christmas tree worm

Christmas tree worms are polychaetes of the genus, Spirobranchus (Serpulidae). These reef- dwelling species live inside tubes that are usually embedded inside the skeletons of corals belonging to either the order Scleractinia (Anthozoa) or to the family Milleporidae (Hydrozoa) (Hoeksema and Ten Hove 2017, Perry et al. 2017). Extended Spirobranchus worms are visible because of their large, bright-colored branchiae, shaped as twin spirals, and a peduncle (stalk) with a calcified spiny operculum on top. Their colormorph variation and the presence of long spines on the tube may serve as protection against predators (Grassle 1973). When in danger, the worms are able to retract quickly inside their tube, while using their operculum as a shield (Hoeksema et al. 2016, Pezner et al. 2017).

Although little is known about predators of Spirobranchus spp. and no actual attacks have been documented (Kupriyanova et al. 2001), predation has been inferred from damaged and/or missing opercula in about 10% of the examined specimens [Nishi and Kikuchi 1996 for Spirobranchus corniculatus (Grube, 1862)]. 

Sponges are known to host a variety of invertebrates, including polychaete worms (Koukouras et al. 1996). Host sponges offer space and can serve as a refuge for such animals if they excrete chemical compounds, which may serve as defense against predators (Waddell and Pawlik 2000). Some encrusting sponges on coral reefs use toxins as an aid to overgrow and kill live corals to create suitable substrate space, but they are not necessarily lethal to the Christmas tree worms that live inside the corals (Hoeksema et al. 2016). Christmas tree worms are polychaetes of the genus Spirobranchus(Serpulidae), which produce calcareous tubes as dwellings that are attached to hard substrate or embedded inside the coral skeletons.

During a survey on sponge–coral interactions at Curaçao (southern Caribbean) in June 2017, the serpulid Spirobranchus giganteus(Pallas, 1766) was observed as associate of at least 10 sponge species with various growth forms (Fig. 1; Electronic supplementary material Figs. S1–15). A worm tube attached to a vase sponge (Fig. 1a) was covered by an orange-veined encrusting sponge (Fig. 1b, c). Dissection of the sponges revealed that worm tubes could be tracked down to the corals that acted as original substrates for the worms. Apparently, the sponges had overgrown the corals that contained the worms. As substitute hosts, they allowed the worms to continue their growth. Spirobranchus worms have also been reported from various Mediterranean sponges, but the nature and mechanism of their association was not explained (Koukouras et al. 1996).

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.

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 use of biological entities as indicators of environmental stress can provide links between changes in ecological conditions and ecosystem productivity. Historically, bioindicators have been used as a rapid-assessment tool of areas declining in sustainability for the inhabiting organisms. This study investigated the utility of sessile, filter feeding Christmas tree worms (Spirobranchus giganteus) as bioindicators of the presence of potential coral reef stressors. Christmas tree worm density was compared at low impact sites (> 200 m from a commercial establishment) and high impact sites (< 200 m from a commercial establishment). For each site, four quadrats were randomly placed along a 10 m transect at 6, 12 and 18 m depths to assess percent live coral cover and Christmas tree worm density. These data were compared with potential environmental stressors such as excess nutrients (nitrite, nitrate, ammonia and phosphate), human gut (Enterococcus) bacteria, sedimentation rates, and sediment particle size distributions between high and low impacted sites and among depths. Approximately 97% of the worms inhabited live coral. Live coral cover was similar for 12 and 18 m at both high and low impacted sites (~ 17 % - 20 %) but significantly lower at 6 m depth (~ 2 % - 8 %). Despite the similarity in live coral cover at depth, there were significantly more Christmas tree worms at 12 m of high impact sites. At all other sites and depths, the worms never exceeded ~ 1.5 worms m-2. At 12 m, water chemistry analyses did not show any differences between site impact except for phosphate, with significantly greater concentrations at high impact sites. Bacterial loads, sedimentation rate and particle size distributions did not show any differences between site impact although there were finer sediments at high impact sites and coarser sediments at low impact sites. S. giganteus may be found at high densities at high impact sites due to a greater availability of food acquired through filter-feeding biota. Therefore, they may be used as novel indicators of the presence of environmental stressors, such as excess nutrients and finer sediments, in Caribbean coral reef systems.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 58-65 from CIEE Bonaire.

