Candona in Spring

First time looking at this little Candona I thought she was a juvenile but those white balls inside her carapace may be eggs; if they are than this is an adult of a species I haven't seen before.

Putman Marsh Pt1-2 5-20-2017

After looking at about 10 pools in the northern Ohio area a small mystery arises. Probably this is one addressed in ostracod literature somewhere but haven't had any luck finding it. In this area covering three counties 11 species of Candona have been found. Four are rather common;

Candona decora

C. crogmaniana

C. distincta

C. elliptica

Photos of these critters are below,

After receiving Dr. v. Grafenstein reply to my query on the disappearance of the Candona genus in spring (see below) I did a little checking of the samples taken and I have to make a major correction. In my original note I stated that mature Candona are never seen in late spring. This is not true. They may be uncommon perhaps they might be considered rare but they not totally gone.

While in the current sampling Candona are still found but adults are rare; unless these are not immature Candona at all but some diminutive species. Going over my notes a May 1, 2017 at Kopf Woods did have a couple of mature female Candona, see below Below are some examples of the small Candona found (not being trained at this it is possible that these are not Candona at all but it my best guess).

So the question is why are no mature Candona found?

Predation is out unless predators focus only on the genus Candona. The others geneses are booming along.

Drawdown is out because of this unusually wet spring the pools are enlarging.

Temperature - why would temperature effect the ability of immature Candona to reach maturity.

May 10,2017 Columbia Reservation May 5, 2017 Burrell Farm

Carisle equestrian 5-03-2017 Left enlarged

Edison Woods 4/22/2017 top right Enlarged

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Ulrich von Grafenstein

Laboratoire des Sciences du Climat et de l'Environnement, France

Hi John,

I'm writing a personal mail rather than a response within Ostracon because i can't sent to Ostracon due to technical problems. I have studied the seasonal frequency Candonas and other fresh water ostracods in several lakes over at least one year (two-weeks interval) and find the same as you in Ohio. Adults disappear in all water depth from 5 m down to 80 m in late spring. I have lots of small juveniles from instars A-6 to A-2 (A = adult, A-1 last instar before A, A-2 second last before A and so on) during the summer and a very abrupt appearance of A-1 and adults in late autumn. My explanation is that those Candonas have developed from deep-lake, cold living forms which need high oxygen concentrations for the most demanding and exciting activity (reproduction). Best oxygen supply is during winter mixes of the water column, which is preceded by a short warming in the sites deeper than the mean summer thermocline, which might trigger the development of first instars. First juveniles develop in shallow water directly after the first spring warming but in early autumn to late autumn in the deeper sites. After strong wind events in summer we sometimes find a few adults, but the main peak of adults is clearly after the autumn-winter cooling.

Would be interesting to know more about your sampling sites (water depth, water temperatures etc.).

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Below many of the ostracods are identified thanks to the help in the past from Professor Alison Smith, any errors in the identification rest solely with me. This is why so many photos are posted, it allows for correction.

Almost 90% of my sampling is done in temporary pools. Most are 10 to 30 cm. deep. The water being so swallow that that the water temperature within days is probably the same as the air temperature. In this part of the U.S. the temperature in winter to spring can commonly go from -17 C. (0 F.) to 15 C. (60 F.). This part of Ohio is in the glaciated section. Below are several examples of the type of pools sampled. This year has been one of the warmest winters on record.

Below is the same pool taken a year apart. Note that in 2016 the pool was ice covered in 2015 it was not.

Kopf Woods Kw6 12-11-2016 Kopf Woods Kw6 12/10/2015

Below the ostracods found in the Dec. 10, 2015 sample. The pool was not ice covered

C. decora C. Crogmaniana C. distincta C. elliptica

As well as one Bradleystrandesia tincta.

On August 17, 2015 no Candona were found and only a 8 B. Tincta.

This pool does not always dry out in 2015 it did not in 2016 it did.

If Candona is oxygen sensitive and disappear as the year progresses than what explains the large increase in the Cladocerans and Copepods?

Perhaps the benthos - if a vernal pool can be said to have a benthos separate from pelagic- the oxygen does not flow down. But the enormous number of copepods and cladocerans are perhaps a current strong enough to prevent oxygen depletion?

The ostracods found in the Dec. 11/2016 sample when the pool was ice covered. By March 16 all the Candona were gone and only B. tincta remained

C. decora left C. crogmaniana C. elliptica

An immature Bradleystrandesia.

By March 28 all the Candona were gone and only B. tincta remained.

Two species, Candona Decora and C. crogmaniana were found in the May 1, 2017. Both had eggs.

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The above pool (Kopf Woods) lies in what is know here as the Lake Plains and is about 1 kilometer from Lake Erie. The pool below from Geauga county Ohio is another temporary pool about 100 kilometers to the east and is in the foot hills of the Appalachian mountains. The difference in Candona species is quite remarkable but the disappearance of the Candona occurs in this area also. The temporary pool below is about 20 cm. deep.

Geauga Gbw 1