Lobophora Variegata Research Articles

Effect of macroalgal competition on growth and survival of juvenile Caribbean corals

Lobophora variegata and Dictyota pulchella are dominant algal components on coral reefs across the Caribbean, but the mechanisms and outcomes of spatial competition between these algae and scleractinian corals are poorly understood. In this study the effects on growth and mortal- ity of juvenile corals by 2 forms of algal competition, shading and abrasion, were investigated. The growth of small Agaricia spp. (<20 mm diameter) was monitored over a 14 mo period on shallow forereefs in Roatan, Honduras. Experimental manipulations of algal shading and algal contact with the periphery of colonies were conducted in isolation from the effects of grazing through the use of exclusion cages. Shading by L. variegata caused an overall loss of coral tissue and significantly increased colony mortality rates from 0 to 50% in 6 mo. The presence of L. variegata around the periphery of a coral colony significantly reduced the overall growth of juvenile corals, decreasing the growth rate to 60% of that of control corals, but had no detectable effect on mortality. Shading by D. pulchella resulted in 99% growth inhibition (i.e. to just 1% of the growth rate of control corals). Peripheral contact with D. pulchella (without shading) also retarded coral growth rates but to a lesser extent: to 31% of that of controls. A synthetic alga made to mimic the action of D. pulchella abrasion caused a similar reduction in growth rate to actual D. pulchella, suggesting that the reduction in coral growth occurred because of physical mechanisms rather than allelochemical inhibition. The severe inhibition of colony growth caused by the proximity of D. pulchella or L. variegata may extend a coral's period of vulnerability to whole colony mortality. Based on the monthly mortality rate observed in uncaged control corals of 0.035 ± 0.135 (SE), peripheral contact with D. pulchella could decrease the survivorship of corals reaching a 3 cm diameter from 29 to <2%. Peripheral contact with L. variegata could likewise decrease cohort survival to 11%. The ability of these common macroalgae to reduce the survivorship of juvenile corals through interference competition could contribute to the perpetuating dominance of macroalgae on many Caribbean reefs.

Antioxidant activities in tropical marine macroalgae from the Yucatan Peninsula, Mexico

Extracts from 48 marine macroalgae species (17 Chlorophyta, 8 Phaeophyta and 23 Rhodophyta) from the coasts of Yucatan and Quintana Roo (Mexico) were evaluated for antioxidant activity. The antioxidant activity was measured with the DPPH (2,2-diphenyl-1-picrylhydrasyl) method, and the phenolic content of each extract were also evaluated. All species exhibited a DPPH radical scavenging activity, and three species (Avrainvillea longicaulis, Chondria baileyana and Lobophora variegata) demonstrated great antioxidant potential with very low oxidation index EC50 (1.44 ± 0.01, 2.84 ± 0.07 and 0.32 ± 0.01 mg mL−1, respectively), significantly equivalent to EC50 of some commercial antioxidants such as α-tocopherol, ascorbic acid, BHA and BHT. Moreover, extracts of the most active species exhibited reducing activities, superoxide anion radical scavenging and inhibition of lipid peroxidation. These results suggest that some macroalgae from the Yucatan peninsula have a great antioxidant potential which could be considered for future applications in medicine, food production or cosmetic industry.

Potential cytotoxic activity of some Brazilian seaweeds on human melanoma cells

In vitro screening of the crude extracts of some Brazilian coastal seaweeds for cytotoxic activity against a cultured human melanoma cancer cell line using the sulphorhodamine B assay was performed. The crude dichloromethane:chloroform extract of Stypopodium zonale showed good cytotoxic activity against the C32 cell line. The crude acetone extract and aqueous phase of Lobophora variegata did not show any activity, but semi-purified fractions XAD LOB I and II could inhibit the growth of melanoma cells. The crude acetone extract of Caulerpa racemosa showed some cytotoxicity, but caulerpin isolated from this extract did not show any such activity. The crude acetone extract of Spatoglossum schroederi was not able to inhibit the growth of C32 melanoma cells.

