The quick and undirty way is to look at the internal septa through the body wall.  The so-called gonads (actually just aggregations of gametes) are located in the sides of the septa near the inner edges.  If it is a healthy male that has had sufficient food and the right conditions to develop sperm, these areas will glisten bright white.  If it is a female they will look dark green to gray.

Cheers, Ron

"The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind. The love for all living creatures is the most noble attribute of man." Charles Darwin (1809-1882)

Thanks for the info on the effect of waves... I was being a little careless with my terminology.  Let me rephrase my question.  You said:

I understand how to provide temperature changes and how to simulate day length changes.  What would you suggest I do to simulate tidal events?

BTW, I definitely plan to get your AHABS articles.  I'm currently working my way through Shick's A Functional Biology of Sea Anemones.  It's a very good book but specific references to the anemones I'm most interested in --E. quadricolor and S. haddoni-- are rather sparse.

The information I'm having the hardest time finding is detailed information about the conditions where these anemones live.  I've collected about 100 images of S. haddoni anemones in the wild, many of them exposed or in very shallow water when the tide is out, so I'm confident they are routinely exposed to waves/surges/tides.  I have much less information about the natural conditions where E. quadricolor anemones live, mostly just short videos.  Since it's difficult to glean much about flow from a video or two, I'm mostly relying on my observations of these anemones over the last several years... and that may not be sufficient when the goal is to induce spawning.

Thanks again for all of the help.

Mark

To mimic tidal events, you will need to find out typical tidal currents in some of the areas where these animals are found.  This information is often available in governementally produced tidal tables for port areas in the region.  Tidal currents vary a lot in various places both in the pattern and in the magnitude.  As an example, it is sometimes considered common folk knowledge that tidal currents in many atolls are minimal, and it is true- some times and for some atolls.  Yet, I was once caught in an ebb tide on Palau that quite literally rolled 1 meter diameter pieces of tabulate acroporids along the bottom and flung Diadema through the water about 2 m above the bottom rather like the echinoderm equivalent of dandilion blossoms.  

Anyway, you can set up pumps to move water in typical tidal patterns, whether or not the tides are diurnal or semi-diurnal, or some other tidal pattern.  Basically this is oscillatory flow with a 12 or 6 hour period of fluctuation.  Then you have to consider that the magnitude of the flow will vary significantly.  As an example in one of my long-ago research areas, at the spring tides, the maximum currents were about 9 knots.  At the neaps, about 2 knots.  Finally, you have to consider that the high and low tides differ from day to day in their times.  As a rule of thumb, any given high or low tide will be about 50 minutes later on a subsequent day.  So, if the maximum flood current is at noon one day, it will be at 1250 the next, and 1340 the following and so on. 

Tidal currents by themselves can be an indicator of season.  In the Pacific NW of the US, the maxium high tides are around mid-day in summer, but are about midnight in winter, and during the spring and fall equinoxes, there are very minimal tidal exchanges for periods of about 14 days.  So... if the organism can sense changes in day length and sense tidal currents, they can "know" physiologically what day it is to within a 3-5 day window of precision, at any time of the year.  If they have a physiological trigger that works on increasing day length and, say, decreasing tidal flux (current flow over the animal), the animal is aware when it is spring, and when it is the equinox and both are good markers for spawning to take advantage of the spring plankton bloom.  If the organisms can sense temperature - that provides one more marker and a "reliabilty" check that it is a good time to spawn.

Now - how do they sense things... Hard to know (not much research)  but consider...  For animals with symbiotic zooxanthellae, as the days increase in lenght the amount of sugars produced increase.  If the physiological trigger is a certain sugar level, it is easy to see how that could be sensed.  With regarding temperatute - all of the animal's physiology is cued to temperature and a 5 degree C temperature rise in the average ambient temperature increases a typical reef animal's metabolism by 50 percent!  So, if spawning occurs when a given hormone concentration rises to a given level, then as the temperature goes up, the hormone concentration rises right along with it, and can be a very precise way of "getting ready," especially if the hormone is triggering maturation of the gametes.  Finally, current flows over the animal can alter water concentrations of, say, oxygen or carbon dioxide and a sudden drop in, for example, carbon dioxide after a prolonged rise (a pattern which would occur if there was a period of neap tides with little current followed by a some stronger currents that pass a threshold level) could easily trigger a spawning event.

As regards images and various anemones... First, the various host anemones are taxonomically different creatures with quite different environments.  Don't make the mistake of considering that what is good for one as being good for another.  That is not the case. 

Additionally, as regards images.  These DO NOT provide unbiased samples or indications of where the animals are found.  They do provide information about what a given photographer wanted to take an image of at the given moment.   I have found S. haddoni in quite shallow waters.  At the same time, and in the same areas, I found them as deep as I wanted to dive; at that area it was a depth of about 50 m.  It would take a lot of transect work to even begin to guess what depth range they prefer.  Most of the published information on these animals has been written by taxonomists such as Daphne Fautin. She is a great taxonomist and scientist, but she isn't an ecologist, and particularly when she was doing her host anemone work, she didn't ask "ecological" questions or sample in a manner that gave the answers to those questions.

It will be difficult to get any real data about distributions with regard to these creatures.  I know - I have looked.

Cheers, Ron

"The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind. The love for all living creatures is the most noble attribute of man." Charles Darwin (1809-1882)

Your image shows a septum protruding from the mouth of the animal.  It may show a gonad - or not - depending up on the physiological condition of the animal.

I think any aquarist who has had these animals for any length of time and has not had a spawning is not properly caring for them.  It indicates a lack of proper food or a lack of proper environmental conditions or both.

Cheers, Ron

"The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind. The love for all living creatures is the most noble attribute of man." Charles Darwin (1809-1882)

They will definitely spawn with only one gender around.

As I said, I can't tell the sex of the individual from that image. If I was there, I could have, but long distance, nope.

I have been telling hobbysist for several years that good and proper care for all their reef animals includes normal variatons in temperature and lighting.  Given those, the animals will spawn.  If you want to mimic spawning in nature rather neatly, you can do it including all cues.  That will ensure spawns, but without any cues - no spawns.  In the cases of most hobbyists, the animals are in an "endless winter" with the temperatures kept too cool (below about 82F) and with no variability.  In these cases, they will put excess energy into cloning.

Asexual reproduction is all well and good, and it is certainly better than nothing, but...

We won't be able breed for hardiness, or specific colors, or other attributes untl we can sexually reproduce the animals.  Given that reefs are doomed, it would be "nice" to have a leg up on domesticating these creatures before we run totally out of pospective brood stock.

Cheers, Ron

"The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind. The love for all living creatures is the most noble attribute of man." Charles Darwin (1809-1882)