Bert W.Hoeksema

A B S T R A C T
Coral-associated invertebrates contribute much to the biodiversity of Caribbean coral reefs. Although the nature
of their symbiotic relation is usually not fully understood, they can cause damage to their hosts, especially when
they occur in high densities. The abundance of seven groups of coral-associated invertebrates was investigated on
reefs along the leeward side of Curaçao, southern Caribbean. In particular, coral barnacles (Pyrgomatidae),
boring mussels (Mytilidae: Leiosolenus spp.), gall crabs (Cryptochiridae), and Christmas tree worms (Serpulidae:
Spirobranchus spp.) were recorded together with their host corals by means of a photo survey at four depths (5,
10, 15, 20 m) and across seven sites with high and five sites with low eutrophication values (based on δ15N
isotope data). Feather duster worms (Sabellidae: Anamobaea), coral blennies (Chaenopsidae: Acanthemblemaria),
and worm snails (Vermetidae: Petaloconchus) were insufficiently abundant for thorough quantitative analyses.
The results show a decrease in the number of barnacles and Christmas tree worms per host over depth, which
could be related to the availability of their host corals. Sites with high δ15N values show a higher abundance of
barnacles and Christmas tree worms per host than sites with low values. This indicates that eutrophication could
be favourable for these filter feeding organisms but when their densities become too high, they tend to overgrow
their hosts and may become a threat to them.

ABSTRACT  

With increasing maritime activities in the proximity of coral reefs, a growing number of manmade structures are becoming available for coral colonisation. Yet, little is known about the sessile community composition of such artificial reefs in comparison with that of natural coral reefs. Here, we compared the diversity of corals and their competitors for substrate space between a centuries-old manmade structure and the nearest natural reef at St. Eustatius, eastern Caribbean. The artificial reef had a significantly lower species richness and fewer competitive interactions than the natural reef. The artificial reef was dominated by a cover of crustose coralline algae and zoantharians, instead of turf algae and fire corals on the natural reef. Significant differences in species compo-sition were also found between exposed and sheltered sites on both reefs. Our study indicates that even a centuries-old manmade reef cannot serve as a surrogate for natural reefs