prophylactic effect of a sun cream containing an inhibitor against jellyfish stings. MATERIAL AND METHOD: We recruited 38 persons who were randomised such that each received two of three possible treatments, one on each underarm. Prophylactic treatment with sun cream containing jellyfish sting inhibitor, ordinary sun cream, and no cream. Their underarms were exposed to wet jellyfish tentacles in a watchglass. The following were recorded: time before pain, skin changes after four minutes, and pain intensity after 10 minutes, registered on a VAS scale. RESULTS: Thirteen of 25 subjects who had the sun cream with jellyfish sting inhibitor did not register any pain after 4 minutes' exposure, compared with two of 25 and two of 26 who had received pre-treatment with ordinary sun cream (p = 0.32) and no pre-treatment (p < 0.001), respectively. On average, subjects who had received prophylactic treatment with sun cream containing jellyfish sting inhibitor recorded a lower VAS score for pain/discomfort after 10 minutes. The difference was 10.6 mm (95 % CI 3.1-17.9) compared with ordinary sun cream and 14.2 mm (95 % CI 6.9-21.5) compared with no pre-treatment. A smaller number of subjects were found to have underarms with inflamed skin when prophylactic cream containing jellyfish sting inhibitor was used (6 of 25) than when ordinary sun cream was used (11 of 25) or no pre-treatment (12 of 26). There were no statistically significant differences between ordinary sun cream and no pre-treatment for any of the three outcomes. INTERPRETATION: Prophylactic treatment with jellyfish sting inhibitor reduces the risk of subjects developing symptoms after exposure to jellyfish tentacles.

Comment on "silent research vessels are not quiet" [J. Acoust. Soc. Am. 121, EL145-EL150].

The recent paper by Ona et al. [J. Acoust. Soc. Am. 121, EL145-EL150] compared avoidance reactions by herring (Clupea harengus) to a traditional and a "silent" research vessel. Surprisingly, the latter evoked the strongest avoidance, leading to the conclusion that "candidate stimuli for vessel avoidance remain obscure." In this Comment, it is emphasized that the otolith organs in fish are linear acceleration detectors with extreme sensitivity to infrasonic particle acceleration. Near-field particle motions generated by a moving hull are mainly in the infrasonic range, and infrasound is particularly potent in evoking directional avoidance responses in several species of fish. The stimuli initiating vessel avoidance may thus include infrasonic particle acceleration.