Latitudinal Differences in Thermal Tolerance Among Microscopic Sporophytes of the Kelp Lessonia Nigrescens (Phaeophyta: Laminariales)L

Latitudinal Differences in Thermal Tolerance among Microscopic Sporophytes of the Kelp Lessonia nigrescens (phaeophyta: Laminariales)l

ENRIQUE A. MARTlNEZ 2

ABSTRACT: The strong temperature increase during the 1982/1983 El Nino event caused local extinction ofmany species in large coastal zones of northern Chile and Peru. One brown algal species affected by massive mortality was the intertidal kelp Lessonia nigrescens Bory, with a latitudinal distribution from Cape Horn (55° S) to Peru (12° S). Between extreme localities of this distribu tion, mean annual seawater temperatures may differ by around lOoC. After the massive mortality of 1982/1983, some populations survived in a few localities of northern Chile, such as Iquique (20° S). I tested the hypothesis that these pop ulations represent thermal ecotypes. Those from the north, close to the El Nino impacted zone, should tolerate higher temperatures than southern populations. Microscopic sporophytes, cultivated from spores ofplants collected in localities at the north, center, and south of Chile, were subjected to three temperature regimes. Two of them included the same average temperature, but different extreme values. Comparisons of thermal tolerance in the microscopic progeny from plants of the three Chilean localities showed that, at higher incubation temperatures, central and northern thermal ecotypes do have higher survival and growth rates than the ecotypes from the south. At lower incubation tem peratures, the growth trend was reversed. Also, as suggested in the literature, sporophytic juveniles seem less tolerant than gametophytic microthalli. How ever, the differences in tolerance between northern and southern thermal eco types do not fully explain the survival of high seawater temperatures such as those of the 1982/1983 El Nino event by the northern populations.

TOLERANCE TO EXTREME temperatures among has been suggested as favoring the dispersal algal populations is crucial in establishing of amphioceanic brown algal species across local and phytogeographic boundaries (pak the Tropics (peters and Breeman 1992). ker et al. 1995). The distribution of brown In brown algae, except in some species algae along the South American Pacific coast such as Ectocarpus siliculosus (Dillw.) Lyngb., is based on such tolerances, especially in de tolerance to high temperatures is less variable termining the upper and lower survival limits than tolerance to lower temperatures (Bree of gametophytic microthalli, which seem man 1988, Luning and Freshwater 1988). more tolerant than the alternate sporophytic Upper survival limits are important for spe phase (Breeman 1988, Peters and Breeman cies of the Pacific coast of North America 1993). The "higher tolerance of microthalli and, particularly,. South America, where nat ural episodic increases of seawater temper atures, attributed to El Nino events (El Nino 1 Funding was provided by grants from UNESCO COMAR/COSALC-vn and from FONDECYT nos. Southern Oscillation [ENSO]), affect large 612-91, 2930016, and 4940012 and DIUC 95/15E. This geographical areas (Quinn et al. 1987). In the study is part of work leading to a Ph.D. degree in ecol ENSO event of 1982/1983, northward and ogy at the Pontificia Universidad Cat61ica de Chile. southward incursions of water masses with Manuscript accepted I May 1998. extreme high temperatures caused massive 2 Departamento de Ecologia, Pontificia Universidad Cat61ica de Chile, Casilla 114-D, Santiago, Chile (fax: mortality of laminarian species in both 56-02-6862621; e-mail: [email protected]). hemispheres, resulting in local extinction of 74 Thermal Tolerance in Lessonia nigrescens-MARTiNEZ 75

