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Populations of many Mediterranean marine species show a strong phylogeographic structure, but the knowledge available for native seaweeds is limited. We investigated the genetic diversity of the green alga Halimeda tuna based on two plastid markers (tufA gene and a newly developed amplicon spanning five ribosomal protein genes and intergenic spacers, the rpl2-rpl14 region). The tufA sequences showed that Mediterranean H. tuna represents a single, well-defined species. The rpl2-rpl14 results highlighted a genetic separation between western and eastern Mediterranean populations; specimens collected from widely scattered locations in the Adriatic/Ionian region shared a haplotype unique to this region, and formed a group separated from all western Mediterranean regions. Specimens from Sardinia also formed a unique haplotype. Within the western Mediterranean basin, a gradual shift in the frequency of haplotypes was apparent along a West-East gradient. Our results represent the first clear evidence of an East-West genetic cleavage in a native Mediterranean macroalga and offer an interesting perspective for further research into fine-scale seaweed population structure in the NW Mediterranean Sea.

Seaweed belongs to marine biota and contains nutrients and secondary metabolites beneficial for health. This study aimed to determine the antidiabetic activity of extracts and fractions of green seaweed Halimeda tuna. The H. tuna sample was extracted with the maceration method using methanol and then partitioned using ethyl acetate and water to obtain ethyl acetate and water fractions. The methanol extract, ethyl acetate fraction, and water fraction of H. tuna were tested for their inhibitory activity against α-amilase and α-glucosidase. The methanol extract and the fractions with the highest inhibitory activity were phytochemically tested and analyzed using gas chromatography–mass spectrometry (GC-MS). The results showed that the ethyl acetate fraction (IC50 = 0.88 ± 0.20 mg/mL) inhibited α-amylase relatively similar to acarbose (IC50 = 0.76 ± 0.04 mg/mL). The methanol extract (IC50 = 0.05 ± 0.01 mg/mL) and the ethyl acetate fraction (IC50 = 0.01 ± 0.00 mg/mL) demonstrated stronger inhibitory activity against α-glucosidase than acarbose (IC50 = 0.27 ± 0.13 mg/mL). Phytochemical testing showed that the methanol extract and the ethyl acetate fraction contained secondary metabolites: alkaloids, flavonoids, steroids, and phenol hydroquinone. The compounds in methanol extract predicted to have inhibitory activity against α-amylase and α-glucosidase were Docosanol, Neophytadiene, Stigmasta-7,22-dien-3-ol,acetate,(3.beta.,5.alpha.,22E), Octadecanoic acid,2-oxo-,methyl ester, and phytol, while those in the ethyl acetate fraction were n-Nonadecane, Phytol, Butyl ester, 14-.Beta.-H-pregna, Octadecenoic acid, and Oleic acid.

This study focuses on the taxonomy of epiphytic diatoms in the area of invasive macroalgae from the genus Caulerpa. Caulerpa species are characterized by the presence of secondary metabolites, such as caulerpenyne (CYN), the main function of which is a chemical defense mechanism against herbivores and epiphytes. Epiphytic diatoms were studied on fronds of Caulerpa taxifolia (“killer seaweed”) and, for comparison, on autochthonous macroalgae Padina sp. and Halimeda tuna at the eastern Adriatic Sea coast (Island of Hvar) in the summer and autumn of 2010. The qualitative analysis was performed with the use of light and scanning electron microscopy. The Shannon–Wiener Diversity Index determined for Caulerpa taxifolia showed a wide range of values (3.11–4.88), with a maximum in August and a minimum in October. While the number of taxa on Caulerpa taxifolia fronds increased from June (41) to August (88), it declined in autumn due to the high relative abundance of Cocconeis caulerpacola, which is a diatom typical for Caulerpa. On the other hand, the largest number of taxa on Padina sp. was observed in September (82). The detailed composition of epiphytic diatoms and seasonal dynamics in the area affected by the invasive macroalga Caulerpa taxifolia have been determined for the first time.

Three seaweeds (Halimeda tuna, Codium bursa and Cystoseira barbata) and one seagrass (Cymodocea nodosa) were collected from the Coast of Montenegro, Gulf of Boka Kotorska and their chemical analysis was performed. In seagrass C. nodosa, three phenolic compounds were identified (diosmetin 7-sulfate, caftaric and coutaric acid). The content of β-glucan, fatty acids, sterols and micro- and macro-elements were investigated among all samples. The highest content of β-glucan was detected in C. nodosa seagrass (13.04±0.42 g/100 g). The highest polyunsaturated fatty acids (PUFAs) level was reported in C. barbata, the brown alga (7.157 mg/g), which also had the significant sterol content (fucosterol, 21.76±0.1 μg/g). Green algae, C. bursa and H. tuna, showed the highest level of sterols (β-sitosterol, 95.21±0.16 μg/g and 73.90±0.08 μg/g, respectively). H. tuna had the highest content of calcium (Ca) in amount of 55125 μg/g. In C. bursa, C. barbata and C. nodosa, the Na/K ratio was low (0.43, 0.46 and 0.69, respectively). This is peer-reviewed version of the folowing article:Milović, S.; Stanković, I.; Nikolić, D.; Radović, J.; Kolundžić, M.; Nikolić, V.; Stanojković, T.; Petović, S.; Kundaković-Vasović, T. Chemical Analysis of Selected Seaweeds and Seagrass from the Adriatic Coast of Montenegro. Chemistry and Biodiversity 2019, 16 (10). [https://doi.org/10.1002/cbdv.201900327].

