Species Of Halimeda Research Articles

STUDY OF POPULATION DYNAMICS AND EXPLOITATION RATES OF CRAYFISH (PANULIRUS SPP) IN SPERMONDE WATERS, MAKASSAR STRAIT

To stimulate catch production and wise management patterns, research is carried out on the study of ecological aspects, estimates of population dynamics and exploitation rates of crayfish (Panulirus Spp) in the Spermonde waters of the Makassar Strait. Based on the COA (Correspondence Analysis) (Ludwig and Reynold, 1988), as well as the analysis of Von Bertalanffy (1938, in Sparre et al., 1989), it was found that the micro-habitat of Panulirus spp., Generally co-exist with massive coral species Alcyonaria (Sarcophyton, Heliophora , and Tubipora), and branching reefs of the Acropora species (Goniopora and Pavona), as well as living with algal grass species of Caulerpa and Halimeda. The growth pattern of Panulirus lobster follows the equation Lt = 46.3561 (1- e -0.1738 (t + 1.7827)), which means that the length decreases at relatively old age. The total mortality coefficient (Z) of population is 0.5066/year, this is relatively the same as the ideal mortality (M) which means optimal utilization, but it is necessary to select catch sizes that are larger than 24 - 27cm (in the range of 34 - 46cm).

Updates on Section Pseudo-opuntia of Halimeda: phylogenetic analyses of H. soniae sp. nov. (Bryopsidales, Chlorophyta) along the Brazilian coast

Abstract Halimeda is a genus of green seaweed showing high morphological plasticity. Studies using molecular markers for species delimitations and phylogenetics have revealed cryptic diversity and new species throughout the world. Seven species of Halimeda are currently recognized in Brazil. The present study describes the new species Halimeda soniae Ximenes, Oliveira-Carvalho, M. E. Bandeira-Pedrosa et Cassano sp. nov. to accommodate the taxon previously identified as Halimeda aff. gracilis for Brazil. Samples of H. soniae were collected in Espírito Santo State (southeastern Brazil), and plastid gene sequences of tufA and rbcL were obtained. Phylogenetic analyses showed that H. soniae belongs to Section Pseudo-opuntia, together with Halimeda gracilis and Halimeda lacrimosa; the three species have overlapping morpho-anatomical features. Phylogenetic analyses suggest that H. gracilis is restricted to the Indo-Pacific Ocean, whereas the other two species appear to be restricted to the Atlantic. Additional research on Caribbean specimens will be necessary to resolve the taxonomic position of the taxa named as H. lacrimosa and H. gracilis in that region. Based on our results, H. gracilis does not occur in the Brazilian marine flora.

Seagrass can mitigate negative ocean acidification effects on calcifying algae

The ultimate effect that ocean acidification (OA) and warming will have on the physiology of calcifying algae is still largely uncertain. Responses depend on the complex interactions between seawater chemistry, global/local stressors and species-specific physiologies. There is a significant gap regarding the effect that metabolic interactions between coexisting species may have on local seawater chemistry and the concurrent effect of OA. Here, we manipulated CO2 and temperature to evaluate the physiological responses of two common photoautotrophs from shallow tropical marine coastal ecosystems in Brazil: the calcifying alga Halimeda cuneata, and the seagrass Halodule wrightii. We tested whether or not seagrass presence can influence the calcification rate of a widespread and abundant species of Halimeda under OA and warming. Our results demonstrate that under elevated CO2, the high photosynthetic rates of H. wrightii contribute to raise H. cuneata calcification more than two-fold and thus we suggest that H. cuneata populations coexisting with H. wrightii may have a higher resilience to OA conditions. This conclusion supports the more general hypothesis that, in coastal and shallow reef environments, the metabolic interactions between calcifying and non-calcifying organisms are instrumental in providing refuge against OA effects and increasing the resilience of the more OA-susceptible species.

