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Front. Mar. Sci. | doi: 10.3389/fmars.2019.00062

Variability of seawater chemistry in a kelp forest environment is linked to in situ transgenerational effects in the purple sea urchin, Strongylocentrotus purpuratus

  • 1University of California, Santa Barbara, United States

While the value of giant kelp (Macrocystis pyrifera) as a habitat-forming foundation species is well-understood, it is unclear how they impact the oxygen concentration and pH of the surrounding seawater, and further, how such a dynamic abiotic environment will affect eco-evolutionary dynamics in a context of global change. Here, we profiled the nearshore kelp forest environment in Southern California to understand changes in dissolved oxygen (DO) and pH with high spatiotemporal resolution. We then examined transgenerational effects using sea urchins (Strongylocentrotus purpuratus) as our study organism.
Using enclosures on the benthos, we conditioned adult sea urchins in situ at two locations - one inside the kelp forest and one outside the kelp forest. After a 11 week conditioning period timed to coincide with gametogenesis in the adults, the urchins were collected, spawned, and cultures of their progeny were raised in the laboratory in order to assess the performance of the progeny to simulated ocean acidification. In terms of the physical observations, we observed significant changes in DO and pH not only when comparing sites inside and outside of the kelp forest, but also between surface and benthic sensors at the same site. DO and pH at the benthos differed in mean, the amplitude of the diel signal, and in the profile of background noise of the signal. Ultimately, these results indicated that both DO and pH were more predictably variable inside of the kelp forest environment. On the biological side, we found that adult sea urchins inside the kelp forest produced more protein-rich eggs that developed into more pH-resilient embryos. Overall, this study in a temperate kelp forest ecosystem is one of the first studies to not only observe biological response to highly characterized environmental variability in situ, but also to observe such changes in a transgenerational context.

Keywords: pH, dissolved oxygen, Coastal variability, Strongylocentrotus purpuratus, Purple urchin, Kelp forest, Macrocystis pyrifera, transgenerational plasticity

Received: 18 Oct 2018; Accepted: 05 Feb 2019.

Edited by:

Iris E. Hendriks, Universitat de les Illes Balears, Spain

Reviewed by:

Laura Ramajo, Adolfo Ibáñez University, Chile
Christopher E. Cornwall, Victoria University of Wellington, New Zealand  

Copyright: © 2019 Hoshijima and Hofmann. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Umihiko Hoshijima, University of California, Santa Barbara, Santa Barbara, United States, uhoshijima@ucsb.edu