Millepora Alcicornis Research Articles

Millepora alcicornis (Cnidaria: Hydrozoa) as substrate for benthic fauna

Universidade Federal do Ceara - Departamento de Biologia (Bloco 906 Campus do Pici, 60455-760 Fortaleza, CE, Brasil) *E-mail: hmc@ufc.br More than half of the world´s species live inside or on other organisms, where they find conditions favorable to their growth (TOWNSEND et al., 2006) and the majority of hard substrata, including the coralline ones, are colonized by perforating and fouling organisms (ZUSCHIN et al., 2001). The living corals create a variety of habitats for a large number of species, giving support for sedentary organisms and food or shelter for mobile ones (REED; MIKKELSEN, 1987; DIAZ-CASTANEDA; ALMEDA-JAUREGUI, 1999). Many taxonomic groups are found associated with corals, including non-colonial organisms such as Crustacea, Mollusca, Polychaeta and Sipuncula, and colonial ones such as Porifera. Each colony forms a community whose members live in a close relationship, though to establish the limits between the diverse types of interactions is not always easy (DAJOZ, 2005). The purpose of this study is to test the hypothesis that the diversity and density of the macrofauna associated with live colonies of Millepora alcicornis is correlated with the volume of the colony in the “Area de Protecao Estadual dos Recifes de Coral (RN)” in Northeastern Brazil. The study area (Maracajau Reef) is located 5 km from the beach, being 9 km in length and 2 km in width, with depths that vary from 1 to 4 meters at low tide (FEITOSA et al., 2002). The waters of the area are warm (average 28oC) and calm during most the year (MMA, 2003). The samples were collected in July and November of 2004 and February of 2005, when 26 reefs where Millepora alcicornis colonies had been located were marked with buoys, by snorkeling. Later, by SCUBA diving, one colony of each reef was chosen randomly and samples were collected from it. The colonies were placed in plastic bags to prevent the loss of the vagile fauna and then extracted from the substratum with the aid of hammer and chisel. Later, the samples were fixed in 4% formalin solution for 24 hours. Each colony was examined, in the laboratory, for removal of the vagile epifauna. In order to measure the colonies´ respective volumes, they were placed in containers with a known volume of water. The colonies were carefully broken up, with hammer and chisel, and the animals carefully removed to prevent damage. The organisms found were preserved in 70% alcohol before sorting and identification. The macrofauna was analyzed with the use of Shannon-Weaner´s diversity (H'), Pielou´s equitability (J´) and Margalef‘s species richness indices, using the Primer 5 (Windows 5.2.4.) program. The density (ind./cm³), the number of individuals (n) and the number of species (s) were compared to the size of the colonies and the epifauna was compared with the infauna, by means of Spearman´s correlation coefficient (r), using the Statistical program (Windows 5.0). Ninety-five (95) non-colonial species and 1,234 organisms were found in association with Millepora alcicornis . Collected colonies had a volume that varied from 130 to 3146 cm³ (863 ± 647 cm³) and a density that varied from 0.01 to 0.27 ind./cm³ (0.07 ± 0.06 ind./cm³). The individuals (n) and species (s) numbers correlated significantly with the colony volume (p 0.05). The animals found in this study belonged to six taxa (Crustacea, Echinodermata, Mollusca, Nemertea, Polychaeta and Sipuncula. The non-colonial organisms found in association with Millepora alcicornis belonged mainly to the taxon Crustacea that occurred in 93% of the samples, followed by Polychaeta (76%), Mollusca (69%), Sipuncula (42%), Echinodermata (38%) and Nemertea (7%).