Effect of water flow on the photosynthesis of three marine macrophytes from a fringing-reef lagoon

We studied the effect of water flow on the reduction of the photosynthetic electron trans- port rates (ETR) of the seagrass Thalassia testudinum and the brown algae Lobophora variegata and Padina sanctae-crucis. The main objective of this study was to contribute to the understanding of the magnitude of carbon limitation in a sheltered, shallow coral reef environment, while improving the use of the fluorescence technique. The results confirm that photosynthesis, in the 3 species, is sink limited at normal seawater pH. Considering that the actinic light intensity chosen for the experimen- tal design was close to saturation irradiance for the 3 species, stronger ETR declines are expected under larger carbon requirements at supersaturating irradiance. The results suggest that photo- synthesis may be strongly carbon limited in sheltered coral reef environments. Nevertheless, pharmacological experiments revealed the occurrence of carbon concentration mechanisms (CCM) related to: (1) the external presence of the enzyme carbonic anhydrase under very low hydrodyna- mics, when the diffusive boundary layers stabilize and enzyme losses are minimal (L. variegata and T. testudinum) and (2) the ability to take up HCO3 - (T. testudinum and P. sanctae-crucis). The possi- bility that the capacity to calcify may be associated with the CCM of P. sanctae-crucis needs further testing. These results suggest that photosynthetic organisms adapted to coral reef systems, where calm, cloudless days with minimal water turbulence and maximum light penetration are common, have developed efficient CCMs. The study also supports the utility of the fluorescence technique for the analysis of the photosynthetic response to hydrodynamics within the limits imposed by the linear- ity between oxygen-based and fluorescence-based photosynthesis determinations. It also empha- sizes the importance of light absorption determinations for accurate estimations of ETR values.

α-Amylase inhibitors from Brazilian seaweeds and their hypoglycemic potential

The acetone crude extract of Lobophora variegata did not show any α-amylase inhibition activity. On the contrary, acetone crude extract of both Spatoglossum schroederi and Caulerpa racemosa inhibited the enzyme activity, with an ED 50 of 0.58 and 0.09 mg/ml.

Iron ore particles on four seaweed species from Camburi Beach (Espírito Santo state, Brazil)

The present study estimated the iron-ore concentration found on four species of seaweed. The species tested grow on a site heavily contaminated by this ore, in the city of Vitória, state of Espírito Santo, Brazil. Under natural conditions, the iron ore reached a temperature 5.0ºC higher than the sand on a sunny day. All the species had iron ore adhered to their fronds. Udotea cyathiformis was the species with the highest iron-ore concentration varing from 0.07 to 0.90 g wet weight, followed by Lobophora variegata (from 0.07 to 0.62 g wet weight), Padina gymnospora (from 0.08 to 0.55 g wet weight) and Ulva fasciata (from 0.05 to 0.25 g wet weight). Even after four changes of water over a 12-hour period, the fronds still had particles adhered to their outside cell wall. All the species showed similar tendencies to release the iron, with the highest percentage of particles (40 to 60%) released in the first change of water.

Differential competitive abilities between Caribbean coral species and a brown alga: a year of experiments and a long-term perspective

