(5) We hypothesise that gall crabs are able to offset negative effects of disturbances via increased reproductive output. Their high population turnover further suggests that they contribute to reef energy cycling by converting host-derived resources into forms accessible to higher life forms.

(4) By calculating turnover and mortality rates, we show that some reefs maintained reproductively active and resilient populations despite extensive bleaching, while compounded stressors at one site led to a population collapse.

(3) Fate-tracking revealed surprisingly high population turnover with steady colonisation and extinction events as well as settlement preferences for already inhabited hosts.

(2) We fate-tracked nearly 800 crabs for 2 years, capturing the 2023 Red Sea bleaching event. In addition, we performed belt transect surveys for comparison. These surveys showed that reef-specific effects drive gall crab abundance and prevalence over cross-shelf gradients.

(4) Our findings emphasize the need to better understand the ecological roles of cryptic symbionts on coral reefs, as these invertebrates are integral parts of multisymbiotic systems, yet their contributions to reef functioning remain largely unquantified. Huge thanks to everyone involved!

(3)The results were surprising: no consistent negative impact of gall crabs on photosynthetic efficiency.
In some cases, we even observed slight increases.
These findings suggest that crabs take a neutral role toward the algal symbionts of stony corals.

(2) Here we applied this technique—a method typically used to assess stress responses in coral algal symbionts—to coral-crab associations for the first time. This allowed us to look for potentially concealed local effects the crabs might have on the zooxanthellae in their hosts' tissue.

(6) Differences in fluorescence expression may be linked to variations in their microhabitats. Crabs living in enclosed galls don't fluoresce, while others inhabiting more open dwellings show vivid fluorescence. Fluorescence may play a role in camouflage on the fluorescent coral host background.

(5) By performing ancestral state reconstruction and combining the morphology results with a phylogenomic reconstruction, we show that fluorescence is phylogenetically widespread in the family. It evolved once in the genus Opecarcinus and was subsequently retained with varying expression levels.

(4) This analysis revealed four distinct fluorescent morphologies (Fluotypes). Each of these fluotypes has distinct characteristics, such as cheliped or abdominal fluorescence.

(3) We developed a fluorescent imaging technique for a multivariate trait analysis based on 27 morphological characters.

(2) We found gall crabs to display a vivid orange fluorescence that is visible without an excitation light source (A). Based on these observations, we hypothesised that it may be an adaptive trait for this family of decapods.

Hey, never apologize for asking random questions about crabs! This is literally my career haha

the crabs perish. They can not survive long without a living host. They feed on coral mucus, so their food source disappears... I'm currently preparing the results of a long-term study on their response to bleaching for publication so stay tuned!

Hello Erick, *almost Dr :) Thanks for your interest in these critters. They can not leave their hosts; the females, especially, are almost forced to stay within their dwellings. When the coral bleaches they can persist, I found them to be actually quite resilient. However, if the host dies

Currently there are nearly 60 described gall crab species that settle on a really diverse set on host families. They are host specific though, to varying degrees. Some species settle on a single host species only, some others are a bit more flexible.

So far we have no strong evidence that their presence has any significant negative effects on their hosts but stay tuned for more research about this soon! 🦀
They do feed on coral mucus but since thats continously produced by the coral it doesn‘t seem to be very energy draining.

Wow it looks like it's fluorescent and red fluorescence is not very common in decapods :O