Predators & defenses
 

photograph of a juvenile leatherback turtle taking a diving bite into a jellyfish, possibly Aurelia sp. courtesy J. Stillwell
Like many other aspects of the biology of large scyphomedusae, little is known about their predators.  In many oceans of the world, including areas of the west coast, leatherback turtles Dermochelys coriacea prey exclusively on different species of jellyfishes.  Other common predators of west-coast species are other jellyfishes. For general defense, jellyfishes rely on their nematocysts and escape swimming behaviour.  Species of Aurelia, and likely many others, may enter a refuge from predation when they reach adult size, at least from other jellyfishes that favour them as prey. For a recent review of predation on jellyfishes and other pelagic cnidarians see Arai 2005 J Mar Biol Ass UK 85: 523. Photograph courtesy J. Stillwell.

 




 

 

 

A juvenile leatherback turtle takes a diving bite
into a jellyfish, possibly Aurelia sp. 0.4X

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Research study 1
 

photograph of a jellyfish Phacellophora camtschatica courtesy Dave Cowles, Walla Walla U, WashingtonIn Saanich Inlet, British Columbia, a variety of gelatinous zooplankton, including both hydromedusae and scyphomedusae, is preyed upon by the jellyfish Phacellophora camtschatica (see photo).  Densities in the Inlet of this predator, of sizes up to drawing of a swimming jellyfish Phacellophora camtscjatoca showing tentacle reversal45cm bell diameter, may reach 1 individual . 1000m3 of water.  Data collected through direct SCUBA-observation (mostly during daytime, but also some collected at night) show that Phacellophora is both an attack and an ambush predator. 

When swimming horizontally, graph showing % of population sizes of Aurelia aurita captured by jellyfishes Phacellophora camtschatica vs. the size of the entire population of A. aurita availablePhacellophora periodically reverses direction and swims back through its already deployed tentacles (see drawing above Right).  Although smaller prey such as hydromedusae may be effectively captured through contact with a single tentacle of the predator, capture of its larger and favoured prey Aurelia labiata requires that it entangle the prey in several tentacles.  Best success comes when the predator’s tentacles adhere to and ensnare the tentacles and oral arms of Aurelia, after which the prey is quickly engulfed and swallowed whole.  Surprisingly, most encounters with Aurelia result in escape (96%).  Aurelia escapes by simply swimming through the tentacles of Phacellophora, which do not adhere well to the slippery bell surface of Aurelia, and sometimes combines this with an accelerated rate of bell contractions. Sometimes, Aurelia may simply stop and allow the predator’s tentacles to pull free of their own accord.  When captured and consumed, a prey Aurelia may be stored and subjected to preliminary digestion in voluminous pockets of the oral arms (the yellowish parts shown in the photograph).  Large individuals of Phacellophora (40cm diameter) may have 4 or more Aurelia, ranging in size from about 10-20cm diameter, within its oral-arm pouches and gastrovascular cavity.

The portion of the Aurelia population captured represents the smaller-sized individuals of those available (see graph on Right). This suggests that A. aurita may reach a size refuge as it grows larger.  Strand & Hamner 1988 Mar Biol 99: 409. Photo courtesy Dave Cowles, Walla Walla U, Washington rosario.wallawalla.edu

NOTE  tentacle length in P. cantschatica can reach up to 17X the bell diameter

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Research study 2
 

Leatherback turtles Dermochelys coriacea are regularly seen off the coast of central California, especially in areas where oceanographic conditions of retention or upwelling tend to concentrate their favoured jellyfish prey.  Aerial surveys between Point Conception and Russian River, California photograph of female leatherback turtle at its nest, courtesy M. Hastingsby NOAA research scientists during 10 summer/autumn periods during 1990-2003 reveal several instances of predation on large jellyfishes Chrysaora fuscescens, C. colorata, and Aurelia spp., mostly in the area between Pt. Reyes and Monterey BayBenson et al. 2007 Fish Bull 105: 337. Photograph courtesy M. Hastings.