The effect of land-based pollution on Bonaire’s coral reef ecosystem has not been well-quantified. Observations of the coral reefs of Bonaire show a great abundance of the polychaete Spirobranchus giganteus. This study investigated whether S. giganteus is sensitive to the environmental stress caused by wastewater pollution and therefore could be used as a bioindicator species of pollution in coral reef health assessments. Pollution indicators were assessed through the analysis of water samples, concentrating on the levels of ammonia, nitrate, nitrite and phosphate, sediment levels, and fecal contamination. To allow for comparison between differing levels of water pollution, six different sites were chosen with various levels of expected pollution impact by their proximity to resorts. Abundance of S. giganteus and coral reef cover at these sites were analyzed through transects at different depths. No significance was found between S. giganteus density and nutrient levels or fecal contamination. This study found a significant positive correlation (r² = 0.936) between S. giganteus density and sedimentation rates, suggesting the possible use of S. giganteus as a bioindicator of sedimentation_stress_on_coral_reefs.

This student research was retrieved from Physis: Journal of Marine Science IX (Spring 2011)19: 20-30 from CIEE Bonaire.

The Christmas Tree worm, Spirobranchus giganteus, is a sessile polychaete found on coral reefs worldwide. Its larvae display photopositive behavior and use chemicals excreted from live coral as a settlement cue. After settlement, the worm grows in concert with the coral for the remainder of its life. S. giganteus displays variable preference for corals as substrate worldwide. It has been shown that the presence of S. giganteus on corals can lessen the effects of disease and coral bleaching on polyps surrounding the worm’s tube, as well as lessening predation by certain corallivores. Due to its potential to maintain healthy corals, it is important to learn more about the ecological role and distribution of S. giganteus. This study aimed to determine at what depth S. giganteus densities are highest, as well as its preferred coral substrate on the fringing reef surrounding Bonaire, Dutch Caribbean. It also intended to demonstrate that the presence of S. giganteus could lessen the effects of disease and bleaching on the corals on which it lives. Using benthic transects at three different depths at two study sites, it was found that S. giganteus density was highest at shallower depths. The preferred substrate was found to be the boulder star coral, Orbicella annularis. Data regarding the effects of S. giganteus on coral disease and bleaching was too limited to determine any relationship between them, but it is recommended that this relationship be investigated in depth due to its possible role in recovering from coral bleaching

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 61-68 from CIEE Bonaire.

Hiding is a common anti-predatory behavior that many organisms utilize. This anti-predatory tactic is adjusted to minimize factors such as lost time spent foraging and reproducing. Variation in hiding exists to minimize these costs while optimizing the benefit of predator avoidance. The hiding behavior of Christmas tree worms, Spirobranchus giganteus, was observed using an artificial stimulus to assess how density (number of individuals cm-2 ), existence within an aggregation or as a solitary individual, the nearest neighbor behavior, and body size affect the re-emergence time of the worms after hiding. This study also assessed the natural hiding responses of S. giganteus using videos. Individuals that were solitary had significantly longer re-emergence times than individuals that were part of an aggregation. These results emphasize the benefits of aggregated living in reducing the hiding time of Christmas tree worms. In aggregations, the re-emergence times of an indirectly stimulated individual increased with distance from the directly stimulated worm. These results could be indicative of a communication system within aggregations. Within these aggregations, reemergence times were consistent regardless of size whereas solitary individuals had significantly longer re-emergence times as the size of the worm increased. Variations in hiding times illustrate the importance of refined behavioral decisions in animals. Hiding behaviors of aggregated individuals could be a useful tool in studying community dynamics, specifically the existence and mechanisms of communication between individuals.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 13-22 from CIEE Bonaire.

Christmas tree worms, Spirobranchus spp. (Serpulidae), are known for their wide range of stony host corals, being either scleractinians or milleporids. Apparently, octocorals overgrowing scleractinians act as secondary hosts for Spirobranchus worms.