Fiddler crab

Abstract: While a great deal of research has been directed at understanding the high productivity of marsh grasses, little attention has been paid to the potential importance of marsh fauna in influencing marsh grass production. The mud fiddler crab, Ucapugnax, excavates burrows in Spartina alterniflora- dominated salt marshes along the East Coast of North America. Here, I examined experimentally the effect of fiddler crab burrowing on S. alterniflora production. At low intertidal heights, S. alterniflora production was robust and characterized by tall-form plants with roots and rhizomes that penetrate deeply into the substrate. At higher tidal heights, low productivity, short-form S. alterniflora with a dense superficial root mat prevailed. Fiddler crabs differentially affected grass production at different tidal heights. In tall-form S. alter? niflora stands at intermediate tidal heights, experimental reduction of fiddler crab density for a single growing season decreased aboveground production by 47% and increased root mat density by 35%. In contrast, on the lower intertidal soft edge of the marsh and in the high intertidal, dense root mat, short-form S. alterniflora zone, experimental reduction of crab density did not have as marked an effect on cordgrass production. Crab burrows were shown to increase soil drainage, soil oxidation- reduction potential, and the in situ decomposition of belowground plant debris. The relationship between fiddler crabs and S. alterniflora appears to represent a facultative mu- tualism. On the seaward edge of marshes in soft sediment that would not otherwise support burrow structures, the roots, rhizomes, and debris of S. alterniflora provide structural support and consequently facilitate burrowing. At intermediate tidal heights, intensive burrowing activity increases aboveground grass production and prevents the establishment ofa dense root mat, while crabs are largely precluded from burrowing in the dense root mat, short-form S. alterniflora stands at higher tidal heights. There? fore, while initially dependent on S. alterniflora in soft sediments, U. pugnax burrowing activity appears to maintain a habitat suitable for continued burrowing, and as a byproduct, increases cordgrass production and maintains tall-form S. alterniflora stands.

Abstract: The common mummichog, Fundulus heteroclitus , functions as both predator and prey in the trophic structure of east coast tidal marshes. Although mummichogs are generally considered important to energy transformations within marshes, few studies have convincingly demonstrated that predation by F. heteroclitus affects the abundance of salt marsh benthic invertebrates. Thus far investigations of this type have dealt only with the direct effects of adult mummichogs. The results of recent experiments have suggested that by controlling smaller predators, mummichogs may indirectly have a positive effect on the densities of some infaunal marsh invertebrates. Our current knowledge of larval and juvenile mummichogs in their natural habitat is minimal. Unlike the adults, which can utilize the intertidal zone only when it is flooded, the young remain on the marsh even at low tide, inhabiting shallow puddles of residual tidal water that form between clumps of vegetation and around fiddler crab ( Uca sp .) burrows. The importance of F. heteroclitus in salt marsh communities will remain incompletely understood unless future studies consider the role of larval and juvenile mummichogs. Although many species of fishes and wading birds feed on mummichogs, the blue crab (Callinectes sapidus) is probably the major predator of adult F. heteroclitus in the intertidal salt marsh. Predation by adult mummichogs and xanthid crabs (e.g., Eurytium limosum ) may contribute to the high mortality of larval and juvenile Fundulus .

Abstract: Semimonthly peaks in courtship behavior of male crabs coincide with peaks in the temporal distribution of receptive females. Females mate once each month, 4 to 5 days before one of the semimonthly spring tides. The relation of the time of reproduction to tide cycles may be an adaptation to increase to a maximum the probability that the final stage of the planktonic larvae will be transported by tidal currents to substrates suitable for adults.