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 315:75-86 (2006) - doi:10.3354/meps315075 Differential competitive abilities between Caribbean coral species and a brown alga: a year of experiments and a long-term perspective Maggy M. Nugues1,*, Rolf P. M. Bak1,2 1Royal Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands 2University of Amsterdam, IBED, PO Box 94766, 1090 GT Amsterdam, The Netherlands *Email: mnugues@nioz.nl ABSTRACT: The competitive replacement of corals by benthic algae is considered key to reef degradation. Such replacement could originate from direct competitive overgrowth of corals by algae or death of corals from other disturbances, followed by an increase in algal abundance. To assess the relative importance of these processes, this study experimentally tested the competitiveness of 6 Caribbean coral species against the brown alga Lobophora variegata on a fringing reef in Curaçao, Netherlands Antilles. This alga has a widespread distribution and is considered particularly aggressive towards corals due to its creeping growth form. We compared the growth of transplanted algae over living and dead coral, as well as coral tissue mortality in the presence and absence of transplanted algae over a 1 yr period. Competitive trends were also related to changes in species abundance from 1973 to 2002 on the same reef. The results indicated that only 1 species, Agaricia agaricites, was competitively inferior to L. variegata and suffered more tissue mortality when exposed to the algae. Surveys of naturally occurring interactions showed that less competitive species were generally more overgrown by L. variegata, further reinforcing our results. Importantly, A. agaricites experienced the greatest decline in percent cover from 1973 to 2002 among the studied species. A large proportion of this decline occurred following the die-off of Diadema antillarum in 1983, which generally marks the onset of increased algal abundance on Caribbean reefs. We concluded that Caribbean corals have different competitive abilities against algae, highlighting the complexity and species-specific nature of coral-algal interactions. Although our data supports that prior death of corals may be generally required for algae to become established, competition with algae could play a significant role in structuring coral communities by reducing the abundance of poor competitive species. We suggest that a species-by-species approach is needed to understand the factors influencing transitions from coral to algal dominance on Caribbean reefs. KEY WORDS: Coral-algal competition · Algae · Coral · Competition · Lobophora variegata · Scleractinian · Caribbean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 315. Online publication date: June 13, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Inhibition of coral recruitment by macroalgae and cyanobacteria

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 323:107-117 (2006) - doi:10.3354/meps323107 Inhibition of coral recruitment by macroalgae and cyanobacteria Ilsa B. Kuffner1,*, Linda J. Walters2, Mikel A. Becerro3, Valerie J. Paul3, Raphael Ritson-Williams3, Kevin S. Beach4 1US Geological Survey, Center for Coastal & Watershed Studies, 600 4th Street South, St. Petersburg, Florida 33701, USA 2University of Central Florida, Department of Biology, 4000 Central Florida Boulevard, Orlando, Florida 32816, USA 3Smithsonian Marine Station at Fort Pierce, 701 Seaway Drive, Fort Pierce, Florida 34949, USA 4University of Tampa, Department of Biology, 401 W Kennedy Boulevard, Tampa, Florida 33606, USA *Email: ikuffner@usgs.gov ABSTRACT: Coral recruitment is a key process in the maintenance and recovery of coral reef ecosystems. While intense competition between coral and algae is often assumed on reefs that have undergone phase shifts from coral to algal dominance, data examining the competitive interactions involved, particularly during the larval and immediate post-settlement stage, are scarce. Using a series of field and outdoor seawater table experiments, we tested the hypothesis that common species of macroalgae and cyanobacteria inhibit coral recruitment. We examined the effects of Lyngbya spp., Dictyota spp., Lobophora variegata (J. V. Lamouroux) Womersley, and Chondrophycus poiteaui (J. V. Lamouroux) Nam (formerly Laurencia poiteaui) on the recruitment success of Porites astreoides larvae. All species but C. poiteaui caused either recruitment inhibition or avoidance behavior in P. astreoides larvae, while L. confervoides and D. menstrualis significantly increased mortality rates of P. astreoides recruits. We also tested the effect of some of these macrophytes on larvae of the gorgonian octocoral Briareum asbestinum. Exposure to Lyngbya majuscula reduced survival and recruitment in the octocoral larvae. Our results provide evidence that algae and cyanobacteria use tactics beyond space occupation to inhibit coral recruitment. On reefs experiencing phase shifts or temporary algal blooms, the restocking of adult coral populations may be slowed due to recruitment inhibition, thereby perpetuating reduced coral cover and limiting coral community recovery. KEY WORDS: Allelopathy · Coral–algae interactions · Dictyota spp. · Lyngbya spp. · Phase shift Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 323. Online publication date: October 05, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Patch dynamics of coral reef macroalgae under chronic and acute disturbance

