Culture studies on some Florida species of Caulerpa: Morphological responses to reduced illumination

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1 British Phycological Journal ISSN: (Print) (Online) Journal homepage: Culture studies on some Florida species of Caulerpa: Morphological responses to reduced illumination Harry E. Calvert To cite this article: Harry E. Calvert (1976) Culture studies on some Florida species of Caulerpa: Morphological responses to reduced illumination, British Phycological Journal, 11:3, , DOI: / To link to this article: Published online: 17 Feb Submit your article to this journal Article views: 299 View related articles Citing articles: 19 View citing articles Full Terms & Conditions of access and use can be found at

2 Brit. phycol. J. 11: September 1976 CULTURE SPECIES OF RESPONSES STUDIES ON SOME FLORIDA CAULERPA: MORPHOLOGICAL TO REDUCED ILLUMINATION By HARRY E. CALVERT* Department of Biology, University of South Florida, Tampa, Florida 33620, U.S.A. The morphological development of three species of Caulerpa, C. sertularioides, C. paspaloides and C. racemosa has been studied in low light culture. The resulting morphologies are described and contrasted with the typical morphologies. Culture forms in all cases were unlike the field forms but each had affinities with other taxa described in the literature. The most important generalized response was a change in the symmetry of the assimilators from radial to bilateral. This response supports an earlier morphologically based theory on the evolutionary relationships among the species of Caulerpa. Caulerpa Lamouroux is a genus composed of many diverse forms, with the same basic morphological scheme common to all species (Fritsch, 1935). The thallus consists of a prostrate stolon which bears branched attaching rhizoids below and erect branches (assimilators) above. The assimilators usually bear numerous determinate branchlets termed ramuli. The range in morphology of the assimilators is probably as broad in Caulerpa as in any algal genus (Borgesen, 1907). Infraspecific variation in morphology is common. Assimilators of some species are so morphologically plastic that transitional forms can be recognized between species. Presence of these intermediate forms makes the boundaries delimiting certain species of Caulerpa uncertain (Gilbert, 1941). The first detailed studies attempting to relate environmental influence to the morphology of Caulerpa were those of Svedelius (1906) and Borgesen (1907). Both stressed the need for knowledge of the relation between habitat and morphological organization. They concluded that all species of Caulerpa could be categorized according to substratum, exposure, and depth preference. Svedelius and Borgesen categorized the development of assimilators into two major groups, the bilateral leaf-like species and the radial species. Bilateral species have ramuli in two opposite ranks on the assimilators giving them a distichous appearance, and in some cases superficially resembling higher plant leaves or fern fronds. The radial species have assimilators with ramuli placed in many directions around the central axes. While this dichotomy adequately characterizes the majority of Caulerpa species, there are a few which do not fit either category. For example, C. flexilis Lamouroux has distichous lateral branches which in turn bear radially placed ramuli. When the habitats of several members of each group were compared, several generalizations were apparent (Svedelius, 1906). Most radial species have their main distribution just below the eulittoral zone. They are more commonly * Present Address: Department of Botany, University of Adelaide, Adelaide, South Australia A 203 Published online 17 Feb 2007

