Reproduction & life history
 
Research study 1
  graph showing number of planulae released by a laboratory population of cup corals Balanophyllia elegands during the course of a yearSexes are separate in cup corals Balanophyllia elegans.  Gametes are produced in gonads located in the internal mesenteries within the digestive cavity.  Studies at Hopkins Marine Station, Pacific Grove, California show that photograph of a group of cup corals Balanophyllia elegans, including a few juvenilesmales are ripe in late summer, while females brood eggs and embryos throughout the year (about 40 per individual).  Cup corals are the only true coral in which a crawling (rather than swimming) planula larva is produced. The planulae are released during winter/early spring, are quite large (2.5-5mm), and are bright orange or crimson red in colour.  They emerge from the parent’s mouth, crawl down its side, and head off a short distance to find a spot to attach and metamorphose (see above graph). Fadlallah & Pearse 1982 Mar Biol 71: 223.
 
Research study 2
 

The planulae crawl for 2-3d over a distance of only about 40cm, then begin to metamorphose.   Potential for spread of a population into a virgin area by bottom-crawling larvae is obviously limited.  It depends upon such factors as adult and larval survival rates, fecundity, age at first reproduction, larval crawling speed, and other factors.  Based on data from field observations in the San Diego region the potential for spread is estimated to be only 7.5cm per year.  This limited potential for colonisation creates a dilemma.  Balanophyllia elegans as a species is thought to be no older than a few million years.  If a “point-source” arrival of the ancestral adults or larvae to the Pacific coast is hypothesised and with a dispersal rate of 7.5cm per year, it would have taken 29 million years for the population to disperse over their known range of 2000km on this coast.  Clearly, methods of dispersal other than crawling must be involved – perhaps rafting of adults on floating substrates, or transport of larvae or broken-off adults in currents.  Gerrodette 1981 Ecology 62: 611.

NOTE  also known as demersal larvae

 
Research study 3
 

graph showing annual production of planula larvae by cup corals Balanophyllia elegans in relation to adult female size
Estimates of life-history parameters for Balanophyllia elegans in the Hopkins Marine Life Refuge, California suggest that first-year juvenile mortality may be as high as 50%, with annual adult mortality being about 10%.  Densities in this area average about 560 individuals . m-2.  Although fecundity is relatively low, at about 30-40 embryos per large female the species has a high intrinsic rate of increase because of high larval survivorship (44%).  The author estimates a life span of 6-11yr for BallanophylliaFadlallah 1983 Oecologia 58: 200.

NOTE  volume V in mm2 of a conically-shaped Balanophyllia is calculated as V = πh/3(oral r2+ (oral r x basal r) + basal r2) where h = height of the skeleton in mm and oral r and basal r are the oral and basal radii, respectively, in mm

 
Research study 4
 

photograph showing close view of a cup coral Balanophyllia elegansStudies at Hopkins Marine Station, Pacific Grove, California show that gametogenesis in Balanophyllia elegans begins at 15mo of age.  Eggs mature and are fertilised in autumn, and planulae are brooded within the female and released in late winter.  Interestingly, long-term (6.5yr) maintenance of cup corals in the laboratory, one-half of the population being kept on an ambient-light schedule and one-half on a 6-mo out-of-phase schedule, shows that light plays no apparent role in timing of reproduction.  For the first 2yr of laboratory containment the timing of release of planulae is variable, explained by the author as perhaps relating to handling disturbance during initial collection and transport.  After 2yr, however, both groups of laboratory-maintained Balanophyllia release their planulae at the same time in winter, coincidental with release in field animals.  The author suggests that declining seawater temperature in winter is likely to be the controlling factor in this “planulation”.  Beauchamp 1993 Invert Repr Dev 23: 171.

 

 

Balanophyllia elegans showing transparency of
tentacles, nematocyst batteries, and mouth 6X

 
Research study 5
 

photograph showing polyp fusion in cup corals Balanophyllia elegans
photograph of skeletons of 2 fused polyps of cup corals Balanophyllia elegans courtesy Sometimes polyps of cup corals Balanophyllia elegans are found with skeletons fused to one another and the question arises as to whether this is the result of asexual fission or just closely settled individuals joining up. Researchers in California analyse the genetic makeup of fused polyps collected at 18 localities over 3000km of west-coast shorelines and conclude that they are not genetically identical and, thus, do not result from asexual budding.  Rather, they occur through fusion of genetically distinct individuals.  Interestingly, transverse cuts (but not longitudinal ones) done experimentally in the lab can lead to the formation of a second, genetically identical individual, but this new individual is located aborally to the original, not side-by-side as seen in fused field animals (see photo above Right). Hellberg & Taylor 2002 Mar Biol 141: 629.

NOTE  because these individuals would, in effect, be joined top-to-bottom, the process would be unlikely to occur in nature or, if it did, at least one of the fused individuals would not be expected to survive 

 
Research study 6
 

graph comparing settlement intensity of cup corals in relation to water movementWould an invertebrate larva with limited dispersal potential be more or less picky about where it settles and metamorphoses than one that disperses over great distances?  Current thinking points to a less-picky strategy because the larvae, by virtue of their proximity to the adults that spawned them, are already in a suitable habitat.  This is tested for larvae of cup corals Balanophyllia elegans by a researcher at the University of California, Santa Cruz. As noted in Research Study 2 above, dispersal distance for cup-coral larvae is usually less than 50cm, and distributions are generally patchy.  The experiments involve measuring settlement times and distances in the presence or absence of natural rock substratum and brisk water movements (>25cm . sec-1).  In the presence of the 2 factors, 90% of larvae settle within 3d, while in the absence of either or both, less than 11% settle in the same period.  Note in the graph that most settlement in ideal conditions (top line) is complete within 2d. The results show that within the limits of just 2 factors tested, cup-coral larvae are, in fact, discriminative. photograph of several cup corals including juvenilesThe author concludes that settlement cues may be more involved than previously thought in generating the patchy distribution of cup corals, a pattern previously attributed to their short-distance dispersal.  Altieri 2003 Biol Bull 204: 241.

NOTE  settlement in the laboratory is usually within 3d, although the larvae may remain competent to settle for up to 14d


Cup corals Balanophyllia elegans thriving in an ideal
habitat, one characterised by rock and brisk, moving
water. Note the several juveniles near the adults 1X

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