The patch dynamics (colonisation rate, growth rate, and extinction rate) are quantified for two dominant species of macroalgae on a Caribbean forereef in Belize: Lobophora variegata (Lamouroux) and Dictyota pulchella (Hornig and Schnetter). Measurements were taken on time scales of days, weeks, months, and years during which three hurricanes occurred. All patches were followed on naturally occurring ramets of dead Montastraeaannularis. The first hurricane (Mitch) caused massive coral mortality and liberated space for algal colonisation. The cover of Lobophora increased throughout the study and herbivores did not appear to limit its cover within a 4 year time frame. In contrast, the cover of D. pulchella fluctuated greatly and showed no net increase, despite an increase in parrotfish biomass and settlement space. Variation in the overall percent cover of an alga is not indicative of the underlying patch dynamics. The steady rise in the cover of Lobophora took place despite a high turnover of patches (12–60% of patches per year). The patch dynamics of Dictyota were slower (7–20%), but a greater patch density and threefold higher lateral growth rate led to greater fluctuations in total cover. The dynamics of algal patches are size-specific such that larger patches are less likely to become extinct during hurricanes.

Interaction between inorganic nutrients and organic matter in controlling coral reef communities in Glovers Reef Belize

We studied the responses of algae, corals, and small fish to elevated inorganic fertilizer, organic matter, and their combination over a 49-day summer period in cages that simulated the coral reef in the remote Glovers reef atoll, Belize. The addition of organic matter reduced while fertilization had no effect on the numbers of herbivorous damsel and parrotfishes. All measures of algal biomass were influenced by fertilization. The combined inorganic and organic enrichment produced the highest algal biomass, which is most likely due to the combined effect of higher nutrients and lower herbivory. The cover of turf and total algae were influenced by all treatments and their interactions and most strongly and positively influenced by fertilization followed by organic matter and the combination of organic matter and inorganic fertilizer. The inorganic and combined treatments were both dominated by two turf algae, Enteromorpha prolifera and Digenia simplex, while the nonfertilized treatments were dominated by brown frondose algae Lobophora variegata, Padina sanctae, and Dictyota cervicornis. The organic matter treatment had greater cover of P. sanctae and D. cervicornis than the untreated control, which was dominated by Lobophora variegata, also the dominant algae on the nearby patch reefs. Crustose corallines grew slowly (∼2.5 mm/49 days) and were not influenced by the treatments when grown on vertical surfaces but decreased on horizontal coral plates in the combined organic matter and fertilization treatment. No mortality occurred for the two coral species that were added to the cages. Porites furcata darkened in the fertilized cages while there was a mix of paling and darkening for a small amount of the coral tissue of Diploria labyrinthiformes. Inorganic fertilization stimulates small filamentous turf algae and Symbiodinium living in coral but inhibits brown frondose algae. Organic matter inhibits small herbivorous fish, L. variegata, and encrusting coralline algae when growing on horizontal surfaces.

Effects of live coral, epilithic algal communities and substrate type on algal recruitment

The recruitment of algae is a critical process during algal colonization and invasions, including coral-to-algal phase shifts. Although algae are widely assumed to colonize and kill corals, there is very little known about the recruitment dynamics of coral reef algae. This study tested the ability of two dominant macroalgae (Fucales including Sargassum spp. and Lobophora variegata) to settle and grow on healthy coral tissue. The study also explored the effects of interactions with prior occupants, and of abiotic substrate properties (texture, and ceramic and carbonate material). The results indicate that healthy corals were able to prevent attachment or survival of recruits of these macroalgae. This is a significant point, since it suggests that the replacement of corals by algae may often require prior stress or death in the coral tissue. Pre-conditioning of plates at different sites had some effects, but these were relatively minor, whereas there was considerable variation within sites. Some of this variation appeared to be related to the amount of turf algae or crustose coralline algae on the plates. Recruitment was generally, but not always, higher on plates with rougher texture. Overall, this preliminary exploration indicates considerable potential for variability in outcomes of algal colonization, with implications for the dynamics of algal invasions. In particular, the results do not support suggestions that planktonic algal propagules can directly settle on and colonize healthy coral tissue.

