Ecological Replacement

Editing the English of manuscripts written by Taiwanese academicians – including those from marine biologists who conduct research on Taiwan’s coral reefs – is a part-time job of mine. I can only imagine the palette of colors and species living there thanks to the Kuroshio Current bringing Indo-Pacific coral larvae into their warm waters. I would love to scuba dive them, but that may not ever be in the cards, so I very much appreciate the papers they request me to edit.

This morning, I received a link in my PNAS feed for an opinion piece about employing the concept of “ecological replacement” in Caribbean coral reefs: Coral species from another ocean may be the only way to save Caribbean reefs, by Alejandro E. Camacho, David A. Dana, and Mikhail Matz, Jan. 22, 2026, https://doi.org/10.1073/pnas.2521543123

The piece attempts to add to the voicing that in-place preservation of historical assemblages of coral species in the Caribbean is no longer appropriate in this age of global climate change. Specifically, they draw attention to losses in tropical American waters too warm to sustain elkhorn coral (Acropora palmata) and staghorn coral (Acropora cervicornis). These two species have historically been the most important reef building species in the Caribbean, yet they have not been recruiting to reefs for several decades. They may be functionally extinct.

Authors review the failures over recent decades in reversing this trend by relying solely on the principal of enhancement. This has been done by planting artificially grown plugs of corals into depauperated natural reefs, while simultaneously limiting fishing and other human activity at those reefs. This is also an example of historical preservation, which is the practice of maintaining species assemblages that existed in pre-Columbian times. Authors point out that this has long been the attitude of NOAA and the Florida Fish and Wildlife Conservation Commission.

Needless to say, historical preservation has failed to save Florida’s subtropical coral reefs, so I agree with Camacho et al., that a different approach is needed. It is easy for me to say that, being a member of a group known as the Torreya Guardians, as we have seen that historical preservation is simply not working for the Florida Torreya (Torreya taxifolia) either. Our goal is to alternatively employ assisted migration in an effort to prevent the extinction of that species, one of the world’s most endangered conifers.

For a while, some scientists hoped that corals might migrate poleward as the oceans warmed, that South Florida and Taiwan corals might shift their ranges a mile or so a year, or whatever, and thus keep pace with climate change. However, Taiwan’s marine biologists have demonstrated through field and theoretical research papers that this cannot occur. Let me emphasize this: they have not demonstrated that it PROBABLY will not occur – they have clear evidence that it CANNOT occur.

Corals discharge eggs and sperm into the sea en masse, their fertilized eggs then floating on the Kuroshio Current and Gulf Stream until their larvae hatch and drop out onto hard surfaces. The key word is “hard,” examples being coral reefs, oyster bars, and rock outcrops. However, benthic substrates downstream of Taiwan and Florida are soft sands and muds, not to mention being too deep to sustain commensal zooxanthellae or reef-associated macroalgae and seagrasses. Instead, bypassing coral larvae simply sink into profundal depths and become food for abyssal creatures.

If Florida and Caribbean corals are to survive warming waters, they will have to adapt in place. The fact that the two most important coral species have not yet done so indicates that either they do not have the genetic capability in the first place or they need more time to reawaken it than they have had to date. In either event, the reefs are dying, fisheries and shellfisheries are languishing, and barren substrates are emerging from formerly living landscapes.

Camacho et al. point out that some Indo-Pacific species of Acropora are super-recruiters that “drive spectacularly rapid reef recoveries” in the Far East, whereas there are no similar over-achievers in the New World. They maintain that state and federal lawmakers and bureaucrats should investigate whether Asian corals can fill the ecological gap left in Caribbean reefs by disappearing American Acropora. They recommend a cautious, step by step approach to determine if this can be done without adverse impacts, and use the term, “ecological replacement.” I like it.

Current national and state laws prohibit such introductions of nonnative saltwater organisms into natural waters. Conservative thinkers justify this, citing precaution against any action that might risk irreversible, unintended, and adverse consequences – think feral cats and mongooses. Laws would thus have to be revised to implement ecological replacement.

In my opinion, precaution was good thinking back in the days before global climate change was evident, and before we knew what enabled an introduced species to become invasive. Those of us who have kept up to date, however, know about the former and can cite the litany of the latter. Thus, precautionary principles applied to Caribbean and Florida coral reefs pales beside the absolute certainty of extirpation, if not actual extinction. Either would result in unacceptable ecologic and economic losses.

I refer you to Comacho et al.’s opinion paper for a better idea of their suggested approach. My own pet mitigation project is preventing the extinction of the Florida Torrey. I have witnessed how its recovery has been set back by the precautionary principle. Assisted migration and ecological replacement are, obviously, not the same. The two, however, are similar in recognizing that insistence on artificial time and space boundaries for species ranges will inevitably fail to preserve our heritage in the face of significant and rapid climate change.

We’re all doin’ what we can – John Lennon.