kelps along hundreds of kilometers of shore line (Gunnill 1985, Tegner and Dayton 1987, Castilla and Camus 1992). In South America 'LAT. S massive mortality mainly affected populations -0 of the intertidal kelp Lessonia nigrescens Bory (Tomicic 1985). The latitudinal distri bution of this species extends over 4000 kID, -10 from Cape Horn (55 0 S) to the Peruvian coast (12-140 S) (Ramirez and Santelices 1991, Peters and Breeman 1993). -20 After the massive mortality ofL. nigrescens of 1982/1983, some populations survived at a few localities in northern Chile, such as Iqui que at 200 S (Soto 1985). These populations -30 are extant today, and some recolonization has taken place nearby (Camus et al. 1994). An explanation for their survival could be -40 their tolerance to high temperatures. Studies on temperature tolerance ofbrown algae from the Pacific coast ofSouth America have stressed both interspecific differences and tolerance of gametophytic microthalli, -50 apparently more resistant than sporophytic individuals (peters and Breeman 1993). Eco typic differences are important in the thermal tolerance of some brown algal species (e.g., FIGURE I. Pacific coast of South America and distri Laminaria saccharina (L.) Lamour. and Ec bution of Lessonia nigrescens (vertical line), modified from Peters and Breeman (1993). Arrows show collection tocarpus siliculosus (Dillw.) Lyngb., which sites of mature fronds of L. nigrescens used in experi differ in growth and survival, respectively, ments on thermal tolerance. under high temperatures [Breeman 1988]). In this study, using the current distribution of L. nigrescens, I tested the hypothesis that (20 0 36' S, 700 10' W), 40 kID south of Iqui thermal tolerance of sporophytic microthalli que; Las Cruces, in the center (33 0 30' S, may be higher in individuals of northern 71 0 38' W); and Pucatrihue, in the south origin, where populations are probably sub (400 27' S, 73 0 46' W). Reproductive fronds of jected to episodic ENSO events. For this L. nigrescens from each site were collected purpose, thermal tolerance was compared from plants in the low intertidal. among cohorts of microscopic sporophytic progeny from L. nigrescens collected at three Annual Regime ofSea Surface Temperatures sites (200 S, 33 0 S, and 41 0 S) over its dis tributional range. Microscopic individuals Temperature records were obtained daily were subjected to three thermal conditions, from the marine research stations closest to and survival and growth of microscopic each sampling site. At Las Cruces and Iqui sporophytes were compared. que, records of the temperature of surface seawater were measured at I-month inter vals, from 4 January to the end of November MATERIALS AND METHODS 1993. Data were taken every 3 days, at Study Sites noon, on the same dates. In the absence of similar records for the southern locality of Sampling sites along the Chilean coast Pucatrihue, only data available for surface (Figure 1) were Aguadita, in the north temperatures measured daily at Mehuin 76 PACIFIC SCIENCE, Volume 53, January 1999

