JOURNAL OF EXPERIMENTAL ZOOLOGY 289:317–321 (2001) © 2001 WILEY-LISS, INC. Influence of Diminished Respiratory Surface Area on Survival of Sea Turtle Embryos ANDREA D. PHILLOTT* AND C. JOHN PARMENTER School of Biological and Environmental Sciences, Central Queensland University, Rockhampton QLD 4702, Australia ABSTRACT It has been suggested that fungal presence on sea turtle eggs may impede gas exchange. To investigate the influence of diminished gas exchange surface upon embryo survivor- ship, flatback (Natator depressus) and green (Chelonia mydas) eggs were painted with petroleum jelly. Variable proportions of the egg surface were covered, including both respiratory and nonrespiratory domains. Embryo survival varied with site inhibited, proportion of eggshell af- fected, and species of turtle. If fungi on the exterior of the eggshell are able to impede respiratory gas exchange, their presence on the upper hemisphere (primary gas exchange area in early incu- bation) will result in the highest embryo mortality. Large eggs are likely to demonstrate a higher survivorship than small eggs, due to their larger available respiratory area and/or to variation in weight or stage-specific embryonic metabolic demands. Interspecific differences in egg size may therefore be a contributory factor to observed mortality rate differences in the natural presence of fungi. J. Exp. Zool. 289:317–321, 2001. © 2001 Wiley-Liss, Inc. Grant sponsor: Centre for Land and Water Resource Management, Central Queensland University; Grant number: JRXWG-131. *Correspondence to: Andrea D. Phillott, School of Biological and Environmental Sciences, Central Queensland University, Rock- hampton QLD 4702, Australia. E-mail: phillota@cqu.edu.au Received 24 May 2000; Accepted 23 October 2000 Microbes have been isolated from the exterior and/or embryonic tissue of unhatched eggs of log- gerhead, Caretta caretta (Ragotzkie, ’59; Wyneken et al., ’88; Peters et al., ’94), green, Chelonia mydas (Bustard and Greenham, ’68; Solomon and Baird, ’80; Whitmore and Dutton, ’85), leatherback, Dermochelys coriacea (Whitmore and Dutton, ’85; Solomon and Tippett, ’87; Chan and Solomon, ’89; Eckert and Eckert, ’90), olive ridley, Lepidochelys olivacea (Mo et al., ’90; Acuna-Mesen, ’92), hawks- bill, Eretmochelys imbricata (Phillott, unpub- lished) and flatback, Natator depressus (Phillott, unpublished) sea turtles. It has not been conclu- sively determined whether the microbes isolated are present as contaminants or infectants. Ragot- zkie (’59) and Peters et al. (’94) considered decayed eggs to be the result of microbial invasion after embryo mortality (due to nest flooding). Solomon and Baird (’80), Solomon and Tippett (’87), Wyne- ken et al. (’88), and Eckert and Eckert (’90) be- lieved microbial pathogens to be implicated in egg failure. Both scenarios appear possible. In the instance of fungal invasion of the viable egg, Solomon and Baird (’80) describe three pos- sible mechanisms for debilitation of the developing embryo: impeded gas exchange as the hyphae in- terweave with the porous eggshell matrix; transfer of fungal spores from the allantois to the embry- onic tissue; and, calcium depletion of the eggshell resulting in retarded embryonic development. Mycoflora have been implicated in a differen- tial species mortality between green and logger- head sea turtle nests at Heron Island and Wreck Island in the southern Great Barrier Reef (Limpus et al., ’83). Although physical and physiological de- fenses (e.g., eggshell structure; anti-pathogenicity of albumen) play an important role in protecting the turtle egg from the biotic nest environment, variation in egg size may result in interspecific variation in response to a similar-sized area of fun- gal growth and subsequent impediment of respira- tory surface area. In order to evaluate embryo sensitivity to in- hibited respiratory exchange, we progressively im- peded eggshell surface from its gas exchange role. Further, to investigate the spatial/regional corre- lation of the impact of any particular proportion impeded, the progression was tested beginning at the top (the “north pole”) of the egg, and at the bottom (“south pole”). It was hypothesized that the starting point could be important, as the most obvious external reflection of the commencement of embryonic growth in sea turtle eggs is a chalky white patch (the “white spot”) that appears at the north pole, then extends downward to encompass