3 2~ H.E. CALVERT members of the lithophytic substratum group and show a preference for high light intensities. Svedelius compared plants of this group growing at different depths (i.e., in different light intensities) and found a tendency for the deeper forms to have longer, thinner assimilators. The bilateral species, in contrast, were observed to have their main distribution in deeper, quieter waters. Svedelius considered that bilateral symmetry is an adaptation to low light conditions, providing a greater surface area which would be more efficient in receiving the diminished light. Later studies have emphasised the importance of environmentally controlled morphological variation (Cribb, 1958; Nizamuddin, 1964; Lipkin, 1973) and transplantation studies have demonstrated it (Tandy, 1934; Rehm, 1969). Factors such as light intensity and degree of water movement have been mentioned in several ecological studies as possibly influencing morphological form (Svedelius, 1906; Borgesen, 1907; Nizamuddin, 1964; Cribb, 1958). Dostal (1946) found that C. prolifera assimilators assumed a thread-like growth form when kept in the dark. Other field and laboratory studies have indicated that the major morphological characters used for differentiation of forms of C. prolifera are significantly influenced by light intensity (Barilotti, 1970). Nasr (1947) cultured C. serrulata and C. racemosa var. clavifera with lower light intensities than typical of their natural habitat. Growth in culture indicated that characters such as the spiral and dentation of C. serrulata assimilators, and radial assimilator symmetry of C. racemosa, are environmentally influenced. If the morphological limits and taxonomy of species in the genus are to be better understood, the range of plasticity must be defined. While engaged in a cytological survey of Caulerpa (Calvert, Dawes & Borowitzka, 1976) the author maintained several species in culture. This paper reports the results of these low light intensity cultures on certain species of Caulerpa from Florida. As the purpose of these cultures was not directed towards morphological variation, no high light control cultures were done. MATERIALS AND METHODS Observations on morphological changes were made on five taxa: C. racemosa var. macrophysa (Kiitzing) Taylor, C. racemosa var. uvifera (Turner) Weber-van Bosse, C. sertularioides f. brevipes (J. Agardh) Svedelius, C. sertularioides f. farlowii (Weber-van Bosse) Borgesen, and C. paspaloides (Bergesen) Greville. Specimens of C. racemosa and C. sertularioides were obtained from inshore waters off the northwest end of Knight's Key, Monroe County, Florida. C. paspaloides was collected near the east swimming beach of Bahia Honda State Park, Monroe County, Florida. Light intensities at the collecting sites were measured with a Sekonic Auto-Lumi Model 86 exposure meter and converted to footcandles with a General Electric conversion scale. Footcandles were then converted to lx using a conversion factor of 1 footcandle = 10"76 Ix. The plants were cleaned of foreign matter and placed in sea water holding tanks, while the morphology of each taxon was examined and photographed. Some plants were established in culture and others were preserved in 5 ~ formaldehyde in seawater for later comparison. The culture apparatus consisted of 40 or 801 glass aquaria fitted with subsand aeration filters covered with a layer of limestone rock. Overhead illumination was provided by Grolux fluorescent lights with a 14/10 h photoperiod. Plants were grown at 24 C in Seven Seas Saltwater medium without nutrient supplement. Samples of all taxa were cultured simultaneously in each vessel. Based on preliminary field and culture observations made during the preceding two years, cultures were maintained for different periods under two distinct light regimes: (i) 35 days at a light intensity of 1350 Ix, and (ii) 100 days at 650 Ix. At the end of each culture period the plants were photographed and preserved for study.

4 Culture studies on Florida Caulerpa 205 FIELD OBSERVATIONS THE KNIGHT'S KEY COLLECTING SITE The substratum of this area is composed of limestone outcroppings with scattered sand patches which support a rich algal flora. Water depth ranges from 0.5 to 1 m with some outcrops just emergent at low tide. Water movement at the site is dominated by the strong Florida current, but the water directly overlying the site is relatively still due to an eddy current generated by the massive water flow around the point. This backwash causes the water to be moderately turbid resulting in a lowered light intensity. The midday light intensity was 3,200-4,300 Ix. The occurrence of mixed limestone and sand substrates resulted in the presence of both lithophytic and psammophytic species of Caulerpa at the Knight's Key site. C. racernosa var. rnacrophysa and var. uvifera were found growing atop the limestone outcroppings near the boundary between the eulittoral and sublittoral zones, where they were slightly emergent at low tide. The growth habit of var. macrophysa is such that it forms large dense mats, with the short assimilators difficult to recognize. Var. uvifera however has a less dense growth habit and its assimilators are more erect and distinct. The two varieties were found growing with one another, suggesting that they might be variable forms of the same plant. However, careful examination always revealed the two assimilator forms to be on separate plants. C. sertularioides f. brevipes and f. farlowii grew on sand patches between the limestone outcroppings or occasionally on the outcrops. They rarely attached directly to the rock but grew along the top of sponge which covered it. The majority of the C. sertularioides growing at this site was f. brevipes, with f. farlowii being much less abundant. Specimens of C. racemosa and C. sertularioides, collected in May for use in the 1350 lx culture experiment, appeared healthy and actively growing. Specimens collected in August were in poorer condition probably due to the higher water temperature (28 C vs 21 C). THE BAHIA HONDA COLLECTING SITE The sand substratum of this area supports a typical tropical Atlantic psammophytic algal community (Taylor, 1960). The depth is 1-2 m and water movement is slight to moderate. Light intensities varied with wave action as wind driven waves brought sand into suspension. Intensities were Ix. Healthy specimens of C. paspaloides were found growing on sand in and around beds of Thalassia testudinum Banks ex K6nig. CULTURE RESULTS The morphological development of Caulerpa in low light showed several features common to all species studied. The frequency of rhizoid and assimilator initiation was reduced, and the rhizoidal system was generally poorly developed presumably due to the lack of water movement in culture. Assimilator development in low light showed characteristics of an etiolated condition, with upright axes becoming elongate, by developing lengthened internodes. Ramuli development was analogous to that in the field for most taxa but was reduced in C.

