月相變化對亞熱帶珊瑚礁成魚生殖與幼魚孵化及沉降日期之影響

Abstract

許多珊瑚礁魚類的生殖活動會根據環境的週期性變化展現規律性以確保成魚產下的卵及孵化的幼魚可在較適合的環境存活。例如，珊瑚礁幼魚的孵化時間會對應月球週期的新月期間，利用黑暗環境躲避掠食者並借助新月期間的大潮沉降至珊瑚礁。過去研究僅針對少數魚種進行月球週期性的調查，目前仍不清楚在相同環境下不同魚種的幼魚與成魚階段的性狀或生殖是否皆會展現月球週期性。因此，本篇研究以台灣沿岸潮間帶常見的亞熱帶、熱帶珊瑚礁魚種為研究對象，以探討成魚生殖與幼魚性狀是否受月球週期的影響。本篇研究假設: (1) 成魚性腺發育高峰(代表即將產卵)應對應滿月期間；目的是讓子代的幼魚期與一至二次的新月期重疊，以利幼魚可在黑暗遮蔽下成功覓食並提高存活率；(2) 幼魚的孵化和沉降日期應對應新月期間；目的是可以在黑暗下躲避掠食者，成功沉降到珊瑚礁。我們在台灣南北部潮間帶實地調查發現八種幾乎四季皆能生存而可觀察其成魚生殖或幼魚性狀之月球週期性的魚類，包含兩種鰕虎科、兩種雀鯛科和四種鳚科 (其中Istiblennius dussumieri與 Abudefduf vaigiensis僅在台灣北部發現)。本研究測量成魚個體的性腺指數 (gonadosomatic index) 及以耳石推算幼魚個體的孵化、沉降日期，並以週期性回歸分析這些成魚和幼魚性狀與月球週期性的關係。大部分鳚科物種，其年齡與濕重在不同季節或月相時期間有顯著的種內差異；而雀鯛科在下弦月期有較高的年齡分布。結果顯示八種成魚中有四種(Bathygobius fuscus、Bathygobius cocosensis、Istiblennius lineatus、A. vaigiensis)的性腺發育高峰對應滿月期間，但Praealticus striatus、Istiblennius edentulus、I. dussumieri 的性腺發育高峰則對應下弦月期至新月期間。然而，八種中僅有兩種(B. cocosensis、A. vaigiensis)的幼魚孵化和沉降日期具有月球週期性，其中僅有A. vaigiensis幼魚大部分集中於新月期間孵化。其他魚種的幼魚孵化及沉降日期在整個月中大致平均分布。這些結果顯示，成魚的性腺發育高峰呈現較明顯的月球週期變化，符合假設；而幼魚的孵化和沉降日期較無明顯的月球週期性，其原因為幼魚可能受季節溫度變化延長或縮短發育時間以提高沉降成功率。本篇研究的分析不僅顯示不同種類的珊瑚礁魚類的生殖策略及入添機制具有不同的月球週期性，也指出環境溫度變化可削減月球週期對幼魚性狀的影響。了解這些機制有助於提升對珊瑚礁魚類多樣性的保育。

The reproductions of reef fishes often synchronize periodic environmental changes, such as lunar cycles, to ensure offspring survival. For example, adults may spawn during full moon to benefit offsprings to hatch or settle in the new moon. Although some studies demonstrate lunar periodicity in a few reef fishes, it remains unclear whether such periodicity in both larval traits and adult reproduction may occur among species. Here, we study lunar periodicity of adult reproduction (i.e., gonad development, indexed by the gonadosomatic index) and larval traits (i.e., the number of individuals hatched or settled in each lunar date) for 8 common small benthic reef fishes in the northern / southern Taiwan. We hypothesized that: (1) adult gonad development peak (i.e., about to spawn) should match full moon to allow larval offspring to correspond to new moon for successfully foraging in darkness and increasing survival; (2) larval hatching and settlement dates should match new moon to avoid predators and successfully settle to the reef. We measured adult GSI and larval hatching and settlement dates. The age and wet weight of most Blenniidae species had intraspecific differences among seasons or lunar phases; Pomacentridae species had older age during the last quarter. We found GSI peaks of Bathygobius cocosensis, Bathygobius fuscus, Istiblennius lineatus, and A. vaigiensis correspond to full moon, while GSI peaks in Praealticus striatus, Istiblennius edentulus, and I. dussumieri match last quarter to new moon. However, only B. cocosensis and A. vaigiensis show lunar periodicity in larval hatching and settlement dates, with only A. vaigiensis larvae concentrating most of their hatching dates during new moon. Larval traits of other species were evenly distributed throughout the month. Consequently, our hypothesis 1, but bit the hypothesis 2, is not supported by data. It is likely that seasonal temperature changes may influence larval durations, confounding lunar periodicity in these larval traits. Our analysis not only shows differential lunar periodicity in the reproductive strategies of adults among reef fishes, but provides evidence that temperature changes may reduce the lunar periodicity on larval traits, influencing recruitment. Thus, our study advances to understand these mechanisms underlying reef fish diversity conservation.