High spatial variability of coral, sponges and gorgonian assemblages in a well preserved reef

The main goal of this research was to obtain baseline field data of the composition of sponges, corals, and gorgonian assemblages that can be used as a reference for future analyses of anthropogenic impact. We tested the hypothesis that relatively homogeneous and well preserved reef units can present notable natural variability in the composition of their communities which are unassociated with changes in land proximity or a human impact gradient. Research was carried out in July 2006 at Los Colorados reef, located in the northwestern region of Pinar del Río Province, Cuba at 12 sampling stations. The biotopes selected were crest, terrace edge and spur and grove. Ecological indicators were diversity of corals, species composition, density of corals, hydrocorals, gorgonians and sponges, and density of selected coral species. A total of 2659 colonies of scleractineans corals representing 36 species were counted. The most abundant species in the crest biotope were Millepora alcicornis, Acropora palmata and Porites astreoides; in the terrace edge and spur and grove, the most abundant species were Siderastrea siderea, Stephanocoenia intersepta, Porites astreoides, Agaricia agaricites and Montastraea cavernosa. We found differences among sites for several indicators (e.g. density of corals, sponges and gorgonians and for selected species), but they could not be associated to any gradient of land influence or human impact. Therefore, sites inside a relatively homogeneous reef unit can present notable natural differences in the composition of their communities.

Cultivo de Millepora alcicornis como uma ferramenta para Restauração e Manejo dos Ecossistemas Recifais do Nordeste do Brasil

This work evaluates the potential for cultivating the calcareous hidroid Millepora alcicornis , which is an important reef builder in Brazil, and its use a...

An overview of the shallow-water calcified hydroids from Brazil (Hydrozoa: Cnidaria), including the description of a new species

Five species of calcified hydroids occur in shallow waters along the Brazilian coast: four milleporids –Millepora alcicornis Linnaeus, Millepora braziliensis Verrill, Millepora nitida Verrill, and a new species, Millepora laboreli – and one stylasterid – Stylaster roseus (Pallas). Compared to the scleractinian corals, the calcified hydroids of Brazil have received little attention. Nevertheless, Milleporidae are an important component of Brazilian reefs, with colonies that can reach up to 2 m in diameter. Among the aspects that have been studied for Millepora spp, their distributions and skeletal morphometries are the most distinctive. Due to their complex taxonomy, several morphometric characters have been used to facilitate their identification. Molecular systematics has also been used as a complementary technique to traditional taxonomic tools. Other aspects of Brazilian Millepora spp, such as their nematocysts, medusae and ecology, have received less attention; nevertheless, the few existing studies reveal several remarkable features of this genus. Comprehensive studies of Brazilian stylasterids are still lacking.

Seasonal changes of benthic and epiphytic dinoflagellates in the Veracruz reef zone, Gulf of Mexico

Benthic/epiphytic dinoflagellates were monitored every 2 wk from May to December 2005 in the Veracruz reef zone, Gulf of Mexico. This assemblage was characterized by low species diversity (at least 17 species from 11 genera) and high abundance: Amphidinium cf. carterae (41 172 cells g -1 substrate wet weight), Prorocentrum lima (29 756 cells g -1 ), Coolia monotis (2724 cells g -1 ), Ostreopsis heptagona (1202 cells g -1 ); P. lima was the dominant species. Clear sea- sonal population dynamics occurred, with the highest abundance in May-June, and the dynamics differed at 2 neighbouring sampling sites. In August to December dinoflagellate abundance de- creased considerably. Most of the epiphytic dinoflagellates did not show any significant preference for a macrophyte substrate (23 macroalgal and 2 seagrass species) or for any species or major algal group, although the seagrass Thalassia testudinum appeared to be the most abundant and perma- nent host species. The highest abundance of P. lima occurred on the chlorophyte Ulva fasciata (30 879 cells g -1 ) and T. testudinum (31 467). Dinoflagellates were usually scarce on dead coral (Acro- pora sp. and Millepora alcicornis) fragments (0 to 5039 cells g -1 ) and surface bottom sediments (2 to 84), and were slightly more abundant on living Diploria strigosa (329 to 1830) and more numerous in a fringing reef zone compared to a reef lagoon near an offshore island. Dinoflagellate abundance was not correlated with any measured physical or chemical parameter (temperature, salinity, pH, dis- solved oxygen, nitrates, nitrites, ammonium, phosphates, precipitation or wind speed and direction). There is a high potential for outbreaks of ciguatera in the studied area.