5 206 H.E. CALVERT racemosa. From a systematic viewpoint the most significant response of Caulerpa development in reduced light was change in symmetry of new assimilators. C. racemosa var. macrophysa (Kiitzing) Taylor Taylor, 1960, p. 153, P1. 17, Fig. 1. Assimilators ofvar, macrophysa are 1-3 cm tall and bear uncrowded imbricate ramuli as opposite pairs. The ramuli consist of a 1-2 mm stalk which supports an abruptly expanded, swollen, subspherical to obconical apex, attaining a diameter of mm (Fig. 1). The first noticeable growth response in the 1350 lx culture occurred after a 2-3 day lag period typical for Caulerpa in culture (Chen & Jacobs, 1968). Growth was initiated in several ways. New stolon growing tips were initiated from the stolon, from assimilator central axes, or from ramuli. Stolon initiation directly from the old stolon was most common and accounted for most of the new stolon growth. The total amount of new stolon growth at the end of 35 days averaged 15 cm. This rate corresponds closely with the 0-4 cm per day observed for C. sertularioides (Mishra & Kefford, 1969). New assimilators developed either as outgrowths of old assimilators or directly from the new stolon, however, initiation of assimilators in culture was never observed from field stolon. The morphology of cultured assimilators showed marked differences from that of field plants (Figs 2, 3). They were commonly more elongate (2-6 cm) with ramuli less regularly placed on the central axes. The radial symmetry typical of the field form persisted. Ramular length remained consistent with field material at 4-5 mm but the abrupt large apical swelling was markedly reduced. Culture ramuli were subcylindrical to clavate with moderately expanded, rounded apices characteristic of C. racemosa var. laetevirens (Montagne) Weber-van Bosse (Weber-van Bosse, 1898, p. 366). At 650 lx, var. macrophysa showed no new growth for 7-14 days. Stolon and rhizoid initiation and development followed the pattern described above at 1350 lx. Few new assimilators developed at 650 Ix and some culture stolons bore none. The assimilators initiated in culture showed marked elongation of up to 10 cm (Figs 4-7). More importantly, the ramular placement did not remain radial but became bilateral with opposite ramuli spaced at 5-7 mm intervals (Figs 5, 7). The ramuli were 2-4 mm long, subcylindrical to clavate with an expanded apex, 1-2 mm in diameter. Several of these assimilators (e.g. Fig. 5) correspond to C. racemosa var. lamourouxii (Turner) Weber-van Bosse (Weber-van Bosse, 1898, p. 368). A few assimilators also showed a tendency toward placement of ramuli on only one side of the central axes (Figs 4, 6). This pattern has been described as vat. lamourouxii f. intermedia Taylor (Taylor, 1960, p. 64). C. racemosa var. uvifera (Turner) Weber-van Bosse Weber-van Bosse, 1898, p. 362, P1. XXXIII, Figs 6, 7, 23; Svedelius, 1906, p. 122, Fig. 15. Assimilators of var. uvifera are 2-5 cm tall bearing crowded, radially placed imbricate ramuli. Ramuli low on the main axis are 1-3 mm long and gradually