(39° 26' S, 73° 13' W) were used. These data TABLE 1 corresponded to the same months mentioned INCUBATION CONDITIONS FOR THREE TEMPERATURE above, but they were collected during 1988. TREATMENTS APPLIED TO MICROSCOPIC PROGENY OF The monthly means of surface temperatures Lessonia nigrescents PLANTS FROM THE NORTH for the three localities were compared using a (AGUADITA), THE CENTER (LAS CRUCES), AND THE SOUTH Kruskal-Wallis test (Siegel and Castellan (PuCATRIIruE) OF CHiLE 1988), because different transformations did not result in normally distributed data. TEMPERATURE VARIABLES CCC) TREATMENT MEAN SE n MIN. MAX. Mortality and Growth ofMicroscopic Plants 1 10.9 0.47 13 9.0 16.0 at Different Temperatures 2 19.0 0.75 12 13.5 22.0 In November 1993, adult plants were col 3 20.8 0.38 13 20.0 24.0 lected from Aguadita (14 November 1993), Las Cruces (15 November 1993), and Puca trihue (27 November 1993). Mature sori from 10 plants were collected and held in the lab mean temperatures (ca. 20°C) but different oratory at ambient seawater temperature. extremes. Treatment 2 differed from treat They were placed on tissue paper at room ment 3 in having a broader range but lower temperature (16°C) for 2 hr, rehydrated in extreme high temperature (Table 1). These 400 ml of 0.45-~m-fi1teredseawater, and agi conditions were replicated three times. Mean tated at 120 rpm on a shaker (Junior Orbit). temperatures of the two warmer treatments Spores were released and each suspension were similar (P> 0.05, Tukey a posteriori was diluted with filtered seawater to 500,000 test), but different from that of the control spores ml-1. This spore suspension was (F = 96.707; df = 2,35; P < 001, one-way poured into 500-ml plastic containers for 12 analysis of variance [ANOVAD. To avoid hr to allow spores to settle on three slides potentially lethal variations, 2 hr were pro placed on the bottom of the containers. gramed from the minimum temperature to Then the remaining suspension was replaced the maximum in the light phase and a similar by 500 ml of filtered seawater, enriched with decrease in the dark phase. sodium nitrate (400 nM, final concentration) Size sampling of microscopic sporophytes and sodium phosphate (20 ~M, final concen on each slide was accomplished by taking tration). Light was provided at a 12: 12 pho nine photographs at regular distances on a S toperiod, with two circular 32W fluorescent cm transect under a light microscope (Nikon tubes (Hitachi FCI2T9/D) providing a pho Biophot). Each photograph included a sam 2 1 2 ton flux density of 40 ~mol m- sec- . Ther pling area of 0.077 mm . mometers were placed in the incubation con Microscopic sporophytes were then sub tainers and temperature was recorded during jected for 12 days to the three temperature light and dark periods to facilitate control of treatments, and a second sampling of the the conditions in the incubation chambers, as slides was conducted at the end of the period. described below. Mortality was estimated by comparing the Before the experiments the settled spores number of dead (bleached) and living sporo were acclimated in separate containers at phytes at the end of the 12-day experiment. 15°C for 3 weeks. During this period, game The size of microscopic juveniles was mea tophytes from each locality grew to maturity sured on magnified images of both sets of and reproduced, producing the next genera samples, and growth was estimated as the tion of sporophytes. percentage increase in length in comparison Mter the acclimation period, the three in with the mean initial sporophyte size. Arcsine cubation conditions for microscopic spo transformed growth percentages of surviving rophytes were as follows: treatment 1 (con microscopic progeny from the three different trol) with lower mean temperature (ca. lJOC) localities and treatments were compared using and treatments 2 and 3 with similar high a two-way ANOVA (Statgraphics 1988). Thermal Tolerance in Lessonia nigrescens-MARTlNEZ 77

20 100

I u ,'..,' 80 0 18 v v I I )- 60 w f- 0: 16 , ::J --.J f- ([ 40 ([ f- 0: 11 I a w I 0 20 0. L: L: w 12 a f- 9 11 13 15 17 19 21 ~ (DC) lO TEMPERATURE JAN MAR MAY JUL SEP NOU FIGURE 3. Mean mortality under three temperature SAMPLING MONTHS treatments (see Table 1) of microscopic progeny of Les sonia nigrescens from three localities along the Chilean FIGURE 2. Mean monthly temperatures (±1 SD) of coast: the north (Aguadita, solid squares), the center surface seawater, measured in northern (lquique, solid (Las Cruces, open squares), and the south (Pucatrihue, bars), central (Las Cruces, open bars), and southern solid triangles). Chile (Mehuin, hatched bars).

