Distributional expansion ofCarpophyllum flexuosumonto wave‐exposed reefs in north‐eastern New Zealand

Abstract

The native fucalean macroalga Carpophyllum flexuosum (Esper) Grev. has recently occupied many reefs on wave-exposed coasts in north-eastern New Zealand. At recently colonised sites, C. flexuosum occurs mainly on coralline-dominated areas with moderate densities of sea urchins (Evechinus chloroticus). At these sites, stipes of C. flexuosum are shorter, with more branching, reduced laminae, and increased stipe weights compared to those at sheltered sites. Survivorship of tagged individuals was less on wave-exposed than on sheltered reefs. On sheltered shores, small C. flexuosum suffered moderate mortality, but large individuals suffered little mortality from any source. All individuals transplanted from sheltered to wave-exposed shores died or became moribund as stipes, whereas those which survived transplanting from wave-exposed to sheltered shores assumed a morphology more characteristic of sheltered sites. Population modelling suggested that the existence of stands of C. flexuosum on wave-exposed shores is dependent on regular recruitment, though it is not clear whether populations are maintained by recruitment from within or without. The establishment of C. flexuosum on wave-exposed shores is correlated with decadal scale decreases in wave energy. We predict that the patchiness of recruitment of C. flexuosum in space and time (and the ubiquity and reproductive characteristics of the dominant laminarian Ecklonia radiata) and its susceptibility to wave action will prevent the fucalean from inducing long-term changes of assemblage organisation.

Relationship between long‐term changes in algal community structure and herbivore diet at the Three Kings Islands, New Zealand

“…Third, these changes occurred during a prolonged period of lower than average SSTs during an El Niño event. A similar pattern was found in other New Zealand seaweeds with Cole et al (2001) describing a correlation between the establishment of Carpophyllumflexuosum and decadal scale decreases in wave energy.…”

Validation of qualitative habitat descriptors commonly used to classify subtidal reef assemblages in north‐eastern New Zealand

“…It may, therefore, underestimate an observer's ability to categorise habitats. For example, the grouping of some urchin barrens quadrats in the C. flexuosum forest group is probably because of the occurrence of small, exposed growth forms of C. flexuosum in the urchin barrens habitat at some sites (Cole et al 2001). This also explains the separation of urchin barrens into two groups, one being urchin barrens with C. flexuosum present, the other being those without it (Fig.…”

Variation in morphological traits over a wave-exposure gradient in one but not in another species of the brown alga Carpophyllum (Fucales)

“…Previous studies have found that algae in more wave-exposed areas tend to be shorter with narrower and thicker lamina and stipes and fewer or no vesicles (Johnson and Koehl 1994, Kawamata 2001, Stewart and Carpenter 2003, Fowler-Walker et al 2006. These patterns have also been detected in Carpophyllum flexulosum (Esper) Greville (Cole et al 2001). Some of these patterns were found in C. maschalocarpum; individuals were shorter, and a lower proportion had vesicles in the more wave-exposed zones.…”