We conducted a population genetic analysis of the stalked kelp,
- Award ID(s):
- 2023555
- NSF-PAR ID:
- 10434109
- Publisher / Repository:
- Environmental Data Initiative
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Pterygophora californica , in the Santa Barbara Channel, California,USA . The results were compared with previous work on the genetic differentiation of giant kelp,Macrocystis pyrifera, in the same region. These two sympatric kelps not only share many life history and dispersal characteristics but also differ in that dislodgedP. californica does not produce floating rafts with buoyant fertile sporophytes, commonly observed forM. pyrifera . We used a comparative population genetic approach with these two species to test the hypothesis that the ability to produce floating rafts increases the genetic connectivity among kelp patches in the Santa Barbara Channel. We quantified the association of habitat continuity and oceanographic distance with the genetic differentiation observed in stalked kelp, like previously conducted for giant kelp. We compared both overall (across all patches) and pairwise (between patches) genetic differentiation. We found that oceanographic transit time, habitat continuity, and geographic distance were all associated with genetic connectivity inP. californica , supporting similar previous findings forM. pyrifera . Controlling for differences in heterozygosity between kelp species using Jost'sD , we showed that global differentiation and pairwise differentiation were similar among patches between the two kelp species, indicating that they have similar dispersal capabilities despite their differences in rafting ability. These results suggest that rafting sporophytes do not play a significant role in effective dispersal ofEST M. pyrifera at ecologically relevant spatial and temporal scales. -
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Abstract Urea is an available and readily used source of nitrogen for giant kelp,
Macrocystis pyrifera , but little is known about its potential importance for sustaining growth. Results of kinetic experiments indicate urea uptake saturates at an average maximum rate (V max) of 0.73–0.92μ mol N g dw−1h−1with a half saturation constant (K s) of 1.02–1.08μ M. The affinity of giant kelp for urea was high relative to that reported for other seaweeds. However, results of similar kinetics experiments with natural, co‐occurring phytoplankton communities indicate that the rate of urea uptake by phytoplankton was > 10‐fold higher than that of giant kelp. Urea uptake by giant kelp decreased 3–12% in darkness (relative to in light) compared to a 66–85% decline for phytoplankton. Similar differences were observed for ammonium and nitrate, suggesting that light intensity and photocycles influence the outcome of competition for N between giant kelp and phytoplankton. Monthly measures of urease in kelp tissues revealed persistent activity at levels that were 100‐fold higher than rates of urea uptake (0.13–0.35μ mol N g fw−1min−1). This finding, coupled with unsuccessful efforts to induce additional urease activity through substrate additions, suggests that urease plays a role in giant kelp physiology beyond that of processing urea taken up from the environment. Collectively, our results suggest giant kelp uses multiple forms of N including urea to sustain year‐round growth. Its consistent capacity to acquire N during both day and night may help offset its low uptake rates relative to phytoplankton and increase its ability to compete for N during periods of low N availability. -
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Production rates reported for canopy‐forming kelps have highlighted the potential contributions of these foundational macroalgal species to carbon cycling and sequestration on a globally relevant scale. Yet, the production dynamics of many kelp species remain poorly resolved. For example, productivity estimates for the widely distributed giant kelp
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These data describe 1987-2019 time series of giant kelp (Macrocystis pyrifera) biomass and associated environmental variables (wave height, nitrate concentration, climate indices) at quarterly and annual time intervals. Data for spatially resolvable variables (giant kelp biomass, wave height, nitrate concentration) pertain to 361 coastline segments (500 m length) in southern and central California where giant kelp was persistent over the sampling period. Data are contained in 5 tables: 1) quarterly time series of giant kelp biomass, wave height, and nitrate concentrations for 361 coastline segments; 2) quarterly time series of aspatial climate indices (NPGO, MEI, PDO); 3) annual time series of giant kelp biomass, wave height, and nitrate concentrations for 361 coastline segments; 4) annual time series of aspatial climate indices (NPGO, MEI, PDO); 5) locations (latitude and longitude of center) of coastline segments. Kelp data are derived from satellite imagery using empirical relationships. Wave data are derived from an empirically validated swell propagation model. Nitrate data are derived from empirical relationships with remotely-sensed sea surface temperature.more » « less
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Abstract Because foundation species create structure in a community, understanding their ecological and evolutionary responses to global change is critical for predicting the ecological and economic management of species and communities that rely on them. Giant kelp (
Macrocystis pyrifera ) is a globally distributed foundation species with seasonal fluctuations in abundance in response to local nutrient levels, storm intensity, and ocean temperatures. Here we examine genetic variation in individual and population‐level responses of early life history stages (zoospore settlement, survival, and gametogenesis) to increased temperatures to determine the potential for natural selection on temperature‐tolerant individuals that would allow adaptation to a changing climate. We collected fertileM. pyrifera sporophyll blades from three sites along the California coast (Los Angeles, Santa Barbara, Monterey Bay) and induced zoospore release in the lab. Spores settled on microscope slides at three treatment temperatures (16, 20, and 22°C), matured for 21 days, and were imaged weekly to determine settlement, survival, and maturation success. On average, individuals from all sites showed lower rates of settlement and maturation in response to increasing temperature. However, the magnitude of the responses to temperature varied among populations. Survival tended to increase with temperature in Los Angeles and Santa Barbara populations but decreased with increasing temperature for the Monterey Bay population. We observed little genetic variation in temperature responses among individuals within sites, suggesting little scope for evolution within populations to increase the resilience ofM. pyrifera populations to warming ocean temperatures and predicted declines in kelp abundance. Yet sufficient dispersal among populations could allow for adaptation of early life history traits among populations via evolutionary rescue of declining populations.
