Faunal variation on pelagic Sargassum

Pelagic Sargassum was collected in late summer, late winter, and early and late spring from inshore waters, the Gulf Stream and the Sargasso Sea of the Western North Atlantic Ocean. The noncolonial macrofauna was picked from the weed samples. The 34 samples contained 67 species and 11,234 individuals. The Shannon-Wiener index of diversity had a mean value of 2.419±0.177 (t.₀₅s _x ^– ) and a statistical range between 1.401 and 3.437 (t.₀₅ s). Mean diversity values were not significantly different among the various sampling series, and diversity did not vary with raft volume. High diversity values were related to an equitable distribution of species resulting from a stable environment and an area low in productivity. Species composition of the Sargassum organisms varied seasonally and geographically. Animals were more abundant in the spring than in the fall samples. Samples collected on a transect in the Gulf Stream and Sargasso Sea maintained a similar faunal composition.Contribution No. 351 from the Virginia Institute of Marine Science, Gloucester Point, Virginia, USA.From a thesis submitted to the faculty of the School of Marine Science, The College of William and Mary, in partial fulfillment of the requirements for the degree of Master of Arts in Marine Science.     

Pigment composition and photosynthesis in Sargassum muticum

Detailed analyses of the seasonal changes in pigment composition of Sargassum muticum (Yendo) Fensholt growing at Bembridge on the Isle of Wight (UK) between April 1977 and June 1978 are presented. These show a large decrease in pigment content as growth proceeds. Laboratory experiments on the change in pigment content of winter-form plants are also reported. The high pigment contents of the winter-form plants and the dilution of pigments with growth are suggested to permit the rapid extension growth of this alga in the spring.     

生物吸附剂-海黍子吸附镍

采用生物吸附剂-海黍子对重金属镍离子进行吸附，做了动力学实验，得到了海黍子吸附镍的动力学方程。研究了溶液的pH值，初始Ni^2 浓度等因素对Ni^2 的吸附特性的影响，得到最佳pH值4～6及最大吸附量0．8283mmo1／g，并用Langmuir和Freundlich方程对吸附等温线进行了拟合，用Langmuir方程拟合相关系数R^2达0．999以上。     

The phytal animals on the thalli of Sargassum serratifolium in the Sargassum region,with reference to their seasonal fluctuations

In the Sargassum region on the coast of Mukaishima, in the Inland Sea of Japan, the phytal animals living on Sargassum serratifolium, and the alga itself as a habitat for phytal animals, were studied from August, 1966 to August, 1968. The standing crop of Sargassum/m² bottom was 4.93 kg/m² (March, 1967) and 3.53 kg/m² (February, 1968) in the most luxuriant season, and 0.4 to 0.5 kg/m² (July, 1967 and 1968) in the off-season. The individual number of phytal animals per mean plant, without sessile fauna, reached a maximum in late winter and early spring (about 130,000 in 1967, 266,000 in 1968) when Sargassum was luxuriant, and a minimum in summer (about 15,000 in both years) when Sargassum was declining. Among the phytal animals, benthonic copepods (Harpacticoida) were very abundant in most seasons. Their dominance decreased in spring, whilst nematode dominance increased. It appears that such seasonal changes are closely related to the standing crop of S. serratifolium. Fluctuations in numbers of most groups of the meiofauna of phytal animals, such as foraminiferans, ostracods, isopods, amphipods, copepods, tanaids and nematodes, are connected with changes in the standing Sargassum crop. Seasonal fluctuations of some groups, such as echinoderms, actinians, mysids and decapod crustaceans (macrofauna), were, however, independent of Sargassum crop variations. The individual number of phytal animals/m² bottom in the Sargassum region were compared with findings of previous studies in other habitats, such as naked sandy and mud bottoms.Contribution No. 100 from the Mukaishima Marine Biological Station.     