6 Culture studies on Florida Caulerpa 207! I Icm '1, cm J 4!5 I ClTI FIGS 1-7. Assimilators of C. racemosa var. macrophysa. Fig. 1. A portion of a plant from Knight's Key showing the natural growth habit. Figs 2, 3. Assimilators grown in culture at 1350 Ix. Note the elongated central axis, reduced ramular swelling, and the retention of radial symmetry. Figs 4-7. Assimilators grown in culture at 650 Ix. Note the bilateral symmetry of ramular initiation. Occasionally the ramuli were limited to one side of the rachis.

7 208 H.E. CALVERT I FIGs Assimilators of C. racemosa var. uvifera. Fig. 8. The natural growth habit of var. uvifera. The ramuli are somewhat underdeveloped probably due to the water turbidity at the Knight's Key collecting site. Figs Assimilators which developed in culture at 650 Ix. These have similar morphologies to var. macrophysa from 1350 Ix culture, but unlike the latter retained radial symmetry at the lower light intensity. FIG. 11. C. sertularioides f. farlowii maintained in culture at 1,350 lx for 1 week. The lower portion of the assimilator with radial symmetry is the normal field morphology while the upper portion with distinct bilateral symmetry developed in culture. FIGS Assimilators of C. sertularioides f. brevipes. Figs 12, 13 are growth responses in culture at 1350 ix. The field morphology of f. brevipes is shown in Fig. 14.

8 Culture studies on Florida Caulerpa 209 enlarge to a rounded apex, mm in diameter. Those above are obconically expanded to a rounded subspherical apex, 2-3 mm in diameter (Fig. 8). Specimens of var. uvifera cultured at 1350 lx showed no new growth and died within two weeks. When grown at 650 lx plants remained healthy and new segments developed. Assimilator initiation in culture was irregular with only two or three developing on each new stolon. These were 5-8 cm tall with radially placed ramuli spaced 2-5 mm apart (Figs 9, I0). The ramuli were cylindrical, 3-5 mm long with rounded, occasionally slightly expanded apices. These assimilators bore a marked resemblance to the culture development of var. macrophysa assimilators at 13501x. It is significant that while new assimilators of var. uvifera retained radial symmetry at 650 lx (Figs 9, 10), those of var. macrophysa developed bilaterally (Figs 5, 7). C. sertularioides f. brevipes (J. Agardh) Svedelius Svedelius. 1906, p. 114, Figs 7, 8; Taylor, 1960, p. 144, PI. 13, Figs 2, 3. Assimilators of f. brevipes are 1-5 cm tall and bear distichous ramuli from the base, forming a flat pinnate blade 8-10 mm wide. The terete ramuli may be opposite or subopposite, curving upwards to mucronate apices. The assimilator margins are parallel and the apex is characteristically blunt (Fig. 14). Cultures of C. sertularioides f. brevipes responded similarly at both 1350 and 650 Ix. Culture assimilators were initiated on the new stolon at much larger intervals than in nature. Field specimens averaged one assimilator per centimetre while in culture the frequency was reduced to one per 5-7 cm. The length of the assimilators increased in culture to cm with a naked stalk below the ramuli varying from cm in length (Figs 12, 13). The central axes occasionally forked in the stalk region or sometimes bore proliferations from the ramular region. Culture ramuli were very fine ( mm diameter) and sometimes shortened resulting in a varying assimilator width of 4-7 mm. Those at the base of the assimilator tended to be longer than above, causing a tapering of the assimilator margin (Fig. 13). The characteristic blunt apex of field specimens was lost. This culture form is similar to f. Iongiseta (Borgesen) Svedelius (Svedelius, 1906, p. 114). In a few instances the central axis of the assimilator extended apically 1-3 cm past the last ramule (Fig. 12). This variation has also been described in the literature as C. plumaris f. flagellata Weber-van Bosse (Weber-van Bosse, 1898, p. 295). C. sertularioides f. farlowii (Weber-van Bosse) Borgesen Borgesen, 1907, p. 365, Fig. 11; Taylor, 1960, p. 144, Pl. 13, Figs 4, 5. The assimilators are 1-4 cm high with ramuli like f. brevipes but radially disposed and crowded on the central axes producing a cylindrical rather than flattened form (Fig. 11). Formfarlowii was included only in the 1350 Ix culture experiment for it was not found during the second collection. Growth response of this form (the only form of C. sertularioides with radially placed ramuli) showed a marked tendency to change symmetry of ramular initiation from radial to bilateral

