The four seas relate to four aspects of the body: Qi, Blood, Water and Grain, and Marrow. Water and grain refers to the products of digestion. Marrow in TCM is the marrow in bones and also the material (neurons etc) that make up the spinal cord and brain. The traditional associations with these aspects of the body are listed below.
Sea of Qi St9, Cv17, Gv15, Gv14
If excess: urgent breathing, red complexion
If deficient: low energy, difficult speaking
Sea of Blood Bl11, St37, St39 (Chong Mai)
If excess: body feels big, do not feel right but no obvious sickness
If deficient: body feels small, feel reduced but not obvious sickness
Sea of Water and Grain St30, St36
If excess: abdominal fullness
If deficient: inability to eat
Good points for improving digestion and access to digestive qi.
Sea of Marrow Gv20, Gv16
If excess: lightness of body and much strength
If deficient: Dizziness, tinnitus, leg pain, impaired vision, desire for sleep
Also very good points for brain function.