Effect of mesograzers and nutrient levels on induction of defenses in several Brazilian macroalgae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 283:113-125 (2004) - doi:10.3354/meps283113 Effect of mesograzers and nutrient levels on induction of defenses in several Brazilian macroalgae Kerstin Weidner1, Bruno G. Lages2, Bernardo A. P. da Gama2, Markus Molis3,4,*, Martin Wahl3, Renato C. Pereira2 1Interdisciplinary Ecology Centre, Technical University Bergakademie Freiberg, Leipziger Straße 29, 09599 Freiberg, Germany 2Departamento de Biologia Marinha, Instituto de Biologia, Universidade Federal Fluminense, CP 100.644, CEP 24001-970 Niterói, Rio de Janeiro, Brazil 3Leibniz Institute of Marine Sciences, Marine Ecology/Marine Zoology, Düsternbrooker Weg 20, 24105 Kiel, Germany 4Present address: Marine Biological Station Helgoland, Foundation Alfred Wegener Institute for Polar and Marine Research,Kurpromenade 201, 27498 Helgoland, Germany *Corresponding author. Email: mmolis@awi-bremerhaven.de ABSTRACT: Herbivory can greatly modify benthic community structure by affecting the distribution of algal species. To deter herbivores, algae have developed several mechanisms, including the induction of chemical and morphological defenses, which may be influenced by nutrient availability. We tested 4 red (Chondrophycus flagellifera, Cryptonemia seminervis, Osmundaria obtusiloba, Pterocladiella capillacea), 4 brown (Dictyota menstrualis, Lobophora variegata, Sargassum vulgare, Stypopodium zonale), and 1 green (Codium decorticatum) algae for inducible defenses following exposure to direct consumption by an amphipod community dominated by Elasmopus brasiliensis. In addition, the effects of water-borne cues from nearby grazed conspecifics and non-grazing consumers on the induction of defenses were examined in C. decorticatum under natural and enhanced (200% natural) nutrient levels. Induction of defense was assessed in choice-feeding assays, using live algae or artificial food containing non-polar extracts of amphipod-exposed (treated) and non-exposed (control) algae. Palatability levels, estimated as the relative difference in wet mass due to consumption in feeding assays between grazer-exposed and control plants, declined significantly in 3 species after the acclimatization period. Tissue from the directly consumed red alga P. capillacea (live alga) was significantly less palatable than tissue from the control plants. Likewise, a significant effect was observed in the brown alga L. variegata. Similar, although not statistically significant, trends were observed in 6 other species. For the green alga C. decorticatum, nutrient enrichment did not affect induction of defenses by herbivores, yet unfertilized plants were more palatable than fertilized conspecifics. KEY WORDS: Plant-animal interaction · Tropical seaweeds · Mesograzer · Nutrient enrichment · Feeding preference Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 283. Online publication date: November 30, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Coral defence against macroalgae: differential effects of mesenterial filaments on the green alga Halimeda opuntia

Several studies have shown that the growth of macroalgae is reduced when in contact with corals, but very few have addressed the mechanisms involved. This study provides for the first time an explicative mechanism for the inhibition of algal growth by scleractinian corals. In experi- mental field contacts between 8 species of scleractinian corals and the green alga Halimeda opuntia, corals extruded their mesenterial filaments (MFs) onto the plant. In some coral species, this extrusion was followed by persistent discolouration of the contacting algal segments. Microscopic examination of these segments revealed migration of chloroplasts away from the surface of segments, as well as the presence of nematocysts from the MFs fired into the algal epidermis. There was a significant rela- tionship between the extent of algal discolouration and both the occurrence and length of the MFs, potentially explaining differences among coral species in their ability to damage algal segments. MF extrusion also occurred in experimental contacts with 2 other species of macroalgae (Lobophora variegata and Dictyota sp.). The use of extruded MFs by scleractinian corals against macroalgae is similar to their aggressive behaviour against other scleractinian coral species. However, the ranking of competitive ability against H. opuntia (measured by the extent of algal discolouration) differed from that established in interspecific aggressions among corals. The great abundance and wide dis- tribution of the species of corals and macroalgae used in this study, together with observations of MFs in natural interactions, suggest that the use of MFs is a common and widespread mechanism of inter- action between corals and macroalgae. We conclude that coral-algal competition involves complex mechanisms and is therefore likely to represent a complex hierarchical structure, in which macro- algae are not always able to overgrow and kill corals.

