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Evaluating the effectiveness of drones for quantifying invasive upside-down jellyfish (Cassiopea sp.) in Lake Macquarie, Australia.

ABSTRACT: Upside-down jellyfish (Cassiopea sp.) are mostly sedentary, benthic jellyfish that have invaded estuarine ecosystems around the world. Monitoring the spread of this invasive jellyfish must contend with high spatial and temporal variability in abundance of individuals, especially around their invasion front. Here, we evaluated the utility of drones to survey invasive Cassiopea in a coastal lake on the east coast of Australia. To assess the efficacy of a drone-based methodology, we compared the densities and counts of Cassiopea from drone observations to conventional boat-based observations and evaluated cost and time efficiency of these methods. We showed that there was no significant difference in Cassiopea density measured by drones compared to boat-based methods along the same transects. However, abundance estimates of Cassiopea derived from scaling-up transect densities were over-inflated by 319% for drones and 178% for boats, compared to drone-based counts of the whole site. Although conventional boat-based survey techniques were cost-efficient in the short-term, we recommend doing whole-of-site counts using drones. This is because it provides a time-saving and precise technique for long-term monitoring of the spatio-temporally dynamic invasion front of Cassiopea in coastal lakes and other sheltered marine habitats with relatively clear water.

SUBMITTER: Rowe CE

PROVIDER: S-EPMC8769344 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Bacteria are important mediators of the larval transition from pelagic to benthic environments for marine organisms. Bacteria can therefore dictate species distribution and success of an individual. Despite the importance of marine bacteria to animal ecology, the identity of inductive microbes for many invertebrates are unknown. Here, we report the first successful isolation of bacteria from natural substrates capable of inducing settlement and metamorphosis of the planula larvae stage of a true jellyfish, the upside-down jellyfish Cassiopea xamachana. Inductive bacteria belonged to multiple phyla, with various capacity to induce settlement and metamorphosis. The most inductive isolates belonged to the genus Pseudoalteromonas, a marine bacterium known to induce the pelago-benthic transition in other marine invertebrates. In sequencing the genome of the isolated Pseudoalteromonas and a semiinductive Vibrio, we found biosynthetic pathways previously implicated in larval settlement were absent in Cassiopea inducing taxa. We instead identified other candidate biosynthetic gene clusters involved in larval metamorphosis. These findings could provide hints to the ecological success of C. xamachana compared to sympatric congeneric species within mangrove environments and provide avenues to investigate the evolution of animal-microbe interactions. IMPORTANCE The pelagic to benthic transition for the larvae of many marine invertebrate species are thought to be triggered by microbial cues. The microbial species and exact cue that initiates this transition remains unknown for many animals. Here, we identify two bacterial species, a Pseudoalteromonas and a Vibrio, isolated from natural substrate that induce settlement and metamorphosis of the upside-down jellyfish Cassiopea xamachana. Genomic sequencing revealed both isolates lacked genes known to induce the life history transition in other marine invertebrates. Instead, we identified other gene clusters that may be important for jellyfish settlement and metamorphosis. This study is the first step to identifying the bacterial cue for C. xamachana, an ecologically important species to coastal ecosystems and an emerging model system. Understanding the bacterial cues provides insight into marine invertebrate ecology and evolution of animal-microbe interactions.

Project description:Ecological profiling of non-native species is essential to predict their dispersal and invasiveness potential across different areas of the world. Cassiopea is a monophyletic taxonomic group of scyphozoan mixotrophic jellyfish including C. andromeda, a recent colonizer of sheltered, shallow-water habitats of the Mediterranean Sea, such as harbors and other light-limited, eutrophic coastal habitats. To assess the ecophysiological plasticity of Cassiopea jellyfish and their potential to spread across the Mare Nostrum by secondary introductions, we investigated rapid photosynthetic responses of jellyfish to irradiance transitions-from reduced to increased irradiance conditions (as paradigm of transition from harbors to coastal, meso/oligotrophic habitats). Laboratory incubation experiments were carried out to compare oxygen fluxes and photobiological variables in Cassiopea sp. immature specimens pre-acclimated to low irradiance (PAR = 200 μmol photons m-2 s-1) and specimens rapidly exposed to higher irradiance levels (PAR = 500 μmol photons m-2 s-1). Comparable photosynthetic potential and high photosynthetic rates were measured at both irradiance values, as also shown by the rapid light curves. No significant differences were observed in terms of symbiont abundance between control and treated specimens. However, jellyfish kept at the low irradiance showed a higher content in chlorophyll a and c (0.76±0.51SD vs 0.46±0.13SD mg g-1 AFDW) and a higher Ci (amount of chlorophyll per cell) compared to jellyfish exposed to higher irradiance levels. The ratio between gross photosynthesis and respiration (P:R) was >1, indicating a significant input from the autotrophic metabolism. Cassiopea sp. specimens showed high photosynthetic performances, at both low and high irradiance, demonstrating high potential to adapt to sudden changes in light exposure. Such photosynthetic plasticity, combined with Cassiopea eurythermal tolerance and mixotrophic behavior, jointly suggest the upside-down jellyfish as a potentially successful invader in the scenario of a warming Mediterranean Sea.

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Evaluating the effectiveness of drones for quantifying invasive upside-down jellyfish (Cassiopea sp.) in Lake Macquarie, Australia.

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