Localized induction of a generalized response against multiple biotic agents in Caribbean sea fans

Although inducible defenses are an important component of the defense systems of a range of mod- ular organisms, little is known about inducible defenses of octocorals. A localized inducible response against multiple enemies was detected in the Caribbean sea fans Gorgonia ventalina L. and G. flabellum L. Field surveys showed that localized purpling, resulting from an increase in the proportion of purple sclerites, was associated with overgrowth by Millepora alcicornis and macroalgae, and infection by the fungus Aspergillus sydowii. To confirm inducibility and to assess specific- ity of the response, a range of treatments—abrasion, cable tie, M. alcicornis, sea fan tissue infected with A. sydowii (diseased allografts), and healthy allo- grafts—was applied to healthy sea fans. After 10 days, all biotic treatments induced a localized physical re- sponse consisting of changes in concentration, type, and color of sclerites; however, antifungal activity of non-polar chemical extracts was unaffected. The pur- pling response appears to be specific to biotic agents and reduces tissue damage in subsequent interactions.

Response of Millepora alcicornis (Milleporina: Milleporidae) to two bleaching events at Puerto Morelos reef, Mexican Caribbean.

Two naturally occurring colonies of Millepora alcicornis were monitored during 1997 and 1998, both years in which this species bleached in the Mexican Caribbean. One colony (HL) was naturally exposed to a high light environment and another nearby colony (LL) was exposed to 5.9 times lower light levels due to shadowing by a pier. For 10 days in August 1997, seawater temperatures in the surrounding reef lagoon rose up to 1.5 degrees C above the 6-year August average. The HL colony bleached to white during this period, whereas, the LL colony remained dark-brown colored. The HL colony recovered its normal dark-brown coloration (reversible bleaching) within several weeks, during which time the seawater temperatures returned to average. The following year, for 10 days, seawater temperatures rose up to 3 degrees C above the 7-year August average and both colonies bleached to white and neither colony recovered (irreversible bleaching). Both colonies were rapidly overgrown by algae and hydroids and, as of June 2003, no recovery has taken place. Prior to the 1997 bleaching, experiments using solar radiation showed that the quantum yield of photosystem II charge separation of branches from HL and LL colonies were affected for several hours by exposure to ultraviolet radiation (UVR, 280 to 400 nm), but recovered by the same evening, suggesting that UVR does not have long-term effects on photochemistry in M. alcicornis. In situ effective quantum yield of photosystem II charge separation (deltaF/Fm') measurements before the 1998 bleaching event indicate that both colonies were healthy in terms of the physiological status of their endosymbionts. During and after the 1998 bleaching event, both colonies showed a reduction in deltaF/Fm' and consequently an increase in excitation pressure on photosystem II. The data suggest that temperature is not the only factor that causes bleaching and that solar radiation may play an important role in coral bleaching.

