Coral reefs are extremely productive ecosystems, but widespread changes to benthic community structure resulting from anthropogenic impacts are likely to impact the transfer of organic matter between trophic levels, altering trophodynamics and functional diversity. We used stable isotope analysis to investigate differences in resource availability, niche width and trophic diversity of seven coral reef fish species representing key functional feeding groups on a sponge-dominated reef and an adjacent, coral-dominated reef. Four out of seven fish species had wider isotopic niches at the sponge-dominated reef compared to the coral-dominated reef, including the obligate corallivore. The proximity of the isotopic niche of the obligate corallivore to the isotopic niche of the detritivore suggests that the obligate corallivore supplemented its diet with detritus at the sponge-dominated reef. Fish sampled at the sponge-dominated reef had a significantly lower mean trophic position, used a lower range of resources (based on δ¹³C range) and obtained more carbon from benthic production than at the coral-dominated reef. Trophic diversity was lower and functional redundancy higher at the sponge-dominated reef, suggesting that fish on the sponge reef had more similar diets to each other than at the coral-dominated site. Observed differences in trophic structure between the two sites are likely due to fewer organic matter pathways supporting secondary production at the sponge-dominated reef, suggesting that transitions sponge-dominated systems will reduce community stability by eroding the potential for niche partitioning and species co-existence.

珊瑚礁是生产力极高的生态系统，但人为影响导致的底栖群落结构的广泛变化可能会影响有机物在营养级之间的转移，改变营养动力学和功能多样性。我们使用稳定同位素分析调查七种珊瑚礁鱼类在资源可用性、生态位宽度和营养多样性方面的差异，这些珊瑚礁鱼类代表海绵为主的珊瑚礁和邻近的珊瑚为主的珊瑚礁上的关键功能摄食群体。与以珊瑚为主的珊瑚礁相比，七分之四的鱼类在以海绵为主的珊瑚礁中拥有更广泛的同位素生态位，其中包括专性食珊瑚动物。专性食珊瑚动物的同位素生态位与食碎屑动物的同位素生态位的接近表明，专性食珊瑚动物在以海绵为主的珊瑚礁中以碎屑补充其饮食。在海绵为主的珊瑚礁中取样的鱼类的平均营养位置明显较低，使用的资源范围也较低（基于 δ ¹³C范围），并且从底栖生产中获得的碳比以珊瑚为主的珊瑚礁更多。以海绵为主的珊瑚礁的营养多样性较低，功能冗余较高，这表明海绵礁上的鱼类比以珊瑚为主的珊瑚礁上的鱼类具有更相似的饮食。观察到的两个地点之间营养结构的差异可能是由于支持海绵主导的珊瑚礁二次生产的有机物质途径较少，这表明海绵主导的系统的过渡将通过侵蚀生态位划分和物种共存的潜力来降低群落稳定性。