Some observations on the mass upstream migration of Varuna litterata (Fabricius) megalopae (Crustacea: Brachyura: Grapsidae) in Fiji by P.A. Ryan and S.C. Choy.

There are only a few records of mass upstream migration by young decapod crustaceans. In April 1987 we observed the masss migration of Varuna litterata in Vago Creek near Suva, Fiji. Behavioural observations and simple physiological experiments were carried out on these larvae both in the field and laboratory. The results are presented in this paper.

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Environmental effects of sediment on New Zealand streams: a review by Paddy A. Ryan

Literature pertaining to sediment in stream ecosystems is reveiewed. Suspended sediment can alter the water chemistry, and cause temperature decreases and turbidity increases. Deposition of sediment may change the character of the substrate, block interstices, and reduce interstitial volume. Turbidity levels as low as 5 NTU can decrease primary productivity by 3-13%. An increase of suspended sediment levels increases the drift fauna and may reduce benthic densities as well as alter community structure. Fish are not so obviously afected, although death resulting from clogging of the gills may occur in sensitive species. Suspended and deposited sediment may alter fish community composition, both by interference with run-riffle-pool sequences and by favouring olfactory feeders over visual feeders. In many situations aesthetic reactions to suspended sediment may be of more concern than biological ones. In already turbid water, a 20-50% reduction in clarity may not be detectable whereas in normally clear water a clarity reduction of 10-15% is distinguishable. Recovery from the effects of suspended sediement deposition is usually rapid, once the source of contamination is removed and as long as the stream is prone to regular spates; the aesthetic recovery may only take days whereas biological recovery may take months.

The success of the Gobiidae in tropical Pacific insular streams by P.A. Ryan

The high islands of the tropical Pacific possess a sparse native fish fauna dominated by the family Gobiidae. Evidence of this domination is presented, together with possible reasons for the success of the Gobiidae. Factors which may have contributed include a marine larval stage, euryhalinity, small size, an excellent climbing ability, a range of trophic level from carnivory through omnivory to herbivory, frequent lack of a gas bladder, and an associated bottom-living life style. The evolution of streams in the high islands of the tropical Pacific is relatively recent, thus there has been little time for colonisation to occur. Furthermore, estuaries in many islands are poorly developed, thereby placing euryhaline estuarine species at a competitive disadvantage.

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Mountain streams in Westland, New Zealand: benthic ecology and management issues by M.J. Winterbourn and P.A. Ryan

1. The West Coast of the South Island, New Zealand (Westland) is a region of mountains, forests, high rainfall, and a history of exploitation. The Southern Alps rise to over 3000 m in the east of the region, and a narrow coastal plain supports some agriculture and the main centres of population.
2. Stream waters in the Southern Alps are characterized by low concentrations of major ions, and most can be described as calcium—sodium—bicarbonate waters. Brown waters with low pH and high concentrations of dissolved organic carbon are common at low and intermediate altitudes.
3. Many mountain streams and rivers provide physically harsh environments for aquatic biota with their rapidly changing flows and frequent spates. Hydrological factors and low nutrient concentrations limit periphyton standing crops, and biomass of coarse detritus is often low. Invertebrate populations are usually dominated by insect larvae that feed primarily on Fine Particulate Organic Matter and stone surface biofilms.
4. Features of the macroinvertebrate stream fauna on the West Coast are the wide range of physicochemical conditions tolerated by many common species, and the numerical dominance of the mayfly Deleatidium (Leptophlebiidae) in many streams. The Plecoptera also exhibit high diversity relative to other parts of the country, and an unusual trend towards terrestrialism is shown by larvae of Gripopterygidae.
5. The West Coast has a long history of coal and gold mining, forestry and farming, activities that have had negative impacts on stream communities and water quality. We discuss some ecological and management issues associated with present day mining practices, and a proposal to take large volumes of alpine stream water for export.

An invasion of the blue moon and blue tiger butterflies (Lepidoptera: Nymphalidae) from Australia, April 1995 by Early, J.W., Parrish, G.R., and Ryan, P.A.

Large numbers of two Australian butterflies, Hvpolimnas bolina nerina and Tirumala hamata hamata, were reported in April-June 1995 in New Zealand, mostly in the north and west of the North Island. Meteorological evidence indicates that they probably arrived on 9-10 April from between about 24 degrees and 32 degrees S on Australia’s east coast, and with a trans-Tasrnan passage time of 54-60 hours. A few specimens of other Australian butterflies (Danaus chrysippus petilia, Cynthia kershawi, Junonia rillida calybe and possibly Melanitis leda bankia (Nymphalidae)) and moths (Utetheisa pulchelloides vaga (Arctiidae) and Elvgaea materna (Noctuidae)) were also recorded over the same period.

