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  Feeding, growth, & regeneration
  Most adult sea stars are carnivorous, and catch and eat live live prey. Some species suspension-feed, while others are omnivorous and may even eat algae. Additionally, many or most species are opportunistic scavengers. Larvae that are planktotrophic feed on phytoplankton.
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  Larval feeding
  Topics in this section include larval feeding, considered here, and ADULT FEEDING, PREY RESOURCES, ENVIRONMENTAL EFFECTS ON FEEDING, INGESTIVE CONDITIONING, and GROWTH & REGENERATION, considered in other sections.
 
Research study 1
  drawing of bipinnaria larva of a sea star showing feeding currents
Feeding in the bipinnaria larvae of bat stars Pateria miniata occurs by phytoplankton cells being swept up in micro-currents generated by beating of cilia in the main ciliary band. The blue arrows in the drawing show the main water currents created as a larva swims along, while the green arrows show some of the micro-currents that carry phytoplankton particles into the mouth. From there the particles move down the esophagus into the stomach (location shown by green dots). Fecal matter is released from the anus.  Strathmann 1971 J Exp Mar Biol Ecol 6: 109.

NOTE  larvae of bat stars Patiria miniata grow well and metamorphose on mixed diets of phytoflagellates Dunaliella tertiolecta and Rhodomonas sp., although larval densities and food concentrations have to be carefully balanced.  Basch 1996 Mar Biol 126: 693.

 
Research study 2
 

drawing showing passive entry of particles into the mouth area in a bipinnaria larvaBy holding bipinnaria larvae of Pisaster ochraceus immotile and immersed on a suction pipette, it can be shown that phytoplankton cells in a water stream directed onto the larvae are actually diverted by hydrodynamic features of the larvae directly into the mouth region without the necessity to be swept in by the ciliated bands.  Once in the quiet-water area of the sub-oral cavity, other cilia near the mouth direct the particles into the mouth for ingestion.  The author points out that no ciliary reversal occurs as has been described for other echinoderm larvae.  Gilmour 1988 p. 253 In, Echinoderm Biology (Burke et al., eds) Balkema, Rotterdam.

NOTE the water streams are pumped past the larva at a rate comparable to the normal swimming velocity of the larva

 
Research study 3
 

drawing of a bipinnaria larva of a sea star capturing and ingesting a plastic microsphereLaboratory culture of larvae of several species of echinoderms at Friday Harbor Laboratories, Washington, including sea stars Dermasterias imbricata, indicate a common pattern of suspension feeding.  The studies involve videotaping larvae as they capture 20µm diameter plastic spheres, simultaneously recording elapsed time, and later measuring lengths of ciliated bands, arm lengths, and so on.  The drawing shows a Dermasterias bipinnaria larva of 630µm in length capturing a single photograph of leather star Dermasterias imbricatasphere over a time span of 1.7sec. Note that the sphere is first captured on one of the ciliary bands lateral to the mouth, then a second time on a transverse band beneath the mouth.  Shortly afterwards the particle is swept into the buccal cavity and ingested. Interestingly, very few particles, even these plastic ones, are lost after capture.  The author notes only 11 incidences of loss out of 491 captures (=2%).  In some cases, the spheres are ingested and swallowed; in other cases, they swirl around for a time in the currents directed into the mouth by adoral cilia and then are eventually ejected, probably by reversal of beat of cilia within and around the buccal cavity.  Hart 1991 Biol Bull 180: 12.

NOTE the ciliated band of the larva is shown by the dark lines

 
Research study 4
 

graphs showing different effects of periods of starvation on growth and metamorphic success of larvae of the sea star Patiria miniataPatchy distribution of planktonic food may impose periodic starvation conditions on sea-star larvae, with negative effects on survivorship, duration of larval life, and post-metamorphic success.  While this is true, a study in Santa Cruz, photograph of a bat star Patiria minataCalifornia on larvae of Patiria miniata shows that such effects occur only if larvae are starved early in development (see graph far Left). If starved later in larval development, but then fed, metamorphic success is about the same as in control animals (see graph near Left).  Allison 1994 Mar Biol 118: 255.

NOTE the author divides the larval period into 8 arbitrary stages as shown on the ordinate axes of the graphs

 
Research study 5
 

drawings of swimming orientations of a bipinnaria larva in normal earth's gravityThe effects of lack of gravity on swimming in early bipinnaria larvae of Pisaster ochraceus are studied in a unique environment: the aquatic research facility aboard the NASA space shuttle Endeavour while in orbit.  Researchers culture early gastrula-stage embryos to the bipinnaria stage on board and analyse swimming behaviours using a motion-analysis system.  Control larvae in a laboratory on earth swim either with their anterior ends oriented vertically or remain more-or-less stationary (see drawings on drawings of a bipinnaria larva of a sea star as it contacts the water surface and swims downwardLeft) and rotate around their longitudinal axes at about 12rpm (at 12oC). Smaller larvae rotate at speeds up to 30rpm.  When in the "holding position", the bulbous anterior ends of a larva rotates in wide circles around the axes, a configuration that presents greater resistance to sinking than the rotational mode used in normal forward swimming. Upon contact with the water surface or an object, the larva swims parallel for a moment, then dives, turns 180o, and then often rotates in one spot (holding behaviour; see drawings on Right). 

In comparison, in low gravity conditions in orbit the bipinnaria larvae swim in randomly oriented straight lines or broad arcs, sometimes spiralling as they go.  These microgravity larvae exhibit no preferred swimming direction, but may sometimes attempt a holding behaviour.  Although gravity responses are not strongly developed even in earth-bound larvae, the authors conclude that development in a microgravity environment has little or no effect on swimming behaviour in Pisaster bipinnaria. The mechanism used by sea-star larvae to sense gravity is not known.  Crawford & Jackson 2002 Can J Zool 80: 2218.

NOTE  the larvae are cultured in 2 carousel systems, one rotating to create the centrifugal equivalent of 1-g (=CONTROL); the other, rotating once every 10min, creating a “microgravity” (=EXPERIMENTAL: really, virtually gravity-free).  Other control cultures are maintained in a laboratory at Cape Canaveral, and treated and observed identically to those on the shuttle

NOTE  for description of this facility and other observations on culturing of P. ochraceus larvae refer to Crawford & Martin 1998 Can J Zool 76: 1641.

 
Research study 6
 

graph of oxygen uptake of larvae of the sea star Mediaster aequalis during developmentEnergy expenditure of larvae of Mediaster aequalis, measured as oxygen consumption from the time of fertilisation, increases rapidly over the first few days, photograph of a sea star Mediaster aequalisthen levels off for the next 5wk. Gastrulation occurs after 5d (at 10oC), and brachiolar arms form after 10d.  After 35d the larvae become competent to metamorphose, and metabolic rates decrease at this time.  Development is fueled solely by lipids.  Lipid stores drop by 64% during the first 76d of development. If metamorphosis is delayed, the remaining lipid stores will sustain metabolic rate for a limited, although undetermined, period.  Bryan 2004 Mar Biol 145: 293.

 
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