Tuatara: Volume 23, Issue 1, July 1977
An Introduction to the Freshwater Crustacea of New Zealand
Despite their vast numbers and the important role they play in freshwater ecosystems, the study of these minute arthropods in New Zealand has remained the prerogative of relatively few specialists. One of the difficulties has been the scattered nature of the information about them, hidden away in a large number of technical papers or publications which are not readily accessible. Perhaps this new book will mark the end of the ‘specialist’ era and stimulate a wider interest in these animals now that a source book of information is available. A plankton net and high quality microscope will always be essential items of equipment but with this illustrated handbook, the identification and study of these tiny crustaceans comes within the reach of any keen student of the natural sciences.
It is in this role as a handbook of basic information about all types of freshwater arthropods found in New Zealand (with the exception of the insects), that this book really excels. It introduces the basic morphology of crustaceans and the methods for their collection in a variety of habitats, before dealing with the thirteen groups of crustcaeans known to occur in New Zealand. Our freshwater crayfish, crab and shrimp are the more obvious members of the fauna, but chapters are also devoted to a number of more obscure freshwater groups such as the Notostraca, Chonchostraca, Syncarida, Tanaidacea and Mysidacea. The syncarids have only recently been discovered in New Zealand in underground interstitial waters. The major chapters cover the more diverse groups of Copepoda, Cladocera, Ostracoda, Isopoda and Amphipoda. Aquatic arachnids, mostly mites, are dealt with in a chapter by Dr V. M. Stout, whose page 40 speciality is included in order to provide a complete coverage of Freshwater Arthropods when this book is considered together with Pendergrast and Cowley's ‘Introduction to the Freshwater Insects of New Zealand’. The final chapter discusses the assemblages of various crustaceans found in different sorts of habitat. To many readers, this is likely to be the most interesting section. It is not as extensive as one might hope for in a book of this type but this is perhaps more an indication of the lack of knowledge than of any shortcoming on the part of the authors.
The chapters on animal groups give an outline of the morphology, types of habitat occupied and features of the life cycle biology. Very often some of this information is drawn from overseas literature with the comment that ‘no information on these aspects exists for the species found in New Zealand’. Thus there are plenty of suggestions for future studies. Keys to species level are given wherever possible. In preparing these keys, the authors have made an extremely commendable effort to illustrate with clear line drawings all the characters necessary for identification. Despite the deceptively straightforward appearance of the keys, however, it should be stressed that identification of such tiny animals is a highly skilled operation, involving dissection, mounting and experienced interpretation. This aspect of the book, by the very nature of the subject, is therefore directed toward the qualified biologist. A substantial bibliography of 252 references provides the keen student of crustacea with plenty of back-up information. Illustrations include eight colour plates, thirty-nine black and white photographs and a wealth of line drawings, all to a high standard.
The authors claim to have addressed the book to ‘students beginning their studies in freshwater ecology’ and to ‘general readers’. It certainly fulfils the needs of the former readers with its coverage of the New Zealand fauna. No textbook can approach it for value and relevance at that level. But I strongly suspect that it will not appeal to the general reader, who looks for fascination in the subject but does not wish to become a freshwater biologist. It is indeed rare to find a book of sufficient technical standard for research students and yet still be entertaining for the general reader. This is a technical book, presenting its facts clearly, precisely and impersonally. It is of obvious value to all teachers and students who will use it as a constant source of reference. The study of freshwater crustacea will never have the wide following of ornithology or entomology and this book is unlikely to change that, but if it encourages more New Zealanders to probe further into the ecology of these tiny arthropods, then it will make a real contribution to the natural sciences in this country.
G. W. GIBBS
Zoogeography of the New Zealand Freshwater Decapoda: a Review
The zoogeography and relationships of the four species of New Zealand freshwater Decapoda (Crustacea: Malacostraca) are reviewed. It is suggested that the fauna is an ancient one which has its closest affinities with the Australian freshwater Decapoda.
Four species of decapod Crustacea occur in New Zealand fresh waters. They are Paratya curvirostris (Heller), a shrimp of the Family Atyidae; two crayfish, Paranephrops planifrons White and Paranephrops zelandicus (White) (Parastacidae); and a small crab, Halicarcinus lacustris, belonging to the Family Hymenosomatidae. The small size of the fauna is probably related to New Zealand's temperate climate (most freshwater decapods are tropical), the country's small size and the long period of isolation since Gondwana broke up in the Cretaceous (Raven and Axelrod, 1972).
