An official website of the United States government
We conducted a population genetic analysis of the stalked kelp, 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 dislodged P. californica does not produce floating rafts with buoyant fertile sporophytes, commonly observed for M. 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 in P. californica, supporting similar previous findings for M. pyrifera. Controlling for differences in heterozygosity between kelp species using Jost’s DEST, 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 of M. pyrifera at ecologically relevant spatial and temporal scales.
more »
« less
Individual and population‐level variation in susceptibility to temperature in early life history stages of giant kelp
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. pyriferasporophyll 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. pyriferapopulations 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.
more »
« less
- Award ID(s):
- 1754449
- PAR ID:
- 10525920
- Publisher / Repository:
- Marine Ecology
- Date Published:
- Journal Name:
- Marine Ecology
- Volume:
- 44
- Issue:
- 6
- ISSN:
- 0173-9565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
These data describe the preferences of two herbivores, the wavy turban snail Megastraea undosa and the Pacific purple urchin Strongylocentrotuts purpuratus for 14 macroalgal species relative to giant kelp Macrocystis pyrifera and the role chemical defenses play in influencing herbivory. Data cover the raw grams consumed and total phenolic content of 15 total macroalgal species found in the Santa Barbara Channel and are taken from three Santa Barbara Coastal Long Term Ecological Research sites (Mohawk Reef, Arroyo Burro Reef, and Naples Reef).more » « less
-
Upwelling provides high amounts of nutrients that support primary production in coastal habitats, including giant kelp Macrocystis pyrifera forests. Growth and recruitment of kelp forests are controlled by environmental conditions, including temperature, nutrient availability, and storms, as well as biotic interactions. However, our understanding of juvenile persistence in the field is extremely limited, particularly the effects of grazing on the survival of early kelp stages and how environmental variability associated with upwelling dynamics may modulate grazing effects. We quantified herbivore impacts on juvenile M. pyrifera by deploying thirteen 24 h caging experiments approximately every 2 wk throughout the upwelling season in a giant kelp forest in Monterey Bay, CA, USA. Experiments spanned a range of natural environmental variation in oxygen, pH, and temperature, conditions known to affect grazer physiology and that are projected to become more extreme under global climate change. Overall, the herbivore community had a large effect on kelp survival, with 68.5% of juvenile kelp removed on average across experiments. Grazing increased throughout the season, which was most strongly correlated with decreasing monthly oxygen variance and weakly correlated with decreasing monthly pH variance and increasing temperature. This suggests that large swings in oxygen during peak kelp recruitment in spring may provide a temporal refuge from grazing, allowing kelp to reach larger sizes by late summer and fall when upwelling has relaxed. This study highlights the potential of current environmental variability, and its predicted increase under future scenarios, to mediate species interactions and habitat persistence.more » « less
-
Abstract Kelp species provide many ecosystem services associated with their three‐dimensional structures. Among these, fast‐growth, canopy‐forming species, like giant kelpMacrocystis pyrifera, are the foundation of kelp forests across many temperate reefs. Giant kelp populations have experienced regional declines in different parts of the world. Giant kelp canopy is very dynamic and can take years to recover from disturbance, challenging comparisons of standing biomass with historical baselines. The Santa Barbara Coastal LTER (SBC LTER), curates a time series of Landsat sensed surface cover and biomass for giant kelp in the west coast of North America. In the last decade, this resource has been fundamental to understanding the species' population dynamics and drivers. However, simple ready‐to‐use summary statistics aimed at classifying regional kelp decline or recovery are not readily available to stakeholders and coastal managers. To this end, we describe here two simple metrics made available through the R package kelpdecline. First, the proportion of Landsat pixels in decline (PPD), in which current biomass is compared with a historical baseline, and second, a pixel occupancy trend (POT), in which current year pixel occupancy is compared to the time‐series long probability of occupancy. The package produces raster maps and output tables summarizing kelp decline and trends over a 0.25 × 0.25° scale. Using kelpdecline, we show how sensitivity analysis onPPDparameter variation can increase the confidence of kelp decline estimates.more » « less
-
These data describe the abundance and size of giant kelp (Macrocystis pyrifera) within permanent plots of SBCLTER's seasonal kelp forest monitoring program to track long-term patterns in species abundance and diversity. The number of giant kelp > 1 m tall were recorded within four contiguous 20 m x 1m permanent plots located within a 40 m x 2 m area. The number of fronds > 1 m tall were counted for each individual and used as an estimate of its size. The experiment was initiated in 2008 at five reef sites along the mainland coast of the Santa Barbara Channel.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/maec.12770
