Stichodactyla gigantea - research articles

ThRoewer

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Incorporating fine‐scale seascape composition in an assessment of habitat quality for the giant sea anemone Stichodactyla gigantea in a coral reef shore zone

Abstract
Habitat loss due to land reclamation often occurs in sandy coral reef shore zones. The giant sea anemone Stichodactyla gigantea, which harbors the false clown anemonefish Amphiprion ocellaris, both of which are potentially flagship species, inhabit these places. To assess habitat quality for S. gigantea, we examined correlative associations between the number and the body size of S. gigantea and the amount of habitat types in fine-scale seascape composition quantified from an enlarged section of a high-resolution (1/2,500) color aerial photograph of the shallow shore zone of Shiraho Reef, Ishigaki Island, Japan. This study confirmed that anemones were most abundant at the edges of dense seagrass beds characterized by shallow sandy bottoms, rock beds, and sparse seagrass beds, while they were less abundant in coral patch reefs. However, anemones inhabiting coral patch reefs were significantly larger and their rate of disappearance over 3 years was lower than those inhabiting other habitats. This suggests that coral patch reefs may be more suitable habitats supporting larger animals and greater persistence of S. gigantea.
The visual census techniques applied here, combined with aerial photography and image-analysis software, may be useful as a simple analytical tool for local assessment of suitable habitats for relatively small-bodied marine fauna in shallow-water seascapes.

I found one particularly interesting notion in this article:
Habitat type, disappearance rate, and settlement of S. gigantea

At the end of the study, 43 anemones existed: nine had disappeared, six had been newly found, and one actinia had divided into three small individuals.
One individual (565 cm2) seemed to have moved about 3 m. All 13 anemones that had inhabited the patch reefs at the outset remained, whereas one of 12 anemones that inhabited the rock beds and eight of 19 anemones that inhabited the sandy bottoms including the sparse seagrass beds had disappeared by the end of the study...

So it seems S. gigantea is actually capable to reproduce via fission.



Fine-scale population structure of two anemones (Stichodactyla gigantea and Heteractis magnifica) in Kimbe Bay, Papua New Guinea

ABSTRACT
Fine-scale population structure of two anemones (Stichodactyla gigantea and Heteractis
magnifica) in Kimbe Bay, Papua New Guinea.
Anemonefish are one of the main groups that have been used over the last decade to
empirically measure larval dispersal and connectivity in coral reef populations. A few
species of anemones are integral to the life history of these fish, as well as other obligate
symbionts, yet the biology and population structure of these anemones remains poorly
understood. The aim of this study was to measure the genetic structure of these anemones
within and between two reefs in order to assess their reproductive mode and dispersal
potential. To do this, we sampled almost exhaustively two anemones species
(Stichodactyla gigantea and Heteractis magnifica) at two small islands in Kimbe Bay
(Papua New Guinea) separated by approximately 25 km. Both the host anemones and the
anemonefish are heavily targeted for the aquarium trade, in addition to the populations
being affected by bleaching pressures (Hill and Scott 2012; Hobbs et al. 2013; Saenz-
Agudelo et al. 2011; Thomas et al. 2014), therefore understanding their biology is crucial
for better management strategies. Panels of microsatellite markers were developed for
each species using next generation sequencing tools. Clonality analyses confirm six pairs
of identical genotypes for S. gigantea (n=350) and zero for H. magnifica (n=128),
indicating presence/absence of asexual reproduction in this region. S. gigantea showed
low structure between islands (FST= 0.003, p-value= 0.000), however, even if the
majority of the individuals were unrelated (r~0), 81 families that shared 50% of their
genetic material formed from two to four members were found. Out of these families,
45% were found with individuals only within Tuare Island, 11% only in Kimbe Island,
and 44% were sharing individuals among islands. In comparison, H. magnifica showed
no structure (FST= 0.002, p-value= 0.278), mean relatedness indicated the majority of
individuals were unrelated, and 31 families were identified. Families again consisted
from two to four members and were found within Kimbe Island 90% of the time, and
shared between islands the remaining 10%. Results show the first genetic evidence of
their reproductive characteristics, high levels of connectivity among islands and
significant levels of genetic relatedness among individuals within islands.
 
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Very interesting.
It seem that there are limited evidence that Gigantea can be force to divided asexually. Some reeders in Australia did it. Also when we bought Gigantea we rarely encounter Gigantea that seem to have divided (either naturally or force) recently. This seem to be another evidence that this can happen with Gigantea.
 
Very interesting.
It seem that there are limited evidence that Gigantea can be force to divided asexually. Some reeders in Australia did it. Also when we bought Gigantea we rarely encounter Gigantea that seem to have divided (either naturally or force) recently. This seem to be another evidence that this can happen with Gigantea.
The studies show that reproduction via fission seems to be not at all unusual for gigantea. But like with magnifica, it seems that there are strains that reproduce regularly via fission while it seems to be completely absent in others.
The question is whether this is determined by genetics or environmental factors.
You see a similar dichotomy in Entacmaea quadricolor and Heteractis magnifica where you find clone colonies in some locations while solitary individuals in other.
To me it seems this is more likely an environmentally triggered reproduction mode than a purely genetic predisposition.
If indeed environmentally triggered, then finding the trigger and being able to control it could make reproducing of these anemones quite simple.

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