NOTE  a later survey method developed by researchers at Moss Landing Marine Laboratories, California involves use of multifrequency echosounders.  Signals obtained are calibrated against results of net tows in the same area.  The researchers focus on areas of central California around San Francisco and Monterey Bay where sightings of leatherback turtles are common  Graham et al. 2010 J Mar Sci 67: 1739

NOTE  data in a study by researchers from Moss Landing Marine Laboratories and Hopkins Marine Station, Pacific Grove, California show that  of occurrence of D. coriacea in the Monterey-Bay region correlates well with time of year (late summer) and, thus, with warmer seawater temperatures.  The authors reckon that the turtles are attracted to large aggregations of scyphomedusae that regularly appear in Monterey Bay during summer.  Starbird et al. 1993 Calif Fish Game 79 (2): 54

Female leatherback Dermochelys
coriacea
at its nest site probably
in northwestern Costa Rica

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Research study 3
 

An interesting study on energy intake of leatherback turtles Dermochelys coriacea in the Cape Breton Island region of Nova Scotia uses cameras mounted on the backs of adults to record prey type, attack behaviour, dive depths and durations, handling times, attack success, and so on.  Primary prey in this area are lion’s mane jellyfishes Cyanea capillata (80-100%) and, to a lesser extent, moon jellies Aurelia aurita.  Now, jellyfishes are about 99% water, so it takes quite a few to satisfy the energy requirements of even a mid-sized leatherback turtle.  In fact, the authors, from Dalhousie University and Canada Department of Fisheries and Oceans, Nova Scotia, find that turtles of 450kg live mass will consume over 70% of their body mass per day, equivalent to about 360 large-sized (40cm bell diameter) jellyfish per day.  Average handling time for the turtle is 1min per jellyfish. Heaslip et al. 2012 Plos ONE 7 (3): 33259. Photographs courtesy the authors.

NOTE  a turtle is approached in a boat and the camera is suction-cupped onto the turtle’s back.  The cameras mostly fall off on their own within a few moments, but those that don’t have a device installed in the mount that releases the camera after a predetermined time.  The cameras have communication and homing devices to enable their recovery after release

The photo series below shows video shots of the turtle (just the top of its head is visible) homing in on a prey lion's-mane jellyfish Cyanea capillata:

 

photograph of leatherback turtle Dermochelys coriacea with video camera mounted,  courtesy Heaslip et al. 2012 Plos ONE 7 (3): 33259 and Canadian Department of Fisheries and Oceans
Adult turtle with video camera mounted

lion's mane jellyfish Cyanea capillata being sighted by predatory leatherback turtle Dermochelys coriacea, courtesy Heaslip et al. 2012 Plos ONE 7 (3): 33259 and Canadian Department of Fisheries and Oceans
Turtle sights prey Cyanea papillata

lion's mane jellyfish Cyanea capillata being homed in on by predatory leatherback turtle Dermochelys coriacea, courtesy Heaslip et al. 2012 Plos ONE 7 (3): 33259 and Canadian Department of Fisheries and Oceans
Turtle homes in on prey, with pilot fishes

lion's mane jellyfish Cyanea capillata being eaten by predatory leatherback turtle Dermochelys coriacea, courtesy Heaslip et al. 2012 Plos ONE 7 (3): 33259 and Canadian Department of Fisheries and Oceans
Turtle eats prey Cyanea
 
 
video showing jellyfish caught in tentacles of a sea anemone

CLICK HERE to see a video of jellyfishes Cyanea sp. getting caught up in the tentacles of sea anemones Metridium sp. The encounters may result in one or other of the participants being eaten, but are unlikely to be anything more than chance.

NOTE the video replays automatically

   
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Research study 4
 

An investigation at Shannon Point Marine Center, Washington of potential nudibranch predators of polyps of the jellyfish Aurelia labiata reveals that 4 species collected on or near a large colony of polyps readily attacked and ate the polyps in the laboratory. Other aspects of the study provide insight into the potential extent of predation by nudibranchs on the little-studied polyp phase of a common jellyfish species. Hoover et al. 2012 Hydrobiologia 690: 199.

NOTE  these include Dendronotus dalli, D. rufus, Flabellina fusca, and Hermissenda crassicornis

 
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