Pleurobrachia bachei

Geographic Range

Sea gooseberries are among the most common comb jellies found in the northern Pacific Ocean. During spring and summer months, vast numbers of them appear in coastal waters stretching from Friday Harbor, Washington to La Jolla Bay, California. There are also reports of this species from as far north as Alaska and as far south as Acapulco, Mexico; recent research has documented them off the coast of Mejillones, Chile. They are considered native to the coast of Ireland as well, being found in Galway Bay, specifically.

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Sea gooseberries thrive in pelagic zones and are most commonly seen at depths of 15-30 meters from the surface. They are typically found 5-10 kilometers from shore. Diel migration is a typical behavior among sea gooseberries, allowing vertical movement within the epipelagic and mesopelagic layers, as deep as 1000 meters. Sea gooseberries seem to prefer more temperate waters and are strictly marine.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Physical Description

Sea gooseberries are elliptical in shape with two long tentacles protruding from each side. These tentacles often measure up to 15 cm in length and, when the animal is not swimming, they hang downward. Several sticky branches lie along each tentacle. Eight comb rows, comprised of fused cilia, run nearly the entire length of the body, from the mouth to the opening at the opposite end of the body. These combs are responsible for propulsion via a beating mechanism and also bend, refracting light and giving the illusion of bioluminescence. Sea gooseberries are colorless or transparent; their tentacles and organs, however, may be colored (most often pink, white, yellow, or orange-brown) and they often have a purple blotch near the pharynx. They grow up to 1.5 cm in diameter, with a slightly greater length.

• Other Physical Features
• radial symmetry radial symmetry

• Sexual Dimorphism
• sexes alike

Development

Sea gooseberries are monomorphic. Eggs develop significantly more quickly (on average 10-15 days) in warmer waters than cooler (20°C versus 15°C, respectively), but mortality rates are also higher in warmer waters. Embryos grow into pelagic cydippid larvae; they do not undergo metamorphosis, as larvae in this stage resemble the adult form. Larvae have been estimated to grow anywhere from 1.5-6.5 mm in 30 days.

Reproduction

Sea gooseberries are hermaphrodites and fertilization occurs externally. Gonadal tissues are located under the comb rows and eggs and sperm are released from the mouth. Sperm is released in pulses for approximately 5 minutes; egg release follows in bursts for 5 to 10 minutes. In lab settings, egg release has been associated with an abundant food source, although results are not conclusive. Successful spawning often depends on several factors, including the viscosity of the spawned material and the flow of the surrounding water.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Sea gooseberries are hermaphroditic and spawn throughout their lifetimes. The greatest populations of these animals are seen during spring and summer months and there is typically a large drop in population size during the winter. The reasons are unknown but possible influences include water temperature and predation. Time to hatching is dependent on water temperature; at 15°C, eggs hatch within 24 hours. Populations typically double in cycles of 25-35 days.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• sequential hermaphrodite
  • protandrous protandrous
• sexual sexual
• fertilization fertilization
  • external external
• broadcast (group) spawning

This species exhibits no parental investment beyond production of gametes.

• Parental Investment
• no parental involvement

Lifespan/Longevity

The lifespan of sea gooseberries typically ranges from 120-180 days during the spring and summer months. During winter months, population sizes decline significantly.

Behavior

Sea gooseberries use their comb rows to create propulsion, which moves them up and down in the water column as they search for food or preferred environmental conditions. These comb jellies are known for their ability to remain still in the water for a relatively long period of time before feeding (rather than just drifting with the water current). In order to capture prey, a sea gooseberry moves horizontally in a semi-circle, allowing its tentacles, which are covered in colloblasts (cells which produce a sticky substance) to dangle from its body. It waits with an open mouth until prey is caught in its tentacles and then retracts them while moving forward, rotating its body around and bringing the prey in. Diel migration has been reported; these animals are likely following the migration of their prey. Sea gooseberries are active during the day and night but are mostly observed, near the water surface, at night. They are often found in large groups, particularly during spring and summer months. These comb jellies, unlike many ctenophores, are not bioluminescent, despite previous reports to the contrary.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• colonial colonial

Home Range

These animals are typically found within 5 km of shore but are not known to have a specific home range or defend a territory.

Communication and Perception

Intracelluar and extracellular recordings have been taken from the comb rows of a closely related species, Pluerobrachia pileus . These recordings show that electrical potentials arise in the animal's cilia, and are triggered by prey activity. An ectodermal nerve net, similar to that of cnidarians, seems to be responsible for the detection of prey. Movements toward or away from prey or predators, respectively, depend on depolarization levels. Sea gooseberries also have an apical sense organ which is responsible for maintaining balance and orientation.

• Communication Channels
• tactile tactile
• electric electric

• Perception Channels
• tactile tactile
• electric electric

Food Habits

Sea gooseberries seem to follow the diel migration of their prey, and diet is somewhat controlled by time of day and location in the water column. These comb jellies feed on plankton and small animals including larval fish, other eggs, and copepods. Specific known prey includes Acartia clausii , Acartia tonsa , Calanus pacificus , Evadne tergestina , Evadne nordmanni , Evadne spinifera , Labidocera trispinosa , Penilia avirostris , Pseudocalanus spp., and Sagitta euneritice .

• Primary Diet
• carnivore carnivore
  • eats eggs
  • eats non-insect arthropods
  • eats other marine invertebrates
• planktivore planktivore

• Animal Foods
• eggs
• aquatic crustaceans
• other marine invertebrates
• zooplankton zooplankton

• Plant Foods
• phytoplankton phytoplankton

• Other Foods
• detritus detritus
• microbes

Predation

Sea gooseberries have little protection against predators. If a predator is detected, they may reverse the direction of their cilial motion, sending them away from danger. Other, larger comb jellies are known to eat this species, as are moon jellies.

Ecosystem Roles

Sea gooseberries are important intermediate consumers in marine ecosystems. During the periods of spring algal blooms, the areas occupied by this species often contain a vast abundance of phtyoplankton and zooplankton, which they consume and help to control. They are also a primary consumer of copepods, and research suggests that they may play a major role in balancing phytoplankton ecosystems by regulating copepod populations. They may be hosts to amphipods; the population cycles and sizes of these parasites seem to be closely related to that of their hosts. They have also been found with parasitic dinoflagellates.

Economic Importance for Humans: Positive

Sea gooseberries may control populations of copepods, reducing declines in phytoplankton and potentially increasing coastal fish catches.

Economic Importance for Humans: Negative

Due to their selective feeding on copepods, these comb jellies may negatively impact fishing as well, if they reduce the populations of these animals too much.

Conservation Status

This species has not been assessed by the IUCN and is not listed as an endangered or threatened species by any agency.

Additional Links

Encyclopedia of Life

Contributors

Jeffery Willis (author), Radford University, Joel Hagen (editor), Radford University, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

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2012. "Pleurobrachia bachei: Sea Gooseberry" (On-line). Encyclopedia of Life. Accessed March 05, 2013 at http://eol.org/pages/393303/overview .