Unexpected richness of reef corals near the southern Amazon River mouth

Manoel Luis Reefs (00° 52’ S, 44° 15’W),located 180 km north of Sao Luis, offMaranhao State, represent the northernmostoutpost of the Brazilian reef coral fauna, andthe closest well-developed reefs to theAmazon River mouth (Figure 1). In July1998, during a reef fish survey along theBrazilian coast, we found a surprising richness of corals and other reef associatedorganisms in the area, including nine speciesof reef corals and two milleporans, six ofwhich were not previously reported for theNorthern coast of Brazil (Belem et al. 1986,Veron 1996). Despite its proximity to the Amazon Rivermouth, the West flowing Equatorial Currentprovides the region with clear and salinewater. The tidal range is about 6.5 m andvisibility ranged between 20 and 30 m duringour 12 day visit. The reef is approximately y-shaped, with about 10 km in its SE-NEaxis (Figure 1). It is constituted by approximately circular pinnacles, ranging from 50 to 300 m in diameter.The pinnacles rise from 25–30 m depth to near the surface, the tops of some being exposed on the lowesttides. Superimposed coralline algal crusts constitute the framework of the reef, which is sparsely covered withcolonies of Agaricia fragilis(Dana), Favia gravidaVerrill, Madracis decactis(Lyman), Meandrina brazilien-sisMilne Edwards & Haime, Montastraea cavernosa(Linne), Mussismilia hispida(Verrill), Poritescf. ast-reoidesLamarck, Scolymia wellsiLaborel, Siderastrea stellataVerrill, Millepora alcicornis(Linne) and abizarre sub-massive form of Millepora,possibly a new species. Fifty-five percent of the reef coral fauna surveyed iscomposed of species widely distributed in the Western Atlantic and 45 % of Brazilian endemics (Belem et al.1986, Hetzel and Castro 1994). At the time of our visit all coral species were bleached. The Manoel Luis Reefs region, due to its proximity to the Amazon River, may play a major role in geneflow between northern and southern Western Atlantic reef fauna. The presence and great abundance ofCaribbean reef organisms which do not occur along the eastern coast of South America, such as the purple reeffish Chromis scotti,provide additional evidence that the Manoel Luis Reefs may be one of the main faunalstepping stones between the Caribbean and the Brazilian coast (Collette & Rutzler 1977).

The role of colony morphology and substratum inclination in the success of Millepora alcicornis on shallow coral reefs

Millepora species are conspicuous members of shallow coral reefs where they occupy a variety of substrata and produce morphologically complex skeletons. This study focuses on the roles of growth on vertical and horizontal surfaces and the production of encrusting bases and branches (a “sheet-tree” morphology) for the success of the Millepora alcicornis on coral reefs. The effects of inclination were investigated by comparing the size and growth rates of M. alcicornis on vertical and horizontal surfaces at 3–5 m depth, in St. John, US Virgin Islands. The consequences of morphological complexity were investigated by comparing polyp density, chlorophyll content and biomass between encrusting bases and branches; the role of branches in asexual reproduction was also quantified. Colonies on vertical surfaces had larger encrusting bases, longer perimeters and lower densities of branches compared to those on horizontal surfaces. Growth rates also varied significantly between surfaces, largely because colonies on horizontal surfaces shrank in area while those on vertical surfaces increased in area, albeit slowly. Branches were not specialized in comparison to encrusting bases in terms of the density of dactylozooids and gastrozooids, chlorophyll content and biomass, but they were effective asexual propagules. During one storm, 79% of the branches were removed from colonies of M. alcicornis, and 4% attached to the substratum to produce new colonies at a density of ≈0.5 colonies.m-2. Anecdotal observations suggest that such storms rarely damaged encrusting bases on vertical surfaces, but often destroyed those on horizontal surfaces. Thus, the encrusting bases on vertical surfaces are likely to be large because of greater age rather than faster growth, while those on horizontal surfaces are likely to be small because they are relatively young and short lived. These findings suggest that the success of M. alcicornis is a result, in part, of the beneficial consequences of their “sheet-tree” morphology, that supports: (a) slow growth and resistance to wave damage of encrusting bases on vertical surfaces, and (b) the use of branches as asexual propagules.

