Stable isotopes indicate ecosystem restructuring following climate‐driven mangrove dieback

Abstract

Extreme climatic events can trigger sudden but often long‐lasting impacts in ecosystems by causing near to complete mortality of foundation (habitat‐forming) species. The magnitude and frequency of such events are expected to rise due to anthropogenic climate change, but the impacts that such events have on many foundation species and the ecosystems that they support remains poorly understood. In many cases, manipulative experimentation is extremely challenging and rarely feasible at a large scale. In late 2015 to early 2016, an extensive area of mangrove forest along ∼ 1000 km of coastline in the Gulf of Carpentaria, Australia, experienced severe dieback, an event associated with climatic extremes. To assess the effect this dieback event had on the mangrove ecosystem, we assessed benthic faunal assemblages and food web structure using stable carbon and nitrogen isotopes in a comparative experiment of impacted forest and adjacent unimpacted forest. Eighteen months after the dieback, the forest that suffered dieback contained significantly fewer crabs that rely on mangrove litter food source but more crabs that rely on microphytobenthos food source than the unimpacted forest. However, the infaunal biomass was largely unaffected by the mortality effect. This is most likely because microphytobenthos was largely unaffected and consequently, this buffered the food web responses. However, overall, the habitat value for mangrove ecosystem services most likely decreased due to lower physical habitat complexity following tree mortality. Longer‐term monitoring could lead to better understanding of biological effects of this extreme event and underlying biological mechanisms that drive changes and recovery.

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

“…changes to MPB  13 C values that were likely associated with lower mangrove C fixation/respiratory inputs following the mangrove mortality. Furthermore, such findings indicate that the reported substantial change to the mangrove benthic faunal assemblage following the mangrove loss (Harada et al, 2019) was probably driven more by modification of physical habitat structure than changes in the use of food resources.…”

“…The samples collected in 2017 showed substantial differences in δ 13 C values between the two forests (Harada et al, 2019) suggesting that they are representative of the dieback impact. The 2017 samples from each forest including the mangrove leaf (n=2), MPB (n=1), algae feeder (n=3), leaf feeder (n=2 to 3), grazer (n=3), filter feeder (n=2) were further measured for carbon isotopic composition of individual amino acids (δ 13 CAA).…”

“…Some of the SIA samples including invertebrates, mangrove and sediment collected in 2017 were used to measure the initial dieback reported in Harada et al (2019).…”

“…CC BY 4.0 License. Harada et al (2019) https://doi.org/10.5194/bg-2019-468 Preprint. Discussion started: 2 March 2020 c Author(s) 2020.…”

“…Disturbances in mangrove forests not only affect recruitment, but can also change the cycling of C, N and S. Loss of mangrove trees and root structures can change organic matter inputs, sediment oxygenation and degradation of sediment organic matter. These changes alter overall sediment conditions, with consequences for benthic assemblages (Sweetman et al, 2010;Bernardino et al, 2018;Harada et al, 2019), sediment C and N stocks (Adame et al, 2018), microbial assemblages, and associated nutrient processes e.g. nitrogen fixation and sulfate reduction (Sjöling et al, 2005).…”