Eh. Meesters et al., Colony size-frequency distributions of scleractinian coral populations: spatial and interspecific variation, MAR ECOL-PR, 209, 2001, pp. 43-54
Colony size is an important characteristic for clonal modular organisms suc
h as corals because life-history processes, e.g. reproduction and mortality
, are strongly related to size. These processes are affected by the environ
ment, and size-frequency distributions of coral populations provide informa
tion on the responses of populations to environmental conditions. We hypoth
esised that the size-frequency structure of coral populations in degraded e
nvironments would differ from those in a more pristine environment. We used
log-transformed colony-size data of 13 coral species from the fringing ree
fs of Curacao, Netherlands Antilles. Data were collected at 4 sites. repres
enting 2 environments: a heavily urbanised coastal area with degraded reefs
, and an upstream control area. Population structure was dependent on speci
es and site. Size-frequency distributions of the same species from differen
t sites were twice as similar as distributions of different species, indica
ting the strong effects of various life-history traits among species. Site
effects were indicated by significant differences between distributions of
Ii species at 4 sites. Mean colony size Varied up to an order of magnitude
between species, and much less between sites; however, in 10 species mean c
olony size was also significantly different among the 4 sites. The pattern
of the differences was not consistent among species, indicating that mean c
olony size in degraded sites was higher for some species and lower for othe
rs. Parameters describing the shape of the population appeared to reflect a
general response to reef condition. In the degraded area, frequency distri
butions tended to show increased negative skewness, occasionally extreme po
sitive kurtosis, and smaller standard deviations: II populations were gener
ally more negatively skewed, with the bulk of the population concentrated i
n the larger size classes; kurtosis was on average higher and extremely pea
ked; and standard deviations indicated that colony size varied less. This e
vidence suggests lower recruitment and higher partial mortality in larger c
olonies in this area. Lower recruitment decreased the influx into the small
er size classes of the populations. and higher partial colony-mortality dec
reased the proportion of colonies in the higher size classes while simultan
eously increasing the proportion of colonies in the medium-sized classes. S
pecies that attained large sizes (indicative of great age) appeared to have
size-frequency distributions skewed to the left, while small species were
more skewed to the right. The data indicate a general dichotomy in coral li
fe-history strategies with respect to colony size. with small species gener
ally having a shorter lifespan and reproduction being relatively frequent a
nd successful. Thus, new input into smaller size classes occurs continuousl
y. Species that attain large sizes live longer and are less dependent on fr
equent recruitment, and consequently populations tend to become 'impoverish
ed' in small colonies, resulting in size-frequency distributions that are s
kewed to the left. Based on changes in population structure, this research
indicates that some species, such as Colpophyllia natans and Diploria labyr
inthiformis, are relatively sensitive to environmental conditions.