Balistes capriscus and Lutjanus campechanus: Tissue stable isotopes and gut contents

The feeding ecology of two reef fishes associated with artificial reefs in the northwest Gulf of Mexico (GoM) was examined using gut contents and natural stable isotopes. Reefs were divided into three regions (east, central, west) across an east to west gradient of increasing reef complexity and salinity. Gray triggerfish (Balistes capriscus) primarily consumed reef-associated prey (xanthid crabs, bivalves, barnacles) and pelagic gastropods, while red snapper (Lutjanus campechanus) diets were mainly comprised of non-reef prey (stomatopods, fishes, portunid crabs). Natural stable isotopes of carbon (d13C), nitrogen (d15N), and sulfur (d34S) were measured in consumer muscle tissue as well as potential primary producers. Gray triggerfish occupied a lower trophic position than red snapper, with lower d13C and d15N values across all size classes and regions, and generally higher d34S values. Red snapper had a smaller range of stable isotope values and corrected standard ellipse areas across all size classes and regions, indicating a smaller isotopic niche. Contribution estimates of particulate organic matter (26 to 54 %) and benthic microalgae (BMA, 47 to 74 %) for both species were similar, with BMA contributions greater across all three size classes (juveniles, sub-adults, adults) of red snapper and all but the juvenile size class for gray triggerfish. Species gut contents and stable isotopes differed by region, with fishes consuming more crabs in the east region and more gastropods in the central and west regions. d13C and d15N values generally decreased from east to west, while d34S increased across this gradient. Results highlight species-specific feeding differences associated with artificial reefs, where gray triggerfish may be more dependent on the reef structure for foraging opportunities. In addition, results offer further information on the integral role of BMA in primary production at nearshore artificial reefs.本研究以栖息于墨西哥湾（Gulf of Mexico，简称GoM）西北部人工鱼礁的两种礁栖鱼类为研究对象，通过胃含物分析与天然稳定同位素技术，对其摄食生态展开了系统研究。研究区域按东西向梯度划分为东、中、西三区，该梯度下鱼礁复杂度与盐度均呈递增趋势。灰鳞鲀（Gray triggerfish，*Balistes capriscus*）主要摄食礁关联猎物（菱蟹科蟹类、双壳类、藤壶）与浮游腹足类；而红鳍笛鲷（red snapper，*Lutjanus campechanus*）的食性则以非礁栖猎物为主，包括口足类、鱼类及梭子蟹科蟹类。本研究测定了消费者肌肉组织与潜在初级生产者的碳（δ¹³C）、氮（δ¹⁵N）及硫（δ³⁴S）天然稳定同位素比值。结果显示，灰鳞鲀的营养级低于红鳍笛鲷：在所有体型分级与区域中，其δ¹³C与δ¹⁵N比值均更低，而δ³⁴S比值整体更高。红鳍笛鲷在所有体型分级与区域中的稳定同位素值范围与校正标准椭圆面积均更小，表明其同位素生态位更窄。两种鱼类的食物来源贡献估算结果相似：颗粒有机物（POM）贡献占比为26%~54%，底栖微藻（benthic microalgae，BMA）贡献占比为47%~74%；其中红鳍笛鲷的三个体型分级（幼鱼、亚成体、成体）均以BMA为主要食物来源，而灰鳞鲀除幼鱼分级外，其余体型分级亦以BMA为主。两种鱼类的胃含物组成与稳定同位素比值均存在显著区域差异：东部区域的个体摄食更多蟹类，中部与西部区域则摄食更多腹足类。δ¹³C与δ¹⁵N比值整体呈自东向西递减趋势，而δ³⁴S比值则随该梯度递增。本研究结果揭示了人工鱼礁生境中两种鱼类的特异性摄食差异，其中灰鳞鲀可能更依赖鱼礁结构获取觅食机会；此外，本研究还进一步阐明了底栖微藻（BMA）在近岸人工鱼礁初级生产中的核心作用。