Phycologia(1984) Volume 23 (3),357-367 Photoperiodicand temperatureresponses in the reproductionof north-easternAtlantic Gigartinu acicularis (Rhodophyta:Gigartinales) M.D. Gunv aNo E.M. CuNNrNcneu Department of Botany, University College, Galway, Ireland M.D. Gurnv eNo E.M. CuNNrNcn,qu(1984) Photoperiodic and temperature responsesin the re- production ofnorth-eastern Atlantic Gigartina acicularis (Rhodophyta: Gigartinales).Phycologia 23:357-367. Gigartina acicularis (Roth) [.amour., a predominantly intertidal red alga,has only rarely been found with reproductive structuresin the British Isles and northern France.Elsewhere in the north-eastern Atlantic, reports of cystocarpic plants are largely from November to February while those of tet- rasporangialplants are from July to October. Male and female plants formed gametangiaonly at daylengthsof 12 h or lessand at temperaturesof 14-18"C.Photon exposures>1.5 mmol m 2 of incandescentlight, given in the middle of a 16 h dark period at l6.C, completely inhibited cystocarp formation, although some carpogonial brancheswere formed at up to 3.34 mmol m 2. Five pho- toperiodic cycles of 8:16 h at 16oCwere the minimum necessaryto induce the formation of car- pogonial branchesand cystocarps.Carpospores gave rise to plants which formed tetrasporangiaat daylengthsof 16,12, l0 and 8 h at 16'C. The precisephotoperiodic and temperaturerequirements for gametangialreproduction in G. acicularis result in gameteformation being limited to autumn in north-easternAtlantic populations.It is suggestedthat, in the northern part ofits range,populations of G. acicularis are largely maintained by vegetative propagation. As one goes further south the gametangialreproductive 'window' gradually enlargesdue to higher ambient temperaturesin the autumn. The paucity ofrecords oftetrasporangial plants in the British Isles,however, needsfurther investigation. This is the first report ofphotoperiodic control ofgametogenesisin the Rhodophyta and the responsewould appear to be true and absolute. INTRODUCTION lantic will not hybridize. These difficulties of identification have been compounded by the vir- Gigartina acicularis (F.ot}r) Lamouroux [see Dix- tual absence of reports of reproductive material on and Irvine (1977) for changein nomenclaturel of G. aciculans, particularly in the north-eastern (Rhodophyta) is a narrow, terete to slightly flat- Atlantic. In the British Isles cystocarpic plants tened, sparingly branched species found in in- have apparently been found only once (Devon tertidal or shallow subtidal habitats in the At- in January 1829; material in BM) and records of lantic and the Mediterranean. It grows most tetrasporangial plants are also very rare (Galway commonly on rocks in sheltered, silty situations, Bay, November 1966; material in GALW). Else- where it often forms conspicuous turfs. In the where in the eastern Atlantic reproductive rec- Atlantic the species has been reported from the ords for G. acicularis are as follows: Gayral ( I 966) British Isles south to Cameroun and from North reported cystocarpic plants from November to Carolina south to Uruguay (Dixon & Irvine 1977). February on the north coast ofFrance; Seoane- Some difficulties have been experienced in dis- Camba (1965) found cystocarpic plants in Jan- tinguishing between certain forms of this species uary and February on the north coast of Spain, and G. teedii (P.ott') Lamouroux, a species with and tetrasporangial plants in July, August and a similar geographical distribution in the north- September; in Portugal, Ardr6 (1969) collected eastern Atlantic. Forms intermediate in mor- tetrasporangial plants in October but did not re- phology have frequently been reported (Harvey port any other reproduction; Gayral (1958) re- 1833;Gayral 1958; Hoek & Donze 1966; Dixon ported cystocarpic plants from August to March & Irvine 1977),but Guiry (1984) has shown that on the coast of Morocco. In the British Isles, cultured plants of these two species from the At- casual examination of populations by one of us 357 358 Phycologia, Vol. 23 (3), 1984 (M.D.G.) over the past decade has revealed not modiflcation in Mclachlan (1973) except that a single fertile plant. Cystocarpic and tetraspo- the disodium glycerophosphate concentration was rangial plants were, however, common at Sines reducedby halfl. Due to a bacterial contaminant, and Sagres, Portugal in January 1977, and cys- a spore-forming Bacillus specieswhich now seems tocarpic plants were abundant at La Toja, Gal- to be common in many laboratories culturing icia, Spain in January 1978. The available phe- marine algae, and which is resistant to a wide nological data on the formation of cystocarps in range of antibiotics (West & Guiry unpubl. data), G. acicularis suggested a photoperiodic response plants were later grown in a modification of Von similar to that described by Liining ( I 9 80, I 9 8 I a, Stosch's medium (VS). Our VS is composed of 198lb) for the formation of tetrasporangia in the equal volumes of the following stock solutions Trailliella-phase of Bonnemaisonia