A NEW SPECIES OF PATIRIELLA 



135 



ZOOGEOGRAPHICAL CONSIDERATIONS. 



The genus Patiriella, as accepted herein, is distributed predominently 

 in temperate seas. No fewer than 1 of the 15 species included occur 

 in Australian waters (Rowe & Gates, 1995). Six of the species 

 (brevispina, calcar, gunni, inornata, parvivipara and vivipara) are 

 endemic to Southern Australia. Two species range across theTasman 

 Sea between southeastern Australia and New Zealand (regularis) or 

 Lord Howe Island and Kermadec Islands (oliveri). One species 

 (pseudoexigua) is essentially tropical, ranging from northeastern 

 Australia north to Japan. The somewhat ubiquitous P. exigua ranges 

 from southern Australia, westward across the southern Indian Ocean 

 to St. Helena Island off southwestern South Africa in the southern 

 Atlantic. Of the other species, dyschta is endemic to South Africa; 

 calcarata is endemic to Juan Fernandez Islands; chilensis occurs 

 between Chile and Peru and, fimbriate/ is distributed from southern 

 Chile to the Falkland-Magellan area and southern Argentina (A.M. 

 Clark, 1993). With the exception of fimbriate/ which has a known 

 depth range from intertidal to c. 300m, species of Patiriella are 

 essentially intertidal, occurring at most to about 30m depth (A.M. 

 Clark, 1993). 



The occurrence of a species of Patiriella isolated on the Dhofar 

 coast of Oman, in the tropical, northwestern Indian Ocean, is 

 difficult to explain; whether as the result of distributive, accidental or 

 vicariant events. 



To seek explanation by a distributive means requires knowledge 

 of reproductive strategies within the genus. Unfortunately, we have 

 been unable to determine reproductive strategy in P. paradoxa 

 through examination of the gonads, since the three specimens 

 collected to date were preserved and dried. Since gonopores do not 

 occur on the oral surface (see p. 1 33), and it is clearly not viviparous, 

 then we assume aboral gonopores occur in P.paradoxa and the 

 strategy involves either planktotrophic or lecithotrophic larvae. 

 However, life histories of at least seven species of Patiriella occur- 

 ring in Australia, including P. regularis which also occurs in New 

 Zealand have been determined (Byrne, 1991: 1992; Byrne and 

 Barker, 1991 ). Of these, regularis exhibits an indirect/planktotrophic 

 developmental pattern with feeding bipinnaria and brachiolaria 

 larvae; gunni, calcar, pseudoexigua exhibit a direct/lecithotrophic 

 developmental pattern with planktonic non-feeding brachiolaria 

 larvae; exigua exhibits direct/lecithotrophic developmental pattern 

 with a benthic non-feeding brachiolaria larva; vivipara and 

 parvivipara exhibit a direct/viviparous pattern of development as 

 intra-ovarian brooders, without larvae. The occurrence on the the 

 Dhofar coast of Oman of Patiriella originating via larval distribution 

 from either southern Africa or the Australasian region, even though 

 the nearest congeners are P. dyscrita (S. Africa) and P. pseudoexigua 

 (recorded as P. exigua by Koehler, 1910), from the northeastern 

 Indian Ocean, is difficult to envisage. The present-day water cur- 

 rents of the Indian Ocean must have been established for at least the 

 last 15-10my, following separation of the Indian Ocean (seeAdams, 

 1981; vanAndel, 1981). The isolation of P. paradoxa, on the Dhofar 

 coast suggests a genetic isolation which is not receiving input from 

 other parts of the generic range. 



An explanation of the origin of the temperate-water genus Patiriella 

 on the tropical Omani coast in association with a secondary agent is. 

 however, not at first sight, unreasonable to propose. For instance, 

 Dartnall (1969a) considered the New Zealand species P. regularis 

 had been introduced intoTasmanian waters amongst oyster spat. The 

 distribution of P. exigua from southern African to St. Helena Island, 

 in the south Atlantic, has been attributed, by Mortensen (1933) to 

 probable transport on the holdfasts of the kelp Ecklonia, which 



though not established itself on St. Helena was washed ashore there. 

