As human develop the lands around wetlands it locks the wetlands in place. As sea level rises, the wetlands will effectively become increasingly "squeezed" between the advancing ocean and the immovable urban infrastructure.
In wetlands that are not bounded by urban development, as sea level rises the wetland habitats migrate landward. The result is that the total area of marsh or mudflat habitat might not change, but rather just displaced landward with the rising sea.
Coastal Squeeze - habitat loss
When wetlands are bounded by development or urbanization along their boundary, as sea level rises, the habitats are prevented from migrating landward. This is the "Coastal Squeeze." The result can be an overall net loss of marsh and mudflat habitats as they are submerged by the rising sea and converted to subtidal habitats.
Coastal Squeeze - Habitat sustainability
To combat the coastal squeeze, wetlands must have an adequate supply of sediment. If there is sufficient sediment supplied to the wetlands, habitats can build upward in place, and maintain area as sea level rises. This is what we have observed in Upper Newport Bay suggesting that under present conditions the wetland habitats are currently sustainable.