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•2 min read•from Frontiers in Marine Science | New and Recent Articles

Thermal tolerance under climate warming in the mangrove fiddler crab Paraleptuca chlorophthalmus: an integrative metabolic and behavioral approach

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Understanding species resilience under climate change demands integrative approaches. This study investigates the thermal tolerance of the mangrove fiddler crab *Paraleptuca chlorophthalmus*, a sentinel species in a rapidly warming region, by characterizing both its metabolic and behavioral responses across a broad thermal gradient. Results reveal a narrower metabolic thermal window than locomotor activity, suggesting behavioral flexibility may buffer against warming’s direct metabolic costs. These findings indicate that *P.
Thermal tolerance under climate warming in the mangrove fiddler crab Paraleptuca chlorophthalmus: an integrative metabolic and behavioral approach

The resilience of coastal ecosystems to climate change hinges on understanding the physiological and behavioral responses of their inhabitants. A recent study published in Elevated temperature alters swimming behavior in Caribbean king crab larvae highlights the vulnerability of marine invertebrates to ocean warming, a trend starkly demonstrated by the findings of this new research on the mangrove fiddler crab *Paraleptuca chlorophthalmus*. This work, which jointly characterized metabolic and behavioral thermal responses – a notable gap in previous research spanning six decades – offers critical insight into the potential for this species, a recognized sentinel of mangrove health, to withstand the projected impacts of climate warming in the western Indian Ocean. The investigation’s focus on both respiration and locomotor activity provides a more nuanced picture than studies examining thermal tolerance in isolation, revealing a fascinating interplay between physiological limits and behavioral flexibility.

The core finding is compelling: while the metabolic rate of *P. chlorophthalmus* exhibits a clear thermal optimum and defined performance limits, its locomotor activity demonstrates a remarkably wider thermal window. This suggests a potential buffering effect, whereby the crabs can maintain activity levels even as their metabolic efficiency declines under warming conditions. This is further contextualized by the implications discussed in Plankton imager 10 monitoring in the southern North Sea: an open workflow for classification, morphometry and DwC-A publication, which emphasizes the broader vulnerability of plankton populations, a crucial food source for many marine species, to climate-driven changes. The study’s use of climate projections under the SSP5-8.5 scenario provides a realistic assessment of future thermal suitability, and the observation of consistent behavioral suitability across the region, despite seasonal respiration variability, is particularly encouraging. While the shipping industry’s recent welcome of proposed recycling yard inclusion, as noted in Shipping Industry Welcomes Proposed Inclusion of Two Indian Ship Recycling Yards to EU List, demonstrates a focus on sustainability in other sectors, this research underscores the equally vital need for understanding and protecting marine biodiversity.

The authors rightly caution that thermal tolerance alone is not a guarantee of persistence. Habitat availability, salinity fluctuations, biotic interactions, and larval dispersal – factors outside the scope of thermal modeling – will ultimately determine the species’ ability to expand into lower-latitude mangroves. This highlights the complexity of predicting species responses to climate change and the importance of integrating diverse datasets and modeling approaches. The unimodal thermal response observed in metabolic rate, while typical for tropical ectotherms, underscores the species' sensitivity to extreme temperatures and the potential for future disruptions if warming exceeds these thresholds. The research’s rigorous methodology, combining closed-chamber respirometry and video tracking, strengthens the validity of its conclusions and provides a valuable framework for future studies examining thermal tolerance in other mangrove-dwelling species.

Ultimately, this study offers a cautiously optimistic perspective on the near-term resilience of *P. chlorophthalmus* to climate warming. However, it serves as a potent reminder that while physiological and behavioral adaptations can provide a buffer, they are not a panacea. The question moving forward is not simply whether this species can tolerate warmer temperatures, but whether the broader ecosystem – with its complex web of interactions and dependencies – can sustain its continued presence and ecological role in a rapidly changing world. Further research focusing on the interplay between thermal tolerance and other environmental stressors, coupled with comprehensive habitat assessments, will be crucial for informing effective conservation strategies and ensuring the long-term health of mangrove ecosystems.

Thermal tolerance is a key determinant factor of species persistence and distribution under climate change, particularly in ectotherms inhabiting highly variable environments such as mangroves, where fiddler crabs must rely on both physiological and behavioral mechanisms to cope with environmental stress such as temperature. Although the thermal limits of the mangrove fiddler crab Paraleptuca chlorophthalmus were first reported over six decades ago, no study has since jointly characterized its metabolic and behavioral thermal responses, despite the species being recognized as a sentinel of mangrove ecosystem health in a region facing rapid climate warming. We investigated oxygen consumption and locomotor activity in 96 adult males across a broad thermal gradient (5–44°C) under controlled acclimation, and fitted thermal performance curves (TPC) and thermal behavioral curves (TBC) to identify optimal temperatures and model-derived thermal performance limits under current and projected climate conditions defined by the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5). Metabolic rate was measured using closed-chamber respirometry, and behavioral responses were quantified through video tracking across the distance covered. Respiration showed a typical tropical-stenotherm, unimodal thermal response, with an optimum near 33°C and model-derived lower and upper performance limits near 11°C and 42°C, whereas locomotor activity remained high and stable across a substantially broader intermediate range (22–38°C), a markedly wider thermal window than metabolic performance. Climate projections showed strong seasonal variability in respiration-based thermal suitability, whereas behavior-based suitability remained consistently high across western Indian Ocean regions under both current and future scenarios. These results suggest that locomotor thermal performance may buffer P. chlorophthalmus against the direct metabolic costs of warming, and that thermal conditions alone are unlikely to constrain its persistence in the region. P. chlorophthalmus therefore appears thermally equipped to expand into lower-latitude mangroves under future warming; whether it does so will depend on habitat availability, salinity, biotic interactions, and larval dispersal, factors beyond the reach of thermal models alone.

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Tagged with

#ecosystem health#Thermal tolerance#Climate warming#Mangroves#Paraleptuca chlorophthalmus#Fiddler crabs#Ectotherms#Metabolic rate#Behavioral responses#Thermal performance curves (TPC)#Thermal behavioral curves (TBC)#Oxygen consumption#Locomotor activity#Respirometry#Thermal gradient#Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5)#Tropical-stenotherm#Species persistence#Distribution#Ecosystem health