 A.M. Clark (1992, in A.M. Clark and Downey) considered this a 

 reasonable supposition since exigua is not recorded from Ascension 

 Island, to the north of St. Helena where the current is from the east. 

 The occurrence of Ecklonia radiata, otherwise known only from 

 around the coasts of South Africa, Australia and New Zealand, 

 which has been recruited to the southeastern coast of Arabia via the 

 deep Antartic current from the south (Sheppard, 1992, in Sheppard, 

 Price and Roberts) might have provided a 'raft' for Patiriella to reach 

 the Dhofar coast, originating either from South Africa or the 

 Patiriella-species-rich southern coast of Australia. However, such 

 'rafting' or 'accidental' introductions tend only to extend species 

 range, as it has done with Ecklonia. To seek a solution here for 

 Patiriella requires invocation of the subsequent evolution of the 

 species P. paradoxa and extinction of its ancestor on the coast of 

 Dhofar. Once again, the genetic and geographic isolation of P. 

 paradoxa would not appear to support such an arguement of its 

 origin on the Dhofar coast, even from its geographically nearest 

 congeners (see above). 



The lack of fossil history of the family Asterinidae does not 

 preclude ancient history. It may be more productive, therefore to 

 seek a linkage between the distribution of Patiriella (particularly 

 considering its very close relationship with Asterina s.s., from the 

 Atlantic, and Patiria, from the North Pacific) and vicarient events in 

 the Indian Ocean. The oceanographic and geological configurations 

 of the area appears to have been relatively stable for at least the last 

 15-10 my (Powell et al., 1981; Adams 1981). 



Coincident with this time the complete opening of Drake's Pas- 

 sage (25-15 mya) established the circum-Antarctic current and a 

 sharp drop occurred in surface and bottom sea-water temperatures 

 (van Andel, 198 1 ). It can be concurred that the present-day areas of 

 upwelling, including those within the Indian Ocean were also 

 established at that time. This is of interest for two reasons. Firstly, a 

 major area of upwelling is known off the coast of Dhofar (fig. 2). 

 This produces turbulent, nutrient-rich surface waters and almost 

 temperate conditions (minimum recorded water temperature of 

 15.9°CnearSadh; Savidge, etal., 1986) which prevail in the coastal 

 region of Dhofar for at least 4 months of the year (June-mid 

 September) (see Currie et al., 1973; Campbell and Morrison, 1988; 

 Miller and Morris, 1988 for details) and this is coincident with the 

 known distribution of P. paradoxa. Secondly, the general temperate- 

 water distribution of species of Patiriella (as included herein), 

 Asterina s.s. (including only species gibbosa, phylactica, stellifera 

 and possibly pancera; according to FWER, unpublished) andPatiria 

 (including species miniata, pectinifera and possibly minor, accord- 

 ing to FWER, unpublished), which appear (with the exceptions of 

 Patiriella pseudoexigua and Asterina stellifera along the tropical 

 west coast of Africa, part of its range) not to extend into locations 

 much, if at all, above the 20°C isotherm (distribution data taken from 

 A.M. Clark, 1993). The implication of the present-day distribution 

 pattern of these three genera is that their ancestor was more wide- 

 spread in cooler parts of the Tethyan system (possibly during the 

 later part of the Oligocene epoch (c. 40-25 mya) (see van Andel, 

 1981 )) and before its closure, following which event the structural 

 differences recognised in separating the three genera would appear 

 to have evolved in the fairly discrete geographical isolation which 

 occurred between them. Although the distribution of its congener 

 pseudoexigua across the tropics from northeastern Australia to 

 southern Japan is somewhat confounding, the isolated, endemic 

 occurrence of P. paradoxa on the southern Arabian coast might be 

 explained in terms of its being a relic. This is all the more likely due 

 to the influence of local seasonal upwelling, providing more temper- 

 ate conditions, suitable for the genus, at least for part of the year, the 