Mediterranean coastal ecosystems experience many local and global stressors and require long-term monitoring to detect and follow trends in community structure. Between 2009 and 2017, we seasonally and annually monitored the spatiotemporal community dynamics at 11 sites on the rocky shores of the southeastern Mediterranean, focusing on the understudied intertidal vermetid reef ecosystem. Marked seasonal trends were found in biodiversity, with the highest diversity in winter and spring. Canopy-forming brown algae, dominating the northwestern Mediterranean intertidal reefs, were generally scarce on the reef platform and almost only found in tidepools. Interannual shifts in community structure were driven mostly by sharp fluctuations in a few dominant native and alien species and the regional mass mortality of an Indo-Pacific mussel in summer 2016. Compared to an older macroalgae dataset, dating back to 1973–1995, we found that some warm-affinity (summer) taxa became more dominant and cold-affinity (winter) species less dominant, while one once conspicuous species, Halimeda tuna, completely disappeared. The observed community shifts are probably driven mostly by stressors related to climate change. We encourage forming a network of long-term, multi-site ecological monitoring programs in the Mediterranean to improve our understanding of ecosystem change and to enable making better predictions at the basin scale.

The macroalgal species, Halimeda tuna , Halimeda opuntia , and Dictyota sp., are modular and clonal organisms that have the capability for morphological plasticity and asexual reproduction through fragmentation. Growth and disturbance factors affect these characteristics and consequently their rate and amount of space capture. A three-dimensional agent-based model SPREAD (Spatially-explicit Reef Algae Dynamics) was used to explore these potential consequences under a range of growth and disturbance conditions, and to investigate the particular conditions leading to variations of these macroalgae in the inshore patch and offshore reefs in the Florida Reef Tract. The morphology of macroalgae, particularly for H. tuna , had an effect on the rate and amount of space occupation, where larger and more upright forms were able to attain greater cover. Even with the more prolific growth forms, space occupation was still limited. Inclusion of fragmentation was needed for greater expansion and to obtain abundances comparable to field observations. Disturbance, whether through herbivory or stronger forces like storms, interacts with fragmentation in determining space occupation patterns of the macroalgae species. High disturbance levels can promote increased fragmentation and spatial cover. However, this appears to be only true for H. opuntia and Dictyota sp., species with relatively high fragment survival capacity. H. tuna achieved higher cover at low disturbances. Strong disturbances leading to larger fragment sizes were detrimental to the spatial spread for all species. Temporally, these macroalgal populations in the studied reefs appeared to be stable overall with seasonal increases and decreases, as was shown possible in the model, observed in the field, and supported in the literature. Based on SPREAD and corroborated with field observations, the combined inherent growth requirements, capability for fragment success, and disturbance through fragment generation influenced the abundance of these macroalgae in inshore patch and offshore reefs which experienced different growth and disturbance conditions. The overall stable macroalgal cover in the observed and simulated Florida Keys reefs permits other organisms, particularly hard corals, to capture space on the reef. Nonetheless, specific local conditions and the timing of macroalgae seasonal increases can impact the spatial spread of other benthic organisms.

Seaweed–coral interactions are increasingly common on modern coral reefs, but the dynamics, processes, and mechanisms affecting these interactions are inadequately understood. We investigated the frequency and effect of seaweed–coral contacts for common seaweeds and corals in Belize. Effects on corals were evaluated by measuring the frequency and extent of bleaching when contacted by various seaweeds, and effects on a common seaweed were evaluated by assessing whether contact with coral made the seaweed more palatable to the sea urchin Diadema antillarum. Coral–seaweed contacts were particularly frequent between Agaricia corals and the seaweed Halimeda opuntia, with this interaction being associated with coral bleaching in 95 % of contacts. Pooling across all coral species, H. opuntia was the seaweed most commonly contacting corals and most frequently associated with localized bleaching at the point of contact. Articulated coralline algae, Halimeda tuna and Lobophora variegata also frequently contacted corals and were commonly associated with bleaching. The common corals Agaricia and Porites bleached with similar frequency when contacted by H. opuntia (95 and 90 %, respectively), but Agaricia experienced more damage than Porites when contacted by articulated coralline algae or H. tuna. When spatially paired individuals of H. opuntia that had been in contact with Agaricia and not in contact with any coral were collected from the reefs and offered to D. antillarum, urchins consumed about 150 % more of thalli that had been competing with Agaricia. Contact and non-contact thalli did not differ in nutritional traits (ash-free-dry-mass, C or N concentrations), suggesting that Halimeda chemical defenses may have been compromised by coral–algal contact. If competition with corals commonly enhances seaweed palatability, then the dynamics and nuances of small-scale seaweed–coral–herbivore interactions at coral edges are deserving of greater attention in that such interactions could scale-up to have important consequences for coral resilience and the persistence of reef structure and function.

The seaweeds resources were sampled from exposed shore of Nathia Gali beach, Karachi coast at low tide. The present data of diversity and biomass of seaweeds provide a comparison of two different periods i.e., from 1989 to 1991 and 2012. A total of 60 taxa were recorded in the coastal area of Nathia Gali; 14 belonging to chlorophyta, 15 to Phaeophyta and 31 to Rhodophyta. The green seaweeds viz, Caulerpa racemosa, Codium iyengarii and Halimeda tuna; brown seaweeds, Cystoseira indica, Iyengaria stellata Padina pavonica and Sargassum boveanum and red seaweeds Gracilaria corticata and Scinaia fascicularis were found to be the dominant species of Nathia Gali. The total biomass 66056.18 g. m-2 was recorded during the study period and the highest biomass was recorded in January (16551.79 g m-2) and the lowest in July (1276.3 g. m-2). In winters, seaweeds biomass and growth increased due to low temperature of air and seawater with low intensity of light and high dissolved nutrients. The richness of seaweed resources in the studied area is due to the intertidal rocks available on the coast but nowadays, there is lot of disturbance due to anthropogenic activities such as discharge of domestic and industrial waste; tanneries effluents; rainfall and associated pollutant from runoff; shipping and agricultural sources. These disturbances play vital role in changing the ecosystem which effects flora and fauna of the coast.

