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1. Individual and population‐level variation in susceptibility to temperature in early life history stages of giant kelp

   https://doi.org/10.1111/maec.12770  

   Kurman, Melissa D.; terHorst, Casey (August 2023, Marine Ecology)

   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. 

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2. Modeling grazer-mediated effects of demographic and material connectivity on giant kelp metapopulation dynamics

   https://doi.org/10.3354/meps14475  

   Detmer, AR (January 2024, Marine Ecology Progress Series)

   From dispersal-based metapopulations to meta-ecosystems that arise from flows of non-living materials, spatial connectivity is a major driver of population dynamics. One potentially important process is material transport between populations also linked by individual dispersal. Here, I explored material and demographic connectivity in metapopulations of giant kelpMacrocystis pyrifera, a foundation species that produces both detritus and reproductive spores. Kelp detritus (drift) subsidizes grazers, helping maintain the kelp forest ecosystem state. Drift could potentially be exchanged among kelp patches, but this is less studied than spore dispersal. Therefore, I built an ordinary differential equation (ODE) model to investigate conditions under which drift and/or spore connectivity promotes the kelp forest state. I fit statistical models (generalized linear mixed models, GLMMs) to observational data and used the GLMM’s predictions to validate the ODE model. My results suggest kelp patch dynamics are best explained by connectivity of both drift and spores, and that the impacts of these forms of connectivity depend on local grazer (urchin) abundance. Both models predicted greater kelp persistence in well-connected patches across a range of urchin densities. These effects were largely driven by drift, which reduced grazing in recipient patches and thereby enhanced spore recruitment. While testing these predictions will require greater empirical quantification of interpatch drift transport, my findings indicate drift connectivity may be an important spatial process in kelp forest systems. More broadly, this work highlights the role of meta-ecosystem dynamics within a single ecosystem type, reinforcing the need to expand traditional metapopulation perspectives to consider multiple forms of spatial connectivity. 

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3. An Automated Method for Mapping Giant Kelp Canopy Dynamics from UAV

   https://doi.org/10.3389/fenvs.2020.587354  

   Cavanaugh, Katherine C.; Cavanaugh, Kyle C.; Bell, Tom W.; Hockridge, Evan G. (February 2021, Frontiers in Environmental Science)

   Satellite and aerial imagery have been used extensively for mapping the abundance and distribution of giant kelp ( Macrocystis pyrifera ) in southern California. There is now great potential for using unoccupied aerial vehicles (UAVs) to map kelp canopy at very high resolutions. However, tides and currents have been shown to affect the amount of floating kelp canopy on the water surface, and the impacts of these processes on remotely sensed kelp estimates in this region have not been fully quantified. UAVs were used to map fine-scale changes in canopy area due to tidal height and current speed at kelp forests off the coast of Palos Verdes, CA and Santa Barbara, CA. An automated method for detecting kelp canopy was developed that was 67% accurate using red-green-blue (RGB) UAV imagery and 93% accurate using multispectral UAV imagery across a range of weather, ocean, and illumination conditions. Increases in tidal height of 1 m reduced the amount of floating kelp canopy by 15% in Santa Barbara and by over 30% in Palos Verdes. The effect of current speed on visible kelp canopy was inconclusive, but there was a trend towards lower canopy area with increased current speed. Therefore, while tidal height and current speed can introduce significant variability to estimates of kelp abundance, the magnitude of this variability is site specific. Still, UAVs are a valuable tool for mapping of kelp canopy and can provide greater spatial resolution and temporal coverage than is possible from many satellite sensors. This data can provide insight into the patterns and drivers of high frequency fluctuations in kelp abundance. 

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4. Distance, elevation and environment as drivers of diversity and divergence in bumble bees across latitude and altitude

   https://doi.org/10.1111/mec.14735  

   Jackson, Jason M.; Pimsler, Meaghan L.; Oyen, Kennan Jeannet; Koch‐Uhuad, Jonathan B.; Herndon, James D.; Strange, James P.; Dillon, Michael E.; Lozier, Jeffrey D. (June 2018, Molecular Ecology)

   Abstract Identifying drivers of dispersal limitation and genetic differentiation is a key goal in biogeography. We examine patterns of population connectivity and genetic diversity using restriction site‐associatedDNAsequencing (RADseq) in two bumble bee species,Bombus vosnesenskiiandBombus bifarius,across latitude and altitude in mountain ranges from California, Oregon and Washington, U.S.A.Bombus vosnesenskii, which occurs across a broader elevational range at most latitudes, exhibits little population structure whileB. bifarius, which occupies a relatively narrow higher elevation niche across most latitudes, exhibits much stronger population differentiation, although gene flow in both species is best explained by isolation with environmental niche resistance. A relationship between elevational habitat breadth and genetic diversity is also apparent, withB. vosnesenskiiexhibiting relatively consistent levels of genetic diversity across its range, whileB. bifariushas reduced genetic diversity at low latitudes, where it is restricted to high‐elevation habitat. The results of this study highlight the importance of the intersect between elevational range and habitat suitability in influencing population connectivity and suggest that future climate warming will have a fragmenting effect even on populations that are presently well connected, as they track their thermal niches upward in montane systems. 

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5. A scaffolded and annotated reference genome of giant kelp (Macrocystis pyrifera)

   https://doi.org/10.1186/s12864-023-09658-x  

   Diesel, Jose; Molano, Gary; Montecinos, Gabriel J; DeWeese, Kelly; Calhoun, Sara; Kuo, Alan; Lipzen, Anna; Salamov, Asaf; Grigoriev, Igor V; Reed, Daniel C; et al (December 2023, BMC Genomics)

   Abstract Macrocystis pyrifera(giant kelp), is a brown macroalga of great ecological importance as a primary producer and structure-forming foundational species that provides habitat for hundreds of species. It has many commercial uses (e.g. source of alginate, fertilizer, cosmetics, feedstock). One of the limitations to exploiting giant kelp’s economic potential and assisting in giant kelp conservation efforts is a lack of genomic tools like a high quality, contiguous reference genome with accurate gene annotations. Reference genomes attempt to capture the complete genomic sequence of an individual or species, and importantly provide a universal structure for comparison across a multitude of genetic experiments, both within and between species. We assembled the giant kelp genome of a haploid female gametophyte de novo using PacBio reads, then ordered contigs into chromosome level scaffolds using Hi-C. We found the giant kelp genome to be 537 MB, with a total of 35 scaffolds and 188 contigs. The assembly N50 is 13,669,674 with GC content of 50.37%. We assessed the genome completeness using BUSCO, and found giant kelp contained 94% of the BUSCO genes from the stramenopile clade. Annotation of the giant kelp genome revealed 25,919 genes. Additionally, we present genetic variation data based on 48 diploid giant kelp sporophytes from three different Southern California populations that confirms the population structure found in other studies of these populations. This work resulted in a high-quality giant kelp genome that greatly increases the genetic knowledge of this ecologically and economically vital species. 

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