Each month, a selected blog from Lizard Island Reef Research Foundation (LIRRF) is featured at the AM. LIRRF supports scientific research & education at the AM’s Lizard Island Research Station on the Great Barrier Reef. This month, we feature: Lizard Island’s smallest fish, and where to find them.

Finally, a long-delayed field trip takes place! Dr Chris Goatley (University of New England) and Dr Simon Brandl (University of Texas Austin) were jointly awarded The John and Laurine Proud Postdoctoral Fellowship for 2020. After two years’ delay forced by COVID-19, they were able to make the first of two annual field trips to Lizard Island in 2022. Here is their report from that trip.

Our project focuses on a group of tiny, camouflaged reef-dwelling fishes known as cryptobenthic fishes or, more simply, cryptos. These fishes are highly abundant on many of the world’s coral reefs, often accounting for half of the fish present on a reef. However, because many crypto species spend their lives hidden from view, they are very difficult to study and have often been overlooked. Recently, we used information on the abundance and lifespans of cryptos from coral reefs around the globe to calculate their potential importance in coral reef food webs. Remarkably, we found that these tiniest of reef fishes may provide more than two-thirds of all the fish tissue consumed by reef predators. In essence, cryptos may form a critical foundation supporting communities of large reef fishes (or anyone who wants to catch or eat those big fish). While this role is clearly important, we currently have a limited understanding of which cryptos live on reefs around the world and an incredibly poor knowledge of what these little fishes eat to support their growth (and, in turn, that of the predators that eat them). In our project, we aim to discover what species of cryptobenthic fishes live on the reefs around Lizard Island and to explore how they differ in their habitat use and diets.

Specimens of different species of the goby genus Eviota collected at Lizard Island. All are less than 3 cm long.

Specimens of different species of the goby genus Eviota collected at Lizard Island. All are less than 3 cm long.

Image: Simon Brandl.
© Simon Brandl.

During our first fellowship field trip to Lizard Island, we used a combination of techniques to survey the crypto communities at Lizard in unprecedented detail. The current “gold-standard” technique for studying cryptos is using enclosed anaesthetic stations, in which we cover a small patch of reef (about the size of a double bed) with a tarp and then pump in a fish anaesthetic (we use clove oil dissolved in alcohol) before collecting all of the anaesthetised cryptos with tweezers and zip-lock bags. This technique is great, as it allows us to collect all of the small fishes in a known area that you would normally never see (the large fishes are usually scared away by the process), but it does mean that you have to remove the fishes from the reef.

Enclosing an area of reef to capture the fishes within.
Enclosing an area of reef to capture the fishes within. Image: Kyra Jean Cipolla.
© Kyra Jean Cipolla.

The second technique we applied aims to reduce our need to collect fishes, by using modern DNA technology. By filtering water through a fine, sterile filter, we can collect “environmental DNA” released by fishes and other reef organisms as shed scales, mucous or faeces. Then, we can amplify the DNA very carefully to avoid contamination and compare the genetic barcodes we recover against known DNA libraries. This means we end up with a list of fishes that have occupied the water we sampled just by doing “filter forensics”. This technique is still relatively new, so by comparing the eDNA data and our enclosed anaesthetic data, we can begin to design new techniques to make our work more fish-friendly in the future.

The final technique we applied focused on understanding the habitats used by crypto species. Modern software and improvements in computer processing power mean we can now build accurate 3D computer models of anything we can photograph. For each of the anaesthetic stations we surveyed, we also made these 3D models, allowing us to compare the shape of the habitat, the availability of crevices for cryptos to hide in, and the species of corals and encrusting reef organisms present in the area. Together these techniques will allow us to begin to build an accurate understanding of the abundance and distribution of cryptos and how habitat availability affects their populations.

Field work at Lizard Island.
Field work at Lizard Island. Image: Kyra Jean Cipolla
© Kyra Jean Cipolla

While we are still very much in the data-analysis stage following our fieldwork, we are beginning to see some interesting findings from our data. Compared to our pilot research conducted in 2018, we were surprised to find smaller numbers of cryptos in our censuses, recording two and a half times fewer fish in 2022 than in previous surveys. Whether this is a reflection of summer versus winter sampling or the major changes that have occurred on the reefs at Lizard in recent years is unknown and a target question for our return trip in 2023. This being said, there are still lots of cryptos out there, with more than ten fishes in every square metre of the reef. Our collections will allow us to assess their diets and look carefully at the species present around Lizard. We have already identified two species that are likely new to science from our collections and are working on describing them with our colleagues in the coming year.

By Dr Chris Goatley | now at University of Southampton, UK, joint 2020 John and Laurine Proud Postdoctoral Fellow. More about Chris and colleague Simon Brandl

To view the original blog and more LIRS blogs, please go to:https://lirrf.org/lizard-islands-smallest-fish-and-where-to-find-them/

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