Life History of Chaetomorpha Valida (Cladophoraceae, Chlorophyta) in Culture
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Botanica Marina 54 (2011): 551–556 © 2011 by Walter de Gruyter • Berlin • Boston. DOI 10.1515/BOT.2011.066 Life history of Chaetomorpha valida (Cladophoraceae, Chlorophyta) in culture Yunyan Deng 2,3 , Xiaorong Tang 4 , Bingxin Huang 1,2 K ü tzing in 1845, there have been several reports of both sexual and Lanping Ding 1,2, * and asexual reproduction, primarily in six marine species, viz., C. linum (Mueller) Kü tzing (Sinha 1958 , Kornmann 1972 ), 1 Shantou University , Shantou 515063 , China, C. aerea (Dillwyn) Kü tzing (Rosenvinge 1892 , Hartmann e-mail: [email protected] 1929 , Sinha 1958 , Price 1967 , Patel 1971 , Kornmann 1972 ), 2 Institute of Oceanology , Chinese Academy of Sciences, C. spiralis C. melago- Qingdao 266071 , China Okamura (Chihara 1958 , Hori 1994 ), nium C. norvegica 3 Graduate University of Chinese Academy of Sciences , (Weber et Mohr) K ü tzing (Patel 1972 ), et C. antennina Beijing 100049 , China Leliaert Rueness (Leliaert et al. 2009 ) and 4 Key Laboratory of Marine Genetics and Breeding (Ocean (Bory de Saint-Vincent) K ü tzing (Leliaert et al. 2011 ). University of China) , Ministry of Education, Qingdao Chaetomorpha valida (Hooker et Harvey) K ü tzing, a 266003 , China marine species originally described from Tasmania, Australia, has been recorded in Australia (Womersley 1984 ), New * Corresponding author Zealand (Womersley 1984 ) and Fiji (South and Skelton 2003 ). It typically grows on mid- to supralittoral rocks that are surf-exposed or subject to strong surge. The species grows Abstract unattached or attached by basal holdfasts. It occurs as scat- tered individuals or as clumps of fi laments. Occasionally, it The marine green alga Chaetomorpha valida (Cladophoraceae, is an understory species (Guiry and Guiry 2011 ). In China, Cladophorales) has been found for several years foul- the species was fi rst reported from sea cucumber aquacul- ing aquaculture ponds along coasts of the cities Dalian and ture ponds in coastal Dalian, Liaoning province (Chi et al. Rongcheng, P.R. China. Using unialgal culture and micro- 2009 ). As a bloom-forming alga in China, it often dominates C. valida scopic observation, we completed the life history of aquaculture ponds and grows more luxuriantly in spring and and discovered fragment regeneration for the fi rst time. The summer than in winter. Massive occurrence of C. valida is a life history comprised an isomorphic alternation between signifi cant nuisance for aquaculturists, especially when loose gametophytes and sporophytes typical of most other members mats accumulate and decompose. Large quantities of thalli of the Cladophorales. Male and female gametes fused into directly interfere with the growth and movement of abalone zygotes then developed into sporophytes. Quadrifl agellate and sea cucumbers. Decomposing algal mats also consume zoospores produced by mature sprophytes gave rise to new dissolved oxygen, producing a hostile physico-chemical envi- gametophytes that yielded bifl agellate gametes. Germination ronment for mariculture. Seasonal abundances of macroalgae of zygotes and zoospores was of the bipolar erect type, as greatly affect water quality and sometimes cause great loss in observed in some other species of Chaetomorpha . Fragment aquaculture (Chi et al. 2009 ). regeneration occurred in both gametophytes and sporophytes Very little is known about the biology of C. valida . This via production of polar algal fragments, which directly devel- study was performed to investigate its life history and thus oped into entire fi laments to give a self-replicating gene- to gain better insight into mechanisms of colonization and ration. The results improved understanding of the seasonal excessive growth. Our results aid in understanding processes abundances of C. valida in spring and summer. underlying differences in algal abundance between spring and summer. Keywords: Chaetomorpha valida; China; fragment regen- eration; life history. Materials and methods Introduction Chaetomorpha specimens were collected from an aquaculture Chaetomorpha is a common and widespread green seaweed pond in Rongcheng, Shandong Province, China on 30 October genus in the order Cladophorales, characterized by unbranched 2008. Specimens were transported in seawater to the labora- fi laments. The life history of Chaetomorpha consists of an tory where healthy individuals were selected and rinsed with alternation between isomorphic gametophytes and sporo- sterilized seawater to remove epiphytes. Initially, thalli were phytes: gametophytes release gametes, which, after fusion, incubated in sterilized seawater at 20 ° C. Sterilized seawater germinate and develop into sporophytes. Mature sporophytes was renewed every day during the fi rst week after collection. discharge zoospores that give rise to new gametophytes After one week, thalli were cut into small pieces (about (Burrows 1991 ). Since the genus was