RESULTS underwent some degree of mortality when incubated at a mean temperature of 19°C Annual Regime ofSea Surface Temperatures (treatment 2). Under this treatment, mortal ity was particularly high (98.5%) for the Mean sea surface temperatures were sig microscopic progeny from the southernmost nificantly higher in Iquique than at the two site, Pucatrihue (Figure 3). After 12 days other localities (Las Cruces and Mehuin) for under higher minimum and maximum tem all sampled months (Kws > 15.3, P < 0.001, peratures (treatment 3), all plants were dead Kruskal-Wallis test); mean values in Las (Figure 3). Cruces were between those of the two ex The surviving microscopic plants in treme localities (Figure 2). At Iquique, cubated at a mean temperature of 19°C during the sampling period, maximum mean (treatment 2) and all of those incubated at a monthly temperatures were never higher mean of 1O.9°C (treatment 1) did grow in the than 18.4°C or below 16°C. The only non l2-day incubation period, The mean initial significant differences in temperatures were size of sporophytes from each locality was those between Mehuin and Las Cruces in 17.6 11m (SD 2.5, n 40) for Iquique, 18.0 September and November (Tukey a posteri = = 11m (SD 3.2, n 40) for Las Cruces, and ori test). = = 15.4 11m (SD = 2.5, n = 15) for Pucatrihue. Growth ranged from 30 to 60%, and greater Mortality and Growth ofMicroscopic Plants differences between localities were observed at Different Temperatures at 19°C than at 10.9°C (Figure 4). The ANOVA (Table 2) showed that growth rates The total number of sporophytes per slide were significantly different according to from each locality and treatment (1-3) was locality (higher growth for sporophytes from as follows: Aguadita: 1, 142; 2, 170; 3, 49; the north) and according to the interaction of Las Cruces: 1, 127; 2, 105; 3, 37; Pucatrihue: locality and temperature. Sporophyte growth 1,80; 2, 65; 3,21. When incubated at a mean from northern and central localities only dif temperature of 10.9°C (treatment 1), no fered at 10.9°C (Scheffe a posteriori test), mortality was observed for microscopic with greater growth in juveniles from the plants of any locality (Figure 3). However, north. As expected, at this lowest incubation progeny of plants from all three localities temperature, growth in juveniles from the 78 PACIFIC SCIENCE, Volume 53, January 1999 south was significantly greater than in those (41 ° S) to northern Chilean localities, but do from the center, but, surprisingly, not differ not exceed 20°C at Iquique (20° S). This pat ent from those from northern Chile (Scheffe a tern may partially explain the high mortality posteriori test, Figure 4). This phenomenon of microscopic juveniles of Lessonia ni probably contributed to the significance of grescens when exposed to thermal regimes. the interaction factor (Table 2). Conversely, Mortality was particularly high in the prog at the warmer temperature, microscopic eny from the southernmost locality, with sporophytes from the colder, southern site about the same effects under treatments 2 had the least growth (Scheffe a posteriori test, and 3 (with the same mean temperatures). Figure 4). Temperature maxima higher than 22°C (the highest value in treatment 2) and up to 24°C were associated with the higher mortality of DISCUSSION microscopic sporophytes in treatment 3. The Typically, the mean monthly temperatures high mortality of microscopic sporophytes of surface seawater increase from southern from the southern locality of Pucatrihue in treatments 2 and 3 indicates much less toler 70 ance to long-term elevated temperatures for the progeny of plants from these naturally 60 II cold environments. This effect may also be seen at even shorter exposures to high tem '" 50 .\' peratures. The experimental period was suffi '-/ 40 li cient to reveal this threshold to thermal I I- tolerance. Also, progeny from the south, :3 30 o surviving to a mean incubation temperature g 20 of 19°C, showed highly reduced growth compared with that shown at 1O.9°C. This 10 further suggests their lesser tolerance to long term exposure to high temperatures. o '-- - 10.9 19 These differences in mortality and growth TEMPERATURE (OC) in plants from extreme localities of the lat itudinal distribution suggest the presence of FIGURE 4. Growth (percentage in 12 days of incuba different reaction norms (sensu Thompson tion) of microscopic sporophytic progeny of Lessonia ni grescens from three localities along the Chilean coast: the 1991). The expression of these norms (de north (solid bars), the center (open bars), and the south tected in the sporophytic progeny beyond (hatched bars). Vertical lines indicate 95% confidence in the intermediate gametophytic phase) also tervals. suggests that such responses are inheritable

TABLE 2

REsULTS OF MULTIFACTOR ANDVA FOR GROWTH RESPONSES IN THE SPORPHYTIC PROGENY OF Lessonia nigrescens FROM THREE LocALITIES, EVALUATED UNDER Two INCUEATION TEMPERATURES, IN COMPARISON WITH CONTROL REGIMES