Morphological analysis of growth forms of branching marine sessile organisms along environmental gradients

In this paper a series of growth forms of the sponge Haliclona oculata, the hydrozoan Millepora alcicornis and the scleractinian coral Pocillopora damicornis are morphologically analysed. The growth forms of these species were collected along a gradient of the amount of water movement. In this analysis it is demonstrated that, although these species are from very different taxonomical groups, the degree of compactness of the growth forms shows a similar trend as a response to the exposure to water movement. In all three species the growth forms gradually change from thin-branching to more compact shapes, as evaluated by measurements of various morphological characteristics. Other morphological measurements, in particular the average distance between branch tips and neighbouring branches (“branch spacing”) show a more species-specific pattern. Species in which fusion of branches is almost never observed, as for example P. damicornis, are characterized by a relatively low standard deviation of branch spacing. Species in which anastomosis frequently occurs (H. oculata and M. alcicornis) are characterized by a relatively high standard deviation in branch spacing. The final aim of this research approach is to use the morphological data acquired here in combination with morphological simulation models to gain a better understanding of the growth and form of these organisms and the impact of the physical environment (hydrodynamics and availability of light required for photosynthesis).

CORAL DISEASE OUTBREAK IN THE FLORIDA KEYS : PLAGUE TYPE II

A coral disease characterized by a novel pattern of rapid tissue destruction first appeared on reefs of the middle Florida Keys in lune 1995. Between lune and October 1995 the disease infected 17 species of scleractinian corals and the hydrocoral Millepora alcicornis. Localized populations of Dichocoenia stokesi, the species most affect­ed, revealed up to 38% mortality. Many colonies exhibited complete tissue loss within days as the disease moved across colonies at rates of up to 2 cm per 24 hr. Typically tissue loss was initiated at the base of the colony and moved upward. At times disease progression halted and colonies retained partial tissue resembling a cap on the top of an otherwise denuded colony. Laboratory cultures of samples from the disease line revealed a dominant bacterium that, when isolated and characterized using genetic and metabolic techniques, most closely matched the genus Sphingomonas. Pure laboratory cultures of the bacterium produced disease in freshly collected coral colonies incu­bated in laboratory aquaria. The disease that we call plague type II appeared on different reefs of sou Florida and the Florida Keys in 1996 and 1997. While coral mortality associated with each of the three outbreaks was regionally confined and did no! recur in subsequent years on the same reefs, the high mortality rates distinguish this disease as one of the most serious yet documented.

Physical Disturbance and Community Structure of Exposed and Protected Reefs: A Case Study from St. John, U.S. Virgin Islands

Major physical disturbances impacted fringing reefs at 4 to 12 m depth off the south coast of St. John, at intervals of 28, 14 and 12 months over a 6 year period (1985–1991). The most wave exposed habitats were dominated by the hydrocoral Millepora alcicornis and the encrusting gorgonian Erythropodium caribaeorum . Both of these species displayed high resistance stability in response to the 1987 bleaching event and to Hurricanes Gilbert (1988) and Hugo (1989). Although Hurricane Hugo was ranked as the most severe hurricane of the past century, it caused comparatively little damage to the shallow exposed reef, illustrating that the effects of physical disturbance may not always conform to a priori predictions based on wave exposure. This counter-intuitive result is explicable when the chronology of disturbance is considered. For example, the shallow exposed community was more heavily damaged than the protected reef by Hurricane Gilbert occurring one year prior to Hurricane Hugo. Sponges and thick mats of E. caribaeorum had accumulated on the protected reef during a 54 month period of little disturbance and were vulnerable to disturbance by virtue of their elevation above the substratum. These organisms were dislodged by extreme water motion generated by Hurricane Hugo. In contrast, the shallow exposed community was still recovering from Hurricane Gilbert when Hurricane Hugo struck. Monitored populations of two coral species, Agaricia agaricites and Tubastrea coccinea , declined over the six year period, but recruitment in 1990 partially compensated for high mortality caused byHurricane Hugo. There were significant increases in the abundance of algal turf on three out of the four study reefs (4 m exposed and protected, 12 m protected) in response to the creation of patch space by the multiple physical disturbances. This study demonstrates the need to interpret recent disturbances in light of the history of past disturbance on the reef.