Paratya curvirostris is found in New Zealand from Northland to just south of Dunedin (46° S), and also occurs on the Chatham Island. It occurs in lowland streams and estuaries where the salinity is less than 20°/oo. Distribution records indicate that its upper altitudinal limit decreases towards the southern limit of its range, suggesting that temperature may be an important factor controlling its distribution (Carpenter, 1976). It apparently occurs only in estuaries when the marine palaemonid shrimp Palaemon affinis is absent. Orr (1971) reported that P. affinis ate P. curvirostris when they were kept in the same aquarium.
The atyid shrimps are primitive carideans that probably originated in a Tethys shallow-water tropical sea during the Cretaceous (Banarescu, 1973). The family is usually described as restricted to fresh water (Barnard, 1950; Ullman, 1967; Yaldwyn, 1954), although a number of species are known to inhabit anchialine* pools with salinities as high as 30°/oo (Holthius, 1973). Atyids are most common in the Indo-Pacific and Caribbean regions (Johnson, 1963; Hedgepeth, 1968).
The antiquity of the family is indicated by the high ratio of cave species, with reduced or absent eye pigmentation (16 species), to page 42 epigean or surface water species with normal eyes (100 species) (Holthius, 1956; Williams, 1964; Yaldwyn, 1954), as ‘cave species may be regarded as relicts of older faunas (Barr, 1968; Vandel, 1966).
|Species||Range||Subspecies given specific rank by|
|P. compressa (De Haan, 1849)||Japan, Korea, Siberia|
|P. annamensis Balss, 1924||Vietnam|
|P. martensi Roux, 1925||Adonnarra (Flores)|
|P. bouvieri Roux, 1926a||New Caledonia|
|P. caledonica Roux, 1926a||New Caledonia|
|P. intermedia Roux, 1926a||New Caledonia||Holthius, 1969|
|P. typa Roux, 1926a||New Caledonia|
|P. australiensis Kemp, 1917||Australia|
|P. atacta Riek, 1953 **||Australia|
|P. tasmaniensis Riek, 1953 †||Australia|
|P. howensis Roux, 1926b||Lord Howe Island|
|P. norfolkensis Kemp, 1917||Norfolk Island||Roux, 1926b|
|P. curvirostris (Heller, 1862)||New Zealand|
Paratya curvirostris is the southernmost species of the Atyidae, and is believed to be one of the most primitive members of the family (Kemp, 1917; Yaldwyn, 1954). The two northernmost species Atyaephyra desmaresti (Millet) and Paratya compressa (De Haan) (Europe and Japan respectively) are also considered to be primitive.
Roux (1962a) placed P. curvirostris in the primitive subgenus Paratya (Paratya) along with P. compressa and P. australiensis Kemp (Australia). The first two species of this group are possibly related to each other as both have the propodus of the third and fourth pereiopods of the male broadened distally, a feature no found in any other species of Paratya. P. australiensis is morphologically very similar to P. norfolkensis and there is more resemblance between these two species than between either of them and P. curvirostris. Holthius page 43 (1969) has suggsted that the subgeneric groupings are artificial, a view supported by Carpenter (1976) on the basis of morphological studies of all three species and biological observations on P. curvirostris.
The available direct evidence indicates that Paratya curvirostris has a mixohaline life cycle (Carpenter, 1976; Garrett, 1974; Nielson, 1972). All three workers showed that juvenile shrimps are found in upper reaches of estuaries and the lower reaches of streams, mature shrimps being found farther up streams. Carpenter (1976) found larvae in the Ashley Estuary (Canterbury), but he also made a case for the larvae to be facultatively mixohaline rather than obligatorily so. This involved an analysis of their distribution which showed in some cases barriers, such as areas of major organic pollution, long distance or actual physical obstruction, which must prevent larvae moving from fresh water breeding areas to estuaries and/or returning. Laboratory studies (Carpenter, 1976; Garrett, 1974) have shown that unfed larvae of P. curvirostris although able to survive at salinities from that of fresh water to sea water (0-36°/oo), survive longest at 20°/oo. This is equivalent to the blood concentration of the adult (Orr, 1971) and suggests that survival time could be related to the need for osmoregulation being less when the blood is isosmotic with the medium. The presence of a larva which can survive at high salinities can be used to explain the occurrence of lite species on the Chatham Islands, as Burling (1961) has shown that both the Southland and East Cape currents flow to the Chatham area from mainland New Zealand. In contrast to P. curvirostris, both P. australiensis and P. compressa have larvae which develop in fresh Water (Bayly and Williams, 1973; Yokoya, 1931), and P. curvirostris also differs from the other species of Paratya which have known life histories in that it is protandrous (Carpenter, 1976). (Protandry is the situation in which all or nearly all the individuals in a population first function as males and then undergo a sex change to become females.)