fi rst established by four cells long) and cultured in enriched seawater (Table 1) 552 Y. Deng et al.: Life history of Chaetomorpha valida in culture Table 1 Enrichments to seawater (for a total of 150 ml). The species was abundant in spring and summer in aqua- culture ponds, less so in winter; it was present year-round. All Component Amount (g) collected specimens were reproductive. NaNO3 6.375 Gametophytic stage NaH2 PO4 ·2H2 O1.080 Tris 9.085 KI 0.125 After several days in culture, heavily pigmented gametangia H3 BO3 4.635 were formed (Figure 3 ). Each vegetative cell except that of FeC6 H5 O7 0.039 basal cells was able to transform into a gametangium. Over Vitamin B1 0.038 100 gametes were produced per gametangium; these were Vitamin B 0.075 × 10 -3 12 released through one or two (sometimes three) papilla-shaped Method: 1.5 ml of the above enrichments was added to 1l seawater. liberation pores (Figure 4) along the lateral cell wall. Most gametes swam rapidly after passing through the liberation pores; sometimes when shed explosively, large number of (Deng et al. 2011 ) in an incubator at 25 ° C and under 72 µ mol gametes massed in a temporary loose cluster. Gametes were photons m -2 s -1 with 10:14 h L:D cycle. Irradiance was mea- ovoid, measuring 4.5 – 7× 8 – 10.5 µ m, and each of them had sured with a quantum photometer (LI-COR, LI-250, Lincoln, a red eyespot and a chloroplast with many pyrenoids. There NE, USA). Gametes were released several days later. Zygotic were two equal fl agella at the anterior of gametes which pro- discs (discoid sporophytes) developing from zygotes were pelled gametes before fusion (Figure 5). There was no mor- removed from the substrata with a micropipette and trans- phological differentiation among gametes. ferred into petri dishes. Unialgal cultures were established by isolation of the zygotic discs. Subsequent cultures were Isogamy derived from them. Enriched seawater used for unialgal culture was renewed every fi ve days. Growth and develop- After being released, gametes were so active that they occa- ment were observed regularly under a light microscope. ssionally collided. When two heterosexual gametes met, Observation and microphotography were conducted with they kept in contact and fused together gradually (Figure 6). Nikon E400 (Tokyo, Japan) and Zeiss Stemi 2000-c (Wetzlar, Gametogamy took place not only between swarmers derived Germany) microscopes, and a Nikon Coolpix 4500 (Tokyo, from different fi laments, but also between those produced Japan) camera. in a single fi lament or even from the same gametangium. Isogamete fusion resulted in quadrifl agellate zygotes, 6 – 10 × 9 – 14 µ m in size with two-eyespots. Zygotes could be Results clearly distinguished from gametes by fl agellum number at the early fusion stage. Morphology and phenology of Chaetomorpha valida Some abnormal fusions were also observed in our study. More than two gametes sometimes fused to form an excep- Thalli of C. valida were light green in color; they were tionally large zygote (Figure 7). Zygotes sometimes fused fi rm and crisp in texture. Uniseriate unbranched fi laments with other zygotes to form a much larger fusion cell. But (Figure 1 ) entangled to form a spongy mass. Filaments were almost all unusually derived zygotes disintegrated shortly unattached or attached with basal holdfast discs. Cells were after fusion. cylindrical without marked constrictions at septa (Figure 2). Cells of unattached fi laments were 265 – 475 µ m in diameter, Germination of zygotes 150 – 700 µ m long and 0.5 – 2.1 times long as broad. Cell walls were 10 – 25 µ m thick, striated and lamellated. Chloroplasts Zygotes lost motility after several minutes and became were parietal and reticulate with numerous pyrenoids. spherical or subspherical after settling on the substratum 12 Figures 1 – 2 Chaetomorpha valida : morphology in culture. (1) General morphology. Scale bar: 1 mm. (2) Cylindrical cells without obvious constrictions at septum. Scale bar: 500 µ m. Y. Deng et al.: Life history of Chaetomorpha valida in culture 553 3 4 5 67 8 910 11 12 13 14 15 Figures 3 – 15 Chaetomorpha valida : reproductive events observed in culture. (3) Early stage of the formation of gametangia. Note gametangia (arrows). Scale bar: 500 µ m. (4) Emptied gametangia. Note liberation pores (arrows). Scale bar: 300 µ m. (5) Gametes with two fl agella. Scale bar: 10 µ m. (6) Two gametes fusing at their posterior ends. Scale bar: 10 µ m. (7) A zygote and a gamete fusing. Scale bar: 10 µ m. (8) A settled zygote. Scale bar: 10 µ m. (9) A zygote elongating to form apical and basal por- tions. Scale bar: 20 µ m. (10) A germling with an apical cell and a basal cell. Scale bar: 40 µ m. (11) A quadrifl agellate zoospore. Scale bar: 10 µ m. (12) Clusters of sporophyte germlings. Scale bar: 300 µ m. (13) Overgrowth of a cell by a neighboring cell (arrow). Scale bar: 500 µ m. (14) Stretch cell transforming into a basal cell of a new fragment; both fragments have same apico-basal polarity. Note stretch cell (arrow).