Temperature Tolerances and Southern African Distribution of a Tropical Freshwater Shrimp Caridina Nilotica (Decapoda: Atyidae)
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Temperature tolerances and southern African distribution of a tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) R.C. Hart Institute for Freshwater Studies, Rhodes University Laboratory estimates of median time of survival (MTS) were Atyid shrimps are ancient inhabitants of fresh water. Today used as an index of the temperature tolerance of the warm they are widespread in fresh waters of the tropics, although water shrimp Caridina nilotica. Tolerance to high (~3O 0c) and low (;§i 10°C) temperature was examined in seasonally some extend into cooler regions (Fryer 1977). The only acclimated shrimps from subtropical Lake Sibaya. The MTS southern African genus in this family is Caridina, with a decreased rapidly above 30 and below 10°C. The MTS maximum of four species recognized by Barnard (1950) and temperature response curve predicted a 'range for activity' Kensley (1972). Distribution records assembled by Barnard extending between 11 to 11,5 °C and 31,5 to 32°C. This tolerance range broadly matches the span of environmental (1950) demonstrate the restriction of Caridina to the north temperatures which shrimps are likely to experience within eastern part of the subcontinent (Figure 1). The most their geographical range, implying that distribution may be widespread species, C. nilotica (Roux), was recorded only temperature related. The physiological restrictions implied by as far south as the Umzimvubu River (ca. 31°30/S) and as the anomalously low upper tolerance limit may be circumvented by avoidance behaviour (e.g. diel offshore far west as Lake Ngami (ca. 22°33/E). I examined the low migrations) in suitable habitats. temperature tolerance of C. nilotica to establish whether . S. Afr. J. Zool. 1983, 18: 67 - 70 its southern distribution limit was likely to be temperature ) 0 related, given the essentially tropical/subtropical status of 1 Laboratoriumbepalings van die mediaanoorlewingstydperk 0 this species. I also examined the upper temperature tolerance 2 (MOT) is gebruik as 'n aanduiding van die temperatuur d toleransie van die warmwatergarnaal Caridina nilotica. of this species following the discovery of an apparently e t Seisoenaal geakklimateerde garnale afkomstig uit die a anomalously low growth rate at 30°C (Hart 1980b) during d subtropiese Sibayameer is vir toleransie tot hoI! (~30 0C) en ( a study of its production ecology and bio-energetics (Hart r lae (;§i 10°C) temperatuur ondersoek. Die MOT het bo 30°C en e 1980a, 1981; Hart & Allanson 1981). Considering its wide h onder 10°C vinnig verminder. Die MOT-temperatuur s i l responskromme het 'n 'verspreiding van aktiwiteit' van 11 tot distribution and abundance in suitable habitats, surprisingly b 11,5 °C en 31,5 tot 32°C voorspel. Hierdie toleransie u P verspreiding stem grootliks ooreen met die spektrum van e omgewingstemperatuur wat garnale binne hulle geografiese h t verspreiding ondervind. Dit wil dus voorkom asof verspreiding 10 15 20 30 35 40 y moontlik temperatuurgebonde kan wees. Die fisiologiese b 15 d beperkings 5005 ge"impliseer deur die onrel!lmatige lae e t boonste toleransiegrens kan in geskikte habitatte omseil word n deur ontwykingsgedrag (bv. daaglikse diepseemigrasies). a r S.-Afr. Tydskr. Diem. 67 - 70 g 1983, 18: e - 20 c £: n ~ e VI c i <II l .. r ~ e co d ~ 25 n u w y o :::> a .... w .... e t :3 )0 a G t e n i b 35 ~ ~ ~ ~ ~ ~ ____L- ____ ____ ____ ____ ____ a S 10 15 20 25 30 35 40 y b LONGI TUDE (D~rH5 Easl) d e R.C. HIII1 c Institute for Freshwater Studies, Rhodes University, Grahamstown 6140, Figure 1 Distribution of Caridina nilotica, C. a/ricana and varieties u (cross hatching), and C. typus (shaded triangles) in southern Africa ac d Republic of South Africa o cording to Barnard (1950). Additional records for C. shown as r nilotica p Received 13 August 1982; accepted 16 October 1982 shaded circles, and for C. typus as open triangles. e R 68 S.-Afr. Tydskr. Dierk. 