On Conch Reef, Florida Keys, USA, we examine relationships between temperature variability measured with a unique, high-resolution sensor network, and the abundance of benthic reef organisms and carbon, nitrogen and oxygen stable isotopic composition of two abundant macroalgal species. Visualization of spatial temperature anomalies mapped onto measured reef bathymetry reveals episodic thermal patchiness and persistent thermal features likely indicating meter scale variability in nutrient supply. These patterns result from the relatively shallow depths of the offshore thermocline and an active internal wave field creating a hydrographic structure conducive to interactions of an offshore, subthermocline nutrient pool with reef topography. The distribution of major benthic reef organism taxa, as well as the stable isotopic composition of C, N and O, from the macroalgae Dictyota menstrualis and Halimeda tuna are all highly variable on scales of less than 10 m and are not necessarily depth-dependent. Covariability between spatial patterns of the temperature minima, depth and d 13 Co fD. menstrualis and H. tuna suggest a role of oceanographic forcing in inorganic carbon acquisition in these species. Comparisons of the measured temperature with the predicted temperature based on d 18 O from H. tuna aragonite suggest a possible influence of low salinity water in the system and non-linear interactions between ambient conditions and calcification at fine temporal and spatial scales. These observations have implications for the interpretation of both contemporary and paleontologic reef environments where oceanographic forcing interacts with complex reef topography.

Macroalgae are modular organisms that can express different morphologies depending on the environment to which they are exposed. Their growth under varying light, temperature, and nutrient regimes, interacting with disturbance factors such as herbivory and hydrodynamics, leads to particular morphological types. The present study illustrates the potential of using morphological variations of benthic modular and/or clonal organisms as indicators of the factors and processes influ- encing them in their particular location. The morphogenetic agent-based model SPREAD (spatially explicit reef algae dynamics) was used to determine the range of potential morphological types in 3 dominant macroalgal species (Halimeda tuna, H. opuntia, and a species of Dictyota) in the Florida Reef Tract. Simulations of growth under a range of light, nutrient, and disturbance conditions simi- larly found at inshore patch and offshore bank reefs led to 6 potential morphological types for H. tuna, 2 for H. opuntia, and 3 for a species of Dictyota. From these potential sets derived from the model, we observed that particular morphological types corresponded to the morphologies found in the 2 reef habitat types. The simulated conditions that led to the formation of these morphologies in the model were similar to the environmental conditions at these sites. In addition to relating combinations of environmental and disturbance factors to macroalgal growth morphologies, the present study pro- vides insights into the differing life-history strategies among the species, and the adaptive value of plasticity expressed by these macroalgae. The morphologies of the successful fragmenters H. opun- tia and a generalized species of Dictyota were more influenced by disturbance. On the other hand, the morphology of the less successful fragmenter H. tuna was strongly influenced by the growth factors of light and nutrients.

Seawater temperature varies across multiple spatial and temporal scales, yet the roles that such variation play in altering biotic interactions are poorly known. We assessed temperature-mediated feeding behavior exhibited by the herbivorous amphipod Ampithoe longimana collected from cold-temperate and subtropical estuaries (27 degrees N and 41 degrees N, respectively). Individuals were offered a pairwise feeding choice between lyophilized seaweeds that provide higher fitness (Ulva intestinalis) or lower fitness (Halimeda tuna, H. opuntia, Amphiroa spp., or Stypopodium zonale). Overall, herbivores preferentially consumed the higher quality U. intestinalis more than any lower quality food. However, the strength of this feeding choice was not consistent. Northern herbivores consumed proportionally more poorer quality tissue at 25 degrees C than at 20 degrees C in two assays (H. opuntia and Amphiroa sp.), consumed less poorer quality tissue at 25 degrees C than at 20 degrees C in one assay (S. zonale), and showed no difference in another assay (H. tuna). Moreover, when offered tissue coated with lipophilic extracts of H. opuntia, northern herbivores consumed more extract-coated tissue at 25 degrees C than at 20 degrees C. In contrast to northern herbivores, the southern herbivores did not alter their feeding choices with temperature. This study represents the first demonstration that short-term (i.e., days-long) variation in ambient temperature alters feeding choices in a marine herbivore.

Antimicrobial screening of 12 different seaweeds extracts namely Chaetomorpha antennina, Dictyota dichotoma, Enteromorpha flexuosa, Laurencia obtusa, Gracilaria corticata, Gracilaria verrucosa, Grateloupia lithophila, Padina boergesenii, Sargassum wightii, Turbinaria conoides, Halimeda tuna and Ulva lactuca was carried out in vitro . The crude extracts were tested against the phytopathogenic bacterium- Pseudomonas syringae causing leaf spot disease of the medicinal plant Gymnema sylvestre . The methanolic extracts of Sargassum wightii showed maximum activity followed by ethyl acetate compared to that of other organic solvent- extracts. Thus, this investigation throws fresh light on the appropriate usage of solvent extraction method in preparing potent biopesticide.

During the past decade, the relative abundance of the brown macroalgae Dictyota spp. has been high in the Florida Keys. Recent studies have shown that members of this genus successfully reproduce via vegetative fragmentation. To investigate the importance of fragmentation on the reef community, this study examined: (1) the degree of epiphytism on benthic organisms, (2) the rate of fragment production through fish foraging activities, (3) the likelihood of fragment entanglement, and (4) the fragment attachment and success rate. It was found that reef fish contributed substantially to the fragment pool; furthermore, most fish-produced fragments produced rhizoids and attached to sand grains within 24 h in the field. Fragments of Dictyota spp. most commonly became entangled around and then attached themselves to the green alga Halimeda tuna, and other Dictyota spp. These results suggest that vegetative fragmentation of Dictyota spp. plays an important role in the changing community structure on the Florida Keys reef tract.

