How do patterns in coastal seascapes influence temperate reef fish assemblages?

Daniel Swadling is a new PhD student at the University of Wollongong who is embarking on a project to better understand the relationship between temperate fishes and their habitats. He also loves his luderick and drummer fishing using an old school Alvey reel, so he is going to fit in just fine and I sense there will be plenty of fishing adventures in the future. Below is his guest post recapping his honours project and where he is heading with his PhD research.

My name is Daniel, I am a PhD student at the University of Wollongong (UOW) recently competing my honours in 2016 under the supervision of Prof. Andy Davis, Dr. Nathan Knott (NSW DPI) and fish thinkers own Matt Rees. I have a passion for the ocean, loving to surf, fish and dive from an early age, inevitably this lead to a curiosity in all things marine, particularly anything relating to fish. My research interests are, but not limited to, marine spatial ecology and acoustic telemetry with a focus on applying these to marine conservation. For this blog, I will give an overview of my honours project and my ambitions for future research.

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Photo: Drummer (Girella elevata) and a Silver Drummer (Kyphosus sydneyanus) near Honeymoon Bay

If you use the coastal marine environment you probably realise it is made up of a range of diverse habitats. When you think of these habitats, like seagrass, reefs or mangroves, it’d be fair to assume that they are independent entities, having little to no effect on one another. But in fact, increasing research has suggested these habitats in coastal settings may be connected to one another by various processes. It is important to understand the connectivity between habitats and its influence on marine species as this information increases knowledge for ecology, be used to enhance or preserve fisheries and be applied in marine reserve design.

The movement of organisms is an ecological process which connects habitats. Many species of fish will use multiple habitats during their lives. For example, many reef fish are known to recruit as larvae to nursery areas such as seagrass beds, and when a certain age or size class is reached juveniles will migrate to rocky reefs where they grow into adults. Fish will do this because nursery areas maximise the survival of juveniles by providing food and refuge from predators. Examples of common species in NSW which are known to undertake these movements are Luderick and Bream. I won’t go into detail but there are a variety of other reasons why fish will perform migrations connecting habitat patches, such as foraging for food, spawning or seasonal migrations. If you are interested in this, I suggest you have a look at this paper:

  • Pittman, S & McAlpine, C 2003, ‘Movements of marine fish and decapod crustaceans: process, theory and application’, Advances in marine biology, vol. 44, pp. 205-94.
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Photo: Luderick (Girella tricuspidata) and Bream (Acanthopagrus australis) at Green Point, Jervis Bay.

The success of these movements and other ecological processes are influenced by the composition (the types) and configuration (geographic arrangement) of habitats within an area. Therefore, changes in these habitat patterns can have a significant effect on the abundance and diversity of species found. This provides the foundation of Seascape Ecology, a relatively new field combining geographical analysis and ecology aiming to explain how habitat patterns over large areas explain the distribution of species.

Seascape Ecology research has been focused on tropical environments, where strong linkages have been found between the abundance and/or diversity of fish and the composition and configuration of seagrass, coral reef and mangrove habitats. Despite these vegetated habitats existing in temperate regions, no one to my knowledge has examined the importance of connectivity between seagrass and rocky reef habitats for temperate reef fish assemblages.

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Photo: Male Blue Groper (Achoerodus viridis) at Huskisson

In my recent honours research, I aimed to examine how habitat patterns in the coastal marine environment impact temperate reef fish assemblages. I used unbaited Remote Underwater Videos (RUVS) at a depth of 1.5m to collect information on the abundance and diversity of fish on 22 reefs around Jervis Bay Marine Park. The RUVs were made by cable tying Go Pros onto a brick with a metal base. In total, 81 species spanning 40 families of fish were recorded, with high abundances of many species targeted by fisheries. This fish data was then correlated to habitat patterns within the seascape derived from seabed mapping.

Like tropical research, my findings demonstrated that changes to the composition and configuration of habitat patterns explain changes in temperate reef fish assemblages. The connectivity (distance) between reefs and seagrass beds was particularly important, with reefs close to seagrass beds harbouring a more abundant and diverse fish assemblage (see figure 1 below). We suggest this relationship is likely due to temperate reef fish using seagrass beds as nurseries or foraging locations.

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Figure 1: Relationships between A) Distance to seagrass and the abundance of mobile taxa such as Bream, Luderick and Tarwhine. As you can see as reefs become further away from seagrass the abundance of mobile taxa decreases.

So, you’re probably wondering why this all matters. Well, understanding the influence of seascape patterns on fish can have significant implications for fisheries and conservation strategies. For example, seagrass habitats are vulnerable to degradation with significant losses and a reduction in quality of this habitat worldwide. The findings of our study demonstrate seagrass beds are important in the life history of many fish and its presence increases the abundance and diversity of fish caught in recreational and commercial fisheries. This information highlights the need to protect and preserve these habitats to enhance fish assemblages and hence promote healthy numbers of fished species. Furthermore, seascape ecology can aid in the efficiency of marine reserve design by allowing managers to determine the optimal areas for protection from readily available habitat maps.

For my PhD, I plan to delve deeper into seascape ecology and explore movement patterns of fish. Specifically, I aim to plan to apply seascape techniques to multiple locations on the NSW coast. In this research, I will incorporate within habitat variables, such as habitat complexity (e.g how many holes a reef has or the number of seagrass shoots) to explain fish distributions. Exploring how habitat patterns influence fish assemblages using a seascape approach provides a solid foundation to infer ecological processes from correlations. However, correlation does not equal causation.  Therefore, I plan to provide stronger evidence of the links between habitats. This will be done using acoustic telemetry (i.e fish tagging) to measure the dispersal of sub-adolescent fish migrating from seagrass nursery areas to adult rocky reef habitats. This information is currently not known and if found will further illustrate the importance of reef-seagrass connectivity for fisheries and conservation.

I hope this insight into my research has been interesting and you may have learned a thing or two. I would like to thank the team at Fish thinkers for giving me the opportunity to present my research on such a fantastic platform. If you have any queries or want to discuss this research feel free to send me an email at dss999@uowmail.edu.au.

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