Dictyota Species Research Articles

Two new species of Dictyota (Dictyotales, Phaeophyceae), D. dimorphosa sp. nov. and D. recumbens sp. nov., based on morphological and molecular investigations

ABSTRACT The brown algal genus Dictyota (Dictyotales, Phaeophyceae) is widespread, particularly in warm temperate and tropical waters, and plays a vital role in coastal ecosystems. This study reassessed the taxonomy of Dictyota, focusing on specimens from Myanmar and Japan, using a combination of morphological and molecular analyses. Molecular phylogenetic analyses using concatenated DNA sequences of rbcL, psaA, psbA, cox1 and cox3 genes revealed that Dictyota specimens from Myanmar, Japan, and other regions, belong to nine different clades, each representing a different species. Based on morphological and molecular data, seven out of these nine clades are identified as known species, while the remaining two clades are described as new species D. recumbens sp. nov. (=D. sp. A) and D. dimorphosa sp. nov. (=D. sp. B). Dictyota recumbens is characterized by the recumbent thallus, with transverse yellowish-green iridescent lines, and the formation of solitary spores irregularly distributed over the thallus. Dictyota dimorphosa is characterized by two morphological forms: decumbent and erect thalli, with bluish iridescence mainly in the decumbent thallus, and the formation of spores in oval ring shapes distributed over both thallus surfaces. Dictyota recumbens was typically found in tropical regions, while D. dimorphosa appears to be a cool-warm temperate species, distributed from northeastern Hokkaido to southern Kyushu with an extension along South Korea. Our molecular phylogenetic analyses have revealed the existence of several species whose names appeared in multiple clades, suggesting the potential for future increases in species diversity and the presence of cryptic species within certain groups.

Tracing the introduction of Dictyota acutiloba (Dictyotales, Phaeophyceae) in the Mediterranean Sea, with a reassessment of its geographic distribution

ABSTRACT In this study we explore the introduction of the brown alga Dictyota acutiloba in the Mediterranean Sea and provide a substantive update on the geographic distribution of this species, which was long thought to be confined to the Pacific Ocean. A critical assessment of published distribution records and additional identifications based on cox1, psbA and rbcL genetic markers confirm the presence of D. acutiloba at a number of locations in the Indo-Pacific as well as three locations along the Israeli coastline in the south-eastern Mediterranean Sea. The close genetic affinity between introduced specimens and those from a population in Hurghada (Red Sea) strongly suggests an introduction via the Suez Canal. The occurrence of D. acutiloba in these regions is further supported by predictions made by correlative ecological niche models (ENMs), which show high suitability values in the northern Red Sea and the Levantine Basin. In contrast, environmental conditions in the western Mediterranean and parts of the north-eastern Mediterranean are currently less favourable, as evidenced by the lower predicted probability of occurrence. Under future scenarios, the suitability of these regions increases. The further spread of D. acutiloba in the eastern Mediterranean seems imminent, and the species may even extend its range to the western Mediterranean Sea, depending on the climate change scenario considered. While D. acutiloba can be relatively easily distinguished from the majority of Mediterranean Dictyota species, it remains difficult to differentiate this species from narrow growth forms of D. dichotoma. Therefore, we recommend the use of molecular markers such as cox1, psbA and rbcL, to unequivocally identify this species and monitor its further spread.

Intra-Species Variations of Bioactive Compounds of Two Dictyota Species from the Adriatic Sea: Antioxidant, Antimicrobial, Dermatological, Dietary, and Neuroprotective Potential.

The marine environment has a significant impact on life on Earth. Organisms residing in it are vital for the ecosystem but also serve as an inexhaustible source of biologically active compounds. Herein, the biodiversity of two brown seaweeds, Dictyota dichotoma and Dictyota fasciola from the Adriatic Sea, was evaluated. The aim of the study was the determination of differences in compound composition while comparing their activities, including antioxidant, antimicrobial, and enzyme inhibition, in connection to human digestion, dermatology, and neurological disorders. Chemical analysis revealed several terpenoids and steroids as dominant molecules, while fucoxanthin was the main identified pigment in both algae. D. dichotoma had higher protein, carbohydrate, and pigment content. Omega-6 and omega-3 fatty acids were identified, with the highest amount of dihomo-γ-linolenic acid and α-linolenic acid in D. dichotoma. Antimicrobial testing revealed a dose-dependent inhibitory activity of methanolic fraction against Escherichia coli and Staphylococcus aureus. Moderate antioxidant activity was observed for both algae fractions, while the dietary potential was high, especially for the D. fasciola dichloromethane fraction, with inhibition percentages of around 92% for α-amylase and 57% for pancreatic lipase at 0.25 mg/mL. These results suggest that Dictyota species might be a potent source of naturally derived agents for obesity and diabetes.

