Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • BCO-DMO Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

This dataset represents a subset of a longer-term monitoring effort of tagged Lottia gigantea individuals conducted across California intertidal sites. The dataset includes annual measurements collected between 2023 and 2024 and associated survey-derived habitat and grazer community metrics. The related dataset (found in the Related Dataset section) contains growth measurements from earlier survey years, but does not include community sampling data.

Variation in biotic communities:

We surveyed L. gigantea habitats to test whether the biotic environment differed among the four range core sites and four expanding edge sites, and whether variation in L. gigantea performance was associated with the biotic environment. We considered Dillon Beach, Bodega Marine Reserve, Fort Ross, and Kruse Ranch to be in the expanded range (Sanford et al., 2019), and Vandenberg, Seal Beach, Soberanes Point, and Hopkins Marine Station to be in the range core. Given that L. gigantea have a patchy distribution (Fenberg & Rivadeneira, 2011), we haphazardly established 50-100 1m² plots with limpets present at each site, across approximately 300 m of intertidal habitat. Each plot was marked with marine epoxy (Zspar splash zone compound) in its center. Within each plot, we tagged a single focal L. gigantea using a small (< 6 mm) Floy Tag fixed to the anterior end of the shell using a small dab of marine epoxy (Zspar splash zone compound). For each tagged focal limpet, we recorded growth rate using calipers to relate performance to variation in environmental factors.

For each plot in summer 2023, we sampled the community of competing species within the territories of the focal limpet from 8 sites. Owl limpets are sympatric with several other intertidal grazing species across their range, including limpets (L. scabra, L. digitalis, L. pelta), chitons (Nutallina spp.), and snails (Tegula funebralis) (Stimson, 1973). L. gigantea territories are clearly recognizable as darker areas on the substrate (Fenberg, 2013), so we counted all individuals of the above mentioned grazing species within the territories of the tagged focal limpets and measured the territory area on imageJ to record density (Schneider et al., 2012). In cases which the territory boundary was uncertain, or territories overlapped, we counted all individuals within a 0.25 m² quadrat, placed with the focal owl limpet at its center. We did not count grazers < 5 mm as Lottia congeners are often indistinguishable at that size, cryptic, and difficult to count accurately.

Quantifying performance:

To quantify performance across the range in response to biotic drivers, we recorded organismal growth rate as a function of the environmental data collected within each 1m² plot. In L. gigantea growth rate is a strong metric for performance and fitness, as shell length scales with gonad mass (Kido & Murray, 2003). We measured shell length for all tagged limpets from the anterior to posterior end of the shell using calipers. Each focal limpet was measured annually between 2021 and 2023 (see Related Dataset for additional data), and because limpet starting size differed, we calculated relative growth rate (RGR) as ln(SL_Final/SL_Initial/Δt), where SL is shell length and t is time (Paine et al., 2012). 

- Loaded tagging.growth.24.csv as table "res1" with empty string and "nd" treated as missing values
- Renamed 19 columns to replace dots and abbreviations with underscores and full names: Territory.Area -> Territory_Area, L.scabra -> L_scabra, L.scabra.density -> L_scabra_density, L.digitalis -> L_digitalis, L.digitalis.density -> L_digitalis_density, L.pelta -> L_pelta, L.pelta.density -> L_pelta_density, Nutallina.density -> Nutallina_density, Nuttallina.sp -> Nuttallina_sp, Tegula.funebralis -> Tegula_funebralis, Tegula.funebralis.density -> Tegula_funebralis_density, Total.grazers -> Total_grazers, Total.grazers.density -> Total_grazers_density, Length_i -> Length_initial, Width_i -> Width_initial, Date_i -> Date_initial, Length_f -> Length_final, Width_f -> Width_final, Date_f -> Date_final
- Stripped leading and trailing whitespace from Date_initial and Date_final columns
- Converted Date_initial from %m/%d/%y format to ISO date format %Y-%m-%d
- Converted Date_final from %m/%d/%y format to ISO date format %Y-%m-%d
- Renamed Nutallina_density to Nuttallina_density (corrected spelling)
- Replaced site code "BMR" with full name "Bodega Marine Reserve" in the Site column
- Output final data to 1000468_v1_limpet_tagging_growth_2023_2024.csv

NSF abstract:
Anthropogenic climate change is shifting the distributions of species across the globe. Such contemporary shifts in species’ ranges may have cascading effects on entire ecosystems. This project disentangles the mechanisms underlying climate-driven species range shifts in marine systems using the intertidal owl limpet as a case study. During the recent marine heatwaves off the Pacific coast of North America, populations at the northern range limit in northern California have expanded, with ongoing reproduction even after termination of the heatwave events. This is therefore an ideal system to explore the dynamics of natural selection that occur as species occupy new regions. Broadly, this project deepens understanding of how range shifts occur in marine systems and furthers the ability to predict future species distributions in response to climate change. The project provides research experiences for high school and undergraduate students from historically underrepresented groups by engaging with existing, demonstrably-effective programs. The investigators host leadership and skill-building workshops for senior female graduate students and engage the public in partnership with the California Academy of Sciences, Bodega Marine Lab, and San Francisco Exploratorium. Finally, the project provides training for a postdoctoral scholar and two graduate students.

Although phenomenological studies suggest that climate-associated range shifts are common in marine systems, to date, mechanistic studies of the climate-organism interactions that alter geographic distributions have largely focused on terrestrial systems. However, dispersal dynamics greatly differ in many marine systems, as currents may frequently transport planktonic larvae into new environmental regimes. This project integrates detailed demographic observations of the recent range expansion of the intertidal owl limpet, Lottia gigantea, with ecological, phenotypic, and genomic measurements of divergence across its range. Specifically, the work 1) documents phenotypic divergence in larval and juvenile traits across the zone of range expansion, 2) uses whole genome sequencing to estimate gene flow across the entire range, 3) identifies genomic patterns of selection across the zone of range expansion and through time, and 4) identifies drivers of variation in performance over latitudinal and microgeographic scales. The ability to monitor this range shift in real time, along with the suitability of this system for tracking individuals across multiple years, allows the investigators to examine the impact of selection in novel range-edge conditions at the phenotypic and genomic levels, and scale from individuals to species-level responses to ongoing environmental change.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.