Intraspecific variation in the organismal stoichiometry of the Least Killifish tracks spatial variation in periphyton composition
Data files
Oct 23, 2025 version files 128.88 KB
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2010-2013_Water_Data.xlsx
17.83 KB
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2012_2013_Fish_Data.xlsx
92.77 KB
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2013_Algae_Data.xlsx
12.04 KB
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README.md
6.24 KB
Abstract
Ecological stoichiometry, the mass-balance relationships in elemental composition among species in an ecosystem, is fundamental to understanding a wide variety of ecological phenomena, from foraging patterns to nutrient cycling (Sterner and Elser 2002). Variation in organismal stoichiometry, be it interspecific or intraspecific, can drive substantial variation in community and ecosystem dynamics (El Sabaawi et al. 2015, Des Roches et al. 2017, Leal et al. 2017a). Here we report a survey of the organismal stoichiometry and trophic niche of H. formosa in eight populations, four from each of two contrasting habitat types. First, we describe variation in water chemistry among a larger set of 17 locations, from which we selected our eight populations for study. We also document variation among these eight locations in the elemental composition of periphyton in the littoral zone, where H. formosa forage. Second, we describe the trophic niche of H. formosa in those eight populations*,* establishing that the fish occupy a trophic position consistent with their being a primary consumer. Third, we examine the organismal stoichiometry in those populations. We show that there is less population variation than has been reported in other species, but the variation that we detected tracks variation in the carbon and nitrogen profiles of the periphyton on which these fish feed.
https://doi.org/10.5061/dryad.3n5tb2rt5
Description of the data and file structure
We sampled water at 17 locations with populations of H. formosa. We selected eight of these locations for stoichiometric and stable isotope analyses: four freshwater springs (McBride’s Slough, Newport Bridge, Shepherd’s Spring, Wacissa River) and four lakes (Harper’s Eyelet, Little Lake Jackson, Moore Lake, Trout Pond). We collected fish via dip netting and sacrificed fish via rapid chilling in an ice slurry, following approved IACUC protocols. We obtained periphyton samples by scraping stems and leaves of aquatic plants, larger rocks, and fallen limbs wherever we saw H. formosa individuals foraging.
Files and variables
File: 2010-2013_Water_Data.xlsx
Description: Water data collected from sites in the years 2010, 2011, 2012, & 2013
Variables
- Site- Location of water collection: McBride’s Slough, Newport Bridge, Shepherd’s Spring, Wacissa River, Harper’s Eyelet, Little Lake Jackson, Moore Lake, Trout Pond
- Chlorophyll_a- Chlorophyll_a Corrected, EPA 445.0 (mg/m^3) - concentration of chlorophyll-a, a pigment found in algae, used to estimate algal biomass in water bodies
- pH- Laboratory pH, SM 4550-H+ -B (mg/L)- acidity or alkalinity of the water. It is important for aquatic life, as most organisms thrive in a narrow pH range.
- Nitrate- Nitrate-N, SM 4500-NO3 E (mg/L)- Nitrate concentration (measured as nitrate-nitrogen) represents the levels of nitrogen in the form of nitrate. Elevated nitrate levels can be a sign of pollution from fertilizers, sewage, or industrial waste, which can harm aquatic ecosystems.
- Total_N (mg/L)- Total Nitrogen, Calculated- Total nitrogen represents the sum of all nitrogen compounds in the water, including nitrate, nitrite, ammonia, and organic nitrogen. It is an indicator of nutrient load and can contribute to eutrophication.
- OrthoPhosphate (mg/L)- Orthophosphate, SM 4500-P E - Orthophosphate is the form of phosphate that is immediately available for biological uptake. Phosphates are essential nutrients for aquatic plants and algae, but excessive amounts can cause water quality issues like algal blooms.
- Total Phosphorus (mg/L)- Total Phosphorus, SM 4500-P E - Total phosphorus represents both organic and inorganic forms of phosphorus in water, including orthophosphate. Like nitrogen, it is a key nutrient that can drive eutrophication if present in excess.
File: 2012_2013_Fish_Data.xlsx
Description: Fish data collected from sites in the years 2012 & 2013
Variables
- Indiv. #- Which individual the data was collected from
- Population- Location of water collection: McBride’s Slough, Newport Bridge, Shepherd’s Spring, Wacissa River, Harper’s Eyelet, Little Lake Jackson, Moore Lake, Trout Pond
- SL (Standard Length) (mm)- The measurement of a fish from the tip of the snout to the base of the tail (caudal peduncle), excluding the tail fin. It is a standard metric used to assess fish size and growth.
- % Nitrogen- The percentage of nitrogen by dry weight in fish tissue. Nitrogen is a key component of proteins and provides insights into the nutritional and metabolic status of the fish.
- % Carbon- The percentage of carbon by dry weight in fish tissue. Carbon is the primary element in organic matter and indicates energy content in the fish’s body.
- % Phosphorus- The percentage of phosphorus by dry weight in fish tissue. Phosphorus is essential for bone formation, cellular energy (ATP), and nucleic acids, and is a limiting nutrient in ecosystems.
- C:N- C:N (Carbon to Nitrogen Ratio): A stoichiometric ratio indicating the balance between carbon and nitrogen in fish tissue. It helps infer protein content and overall nutrient quality.
- C:P- C:P (Carbon to Phosphorus Ratio): This ratio reflects the balance of carbon to phosphorus in fish tissue, providing insight into nutrient demands and growth limitations, especially in relation to skeletal development and metabolic processes.