Desalination effects on macroalgae (part A): Laboratory-controlled experiments with Dictyota spp. from the Pacific Ocean and Mediterranean Sea

Desalination brines from direct seawater intake that get discharged to coastal areas may produce stress responses on benthic marine communities, mostly due to its excess salinity, and especially on sessile organisms; in this context, macroalgae have been understudied in desalination ecotoxicological investigations. In this study, we assessed the short- and long-term cellular tolerance responses in two brown species of the macroalgae genus Dictyota through controlled laboratory conditions. Dictyota kunthii was collected from the eastern Pacific Ocean (average salinity, ~34 psu), whereas Dictyota dichotoma was from the Mediterranean Sea (average salinity, ~37 psu). Each macroalgae species was exposed for up to 7 days to two conditions with increased salinity values: +2 and +7 psu above their natural average salinity. Photosynthetic parameters and oxidative stress measurements were determined. The results showed that, in both Dictyota species, high salinity values induced reduced photoinhibition (Fv/Fm) but increased the primary productivity (ETRmax) and light requirement (EkETR) especially after 7 days. Conversely, the photosynthetic efficiency (αETR) decreased in hypersalinity treatments in D. dichotoma, while there were no changes in D. kunthii. The reactive oxygen species hydrogen peroxide (H2O2) was greater at high salinity values at 3 days for D. dichotoma and after 7 days in D. kunthii, while lipid peroxidation decreases under hypersalinity with time in both species. Despite the evident H2O2 accumulation in both species against hypersalinity, it did not produce oxidative damage and important impairment in the photosynthetic apparatus. These results contribute to understanding the tolerance strategies at the cellular level of Dictyota spp., which may be considered as potential candidates for biomonitoring of desalination impacts in the field.

The Biodiversity of the Genus Dictyota: Phytochemical and Pharmacological Natural Products Prospectives.

Although a broad variety of classes of bioactive compounds have already been isolated from seaweeds of the genus Dictyota, most different species are still chemically and biologically unexplored. Dictyota species are well-known brown seaweeds belonging to the Dictyotaceae (Phaeophyta). The phytochemical composition within the genus Dictyota has recently received considerable interest, and a vast array of components, including diterpenes, sesquiterepenes, sterols, amino acids, as well as saturated and polyunsaturated fatty acids, have been characterized. The contribution of these valued metabolites to the biological potential, which includes anti-proliferative, anti-microbial, antiviral, antioxidant, anti-inflammatory, and anti-hyperpigmentation activities, of the genus Dictyota has also been explored. Therefore, this is the most comprehensive review, focusing on the published literature relevant to the chemically and pharmacologically diverse biopharmaceuticals isolated from different species of the genus Dictyota during the period from 1976 to now.

Chemical variation and analysis of diterpenes from seaweed Dictyota menstrualis under controlled conditions

Brown algae are a rich source of valuable compounds. The Dictyota species are resources tapped to obtain diterpenes with important bioactivities, that seem to have potential pharmaceutical applications. The bioprocess engineering of seaweeds to produce these compounds is an emerging area of marine biotechnology and species from the Dictyota genus could represent an attractive model to understand not only physiology but also the production of metabolites. In this study, a system for long-term experiments in the laboratory of algae Dictyota menstrualis using the resource of natural seawater, was developed, as a proposal of a low-cost medium for storing biomass and analyzing diterpenoid profile. Two experiments were proposed and using chemical analysis GC–MS it was possible to monitor 11 important diterpenes over time. In Experiment 1 (E1), qualitative comparisons of crude extracts obtained from field samples, initial analysis (AI) and final analysis (FA) of samples after 180 days in maintenance allowed the detection and stability of the chemical profiles of the diterpenes in these two evaluated times. This highlight that production of hydroxy-type dichotomane (17.5%) and acetyl-type xeniane (24.01%) diterpenes was favored under controlled conditions. In Experiment 2 (E2), the maintenance system was monitored every 30 days for 122 days, with respective comparisons of the chemical profile. Important events like the production of acetylated versions, for example, the acetoxy-type dichotomane with 38% at 122 days. Our results showed that the populations of D. menstrualis collected in different places and dates, with technical replicas, survived under laboratory conditions for a period of 4 to 6 months, reporting for the first time, detection of these metabolites under laboratory conditions. These findings propose this alga as target species for the maintenance of algal biomass, which may represent an interesting sustainable way to obtain diterpenes.

