Marine Biology

Morphological Adaptations

Few morphological adaptations among estuarine organisms can be attributed simply to living under conditions of fluctuating temperature and salinity. Most are adaptations to a given habitat, such as burrowing into mud. Mud dwelling organisms, whether estuarine or not, often have fine fringes of hair or seta which guard  the entrances to respiratory chambers to prevent clogging by silt particles. Such a situation prevails for estuarine crabs and many bivalve mollusks.

Other morphological changes in estuarine organisms; include a smaller body size than relatives living in the sea and a reduced number vertebrate among fishes. Reproduction is also affected. Marine species in an estuary often have a lowered reproductive rate and lowered fecundity. Freshwater species may be partially sterile.

There are also certain morphological adaptations among vascular plants living in estuaries and  salt marshes. All are relatively small, perhaps the result of long-term selection stemming from water stress. All have a special tissue, the aeranchyma that supplies oxygen to the roots embedded in anoxic mud. This tissue may also bring oxygen indirectly to animals in the mud. Many plants also have mechanisms for dealing with salinity. Some such as Spartima alterniflora, have gland for eliminating salt; thus they maintain a stable water balance. Others have extensive stores of cabohydrate sinteh roots to provide a sugar source to cope with salinity fluctuation. Many also have high lignin content, which may be an adaptation to add strength to the plant to cope with high internal salinity. Abundant stomata and thin cuticle are suggestive of high transpiration rates.