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.