Communities of constructional lips and cup reef rims in Bermuda

Constructional lips and cup reef rims are little studied reef features typical of very turbulent conditions. The relatively low diversity community of these structures consists of three components, and algal mat dominated by Herposiphonia secunda, an encrusting calcareous biota characterised by crustose coralline algae and the vermetid gastropod Dendropoma corrodens, which together are the main hermatypic components, and an endolithic component with very abundant boring sponges, polychaetes, crustaceans and sipunculids. In northerly areas of Bermuda, the hydrozoan Millepora alcicornis is a prominent member of the community while to the south the urchin Echinometra lucunter is abundant. On the south side of Bermuda the community traps sediment which is deposited in the void spaces. The environment shows reduced grazing and this may account for the presence of several relict and rare species.

Elevated temperatures and bleaching on a high latitude coral reef: the 1988 Bermuda event

Sea temperatures were normal in Bermuda during 1987, when Bermuda escaped the episodes of coral bleaching which were prevalent throughout the Caribbean region. Survey transecs in 1988 on 4–6 m reefs located on the rim margin and on a lagoonal patch reef revealed bleaching only of zoanthids between May and July. Transect and tow surveys in August and September revealed bleaching of several coral species;Millepora alcicornis on rim reefs was the most extensively affected. The frequency of bleaching in this species,Montastrea annularis and perhapsDiploria labyrinthiformis was significantly higher on outer reefs than on inshore reefs. This bleaching period coincided with the longest period of elevated sea temperatures in Bermuda in 38 years (28.9–30.9°C inshore, >28° offshore). By December, when temperatures had returned to normal, bleaching of seleractinians continued, but bleaching ofM. alcicornis on the outer reefs was greatly reduced. Our observations suggest that corals which normally experience wide temperature ranges are less sensitive to thermal stress, and that high-latitude reef corals are sensitive to elevated temperatures which are within the normal thermal range of corals at lower latitudes.

Animal-plant defense associations: Effects on the distribution and abundance of tropical reef macrophytes

This study, conducted at Carrie Bow Cay, Belize during 2–24 April 1985, documents a refuge from predation afforded a group of marine algae by the purple sea fan, Gorgonia ventalina Linnaeus, and the fire coral, Millepora alcicornis Lamarck. There was a highly significant ( P<0.05) association of Galaxaura cylindrica (Ell. & Sol.) Lamour., Dictyota spp., Laurencia poitei (Lamour.) Howe, Lobophora variegata (Lamour.) Womersley, Chondria sp., and Amphiroa rigida Lamour. within 2 cm of the base of Gorgonia ventalina. Species positively associated (within 2 cm) with Millepora alcicornis were Galaxaura cylindrica, Dictyota spp., Laurencia poitei, and Amphiroa fragilissima (L.) Lamour. Only the diminutive turf-form of Digenia simplex (Wulf.) C. Ag. was negatively associated with the sessile animals within the 5-cm zones ( P<0.01). However, we observed that the upright frondose form of D. simplex, on the average, was restricted to within 6.0 cm of either Gorgonia ventalina or Millepora alcicornis. Almost twice as many taxa occurred within 9 cm of Gorgonia ventalina and Millepora alcicornis as within 9 cm of an equal number of random points lacking Gorgonia and Millepora alcicornis, and seven species were found in samples only near (within 10 cm) the two invertebrates. The association of 11 macroalgal taxa with either Gorgonia ventalina or Millepora alcicornis resulted in considerably greater survivorship over 66 h in the presence of grazing activity by fishes (mainly Acanthuridae and Scaridae). Also, only half as much of the palatable alga Acanthophora spicifera (Vahl) Boerg. was eaten when experimentally placed near (5 cm) either Gorgonia ventalina or Millepora alcicornis than when located 30 cm away. About half of the losses occurred within the first 1.5 h and were entirely due to herbivorous fishes, as evidenced by direct observations and grazing scars. The interrelationships studied here, where abundant sessile animals provide a significant refuge from predation for at least 11 relatively edible macroalgae, clearly augment the abundances of certain taxa in microhabitats throughout the reef system. These findings document a type of interaction among sessile organisms that may be important in the development and organization of communities in predation-mediated systems.

