Modular organisms consist of repeated building blocks. An important consequ
ence of modularity may be reflected in the ability of a colony to continual
ly reallocate priority of resource transport among its units in response to
stress. Hermatypic corals, the main organisms constructing tropical reefs,
are prone to damage by a multitude of agents. Since colonization of lesion
s by competitors is a potent threat to colonial organisms, fast recovery is
an important component of colony survival. Previous regeneration studies h
ave claimed that the energy requirements of this essential process are fuel
ed only by the polyps directly bordering the injured area. This "localized
regeneration hypothesis" rejects the necessity for wide colony integration
during regeneration and sees no advantage to large colony size. The objecti
ve of the present study was to test an alternative regeneration hypothesis
that argues, in contrast, that injury repair (i.e., closure of lesions by n
ewly formed tissues) in corals may require extended colony integration (i.e
., internal translocation of resources from sites of acquisition to sites o
f maximal demand). To test our hypothesis we examined: (1) the relationship
between colony size and percentage recovery of lesions differing in size a
nd shape; and (2) the effect of different sized lesions on the fecundity of
polyps located at increasing distances from the lesion site. Both experime
nts were conducted on the common, spherically shaped coral Favia favus in t
he Red Sea near Eilat, Israel. The relatively small lesions (<1 cm(2)) were
the only ones to support the localized regeneration hypothesis, since thei
r recovery was unaffected by colony size. However, the two larger lesion ty
pes (approximate sizes of 2 cm(2) and 3 cm(2)) confirmed the importance of
large colony size for achieving fast recovery. In the second experiment we
found that small lesions, repeated monthly, caused only a localized reducti
on in fecundity, while larger monthly repeated lesions caused significant r
eductions in fecundity up to a distance of 15 cm away from their site. Both
experiments indicate that regeneration from injury may require an extended
magnitude of energy integration throughout the colony, and that the extent
of this integration is regulated by the colony in accordance with lesion c
haracteristics. It is also concluded that in long-lived organisms such as c
orals, there is a priority of energy allocation to recovery rather than to
reproduction. Our findings reveal the existence of injury thresholds within
a colony that determine energy allocation and intra-colonial translocation
of energy products toward regions of maximal demand. We suggest that such
injury thresholds may characterize many other coral species and that colony
integration during stress is a basic life-preserving ability and one of th
e most important advantages of clonal and colonial organisms.