Understanding how marine species adapt to environmental changes is crucial for predicting coastal population dynamics. Extreme sea surface temperature (SST) anomalies have highlighted the need for intertidal research focusing on thermal tolerance and habitat shifts. However, in situ monitoring in wave-dominated rocky intertidal ecosystems presents significant challenges due to harsh conditions. Mollusc shells have emerged as high-resolution sea-surface temperature proxies and archival growth records, but this has not been demonstrated for the tropical rocky intertidal environment, which is characterized by warmer waters, mixed tides, trade-wind patterns, and significant wave action. The endemic Hawaiian intertidal limpet, *Cellana sandwicensis*, a significant biocultural resource, is an ideal candidate for such a study. This research aims to reconstruct the near-daily spatiotemporal oxygen isotope signatures of *C. sandwicensis* to understand its response to environmental factors and provide a high-resolution proxy for tropical intertidal climate.

Numerous studies have successfully reconstructed seasonal to millennial SST from mollusc shells in mid-to-high latitudes, where δ¹⁸O is strongly correlated with seawater temperature. However, low-latitude SST proxies are limited, mainly to subtidal organisms (corals), due to the confounding effects of hydrological processes on δ¹⁸O. Mollusc limpet shells, with their wide distribution, sequential growth, and archeological preservation, offer potential as a tropical intertidal climate proxy. Previous studies have shown that limpet shells can reveal seasonal growth patterns, but high-resolution reconstructions, particularly in the tropical intertidal zone, have been lacking. Existing research on *Cellana* species in the Hawaiian archipelago is limited due to the challenging environmental conditions. This study builds upon previous work on molluscan sclerochronology and geochemical proxies, expanding their application to a tropical intertidal setting.

The study used three *C. sandwicensis* shells: two modern and one historical. Shell microstructure was characterized using Scanning Electron Microscopy (SEM) and Raman microscopy, identifying suitable calcite layers (M+2) for isotopic analysis. Secondary Ion Mass Spectrometry (SIMS) was used to analyze oxygen isotopes (δ¹⁸O) at a near-daily spatial scale, with measurements taken across a 15 µm² area representing 1-3 days of growth. The δ¹⁸O values were compared to calculated values using established equilibrium fractionation equations, considering seawater temperature and salinity. Growth lines were classified into major (annual), minor (lunar), and micro (tidal) increments, providing a sclerochronological framework. The von Bertalanffy growth function (VBGF) was used to model shell growth, comparing individual and pooled data. Sea surface temperature (SST) was reconstructed from the historical specimen by modeling across a range of salinities. Daily and monthly growth rates were analyzed to understand temporal changes in growth, considering factors like spawning periods and environmental conditions. The study site, Ka’alawai on Oahu, Hawaii, is characterized by a mixed tidal cycle, significant wave action, and a unique geochemical profile due to submarine groundwater discharge. Data from _in situ_ PacIOOS Nearshore Sensor 04 (NS04) were used to obtain sea-surface temperatures.

SIMS analysis achieved sub-weekly to daily resolution in the oxygen isotope profile of *C. sandwicensis*, the highest spatiotemporal resolution reported for a tropical intertidal limpet. A strong correlation between measured and calculated δ¹⁸O values validated the use of limpet shell records for seasonal interpretations of growth and life history. The historical specimen (BPBM) exhibited a wide δ¹⁸O range, suggesting a more aerially exposed environment compared to the modern specimens. Reconstructed SST for BPBM, at a salinity of 42 psu, ranged from 15.5 °C to 38.0 °C. Shell growth lines reflected tidal patterns, with narrower bands during spring tides and wider bands during neap tides. Wave exposure appeared to interrupt consistent daily growth patterns. Modern specimens showed growth cessation during primary and secondary spawning periods (December-March and June-August, respectively). The VBGF model indicated determinate growth for *C. sandwicensis*, with a maximum shell length (L∞) of 75.233 mm and a growth coefficient (K) of 0.0371. Estimated longevity was 5 years for the historical specimen, similar to other *Cellana* species. Age-at-maturity was estimated to be 8–9 months (~21 mm shell length), differing from previous reports. Daily growth rates varied seasonally and were correlated with growth frequency.

The high-resolution oxygen isotope data provide valuable insights into the life history and environmental responses of *C. sandwicensis*. The study demonstrates the potential of limpet shells as a reliable proxy for reconstructing tropical intertidal climate, particularly in areas with limited instrumental data. While the strong correlation between measured and calculated δ¹⁸O values supports the use of this proxy, future studies should validate the isotopic equilibrium assumption using conventional gas source mass spectrometry (GSMS) and SIMS. The observed growth patterns, including the effects of tides, waves, and spawning periods, reveal the complex interplay between biological and environmental factors shaping limpet growth. The reconstructed thermal thresholds and growth rates provide crucial information for understanding *C. sandwicensis* ecology and informing management strategies for this important biocultural resource. The use of archival specimens extends the temporal reach of this methodology, opening avenues for paleoecological research in the Hawaiian Islands.

This research successfully demonstrates a robust method for reconstructing near-daily life-history and environmental information from the shells of tropical intertidal limpets using SIMS oxygen isotope analysis. The study provides a new high-resolution proxy for tropical intertidal climatology and reveals important details about the growth patterns and longevity of *C. sandwicensis*. Future work should focus on validating the isotopic equilibrium assumption and further investigating the impacts of various environmental factors on limpet growth and population dynamics. The methodology developed here can be applied to other tropical intertidal mollusc species and archeological contexts.

The study's interpretation of δ¹⁸O values relies on the assumption of isotopic equilibrium between biogenic calcite and seawater, which needs further validation. The exact location of the historical specimen is unknown, potentially introducing uncertainty in the environmental reconstruction. While the study considers several environmental factors, other variables (such as food availability and specific microhabitat conditions) may also influence limpet growth. The sample size of three shells, though providing valuable insights, limits the statistical power of some analyses.