101-9 Looking Back to Look Ahead: Effects of Anoxia and Acidification on Functional Diversity during the Late Triassic in Panthalassa

Abstract:

Late Triassic marine communities experienced deoxygenation and acidification associated with volcanism, resulting in the depletion and extinction of taxa. This event could be used to forecast how ecosystems today may respond to similar disturbances. Functional diversity—the number and types of functions—influences ecological processes, is crucial for ecosystem stability and resilience, and has become a focus for conservation. To better assess how the productivity of shallow-marine ecosystems has fluctuated due to anoxia and ocean acidification in the past, here we quantify changes in functional diversity throughout the Norian and Rhaetian stages of the Late Triassic in New York Canyon, Nevada (USA). Four traits (tiering, feeding, motility, and mineralogy) were assigned to 170 genera from the Gabbs Formation to assess changes in functional diversity. 154 Norian and 67 Rhaetian taxa correspond to 31 and 22 unique functional entities (FEs) respectively. Functional redundancy (average taxa per FE; 4.97 to 3.05), over-redundancy (proportion of taxa filling FEs above the average; 0.46 to 0.32), and vulnerability (FEs containing one taxon; 0.42 to 0.32) were all lower in the Rhaetian, suggesting reduced ecosystem functioning before the end-Triassic mass extinction. Multivariate measures show decreased functional richness (volume of functional space), but increased divergence (how much abundance is at the edges of functional space) and evenness (distribution of traits among functional space). Despite substantial diversity loss, the distribution of genera among functions does not differ (Spearman’s ρ = 0.79, p < 0.001). In the Rhaetian, ten functions disappeared, with rare functions preferentially lost, and one new function emerged. In addition, the most abundant functional group (low-tiering, sessile attached, filter-feeding, mixed aragonitic and calcitic taxa) declined by 53.1%—consistent with reduced carbonate production indicative of acidification. Overall, functional space contracted in the Rhaetian but traits were more evenly distributed among functions. Despite most FEs persisting, declines within FEs could have changed the rates at which functions were performed, lowering productivity. These results suggest that disturbances preceding the end-Triassic mass extinction may have weakened functional capacity, thereby disrupting the ecosystem's natural functioning. This work is relevant to modern marine research, where the preservation of functionally important taxa should be prioritized over taxon richness in the face of anthropogenically-altered ecosystems.

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