Diversity of Halimeda (Chlorophyta) from the Thai–Malay Peninsula

:The Thai–Malay Peninsula separates the Andaman Sea from the Gulf of Thailand. This barrier is known to affect species distribution and genetic diversity of marine organisms. Biodiversity studies need a correct species taxonomy to interpret their biogeography; this is especially relevant in marine algae where morphological characters are few or cryptic. We address species distributions of the important macroalgal genus Halimeda. The combination of morphological data and chloroplast tufA gene sequences were used to identify species, and to reveal the variation among Halimeda species around the Thai–Malay Peninsula. The morpho-anatomical and molecular analysis showed eight species of Halimeda in Thai and Malaysian waters: Halimeda borneensis, H. discoidea, H. gigas, H. macroloba, H. micronesica, H. minima, H. opuntia, H. renschii, and two undescribed species. Three species, H. minima, H. renschii and H. micronesica, were reported for the first time from the area. Species variation was much greater in the Andaman Sea than in the Gulf of Thailand. Our results show great variation in species composition and genetic variation between the two sides of the peninsula, which could be due to differences in sea-surface currents and environmental differences between the two sides of this important marine barrier.

Calcareous green alga H alimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps

We investigated ecological, physiological, and skeletal characteristics of the calcifying green alga Halimeda grown at CO2 seeps (pHtotal ∼ 7.8) and compared them to those at control reefs with ambient CO2 conditions (pHtotal ∼ 8.1). Six species of Halimeda were recorded at both the high CO2 and control sites. For the two most abundant species Halimeda digitata and Halimeda opuntia we determined in situ light and dark oxygen fluxes and calcification rates, carbon contents and stable isotope signatures. In both species, rates of calcification in the light increased at the high CO2 site compared to controls (131% and 41%, respectively). In the dark, calcification was not affected by elevated CO2 in H. digitata, whereas it was reduced by 167% in H. opuntia, suggesting nocturnal decalcification. Calculated net calcification of both species was similar between seep and control sites, i.e., the observed increased calcification in light compensated for reduced dark calcification. However, inorganic carbon content increased (22%) in H. digitata and decreased (−8%) in H. opuntia at the seep site compared to controls. Significantly, lighter carbon isotope signatures of H. digitata and H. opuntia phylloids at high CO2 (1.01‰ [parts per thousand] and 1.94‰, respectively) indicate increased photosynthetic uptake of CO2 over HCO3− potentially reducing dissolved inorganic carbon limitation at the seep site. Moreover, H. digitata and H. opuntia specimens transplanted for 14 d from the control to the seep site exhibited similar δ13C signatures as specimens grown there. These results suggest that the Halimeda spp. investigated can acclimatize and will likely still be capable to grow and calcify in P CO 2 conditions exceeding most pessimistic future CO2 projections.

Two species of Halimeda, a calcifying genus of tropical macroalgae, are robust to epiphytism by cyanobacteria

Cyanobacteria, an increasingly important epiphyte on macroalgae and seagrass, have been shown to have strong effects on its hosts; this association has been identified as a driving mechanism that maintains algal blooms on coral reefs. We examined both the costs and benefits of epiphytism on 2 algal congeners of Halimeda (H. tuna and H. opuntia), both of which are abundant members of tropical reef communities in the Caribbean. To evaluate potential benefits of an associational defense as well as costs to growth, we manipulated herbivore access to (uncaged/caged) and cyanobacteria presence on (epiphytized/cleaned) 2 species of Halimeda on shallow patch reefs in Belize and measured change in branch length and segment number after 10 (H. tuna) and 5 (H. opuntia) days. Cyanobacterial epiphytes did not serve as an associational defense from herbivory as there were no differences between caged and uncaged treatments for either response variable. The presence of cyanobacterial epiphytes did not affect the growth of branches or net generation of new segments, demonstrating there was also no cost to growth. The robustness of both species of Halimeda to epiphytism contrasts strongly with recent research that found strong effects of epiphytes on several other species of tropical algae. Our results may be attributed to the unique characteristics of Halimeda, a heavily physically and chemically defended algal genus, and the shallow nature of the patch reefs reducing the potential for significant light limitation. These findings suggest that close interactions such as epiphytism may not be as generalizable as originally assumed; studies must consider differences among host species, as this may lead to a better understanding of community-wide effects.

