Seto Marine Biological Laboratory is situated in the southern part of the west coast of the Kii Peninsula, and in the bay mouth of Tanaba Bay, which is situated at the point where Kii Strait meets the Pacific Ocean. The name Seto came not from the Seto Inland Sea, but from Seto Kanayama Town, where the laboratory was established. The laboratory is founded in the head of Cape Bansho Zaki, and facing north to Tanabe Bay and south to Kanayama Bay.
The climate of the area is warm and mild (temperate to subtropical). The mean temperature in the mid winter is around 7oC. It seldom snows. It is windy though. The temperature in summer can reach to more than 30oC. Rainy season is June. It also rains a lot in September and October due to the attach of typhoon.
The marine climate is also warm and mild because it is strongly influenced by a branch of Kuroshio Current. The temperature of the surface water near the tip of the cape is 20oC in annual average, and seldom become less than 12oC. Salinity ranges from 31 to 35, and transparency is around 8 m. Tidal range is as wide as 1.4 to 2.0 m.
The topography along the coasts of Kanayama Bay is complicated with steep cliff and many embayments. Sunken rocks and small islands are scattered. The substratum is diverse from bare rock to mud through gravel and coarse sands.
The water depth at the central part of Tanabe Bay (North of the laboratory) is around 30 m. The development of the sandy shore and tidal flats are week. Open water marine faunae can be found in the rocky shores of the bay mouth area. Many tide pools can be found in the rocky shores. The south side of the laboratory such as Engetsu Island is a marine conservation area, and the bottom of the area is sandy.
The Hatake-Jima experimental field is situated in the southeast part of Tanabe Bay. Basically, the environment around the area shows characteristics of strong embayment. However, variety of habitats can be found there, and most species of the bay can be discovered if one surveys around the island.
Tidal flats had been found in the bay head of Tanabe Bay, but are reduced due to the human activities.