Ditch the cereal and sausage links. Have oatmeal and add 3 more egg whites to your breakfast. That along with adding at least one whey protein shake post workout your diet looks ok, but I would like to see your exercise routine.
The problem with heavily training in cardio is that after 30 minutes, your body burns fat AND muscle indescriminately. This is why I always train shorter high intensity interval training workouts (HIIT), which is very key to preserving that muscle. Since you are training for triathalons, endurance is your thing so you are going to have to sacrifice some of that muscle during those long cardio endurance sessions
. The key will be to lose as little as possible. In order to do that make sure that you are taking in at least 1 gram of protein per pound of of your bodyweight. Also, don't do 30+ min cardio workouts on the days in which you weight train. I recommend doing a 3 day weight training split and then doing cardio the 4 days that you aren't lifting and making sure that you are getting enough rest per bodypart that you are working out in order for the muscle to continue to grow and repair itself between sessions.
Hope that helps.