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Histological Analysis of Reproductive Trends of Three Porites Species from Kane'ohe Bay, Hawai'i1

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Histological Analysis of Reproductive Trends of Three Porites Species from Kane'ohe Bay, Hawai'i1 Pacific Science, vol. 54, no. 2: 195-200 © 2000 by University of Hawai'i Press. All rights reserved Histological Analysis of Reproductive Trends of Three Porites Species from Kane'ohe Bay, Hawai'i1 ELIZABETH G. NEVES2 ABSTRACT: Gonad development and synchrony among Porites compressa, P. Zobata, and P. evermanni colonies, collected in Kane'ohe Bay during the sum­ mer of 1997, were histologically examined and compared. All three species are gonochoric broadcast spawners, releasing gametes predominantly around the time of full moon during the breeding season. Histological sections of fertile polyps confirmed the maturity of gonads and presence of zooxanthellae sur­ rounding the oocytes and moving into the ooplasm of the mature eggs before spawning. IT HAS BEEN DEMONSTRATED that mode and Contributing to the knowledge of Porites timing of reproduction, gametogenesis, and species, the most conimon and widespread early development are variable among scler­ genus of hermatypic corals in Hawai'i and in actinian corals (Connell 1973, Campbell many other tropical regions (Maragos 1977), 1974, Szmant-Froelich et al. 1985, Szmant this study provides detailed histological in­ 1986, Babcock et al. 1986, Richmond and formation on reproductive trends of P. com­ Hunter 1990). Regardless of the mode of re­ pressa, P. Zobata, and P. evermanni collected production most coral species show a peri­ in Kane'ohe Bay (O'ahu, Hawai'i). odicity in larval or gamete release. Tempera" ture variation, lunar and tidal cycles, variations in nocturnal illumination, and the diel light-dark cycle appear to influence the MATERIALS AND METHODS release of larvae and gametes (Kojis and Colonies were collected in Kane'ohe Bay Quinn 1981, Jokiel et al. 1985, Hunter 1989). from shallow reef flats around Coconut Variations in reproductive strategies Island, Kekepa, and Ahuolaka at approxi­ among Porites species have been described mately fortnightly intervals in June and July (Stimson 1978, Kojis and Quinn 1981, Tom­ 1997. Branches of P. compressa and small ascik and Sander 1987, Richmond and fragments of P. Zobata and P. evermanni were Hunter 1990, Glynn et al. 1994). Porites as­ sampled haphazardly at 2 to 5 m depth. treoides is a hermaphroditic brooder (Chor­ Previous studies suggested that spawning nesky and Peters 1987); P. murrayensis and in Porites species in 1997 in Kane'ohe Bay P. panamensis are gonochoric brooders would occur in June, July, and August, dur­ (Richmond and Hunter 1990, Glynn et al. ing the full moon and new moon. Therefore, 1994). Porites Zobata, P. compressa, P. ever­ to assess the gamete developmental stage be­ manni, P. austraZensis, and P. Zutea are gon- fore first spawning, samples of each colony ._ QchQric broa4cast spawners (Stimson 1978, were collected on 18~19 June,.2 days before Kojis and Quinn 1981, Szmant 1986, Rich­ full moon. During the full moon, on 20-21 mond and Hunter 1990, Glynn et al. 1994). June, two colonies of P. Zobata and one col­ ony each of P. evermanni and P. compressa were sampled. On 4-6 July, during the new 1 This research was supported by the Edwin W. Pauley moon, three colonies of P. Zobata and two Foundation. Manuscript accepted 30 August 1999. colonies each of P. evermanni and P. com­ 2 Museu Nacional/Universidade Federal do Rio de Janeiro, Depto. Invertebrados, Rio' de Janeiro, Brazil, pressa were collected. Fragments of three CEP 22940-040 (E-mail: [email protected]). colonies each of P. evermanni and P. com- 195 196 PACIFIC SCIENCE, Volume 54, April 2000 pressa and two colonies of P. lobata were absorbed by maternal tissue after a short collected at the full moon on 19-20 July. period of degeneration. Colorless lipid vesi­ Specimens were fixed in 10% formalin for cles imparted a frothy appearance to the 24-48 hr and decalcified in a solution of 4% ooplasm. Mature, prespawning oocytes had formic acid and 2% Formalin. Polyps were zooxanthellae centrally concentrated in the dehydrated in ethanol series and cleared in ooplasm (late stage IV). xylene for routine paraffin embedding. Serial Sperm clusters were distinguishable from transversal sections cut from paraplast blocks oocytes primarily by the absence of germinal at 6.0 to 7.0 ~m were placed on glass slides, vesicles. Mature spermaries had a lumen, and deparaffinized in xylene, rehydrated through spermatozoa were arranged with the pink graded ethanols to water, and stained with transparent tails projecting toward the lumen Mallory's triple stain. Longitudinal sections and the dark condensed heads located pe­ were prepared for colonies of P. evermanni ripherally. Gonads containing partially and considered unfertile. completely spawned spermaries appeared as Histological sections of fertile polyps were irregular pouches or spaces with a few resid­ examined to determine sexuality, pattern of ual, mature spermatozoa. gonad arrangement, maturity of gonads be­ fore spawning, and mode of reproduction. Porites