MEPS 391:13-19 (2009) - doi:10.3354/meps08107
Variation in brooding period masks similarities in response to changing temperatures
Erica L. Westerman1,*, Robert Whitlatch2, Jennifer A. Dijkstra3, Larry G. Harris3
ABSTRACT: Increased awareness of climate change and invasive species has resulted in a surge of studies on how climate change impacts the invasibility of communities. A common method of study is comparing temperature ranges of native or naturalized species to those of highly invasive species. Two fouling community animals that have been so compared are the ascidians Botryllus schlosseri and Botrylloides violaceus. However, temperature range comparisons of different life history traits yield conflicting results. We examined the 2 species to identify a characteristic that could explain these discrepancies and found a single outstanding feature: the brooding period in B. violaceus is at least 5 times that of B. schlosseri. To determine if this elongated brooding period accounted for the observed discrepancies in temperature range, the relationship between recruitment and temperature was reanalyzed using estimated fertilization times for 2001–2006 recruitment at the Groton Long Point Marina and the University of Connecticut, Avery Point, and 2006 recruitment at the University of Maine Darling Marine Center. Estimated fertilization occurred at the same water temperatures for B. violaceus and B. schlosseri colonies. The observed delay in initial recruitment of B. violaceus resulted from the elongated brooding period, not a delay in fertilization due to water temperature. Analyzing recruitment data without incorporating brooding period may not be representative of reproductive environmental requirements and ranges for animals with brooding periods, and may result in uninformative conclusions when comparing species whose brooding periods differ significantly.
KEY WORDS: Invasive species · Recruitment · Abiotic factors · Ascidians
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