SOURCE OF VARIATION SUM OF SQUARES df MEAN SQUARE F P

Main effects 0.899 3 0.299 6.6 0.0002 Locality 0.772 2 0.386 8.5 0.0002 Temperature 0.128 I 0.128 2.8 0.0949 Two-factor interactions 1.286 2 0.643 14.1 <0.0001 Locality and temperature 1.286 2 0.643 14.1 <0.0001 Residual 27.028 593 0.046 Total 29.214 598 Thermal Tolerance in Lessonia nigrescens-MARriNEz 79 features in populations of L. nigrescens from scopic juveniles, the experimentally deter different latitudinal distribution. mined tolerance of northern microscopic Peters and Breeman (1993) showed that sporophytes of L. nigrescens was not high even haploid gametophytic microthalli of enough to account for the survival of some L. nigrescens from southern Chile (ca. 39° S) populations to the ENSO event of 1982/ survived after exposure to a temperature of 1983. Further complicating this issue is that 24.4°C for 2 weeks. This period is 2 days ecotypic differences within northern pop longer than the one used in my study (12 ulations in 1982/1983 may have been even days), in which I found higher mortality of weaker than those observed today between microscopic sporophytes at a mean tempera northern and southern populations. ture around 20°C, occasionally peaking to Thus, another explanation for the survival 24°C. All this evidence confirms that sporo of some populations is that they were not phytes are less tolerant than gametophytic actually exposed to high temperatures and microthalli, as suggested by Breeman (1988). somehow remained isolated from increases in The results of this study indicate that surface seawater temperature. For example, microscopic sporophytes from northern sites colder water masses remaining close to shore are more tolerant to high temperatures than during the ENSO event may have allowed those from southern, colder latitudes. How survival of today's extant populations. These ever, for several reasons, this higher tolerance masses could have remained from previous of northern plants does not fully explain the upwelling events or they might have been survival of populations extant today, after cooled by waters emerging from under the strong ENSO event in 1982/1983. The ground. This last phenomenon has been re possibility that even more resistant game ported in other parts of the world, such as tophytic microthalli could contribute to such Port Miou, France (Potie 1973, Scanvic survival might also be misleading. Game 1983), and also for some localities of north tophytic stages have a short life span, proba ern Chile, included Aguadita, where sifting bly shorter than the several weeks that high subterranean waters are associated with temperatures (above 24°C) occurred during transverse geological faults (L. Velozo, pers. the strong ENSO event of 1982/1983. In fact, comm.). Nutrient depletion is usually asso when haploid spores of L. nigrescens are ciated with ENSO events and the interaction released, they settle and may produce new with high temperatures seems to be the criti sporophytes within a couple of days, and cal factor causing massive algal mortality female individuals can be fertilized at the (Gerard 1997). In December 1982, at least in single-cell stage, before the settled spore un some locations in northern Chile, nutrients dergoes mitosis (pers. obs.). The short period such as nitrate, nitrite, and phosphate oc between spore release and fertilization of ga curred in higher concentrations at the sea metophytes would likely have caused the less surface than in other ENSO events (Diaz tolerant young sporophytes to be exposed 1984). Thus, isolated areas of the coast might almost immediately, for several weeks, to the have had lower temperatures and/or enough high temperatures of the ENSO event (ca. nutrients to allow these algae to withstand 30°C in 1982/1983). Further, the germination the critical conditions that occur during these potential of nonsettled spores remaining in events. the plankton for 1 or 2 days is rapidly re The small difference in mortality between duced (Hoffmann and Camus 1989). Even the progenies of plants from north and cen if those spores do germinate, only 1 day in tral Chile suggests that the great distance and a spore suspension reduces their adhesive different temperature regimes between these capacity (pers. obs.). Consequently, during localities is not reflected in noticeable adap ENSO events, the less-tolerant microscopic tation, at least as revealed in physiological sporophytes would be quickly exposed to properties. In other brown algal species such critical high temperatures. differences may be expressed even at very Compared with that of southern micro- short distances, as are those in strains of 80 PACIFIC SCIENCE, Volume 53, January 1999