Palaeoecological Implications of Corallinacean Red Algae and Halimedacean Green Algae from the Prang Formation of South Shillong Plateau, Meghalaya

Abstract The southwestern part of south Shillong plateau (Meghalaya, N-E India), designated as Sylhet Limestone Group is sub-divided into three lithounits i.e., Lakadong, Umlatdoh and Prang formations in ascending order. The Prang Formation is the youngest lithostratigraphic unit of the Sylhet Limestone Group and has been dated as Middle to early Upper Eocene based on the benthic foraminifera studies. Thin section analysis of carbonate rocks from Prang Formation, exposed in the Bholaganj limestone quarry yielded a rich assemblage of calcareous algae. The coralline algal assemblage comprises both non-geniculate and geniculate forms. The green algae are represented by species of Halimeda belonging to the family Halimedaceae. Palaeoecological interpretation based on diversity, growth-form analysis and taphonomic aspects of the algal assemblage indicate that in all probabilities the deposition of Prang Formation occurred in shallow, warm, shelf environment of normal salinity within the transgressive phase.

Effects of estimated herbivory on the reproductive potential of four East African algal species – a mechanism behind ecosystem shifts on coral reefs?

The aim of this field study was to investigate effects of estimated fish- and sea urchin herbivory on the reproductive potential of four species of macroalgae; Halimeda macroloba (Decasine), H. renschii (Hauck), Turbinaria ornata (Turner) and Padina boergesenii (Allender et Kraft). Fish and sea urchin herbivory were calculated based on reported consumption rates for their biomass estimates. We hypothesized that reduced herbivory would increase algal size and the reproductive potential, which may promote algal recruitment and be one of the driving mechanisms behind algal shifts and persistent algae-dominated reefs. Algae were investigated in field sites where the estimated fish- and or sea urchin herbivory differed. Our results suggest that algal fecundity of T. ornata and P. boergesenii are positively correlated to their size. Fecundity of T. ornata was higher and individuals grew larger in areas where estimated fish herbivory was lower. The two species of Halimeda grew larger and had higher fecundity in areas where estimated sea urchin herbivory was lower. P. boergesenii responded ambiguously to patterns in herbivory. Due to species-specific responses to different herbivores, it is difficult to generalize about effects of overfishing on algal fecundity.

Origin Of Calcareous Sediments in the Holocene Pigeon Creek Tidal Lagoon and Tidal Delta, San Salvador Island, Bahamas

A sedimentological survey of the southwest arm of the Holocene Pigeon Creek tidal lagoon on San Salvador Island, Bahamas was conducted to determine the origin and distribution of calcareous sediments. Transect surveys, surface samples, and sediment cores were collected and examined to determine the abundance and distribution of sediments and sediment producers in the lagoon and associated tidal delta. The study area has three regions: an extensive tidal to shallow, subtidal flat; a tidal channel near the entrance to the lagoon; and a lobate, ebb-dominated tidal delta. Tidal flat sediments were extensively bioturbated and heavily rooted by Thalassia testudinum. Tidal flat sediments ranged from coarse, calcareous sand to calcareous muds, and were rich in gastropod shells, foraminifera, calcareous algae, and pelletal calcareous mud. The tidal flat sediments are assigned to a pellet-lime wackestone to muddy lime packstone lithofacies. Calcareous green algae are the primary producers of calcareous sediments in the lagoon with species of Halimeda and Penicillus being the dominant genera. Surface samples taken from the coarse channel lag of the tidal channel consisted primarily of whole and fragmented bivalves and gastropods. Most of the bivalves were oriented convex upward. Surface samples taken from ripples, mega-ripples, and sand waves of the tidal delta are dominated by well-sorted, well-rounded, and polished sand-size grains (1-2 mm in diameter). This sediment was dominated by bioclasts (bivalves, gastropods, calcareous algae, foraminifera) and minor ooids. Sediments of the tidal channel and tidal delta are assigned to a lime packstone to grainstone lithofacies. The coarsest fraction (> 2 mm) accumulated on the lee slopes and troughs of large, tidal and wave produced ripples. Ripples for both ebb- and flood tides are strongly asymmetrical, but symmetrical ripples are common, indicating that significant migration of the tidal delta does not occur during normal tidal events. A low energy, shallowing upward cycle is well illustrated in the lagoon, and the presence of a depaurperate biofacies and heavily bioturbated and rooted lithofacies typify a carbonate lagoon depositional environment.