9 210 H.E. CALVERT (Fig. 11). The culture morphology of f. farlowii closely matched that brevipes in culture. of f. C. paspaloides (Bory) Greville Greville, 1830, p. lxiv; Taylor, 1960, p. 149, PI. 16, Fig cm A, 3 cm A B FIGS 15, 16. Assimilators of C. paspaloides. Fig. 15(A). The field morphology of an assimilator from the Bahia Honda collecting site. Note that the foliar branches bear three ranks of ramuli. (B). A transverse section of a foliar branch revealing the tri.. stichous ramuli (mag. 5 x A). Fig. 16(A). An assimilator grown in culture at 650 Ix. Note that the foliar branches have produced only two sets of ramuli. (B). A transverse section of a foliar branch showing the distichous ramular arrangement (mag. 2 A).

10 Culture studies on Florida Caulerpa 211 The assimilators of C. paspaloides consist of a basal stipe 3-5 cm long, occasionally dichotomously branched. The stipe apex is palmately forked giving rise to four to six foliar branchlets. Each foliar branchlet is 5-7 cm long and is beset with three rows of ramuli. The ramuli are about 3 mm long and spaced at mm intervals. Each bears simple or dichotomously branched, biseriate pinnae (Fig. 15). The developmental responses of C. paspaloides assimilators were similar at 1,350 and 650 Ix. Culture assimilators reached an overall height of cm or two to three times that of the field material (Fig. 16). The basal stipe elongated to 8-15 cm and forked irregularly above, one to three times. The forking pattern varied from a simple dichotomy to digitate, producing from two to four sets of foliar branchlets on a single assimilator. Each set of palmate foliar branchlets consisted of two to four branchlets, each 7-12 cm long and mm wide. Unlike the field form, each foliar branch developing in culture produced only two sets of ramuli [Fig. 16(B)]. The change from tristichous to distichous placement of ramuli constitutes a transition from radial to bilateral symmetry. Occasionally the development of a foliar branchlet was initiated with tristichous ramular placement but this always changed to the bilateral form as development continued. Ramuli were 5-9 mm long and varied in arrangement on the central axis of the foliar branchlet from opposite to alternate. Each bore simple unilateral ultimate branchlets or pinnae on the upper side. The pinnae were normally biseriate below but above became uniseriate. This culture form corresponds with the description of C. paspaloides var. wurdemannii Weber-van Bosse (Weber-van Bosse, 1898, p. 353). DISCUSSION Change in the symmetry of ramular placement is an important developmental response from an evolutionary standpoint. Svedelius (1906) and Borgesen (1907) considered that assimilator symmetry is of significance in understanding the evolutionary relationships in Caulerpa. They suggested that the genus originated in shallow water, with the most primitive species, having radially symmetrical assimilators and being adapted to relatively high light intensities. Caulerpa is thought to have evolved into deeper water from the lower eulittoral and upper sublittoral zones. In adapting to the lower light environment, the assimilators of later species developed bilateral symmetry. Present observations agree with earlier studies which described Caulerpa as having a plastic assimilator morphology (Weber-van Bosse, 1898; Eubank, 1946; Svedelius, 1906; Borgesen, 1907; Fritsch, 1935; Gilbert, 1941; Taylor, 1960), and agree with other reports suggesting that light intensity is an important causal factor in the observed variation (Tandy, 1934; Nasr, 1947; Nizamuddin, 1964; Rehm, 1969; Barilotti, 1970; Lipkin, 1973; Peterson, 1972). The results of this study support the Svedelius hypothesis by demonstrating that certain radial taxa of Caulerpa have the potential to change to bilateral assimilator symmetry when placed in a low light environment. Such a developmental transition has been observed in C. sertularioides f. farlowii, C. paspaloides, and C. racemosa var. macrophysa.

