When I first became interested in Oyster Restoration this book was recommended to me - now as a graduate student at San Francisco State University studying olympia oysters I finally got a chance. On the whole, this is a great read. Brennan's recounting of the history of oyster mariculture, and more broadly of the history of Point Reyes is as interesting as it is delightful! The political and personal intrigue involved with all of the characters Brennan introduces is similarly engaging, and it was fun to see names and faces of folks who I know on a professional level turn up. In one of our introductory courses we used the DBOC battle as a case study for debating the pro-con of aquaculture in the marine environment, so it was interesting to read a more thorough take on the whole debacle.
However, I was truly surprised to see Brennan make the claim that Olympia Oysters are non-native not only to Drake's Estero, but to San Francisco Bay (pgs. 196-197, various other places). This did not square away with my knowledge of the subject, so I did some research on the claim. Her citation of Konzak et al. (2011) is somewhat misleading - the authors did find only 9 oysters, but these composed 9% of all shellfish species identified, and 26% of all native species identified. These were also not wholesale excavations of the shellmounds, just a few representative samples. The two contributing authors who performed the shell analysis, both of whom are well regarded marine ecologists with many publications on O. lurida, make no note of these shells potentially being as few as 5 oysters.
In a similar vein, the the Konzak et al (2011), who Brennan cites for this, rely on Milliken et al. (2007) to expand on pre-historic populations of olympia oysters in SF Bay. Unfortunately, Brennan makes a speculative claim about how olympia oysters may have entered the ecosystem based on the account of John Stillwell Morgan, who both did not find olympia oysters in SF Bay and imported massive amounts of them from Willapa Bay (pgs 52-58). Of course, as Brennan and Konzak et al (2011) both state, Olympia Oysters were likely misidentified as Pacific Oysters by researchers who were looking for them. Believing the account of Morgan may be flawed for several reasons, namely that he may have been looking for an oyster that matched his familiar Eastern Oysters, a reef forming oyster that is both larger, and has more noticeable vertical relief than a flat olympia oyster. Furthermore, olympia oyster populations are known to have large inter-annual variability in SF Bay due to freshwater inputs from large rain events, and 1850 (the year Morgan arrived in San Francisco) still ranks as the 15th wettest in recorded history.
To underscore this point, Millikan et al. (2007) make no indication of large amounts of shell deposited from human activity, instead referencing other studies with hypotheses on shifts in human behavior regarding shellfish cultivation. Millikan et al. (2007) is quite thorough, so I'm not sure why Brennan felt the need to speculate in this manner - presumably if shell had appeared in the fossil record from an extraneous source Millikan et al. (2007) would have at least speculated on this. Further genetic studies of O. lurida (Silliman 2019) have identified distinct populations along a latitudinal gradient, including distinct populations in San Francisco Bay and Willapa Bay. Other analyses of estuaries along the West Coast have identified pre-historic olympia oyster shell deposits - it seems unlikely that San Francisco would have been somehow skipped over. Dredging for oyster shells in southern San Francisco Bay continues even today - 40,000 tons of shell per year (Baykeeper) - and it seems unlikely that mariculture operations would have created this quantity (both in amount and in extent in geologic strata) for how (relatively) short a time frame they operated.
I believe this faulty reasoning ultimately stems from a generalization of the habitat of San Francisco Bay and Drake's Estero. Brennan characterizes the Estero, and alludes to San Francisco Bay similarly, as being "soft-bottomed estuaries". This is largely true, and Konzak et al. (2011) found mostly clams and other soft-bottom dwelling shellfish in the estero. However, anyone who has ever been to the intertidal in these locations knows there are abundant naturally formed cobbles, rocks, boulders, and various other kinds of hard substrate that populations of oysters could have used (and still do use!) as habitat.
Most studies of the environmental benefits of olympia oysters have so far agreed that they likely played a marginal role in these ecosystems, especially when compared to other species of oysters. However, there is still much to learn about how this species may benefit the environment today. It is unfortunate that Brennan's narrative leans heavily on the olympia oyster being "non-native", as it is wholly unnecessary to make the case for the shutdown of DBOC. It is unclear if Brennan reached out to the authors of any of the studies I mentioned here, but given how many of the authors involved remain engaged in oyster restoration projects today, it seems hard to imagine this to be the case. As easy as it is to dismiss oyster restoration as "trendy", it would probably have been beneficial to speak with scientists involved with the current restoration of the species to gain a more thorough account of olympia oysters that does not rely on accounts of mariculture entrepreneurs from the 19th century. Citations of Carpenter (1864), Baker (1995), Bonnot (1935), and many other seminal studies and reviews of olympia oyster populations throughout the West Coast are also not included by Brennan.
This is a long review, but overall I really did enjoy this book. The debate over what wilderness should mean is incredibly interesting, and despite being from a oyster sympathetic background I find myself personally siding against the farm in this battle. That being said, the innacuracies regarding olympia oysters are frustrating, and I wish that aspect of the oyster narrative was better done. Many millions of dollars still go towards these projects, Brennan disagrees with a vast body of scientists, studies, and evidence with advancing the claim that olympia oysters are non-native.
TLDR: The book is great, especially with respect to the people, drama, and political intrigue. Olympia oysters are almost certainly native to the area. They probably didn't have an immense ecological impact, so any claims they did by the farm are dubious at best. The picture drawn for oyster restoration projects is dismissive, and Brennan should have done more legwork for that aspect of the story. Reading about Point Reyes inspired me to go hiking around the area some more, and if only for that reason I am happy to have read the book!