Title

Comparisons of habitat use and diet of herbivorous kyphosids (Genus Kyphosus) in tropical and temperate reefs

Date of Award

2017

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Science

First Advisor

Associate Professor Glenn Hyndes

Second Advisor

Dr Alan Kendrick

Third Advisor

Dr Shaun Wilson

Abstract

Kyphosids are a well-represented group of mainly herbivorous fishes distributed worldwide. Species within the genus Kyphosus are commonly found in both tropical and temperate areas, with Western Australia having especially high Kyphosus diversity and abundance compared to other regions. Despite being common fishes, much of the ecology of this Genus has not been described. The aim of this study is to compare habitat and food resource use of Kyphosus species in both tropical and temperate reef areas of Western Australia to provide new information about their ecological roles in these systems. To achieve this, the relationship between the abundances of three temperate species (K. sydneyanus, K. gladius, and K. cornelii) and environmental characteristics has been investigated across 20 sites within Marmion Marine Park, on the south-west coast of Australia. All temperate Kyphosus species were found to be significantly more abundant in high-relief reef areas (P < 0.01) and particularly inshore areas (0 to 1 nm from the coast). Juveniles (Lt < 30 cm) were present only in shallow reefs (0 to 6 m) and mostly inshore. Distance-based redundancy analysis showed that most of the variability in juvenile abundance (72-77%) was explained by reef structures (i.e. number of arches, caves, drop-offs, and general vertical relief) and algal assemblages (i.e. E. radiata, green algae, and Sargassum spp.). Changes in abundance of adult fish (Lt ≥ 30cm) were less strongly related to environmental variables (52- 58%), although the number of caves and drop-offs was positively correlated with all three species.

Analysis of the stomach contents of K. sydneyanus, K. gladius, and K. cornelii showed strong differences in diet composition between all species (p < 0.001). An ontogenetic shift in was also present in the first two species (p < 0.001). K. sydneyanus and K. gladius consumed mostly brown macroalgae. However, K. sydneyanus consumed more Sargassum spp. (up to 44% in adults), while K. gladius generally had a higher content of E. radiata in their stomachs (up to 47% in adults). Juveniles of both species consumed less kelp and Sargassum than adults and more green epiphytes (e.g. Derbesia sp.) and red algae (Hypnea sp.). Conversely, the diet of K. cornelii consisted almost entirely of red and green epiphytes, such as Hypnea sp. (30-33%) and Ulva sp. (15- 31%) at both life stages. These results indicate that both K. sydneyanus and K. gladius act as browsers as adults, whilst K. cornelii are grazers. The analyses of the head, mouth, and teeth morphological traits, although showing significant (p < 0.001) differences among species, are not good predictors of diet.

In the coral reef area of Ningaloo Reef, situated in the north-west corner of Western Australia, all Kyphosus species had a higher number of adults on shallow reef slopes exposed to prevailing waves, while juveniles were found predominantly inshore. Environmental variables explained much of the variation in abundances of all surveyed species, in particular of adult K. bigibbus (92%), and K. vaigiensis (91%). Dietary analysis across the two most common Kyphosus species in this tropical area (K. bigibbus and K. cinerascens) found K. bigibbus feed predominantly on brown macroalgae and K. cinerascens on red epiphytes and turf algae. These results suggest a different functional role for these two species, with K. bigibbus acting as a browser and K. cinerascens as a grazer. As with temperate species, morphological traits were significantly different between the two species, but did not explain interspecific variability in diet.

The general differentiation in both distribution and diet among Kyphosus species showed that sympatric species can represent different functional roles (i.e. browsers and grazers). This implies that species need to be identified in monitoring and research programs to avoid erroneous estimates of herbivory activity. Thus, the results here offer a more defined description of the role of Kyphosus species, in both temperate and tropical reef habitats as an essential group of fish participating in different functional groups and at different latitudes in one of the fundamental processes of marine ecosystems which is herbivory.

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