Tectonic factors such as increased levels of activity at mid-ocean ridges are thought to have a large but very slow effect on sea level.  Thus, we do not need to worry about them with regard to how soon beachfront property will become an attraction for scuba divers (unless you built in an earthquake-prone region).  However, they do play an important role in explaining globally high sea level in the Cretaceous, for example.  Glacial melting and freezing and other temperature-related factors are the only fast ways to change global sea level.

One potentially major feedback mechanism with molluscan connections comes from methane.  Methane seeps on the seafloor provide habitat for assorted exotic deep-sea mollusks, including mussels and odd gastropods.  Under cold temperatures and high pressure, methane and water can form an ice-like substance (a gas hydrate), very widespread on the ocean floor.  If the oceans warm up enough, the hydrate can dissociate and the methane will bubble up to the surface and go into the atmosphere, where it is a very effective greenhouse gas.  Widespread methane release probably provided much of the impetus for the highest global temperatures since the Cretaceous, in the latest Paleocene.  Temperatures remained globally warm for a while, with incredibly diverse tropical seagrass beds in Europe (over 1000 known mollusk species) and warm climates in the Canadian high Arctic.

    Dr. David Campbell
    "Old Seashells"
    Biology Department
    Saint Mary's College of Maryland
    18952 E. Fisher Road
    St. Mary's City, MD  20686-3001 USA
    [log in to unmask], 301 862-0372 Fax: 301 862-0996
"Mollusks murmured 'Morning!'.  And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!