Cranefly larvae (Diptera: Tipulidae) living in jelly masses by R.A. Beaver and P.A. Ryan

The immature stages of the cranefly, Limonia (Geranomyia) vitiella Alexander are found mostly on the leaves of Pandanus in moist habitats in the rain forest on the island of Viti Levu, Fiji. The larva lives within a tube of jelly on the upper leaf surface, emerging to feed on decaying and dead epiphylls. and associated microbes. When mature, it usually moves to the lower leaf surface where a larger mass of jelly is produced, within which it pupates. The jelly protects the immature stages against desiccation, and natural enemies. The species occurred patchily in both space and time.

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Distribution, ecology, and conservation status of freshwater Idoteidae (Isopoda) in southern New Zealand by Chadderton, W.L., Ryan, P.A., & Winterbourn, M.J.

Three species of Idoteidae, Austridotea lacustris, A. annectens, and A. benhami, are known from the South Island of New Zealand and some of its outlying islands. All three have largely coastal distributions, with A. lacustris and A. annectens inhabiting both fresh and brackish water. They feed mainly on plant detritus and, to a lesser extent, algae and invertebrates. A. lacustris is known from Stewart Island, Campbell Island, Pitt Island, and the south of the South Island. On Stewart Island, many stream populations of A. lacustris occur immediately above the upper limit of tidal influence, but on Campbell island, the species penetrates much further inland. A. annectens has been found on Stewart Island, Pitt Island, and the southern South island as far north as Banks Peninsula. It lives in freshwater streams and brackish lagoons. A. annectens has a 1-year life cycle with young released in spring. A. benhami is known only from a few freshwater streams near Dunedin (South island) and appears to be the most endangered of the three species. Habitat protection by vegetated riparian strips is proposed to reduce potentially harmful effects on its populations.

Impacts of global warming on New Zealand freshwater organisms: a preview and review by Ryan, P.A. & Ryan, A. P.

Global warming is a reality and there is evidence that some New Zealand freshwaters have already increased by as much as 1.6 °C over a 17-year period. Temperature increases may cause a southwards retreat of vulnerable aquatic species in New Zealand as a 3°C temperature increase will shift a derived degree day / latitude regression 670 km southward. Introduced salmonids, stream invertebrates and non-diadromous native fishes may be unable to make compensatory migrations and be extirpated from portions of their range. Diadromous galaxiids may be harmed by egg loss due to increased flood frequency. Existing evidence on genetic heterogeneity of stream insects is ambiguous but some species may have the genetic capacity to cope with increased temperatures. Maintenance or enhancement of riparian vegetation is likely to be important to keep adult stream insects within their temperature tolerance ranges. Higher CO2 levels may result in reductions in nitrogen levels in leaves that fall into streams, thereby reducing food value to aquatic consumers. Higher temperatures may also produce faster growth rates but smaller adult size in some freshwater invertebrates. An increase in the frequency of extreme climatic events will have the capacity to alter aquatic community structure and higher temperatures may enhance the reproduction of parasites with consequent negative effects on their hosts. Furthermore, warmer stream temperatures could increase the possibility of aquarium escapees establishing in northern waters.

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Southern, W., Ash, J., Brodie, J., Ryan, P.A. 1986. The flora, fauna and water chemistry of Tagimaucia Crater, a tropical highland lake and swamp in Fiji. Freshwater Biology 16: 509-520

SUMMARY. 1. Tagimaucia crater lake and swamp are located at an altitude of 820m In Taveuni, Fiji (lat. I6''S; long. 179°56'W). Rainfall exceeds evaporation in all seasons and residence time for water in the shallow lake (2.5-5.5 m deep) is only 4 days. 2. Dissolved ion concentrations are low (conductivity 14-18//Scm"' at 25X). and the water is slightly acidic (pH5.()-6.5 at 25°C). Median total phosphorus (0.5gm~"') and total nitrogen (3.3gm~"') are moderately high and probably represent dissolved and suspended organic matter. Median chlorophyll a concentrations (2.5 mg"'') were low and indicate low phytoplankton productivity. 3. The swamp vegetation is dominated by Leptronia articulata (Retz.) Domin and algae which form floating sedge peat islands, and Pandanus taveunienis St John and other small trees where alluvium and colluvium arc infilling the margins of the crater. The surrounding slopes are forested. 4. The fauna of the lake and swamp are low in both diversity and abundance. The only aquatic vertebrates observed were Anguilla eels and cane toads, Bufo marinus L., and the only bird was the swamp harrier, Circus approximans approximans Peale. A variety of aquatic insects were observed but crustaceans and other invertebrate taxa were scarcely recorded. 5. Although the swamp and lake are otherwise undisturbed, several recently introduced plants and animals have been recorded. Click here for a PDF.

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