A Comparative Study of Some Aspects of the Biology and Ecology ofSesarma CatenataOrt. andCyclograpsus PunctatusM. Edw., with Additional Observations onSesarma MeinertiDe Man

Abstract

In the estuary of the Kowie River in the Eastern Cape Province there occur two amphibious grapsoid crabs, Sesarma catenata Ort. and Cyc/ograpsus punctatus M. Edw. They live together in many places, commonly inhabiting the same burrows in the muddy banks of the river. The present exploratory study of these two species has been undertaken to enhance our knowledge of their biology as well as our understanding of the relations between these two very similar animals which live in such close proximity one to another. THE HABITAT The Kowie River empties into the sea at Port Alfred, and is broad, winding and shallow. The tidal limit lies 13 miles from the mouth and over most of this length extensive, gently sloping mudbanks are left exposed at low tide. The level of mean high tide is marked by a low salting cliff which is surmounted with vegetation. At Port Alfred itself the river runs between steep, stony, artificial dykes and on either side lie lagoons (Fig. 1). The lagoons on the East Bank (1, 2 and 3) are almost completely cut off from the river although an exchange of water does take place via seepage points in the dyke. The two western lagoons (4 and 5) are fully tidal. Large areas of the intertidal zone in the estuary are colonised by the tall, coarse marsh grass Spartina capensis Nees (S. stricta Roth.). This usually disappears about the level of High Water Neaps (HWN), to be replaced by a zone of typical salt marsh plants, dominated by Arthrocnemum, especially A. pillansii Moss, which has long stems, prostrate and woody at the base and terminating in erect green succulent tips. With the Arthrocnemum there may be mingled Spartina and Triglochin bulbosum L., particularly in low wet situations, and towards High Water Springs (HWS) Chenolea diffusa Thunb. A short distance below HWS Limonium scabrum (Thunb.) O.K. appears and spreads upwards, presently to give way to grasses, shrubs and trees. The zonation of plants on the banks of four of the five lagoons is very much the same as that along the river banks. The banks of Lagoon 4 (known locally as Little Beach) are sandy and devoid of vegetation. The two lagoons which lie furthest from the sea (3 and 5)contain masses of drifted algae, in particular the slender, branched brown alga Graci/aria verrucosa (Huds.

Carapace and branchial water circulation, and water-related behaviours in the semaphore crabHeloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

“…Many intertidal and supratidal crabs retain water within their branchial chambers while active on land (Mfiller 1869, Verwey 1930, Olthof 1936, Alexander and Ewer 1969, Fielder 1970, Hartnoll 1973, Crane 1975, Quinn 1980, Wood and Randall 1981, Hawkins and Jones 1982, Felgenhauer and Abele 1983, Wolcott 1984, Burggren et al 1985, Burnett and McMahon 1987, Santos et al 1987. Water availability and water economy are therefore important factors in the lives of these crabs.…”

“…These setae usually cover the pterygostomial regions, but may also extend across the lateral regions of the branchiostegites and dorsal carapace (e.g. Alexander and Ewer 1969, Hawkins and Jones 1982, Felgenhauer and Abele 1983. While sesarmids (family Grapsidae) possess perhaps the most highly de-276 D.P.…”

“…Water is drawn back into the branchial chambers via apertures at the base of the claws, legs and carapace (e.g. Verwey 1930, Alexander and Ewer 1969, Hawkins and Jones 1982, Felgenhauer and Abele 1983, Santos et al 1987.…”

The Functional Morphology of the Fore-Gut of Three Species of Decapod Crustacea: Cyclograpsus Punctatus Milne-Edwards, Diogenes Brevirostris Stimpson, and Upogebia Africana (Ortmann)

“…According to Alexander and Ewer (1969) the crab C. punctatus is a general scavenger which eats large pieces of food, including coarse vegetable matter and small animals (isopods, zoaea, polychaets). Before entering the stomach the food is shredded by the chelae and sliced by the mandibles.…”

Physiological Adaptation of the Amphibious Rocks Crab Grapsus tenuicrustatus from the Red Sea

“…In earlier studies, Hawkins and Jones (1982) have investigated gill area in two mud crabs, Helice crassa and Macrophthalamus hertipes, both of which are littoral but the former extends into semi-terrestrial condition and the latter remains immersed. In general amphibious crabs from terrestrial and semi-terrestrial habitat have fewer gills, reduced gill surface area and more efficient branchial ventilation when in air relative to aquatic species (Eshky, 1985 and1992a&b;Eshky et al, 1990;Hawkins and Jones, 1982;Gray, 1957;Alexander and Ewer, 1969;Greenway and Taylor, 1976;and Diaz and Rodrigues, 1977).…”