Can facultative cleaners replace dedicated cleaners?
Although they are the most prominent species of facultative cleaner fish on Caribbean reefs (Feddern 1965, Losey 1974), previous studies ofThalassoma bifasciatum cleaning behavior have reported contrasting results. However, sampling methods across studies have not been consistent. Losey (1974) specifically obserbed and collectedT. bifasciatum paired with Elacatinus spp . at prominent cleaning stations. Dunkley et al. (2018) used focal surveys and video analyses, and our study collected individuals haphazardly from local populations. Losey (1974) found that T. bifasciatum associated with goby cleaning stations spent the majority of their time cleaning while also cleaning a greater diversity of hosts and consuming more gnathiids than Elacatinus spp. Conversely, Dunkley et al. (2018) found that T. bifasciatum spent most of their time foraging on the benthos and interacted with a narrower range of client species compared to dedicated cleaners. However, they did observe a single cleaning station where T. bifasciatum cleaned more often than any other cleaners but only cleaned Acanthurid surgeonfishes. Both studies found that the majority of T. bifasciatum clients were comprised of mobile species such as Acanthurids and Labrid parrotfishes. This means most resident reef species such as Pomacentrids, Holocentrids, Haemulids, and the predatory Serranids, all of which solicit cleaners, would be reliant on alternative cleaning sources (Walsh et al. 2017). Our results show that, although they were less likely to clean thanE. evelynae (100% vs. 64%), T. bifasciatum can consume as many gnathiids as the dedicated cleaners. This is similar to findings from Pacific cleaners (Grutter and Feeney 2016). Further, the maximum gnathiid count for T. bifasciatum was nearly five times higher than that of E. evelynae (138 vs. 29), suggesting that T. bifasciatum has a higher maximum potential for gnathiid consumption. While previous studies have found that only juveniles engage in cleaning behaviors (Feddern 1965, Itzkowitz 1979, Losey 1974), we found evidence of cleaning in the gut contents of all life history stages (juvenile, sub-adult, adult, and terminal male). Thus, dedicated cleaners seem to consume gnathiids more consistently and with less variance compared to the facultative wrasse individuals, but perhaps with a lower ceiling in terms of potential consumption due to their smaller size.
Based solely on the amount of gnathiids consumed, facultative cleaners appear capable of replacing dedicated cleaners (Fig. 3). Indeed, they may be able to impact gnathiid populations solely based on predation pressure. This is supported by the fact that reefs with low coral cover but high T. bifasciatum abundance had lower than expected gnathiid densities (Artim et al. 2020). However, given the apparent differences in client diversity, it seems that in the absence of dedicated cleaners there would be a notable gap where certain species may suffer an increased parasite burden while also lacking the additional benefits cleaning services provide. It seems more likely that facultative cleaners such as T. bifasciatum and dedicated cleaners such as E. evelynae occupy complementary cleaner roles as opposed to redundant cleaner roles.