11 212 H.E. CALVERT The responses of C. sertularioides to reduced light is illustrative of the trend in developmental assimilator change. Development of assimilators resembling f. longiseta on f. brevipes plants suggests that the morphological differences between the two taxa are environmentally controlled. Svedelius (1906) reported both f. brevipes and f. longiseta from Ceylon. In describing the habitat of f. brevipes he stated, "a common littoral form at the surface of the water and seems to prefer spots somewhat exposed". Regarding f. longiseta he wrote, "it occurs scarcely ever if at all in the upper part of the littoral zone, but usually in somewhat deeper water". The culture results correlate with these field observations and suggest that light intensity affects these form changes. Thus, the current taxonomic recognition of these two taxa at the form level seems justified. The transition to bilateral symmetry of C. sertularioides f. farlowii suggests that this radial form is adapted to a relatively high light intensity. The apparent environmental control of the radial symmetry of f. farlowii seemingly supports its position at the form level. However, this taxon is found growing in the same habitats, occasionally as separate plants in the same mats, with bilateral forms of C. sertularioides. Indeed in this study both f. farlowii and f. brevipes were collected from the same habitat. This suggests that although f. farlowii has a range of morphological variation which overlaps that of the other forms, the overlap is not complete. Formfarlowii has an extended range of morphological variation, and probably a different genetic potential than the other form of C. sertularioides. This difference is not reflected in the current recognition of the taxon as a form, since subspecies and varieties are usually associated with inheritable differences whereas forms are normally associated with environmentally caused differences of a minor nature (Porter, 1967). It is proposed to elevate f. farlowii (Weber-van Bosse) Borgesen (Borgesen, 1907, p. 365, Fig. 11) to var. farlowii (Weber-van Bosse) comb. nov. as this better describes its relation with the other taxa of C. sertularioides. The presence of this radial variety in the otherwise bilateral C. sertularioides may indicate that var. farlowii is the most primitive taxon in the species. If so, it is a possible link between the primitive radial species of Caulerpa and the bilateral forms of C. sertularioides. Symmetry change in reduced light was also marked for C. racemosa var. macrophysa. While remaining radial at 1,350 Ix, ramular placement became bilateral at 650 Ix. The development of var. macrophysa assimilators near var. lamourouxii emphasizes the close relationship between these two taxa. When Taylor (1928) elevated C. racemosa var. clavifera f. macrophysa (Kiitzing) Weber-van Bosse to var. macrophysa, he observed that the nearest related taxon is var. lamourouxii. Present results suggest that the two may be more closely related than presently indicated. Further culture experiments especially with var. lamourouxii in higher light intensities are needed to better evaluate this possibility. Retention of radial symmetry by C. racemosa var. uvifera in low light intensity is inconsistent with earlier studies. Nasr (1947) and Peterson (1972) reported transitions of the typical radial assimilators to bilateral ones resembling var. lamourouxii. Both of these studies used plants from the Indo-Pacific population of var. uvifera. The author has also observed the same transition to bilateral