Asexual propagation in the coral reef macroalga Halimeda (Chlorophyta, Bryopsidales): production, dispersal and attachment of small fragments

Siphonous, green macroalgae of the genus Halimeda are ubiquitous and ecologically important in tropical and subtropical marine environments. It has been hypothesized that the abundance of Halimeda on coral reefs is in part due to the ability of this genus to propagate asexually via vegetative fragmentation. However, vegetative fragmentation has only been documented for H. discoidea in a laboratory setting. To test the hypothesis that vegetative fragmentation contributes to field populations of Halimeda, we examined three aspects of fragmentation by H. tuna (Ellis and Solander) Lamouroux, H. opuntia (Linneaus) Lamouroux and H. goreaui Taylor on Conch Reef in the Florida Keys: (1) short-term (8 days) and long-term (14 weeks) fragment survival and rhizoid production in the laboratory and field (7 and 21 m), (2) size of the fragment pool and (3) influences of herbivory and water motion on production and dispersal of fragments. Although morphologically similar to H. discoidea, only a small percentage of H. tuna fragments survived. Fragments of H. opuntia and H. goreaui were more robust, and survival and rhizoid production were positively correlated with size in short-term trials. In 14-week field trials, one-third or fewer fragments of any species survived at 7 m, potentially because fragments were covered by large amounts of sediment. Survivors included some buried, seemingly dead individuals that turned green when exposed to light, highlighting the remarkable ability of this genus to survive disturbances. There was much less sediment accumulation at 21 m, where more fragments survived. Most (93%) eight-segment fragments of H. opuntia produced attachment rhizoids by the end of the 14-week trial. Overall, a range of 4.7–9.4 fragments of Halimeda m −2 day −1 were found on Conch Reef; most fragments were generated by H. goreaui. Fish bite marks were evident on 75–85% of the individuals of H. tuna and the number of bites per thallus ranged from 1 to 23. Herbivorous reef fish commonly fed on all three species of Halimeda. Some fish consumed the biomass, while others rejected most bites. For example, 83% of bites were rejected by the blue-striped grunt. Dispersal distances for rejected bites ranged from 0 to 31 m. Water motion was also responsible for fragment dispersal; experimentally produced fragments moved up to 48 cm day −1. Results presented here suggest that asexual propagation of fragments of Halimeda is an important component of the life-history of this genus and vegetative fragmentation contributes to the abundance of this genus on coral reefs.

Diversity of the green algal genus Halimeda in the Chagos Archipelago, central Indian Ocean

Ten species of Halimeda were found at depths between 6 and 46 m on the outer reef slopes and in the lagoons of Peros Bahnos and Salomon Atolls in the north of the Chagos Archipelago, central Indian Ocean. This Halimeda flora is similar to that of mid-ocean Pacific reefs and considerably richer than elsewhere in the Indian Ocean. Halimeda minima (W.R. Taylor) L.H. Colinvaux is reported for the first time outside the Pacific Ocean.

Activation of chemical defenses in the tropical green algae Halimeda spp.