The epibionts of Sargassum muticum in British waters

This study was initiated by suggestions that the Japanese brown alga Sargassum muticum (Yendo) Fensholt, recently found to be invading shores along the eastern Solent (Southern England), might replace certain common native plants, to the possible detriment of local epibiont communities. Eighty animal, 52 plant and 9 fungal species have been identified from S. muticum plants collected at four different localities. Animal fouling was most conspicuous on permanently submerged plants growing along the edge of floating harbour installations. Algal epibionts were most numerous and varied on S. muticum from tidal lagoons on a well-scoured but sheltered rocky shore. Most of the epibionts colonised the perennial portions of the plants, close to the holdfast. A few settled along the fronds in summer, but none were found in the region of the secondary and tertiary apical meristems. Seasonal variations in the abundance and diversity of algal epibionts were observed; most were restricted to summer, but winter and all-year-round species were also noted. Fungal studies on S. muticum have isolated only saprophytic species, which are also common locally on other Phaeophyceae. Overall, these data suggest that S. muticum can support a considerable epibiota and, therefore, its introduction seems unlikely to result in a significant change in local epiphyte communities.     

Sediment tolerance of Sargassum algae inhabiting sediment-covered rocky reefs

Although sediment deposition has detrimental effects on macroalgal settlement and recruitment, fucoid algae (mainly Sargassum duplicatum) thrive on rocky reefs always overlaid with fine sediments in sheltered sites of Kagoshima, Japan. The aim of the present study was to assess their ability to settle and recruit onto sediment-covered substrata. A transplant experiment using boulders with Sargassum juveniles attached showed that the 30-day survival rate was as high as 50% even for the juvenile stage (<10 mm) on boulders completely buried with sediment. In addition, an outdoor tank experiment testing the effects of different sediment thicknesses (0–4 mm) on already settled 4-day old S. duplicatum germlings indicated significant reductions in growth by the presence of sediment cover even at 0.5 mm but no significant increase in mortality up to 2 mm. Furthermore, an in situ experiment in which sterilized cobbles were placed at a sediment-covered site to allow sediment to settle over them before the embryo release showed a uniformly high recruitment of Sargassum over the cobbles. This suggests the presence of unknown mechanisms to allow the settlement of propagules on substrata thinly but completely covered by fine sediments.     

Seasonal changes in the chemical composition of Sargassum muticum

The alga Sargassum muticum (Yendo) Fensholt, a member of the Phaeophyceae, exhibits a growth cycle at Bembridge, Isle of Wight (UK), in which large annual fronds develop from much smaller perennating structures. Seasonal changes between April 1977 and June 1978 in the chemical composition of the alga were recorded. The content of inorganic ions, alginate and the dry weight: fresh weight ratio were relatively constant. Mannitol, laminaran and polyphenolic compounds were at their maxima in early summer (June/July), when the plant was undergoing rapid extension growth. In contrast, the protein content was highest in winter and early spring. It was concluded that the elongation phase which occurred in the spring was not supported by the use of stored polysaccharide reserves, since the amounts present were insufficient for this purpose and increased during the period of most rapid growth.     

Antheridium development of Sargassum fulvellum and S. kjellmanianum

The antheridium development of Sargassum fulvellum Ag. and S. kjellmanianum Yendo was investigated. The characteristics of meiosis were observed at the first division of the antheridium in both species. The chromosome number observed was 32 in both species. Six divisions were observed during the development of the antheridium, and the first two divisions were meiotic. 64 nuclei were formed in each antheridium, and cytoplasmic cleavage occurred after the final division. The manner of antheridium development in both species is similar to that already reported from Japan for 7 species of the genus Sargassum.     

Factors influencing the gas composition in the vesicles of Sargassum

The composition of gas in the vesicles of Sargassum cf. leptopodum Sonder has been investigated. The oxygen content depends upon the oxygen partial pressure of the surrounding medium. It does not depend upon the photosynthetic activity of the vesicle. Evidence is provided that the lower limit of the vertical distribution zone of Sargassum cf. leptopodum Sonder is not controlled by the vesicles' capability of resisting hydrostatic pressure.     

On the antheridium development of Sargassum micracanthum and S. ringgoldianum

The antheridium development of Sargassum micracanthum Yendo and S. ringgoldianum Harvey was investigated with the iron-alum haematoxylin staining method and the aceto-carmine squash technique. Synapsis occurred at the prophase in the first division while the chromatin threads were still contracted, and the nucleus passed through diakinesis. The first two divisions in the antheridium were meiotic, and the four other divisions (mitosis) followed without cytokinesis. In S. micracanthum and S. ringgoldianum, 31 and 32 chromosomes respectively were counted at prometaphase in the first division, 64 sperm nuclei were organized in the final division. After the final division cytoplasmic cleavage occurred, and 64 sperm cells were finally completed in an antheridium. Centrosomes and asters could not be discerned at any of the divisions, because of limited magnification facilities. A peculiarly shaped small body was observed at the prophase of the first division, but not thereafter.     

