The trophic role of cardinalfishes (family Apogonidae) on coral reefs

Marnane, Michael John (2001) The trophic role of cardinalfishes (family Apogonidae) on coral reefs. PhD thesis, James Cook University.

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Abstract

Cardinalfishes (Family Apogonidae) form the major component of nocturnal fish assemblages on Indo-Pacific reefs, however, they have been largely overlooked in studies of reef tropho-dynamics. This project examined patterns of distribution, abundance and biomass as well as diet, defecation rates and life history parameters of apogonids to determine their importance in reef processes. Patterns of relative abundance and biomass of apogonids were investigated using daytime visual censuses conducted over a range of spatial scales at One Tree Reef and Lizard Island, Great Barrier Reef, Australia. Patterns of apogonid abundance and biomass over reef-wide scales were most strongly related to the degree of wave exposure. The highest abundance and biomass were recorded from lagoonal reef slopes and bases (0.3 to 2.1 fish m⁻²; 2.2 to 5.1 g m⁻²), followed by leeward reef slopes and bases. The lowest values (<0.2 fish m⁻²; <1.3 g m⁻²) were recorded from exposed locations and reef flats. Patterns were consistent at both One Tree Reef and Lizard Island. This suggests that apogonids are likely to be most important in lagoonal and sheltered systems.

The strength of the relationship between apogonids and their diurnal resting sites was examined in three common species within the One Tree Reef lagoon. Adult Apogon doederlini, Cheilodipterus artus and Cheilodipterus quinquilineatus were individually tagged using visual fluorescent implants and monitored over 16 months to record their persistence at resting sites. Tagged fish were found within an average of 36 to 79 cm of their initial resting positions during each census throughout an 8 month period in A. doederlini and A. leptacanthus and throughout a 16 month period in C. artus and C. quinquilineatus. In addition, 56 to 81% of tagged fish displaced ~1 km, and 33 to 63% of tagged fish displaced ~2 km returned to their point of collection within 3 days. As apogonids are often found densely aggregated at resting sites, their extended use of specific sites on reefs represents a localised, predictable resource for predators and a significant source of spatial variability in nutrient input to reef systems via faeces.

To assess the trophic role of apogonids on reefs, diet, diel feeding behaviour and nocturnal foraging were examined in seven species in the One Tree Reef lagoon. Between 64 and 93% of fish collected at dawn had identifiable material in the stomach compared with 5 to 36% of fish collected at dusk, suggesting that all seven species were predominantly nocturnal feeders. The movement of apogonids between resting sites and feeding grounds was examined using day and night visual surveys. Apogonids shared restricted resting habitats by day but moved into a range of habitats at night. Species were spatially segregated at night, both horizontally and vertically in the water column. Most species had generalised diets containing primarily emergent plankton and benthic invertebrates, suggesting a role in recycling rather than importation of nutrients and energy on reefs. Dietary differences among species appeared to be driven largely by their feeding positions in the water column at night. Since apogonids feed in a range of habitats then return to restricted resting sites during the day they are likely to play an important role in concentrating nutrients and energy on reefs, providing localised and predictable resources for both predators and detritivore communities.

To investigate the importance of apogonids in the transfer of energy to higher trophic levels, the turnover rates of four common species were examined within the One Tree Reef lagoon. Three independent methods were used: (1) Mortality estimates were calculated from the disappearance of tagged fish over time. Mortality rates were highest in Apogon cyanosoma (97.2 % mortality y⁻¹) followed by Apogon doederlini (89.6 %), Cheilodipterus quinquilineatus (83.7 %) and Cheilodipterus artus (78.0 %). (2) Longevity estimates were obtained through otolith analysis of the largest 5 % of individuals of each species collected throughout the course of the study. A. cyanosoma and A. doederlini appeared to reach a maximum age of around 1 year whilst C. quinquilineatus and C. anus reached at least 3 years. (3) Populations were surveyed at four-monthly intervals over a period of 2 years. Population dynamics of each species reflected estimates of mortality and longevity. Adult populations of A. cyanosoma and A. doederlini were found to vary by an order of magnitude throughout a yearly time-frame, primarily driven by variable episodes of recruitment followed by high rates of mortality. C. quinquilineatus and C. anus populations were more stable, with adult numbers fluctuating by two to three-fold over the course of a year. Additional estimates for 6 species of apogonids from Lizard Island indicate maximum longevities of only one year in most species. Apogonids have much faster turnover rates than most comparatively-sized reef fish taxa and may therefore play a major role in the transfer of energy to higher trophic levels.

Defecation rates in apogonids were examined in four species from the One Tree Reef lagoon through the collection of faeces from individuals between dawn and dusk. Fish were collected between 0430 and 0515 hrs and transferred to individual containers from which faeces were collected over the following 12 hrs, then filtered onto pre-weighed filter papers and dried at 60°C. The dry weight of faeces produced by each fish was regressed against wet body weight to obtain defecation rates for each species. These defecation rates were then multiplied by apogonid biomass estimates to obtain defecation rates per m² of reef. The estimated defecation rate for all combined apogonids at resting sites was 693 ± 260 mg dry faeces m⁻² day⁻¹. This rate was comparable to defecation rates for resting schools of haemulids from the Caribbean which were found to enhance local coral growth.

In summary, apogonids play a role which is functionally very different to that of diurnal planktivores. Apogonids are major predators of emergent plankton, a trophic pathway that has received little attention on reefs. This material is consumed in a range of reef and non-reef habitats, then concentrated in the form of fish biomass and faeces at restricted resting sites on the reef. Energy is rapidly transferred to higher trophic levels through fast biomass turnover rates, and to detritivores through a significant input of faeces at the resting sites. Since apogonids return to the same resting sites on a daily basis for extended periods of time, resting schools of apogonids are likely to represent a significant predictable resource for both predators and detritivore communities. Apogonids are generally missed or underestimated in visual censuses of reef fish assemblages, however, this thesis suggests that apogonids form an important component in reef processes. A failure to incorporate apogonids in studies of the role of fishes on reefs is likely to result in an incomplete model of reef system function.

Item ID: 33781
Item Type: Thesis (PhD)
Keywords: abundance; Apogonidae; biomass; cardinalfishes; diet; distribution; feeding behaviour; foraging; Lizard Island; mortality; One Tree Island; population dynamics
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Marnane, M.J. (2000) Site fidelity and homing behaviour in coral reef cardinalfishes. Journal of Fish Biology, 57 (6). pp. 1590-1600.

Marnane, Michael J., and Bellwood, David R. (2002) Diet and nocturnal foraging in cardinalfishes (Apogonidae) at One Tree Reef, Great Barrier Reef, Australia. Marine Ecology Progress Series, 231. pp. 261-268.

Date Deposited: 21 Jul 2015 04:38
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060202 Community Ecology (excl Invasive Species Ecology) @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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