Halimeda spp. are among the most common seaweeds on tropical reefs where herbivory is intense. These calcified seaweeds produce diterpenoid feeding deterrents; the major metabolites are halimedatetraacetate and halimedatrial. We found that most species of Halimeda on Guam immediately convert the less-deterrent secondary metabolite halimedatetraacetate to the more potent feeding deterrent halimedatrial when plants are injured by grinding or crushing. This conversion would therefore occur when fishes bite or chew Halimeda plants. We term this process of rapid conversion “activation”. Extracts from injured plants contained higher amounts of halimedatrial and were more deterrent toward herbivorous fishes than extracts from control plants. Herbivore-activated defenses are common in many families of terrestrial plants: however, this is the first example of an activated defense in a marine plant.

Deep-water green algae from the Bahamas, including Cladophora vandenhoekii sp. nov. (Cladophorales)

Studies on deep-water green algae (Chlorophyta) collected using the submersible Johnson-sea-Link I off San Salvador Island, Bahamas, revealed species belonging to the Cladophorales, Siphonocladales and Bryopsidales. All were either siphonous or giant-celled types, suggesting that these morphologies are the dominant forms of green algae in the Caribbean deep-water flora. Twenty-five taxa are reported, excluding species of Halimeda and an undescribed tetrasporalean alga. Cladophora vandenhoekii sp. nov. (Cladophorales) is apparently a deep-water endemic, remarkable for its exceptionally large cells and net-like appearance. The genus Johnson-sea-linkia Earle et Eiseman is considered to be a synonym of Rhipiliopsis A. Gepp et E. S. Gepp, and the combination R. profunda (Eiseman et Earle) J. Norris et S. Blair is proposed. Microdictyon laxereticulatum Setchell and Avrainvillea lacerata J. Agardh are newly reported from the western Atlantic, and II taxa are now reported for the Bahamas: Cladophora coelothrix Kützing, C. pellucidoidea van den Hoek, Anadyoneme saldanhae Joly et Oliveira Filho, A. linkinana D. Littler et M. Littler, Microdictyon boergesenii Setchell, Struvea anastomosans (Harvey) Piccone et Grunow ex Piccone, Pseudocodium floridanum Dawes et Mathieson, Codium isthmocladum subsp. clavatum (Collins et Hervey) Silva, Bryopsis ramulosa Montagne, Caulerpa racemosa var. occidentalis (J. Agardh) Børgesen, and C. peltata Lamouroux. Twenty-one species are reported from depths of > 20 m more than their previous records. Fifteen of these were found at depths > 50 m greater than previously recorded, eight of which were known only from the intertidal or from water shallower than 10 m.

Use of ingested algal diterpenoids by Elysia halimedae Macnae (Opisthobranchia : Ascoglossa) as antipredator defenses

Marine mollusks of the Order Ascoglossa (= Sacoglossa) are specialized herbivores of tropical green seaweeds and other seaweeds (diatoms, red algae, seagrasses). In this study, we investigated the feeding relationship between the ascoglossan Elysia halimedae Macnae and its preferred food, the seaweed Halimeda macroloba Decaisne. The toxic diterpenoid metabolites of many species of Halimeda have been shown to act as feeding deterrents toward nonspecialized grazers such as herbivorous fishes. However, E. halimedae feeds only on species of Halimeda and prefers young plant growth, which contains the highest concentrations of the Halimeda compounds. Our observations suggest that E. halimedae modifies the major diterpenoid from H. macroloba and sequesters and stores this modified compound for its own defense. When irritated, Elysia secretes large amounts of mucus containing this defensive compound. The compound occurs in Elysia as ≈ 7% of the whole animal dry mass. Similar high concentrations of the compound are found in the egg masses of E. halimedae. We isolated and determined the structure of the ascoglossan compound and tested the compound in field assays toward carnivorous and herbivorous fishes on Guam. This compound is a significant feeding deterrent at naturally occurring concentrations toward potential predators. Thus, E. halimedae is adapted to feed on toxic algae and utilizes the algal chemical defenses for its own defense against predation.

