Ecological Archives A022-091-A2

Douglas J. McCauley, Hillary S. Young, Robert B. Dunbar, James A. Estes, Brice X. Semmens, and Fiorenza Micheli. 2012. Assessing the effects of large mobile predators on ecosystem connectivity. Ecological Applications 22:1711–1717. http://dx.doi.org/10.1890/11-1653.1

Appendix B. Description of the stable isotope values of lower trophic level organisms and resident predatory fish collected from lagoon, forereef, and pelagic habitats.

δ13C and δ15N values of selected lower trophic level organisms collected from lagoon, forereef, and pelagic habitats correspond well with values obtained from resident predatory fish that were used as end member sources in the stable isotope mixing models (Fig. B1).The forereef source was defined using the isotope values of multiple low mobility adult forereef groupers (yellow circle); Cephalopholis argus (n = 16), Epinephelus polyphekadion (n = 1), Epinephelus tauvina (n = 1), Epinephelus merra (n = 1), and Epinephelus macrospilos (n = 1); the pelagic source using the values of the yellowfin tuna, Thunnus albacares (n = 27; blue circle); and the lagoon source using values of adult blacktail snapper Lutjanus fulvus (n = 24; green circle). Statistical differences between the isotope ratios of these three end member consumers were evaluated using Kruskal-Wallis tests and post-hoc Wilcoxon comparison (evaluated for significance using Holm's sequential Bonferroni correction); statistics computer in program R (R Development Core Team). δ13C values for each end member consumer exhibited strong and significant discrimination from one another (all: χ2 = 61.1; P < 0.0001; pelagic vs. reef: W = 540; P < 0.0001; pelagic vs. lagoon: W = 648; P < 0.0001; reef vs. lagoon: W = 472; P < 0.0001; Fig. 2). δ15N values of end members showed less separation, but remained significantly different from one another (all: χ2 = 37.5; P < 0.0001; pelagic vs. reef: W = 370; P = 0.03; pelagic vs. lagoon: W = 72; P < 0.0001; reef vs. lagoon: W = 10; P < 0.0001).

A review of the literature on the movement and life history of each of these three species (and closely related congeners) demonstrates that each species is highly unlikely to range and feed in habitats other than the source habitats from which they were collected (Block and Stevens 2001, Kaunda-Arara and Rose 2004, Popple and Hunte 2005, Schroepfer and Szedlmayer 2006, Graham et al. 2007, Schaefer et al. 2007, Verweij et al. 2007, Meyer 2008, Nanami and Yamada 2008, Dierking et al. 2009). Focal predators were assumed to feed along with, not necessarily upon source predators. By isotopically defining our three habitat sources using the integrative isotope values of these source predators, we were able to avoid making uninformed assumptions about which of the myriad potential prey items in this diverse system are actually being consumed by focal predators.

Offshore plankton collected in surface and sub-surface tows using a 50 μm plankton net were used to characterize the base of the pelagic habitat (n = 35; orange circle). Mixed turf algae collected from the forereef were used to characterize this habitat (n = 27; purple circle) and mixed turfs collected in the lagoon were used to isotopically characterize the lagoons (n = 9; pink circle). The values of lower trophic level organisms were adjusted to reflect the hypothesized trophic distance between these taxa and the end member fish predators in each source habitat (inshore/benthic food chains presumed to be longer than pelagic food chains: pelagic = 2 trophic steps; forereef and lagoon = 2.5 trophic steps; steps made utilizing calculated in-situ fractionation values at Palmyra). Hypothesized distances between the bottom and top of these food webs are generalized from observations of the δ15N of end member sources consumers: yellowfin tuna (pelagic source) are 0.28‰ below grouper (reef source), and blacktail snapper (post-adjustment; lagoon source) are 0.16‰ below grouper. End member source consumers in this graph are plotted uncorrected. Because of the uncertainties about the true length of food chains in each these habitats or their distance relative to one another, these must be judged as only qualitative comparisons. The general concordance, however, of isotopic values between lower trophic level organisms and resident predators in each source habitats does suggest that resident predator values provide appropriate approximations of source specific end member isotopic values.

Fig. B1 Plot of δ13C and δ15N values (mean ± 1 SD) of selected lower trophic level organisms and the resident predatory fish (L. fulvus, Epinephelidae, T. albacares) collected from lagoon, forereef, and pelagic habitats which were used as end member sources in mixing models.


Literature Cited

Block, B. A., and E. D. Stevens (Eds). 2001. Tuna: physiology, ecology, and evolution. San Diego: Academic Press.

Dierking, J., I. D. Williams, and W. J. Walsh. 2009. Diet composition and prey selection of the introduced grouper species peacock hind (Cephalopholis argus) in Hawaii. Fish B-NOAA 107:464–476.

Graham, B. S., D. Grubbs, K. Holland, and B. N. Popp. 2007. A rapid ontogenetic shift in the diet of juvenile yellowfin tuna from Hawaii. Marine Biology 150:647–658.

Kaunda-Arara, B. and G. A. Rose. 2004. Homing and site fidelity in the greasy grouper Epinephelus tauvina (Serranidae) within a Marine protected area in coastal Kenya. Marine Ecology Progress Series 277:245–251.

Meyer, A. L. 2008. An ecological comparison of Cephalopholis argus between native and introduced populations (PhD dissertation). Honolulu, HI: University of Hawaii.

Nanami, A. and Yamada H. 2008. Size and spatial arrangement of home range of checkered snapper Lutjanus decussatus (Lutjanidae) in an Okinawan coral reef determined using a portable GPS receiver. Marine Biology 153:1103–1111.

Popple, I. D. and W. Hunte. 2005. Movement patterns of Cephalopholis cruentata in a marine reserve in St Lucia, WI, obtained from ultrasonic telemetry. Journal of Fish Biology 67:981–992.

R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org.

Schaefer, K. M., D. W. Fuller, and B. A. Block. 2007. Movements, behavior, and habitat utilization of yellowfin tuna (Thunnus albacares) in the northeastern Pacific Ocean, ascertained through archival tag data. Marine Biology 152:503–525.

Schroepfer, R. L. and S. T. Szedlmayer. 2006. Estimates of residence and site fidelity for red snapper Lutjanus campechanhus on artificial reefs in the northeastern Gulf of Mexico. Bulletin of Marine Science 78: 93–101.

Verweij, M. C., I. Nagelkerken, K. E. M. Hol, A. H. J. B. van den Beld, and G. van der Velde. 2007. Space use of Lutjanus apodus including movement between a putative nursery and a coral reef. Bulletin of Marine Science 81:127–138.


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