Ashort note onfactors affecting the geographic distribution of the burrowing ocypodid crab, Paratylodiplax blephariskios: temperature, habitat and competition
The known distribution of Paratylodiplax blephariskios extends from the Morrumbene estuary in Mozambique to the Mngazana estuary in the Eastern Cape. Laboratory data on the temperature tolerance of P. blephariskios indicated that the crab could survive temperatures between 12.5°C and 35°C and should be able to survive further south in estuaries at least as far as the Swartkops. Apart from its occurrence in the Mngazana estuary, the range of P. blephariskios does not overlap with its congenerics, P. algoensis and P. edwardsii. While P. blephariskios is restricted to subtidal habitats, P. edwardsii and P. algoensis are intertidal. P. blephariskios is likely to compete with P. algoensis, which occurs in muddy substrata at the spring tide low water mark, and the anomuran Upogebia africana, which is abundant in soft substrata in warm-temperate estuaries. Whilst there are no data indicating the occurrence of P. blephariskios in the tropics, the crab should occur in estuaries containing suitably muddy substrata at least as far south as the Swartkops. However, it would appear that insufficient areas of suitably muddy habitat have prevented P. blephariskios from establishing viable populations in estuaries south of the Mngazana.