鼠尾藻提取物对亚历山大藻的化感效应

研究不同浓度的鼠尾藻组织蒸馏水及4种不同极性有机溶剂(甲醇、丙酮、乙醚、氯仿)提取物对亚历山大藻的生长抑制作用.结果表明:鼠尾藻组织甲醇提取物对亚历山大藻的生长抑制活性最强,大于3×10-8 mg kg-1浓度作用下亚历山大藻在1 d内完全死亡;鼠尾藻组织蒸馏水抽提物与对照组相比在各个浓度时均能显著抑制亚历山大藻的生长,但即使在最高浓度1.6×10-6mg kg-1下亦对其无致死效应;其他3种有机溶剂提取物对亚历山大藻的生长无明显影响.表明鼠尾藻组织中含有的对亚历山大藻具有抑制作用的活性物质具有较高的极性.对鼠尾藻甲醇提取物进行液液萃取,将其分离为石油醚相、乙酸乙酯相、正丁醇相和蒸馏水相,并对亚历山大藻进行生物活性检测.结果发现,石油醚相和乙酸乙酯相具有较强的杀藻活性,表明脂肪酸可能是鼠尾藻组织内抑制亚历山大藻生长的克生物质的重要组成成分之一.图3参36     

Extirpation of Macroalgae (Sargassum spp.) on the Subtropical East Australian Coast

Abstract: Populations of large brown algae of the Laminariales and Fucales (Phaeophyta) have declined or been extirpated from many locations on temperate coasts worldwide. We conducted field surveys and a literature review, and examined herbarium specimens, through which we discovered previously unreported extirpations of large brown algal species from a tropical and subtropical coastline. Sargassum amaliae, S. aquifolium, S. carpophyllum, S. polycystum, and S. spinifex were common habitat‐forming macroalgae that supported diverse assemblages of invertebrates and smaller algae before urbanization began in 1970 along the 45‐km length of Sunshine Coast in Queensland, Australia. Causes of these extirpations are not known, but are consistent with losses of other large brown algal species from coastal areas undergoing urbanization or eutrophication. Sargassum spp. do not have the characteristics thought to protect marine species from extinction (large geographical ranges, occurrence on many different substrata, long‐distance dispersal). Some local Sargassum spp. are endemic to eastern Australia. Abundance of Sargassum is limited by suitable substrata on the sandy southern Queensland coast (370 km). These substrata are 12 rocky headlands separated by long (5–105 km) sandy beaches. Most multicellular propagules (the only motile stage in Sargassum) settle within 1–3 m of parental thalli, which restricts long‐distance dispersal needed to maintain connectivity among populations and to recolonize areas of the headlands from which populations have been extirpated. Local Sargassum spp. could be categorized as data deficient by the International Union for Conservation of Nature (IUCN), but the IUCN vulnerable category is more accurate given extirpations, limited habitat, and the lack of connectivity among populations.     

Pelagic Sargassum community change over a 40-year period: temporal and spatial variability

Pelagic forms of the brown algae (Phaeophyceae) Sargassum spp. and their conspicuous rafts are defining characteristics of the Sargasso Sea in the western North Atlantic. Given rising temperatures and acidity in the surface ocean, we hypothesized that macrofauna associated with Sargassum in the Sargasso Sea have changed with respect to species composition, diversity, evenness, and sessile epibiota coverage since studies were conducted 40 years ago. Sargassum communities were sampled along a transect through the Sargasso Sea in 2011 and 2012 and compared to samples collected in the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone from 1966 to 1975. Mobile macrofauna communities exhibited changes in community structure and declines in diversity and evenness within a 6-month time period (August 2011–February 2012). Equivalent declines in diversity and evenness were recorded in the same region (Sargasso Sea, 25°–29°N) in 1972–1973. Recent community structures were unlike any documented historically, whether compared to sites of the same latitude range within the Sargasso Sea, or the broader historical dataset of sites ranging across the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone. Recent samples also recorded low coverage by sessile epibionts, both calcifying forms and hydroids. The diversity and species composition of macrofauna communities associated with Sargassum might be inherently unstable. While several biological and oceanographic factors might have contributed to these observations, including a decline in pH, increase in summer temperatures, and changes in the abundance and distribution of Sargassum seaweed in the area, it is not currently possible to attribute direct causal links.     