We conducted a manipulative nutrient enrichment study to examine the physiological and growth dynamics of the common tropical reef alga Halimeda tuna from shallow and deep coral reef environments on Conch Reef, in the Florida Keys. Paradoxically, H. tuna exhibited higher growth rates at depth (low light and below saturating irradiances) than at shallow sites (high light and at or above saturating irradiances). We hypothesized that the differences in growth rates were caused by differing nutrient environments at the two sites potentially caused by the influence of internal tidal bores that elevate nutrient concentrations with depth on Conch Reef. We tested this hypothesis by manipulating nutrients in a 10-d field experiment, after which we assessed growth, photosynthetic pigments, tissue nutrients, and other physiological parameters. H. tuna from the shallow back reef site exhibited nutrient limitation, as indicated by increases in growth rates, pigmentation, tissue nutrients, segment size, and photosynthetic rates, after enrichment. At the deep site, growth rates were not significantly different between controls and nutrient-enriched algae. Shallow enriched samples achieved levels of growth that were not significantly different from deep control or enriched samples. Algae from the deep site responded positively to enrichment for some physiological parameters; this suggests an opportunistic strategy in an environment that is known to experience frequent and significant pulses of nutrients from internal tides. Our results document differential nutrient limitation for H. tuna from two sites on Conch Reef where, in general, algae from the shallow site were more nutrient limited than those from the deep site. Finally, this provides some evidence that tropical reef communities may be adapted to large-scale physical processes such as internal tides.

The photosynthetic performance, pigmentation, and growth of a Halimeda community were studied over a depth gradient on Conch Reef, Florida Keys, USA during summer-fall periods of 5 consecutive years. The physiology and growth of H. tuna (Ellis & Solander) Lamouroux and H. opuntia (L.) Lamouroux on this algal dominated reef were highly variable. Maximum rate of net photosynthesis (P-max ), respiration rate, and quantum efficiency (alpha) did not differ between populations of either species at 7 versus 21 m, even though the 21-m site received a 66% lower photon flux density (PFD). Physiological parameters, as well as levels of photosynthetic pigments, varied temporally. P-max , saturation irradiance, compensation irradiance, and growth were greatest in summer months, whereas alpha, chl a , chl b , and carotenoid concentrations were elevated each fall. Halimeda tuna growth rates were higher at 7 m compared with 21 m for only two of five growth trials. This may have arisen from variability in light and nutrient availability. Individuals growing at 7 m received a 29% greater PFD in August 2001 than in 1999. In August 1999 and 2001 seawater temperatures were uniform over the 14-m gradient, whereas in August 2000 cold water regularly intruded upon the 21-m but not the 7-m site. These results illustrate the potentially dynamic relationship between nutrients, irradiance, and algal productivity. This suggests the necessity of long-term monitoring over spatial and temporal gradients to accurately characterize factors that impact productivity.

Growth, survivorship, recruitment, and reproduction of Halimeda tuna, a dominant green alga in many reef systems of the Florida Keys, were monitored at a shallow back reef (4–7m) and deep reef slope (15–22 m) on Conch Reef. Despite lower light intensities and similar grazing pressures, amphipod infestations, and epiphyte loads at both sites, the deeper site exhibited significantly higher growth rates in summer months over a 4-year period than found for the shallow population, possibly because of higher nutrient levels at depth and photoinhibition of shallow plants. Sexual reproductive events occurred simultaneously across the entire reef, with up to 5% of the population at both sites developing gametangia. New upright axes formed from zygotes, asexual fragmentation, or vegetative runners. Plants appear to have persistent basal stumps that survive harsh environmental conditions, even if upright, photosynthetic axes are removed. Sexual reproduction and ‘smothering’ by epiphyte overgrowth are hypothesized to be two causes of death for individuals.

The subtidal epiphytic communities of both macroalgae and microalgae of the Aegean Sea have been inadequately investigated. In this paper epiphytic algal assemblages thriving on different hosts [i.e. the phaeophyte Padina pavonia (L.) LAMOUROUX, the chlorophyte Halimeda tuna (ELLIS et SOLANDER) LAMOUROUX and the seagrass Posidonia oceanica (L.) DELILE], were studied in a typical oligotrophic site of the Aegean Sea (Dikastika, Attica Peninsula) during the course of one year (June 1997-May 1998). A total of 47 taxa of epiphytic macroalgae were identified, with Hypnophyceae and Ephemerophyceae being the dominant life forms. The major algal groups (rhodophytes, phaeophytes, chlorophytes) showed a distinct seasonality, with rhodophytes predominating on all hosts. The majority of epiphytes favoured a certain position on the host thallus or blade. A distinct vertical zonation pattern was found, with epiphytes covering only certain host areas (upper-, middle-, lower parts of the plant), and further differentiated between the frond edge and blade's lamina. A total of 175 taxa of diatoms were identified and the diatom assemblages bear great resemblance to typical epiphytic floras, with dominant genera Mastogloia, Amphora, Nitzschia, Diploneis, Navicula and Cocconeis. Mass development of epiphytic diatoms on certain hosts implies host preference, but no host-specificity could be ascertained. The total epiphytic species composition seems to be affected by the seasonal alteration of abiotic factors. Epiphytic macroalgal species abundance and diversity was the highest during spring, having a possible competitive influence on the epiphytic diatom growth, whereas higher species abundance of diatoms during summer might furthermore be attributed to the surface increase of macroalgae.

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 2 1 in), (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 cut 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. (C) 2002 Elsevier Science B.V. All rights reserved.

We investigated the cytotoxic, neurotoxic, apoptotic and antiproliferative effects of extracts from Petalonia fascia, Jania longifurca and Halimeda tuna on the MCF-7 breast cancer cell line. J. longifurca extracts were more toxic than those of P. fascia and H. tuna. The algal extracts showed significant toxic effects at different dilutions. The toxic effects were due to increased oxidative stress and resulted in apoptosis. Algal toxicity may exert negative effects through the food chain or by direct interaction. Algal toxicity also has potential for cancer therapy. The toxic effects that we observed may be especially important for therapy for breast tumors.