12 Culture studies on Florida Caulerpa 213 symmetry in culture with var. uvifera from the Red Sea (unpublished data). This inconsistency suggests an evolutionary difference between the Red Sea- Indo-Pacific population of C. racemosa var. uvifera and its Atlantic population. Such a difference is not altogether surprising, for the fits of several Caulerpa taxa between these two large populations are not always exact (Taylor, 1967). The morphological observations presented here support the Svedelius hypothesis on the origin and evolutionary direction of Caulerpa. They demonstrate that some of the radial species do have the potential for change in assimilator morphology to bilateral symmetry. Thus, if Caulerpa originated as radial forms in shallow water, the bilateral forms could have developed as the genus extended its range sublittorally. Recently a phylogenetic tree (based on organellar ultrastructure) has been developed for Caulerpa (Calvert et al., 1976) and this further supports Svedelius by correlating primitive chloroplast characters with radial species and more advanced chloroplast characters with bilateral species. ACKNOWLEDGEMENTS This work is based on a portion of a thesis submitted to the Deparment of Biology, University of South Florida, in partial fulfilment of the requirements for the Ph.D. I wish to thank Dr Clinton J. Dawes for supervising and encouraging the work. I am also grateful to Professor H. B. S. Womersley for aiding in the determination of C. racemosa var. macroph.vsa and for critically reading the manuscript. Thanks are also due to Judy Mason and Cheryl Anderson for completion of the illustrations. Preparation of the manuscript was supported by the Department of Botany, University of Adelaide, South Australia. REFERENCES BARILOVrl, D. C., Non-genetic morphological variation in Caulerpaprolifera (Forssk~.l) Lamouroux. M.S. Thesis, University of South Florida. 62 pp. BORGESEN, F., An ecological and systematic account of the Caulerpas of the Danish West Indies. K. danske Vidensk. Selsk. Skr., Ser. VII. Naturvid. og Math. AJd.,4: CALVERT, n. E., DAWES, C. J. BOROWITZKA, M. A., Phylogenetic relationships of Caulerpa (Chlorophyta) based on comparative chloroplast ultrastructure. J. Phycol., 12: (in press). CHEN, J. C. W. & JACOBS, W. P., The initiation and elongation of rhizoid clusters in Caulerpa prolifera. Am. J. Bot., 55: CRmB, A. B., Records of marine algae from south-eastern Queensland, IV. Caulerpa. Dept. Bot. Univ. Qd., 3: DOSTAL, R., Morphogenetic studies on Caulerpa prolifera. Bull. int. Acad. tchdque. Sci., 46: EUaANK, L. L., Hawaiian representatives of the genus Caulerpa. Univ. Calif. PubL Bot., 18: FRITSCn, F. E., The Structure and Reproduction of the Algae. Vol. 1. University Press, Cambridge, 791 pp. GILBERT, W. J., Notes on Caulerpa from Java and the Philippines. Pap. Mich. Acad. Sci., 27: 'GREVILLE, R. K., Algae Brittanicae. Maclachlan & Stewart, Edinburgh. LIpKrN, Y., Ecological distribution of Caulerpa in the Red Sea. J. mar. biol. Ass. India, 15: MISHRA, A. K. & KEFFORD, N. P., Developmental studies on the coenocytic alga, Caulerpa sertularioides. J. PhycoL, 5: NASR, A. H., Synopsis of the marine algae of the Egyptian Red Sea coast. Bull. Fac. Sci., Eg)pt. Univ., 26: NIZAMUDDIN, M., Studies on the genus Caulerpa from Karachi. Botanica mar., 6 (3-4): PETErtSON, R. D., Effects of light intensity on the morphology and productivity of Caulerpa racemosa (Forssk~l) J. Agardh. Micronesica, 8: PORTER, C. L., Taxonomy of flowering plants. 2nd edn., W. H. Freeman, San Francisco, 472 pp.

13 214 H.E. CALVERT REHM, A. E., The biology of Caulerpa racemosa (Forssk~tl) J. Agardh. in Puerto Rico. M.Sc. Thesis, University of Puerto Rico. 57 pp. SVEDELIUS, N., Reports on the marine algae of Ceylon. Ecological and systematic studies of the Ceylon species of Caulerpa. Rep. Ceylon mar. biol. Lab., 4: TANDY, G., Experimental taxonomy in marine algae, with special reference to Caulerpa. Proc. Linn. Soc. Lond., 146: TAYLOR, W. R., The marine algae of Florida with special reference to the Dry Tortugas. Tortugas Lab. 28: TAYLOR, W. R., Marine Algae of the eastern tropical and subtropical coasts of the Americas. Univ. Michigan Press, Ann Arbor, 870 pp., pls TAYLOR, W. R., Species of Caulerpa (Chlorophyceae) collected on the international Indian Ocean expedition. Blumea, 15: WEBER-VAN BOSSE, A., Monographie des Caulerpes. Ann. Jard. bot. Buitenz., 15: , pls