Concise review of the genus Dictyota J.V. Lamouroux

The genus Dictyota (Dictyotales, Phaeophyceae) comprises parenchymatous algae occurring predominantly in tropical to warm-temperate waters and has gathered attention due to its diverse secondary metabolites with antibiofouling and pharmaceutical potential, its oil content, and its potential as animal feed. This has resulted in an increase in economic potential during the last decade. In this review, we summarise the recent knowledge on the genus and concentrate on the applications and the economic potential of Dictyota. In addition, the review summarises the taxonomy, anatomy, cytology, genetic data, life history, chemical composition, nutritional value and ecological and economic importance of Dictyota species. Currently, around 100 species are recognised together with the morphologically similar and closely related genera Dilophus, Canistrocarpus and Rugulopteryx (tribus Dictyoteae). The thallus is characterised by one or more lens-shaped apical cells that divide into cortical and medullary cell layers. Species typically grow in rocky intertidal pools and subtidal areas. Dictyota is consumed locally in the Caribbean, Malayan-Indonesian and Hawaiian regions. Extracts of Dictyota which contain active compounds, such as diterpenes and phlorotannins, have been attributed antimicrobial, health and wellness promoting effects which render them promising candidates for the design of functional foods, phytomedicinal products, and cosmetics. The high fraction of lipids and fatty acids has propelled emerging applications in the biofuel industry and as a feedstock species.

New record of the rare brown alga Dictyota hauckiana from Vietnam

Abstract In the present paper, Dictyota hauckiana is reported for the first time from Vietnam. It was found growing with other marine macroalgae nearshore, at 1–2 m depth in Ninh Hai waters, Ninh Thuan province. Morphological observations and phylogenetic analysis based on the concatenated rbcL and psbA are presented. There are now 13 species of Dictyota known from Vietnamese waters.

Dictyota korowai sp. nov. (Dictyotales, Phaeophyceae) from Manawatāwhi/Three Kings Islands, northern New Zealand, previously confused with Dictyota intermedia

ABSTRACTA new species of Dictyota (Dictyotales, Phaeophyceae), formerly identified as D. intermedia, is described from Manawatāwhi/Three Kings Islands. Morphological and anatomical features, in addition to molecular sequence data, of specimens collected from Manawatāwhi and Rangitāhua/Kermadec Islands were compared and enabled us to confirm that D. intermedia is present at Rangitāhua and differs from specimens collected at Manawatāwhi. Dictyota korowai sp. nov. is endemic to Manawatāwhi and possesses distinctive morphological features including the development of tongue-like proliferations on both surfaces of the blades and a thickened midrib which extends from the base into the lower portion of the axes. The presence of D. sandvicensis on Rangitāhua is reported for the first time, a new record for the New Zealand macroalgal flora.

Molecular evidence of the presence of Dictyota dichotoma (Dictyotales: Phaeophyceae) in Argentina based on sequences from mtDNA and cpDNA and a discussion of its possible origin