Studies of factors aAecting host plant spe- cialization by herbivores commonly highlight the value of the plant as both food and habitat, but often cannot distinguish the relative importance of these plant traits. A diAerent approach is to study non-herbivorous ani- mals that specialize on particular plants but do not feed on tissue from these plants. Such animals will not be aAected directly by the nutritional, chemical, or mor- phological traits that determine the value of the plant as a food. This study reports on a filter-feeding amphipod, Ericthonius brasiliensis, that lives in domiciles it con- structs by curling terminal segments of the green, cal- cified, and chemically defended seaweed Halimeda tuna. We examined the temporal (1850s-1990s) and spatial (Caribbean, Mediterranean, and Pacific regions) scale of the association, the factors that may select for spe- cialization on H. tuna, and the eAect of the amphipod on growth of its host. Sampling along 125 km of coral reefs in the Florida Keys (USA) indicated that almost all populations of H. tuna had been colonized by this amphipod. Infested plants occurred on nine of ten reefs that supported H. tuna populations, with between 8 and 75% of the plants on those reefs colonized by the am- phipod. For infested plants, 2-23% of all segments on each plant had been curled by the amphipod. Common co-occurring congeners of H. tuna (H. opuntia and H. goreaui) were never used for domicile construction. A survey of 1498 Halimeda specimens collected during the last 140 years and archived in the U.S. National Museum of Natural History (Smithsonian Institution, Washington, D.C.) indicated that the association has existed for >100 years and occurs throughout the Ca- ribbean region, never in the Indo-Pacific or Mediterra- nean, and only on H. tuna. Predation by fishes could select for amphipod specialization on H. tuna. Labo- ratory experiments demonstrated that amphipods in- habiting curled segments of H. tuna were relatively immune from fish predation while those on the exterior surface of the plant or in open water were rapidly eaten. Segments of H. tuna are large enough to provide full protection from predators, while those of the co- occurring congeners H. goreaui and H. opuntia are of a size that may provide only partial protection. Experi- mental addition of E. brasiliensis to H. tuna plants in the field significantly decreased segment accumulation on infested relative to uninfested control plants. Whether this negative eAect was a direct or indirect consequence of amphipod occupancy is unclear. Rolling plant portions into domiciles could directly decrease host growth by increasing shading and decreasing ex- posure of plant surface area to water column nutrient flux. Amphipod occupancy could indirectly slow net host growth if fishes selectively feed on plant sections occupied by amphipods. Underwater video showed that herbivorous fishes did not graze infested plants more than uninfested plants, but small predatory fishes did prefer feeding from infested plants. These non-herbiv- orous fishes may slow host growth by damaging the terminal meristematic tissues of plants during attacks on amphipods. This study demonstrates that habitat specialists can negatively impact hosts without con- suming them and that specialization on a plant can occur due to its habitat value alone (as opposed to its value as a food).

— Photoinhibition of photosynthesis was investigated in the Mediterranean green alga Halimeda tuna measuring pulse amplitude modulation (PAM) chlorophyll fluorescence and oxygen evolution in situ under solar radiation. Exposure to solar radiation at the surface caused a drastic decline in the photosynthetic quantum yield accompanied by a decline in the photochemical quenching, while the nonphotochemical quenching dramatically increased. The algae recovered from these effects within a few hours indicating that these are mainly due to reversible photoinhibition and only to a smaller extent to nonreversible photodamage. Individuals harvested from deeper waters were more affected than those from shallower waters. Photoinhibition occurs in this alga even in its natural habitat when the sun is at high angles as shown by measuring the fluorescence parameters at hourly intervals during the course of the day. Photoinhibition was less pronounced when the short wavelength band was increasingly removed from solar radiation using cut-off filters. After exposure of thalli to solar radiation at the water surface, oxygen production decreased drastically within 30 min; this inhibition was even more pronounced in algae harvested from deeper waters. Oxygen measurements at different depths showed optimal photosynthesis at a depth of 1 m. Also for photosynthetic oxygen production inhibited by high solar irradiance at least partial recovery could be observed within several hours. Despite the fact that UVB accounts for a very small fraction of solar radiation, it has a considerable effect on photosynthesis, whereas UVA seems to contribute only little to photoinhibition in H. tuna.

Photoinhibition of macroalgae in the epilithic algal community (EAC) of coral reefs was studied using chlorophyll fluorescence techniques at One Tree Island, Great Barrier Reef, Australia. F-v/F-m (variable to maximum fluorescence, darkened samples) of shallow macroalgae declined by 50% on fine summer and winter days, recovering in late afternoon. Within a species, thalli from low-light habitats were more photoinhibited (2h at 1400 mu mol m(-2) s(-1)) than those from high-light habitats. The sensitivity of Lobophora variegata (Phaeophyta) and Chlorodesmis fastigiata (Chlorophyta) increased with depth (1 versus 20 m). However, shallow Halimeda tuna (Chlorophyta) plants growing between corals were more photoinhibited than those from deep, open areas.

Campanularia everta is an epiphytic hydroid that may form dense populations on the macroalga Halimeda tuna. The main objects of this study were to quantify sexual reporduction and estimate sexual reproductive output of this hydroid. Sexual reproduction occurred from mid-October to mid-December 1991 along the Spanish Mediterranean coast. During this period, male and female colonies formed gonangia. Four oocytes mature in each female gonangium, and embryonic development starts probably after internal fertilization occurs. Planulae complete their development within a mucus sheath attached to the top of the gonotheca (acrocyst). Eight successive gonangia with a life-span of ≈1 wk each were formed over a 2 mo period. The fertile period was characterized by high initial production of gonangia followed by a progressive decline resulting from a decrease both in the number of fertile colonies and in the gonangia density of fertile colonies. Annual production was estimated at ≈42000 gonangia m-2, representing 83000 oocytes m-2. The high fertilization rates observed (77 to 100%) yielded a minimum production of 64000 planulae m-2. Reproduction in C. everta is characterized by: (1) a high number of larvae produced m-2; (2) formation and gradual release of larvae throughout the sexual reproduction period; (3) direct formation of planulae with no intermediate medusa stage; (4) low dispersive ability of the planula. All these mechanisms are part of a reproductive strategy designed to ensure the permanence of the population in its habitat.