- N:P- N:P (Nitrogen to Phosphorus Ratio): The ratio of nitrogen to phosphorus in fish tissue. It is used to assess nutrient allocation strategies and can reflect the nutritional ecology and physiological condition
File: 2013_Algae_Data.xlsx
Description: Algae/Periphyton data collected from 8 sites in the year 2013
Variables
- Sample ID- ID of the Periphyton sample
- d13C (δ13C)- The ratio of the stable isotopes 13C to 12C in periphyton, expressed in ‰ (per mil) relative to a standard. It provides insights into the carbon source used by the algae (e.g., atmospheric CO₂ vs. bicarbonate) and can help trace food web carbon flow.
- d15N (δ15N)- The ratio of 15N to 14N, also expressed in ‰ relative to a standard. δ15N is commonly used to infer nitrogen sources (e.g., agricultural runoff, sewage) and trophic position within food webs.
- C Amount (µg)- The absolute amount of carbon in micrograms measured in the periphyton sample. It reflects the total carbon content in the analyzed mass.
- N Amount (µg)- The absolute amount of nitrogen in micrograms in the sample. It indicates the total nitrogen content present in the sample.
- Amount (mg)- The total dry mass of the periphyton sample used for analysis, measured in milligrams. This contextualizes the elemental concentrations.
- %P- The proportion of phosphorus by weight in the periphyton sample. Phosphorus is a key nutrient that often limits algal growth, making %P important in assessing nutrient status.
- %C- The proportion of carbon by dry weight in the periphyton. It is a fundamental measure of organic matter content and energy potential.
- %N- The proportion of nitrogen by dry weight in the periphyton. It reflects protein and nutrient content, important for ecological and stoichiometric studies.
- C:N- The ratio of total carbon to nitrogen in the sample. A higher ratio may indicate carbon-rich, nutrient-poor material, while a lower ratio can suggest higher nutrient quality or nitrogen enrichment.
Code/software
N/A
We sampled water at 17 locations with populations of H. formosa. These locations embraced a variety of habitats, including springs, wooded swamps, open canopy lakes, and freshwater marshes. We selected eight of these locations for stoichiometric and stable isotope analyses: four freshwater springs (McBride’s Slough, Newport Bridge, Shepherd’s Spring, Wacissa River) and four lakes (Harper’s Eyelet, Little Lake Jackson, Moore Lake, Trout Pond). We chose these eight locations for two reasons. First, they spanned a wide range of water chemistry parameters. Second, the populations of H. formosa in these locations displays a wide range of population densities and life histories (Schrader and Travis 2012, Macrae and Travis 2014).
We collected fish via dip netting in the shallow littoral zone, typically at depths less than 0.30 m. We sacrificed fish via rapid chilling in an ice slurry, following approved IACUC protocols. We obtained periphyton samples by scraping stems and leaves of aquatic plants, larger rocks, and fallen limbs wherever we saw H. formosa individuals foraging. We placed all samples on ice for return to the laboratory.
Water Chemistry Methods
We collected water samples by lowering a Nalgene bottle on a long pole into clear water, approximately 1.5 meters from the shoreline and away from aquatic vegetation. We filtered the water on site by pouring through a 10 μl filter and immediately placed the filtered water on ice for transport the same day to Akuritlabs, Inc., in Tallahassee (National Environmental Laboratory Certification E81350) for analyses. We obtained data on pH, concentrations of chlorophyll a, total nitrogen, organic nitrogen, nitrite, nitrate, ionized and unionized ammonia, total phosphorus, and orthophosphate. For analyses, we used data only on pH, chlorophyll a, nitrate, and total nitrogen because only for these variables were concentrations above the detection limit at all locations.
Elemental composition and isotope methods
We prepared fish tissue and periphyton samples for elemental and isotope analyses following Aresco et al. (2015). In brief, upon return to the laboratory, we removed and discarded all internal organs, including reproductive tissue, gut, and liver/viscera, where lipids are stored for future use (McManus and Travis 1998), and freeze-dried the carcasses. We freeze-dried all periphyton samples in the same manner. We ground all freeze-dried material to a fine powder using a WiglBug Model 3110B, rinsing the capsule and grinding bearing with ethanol between samples. For analyses of carbon and nitrogen, we prepared ground material in small tin capsules with, on average, 1 mg fish tissue and 2 mg periphyton. These samples were analyzed using the elemental analyzer and continuous flow isotope ratio mass spectrometer at the University of California, Davis, Stable Isotope Facility.
We analyzed total phosphorus concentration in fish tissue as concentration of 31P with the Thermo 2 inductively coupled plasma mass spectrometry system (ICP-MS) in the Geochemistry Lab at the National High Magnetic Field Laboratory in Tallahassee, Florida. The ICP-MS method is especially accurate for small amounts of sample material or samples with low concentrations of total phosphorus (Cooper et al. 2005; Wilschefski and Baxter 2019). We prepared samples by dissolving them in nitric acid, following protocols described in Wilschefski and Baxter (2019), using 1 ppm phosphorus and 2 ppb indium as internal standards.
Calculation of baseline δ15N values and H. formosa trophic position
We estimated the trophic position of individual H. formosa by correcting for the variation in δ15N values of the identifiable primary producers (trophic level 1; Vander Zanden et al., 1999). For baseline δ15N values, we used those estimated from the periphyton samples at each site. We used the equation
Trophic Position = [(δ^15^N-δ^15^Nbaseline)/3.4]+1,
where 3.4% is the mean enrichment of δ15N between trophic levels as determined in previous studies of fish that have the same range of longevity and tissue turnover rates as fish species in the sites we sampled (Vander Zanden et al., 1999; Aresco et al., 2015).