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Giant kelpMacrocystis pyriferaprovides the foundation for immense biodiversity on the coast of California, USA. Kelp forests can change seawater retention time, altering water chemistry, including pH and dissolved oxygen (DO), as well as the magnitude and predictability of variability in the same properties. Environmental heterogeneity across space and time could drive organismal performance and processes such as transgenerational plasticity (TGP), where parental experience modifies the offspring phenotype, potentially conferring tolerance to future environmental stress. We monitored environmental variability by deploying temperature, pH, and DO sensors inside and outside a temperate kelp forest in the Santa Barbara Channel (SBC) throughout the gametogenesis period of a key herbivore, the purple urchinStrongylocentrotus purpuratus. Over the 6 mo period, pH and temperature were slightly elevated inside the kelp forest, accompanied by more predictable, low-frequency variability relative to outside. AdultS. purpuratuswere conditioned inside and outside the kelp spanning gametogenesis. The urchins were spawned and their larvae were raised under high (1053 µatm) and lowpCO2(435 µatm) at 15°C in the laboratory to assess their physiological response to the maternal and developmental environments. Larvae raised under highpCO2were more susceptible to acute thermal stress; however, within each larval treatment, progeny from outside-conditioned mothers had a 0.4°C higher lethal temperature (LT50). Our results indicate that heterogeneity in abiotic factors associated with kelp can have transgenerational effects in the field, and interactions between factors, including temperature and pH, will impact purple urchins as local variability associated with marine heatwaves and upwelling evolves with climate change.
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Variability in grazing on juvenile giant kelp throughout an upwelling season
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.
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- PAR ID:
- 10411365
- Publisher / Repository:
- Marine Ecology Progress Series
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 693
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 83 to 93
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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