ABSTRACTDictyota is a brown algae genus inhabiting tropical to warm temperate environments where it is an important food source, shelter and substrate to several species of invertebrates and other algae. The taxonomy of this genus is troublesome, with poor species delimitation and doubtful records in the literature. Dictyota dichotoma, the type species of the genus, was commonly accepted as a cosmopolitan species because of the inaccurate geographical distributional range as a consequence of misidentification in several parts of the world. Recent studies with molecular data revealed new species and a new understanding of the evolution and biogeography of the genus Dictyota. These studies confined natural populations of D. dichotoma to Europe (Atlantic and Mediterranean coasts) and Macaronesian islands (Azores, Madeira and Canary archipelagos). Also, they confirmed its presence in South Africa, but whether the species was native or introduced in South Africa could not be verified. In the present study two regions of cpDNA (psbA, rbcL) and one region of mtDNA (nad1) from Argentinian samples, identified morphologically as D. dichotoma, were analysed and compared to other Dictyota species. The identity of these samples as D. dichotoma was confirmed. A haplotype network analysis using all available psbA sequences distinguished seven haplotypes divided into two geographic groups: Atlantic–Mediterranean and Canarian. In Argentina and South Africa only the most common haplotype of the Atlantic–Mediterranean group was observed. According to the paleoceanographic currents and the presence of a European haplotype, the introduced nature of D. dichotoma is indicated.

Tracing the introduction history of the brown seaweed Dictyota cyanoloma (Phaeophyceae, Dictyotales) in Europe

ABSTRACTDictyota cyanoloma has recently been described from the Mediterranean Sea and Macaronesia but doubt had arisen as to whether this species was truly native in Europe. The species is mainly found on non-natural substrata (harbour walls, marinas, boat hulls, etc.), strongly suggesting that it is an introduction. Molecular sequence information from historical herbarium samples proves the presence of D. cyanoloma in the Adriatic Sea as early as 1935. Since approximately the year 2000, however, the number of records as well as the geographic range of the species has expanded significantly. The present-day distribution of D. cyanoloma occupies most of the Mediterranean Sea, Macaronesia, NW Africa and southern Portugal, but recent records from Galicia and SW England (Falmouth, Cornwall) indicate that the species is rapidly expanding northward. Collections from Australia demonstrated that the species is also present from Perth in Western Australia, over much of the southern Australian coastline up to Minnie Water in New South Wales. Phylogenetic analyses resolve D. cyanoloma in a sister clade to a previously unreported Australian Dictyota species. Analysis of genetic diversity of the mitochondrial markers (nad6–nad11 and atp9–orf11) reveals that even though Australian populations contain a much higher haplotype richness, European populations are also fairly diverse. Furthermore, only two out of 25 haplotypes are shared between both regions. These somewhat counterintuitive results could be indicative of a more complicated introduction history.

Dictyota chalchicueyecanensis sp. nov. (Dictyotales, Phaeophyceae) en el Golfo de México: evidencias moleculares y morfológicas

Background. Species of the Dictyota genus have a high phenotypic plasticity that contrasts with their limited morphological diagnostic characteristics, which has led to some uncertainty in identifying species in the Gulf of Mexico. Recent studies worldwide have focused on Dictyota species phylogenies, which are the basis for contrasting and interpreting the results of this study. Goals. In our research, we found evidence of a new species belonging to the Dictyota genus in three localities in the state of Veracruz, Mexico (Playa Hermosa, Punta Puntillas y Villa Rica). Methods. Phylogenetic and molecular analyses of partial sequences of the psbA and cox1 genes were performed, complemented by morphological analysis. Results. In phylogenetic analysis of partial sequences of psbA and cox1, we established that samples of the new species form a well-supported monophyletic clade. In addition, the genetic divergence values that were obtained are within the interspecific values for the genus, allowing us to segregate the Dictyota chalchicueyecanensis sp. nov. from the rest of the species of this genus. Morphologically this new species is characterized by an erect thallus, light brown and lacking iridescence, stiff to the touch, with a discoid holdfast, rounded apices, dichotomous branching, dentated margins, with minute teeth, triangular to spinose in shape that are directed toward the apices. Sporangia are isolated or grouped on both sides of the thallus and germinate regularly in interdichotomous basal portions. Conclusion. These results allow us to expand the diversity of the genus Dictyota worldwide, incorporating D. chalchicueyecanensis as a probable new species endemic to Mexico.