Southern Caribbean Cryptic Scleractinian Reef Corals from Bonaire, N.A.

At 14 sites along the west coast of the southern Caribbean island of Bonaire, Netherlands Antilles, 5045 living scleractinian corals in 1101 reef-growth-framework cavities over the depth range 12 m to 43 m were identified and counted. The sample comprises 28 hermatypic coral taxa, the ahermatype Tubastrea coccinea, and the hydrozoan Millepora alcicornis. Although there is no known fossil record of scleractinian reef corals in cavities, there is a record for the taxa living on the reef surface that also inhabit modern reef cavities. This permits speculation that the modern Caribbean cryptic scleractinian coral assemblage may have roots extending into the Tertiary, and at the family level, possibly into the Mesozoic. The common presence of 8 genera, amounting to 44% of the southern Caribbean cryptic coral assemblage, in reef cavities in both the southern Caribbean and the southwestern Pacific, supports the antiquity of the cryptic coral biota, by suggesting that at least those genera may have already been in cavities before the rise of the Isthmus of Panama.

Taxonomic Characters in Caribbean Millepora Species (Hydrozoa, Coelenterata)

In order to find characters in Millepora species with a higher diagnostic value than the growth form (on which species delimitation is hitherto based) a comparison is made of the surface structure, microstructure of the skeleton, structure of the ampullae coverings, size of the gastropores and dactylopores, and pore density in specimens of the four species occurring in the Caribbean region: Millepora alcicornis, M. complanata, M. squarrosa, and M. striata. While most characters are of little taxonomic value, pore sizes and densities are surprisingly useful. The species are diagnosed and some biogeographical remarks are given.

Spatial Variations in Density and Size of the Echinoid Diadema Antillarum Philippi on some Venezuelan Coral Reefs

The distribution, population density and size structure of Diadema antillarum Philippi was found to vary with reef locality, food availability and the structural complexity of the reef. Structural complexity was classified according to the growth morphology and abundance of the coral species found in the different reef zones. Mean urchin density in the reef varied between 2.6 and 3.7 ind. m−2. High densities (4.0-7.0 ind. m−2) were found in the upper reef zone, which was characterized by high structural complexity, and by a dominance of the coral species Acropora palmata, A. cervicornis, Montastrea annularis and the hydrozoans Millepora alcicornis and M. complanata. Low densities (1.5-4.0 ind. m−2) were found in the deep fore reef and flat reef platform, which were characterized by low structural complexity.

Transplantation Experiments with Caribbean Millepora Species (Hydrozoa, Coelenterata), Including Some Ecological Observations on Growth Forms

The historical background of the taxonomic problems in the fire-coral, Millepora, is reviewed. The growth forms of the Caribbean species: Millepora alcicornis Linnaeus, M. complanata Lamarck and M. squarrosa Lamarck are investigated in relation with environmental factors: water movement, current, light and turbidity. Several sites on Curaçao and Bonaire were visited and all forms of Millepora collected. The localities have been divided in biotopes and the relative frequencies of the growth forms in these biotopes were studied. Some relations between growth forms and environment were found: delicately branched forms appear in deeper, quieter waters, sturdy forms in sites with strong water movement, incrusting forms in turbid and also in turbulent sites. At sites with strong current Millepora corals are most abundant. The effect of transplantations on the growth forms of the three species has been studied. The transplantations caused changes in the growth form, which was most conspicuous in M. complanata.

Skeleton growth of the hydrocoral Millepora complanata Lamarck in relation to light

The daily length increment of the skeleton of the distal growing edge of Millepora complanata from Discovery Bay, Jamaica, was measured by laser diffraction. The individual variation in growth rates between adjacent and morphologically comparable parts of the same colony was pronounced. There was a significant correlation between length increment rate and light intensity. When daytime light intensities were high the length increment rates were slightly, but significantly, larger during night than during day.A few measurements are also reported for Millepora alcicornis.