Dear all,
I was wondering if alternating immersion and emergence times are essential for intertidal fauna and flora in an estuary? Several species found in the intertidal zones of the estuary are also found in the sub-tidal zone. This is of course not the case for some plants that are only found in the intertidal zone and never in the subtidal zone. So, what do you think would happen if the high tide was maintained for a whole day several times a year, or even 2 consecutive days? Are there any species that you know of that would absolutely need to alternate between immersion and emersion for at least a few hours?
Hello Mario; In the rocky intertidal of Southern California, mussels are limited to the upper intertidal. Those whose larvae settle out low in the intertidal or in the subtidal get eaten by starfish. The starfish don't tolerate the exposure at low tide and must retreat down as the tide falls. They then move up to prey on mussels as the tide rises. So, the mussels occur only in the upper intertidal where the starfish can't reach. If the tide stayed high, the mussels would be accessible to the starfish. There are surely estuarian examples that are similar. Best regards, Jim Des Lauriers
A number of insect species live in tidally influenced habitats and have, or may have, different periods of time that their individuals can persist in the subsurface during flooding. They require recurring periods of time for food acquisition and other activities during low tide. Examples include species of the Tribus Bembdiini among ground beetles. For an indication of increased mortality rates due to prolonged inundation for an ant species of mangrove swamps, see Nielsen (1997): Nesting biology of the mangrove mud-nesting ant Polyrhachis sokolova Forel (Hymenoptera, Formicidae) in northern Australia.
As Jim pointed out, predation in the submerged period is a big part of the story. Perhaps go around to estuaries that have become artificially closed through human agency, and see how things change over time.