Two New Species of the Genus Dictyota (Phaeophyceae: Dictyotales) from the Mexican Caribbean

During a molecular characterization of the genus Dictyota J. V. Lamouroux (Phaeophyceae, Dictyotales) along the Mexican coasts of the Gulf of Mexico and the Mexican Caribbean, using psbA and cox1 genes, it was found that two particular collections did not match with the sequences published for a total of 39 species of Dictyota. For each gene, both collections diverged in high-uncorrected “p” distance values with respect to other related species. This high genetic divergence was corroborated by morphological analysis. Hence, we proposed Dictyota mayae J. Lozano-Orozco & Sentíes and Dictyota pedrochei J. Lozano-Orozco & Sentíes as new species.

Chemical similarity between Dictyota caribaea and Dictyota menstrualis (Dictyotaceae, Phaeophyceae) from the coast of Rio de Janeiro, Brazil

• The chemical similarity between two Southeastern Brazilian Dictyota species is proposed: Dictyota caribaea and Dicyota menstrualis.

Anti-Infective Potential of Marine Invertebrates and Seaweeds from the Brazilian Coast

This manuscript describes the evaluation of anti-infective potential in vitro of organic extracts from nine sponges, one ascidian, two octocorals, one bryozoan, and 27 seaweed species collected along the Brazilian coast. Antimicrobial activity was tested against Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATCC 29212), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922) and Candida albicans (ATCC 10231) by the disk diffusion method. Antiprotozoal activity was evaluated against Leishmania braziliensis (MHOM/BR/96/LSC96-H3) promastigotes and Trypanosoma cruzi (MHOM/BR/00/Y) epimastigotes by MTT assay. Activity against intracellular amastigotes of T. cruzi and L. brasiliensis in murine macrophages was also evaluated. Antiviral activity was tested against Herpes Simplex Virus type 1 (HSV-1, KOS strain) by the plaque number reduction assay (IC50). Cytotoxicity on VERO cells was evaluated by the MTT assay (CC50). The results were expressed as SI = CC50/IC50. The most promising antimicrobial results were obtained against S. aureus and C. albicans with Dragmacidon reticulatum. Among the seaweeds, only Osmundaria obtusiloba showed moderate activity against P. aeruginosa. Concerning antiprotozoal activity, Bugula neritina, Carijoa riseii, Dragmaxia anomala and Haliclona (Halichoclona) sp. showed the most interesting results, mainly against extracellular promastigote forms of L. braziliensis (66, 35.9, 97.2, and 43.6% inhibition, respectively). Moreover, six species of seaweeds Anadyomene saldanhae, Caulerpa cupressoides, Canistrocarpus cervicornis, Dictyota sp., Ochtodes secundiramea, and Padina sp. showed promising results against L. braziliensis (87.9, 51.7, 85.9, 93.3, 99.7, and 80.9% inhibition, respectively), and only Dictyota sp. was effective against T. cruzi (60.4% inhibition). Finally, the antiherpes activity was also evaluated, with Haliclona (Halichoclona) sp. and Petromica citrina showing the best results (SI = 11.9 and SI > 5, respectively). All the active extracts deserve special attention in further studies to chemically characterize the bioactive compounds, and to perform more refined biological assays.

Taxonomy of the Dictyota ciliolata–crenulata complex (Dictyotales, Phaeophyceae)

Tronholm A., Afonso-Carrillo J., Sansón M., Leliaert F., Fernández-García C., and De Clerck O. 2013. Taxonomy of the Dictyota ciliolata–crenulata complex (Dictyotales, Phaeophyceae). Phycologia 52: 171–181. DOI: 10.2216/12-005.1We reassessed the taxonomy of dentate Dictyota species formerly attributed to D. ciliolata and D. crenulata. Both taxa have long been assumed to be broadly distributed in tropical to warm-temperate seas. Recent molecular data, however, provided evidence that D. crenulata constituted a complex of at least four species with restricted geographical distributions. Based on those results and careful morphological examination, we split D. crenulata sensu lato into D. crenulata sensu stricto restricted to Pacific Central America, D. jamaicensis with a tropical amphi-Atlantic distribution and D. canariensis and D. pleiacantha sp. nov. from Macaronesia. Morphological analysis showed that these species were distinguished by subtle morphological differences. In contrast to D. crenulata sensu lato, the wide tropical distribution of D. ciliolata was confirmed by DNA data. In addition, psbA sequence analysis did not provide evidence to segregate D. menstrualis and D. plectens from D. ciliolata.

