I'm having photos rejected on here that have been accepted by Shutterstock

The face needs to be sharpened a little and the shadows need to be brightened up.

Hello,

I think you can add a bit more contrast. The green water is fine, as I guess this is not a wild dolphin the green is reflected from the bottom of the swimming pool.

Adobe Stock has stricter requirements for sharpness, noise reduction etc., Adobe targets a more demanding clientele, such as designers and advertisers, which leads to a more selective approach.
Acceptance also depends on the reviewer, and some moderators may be stricter than others. 
If an image is rejected, it may be useful to check the quality at 100% and above before submitting it again.

Shutterstock is a different company, they are free to accept the assets that Adobe refuses. 

Adobe Stock is not the same as other services. 

Which rejection reason was given?  

Most aquatic parks and zoos don't permit the commercial use of animal photos.  You would need to submit signed release forms from the park's owners to use the image commercially.   Read the Contributor User Guide for more details.

• https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
• https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html
• https://helpx.adobe.com/stock/contributor/user-guide.html/stock/contributor/help/photography-illustrations.ug.html
• https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html
• Model/Property Releases:
  https://helpx.adobe.com/stock/contributor/help/model-release.html
  https://helpx.adobe.com/stock/contributor/help/property-release.html