hamifera (all in 500 ml glass-distilled water): 21.26 g Hariot. Llsing cultured plants isolated from the NaNOr; 2.68 g Na, or-beta-glycerophosphate; north coast of France and from the south coast 0.139 g FeSO.'7HrO; 0.98 g Mn Clr'4HrO; 1.86 of England we here attempt to explain the re- g Naz EDTA'2H'O;0.05 g Biotin; and 0. I g productive periodicity of G. acicularls and the Aneurine HCI and 0.2 mg Vitamin B,r. Two me- lack of records of reproductive plants from the dia types are made up from this stock solution: British Isles. A preliminary account of this study haltstrength VS, to which l0 ml of VS solution was given in Guiry and Cunningham (19E3). is added to each litre of sterilized seawater and quarter-strength, to which 5 ml is added. The absence of a TRIS buffer in VS may help to re- MATERIALS AND METHODS duce bacterial contamination (cf. van der Meer I 982). Initial attempts to isolate Gigartina acicularis Photon flux densities were measured using a into culture using plants collected in January in LI-COR Model 185-8 meter and a LI-I90SB Portugal (1977) and Spain (1978) were unsuc- quantum sensor. Light sources were directly cessful owing to necrosis (cf. West & Guiry 1982, above the cultures and reflected light from the p. 206), which is enhanced by the use of full- sides and bases ofthe culture cabinets was taken strength, enriched seawater media. Tetrasporan- into account in all measurements. Fluorescent gial plants of Gigartina acicularis were collected light was provided by cool-white 65180 W tubes; in the lower intertidal at Santec, a few kilometres incandescent light was provided by 60 W house- west ofRoscoff, on the north coast ofFrance on hold tungsten bulbs. Temperature was measured l5 September 198 1. Cultures (isolate 382) were using nickel-chromium/nickel-aluminium ther- established from tetraspores released overnight mocouples immersed in 250 ml distilled water. at room temperature (approx. 15'C) and inocu- (This was the volume ofthe culture medium used lated onto glass slides using a fine Pasteur pipette. in the temperature experiments.) In all studies The plants were initially grown in a north-facing temperature is expressed as the variation found window at the Station Biologique de Roscoffwith in these volumes of water. frequent changes of unenriched sterile seawater. A preliminary study of a field population of The resulting sporelings were transported to Ire- Gigartina acicularis atNew Quay, Co. Clare, Ire- land in a cooled container. Additionally, plants land (53"09.5'N, 9o05'W) was carried out from were isolated vegetatively from G. acicularis September 1982 through April 1983. The site populations from mid-intertidal pools at I(im- was visited at fortnightly intervals. Plants were meridge Ledges, Dorset, UK in April 198 1 (iso- sampled haphazardly within a 0.025 m'z fixed late 371). Whole plants were transported to Ire- quadrat. These samples were examined micro- land in sterilized seawater in a cooled container. scopically in the laboratory for reproduction. Growing tips were excised and cultured in en- Seawater temperatures were taken at the turn of riched seawater at low photon flux densities (3- the tide. 2 5 rrmol m s-t) at 16 + 1'C, 16:8 h until the Seawater temperatures for the period 1974- plants were free of algal contaminants. 1981 were obtained from the Shellfish Research Plants were grown in several types ofenriched- Laboratory, Carna, Co. Galway, which is about seawater media throughout this study but for 75 km due west of the New Quay site. Temper- each experiment the medium type was standard. ature is continuously recorded at the intake point Initially, plants were grown in quarter-strength for the Laboratory's seawater pumps. Daylength Provasoli's Enriched Seawater [PES; West's readings were obtained for Shannon Airport, Co. Guiry and Cunningham: Gigartina acicularis 359 Clare which is about 70 km south of the study continuously. Male and female plants were iso- site. lated into separate culture for further investiga- tion of the photoperiodic response. Effects of temperature on cystocarp RESULTS formation Growth of plants in culture Stock cultures of male plants of isolate 382 from Franceweremaintainedat l6 + 1'C, 8: l6 h, 20 Vegetativeplants from Britain (isolate371) grown pmol m-2 s-r, and female plants were grown at in full-strength media becamegreen distally and 16 + 1"C, 16:8 h, 20 pmol m-2 s-t, for at least ultimately died. Eventually, it was found that one month beforehand. Under these conditions quarter-strengthPES or VS would support the males formed an abundance of spermatia and A single vegetative plant was isolated $owth. the females did not form carpogonial branches. which when 25-30 mm long grew at 5-7 mm per Each experimental culture dish contained one weekat 16 + 1'C, t6:8 h, 20-25p.molm-2 s-1. pretreated male and flve pretreated female plants. Plantsgrown from this isolate did not reproduce The dishes were then placed at 8:16 h, 20-30 over a period of 8 months under these condi- pmol m-2 s 1,at each of the temperatures shown tions.