溫度對珊瑚礁魚仔魚期的影響取決於體型大小

Abstract

仔魚期間的數量變化是影響族群動態的關鍵。海洋暖化下魚類族群數量會大幅波動，而探討升溫對仔魚期期間長短的影響可幫助了解暖化對族群數量的影響機制。在不同魚種間，仔魚的體型有很大的變異。然而，升溫時不同體型大小的魚種的仔魚期的變化目前仍不太清楚。有關體重、溫度和成長代謝之間的關係存在著二個對立的假說。克萊柏定律 (Kleiber' s law or 3/4-power law) 假設體重和溫度對成長代謝的影響是獨立的。然而，代謝水平假說 (Metabolic-level boundaries hypothesis) 指出溫度和成長代謝的關係隨著體型大小不同。基於仔魚期會反映成長率的趨勢，根據代謝水平假說，升溫對仔魚期的影響應該會隨魚種體型大小改變。為了測試這個假說，我們合併1)臺灣到日本的潮間帶多種珊瑚礁魚類採樣、溫度資料以及2)文獻資料，以利用30種珊瑚礁魚種的資料來評估溫度對仔魚期的影響是否會隨仔魚體型大小而不同。我們利用群集分析將不同魚種的仔魚沉降全長分出小、中、大三個群集。我們發現小型魚的仔魚期在涼、暖季均隨升溫有非線性的變化；涼季時，小型魚的仔魚期隨緯度和溫度變化呈現鐘形變化接著逐漸下降，但在緯度較低時，仔魚期隨著升溫增加。中型魚仔魚期在涼季時則多呈現下降的線性趨勢，但在暖季時隨著緯度和溫度出現下降又上升非線性變化。部分大型魚仔魚期則在低緯度暖季呈現些微上升的線性趨勢。這些結果顯示小型魚仔魚期對升溫呈現較明顯的非線性趨勢，而中、大型魚仔魚期則多呈現線性趨勢。這可能代表體型較小的魚類族群的入添量在不同緯度和季節間都容易隨升溫而有變化，但體型較大的魚類族群入添量則特別在暖季的低緯度海域會隨升溫而波動。

The larval stage is the key stage that determines changes in the abundance of fish populations. As ocean warming will cause fluctuations in fish population sizes, it will help to understand the effects of warming on fish populations by assessing the effects of temperature on the duration time of the larval stage. There is considerable variation in the size of fish larvae. However, the response of larval duration in fish of different sizes to increasing temperature is still not well understood. There are two opposing hypotheses regarding the relationship between body mass, temperature, and growth metabolism. Kleiber's law assumes that the effects of body mass and temperature on growth metabolism are independent. However, the metabolic-level boundaries hypothesis suggests that the relationship between temperature and growth metabolism varies with body size. Since larval growth rates will reflect larval duration, based on the metabolic level boundaries hypothesis, the effects of temperature on larval duration should vary with body size. To test this hypothesis, we combined 1) intertidal surveys of multiple reef fishes in Taiwan and Japan and 2) literature data, in total 30 reef fish species, to assess whether the effects of temperature on larval duration vary with body size. We conducted cluster analysis to classify larvae into small, medium, and large size groups. We found that larval duration of small-sized fish exhibits a non-linear response to increasing temperature in both cool and warm seasons: in the cool season, larval duration of small-sized fish shows a bell-shaped change with increasing temperature (or decreasing latitude) and then a gradual decrease followed by an increase with increasing temperature (or decreasing latitude). Medium-sized fish, on the other hand, generally exhibit a linear decrease in larval duration during the cool season, but a non-linear decrease followed by an increase with latitude and temperature during the warm season. In contrast, large-sized fish show a slight linear increase during the warm season at low latitudes. These results indicate that the larval duration of small-sized fish shows a more pronounced non-linear trend in response to warming, while medium- and large-sized fish show more linear trends. This may indicate that the recruitment of smaller fish populations tends to fluctuate with warming at different latitudes and seasons, while the recruitment of larger fish populations may fluctuate with warming especially at lower latitudes during the warm season.