Macroalgae are very abundant organisms in Indonesian coastal zone. They comprise 8.6% of the total marine organisms.The aim of the research was to identify macroalgae in Waisai Coast Raja Ampat. The results showed that 38 macroalgae were found in Waisai Coast Raja Ampat but only 29 species of macroalgae can be identified. Macroalgae found in Waisai Coast Raja Ampat are green algae, red algae and brown algae. Green algae found and identified are Caulerpa macra (Weber-van Bosse) Draisma & Prud’homme, Caulerpa racemosa var. macrophysa (Sonder wx Kutzing) W.R.Taylor, Caulerpa sertularoides (S. Gmelin) Howe f. brevipes (J. Agardh Svedilus), Caulerpa cupressoides (Vahl) C. Agardh, Halimeda discoidea Decaisne, Halimeda Opuntia (Linnaeus) J.V. Lamoroux, Halimeda tuna (J. Ellis & Solander) J.V. Lamoroux, Halimeda cylindraceae Decaisne, Halimeda macroloba Decaisne, Avrainvillea erecta (Berkeley) A. Gepp & E.S. Gepp, Codium geppiorum O.C.Schmidt, Boergesenia forbesii (Hardvey) Feldmann, Valonia ventricosa J. Agardh, Dictyosphaeria cavernosa (Forsskål) Børgesen, Chaetomorpha spiralisOkamura, Anadyomene wrightii Harvey ex. J. E. Gray, Neomeris annulata Dickie. Red algae species found and successfully identified areAcanthophora spicifera (M. Vahl) Børgesen, Laurencia papilosa (C. Agardh) Greville, Gracilaria salicornia (C. Agardh) E.Y. Dawson, Amphiora fragilissima (Linnaeus) J.V. Lamoroux, Hypnea pannosa J. Agardh. Brown algae species found and identified are Hormophysa cuneiformis (J.F. Gmelin) P.C. Silva, Sargassum aquifolium (Turner) C. Agardh, Sargassum polycystum C. Agardh, Turbinaria ornata (Turner) J. Agardh, Padina australis Hauck, Canistrocarpus cervicornis (Kutzing) De Paula & De Clerck Hydroclathrus clatratus (C. Agardh ) M. Howe. The only species found in Indonesia is Sargassum aquifolium.

The gametangia of the green seaweed Halimeda tuna are spherical bodies of diameter up to 250–300 μm. They are clustered in groups of 8–10 on hundreds of threads sprouting from all pale white segments of the fertile individuals. In addition to gametes, starch-containing chloroplasts, naked starch grains and two types of spherical bodies different in size and ultrastructure are the main corpuscular components. A layer of amorphous material of irregular thickness underlies the walls which are finely and evenly rough, structureless, electron translucent and 1–1.5 μm thick. Gametangia with superficial wall warts were found also.

A deep-water community dominated by Halimeda tuna and Mesophyllum lichenoides is described from the rocky bottoms of the North-Western Mediterranean. Other sciaphilic algae such as Udotea petiolata, some Peyssonnelia species and Lithophyllum expansum are also abundant. Algal biomass ranges between 1200 and 2100 g dw m-2 while percentage coverage ranges from 180 to 400%. The variations observed in algal coverage adequately describe the seasonal pattern of the community, which is characterized by a high development of erect algae in summer months and a low development in winter. The species richness, as well as both species and pattern diversity reach a maximum in summer. Summer's maximum irradiances and the low irradiances received between November and February seem to account for the seasonal pattern described above. Community structure and environmental factors affecting the deep-water Halimeda populations from the North Western Mediterranean are compared with those found in other deep-water seaweed communities from the Mediterranean and other seas. Finally, the phytosociological affinities between these Halimeda populations and the deep-water Mediterranean associations previously described is assessed.Se describe una comunidad dominada por Halimeda tuna y Mesophyllum lichenoides en los fondos rocosos profundos del Mediterráneo Noroccidental. Dichas especies coexisten con Udotea petiolata, diversas especies de Peyssonnelia y Lithophyllum expansum, como especies más aparentes. La biomasa algal oscila entre 1200 y 2100 g ps m-2 mientras que el porcentaje de recubrimiento varía entre el 180 y el 400 %. Las variaciones encontradas en el recubrimiento algal describen adecuadamente el comportamiento estacional de la comunidad, el cual se caracteriza por un elevado desarrollo del estrato erecto durante el verano. La riqueza específica y la diversidad son también elevadas en verano. La mayor disponibilidad de luz veraniega parece explicar este comportamiento. La estructura de la comunidad y los factores ambientales a los que está sometida se comparan con los descritos en otras comunidades profundas del Mediterráneo y otros mares. Finalmente, se discute la afinidad de estas poblaciones de Halimeda con las distintas asociaciones descritas en la zona circalitoral del Mediterráneo Occidental.

Halituna(1), a novel diterpene aldehyde possessing a unique cyclopentadieno[c]pyran ring system, has been isolated from the marine alga Halimeda tuna. The structure of 1 was elucidated by spectroscopic techniques. Halitunal shows antiviral activity against murine coronavirus A59 in-vitro., Halitunal, a novel diterpene aldehyde, has been isolated from the marine alga Halimeda tuna, and its structure elucidated by spectroscopic methods. Halitunal bears a unique cyclopentadieno[c]pyran ring system and shows activity against mouse coronavirus.

The marine flora and vegetation in the small desert islands Kira Panagia and Piperi situated NNN of Alonissos, Aegean Sea, Greece were investigated in order to create a marine park for the protection of the Mediterranean Seal (Monarchus monarchus). The flora was rich with almost 110 algae species in both of the investigated stations. Seven marine plant communities were recognized, two of which belong to the sciophiles (Halimeda tuna andDilophus spiralis), and the other five to the photophiles growing in the hard rocky substrates. From the chloridic element the atlantic-subtropical are the main representatives with Sorensen index ⊥0,41, R/P ratio ⊥ 2,65 and R+C/P ⊥ 3,3,so that means subtropical character of the marine flora. Finally the amount of dry biomass in both stations was very rich and typical of this rocky, exposed and clear biotope. Therefore these small islands could probably be utilised for the creation of a marine plant park which is to become an excellent shelter for the mediterranean seal that is gradually becoming rarer in the Mediterranean.

