Diversity

Brachyuran crabs of various families are known as obligate associates of stony corals, with many of these species living as endosymbionts inside the skeleton of their hosts. In particular, coral gall crabs (Cryptochiridae) have been well studied in tropical coral reefs around the world. These crabs can be recognized by the shape of their dwellings (or pits), which may be crescent-shaped or resemble a slit, a canopy, a basket, or a gall, depending on the identity and morphology of their host, and on the position inside the host’s skeleton. Cryptochirids are each known to be associated with a few scleractinian host species (Anthozoa: Scleractinia) or only one. Crabs of the species Latopilumnus tubicolus Türkay and Schuhmacher, 1985 (Pilumnidae), have so far only been reported as endosymbionts of the Indo-Pacific scleractinian Tubastraea micranthus (Ehrenberg, 1834). Their dwellings are unique because they start in one of the coral’s calyces from where they penetrate deep inside the coral branches, becoming long and tubular, whereas the pits (or cysts) of cryptochirids remain relatively shallow.

Article referenced in BioNews 34 article "New discoveries on relationships between host corals, crabs and christmas tree worms"

Caribbean Christmas tree worms (Annelida: Polychaeta: Serpulidae: Spirobranchus) are considered host generalists in their associations with anthozoan (Scleractinia) and hydrozoan (Millepora) stony corals. As planktonic larvae, they settle on coral surfaces and start secreting a calcareous tube to be used as a dwelling. This tube usually becomes overgrown by the host coral (except for its opening) and may get encapsulated deep inside the coral skeleton. In this manner, the well-protected worms grow and survive predation and other hazards, allowing them to live for over four decades. When the host corals are overgrown by other organisms, such as octocorals and sponges, these may act as secondary hosts.

The long lists of Caribbean host species suggest that the recorded number has reached a maximum. However, recent surveys (2015–2019) in the southern and eastern Caribbean, as well as in the Greater Antilles, enabled us to establish new records of two primary hosts (scleractinians) and two secondary hosts (a zoantharian and an ascidian).

Article referenced in BioNews 34 article "New discoveries on relationships between host corals, crabs and christmas tree worms"

Among symbiotic associations, cases of pseudo-auto-epizoism, in which a species uses a resembling but not directly related species as substrate, are poorly documented in coral reef ecosystems. In the present study, we assessed the distribution of an association between the hydrocorals Stylaster roseus  and Millepora alcicornis  on about 50% of coral reef sites studied in Bonaire, southern Caribbean. Although previously thought to be uncommon, associations between the lace coral S. roseus and the fire coral M. alcicornis  were observed at both the windward and leeward sides of Bonaire, mainly between 15 and 25 m depth, reaching a maximum occupation of 47 S. roseus  colonies on a single M. alcicornis  colony. Both species’ tissues did not show any signs of injuries, while an in-depth inspection of the contact points of their skeletons revealed that both partners can partially overgrow each other. How it is possible that S. roseus  is able to settle on the stinging tissue of Millepora  as well as how, by contrast, the latter may facilitate the lace coral by o ering a certain degree of protection are questions that deserve further investigations

Species of the anthozoan order Zoantharia (=Zoanthidea) are common components of subtropical and tropical shallow water coral reefs. Despite a long history of research on their species diversity in the Caribbean, many regions within this sea remain underexamined. One such region is the Dutch Caribbean, including the islands of St. Eustatius, St. Maarten, Saba, Aruba, Bonaire, and Curaçao, as well as the Saba Bank, for which no definitive species list exists. Here, combining examinations of specimens housed in the Naturalis Biodiversity Center collection with new specimens and records from field expeditions, we provide a list of zoantharian species found within the Dutch Caribbean. Our results demonstrate the presence at least 16 described species, including the newly described Parazoanthus atlanticus, and the additional potential presence of up to four undescribed species. These records of new and undescribed species demonstrate that although the zoantharian research history of the Caribbean is long, further discoveries remain to be found. In light of biodiversity loss and increasing anthropogenic pressure on declining coral reefs, documenting the diversity of zoantharians and other coral reef species to provide baseline data takes on a new urgency.

A team of researchers from Naturalis Biodiversity Center, ANEMOON Foundation, and colleagues from various intitutes, performed several bodiversity surveys in the Dutch Caribbean (Bonaire, Curaçao, Sint Eustatius). These expeditions were organized by professor Bert Hoeksema, who is the coral expert at Naturalis and honorary professor of tropical marine biodiversity at the University of Groningen. The team discovered, amongst others, some new associations for Christmas tree worms (Spirobranchus spp.) as symbionts within different coral species. These worms live partly inside the coral and appeared to be able survive when the host coral becomes covered by encrusting animals, who then serves as a secondary host. Surprisingly, most discoveries were made in very shallow water (less than 2 m depth), where scuba divers may spend less time when compared to greater depths.

Caribbean Christmas tree worms (Annelida: Polychaeta: Serpulidae: Spirobranchus) are considered host generalists in their associations with anthozoan (Scleractinia) and hydrozoan (Millepora) stony corals. As planktonic larvae, they settle on coral surfaces and start secreting a calcareous tube to be used as a dwelling. This tube usually becomes overgrown by the host coral (except for its opening) and may get encapsulated deep inside the coral skeleton. In this manner, the well-protected worms grow and survive predation and other hazards, allowing them to live for over four decades. When the host corals are overgrown by other organisms, such as octocorals and sponges, these may act as secondary hosts.