Biology subjects

Gemmell, B.

Publications and source records attributed to Gemmell, B..

5 recordsLinked to original sources

bioRxiv2024

Impactful feeding ecology of a predatory guild of oceanic jellies

Planktonic organisms are integral members of open ocean ecosystems and are critical drivers of material cycles in the worlds oceans. Ctenophores may be numerically dominant predators in these oceanic ecosystems but have been ignored due to the difficulty in both sampling and handling their extremely delicate, gelatinous bodies. To better understand their trophic impact, we combined SCUBA with novel imaging techniques to non-invasively document prey ingestion patterns of four widespread oceanic ctenophore species. We found that these ctenophores ingested 32 prey per hour and the most voracious species ingested nearly 50 prey per hour. Further, the size and number of prey ingested increased with ctenophore size. At these rates, lobate and cestid ctenophores consume prey at similar rates to their highly impactful coastal relative, Mnemiopsis leidyi and are likely the most impactful planktonic predator in the open oceans. Further, we showed that although major dietary components overlapped, different oceanic ctenophore species appear to specialize on different members of the plankton. Since these oceanic ctenophore species frequently co-occur, they comprise a powerful guild of influential planktonic predators with synergistic impacts. These results indicate that epipelagic ctenophores have much greater trophic effects on material cycles over broad areas of the open ocean than previously considered. Models of oceanic carbon cycling will benefit by more fully incorporating the impacts of oceanic ctenophores on their planktonic prey.

ecology↗

bioRxiv2022

Aggregation and Defence

Cassiopea sp., the Upside-Down Jellyfish, are considered to be sedentary epibenthic organisms which exhibit little to no movement on the seafloor. In this study, we use time-lapse videography of a Cassiopea population in the Florida Keys to demonstrate that Cassiopea sp. exhibit a greater degree of benthic locomotion than previously understood, with animals covering distances up to 178 cm per day. In addition, Cassiopea seem to aggregate on the bottom, with average number of neighbours consistently higher than would be expected for random distributions. Given the ability of Cassiopea to release nematocysts directly into the water column, we present this aggregation as a potential defensive behaviour in this species.

ecology↗

bioRxiv2020

Field testing of biohybrid robotic jellyfish to demonstrate enhanced swimming speeds

Biohybrid robotic designs incorporating live animals and self-contained microelectronic systems can leverage the animals own metabolism to reduce power constraints and act as natural chassis and actuators with damage tolerance. Previous work established that biohybrid robotic jellyfish can exhibit enhanced speeds up to 2.8 times their baseline behavior in laboratory environments. However, it remains unknown if the results could be applied in natural, dynamic ocean environments and what factors can contribute to large animal variability. Deploying this system in the coastal waters of Massachusetts, we validate and extend prior laboratory work by demonstrating increases in jellyfish swimming speeds up to 2.3 times greater than their baseline, with absolute swimming speeds up to 6.6 {+/-} 0.3 cm s-1. These experimental swimming speeds are predicted using a hydrodynamic model with morphological and time-dependent input parameters obtained from field experiment videos. The theoretical model can provide a basis to choose specific jellyfish with desirable traits to maximize enhancements from robotic manipulation. With future work to increase maneuverability and incorporate sensors, biohybrid robotic jellyfish can potentially be used track environmental changes in applications for ocean monitoring.

bioengineering↗

bioRxiv2019

Benthic jellyfish dominate water mixing in mangrove ecosystems

Water mixing is a critical mechanism in marine habitats that governs many important processes, including nutrient transport. Physical mechanisms, such as winds or tides, are primarily responsible for mixing effects in shallow coastal systems, but the sheltered habitats adjacent to mangroves experience very low turbulence and vertical mixing. The significance of biogenic mixing in pelagic habitats has been investigated but remains unclear. In this study we show that the upside-down jellyfish Cassiopea sp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat (< 2 m deep). The mixing contribution was determined by means of high-resolution flow velocimetry methods in both the laboratory and in the natural environment. We demonstrate that Cassiopea sp. continuously pumps water from the benthos upward in a vertical jet with flow velocities on the scale of centimeters per second. The volumetric flow rate was calculated to be 212 l h-1 for average sized animals (8.6 cm bell diameter), which translates to turnover of the entire water column every 15 minutes for a median population density (29 animals m-2). In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at an average rate of 2.64 ml h-1 per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing, suggest a role for Cassiopea sp. as an ecosystem engineer in mangrove habitats. Significance StatementWater mixing is a critical process for aquatic life. Coastal mangrove habitats are vital nurseries for commercially and ecologically important species, but these sheltered habitats experience little water mixing. The upside-down jellyfish, Cassiopea sp., occurs in circumtropical mangrove habitats at high densities. They are epibenthic and pulse nearly continuously, producing a vertical current that transports hundreds of liters of seawater per hour. This results in turnover of the entire water column every 15 minutes for an average population. Additionally, Cassiopea sp. can greatly expedite the transport of nutrient-rich water from sediments into the water column. Thus, Cassiopea sp. represents a previously unrecognized ecosystem engineer that can affect primary productivity, nutrient distribution, and alter new habitats as their range is expanding.

ecology↗

bioRxiv2019

Primitive and modern swimmers solve the challenges of turning similarly to achieve high maneuverability

Animal swimmers alter trajectories - or turn - for a variety of critical life functions such as feeding, mating and avoiding predation. Yet turning represents a fundamental dilemma based in rotational dynamics: the torque powering a turn is favored by an expanded body configuration, yet minimizing the resistance to a turn (the moment of inertia) is favored by a contracted body configuration. How do animals balance these opposing demands to achieve high maneuverability? By noninvasively measuring fluid and body motions, we found that both jellyfish (Aurelia aurita) and fish (Danio rerio) initially maximized torque using previously undescribed, rapid body movements. Both species then minimized resistance to turning by bending their bodies to reduce their moment of inertia. Use of this sequential solution by such distantly related animals as an invertebrate and a vertebrate suggests strong selection for these turning dynamics that may extend to other swimmers and inform future vehicle designs.

zoology↗