Codium fragile: Morphological and molecular variation present in native and introduced subspecies in Auckland

Abstract

The green alga Codium fragile is a cosmopolitan species appearing along temperate coasts in both hemispheres. A native subspecies, Codium fragile ssp. novae-zelandiae is found throughout New Zealand, and is abundant on the west coast of Auckland. A second subspecies, Codium fragile ssp. fragile is regarded as highly invasive. It has spread widely from its native range in Japan, and has been known in New Zealand since 1973, when it was reported from the Waitemata Harbour in Auckland. The two subspecies are known to exhibit morphological and molecular variation, although these had never been evaluated together. C. fragile is known to occur throughout New Zealand but prior to this study the ranges of the two subspecies were not known; in part due to a lack of reliable diagnostic field characters. This study compared variation between subspecies and locations in Auckland, utilising six categorical shape descriptors, eleven anatomical utricle morphometrics, eight wholethallus morphometrics, and six shape statistics derived from a morphometric landmark analysis. The taxonomic utility of the various morphometric data sets was assessed by linear discriminant analysis. The plastid marker rps3-rpl16 was used to distinguish between subspecies of C. fragile. Additional specimens from around New Zealand were also sequenced. Morphometric characters varied with environment type for both subspecies, and this variation superseded any phenotypic variability. Accurate delimitation was not possible; the discriminant analyses performed no better than random chance with all combinations of the morphological data. Utricle characters and measurements were also shown to vary within individual thalli and between different preservation methods. Therefore I recommend that multiple utricles and thalli are necessary to describe the total morphological variation within a population. Both ssp. fragile and ssp. novae-zelandiae were found throughout New Zealand. The known range of ssp. fragile in New Zealand has been expanded by this study. Mixed populations of both subspecies were recorded for the first time at three sites in Auckland. Given the extensive morphological variability observed in Auckland, future studies of C. fragile should utilise molecular tools for accurate identification.