It is possible that the ancestral Paratya had a marine larva, which has been retained only in the New Zealand species because competitively superior palaemonid shrimps are absent from the upper reaches of New Zealand estuaries. In Tasmania, palaemonids occur in estuaries in salinities as low as 3°/oo (Walker, 1972) and the competition from these could have contributed to P. australiensis developing a completely freshwater larva (T. M. Walker, pers. comm.). The occurrence of well developed rapids in the lower reaches of Tasmanian streams is probably sufficient to prevent shrimps returning upstream from estuarine areas to streams (Walker, 1972) and this, too, would select against a mixohaline larva.
An alternative theory suggested by Carpenter (1976) is that the mixohaline larva also could have been an important survival mechanism for the species as the New Zealand archipelago has been in a constant state of change since at least the Eocene (Fleming, page 44 1975). A mixohaline larva would have been able to colonise new land masses and prevent extinction of island populations by submergence. This whole question remains conjectural, particularly as the presence of an obligatory mixohaline larva has yet to be proven unequivocably.
In summary, it seems probable that the present species of Paratya, which are rather poor at coexisting with palaemonids (Orr, 1971; Walker, 1972) and are at a disadvantage with more advanced genera of the family (Riek, 1959), are the remaining members of a genus which was widespread before the palaemonids and more advanced atyids had diversified.
The endemic crayfish genus Paranephrops contains two allopatric species that probably separated in the early Pliocene, and became isolated by the Pleistocene (Hopkins, 1970) when the Main Dividing Range reached its present configuration (Fleming, 1962). Paranephrops planifrons is found on both sides of Cook Strait, as far south as Jackson's Bay on the west coast of the South Island and as far south as Ward (Marlborough), east of the Main Divide (Hopkins, 1970). Archey (1915) found that populations of the species form a cline from Northland to Westland, with individuals from Westland resembling the second species, Paranephrops zelandica. P. zelandica occurs from Cheviot (North Canterbury) to Southland, on the east of the Main Divide. Both species occupy similar habitats: under stones, in banks, and in aquatic vegetation in streams, rivers and lakes, from sea level to an altitude somewhere between 1500 m and 2500 m.
The family Parastacidae is restricted to the Southern Hemisphere. Species occur in Madagascar, Australia, New Guinea, New Zealand and South America, each region having a fauna endemic at the generic level (Riek, 1972). This high endemicity indicates that the family is ancient. Support for this contention is provided by Schaeffer (1971) who suggested that the Temnocephalida (Platyhelminthes) were originally restricted to a commensal life on crayfish in the south-east Australia, New Zealand region.
The present distribution of the Parastacidae fits quite well with a Gondwana origin for the crayfish except that none occur in South Africa. However, this is not necessarily a problem as Banarescu (1971) and Huxley (1881) both considered that crayfish may have become extinct in South Africa through not being able to co-exist with more recently evolved freshwater crabs of the family Potamonidae. Little evidence exists to support this theory, except that parastacids and potamonids are rarely found together (Banarescu, 1971).
Paranephrops is closely related to the Tasmanian Parastacoides and the Australian Cherax, differing from these two genera in the configuration of the carapace grooves, the shape of the chelae and the form of the rostrum (Hobbs, 1974).page 45
The crab, Haticarcinus lacustris, has a restricted distribution in New Zealand, and is known to occur only in a few lakes in the Auckland region (Melrose, 1975). Nothing is known of its biology in New Zealand. K. Walker (1969) studied some aspects of its ecology in Australia where it lives on submerged macrophytes or the root systems of emergent macrophytes. Like most decapods, H. lacustris appears to be omnivorous. In the laboratory, Walker found it survived at salinities from 0-36°/oo.
