Is the Red Alga Meristotheca Papulosa Annual? -Monitoring Of
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Aquacult. Sci. 67（1），49－56（2019） Is the red alga Meristotheca papulosa annual? - Monitoring of tagged thalli at Banda, Tateyama, Central Pacific coast of Japan- 1,＊ 1, 2 1 1 Boryuan CHEN , Shingo AKITA , Akito UEHARA and Daisuke FUJITA Abstract: Meristotheca papulosa is a commercially important red alga used for human consumption. It has been reported as an annual species in Kagoshima Prefecture but has been suggested to be perennial in Kochi Prefecture. In the present study, thalli were indirectly monitored at Banda, Chiba Prefecture. A caged culture and feeding test recording were also conducted. Among the nine thalli tagged in March or April 2016, three survived the winter but disappeared in July 2017. After reaching a maximum length in May, the thallus size decreased from June to November 2016. However, the thalli began to regrow in December 2016. Bite marks were common on the thalli; appearance of herbivorous fishes was recorded by the interval camera. An in-situ culture was conducted by transplanting six thalli each inside and outside of a cage from March to October 2016. After reaching the maximum weight in June, thalli located outside of the cage disappeared in July, but those located inside of the cage survived until September. Aplysia parvula, which was able to intrude the cage, were noted to be influential grazers on the thalli. These results suggest that M. papulosa is perennial but its longevity is affected by wave action and grazing. Key words: Meristotheca papulosa; Perennial; Caging; Grazer were Kagoshima Prefecture in Kyushu (250 to Introduction 300 tons/year) and Izu Islands on the central Pacific coast of Japan (200 to 300 tons/year) Meristotheca papulosa (Montagne) J. Agardh (Shinmura 2000) (Fig. 1). Although recent (Gigartinales, Solieriaceae) is a commercially official statistics are not available, intensive important red alga in Japan. The species is harvests have reduced its abundance, resulting consumed as red, green (boiled), or white in the designation as a near-threatened species (bleached) form in seaweed salad and gar- in the Red Data Book of Japan (Ministry of the nish (Ohno 2004; Mouritsen 2013). This is a Environment HP). In addition, the price of this branched, membranous cartilaginous alga that alga is increasing; in 2017, an internet search primarily grows in the subtidal zones between showed that the commercial price of packed 1 and 20 m in depth in the warm temperate to dry material (20 g, from Kozu-shima, one of the tropical coasts in the Indo-Pacific (Guiry and Izu Islands) was 690 yen, i.e., 34,500 yen/kg Guiry 2017). In Japan, M. papulosa occurs on or USD 305. Hitherto, many studies have been the central to southern Pacific coasts of Honshu, conducted on M. papulosa to understand the Shikoku, Kyushu, and Okinawa. At the end of phenology (Shinmura 1974a, b; Serisawa et al. the 20th century, the major producing areas 2000), vertical distribution (Mine et al. 1994), Received 23 October 2018; Accepted 8 February 2019. 1 Laboratory of Applied Phycology, Graduate School of Tokyo University of Marine Science and Technology, 4-5-7 Minato-ku, Tokyo 108-8477, Japan. 2 Current affiliation: Kobe University Research Center for Inland Seas, Rokkodai 1-1, Kobe 657-8501, Japan. ＊Corresponding author: Tel, (+81) 80-4363-2730; E-mail, [email protected] (B. Chen). 50 B. Chen, S. Akita, A. Uehara and D. Fujita physiology of photosynthesis (Murase et al. Tagging and Monitoring of M. papulosa 2008; Lideman et al. 2011), and to challenge To monitor M. papulosa, nine small thalli cultures (Kimura 1992; Kida and Taniguchi (< 10 cm) were tagged at a depth of 4.5 m and 1992; Huang and Fujita 1997; Hamaoka et al. observed monthly by SCUBA diving from 2007; Kida 2010). However, all of these stud- March 2016 to August 2017. For tagging, stain- ies were conducted from western to south- less steel piles (6×15 mm) were stuck into bed ern Japan. Longevity of M. papulosa was rock next to each thallus by using hammer. On reported differently among the above studies. each pile, a plastic numbered card was tied with Shinmura (1974b), who examined a popula- a cable band in advance. Direct marking was tion in Kagoshima Pref., Kyushu, reported not adopted to avoid damage by abrasion. M. papulosa to be an annual species that dis- Four thalli were tagged in March and an appears during summer. On the contrary, additional five were tagged in April because of Serisawa et al. (2000), who studied the alga in low density (< 0.01 thallus/m2) of M. papulosa. Shikoku, Kochi Prefecture, noted that a few During the monitoring, total length of thallus thalli survived autumn and regrew in winter, (from apex of branch to holdfast), presence