Read below for a great summary by Kai Paijmans on his research examining the distribution of rockpool fishes. Kai’s project was for a 3rd year UOW research subject, where he was supervised by Dr. Marian Wong and Ben Gooden.
Close to home: what drives the distribution of intertidal rockpool fishes?
Rocky intertidal shores are right on the edge of our home – between the known of the shores and the vast unknown of the world’s oceans. Although regularly overstepped by many of us, rockpool life is largely overlooked in favor of large charismatic and untouchable creatures of the open and comparatively inaccessible ocean. It is important to understand the ecological processes occurring on rocky shores as they are right on our doorstep; heavily used for, and potentially impacted upon by recreation.
Rockpools contain fascinating communities of weird creatures that many of us peer at when we walk along the shore. I have studied rockpool fishes on shores surrounding Wollongong in South Eastern Australia. My study aimed to identify what factors drive the distribution of rockpool fishes across intertidal rocky shores. I used a bilge pump to empty pools so as all the fish within a given pool could be captured, identified and measured before release.
Due to the periodic isolation of rockpools during low tide these ‘micro habitats’ produce dynamic and harsh environmental conditions. Large variation in temperature, dissolved oxygen and pH mean that the organisms that inhabit pools need to be tolerant to a dynamic environment and actively select pools with favorable environmental conditions.
If fish species base their pool selection solely on favorable environmental conditions, we could expect that the distribution of different fish species would be correlated with certain environmental conditions. This has been found to be the case with several rockpool fish communities studied globally.
Interestingly my studies found that the distribution of fishes in rockpools in South Eastern Australia was correlated not with abiotic (non-living) environmental conditions, but rather with biotic factors: Namely the presence of the Cocos Frill Goby (Bathygobius cocosensis). I found that the abundance of other fish species was significantly less in pools where the Cocos Frill Goby was present.
These results imply that the Cocos Frill Goby is competitively dominant within this ecosystem and therefore limits the distribution of other fish species, although the precise mechanism by which the Cocos Frill Goby excludes other species remains to be determined. The findings of this study provide the first evidence that competition may be a key determinant of the distribution of fishes on the intertidal rocky shores of South Eastern Australia, challenging the notion that abiotic environmental parameters are the main driving factors of fish distributions on intertidal rocky shores.
My future studies may confirm that competition among fish species is a key factor driving the large diversity of species that live in rockpools on the intertidal rocky shore.
Any questions, thoughts, feedback or constructive criticisms are welcome.