Chemically mediated interactions between macroalgae Dictyota spp. and multiple life-history stages of the coral Porites astreoides

Competition between corals and macroalgae is often assumed to occur on reefs, espe- cially those that have undergone shifts from coral to algal dominance; however, data examining these competitive interactions, especially during the early life-history stages of corals, are scarce. We con- ducted a series of field and outdoor seawater-table experiments to test the hypothesis that allelo- pathy (chemical inhibition) mediates interactions between 2 common brown macroalgae, Dictyota pulchella and D. pinnatifida, and the coral Porites astreoides at different life-history stages of the coral. D. pinnatifida significantly reduced larval survival and larval recruitment. The extracts of both D. pinnatifida and D. pulchella significantly reduced larval survival, and the extract of D. pulchella also negatively influenced larval recruitment. There was no measurable effect of the crude extracts from Dictyota spp. on the photophysiology of adult corals. Our results provide evidence that these Dictyota species chemically compete with P. astreoides by negatively affecting larval settlement and recruitment as well as the survival of larvae and new recruits. Macroalgae may perpetuate their dom- inance on degraded reefs by chemically inhibiting the process of coral recruitment.

NICHE PARTITIONING AND THE COEXISTENCE OF TWO CRYPTIC DICTYOTA (DICTYOTALES, PHAEOPHYCEAE) SPECIES FROM THE CANARY ISLANDS1

Coexistence in a homogeneous environment requires species to specialize in distinct niches. Sympatry of cryptic species is of special interest to both ecologists and evolutionary biologists because the mechanisms that facilitate their persistent coexistence are obscure. In this study, we report on two sympatric Dictyota species, D. dichotoma (Huds.) J. V. Lamour. and the newly described species D. cymatophila sp. nov., from the Canary Islands. Gene sequence data (rbcL, psbA, nad1, cox1, cox3, and LSU rDNA) demonstrate that D. dichotoma and D. cymatophila do not represent sister species. Rather, D. cymatophila and D. dichotoma have converged on a nearly identical morphology, only to be distinguished with detailed morphometric observations. Both species co‐occur in eulittoral pools and the shallow subtidal in Tenerife. Even though D. cymatophila was more dominant in wave‐exposed places and D. dichotoma in less exposed areas, the spatial distribution of both species overlapped in intermediate habitats. The species display radically different phenologies. D. dichotoma reached its highest density in winter and early spring and disappeared nearly completely in autumn, while D. cymatophila dominated the study site from July until November. The timing of gamete release also differs between both species, D. dichotoma releasing gametes twice every lunar cycle, while the release of gametes in D. cymatophila occurred roughly every other day.

Associational defense against herbivory between brown seaweeds

Pereira R.C., Bianco É.M., Bueno L.B., de Oliveira M.A.L., Pamplona O.S. and da Gama B.A.P. 2010. Associational defense against herbivory between brown seaweeds. Phycologia 49: 424–428. DOI: 10.2216/09-84.1Several associations between marine organisms have been hypothesised to be chemically mediated, but few examples have been experimentally investigated to date. In the Brazilian littoral, the presence of Dictyota species living on various species of Sargassum is a very common feature, and here we present experimental evidence that the association between the brown seaweeds Dictyota sp. and Sargassum furcatum is chemically mediated. When separated but offered simultaneously to the herbivorous sea urchin Lytechinus variegatus, S. furcatum was more highly consumed than Dictyota sp. However, when S. furcatum was tied to Dictyota sp., it was significantly less consumed by L. variegatus. Crude extracts of Dictyota sp. were significantly less consumed by L. variegatus than were extracts of S. furcatum when the extracts were offered individually or paired. Plastic mimics of Dictyota sp. did not provide protection against consumption of S. furcatum by L. variegatus, confirming that S. furcatum protection was due to Dictyota sp. chemicals. Associational defense is defined as protection gained by an organism from living in association with another species. Clearly, chemicals produced by Dictyota sp. can provide an associational refuge. Considering that Dictyota species are frequently found growing epiphytically on many benthic species, associational defenses involving Dictyota spp. may be an important aspect to the structure and dynamics of many coastal communities.

Capturing the dynamics in benthic structures: environmental effects on morphology in the macroalgal genera Halimeda and Dictyota

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.