Chemical defense and chemical variation in some tropical Pacific species of Halimeda (Halimedaceae; Chlorophyta)

Over a dozen species of the genus Halimeda have been chemically investigated and found to produce the diterpenoid metabolites halimedatrial (1) and halimedatetraacetate (2) in varying concentrations. These meabolites have been proposed to play a role in chemical defense against herbivores based on their chemical structures and their demonstrated biological activities in laboratory and aquarium assays. We examined and compared the feeding deterrent effects of these two compounds tovard herbivorous fishes in field experiments on Guam reefs. Halimedatrial is a more effective feeding deterrent than halimedatetraacetate. It is the major secondary metabolite in young Halimeda macroloba and in the newly produced segments of growing plants. The organic extracts from young plants and new segments were significantly more deterrent than extracts from mature plant tissue. Some populations of Halimeda growing in reef-slope habitats, where herbivory is intense, also have high concentrations of halimedatrial. We compared extracts between reef slope and reef flat collections of Halimeda opuntia on Guam and Pohnpei (= Ponape), and H. discoidea and H. macroloba on Guam. We found that halimedtrial was the major metabolite in reef-slope collections of H. opuntia from Pohnpei and Pago Bay, Guam, and that halimedatetraacetate was the major metabolite a non-reef slope populations. In the cases examined, chemical defenses were greatest in (1) plant parts and (2) populations that were at greatest risk to herbivores.

A comparison of nutrient- and light-limited photosynthesis in psammophytic versus epilithic forms of Halimeda (Caulerpales, Halimedaceae) from the Bahamas

The relative nutritional status, with respect to phosphorus (P i ) vs. nitrogen (N) limitation, and light-limited photosynthesis (P s ) was examined over a broad range of quantum fluxes (I) for four Halimeda species, Halimeda tuna (Ellis and Solander) Lamouroux, H. simulans Howe, H. lacrimosa Howe and H. copiosa Goreau and Graham, taken from clear, shallow, Bahamian waters. The results support the hypothesis that psammophytic forms (i.e., sand dwellers anchored by a bulbous rhizoidal system) differ in nutrient status from epilithic forms (i.e., attached to rock by inconspicuous rhizoids). Maximum photosynthetic rates (Pmax) for the epilithic species H. lacrimos and H. copiosa decreased (P<0.05) following P i enrichment, but increased (P<0.05) following N pulses. Conversely, following brief exposures to P i , Pmax in the sand-dwelling forms H. tuna and H. simulans was elevated (P<0.05). These findings suggest that shallow species of Halimeda are adapted to take advantage of episodic nutrient pulses, and that partitioning of limiting resources may occur between the various life forms. Shallow water Halimeda species appear well adapted to variable light regimes, including low light conditions. In all cases, light-saturated photosyntheses (I k ) occurred at irradiances much lower than the ambient levels available on typical sunny days. Associated with low saturation irradiances were low light requirements for photosynthetic compensation (I c ) and reasonably efficient use of low photon flux densities as indicated by relatively steep slopes (α) of the P s vs. I curves. Of the four species, H. copiosa was the most shade adapted, with considerably higher α values and considerably lower I c , I k and photoinhibition values.

Studies on Halimeda

Seventeen species of Halimeda have been grown in the laboratory in an open-circuit seawater cascade during a 6 year period. All but one grew vegetatively (generated new segments) to some extent and several species grew luxuriantly. A few species also reproduced vegetatively by developing new plants at the ends of fine runners. However, most significant was the production of gametangia by all the species in the cascade whilst several of those species, plus one not grown in the cascade, were also observed fertile in the field. Different material from a single collection sometimes became fertile in the cascade in successive years and then often at very similar times, suggesting a distinct seasonality and response to environmental stimuli. Some lunar periodicity was also detected in the fertility of three species. Species-specific differences in the structure of gametangial clusters, particularly the size of the gametangia, were observed. In all species examined, gametophore branches ended in unexpanded tips which often had a distinct, thickened cap. Upon maturity, the contents of all the gametangia in a cluster were explosively released through these discharge papillae. This release usually commenced only 5 to 15 minutes after the plants were re-illuminated on the day following the appearance of gametangia although two species, H. incrassata and H. melanesica, often released their gametes in the late afternoon.

