Bioerosion in coral reef communities in southwest Puerto Rico
by the sea urchin
Echinometra viridis
Received: 9 February 2001 / Accepted: 21 February 2003 / Published online: 26 March 2003
Ó Springer-Verlag 2003
Abstract Bioerosion is one of the most important struc-
turing forces in coral reef communities. The bioerosion
impact of several species of fish, sponges and sea urchins
have been estimated in the Caribbean; however, there is
no information for one important species, the red sea
urchin Echinometra viridis. This species can be found in
high densities in many localities. In this study, bioerosion
rates for E. viridis were estimated in two patch reefs off La
Parguera, southwest Puerto Rico, using the population
size-class distribution, average densities, and the CaCO
3
content in fecal pellets produced over 24 h. Average
densities of urchins along four depth intervals were esti-
mated using 40-m transect lines and 1-m
2
quadrats. Av-
erage size and size-structure distribution were estimated
by measuring the diameter of 180–220 urchins haphaz-
ardly collected at each of the four depth intervals. The
ignition–loss method was used to estimate the daily rate of
bioerosion. Fecal pellets produced by the urchins over a
24 h period were collected in buckets, rinsed in fresh wa-
ter, dried for 24 h at 70°C, and then burned in a furnace at
550°C, first to eliminate organics, and then at 1000°C until
constant weight to determine the amount of calcium
carbonate (CaCO
3
) in the fecal pellets. HCl (10%) was
then added to the remainder of the sample to test for
presence of CaCO
3
. Average individual CaCO
3
bioero-
sion rates were estimated at 0.181±0.104 g day
)1
. Aver-
age densities (0.77–62.0 ind. m
)2
), size (2.01–2.44 cm)
and average bioerosion rates (0.114–4.14 kg m
)2
year
)1
)
were significantly higher in shallow areas (1–3 m) in both
reefs. Bioerosion rates were low compared to those re-
ported for parrotfish, endolithic sponges and the black sea
urchin D. antillarum, but they were higher than those re-
ported for other small-sized sea urchins in the Caribbean
and the Indo-Pacific.
Introduction
Sea urchins graze over the substrate of coral reef com-
munities, opening space for recruitment by corals and
other marine invertebrates. High densities of urchins
have been reported to regulate the abundance, compo-
sition and size of algal communities and their primary
productivity (Hutchings 1986; Ruyter van Steveninck
and Breeman 1987; Prince 1995). These algal commu-
nities compete with corals for substrate (Hutchings 1986;
Foster 1987; Hughes et al. 1987; Ruyter van Steveninck
and Breeman 1987; Ogden et al. 1989; Carpenter 1990a,
1990b; Prince 1995). Urchins are considered major bio-
eroders in coral reef communities. The bioerosion im-
pact of different species of sea urchin is dependent upon
their population densities, average size, environmental
conditions and behavior, which can vary in space and
time within (depth gradient) and across different reefs
(Weil 1980; Weil et al. 1984; Spencer 1985; Foster 1987;
Levitan 1989; Hart and Chia 1990; McClanahan and
Kurtis 1991; Keesing 1992; Risk et al. 1995; Conand
et al. 1997).
Echinometra viridis is a small (0.5–4.1 cm diameter),
long-spined, red sea urchin that inhabits shallow Ca-
ribbean reefs and lagoon areas. High densities of this
urchin have been observed in several patch reefs and
fringing coral reefs in La Parguera, Puerto Rico. Where
they are highly abundant this urchin could play a sig-
nificant role in the degradation of reefs. In many reefs of
La Parguera, corals and carbonate structures have been
heavily bioeroded. Many of the colonies show signs of
mortality, and their skeletons have been carved by
bioerosion, producing large concave cavities and debil-
itating the structure which eventually breaks the colonies
apart. No studies have been conducted to determine the
bioerosive impact of E. viridis on Caribbean coral reefs.
In this study, the potential impact of E. viridis on reef
structures was assessed by estimating their bioerosion
impact using their population size structure and densi-
ties at each of four depth intervals along the depth
Marine Biology (2003) 143: 79–84
DOI 10.1007/s00227-003-1056-1
S. P. Griffin Æ R. P. Garcı
´
a Æ E. Weil
Communicated by P.W. Sammarco, Chauvin
S. P. Griffin (&) Æ R. P. Garcı
´
a Æ E. Weil
University of Puerto Rico, Department of Marine Sciences,
PO Box 908, 00667 Lajas, PR, Puerto Rico
E-mail: griffin@caribe.net