Using Rockpool Fish Behaviour to Understand why Rockpools are so Species Rich

Blenny

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The Cocos frill goby (Bathygobius cocosensis) and the Eastern jumping blenny (Lepidoblennius haplodactylus) dominate intertidal rockpools in south eastern Australia making them ideal species to use when investigating the diversity of rockpool fish communities. Beautiful illustrations by Tilley Wood (Instagram: @tilleymadethis).

Following on from a previous fish thinkers guest post: “Close to home: what drives the distribution of intertidal rockpool fishes?”, University of Wollongong Researchers  Kai Paijmans and Dr Marian Wong  have published new research that offers novel insight into the secretive goings on of rockpool fish communities.

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For those who aren’t inclined to wade through scientific literature, Below is an overview by lead author Kai for your enjoyment.

I have spent the last 3 years catching, counting, measuring, tagging, observing and even determining the sex of rockpool fishes along rocky shores of south eastern NSW, Australia. My aim being to understand how incredibly diverse communities of fish can inhabit such confined habitats. Two species in particular (The Cocos frill goby and the Eastern jumping blenny) provide an ideal opportunity to investigate this aim because they occur together in large numbers within rockpools and occupy similar habitats. Preliminary investigations which are described in my previous post suggest that the Cocos frill goby may be competitively dominant, limiting the distribution of other species. However, if this is the case how do competitively inferior species (e.g. the Eastern Jumping blenny) persist in high numbers?

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A Cocos frill goby; a small but highly aggressive species found in marine rockpools

To understand if the Cocos frill goby is indeed competitively dominant, I conducted a series of aquarium based contest experiments which involved placing a goby and blenny in an aquarium designed to replicate a natural rockpool. The pair where given a single rock shelter to compete over, meaning dominance could be determined by observing which species gained access to the shelter and which was “kicked out”. The results clearly showed the goby to be a superior competitor, being highly aggressive and winning access to the shelter in almost 100% of trials. Interestingly, the blennies changed their choice of habitat when in the same pool as a goby. When solitary blennies hung out on the bottom of the pool, however when in with a goby they moved onto the side walls. This behaviour suggests that “microhabitat partitioning” is occurring between species within a single pool. By hanging out in slightly different areas within a rockpool the blennies can avoid the highly aggressive gobies whilst still residing in the same pools.

To further understand how competitively inferior species (such as the Eastern jumping blenny) live in such confined spaces with their highly aggressive pool-mates, I captured tagged and released both gobies and blennies in rockpools along a stretch of coastline close to my hometown of Wollongong.  By repetitively returning to the same pools and identifying fish based on their tag colours, I could measure the attachment that each individual fish shows to a “home” pool. Results revealed that gobies were far more attached to a specific pool than blennies, suggesting that blennies are more flexible with their living arrangements and hence likely avoid aggressive confrontations by simply moving pool.

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So why is it important to understand the social politics of fish in rockpools? Well aside from the fact that rockpool life is fascinating, understanding how multiple species can get along and coexist provides insight into how biodiversity is maintained. Typically, biodiversity is understood as a function of habitat availability with more habitats meaning more species. However, it is also important (as demonstrated by this study of rockpool fish) to consider the interactions between species and the behaviours displayed in response to those interactions.

If you do want to take a look at the full article and don’t have access past the paywall then Kai can provide a PDF if you email him at kp094@uowmail.edu.au

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