鼠尾藻和鸭毛藻水提液对三角褐指藻的抑制作用

调查了鼠尾藻Sargassum thunbergii和鸭毛藻Symphyocladia latiuscula水提液对三角褐指藻Phaeodactylum tricornutum 生长的抑制作用.结果表明,海藻水提液明显抑制三角褐指藻生长,并且这种抑制作用来自藻体活性物质(化感物质);鼠尾藻和鸭毛藻的化感物质既溶于水也溶于乙醇,随时间可能被三角褐指藻消耗尽或发生降解,因而抑制作用减弱以至消失,最大抑制发生在接种4 d.鼠尾藻和鸭毛藻水提液抑制三角褐指藻生长的半效应质量浓度(EC_(50,96h))分别为4.37g·L~(-1)和3.59g·L~(-1),暗示三角褐指藻对鸭毛藻水提液抑制的反应更敏感.     

Fatty acid composition of flora and fauna associated with Sargassum mats in the Gulf of Mexico

Feeding ecology of organisms associated with floating Sargassum in the northwestern Gulf of Mexico was assessed using fatty acids. Nineteen groups were collected from the Sargassum community including four autotrophs, eight invertebrates, five juvenile fishes, and two adult fishes. Spatial and temporal variability in polyunsaturated fatty acid (PUFA) signatures of selected taxa (Sargassum fluitans [autotroph], Leander tenuicornis [primary heterotroph], Balistes capriscus [secondary heterotroph]) was examined to quantify natural variation within these dietary tracers. Although PUFA signatures varied seasonally for all three taxa, no differences were detected between samples collected in year 2000 and 2001 or from different sample locations in the northwest Gulf. PUFA signatures made up 16.3–62.3% of the total fatty acid composition of main autotrophs present in the pelagic environment [particulate organic matter (POM), epiphytic algae, S. fluitans, S. natans], and PUFA profiles of selected primary producers were distinct. Specifically, levels of 20:5n−3, 22:5n−3, and 22:6n−3 were significantly higher in POM than Sargassum spp. or epiphytic algae (Cladophora sp.). Dominant PUFA in the tissue of invertebrate and vertebrate consumers were 18:2n−6, 20:4n−6, 20:5n−3, 22:5n−3, 22:6n−3 and multivariate analyses indicated that PUFA signatures of all consumers were highly similar to POM. As a result, heterotrophs utilizing the Sargassum complex may rely heavily on phytoplankton production rather than production by Sargassum or associated epiphytic algae.     

Recent expansion led to the lack of genetic structure of Sargassum aquifolium populations in Southeast Asia

Phylogeographical study of the brown macroalga, Sargassum aquifolium using nuclear internal transcribed spacer 2, plastidal RuBisCo spacer, and mitochondrial cytochrome oxidase subunit-III revealed the populations in Southeast Asia to be homogeneous. On the other hand, genetic differences were detected between populations from Southeast Asia and western Pacific Islands/Guam, suggesting the presence of genetic break between these regions. This further suggests that populations of S. aquifolium may have survived east of Sunda Shelf during the Last Glacial Maximum and recent recolonization led to homogeneity of the populations in the Sunda Shelf region. Recolonization could be facilitated by year-round reproduction of the populations and dispersal of germlings on floating thalli by coastal currents. Restricted current flow across Maluku Sea and directional equatorial current flows could have isolated the Pacific Island and Guam populations from those of Southeast Asia. Our results support the presence of multiple refugia as the source of different lineages of S. aquifolium populations with a lack of secondary contact in the post-glacial dispersal between Southeast Asia and western Pacific as the mechanisms behind the phylogeographical patterns observed.     