or suggesting that the species is perennial. As the absence of bite marks, and thallus color were above two phenological studies are based on recorded for each tagged thallus. In addition, the field observation and monthly harvest for photos of one tagged thallus were taken every morphometry and biomass evaluation, monitor- five minutes using an interval camera (Recolo ing of tagged thalli is needed to confirm if this IR5, KING JIM, Japan) to record visiting and species lives for more than a year. This informa- feeding by herbivores from July 11 to 12, 2017, tion is necessary to design stock management during which bite marks were frequently recog- plans and to improve the growth of the spe- nized on the tagged thalli. Water temperature cies. Therefore, we monitored tagged thalli of was recorded once per hour with a HOBO pen- M. papulosa in shallow waters in Tateyama. In dant logger (UA-002-64, Onset Computer, Co., addition, a caging experiment and feeding test was conducted to detect potential factors affect- ing the survival of thalli in the declining season. Materials and Methods Study sites The monitoring of tagged thalli was con- ducted at Banda (E139°46′12′′ N34°58′30′′), Tateyama, located on the northern coast of Boso Peninsula, central Pacific coast of Japan (Fig. 1). We selected Banda as the study site for monitoring and experiments because Banda is convenient for monitoring and managing exper- iments due to the presence of Field Science Center (Banda) of Tokyo University of Marine Science and Technology. The Banda coast is composed of bedrock, collapsed rocks and sands. On the subtidal hard substrata, geli- diacean species are dominant from 2 to 6 m depths, while Ecklonia or Sargassum forests are dominant in shallow waters. M. papulosa is Fig. 1. Geographic location of the study site at Banda, sparsely distributed in the gelidiacean zone. Tateyama, Chiba Prefecture, Japan. Confirm longevity and factor affecting thalli 51 USA) attached to a 2 kg weight at a depth of Astralium haematragum) which inhabit around 4.5 m from March 2016 to August 2017. the study site were collected by SCUBA diving and brought back to laboratory with bucket in Caging experiment September 2017. In laboratory, each aquarium Growth from March to October 2016, was was sectioned by two mesh plates, collected compared between thalli transplanted inside animals were exposed to M. papulosa for seven and outside of a cage. A stainless cubic mesh days after they were precultured in each com- cage (25×25×25 cm with 5.5 mm mesh) was partment of the aquarium without any diet for deployed on the sea bottom at 4.5 m depth on seven days. For feeding, three pieces (including March 27, 2016. One non-discolored red thal- apex) of approximately equal size (wet weight: lus without any visible damage was collected 1.0±0.02 g), were cut from branches of the col- from 4.5 m in depth by SCUBA diving and lected thallus and placed at the bottom of com- brought back to the laboratory in the Field partments in the aquaria. Wet weight of each Science Center. No more thalli were collected thallus was measured every day during the at the commencement of the experiment. In span of experiments. To compare the feeding the laboratory, after being kept in running rate among three animals, relative daily decre- water for one day, 12 pieces (including apex) ment (RDDs) of thallus per animal weight was of approximately equal size (wet weight: 0.6± calculated using the following equation: 0.2 g), were cut from branches of the collected RDDs = [(ln W - W )/(t - t )]/animal weight (g) thallus. Six pieces were inserted into each of 1 0 1 0 (1), two cremona ropes at an interval of 5 cm. One of each of these ropes was tied inside and out- where W1 and W0 are the weight of explant at side of the cage (10 cm above the bottom). time t1 and t0, respectively. Every month, these ropes were returned to the To evaluate the effects of caging, significant laboratory to measure the wet weight of the difference of RDDs were tested by Tukeyʼs thallus (excess water was removed with paper honest significant difference (HSD) test using towel) and the presence or absence of bite statistical software R version 3.3.2 (R core team marks was recorded by taking photos. All thalli 2015). were removed from ropes for measurement and inserted again into ropes before returning to Results the cage. This experiment continued for seven months. Relative growth rate (RGR, %/day) During the study period, the highest and was calculated using the following equation: lowest temperatures were 27.7°C (August 2017) and 14.0°C (February 2017), respectively, while RGR=[(ln W - In W )/(t - t )]×100 (1), 1 0 1 0 the yearly average temperature was 20.9±3.5°C where W1 and W0 are the weight of explant at in 2016 and 18.8±3.9°C in 2017 (Fig.