The impact of Dictyota spp. on Halimeda populations of Conch Reef, Florida Keys

Species of the brown alga Dictyota dominate the reef tract in the Florida Keys. In surveys during summer and fall months between 1994 and 2001, Dictyota occupied as much as 70% of the benthos on Conch Reef. Dictyota spp. were found growing epiphytically on Halimeda tuna, Halimeda opuntia, Lobophora variegata, Galaxura sp., fire coral, hard corals, soft corals, bryozoans and a variety of sponges on Conch Reef. From 1994 to 2001, the percent coverage of Halimeda spp. declined from 15% to 3% on the same reef. In Aug. 1999, 2000 and 2001, on average, 56% of two Halimeda species on Conch Reef had >50% of their thalli covered by Dictyota menstrualis and Dictyota pulchella. To address the impact of Dictyota on Halimeda, short-term growth of unepiphytized and heavily epiphytized (>50% Dictyota cover) H. tuna were compared with unepiphytized H. tuna to which a Dictyota mimic was attached. The number of new segments per plant ranged from 1 to 174 over 9 days. Halimeda thalli with >50% Dicytota cover and thalli covered with Dictyota mimic grew significantly slower than unepiphytized thalli. A second short-term experiment addressed the impact of neighboring Dictyota on the growth and metabolism of unepiphytized H. tuna. Augmenting or clearing epilithic Dictyota around but not in contact with H. tuna had no impact on growth or metabolism of H. tuna. Unepiphytized and heavily epiphytized H. tuna were also collected for studies of metabolism. This work indicated that epiphytic Dictyota negatively impacts metabolic rates of H. tuna in part by shading H. tuna thalli. This negative impact was also in part chemically mediated, as exposure to Dictyota-conditioned water elevated respiration rates in the same manner as seen in the metabolic studies of naturally epiphytized H. tuna.

Seaweed resistance to microbial attack: a targeted chemical defense against marine fungi.

Pathogenic microbes can devastate populations of marine plants and animals. Yet, many sessile organisms such as seaweeds and sponges suffer remarkably low levels of microbial infection, despite lacking cell-based immune systems. Antimicrobial defenses of marine organisms are largely uncharacterized, although from a small number of studies it appears that chemical defenses may improve host resistance. In this study, we asked whether the common seaweed Lobophora variegata is chemically defended against potentially deleterious microorganisms. Using bioassay-guided fractionation, we isolated and characterized a 22-membered cyclic lactone, lobophorolide (1), of presumed polyketide origin, with sub-microM activity against pathogenic and saprophytic marine fungi. Deterrent concentrations of 1 were found in 46 of 51 samples collected from 10 locations in the Bahamas over a 4-year period. Lobophorolide (1) is structurally unprecedented, yet parts of the molecule are related to tolytoxin, the scytophycins, and the swinholides, macrolides previously isolated from terrestrial cyanobacteria and from marine sponges and gastropods. Until now, compounds of this structural class have not been associated with marine macrophytes. Our findings suggest that seaweeds use targeted antimicrobial chemical defense strategies and that secondary metabolites important in the ecological interactions between marine macroorganisms and microorganisms could be a promising source of novel bioactive compounds.

Seasonal variations of bromophenols in brown algae (Padina arborescens, Sargassum siliquastrum, and Lobophora variegata) collected in Hong Kong.

