An investigation into the trophic nature of small reef fish from the tribe Salariini, family Blenniidae

Wilson, Shaun Kevin (2001) An investigation into the trophic nature of small reef fish from the tribe Salariini, family Blenniidae. PhD thesis, James Cook University.

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Abstract

The nutritional value of detritus to small coral reef fishes was examined by assessing the trophic status of salariin blennies on the Great Barrier Reef, Australia. It is often assumed that filamentous algae satisfies the dietary requirements of fish feeding on the epilithc algal matrix (EAM); however, gut content analysis of nine blenny species, from five genera, found they all ingested predominantly detrital aggregates and only small amounts of filamentous algae. For the representative species examined in greater detail, Salarias patzneri, detrital aggregates were the dominant item ingested irrespective of season or age. Comparisons of S. patzneri gut contents with EAM samples from within their territories showed that S. patzneri ingested a significantly higher proportion of particles <125µm and significantly lower proportion of filamentous algae than was present in their territory.

Visual examination of particulates <125µm collected from Salarias patzneri territories found that organic matter was almost exclusively in the form of amorphic detrital aggregates. Biochemical comparisons of detrital particles <125µm with filamentous algae determined that protein:energy ratios of particulates <125µm were slightly higher than those of filamentous algae, suggesting detritus is of comparable, if not slightly higher nutritional value than filamentous algae. The mean protein:energy ratio of particulates <125µm in the summer (11.3 ± 0.8 mg.Kj⁻¹) and winter (10.3 ± 1.3 mg.Kj⁻¹) was also greater than values required to sustain fish growth. The organic content of particulates <125µm was high (15-20%), and, overall, these particles accounted for approximately 41-44% of the total organic matter in the EAM. Detrital particulates <125µm were therefore a nutritionally valuable and abundant component of the EAM in S. patzneri territories.

Lipid biomarkers were used to identify the source of amorphic detritus <125µm in Salarias patzneri territories. Fatty acid, hydrocarbon and sterol profiles from detrital aggregates and filamentous algae samples were similar, suggesting a large portion of the amorphic detritus is derived from filamentous algae. However, differences in the relative concentration of specific lipid biomarkers in detritus and algal samples indicated additional inputs to the detritus from microalgae, coral mucus and bacteria.

The concentration of fatty acid biomarkers in Salarias patzneri tissues were also compared to detritus and filamentous algae samples to assess which of these resources were assimilated by blennies. The ratio of the fatty acid 16:1ω7 to 16:0 and the percentage of 18:2ω7 in detrital samples and S. patzneri tissues were similar; however, the ratio/ percentage of these dietary biomarkers were significantly different in filamentous algae and S. patzneri tissues. This difference suggested that S. patzneri assimilated lipids primarily from detrital aggregates rather than filamentous algae.

Detrital aggregates therefore represent 62 ± 5% of S. patzneri gut contents, are of a high nutritional value, represent a major source of organic matter available to S. patzneri in their territories and are assimilated by this species. Salarias patzneri can, therefore, unequivocally be classified as a detritivorous fish, and, based on the gut contents of 9 salariin species, other blennies are also likely to be detritivores.

As a group, salariin blennies were most abundant, and biomass estimates greatest, on the tops of exposed seaward reefs. At a finer spatial scale, individual species showed a preference for dead coral microhabitats. It is hypothesised that both broad and fine scale habitat associations of blennies are partially related to the availability and quality of detritus. On the exposed reef crests at Lizard Island, where the number and biomass of detritivorous and herbivorous fishes is greatest, blennies accounted for approximately half of the density and one fifth of the estimated biomass of territorial detritivores. Compared to other functional groups, territorial detritivores accounted for approximately a third of all detritivorous/herbivorous fishes and one quarter of total biomass estimates on exposed reef tops. The substantial contribution of blennies and other detritivores to fish assemblages that feed on the EAM, relatively high nutritional value and abundance of detritus, combined with its undeniable contribution to blenny diets, indicates that detritus and detritivorous fishes are an integral and important component of coral reef trophodynamics.

Item ID: 27239
Item Type: Thesis (PhD)
Keywords: blennies; diet; feeding selectivity; Great Barrier Reef; GBR; gut-content analysis; herbivorous fishes; trophic status
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Wilson, S.K. (2000) Trophic status and feeding selectivity of blennies (Blenniidae: Salariini). Marine Biology, 136 (3). pp. 431-437.

Wilson, S.K. (2001) Multiscale habitat associations of detrivorous blennies (Blenniidae: Salariini). Coral Reefs, 20 (3). pp. 245-251.

Wilson, Shaun (2002) Nutritional value of detritus and algae in blenny territories on the Great Barrier Reef. Journal of Experimental Marine Biology and Ecology, 271 (24). pp. 155-169.

Wilson, Shaun, Burns, Kathryn, and Codi, Susan (2001) Identifying sources of organic matter in sediments from a detritivorous coral reef fish territory. Organic Geochemistry, 32 (10). pp. 1257-1269.

Wilson, Shaun K., Burns, Kathryn, and Codi, Susan (2001) Sources of dietary lipids in the coral reef blenny Salarias patzneri. Marine Ecology-Progress Series, 222 . pp. 291-296.

Date Deposited: 25 Jun 2013 00:06
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 51%
97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 49%
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