Scytosiphon lomentaria (Lyngbye) Link, CASTILLA, J. c., and P. A CAMUS. 1992. The where extents of tolerance to temperature Humboldt-El Nino scenario: Coastal and salinity are higWy different, even over benthic resources and anthropogenic in very small spatial scales (Kristiansen et al. fluences, with particular reference to the 1994). Thus, L. nigrescens should not be 1982/83 ENSO. In A I. L. Payne, K. H. considered a potential indicator species of Brink, K. H. Mann, and R. Hilborn, eds. surface-water heating during global warming Benguela trophic functioning. S. Mr. J. events in northern Chile. The disappearance Mar. Sci. 12: 703-712. of populations might reflect slight variations DiAz, M. 1984. Distribuci6n de fosfatos, ni in the temperature of water masses, but tratos y nitritos en una secci6n frente a occurring over a very short period of time. Iquique (200 16' S), Diciembre 1982. In Conversely, the time scale at which global vest. Pesq. 31: 103-108. warming might occur is considerably longer GERARD, V. A. 1997. The role of nitrogen (Lubchenco et al. 1993), and some level of nutrition in high-temperature tolerance of physiological accommodation would be ex the kelp, Laminaria saccharina (Chromo pected. But phenotypic acclimation is possi phyta). J. Phycol. 33: 800-810. ble on very short time scales. GUNNILL, F. C. 1985. Population fluctua tions of seven macroalgae in southern California during 1981-1983 including ACKNOWLEDGMENTS effects of severe storms and El Nino. J. Exp. Mar. BioI. Ecol. 85: 149-164. I appreciate funding provided by grants HOFFMANN, A J., and P. CAMUS. 1989. Sink from UNESCO COMAR/COSALC-VII, ing rates and viability of spores from ben FONDECYT (612-91, 2930016, 4940012), thic algae in central Chile. J. Exp. Mar. and DIUC (95-l5E). Temperature records BioI. Ecol. 126:281-291. for localities were kindly provided by Raquel KRISTIANSEN, A, P. M. PEDERSEN, and L. Pinto (Iquique), Dr. Juan Carlos Castilla MOSEHOLM. 1994. Salinity-temperature (Las Cruces), and Alejandro Buschmann effects on growth and reproduction of (Mehuin). I greatly appreciate the use of Scytosiphon lomentaria (Fucophyceae) their facilities during my sampling at the along the salinity gradient in Danish three localities along the Chilean coast. Dis waters. Phycologia 33: 444-454. cussions with my thesis advisor, Dr. Bernabe LUBCHENCO, J., S. A NAVARRETE, B. N. Santelices, and with Patricio Camus were TISSOT, and J. C. CASTILLA. 1993. Possible also important. ecological responses to global climate change: Nearshore benthic biota of north eastern Pacific coastal ecosystems. Pages LITERATURE CITED 147-166 in Earth system responses to BREEMAN, A M. 1988. Relative importance global change: Contrasts between North of temperature and other factors in de and South America. Academic Press. termining geographical boundaries of sea LUNING, K., and W. FRESHWATER. 1988. weeds: Experimental and phenological Temperature tolerance of Northeast Pa evidence. Helgol. Meeresunters. 42: 199 cific marine algae. J. Phycol. 24: 310-315. 241. PAKKER, H. A, A. M. BREEMAN, W. F. CAMUS, P. A., E. o. VASQUEZ, E. O. GONZA PRUD'HOMME VAN REINE, and C. VAN DEN LEZ, and L. E. GALAZ. 1994. Fenologia HOEK. 1995. A comparative study of tem espacial de la diversidad intermareal en el perature responses of Caribbean seaweeds norte de Chile: Patrones comunitarios de from different biogeographical groups. variaci6n geognifica e impacto de los J. Phycol. 31 :499-507. procesos de extinci6n-recolonizaci6n post PETERS, A. F., and A M. BREEMAN. 1992. El Nino 82/83. Medio Ambiente 12:57 Temperature responses of disjunct tem 68. perate brown algae indicate long-distance Thermal Tolerance in Lessonia nigrescens-MARTlNEZ 81

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