Asymmetric genetic exchange in the brown seaweed Sargassum fusiforme (Phaeophyceae) driven by oceanic currents

Geological phenomena (e.g. drastic sea level fluctuations during the Quaternary Ice Age in the Northern Hemisphere) have been demonstrated to intensively affect the biogeographic patterns and tempo-spatial compositions of genetic diversity of marine organisms. However, it is poorly understood whether contemporary factors such as oceanic surface currents have also shaped inter-regional population genetics of specific coastal marine flora, with or without limited dispersal capability. In this study, we determined mtDNA Cox1 gene sequences of the brown seaweed Sargassum fusiforme from nine populations along the Chinese coast and one population from the west coast of South Korea, in an effort to understand what factors are contributing to their current genetic structure and geographic distribution patterns. Genetic analyses indicated a deep genetic break between the Yellow-Bohai Sea (YBS) and the other two marginal seas, the East China Sea (ECS) and the South China Sea (SCS). In particular, the amount of genetic exchange from the SCS to each of the ECS and YBS was significantly higher than that from the opposite directions. Our analyses supports the hypothesis that biogeographic patterns of genetic variation in S. fusiforme are probably an interactive consequence of post-glacial colonization from two scattered refugia driven by the offshore Kuroshio Current and asymmetric gene flow among adjacent sea margins.     

Effects of herbivory on zonation of Sargassum spp. within fringing reefs of the central Great Barrier Reef

A combination of small-scale transplants and herbivore exclusion was used to test the importance of herbivory, physiological tolerance limits, and recruitment and dispersal in regulating the distribution and abundance of the genus Sargassum on two nearshore fringing reefs of the central Great Barrier Reef, during 1992/1993. Sargassum (predominantly S. oligocystum and S. tenerrimum) were transplanted from reef-flat zones where they normally grow, to a seaward coral zone where they are not normally found. At Great Palm Island, coral-zone transplants only survived if protected from herbivores. At Brook Island, survival of uncaged coral-zone transplants was more variable but not significantly lower than plants returned to the Sargassum zone. Thus herbivory may be a major cause of the zonation patterns of adult Sargassum on these fringing reefs, but the importance of this factor varies between and within reefs. Since protected Sargassum survived and grew for up to 6 mo in the coral zone, the adult algae are not physiologically limited by any physical or chemical differences between zones. However, Sargassum recruitment to the coral zone was very low (mean 2.7 recruits m⁻² over 13 mo), and was not significantly affected by herbivores. Since rates of herbivory were relatively slow, effective exclusion of Sargassum from the coral zone by herbivores may depend on low recruitment of the algae. In a broader context, the distribution of Sargassum may depend on the combined spatial patterns of herbivory and recruitment. Received: 24 January 1997 / Accepted: 12 May 1997     

Among-habitat variation in herbivory on Sargassum spp. on a mid-shelf reef in the northern Great Barrier Reef

Herbivory is widely acknowledged as a key process determining the benthic community structure and resilience of coral reefs. Despite numerous studies that have examined herbivory across reef gradients in the Caribbean, few studies have directly quantified this process on Pacific reefs. Bioassays of two species of erect macroalgae (Sargassum swartzii and S. cristaefolium) were used to quantify variation in grazing intensity across seven habitats of varying depth and wave exposure on a mid-shelf reef in the northern Great Barrier Reef. Removal rates of Sargassum varied significantly among habitats, with both species displaying broadly similar patterns. The shallow habitats on the exposed aspect of the reef (i.e. reef crest, flat and back reef) experienced the highest reductions in mass (81.4–91.6% day⁻¹) for both S. swartzii and S. cristaefolium, while the deeper exposed habitats (reef slope and base) displayed the lowest reductions (3.8–13.4% day⁻¹) over a 24 h period. In contrast, the grazing intensity varied between the two species in the three habitats on the leeward aspect of the reef. Reductions in mass remained relatively high for S. swartzii on the patch reef and sheltered reef base and flat (62.7–76.5% day⁻¹) but were considerably lower for S. cristaefolium (37.9–63.5% day⁻¹) across the same habitats. Surprisingly, the rates of removal of Sargassum displayed no relationship with the density or biomass of roving herbivorous fishes or those species known to consume erect macroalgae, either collectively or independently. These results suggest that the relationship between browsing rates and herbivorous fish biomass is complex and may be driven by species that are underestimated in visual surveys. Direct quantification of browsing intensity using assays revealed a different pattern to inferences based on herbivore densities and highlights the potential difficulties of evaluating ecosystem processes based on visual census data alone.