Food preferences of sea urchin Paracentrotus lividus Lamarck have been studied under laboratory conditions. Four different experiments were carried out using tanks filled with fresh seawater. Six individuals were placed in each tank and they were offered pairs of algal species to select and feed upon. Gut content analysis showed that it fed selectively on these algae. The range of feeding preference from “preferred” to “non preferred” was: Ulva rigida > Dictyota dichotoma Enteromorpha linza Cymodocea nodosa Codium fragile Cladophora prolifera Padina pavonica Halopteris scoparia Cysloseira spinosa Posidonia oceanica Halimeda tuna Digenea simplex.

9 pages, 8 figures, 1 table, The thalli of Halimeda tuna (Ellis & Solander) grow horizontally from rocky surfaces and present an upper and lower surface which can be colonized by epiphytes. Thalli of H. tuna were collected twice a month from March 1985 to March 1986 at Tossa de Mar (northeast Spain). Thirty five species of hydroid were recorded living on H. tuna thalli; of these, the 15 most abundant species were classified into three groups on the basis of their horizontal zonation on the thalli: those most abundant on the proximal, medial or distal articles. Those hydroids common on the proximal (oldest) articles were relatively large and were present throughout the year, those common on the medial articles were smaller and often occurred in dense monospecific patches, while those common on the distal (youngest) articles were present for only short periods and were the most opportunistic hydroids found on H. tuna. We hypothesize that this zonation reflects interspecific niche-selection, enabling successful competition for space with other hydroids, algae and bryozonas. Three hydroid species were more abundant on the upper surfaces of the algae than on the lower, probably because of gravitationally enhanced settlement of planula larvae coupled with (unusually) limited hydrorhizal growth on the underside. Three opportunistic species were more common on the lower surfaces of the thalli, possibly reflecting the greater availability of substratum in the shade, where epiphytic algae were less abundant. Many hydroids declined in abundance in summer because of the death of old thalli, the growth of new thalli and of apical articles on existing thalli, and possibly because of interspecific competition with epiphytic algae. The death of old thalli and the growth of new thalli reduced the abundance of epiphytic algae; this may have facilitated the increase in abundance of hydroids recorded in the autumn. © 1991 Springer-Verlag

Calcareous algae are common components in the shallow-marine limestones of the Drunka Formation (Early Eocene) cropping out on both banks of Nile between Sohag and Quena. Calcareous algae include: Acicularia valeti Segonzac, Sandalia pavsici Radoicic, Clypeina occidentalis (Johnson and Kaska), C. cf. rotella Jing, Terquemella bellovacensis Munier-Chalmas (Dasycladales), Ovulites arabica (Pfender), O. pyriformis Schwager, O. margaritula (Lamarck), O. elongata Lamarck (Udoteaceae), Halimeda tuna (Ellis and Solander) Lamouroux, H. opuntia (Linneaus) Lamouroux and H. fragilis Taylor (Halimedaceae). Niloporella subglobosa n.gen.n.sp. and Acicularia robusta n.sp. are new calcareous algae. Among fossil Halimeda three evolutionary lineages are recognized in the the Mesozoic and early Cenozoic that derive from Paleozoic Protohalimedaceae: Halimeda cylindracea lineage, H. incrassata, and H. opuntia.

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

The mature Halimeda tuna spermatozoid was studied under the electron microscope. It is pear-shaped and biflagellate. The nucleus is an uncondensed structure except for a few opaque (chromatin) aggregations and shows a rounded profile. The endoplasmic reticulum is a rather well-developed system of rough cisternae engaged in synthesis and storage of proteins. Free ribosomes are numerous. A large mitochondrial apparatus shaped like a horseshoe lies in the anterior gamete region. Only one single plastid is found, and it exhibits a deeply indented outline, a partially structured matrix, osmiophilic globules, and three to four starch grains. The axoneme pattern is 9 + 2. B tubules show septate lumina. A peculiar structure provided with a three-layered shell covering materials of varying electrondensity lies on the upper surface of both basal bodies. The flagellar root system exhibits a cruciate pattern and sets having an inconstant number of microtubules – ie, three, four, or five.

In July and August of 1977, samples of Halimeda tuna (Ellis & Solander) Lamouroux, Calpomenia sinuosa (Mertens & Roth) Derbes & Solier, and Pterocladia pinnata (Hudson) Papenfuss were collected along the coast of Ras Beirut, Lebanon and analyzed for lead, cadmium, copper, nickel and iron. The metal concentrations were quite similar in all three algae, except for iron, which was markedly higher in C. sinuosa, and lead, which was considerably lower in P. pinnata than in the other two species. These metal levels, particularly of lead, copper, and nickel seem to be rather high and may, in part, be due to untreated domestic sewage, industrial effluent, automobile exhaust, and outdoor incineration.

Calcification and photosynthetic rates in Halimeda tuna were measured by the 14C method under conditions of differing pH and total inorganic carbon (ΣCO2) concentrations. The effects of pH and ΣCO2 on photosynthesis and respiration were also monitored with a polarographic O2 electrode. The results obtained indicate that the intercellular pH and ΣCO2 differ from those of the external medium. Experiments carried out over a range of pH values show that Halimeda can use HCO−3HCO3- for photosynthesis. Photosynthesis appears to stimulate calcification by removing CO2 from the intercellular spaces. As these spaces are isolated from the external sea water by the layer of cell wall of the adpressed peripheral utricles, the removal of CO2 results in a rise in [CO2−3CO32-] and a rise in pH. This results in an increased rate of CaCO3 precipitation. Respiratory CO2 evolution has an inhibitory effect on calcification by decreasing the pH and [CO2−3CO32-]. A model for calcification in Halimeda is proposed based on the results of this and previous papers. Calcification in Halimeda is seen to be a result of the anatomy of the thallus in which the sites of calcification are within a semi-isolated chamber where removal or addition of CO2 due to photosynthesis or respiration can effectively change [COCO2−3CO32-] thereby resulting in precipitation of CaCO3. In the Appendix to this paper theoretical calculations illustrate the effects of CO2, HCO−3HCO3-⁠, and CO2−3CO32- removal or addition in a closed system on the relative concentrations of the other inorganic carbon species.

