Giganteas tracked by aerial photos

Randy Holmes-Farley

Reef Chemist
Premium Member
Here's an interesting way to track where giganteas live, their populations, how large they are, etc:

Incorporating fine-scale seascape composition in an assessment of habitat quality for the giant sea anemone Stichodactyla gigantea in a coral reef shore zone. Hattori, Akihisa; Kobayashi, Miyako. Faculty of Liberal Arts and Education, Shiga University, 2-5-1 Hiratsu, Otsu, Shiga, Japan. Ecological Research (2009), 24(2), 415-422.

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 examd. correlative assocns. between the no. and the body size of S. gigantea and the amt. of habitat types in fine-scale seascape compn. quantified from an enlarged section of a high-resoln. (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 photog. and image-anal. software, may be useful as a simple anal. tool for local assessment of suitable habitats for relatively small-bodied marine fauna in shallow-water seascapes.
 
I was browsing the archives and saw this. I've got the photos, pm me if you would like to see them. They aren't very good quality though
 
One thing missing that I would have liked to see (or maybe it is somehow there, but I missed it) is an analysis of the depth distriibution of giganteas RELATIVE to the total depth distribution present in the survey.

For example, does Figure 3b really show that giganteas prefer to be at 40-60 cm depth (at lowest tide), or is that simply the most common depth in the survey area?
 
I started writing this post about three times and deleted my response because I kept thinking about this question in slightly different terms.

I think the issue is that they were evaluating optimal "environments" separate from optimal "depths". The entire study area could be considered shallow water, since the deepest area was 1.4 meters, but you are absolutely correct that they don't specifically evaluate depth within this range. I think the rationale was that the purpose of the study was to focus on photographic evaluation of environment - and you can't assess depth from a photograph.

Also, note that in the second paragraph of the Discussion, they mention that they are using average anemone body size as an indicator of "most suitable habitat" - not numbers of anemones present, or even survivability of anemones. It so happens that fewer anemones were actually present on patch reefs in the study area, but they were larger in size and had a higher survivability rate.

Also, they assume that S. gigantea is not mobile, and for purposes of this study the individuals were not - only one individual moved 3 meters. This would suggest a random distribution of juveniles across the reef, and that juveniles only settle/attach in a portion of environments, and they only survive and thrive in a subset of these. I had wondered whether anemones might settle in shallower environments and gradually move towards deeper environments as they mature, but this study appears to refute that.
 
Last edited:
So with all this informat i am willing to think maybe just maybe they do split/divide. It will be interesting to see if anyone can find information with pictures of this taking place. Thank you for the amazing paper..
 
So with all this informat i am willing to think maybe just maybe they do split/divide.

Why?

In the paper they do mention one individual that may have split. But they did not see the event happen - they just returned and found three individuals where one used to be.

If in fact S. gigantea is capable of asexual reproduction, it is a very rare occurrence. Certainly much rarer than sexual reproduction.
 
yes but if that can happen then people can cut them up like frags. I did see some were on the internet someone cutting up an anemone and it did just fine. Let me see if i can locate the thread again.
 
"anemones" are getting chop fragged all the time but I've never heard of Stichodactyla gigantea being chop fragged successfully..............
 
Back
Top