1983, 18(2) little is known of the ecology of C. nilotico. Some insights survivorship curves were very similar for both arithmetic into its ecology are provided by a consideration of its and loglo transformations of survival time. Only the loglo temperature tolerances, which I report here, together with survival plots are reported below. additional distribution records. Results and Discussion Materials and Methods Low-temperature tolerance All the shrimps in this study were originally collected from Survivorship curves for low temperature series are shown vegetated littoral margins of sUbtropical Lake Sibaya in Figure 2, and Table 1 summarizes the MTS estimates and (27°25/S/32°40/E) and exhibited the typical characteristics related experimental infonnation for both upper and lower of C. nilotico (Roux). Animals freshly collected in August, temperature series. Predictably, MTS decreased with the cool season, were used for the low temperature decreasing temperature. In all the low temperature series experiments. For the high temperature experiments, animals apart from the 'acclimated' batch at 7°C, probits of sur were drawn from a flourishing, longstanding laboratory vival were 'split' (Finney 1952). This indicated the possibility culture acclimated to 30°C for one week prior to the that more than one cause of death was involved (Hill & experiments. Details of this culture have been described by AIlanson 1971). Surprisingly, animals acclimated for 12 days Hart (l980a,b). at 10 °C prior to exposure at 7 °C (the 'acclimated' batch), Medium-sized shrimps (3 - 5 mm carapace length) were demonstrated a lower MTS than animals transferred directly randomly selected and placed individually in glass jars to 7 °C from ca. 18°C (Table 1). This difference containing"" 100 mfof lake water for the low temperature presumably reflects a depression of survival consequent to series and conditioned water from the parent culture vessel protracted low-temperature stress during the acclimation for the high temperature experiments. Animals were not fed period. While this suggests that acclimation does not im during the experiments as pilot studies demonstrated the lack prove low-temperature survival for all individuals, there are of any feeding response during high or low thermal stress. indications from Figure 2 that a residual proportion of ac Low-temperature tolerances were determined in a climated individuals survived longer than their non refrigerated incubator. Shrimps were cooled from ambient acclimated counterparts. Ecologically though, this is unlike ("" 18°C) to the experimental temperatures of 5, 7 and ly to be significant since at these low temperatures shrimps 10 °C (± 0,2 0C) over periods of 6, 5 and 4 h, respectively. were prostrate virtually from the outset and unlikely to sur Control series were run at room temperature ("" 18°C). Test vive the depredations of nature. ) jars were covered with gas-permeable polythene sheeting to 0 1 reduce evaporative losses. Water was not changed during 0 99 99 2 98 ~rol 98 the experiments, in view of their generally short duration. ~ d 95 - 95 e Tolerance to high temperatures was measured in thermo t -- ~ 90 90 a statically controlled water baths. Shrimps, acclimated to d :; 80 80 ( 30°C for one week, were heated to experimental ~ 70 70 r V' e 60 60 h temperatures of 32,5; 33,5 and 34,5 °C (±0,2 0C) within u.. 50 50 s i '" 40 40 l 1 h. A control series was maintained at 30°C. Test jars were ;5 30 30 b ifi 20 20 u covered with coarse nylon mesh to prevent the animals jum u P a: 10 10 e ping out of the containers under thermal stress, while en ~ 5 5 h t suring adequate gaseous interchange with the atmosphere. 2 2 y 1 1 b Evaporative losses were made good with distilled water once 1 5 10 20 50 100 200 500 1000 d e or twice daily, and water was completely renewed every two SURVIVAL TIME (Hrs) t n to three days during the longer experiments. a Figure 2 Survival of Caridina nilotica at low temperatures. Percentage r Shrimps were examined at intervals of 2 to 4 h during g survival is plotted on probit scale. e the extreme-temperature experiments, and every 8 to 24 h c n e under more moderate experimental temperatures. Under c i Table 1 Median time of survival (MTS) estimates l high and low thennal stress, animals became very quiescent, r for Caridina nilotica exposed to low and high e and tended to collapse onto their lateral surfaces. The beat d temperatures n of the scaphognathite decreased slowly. Death was diag u y nosed when the scaphognathite failed to resume beating Temr.erature MTS Number of a following gentle prodding of the shrimps with a blunt 0c) (h) shrimps w e t probe (Hill & Allanson 1971). Water temperatures were a Low 5,0 17 30 G measured to 0,05 °C in test jars at each observation. Mean 7,0 (Acclimated) 30 25 t e experimental temperatures were calculated from these 7,1 44 30 n i 9,9 237 55 b readings. Survival times reported below refer to the inter a 18,2 (Control) ooa 30 S val between the start of an experiment and the diagnosis y of death. Percentage survival was plotted against survival High 30,0 (Control) 00" 20 b 32,4 166 20 d time in hours on probability paper (Finney 1952). The me e c dian time of survival (MTS) - the time taken for 50070 of 33,3 81 20 u 34,6 14 20 d o the animals to die - was estimated from lines fitted by eye r p to the probit plots. Estimates of MTS and the shape of the "Negligible mortality - MTS is normal physiological lifespan e R S.