SUMMARYThe eyespotted (female) Halimeda tuna gamete has been studied under the electron microscope. It has an uncondensed nucleus showing a ribosome-studded envelope and inner (chromatin) aggregations, a rough endoplasmic reticulum and a rather large amount of free ribosomes. The single plastid is provided with a large thylakoidal outfit, 4–6 starch grains and rows of concentrically arranged double membranes. From 4 to 6 mitochondria are present. The Golgi apparatus consists of 2–3 stacks of a few poorly developed saccules and a large population of vesicles very rich in polysaccharide contents.The ultrastructural features of the female H. tuna gamete are compared with those of the spermatozoid.

The effects of a number of metabolic inhibitors on calcification and photosynthesis in Halimeda tuna, H. discoidea, and H. macroloba are described. The inhibitors used are CCCP, DNP, DCMU, azide, cyanide, chloramphenicol, cycloheximide, and Diamox. The effects of these inhibitors, although complex, are consistent with our model of calcification in Halimeda. Inhibition of photosynthetic CO2 uptake inhibits calcification as does stimulation of respiratory CO2 evolution (i.e. uncoupling). There is also indirect evidence for the presence of a possible light stimulated H+ efflux which inhibits calcification. The observed calcification rate is therefore the result of a number of factors which affect the concentration of CO⅔−and the pH in the intercellular space of the Halimeda thallus. The results obtained with the carbonic anhydrase inhibitor Diamox provide further evidence for the effective separation of the intercellular space from the external medium by the appressed peripheral utricles.

Endophytic bacteria are reported inside the thallus of Halimeda tuna and Udolea peliolala, between the siphons and within coenocytic filaments. They are usually located in the vacuole and, preferentially, very near the chloroplasts.

Twelve species of intertidal algae and molluscs from Ras Beirut, Lebanon have been investigated for their heavy metal content. Atomic absorption spectrophotometric analysis showed that the algae and molluscs concentrated similar levels of most metals. However, of the twelve organisms, Brachydontes variabilis had the highest copper, Patella coerulea and Colpomenia sinuosa had the highest iron, and Pinctada radiata had the highest zinc values with rather elevated cadmium. Cystoseira spinosa concentrated the lowest levels of zinc, and nickel was variable in all organisms. Seasonal comparisons of metal levels were also considered in three algae and three molluscs studied previously. The only signs of seasonal variation in the algae were with nickel and iron in Halimeda tuna and lead in Pterocladia pinnata. Both cadmium and lead were generally lowest in the spring samples of the algae. Lead and nickel concentrations in the molluscs were generally highest in the summer and lowest in the spring. Slight seasonal trends were seen with lead and iron in Brachydontes variabilis and lead in Monodonta turbinata. The lack of comparison data from the Mediterranean, particularly the eastern basin, makes it essential that studies of this nature be continued.

SUMMARYThe structure of the mitochondria found in the cytoplasm of the coenocytic alga Halimeda tuna (Ell. et Sol.) Lamour. is described. The material was examined with the electron microscope following glutaraldheyde-osmium tetroxide fixation. Generally these organelles show an amoeboid elongated form with the laminar cristae parallely arranged to its main axis. Frequently a swelling of the central zone is noted; in that case the cristae run very closely to the inner mitochondrial membrane. Sometimes in the middle portion of the matrix, that is less electron-dense, bundles of parallel tubules 230 A in diameter, are observed. The probable space arrangement of this type of mitochondria is diagramatically shown. It is also pointed out the resemblance of such mitochondria with similar ones described in certain animal tissues.

Publisher Summary The first English description of Halimeda was given by Parkinson in the 1640s. He called it Opuntia marina (the sea garland) and captured the essence of the species then known as “H. tuna” of the Mediterranean. The discovery of other species, in the intervening years, has shown that the genus is not always dainty, and the descriptive terminology has grown accordingly. The overall appearance of the genus is characteristic. It can be identified almost at once because it looks like some form of underwater cactus, with photosynthetic portions consisting of a series of calcified segments or joints, the strung leaves of Parkinson, which may be arranged in some branching pattern. The plant body, or Thallus, also possesses a holdfast that provides attachment to or in the substrate. This chapter explains the structure and composition of this cellulose free plant and summarizes the unusual structure and chemistry of Halimeda. It outlines the history of Halimeda studies, discoveries, various old and modern taxonomies, the culture procedures for field and laboratory, its growth and calcification, reproduction, biogeography, and phylogeny and productivity. The chapter also discusses the distribution of Halimeda in two reef systems: The Glory Be Reef and the Enewetak Atoll.

Fornells Bay is an enclosed embayment located in the north of the Balearic Platform in the Western Mediterranean. It displays bioelastic sedimentation with strong terrigenous influences. The plant communities responsible for the carbonate sediment input are the seagrasses Posidonia oceanica and Cymodocea nodosa, and red and green algae, the most important of which is Halimeda tuna. The distribution of the latter is clearly related to bathymetry and it forms the principal bioclastic component ( > 40%) in shallow sediments (0–25 m). Red algae are found below 30 m with a characteristic branching coralline algae sea floor. Organic matter in the finest-grained facies attains 6.59%. The bay exhibits a hydrodynamic gradient from low in the interior where there is a terrigenous influence to high in the outer open marine sectors. The presence of Halimeda-rich carbonates and fine-grained terrigenous sediments within Balearic embayments provides an example of Chloralgal facies in a region where Foramol would have been expected. The system described provides new data for the interpretation of fossil temperate-water carbonates.