Distributions and seasonal variations of the key seafood flavor compounds including 2-bromophenol, 4-bromophenol, 2,4-dibromophenol, 2,6-dibromophenol, and 2,4,6-tribromophenol in three species of brown algae (Padina arborescens, Sargassum siliquastrum, and Lobophora variegata) found in Hong Kong waters were investigated. Bromophenols were extracted by simultaneous steam distillation and solvent extraction apparatus and analyzed by gas chromatography-mass spectrometry. On a dried weight basis, the total bromophenol content (TBC) determined varied widely with seasons (from 40.9 to 7030 ng/g). The TBCs detected were higher in winter and lower in summer. Except for 2-bromophenol, the rest of the bromophenols were detected in all of the algal samples. The TBC of L. variegata was generally the highest among all of the algae collected. Relatively high concentrations of bromophenols in algae supported the fact that marine algae were major producers of bromophenols in the marine environment.

Effects of competition and herbivory on interactions between a hard coral and a brown alga

Despite widespread acceptance of the negative effects of macroalgae on corals, very few studies have experimentally tested the competitive nature of the interaction, and most have ignored the potential effects of corals on algae. We report the effects of herbivory and competition on the growth of the branching scleractinian coral Porites cylindrica Dana and the creeping foliose brown alga Lobophora variegata (Lamouroux) Womersley, on an inshore fringing reef of the central Great Barrier Reef. L. variegata overgrows branches of P. cylindrica from the base up, forming a distinct boundary between the alga and the coral tissue. The experiment used exclusion cages to test for effects of herbivores, and removal of algae and coral tissue, at their interaction boundary, to test for inhibition of the competitors by each other. Comparisons of coral branches with the algae present or removed showed that the presence and overgrowth of the alga caused significant coral tissue mortality. Comparisons of branches with coral tissue unmanipulated or damaged showed that the coral inhibited the overgrowth by L. variegata, but that the algae were markedly superior competitors. Importantly, reduced herbivory resulted in faster algal growth and consequent overgrowth and mortality of coral tissue, demonstrating the critical importance of herbivory to the outcome of the competitive interaction.

The effects of nutrients and herbivory on competition between a hard coral (Poritescylindrica) and a brown alga (Lobophora variegata)

Coral reef degradation often involves a phase shift from coral‐ to macroalgal‐dominated reefs. Declining levels of herbivory or increasing supply of nutrients have both been suggested as a cause of increased algal abundance and consequent competitive overgrowth of corals. However, explicit demonstration of the processes involved and their relative strengths requires simultaneous tests of all three factors: competition, herbivory, and nutrient effects. We experimentally tested the factorial effects of nutrients and herbivory on the competitive interaction between a brown alga Lobophora variegata and a scleractinian coral Porites cylindrica. The results of the experiment show that coral tissue mortality was strongly enhanced by the presence of the competitor (L. variegata), and this effect was significantly greater when herbivores were excluded. In contrast, the coral growth (skeletal extension) of P. cylindrica was not significantly affected by any treatments. The addition of nutrients did not have a significant effect on corals overall, but had a small effect on algal growth and consequent coral tissue mortality when herbivores were excluded. The factorial combination of treatments in this experiment allows interpretation of the causal relationships between each factor, demonstrating that nutrient effects on algal growth only led to competitive effects on corals when herbivory was insufficient to consume excess algal growth and that both herbivore and nutrient effects on corals were dependent on the strength and outcome of the competitive interaction between corals and algae.