Hymenosomatid crabs are widely distributed in the Indo-West Pacific and although most species are marine, six species in two genera are restricted to inland waters. Only H. lacustris is widespread and as well as New Zealand and Australia, is found in Tasmania, King Island, Lord Howe Island and Norfolk Island (Holthius, 1968). Chilton (1915) suggested that the species was ancient, possibly Cretaceous in origin, and he postulated a trans-Tasman land bridge to account for its present distribution.
A different view was taken by both Lucas (1970) and K. Walker (1969) who suggested that the species had a more recent origin, possibly evolving from Halicarcinus paralacustris Lucas, which lives in estuaries in south-eastern Australia. As H. lacustris does not have a free-living larva, oceanic dispersal cannot account for the present distribution of the species if it arose in south-east Australia. Lucas therefore suggested that adult crabs could have been carried across the Tasman Sea by birds. This is theoretically possible as he found a crab could survive in the laboratory for more than four days, long enough for a bird to fly the Tasman Sea. However, it is unlikely that a crab would survive such a flight, for if it was close enough to the bird's plumage to escape wind desiccation it would be under considerable thermal stress. The localised occurrence of the species in New Zealand (Melrose, 1975) also indicates that dispersal by birds is unlikely, as if some crabs could have been carried across the Tasman Sea, others surely would have been carried short distances around New Zealand. On the other hand, the suggestion of K. Walker (1969) that adult crabs could have been rafted across the Tasman appears to be a more reasonable one considering the wide range of salinity tolerance of H. lacustris.
Lucas (1970) also has claimed that the lack of fossil freshwater Hymenosomatidae indicated a relatively recent origin. This argument is tenuous, as the chance of a soft-shelled freshwater animal becoming fossilised is remote and if it does happen the appropriate stratum still has to be discovered.
As the six geographic isolates of H. lacustris are morphologically similar (Chilton, 1915), the ancestor of the species either had to be widespread, or dispersal occurred from a single point of origin. I believe that the first of these alternatives is the more unlikely, as the only extant species that is likely to be ancestral to H. lacustris is H. paralacustris, which has been found only in south-east Australia. page 46 On the other hand, the five freshwater species of Halicarcinus as well as H. paralacustris may not be congeneric with the marine species presently placed in the genus (Holthius, 1968). Thus the occurrence of H. paralacustris in estuaries may be the result of a reinvasion of the marine environment. This view is supported by K. Walker (1969) who found that H. lacustris could not co-exist with freshwater crayfish in the laboratory and is found most often in brackish water (in which crayfish do not occur) in Australia. He suggested that the crabs may have been forced into the estuarine environment to escape predation by crayfish, eventually giving rise to a sibling species which occurs only in estuaries.
If we assume that it is more likely that H. lacustris gave rise to H. paralacustris rather than vice versa, it is easier to accept the suggestion of Chilton (1915) that H. lacustris is an ancient species that arose prior to the break-up of Gondwana. The present fragmented distribution can be interpreted as the result of environmental changes, including the effects of predation by parastacid crayfish, in the intervening period.
From this discussion it should be clear that our understanding of the zoogeography of New Zealand's freshwater Decapoda rests largely on speculation. Existing information leads me to the conclusion that the freshwater decapod fauna of New Zealand is an ancient one although a lack of detailed systematic studies of all three families prevents many definitive statements being made. The relationships of the Paratya species are at best confused, although the morphological similarity of the secondary sexual characters of P. compressa and P. curvirostris suggests an affinity, despite important differences in the breeding biology of the two species (Carpenter, 1976). The taxonomy of the Hymenosomatidae is now under review (Lucas, 1975) and when this work is completed it may help clarify the relationships of the freshwater Halicarcinus to other members of the family.
Despite these limitations, it can be stated that the New Zealand freshwater crayfish and crab are closely related to members of the Australian fauna. In this respect they resemble a number of other freshwater crustacean groups such as the Syncarida (Schminke, 1975) and Cladocera (Brehm, 1956).
In wish to thank Dr M. J. Winterbourn for criticising the manuscript and helping to clarify some of the ideas expressed.
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† Present address: Research Division, Ministry of Agriculture and Fisheries, Palmerston North, New Zealand
* ‘anchialine’ — a term introduced by Holthius (1973) to describe pools with no surface connection with the sea, containing salt or brackish water, which fluctuates with the tides.
** W. D. Williams (ms.) has synonymised P. atacta and P. tasmaniensis with P. australiensis, but this unpublished revision will not be followed here.
† Walker (1972) in an unpublished thesis has shown P. tasmaniensis to be synonymous with P. australiensis.