Virgin Islands National Park: Coral Reef: Populations Dynamics: Population Projections

In this study, size-based matrix models for the reef-building coral Orbicella
annularis at 14-m depth on the Tektite reef in St. John, U.S. Virgin Islands, were
used to: (1) explore the demography of changing coral cover over 25 yr, (2) test for
spatial homogeneity in demographic properties through a contrast with a previous
study (at Yawzi Point, Edmunds and Elahi 2007), and (3) evaluate the potential for
future population stability. During three, five year intervals from 1988 to 2002,
St. John was affected by hurricanes and bleaching, yet coral cover at Tektite
increased from 33% to 49%; from 2002 to 2007, it declined to 27%; and from 2010 to
2013, it stabilized at ∼ 28%. Over a quarter-century, colonies > 50 cm2 became rare,
the abundance of colonies ≤ 50 cm2 increased from 58% (1988) to 92% (2013), and
population density doubled to 67 colonies m-2 by 2013. Population growth (λ) was
greater at Tektite (1.152 ≥ λ ≥ 1.018) than Yawzi Point (0.679 ≥ λ ≥ 0.586), and
while population size at Tektite declined due to bleaching and disease in 2005
(λ = 0.753 over 2003–2008), it recovered between 2008 and 2013 (λ = 0.966); the
population at Yawzi Point declined from 1988 to 2003 without signs of recovery.
Projections suggest a continuation of recent conditions could allow O. annularis at
Tektite to retain ∼ 9% cover after 100 yr, but with a return to the rates of growth
and survival of 1993–1998, it could attain coverage similar to that of 1988 (33%) in
∼ 15 yr.

本研究以美属维尔京群岛圣约翰岛Tektite礁14米水深处的造礁珊瑚（reef-building coral）环纹扁脑珊瑚（Orbicella annularis）的基于体型的矩阵模型为研究工具，开展三项分析：（1）探究25年间珊瑚盖度变化的种群动态；（2）通过与既往研究（Yawzi Point海域，Edmunds与Elahi，2007年）对比，检验种群动态特征的空间均质性；（3）评估种群未来维持稳定的潜力。1988至2002年的三个五年间隔期内，圣约翰岛先后遭受飓风与珊瑚白化影响，但Tektite礁的珊瑚盖度仍从33%升至49%；2002至2007年，盖度降至27%；2010至2013年则稳定在约28%。在25余年的观测周期内，体型大于50cm²的珊瑚群体逐渐罕见，体型≤50cm²的群体占比从1988年的58%升至2013年的92%，种群密度翻倍至每平方米67个群体（截至2013年）。种群有限增长率（λ）在Tektite礁区间为1.018≤λ≤1.152，显著高于Yawzi Point的0.586≤λ≤0.679；2005年受白化与病害影响，Tektite礁种群规模在2003-2008年间出现下降（λ=0.753），但2008至2013年间实现恢复（λ=0.966）；而Yawzi Point的种群在1988至2003年间持续衰退，未出现恢复迹象。模型预测显示，若维持当前环境条件，Tektite礁的环纹扁脑珊瑚（O. annularis）在100年后仍可保有约9%的盖度；但若恢复至1993-1998年的生长与存活速率，则可在约15年内恢复至1988年的盖度水平（33%）。