Separation, identification and quantification of photosynthetic pigments from three Red Sea seaweeds using reversed-phase high-performance liquid chromatography

Thirty one photosynthetic pigments (chlorophylls, carotenoids and degradation products) from the seaweeds, Codium dwarkense, (Chlorophyta), , Laurencia obtusa , (Rhodophyta) and , Lobophora variegata , (Phaeophyta), were separated in a single-step procedure by reversed phase high-performance liquid chromatography. An elution gradient of methanol, acetone and ammonium acetate solution, and a program time of 65 min, was used to obtain high resolution peaks. Eighteen photosynthetic pigments were separated from C. dwarkense , sixteen from L. obtusa and fourteen from L. variegata . Chlorophyll b , micronone, microxanthin, neoxanthin, siphonein and siphonoxanthin were the most typical and characteristic pigments of C. dwarkense , while chlorophyll c1, c2 , fucoxanthin, fucoxanthol, flavoxanthin, diatoxanthin were the most typical pigments in L. variegata . In L. obtusa , chlorophyll d , α-cryptoxanthin, β-cryptoxanthin and fucoxanthin were the most abundant pigments. KEY WORDS: Codium dwarkense, Laurencia obtuse, Lobophora variegata, Chlorophylls, Carotenoids, HPLC Egyptian Journal of Biology Vol.4 2002: 1-6

Algal growth and species composition under experimental control of herbivory, phosphorus and coral abundance in Glovers Reef, Belize

The proliferation of algae on disturbed coral reefs has often been attributed to (1) a loss of large-bodied herbivorous fishes, (2) increases in sea water nutrient concentrations, particularly phosphorus, and (3) a loss of hard coral cover or a combination of these and other factors. We performed replicated small-scale caging experiments in the offshore lagoon of Glovers Reef atoll, Belize where three treatments had closed-top (no large-bodied herbivores) and one treatment had open-top cages (grazing by large-bodied herbivores). Closed-top treatments simulated a reduced-herbivory situation, excluding large fishes but including small herbivorous fishes such as damselfishes and small parrotfishes. Treatments in the closed-top cages included the addition of high phosphorus fertilizer, live branches of Acropora cervicornis and a third unmanipulated control treatment. Colonization, algal biomass and species composition on dead A. palmata “plates” were studied weekly for 50 days in each of the four treatments. Fertilization doubled the concentration of phosphorus from 0.35 to 0.77 μM. Closed-top cages, particularly the fertilizer and A. cervicornis additions, attracted more small-bodied parrotfish and damselfish than the open-top cages such that there was moderate levels of herbivory in closed-top cages. The open-top cages did, however, have a higher abundance of the chemically and morphologically defended erect algal species including Caulerpa cupressoides, Laurencia obtusa, Dictyota menstrualis and Lobophora variegata. The most herbivore-resistant calcareous green algae (i.e. Halimeda) were, however, uncommon in all treatments. Algal biomass increased and fluctuated simultaneously in all treatments over time, but algal biomass, as measured by wet, dry and decalcified weight, did not differ greatly between the treatments with only marginally higher biomass ( p<0.06) in the fertilized compared to open-top cages. Algal species composition was influenced by all treatments with a maximum between-treatment Bray–Curtis similarity of only 29%. The fertilized cages showed rapid colonization by a mixed turf community largely composed of the filamentous brown ( Hincksia mitchelliae) and green ( Enteromorpha prolifera) species. Algal cover in the fertilized cages leveled at 80% after 20 days compared to less than 50% in the other treatments. There was no evidence that A. cervicornis suppressed algal colonization compared to the unmanipulated controls. Instead, the herbivore susceptible Padina sanctae-crucis was the most abundant algae followed by Jania capillacea in this treatment in contrast to the more chemically defended Dictyota menstrualis that dominated the unmanipulated controls. We conclude that A. cervicornis was not suppressing algae as a group and its loss cannot account for the observed changes in algal abundance in most reefs except for creating space. In contrast, A. cervicornis appears to attract aggressive damselfish that may reduce herbivory by larger herbivores. Phosphorus enrichment can lead to rapid colonization of space by filamentous turf communities but not high biomass and dominance of erect frondose algae within 50 days. Moderate levels of herbivory by large-bodied herbivores promoted moderately herbivore-resistant erect brown and green algae that are commonly reported on disturbed reefs. Consequently, all the studied factors influenced algal communities but seldom as commonly predicted.