Suspended silt and salinity tolerances of the first zoeal stage of the fiddler crab Uca annulipes (Decapoda: Brachyura) and why marine connectivity is essential to the survival of the species

Abstract

Online) Journal homepage: http://www.tandfonline.com/loi/tams20 Suspended silt and salinity tolerances of the first zoeal stage of the fiddler crab Uca annulipes (Decapoda: Brachyura) and why marine connectivity is essential to the survival of the species N Peer, NAF Miranda & R PerissinottoSuspended silt and salinity tolerances of the first zoeal stage of the fiddler crab Uca annulipes (Decapoda: Brachyura) and why marine connectivity is essential to the survival of the species Fiddler crabs (Uca spp.) undergo the zoeal stage of development in open-ocean waters, where they experience stable salinity levels, low turbidity and reduced predation. The St Lucia estuarine system has undergone many geomorphological changes, both natural and anthropogenic, and the estuary mouth has been closed since the early 2000s. Despite recent attempts to improve marine connectivity, it remains limited, occurring primarily on the flood tide through channels connected to the adjacent Mfolozi River. Larval export from the St Lucia Estuary is therefore almost non-existent. A laboratory study was undertaken to examine the silt and salinity tolerance of Uca annulipes first stage zoeae, to investigate whether survival in the closed-estuary conditions would be possible. Salinity tolerance was narrow, with zoeae displaying 100% mortality at salinities <20 and >35 after five days. Zoeae were widely tolerant to silt loading and did not display a significant decrease in survival over a range of 0-1 000 NTU. A limited salinity tolerance is in accordance with the life-history strategy of fiddler crabs, and a high tolerance to turbid waters can be advantageous to small-bodied merozooplankton. Given the stenohaline nature of the zoeae, marine connectivity is therefore essential for the persistence of U. annulipes in this estuarine habitat.

Larval dispersal of Brachyura in the largest estuarine / marine system in the world

“…This family export strategy to the adjacent continental shelf is already known [4,[138][139][140]. These larvae are unable to survive in the low salinity of the estuarine environment for a long time, as experimentally verified for Austruca annulipes (H. Milne Edwards, 1837) [141], Leptuca leptodactyla (Rathbun, in Rankin, 1898) [142], Minuca minax (Le Conte, 1855) [143], M. rapax [144], Minuca vocator (Herbst, 1804) [145] and U. cordatus [146]. Except for L. cumulanta, which retains all larval stages in the estuary [29], so that ZI and ZII larvae may have been accidentally dragged by currents to the continental shelf, thus justifying the single occurrence 23 km from the coast.…”

Feeding ecology and bioturbation of fiddler crab Uca princeps (Smith, 1870) (Brachyura, Ocypodidae) in a peri-urban wetland in an arid region

“…The evacuation rate is directly related to consumption and was higher than other species in tropical regions, such as Uca rapax and Uca annulipes, which have an evacuation rate of 0.59 h − 1 and 0.79 h − 1 , respectively (Koch, 1999;Peer et al, 2016). The high evacuation rates of U. princeps (0.85 h − 1 ) indicate high metabolic activity and are directly related to the assimilation e ciency of organic matter (Koch and Wolf, 2002;Peer et al, 2016). The lower evacuation rate of females suggests being associated with this e ciency in selecting food quality.…”

“…Likewise, the high biomass of ddler crabs in wetlands signi cantly increases food demand and affects other epibenthic and meiofauna biodiversity (Peer et al, 2016).…”