lobata Oocyte and spermary developmental stages were classified according to the criteria Mode of reproduction, gonad structure, adopted by Glynn et al. (1994). and stage ofgamete development of P. lobata were similar to those in P. compressa. Early spermatogenic cells and immature testicular cysts were found throughout the RESULTS sampling period. The former were charac­ Porites compressa terized as small groups of blue-staining cells aggregated in the gastrodermis ofmesenteries Porites compressa is gonochoric and re­ adjacent to the mesoglea, and the latter were leases gametes that are fertilized externally. composed of a peripheral layer of spermato­ Lunar periodicity of gamete shedding was gonia and an inner layer containing sperma­ observed when colonies held in shallow out­ tids. Immature cysts had a centrally located door tanks spawned during full moon periods lumen. on 21-24 June and 20-21 July (summer Male and female colonies were observed 1997) (Table 1). releasing gametes in June, during the first Gonads formed between retractor muscles spawning event. As in P. compressa, P. 10­ and septal filaments within complete mesen­ bata showed increased egg development to­ teries. Gametes of various sizes were charac­ ward July full moon. However, during the terized in stages III and IV. Stained mature second spawning event, only female colonies oocyte color varied from dark pink to pur­ were observed releasing gametes (Table 1). plish. Numerous zooxanthellae were ob­ served within ovarian membranes surround­ Porites evermanni ing oocytes (stage III) or inside ooplasm (stage IV}.-Late stage of -egg development This study c.onfirmedthaCf.el'et:mJl1t1'li is was characterized by the migration of zoo­ a gonochoric species with broadcast spawn­ xanthellae into the ooplasm and movement ing, because the reproductive colonies had ofthe nucleus toward the periphery ofthe cell either sperm or eggs, without brooded larvae. (Glynn et al. 1994). Not all oocytes were shed Although gonads were found in four sampled in June or July during the full moon spawn­ colonies, three male and one female, no ing events. Oocytes that were unspawned spawning event was observed during the were generally smaller and appeared to be summer of 1997. Mature eggs appeared on less mature. It is likely that they were re- complete and incomplete mesenteries. Com- Histological Analysis of Reproductive Trends of Porites-NEVEs 197 TABLE I concentrated later in development (stage IV) NUMBER OF FERTILE COLONIES FoUND ON DIFFERENT (Figure 2). Resorption of oocytes was in­ SAMPLING DATES (PARENTHESES REpRESENT TOTAL ferred through loss of integrity and colorless NUMBER OF COLONIES COLLECTED IN EACH PERIOD) aspect, which was verified in stage III and IV oocytes. Most resorbing oocytes in P. ever­ Porites Porites Porites manni were surrounded by and contained DATE compressa lobata evermanni zooxanthellae. 18-19 June" 2 (3) I (I) 0(1) Most spermaries were immature, without 20-21 June' I (I) I (2) o(I) spermatozoa, and commonly had one or two 4-6 July' 2 (2) 2 (3) 2 (2) holotrichous nematocysts. Unfertile colonies 19-20 July 2 (3) 2 (2) 2 (3) had brownish, swollen mesenteries with clus­ "Two days before full moon. ters of early reproductive cells. •During full moon. 'During new moon. DISCUSSION plete mesenteries contained at least 10 eggs, Despite the small sample size, this study and incomplete mesenteries had less than 3 confirmed some important aspects of the re­ eggs (Figure 1). Histological analysis of ma­ productive biology of three species of Por­ ture eggs showed the presence of lipid drop­ itidae from the central Pacific region. Al­ lets and zooxanthellae. Zooxanthellae were though histology has disadvantages, which initially abundant in the gastroderm sur­ include possible inaccuracies in oocyte size rounding the oocytes and were incorporated measurements due to shrinkage of tissues into the cytoplasm and became centrally (Harriott 1983) and underestimating oocyte FIGURE 1. Porites evermanni. Fertile mesentery with stage III oocytes. Scale bar = 100 Jlffi. 198 PACIFIC SCIENCE, Volume 54, April 2000 FIGURE 2. Porites evermanni. Stage IV oocyte (Z, zooxanthellae). Scale bar = 100 IlID. numbers by failing to section whole gonads during late stage IV when they became cen­ or polyps (Harrison and Wallace 1990), it is trally concentrated in the ooplasm. Accord­ essential for analysis of the stages of gonadal ing to Beneyahu et al. (1992) acquisition of development and as a means to determine algal symbionts in mature oocytes only could sexual patterns among corals. indicate a seasonal trend. Studies dealing This study indicated that P. compressa, P. with timing and mechanisms of acquisition lobata, and P. evermanni exhibited similar are needed, because the presence of zoo­ patterns of sexual reproduction. All of them xanthellae is considered essential for some were gonochoric and released gametes for coral planulae to achieve competence (Rich­ external fertilization and development. As mond 1987). previously recorded by Stimson (1978) and Resorption of stage III and IV oocytes Hunter (1988), P. compressa and P. lobata was apparent in all three species.
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