Reef to basin sediment transport using Halimeda as a sediment tracer, Grand Cayman Island, West Indies

Fragments of the calcareous green alga Halimeda form a large part of the sediment in the fringing reef system and adjacent deep marine environments of Grand Cayman Island, West Indies. Nine species combine to form three depth-related assemblages that are characteristic of the major reef-related environments (lagoonpatch reef, reef terraces, and deep reef). These modern plant assemblages form the basis of the use of Halimeda as a sediment tracer. Halimeda-based tracer studies of Holocene sediments indicate that only sediments containing deep reef species of Halimeda are presently being transported through the reef system by sediment creep and being deposited at the juncture of the upper and lower island slope. Sediments containing shallow reef Halimeda are retained within the reef and lithified by marine carbonate cements. Tracer studies of Pleistocene sediment indicate large amounts of reef-derived carbonate sand containing deep water Halimeda were produced during interglacial high stands of sea level. Much of this material was removed by turbidity currents moving out of the reef system to the island slope down submarine channels perpendicular to the reef trend. These channels may still be identified on bathymetric profiles, but are no longer receiving coarse reef debris and are veneered with a blanket of pelagic carbonate mud.

Halimeda contribution to organic and inorganic production in a Tahitian reef system

Of the seven species of Halimeda inhabiting a lagoon on Moorea island, three representing 10% of the algal covering and averaging 111 g of dry weight m-2, have been studied in the course of a year. The biomass, measured bimonthly, stresses a slight seasonal variability in the species life. The main decrease was reported for H. opuntia after a fruiting event, which happened in October. The primary production was assessed, in situ, periodically over a year, by measuring oxygen variations in enclosures. Either expressed on specific-weight basis or in area units, the highest primary productions were recorded for H. opuntia. Productions and biomasses vary simultaneously during the year. The three species produce all together about 6 g C m-2y-1. The growth rate of the sand-dwelling H. incrassata f. ovata was followed during the year by staining, in the field, individuals with alizarin Red-S. The average rates measured were 3.3 segments ind-1d-1 and 0.17 gdw d-1m-2. The contribution of the three species to the carbonate budget of the reef was estimated by total alkalinity measurements during 24-h cycles. H. opuntia had the highest CaCO3 production. For the three species studied, CaCO3 production of 1.4 kg m-2y-1, which could correspond to a 0.4mm/year accretion of the studied reefal system, was estimated.

The deep-water species of Halimeda Lamouroux (Halimedaceae, Chlorophyta) from San Salvador Island, Bahamas: species composition, distribution and depth records

Caribbean species of Halimeda from the steep slopes of San Salvador Island, Bahamas, were collected along vertical transects between 25 and 255 m, on the northeast, northwest, west, southwest and south sides of the island, using the Harbor Branch Oceanographic Institution's submersible Johnson Sea Link I. The characteristics delineating species (segment and utricle size) were assessed for selected species, and the depth and western Atlantic distributions of the species reviewed. Halimeda copiosa was found to show a variation of surface utricle diameter with depth, with the deeper plants having 15% larger diameter utricles than the shallower plants. Of the seven species, one variety and one form of Halimeda studied from our submersible dive sites, H. copiosa, H. cryptica and H. gracilis grew to the greatest depths, from 120 to 150-m depths. H. lacrimosa var. globosa was found growing to 91 m, and H. tuna f. platydisca and H. discoidea to a depth of 73 m. Those of lesser depth, to 61 m, were H. goreauii, H. tuna f. tuna and H. lacrimosa var. lacrimosa. These represent substantial increases in depth distribution of the nine taxa found.