Sargassum Beds Research Articles

Concentrations of trace elements in sea urchins and macroalgae commonly present in Sargassum beds: implications for trophic transfer

AbstractThe aim of the study was to evaluate the dynamic of cadmium, lead, copper, zinc, and iron among lower trophic levels, sea urchins and macroalgae. Diets and isotopic values were used in combination to explore trophic positions and potential transference of metals from primary producers to consumers. Concentrations of trace elements were measured in two species of sea urchin (Tripneustes depressus and Eucidaris thouarsii) and nine macroalgae that are usually used as food in four Sargassum beds, one of which is close to a phosphorite mine. Specimens were collected when Sargassum fronds were at their greatest (winter) and lowest (summer) abundance. Highest concentrations of Cd, and Cu in both urchin species were recorded in winter at the site near the phosphorite mine. Concentrations of Pb in T. depressus were below the detectable limit, whereas E. thouarsii, which in addition to a high concentration of Pb, had high amounts of Cu and Zn. Gut content analysis, indicates that the diet of both sea urchins at the four sites and two collection dates is mainly macroalgae. The δ15N isotopic values in sea urchins in a typical Sargassum bed were in good agreement with a diet dominated by macroalgae, with T. depressus having herbivorous habits and E. thouarsii having omnivorous habits in this environment. We found macroalgae important in the dynamics of metals in food webs, potentially contributing to transferring Cd, Cu, and Zn to key invertebrate species, such as sea urchins, indicating connectivity of food webs and ecological structuring of marine environments.

Seasonal changes in water quality and Sargassum biomass in southwest Australia

Sargassum C. Agardh is one of the most diverse genera of marine macro-algae and commonly inhabits shallow tropical and sub-tropical waters. This study aimed to investigate the effect of seasonality and the associated water quality changes on the distribution, canopy cover, mean thallus length and the biomass of Sargassum beds around Point Peron, Shoalwater Islands Marine Park, Southwest Australia. Samples of Sargassum and seawater were collected every three months from summer 2012 to summer 2014 from four different reef zones. A combination of in situ observations and WorldView-2 satellite remote-sensing images were used to map the spatial distribution of Sargassum beds and other associated benthic habitats. The results demonstrated a strong seasonal variation in the environmental parameters, canopy cover, mean thallus length, and biomass of Sargassum, which were significantly (P < 0.05) influenced by the nutrient concentration (PO43-, NO3-, NH4+) and rainfall. However, no variation in any studied parameter was observed among the four reef zones. The highest Sargassum biomass peaks occurred between late spring and early summer (from September to January). The results provide essential information to guide effective conservation and management, as well as sustainable utilisation of this coastal marine renewable resource.

Temporal changes in the biomass and distribution of Sargassum beds along the southeastern coast of the Baja California Peninsula

Changes in the distribution, surface canopy, biomass, and standing crop of Sargassum beds (Phaeophyceae) along the southeastern coast of the Baja California Peninsula (Mexico) are described and compared with previous estimates. Also, Sargassum biomass was correlated with latitude. Species were identified and surface canopy, biomass, standing crop, and length structure were estimated for 72 Sargassum beds in 3 localities in 2006. The extent of each bed was determined using GPS. The perimeter of each bed was drawn and its canopy area was calculated. The average biomass was estimated, using quadrats that were randomly distributed over the beds. The highest average biomass was found at Mulegé, with significant differences in the other 2 study areas (Concepción and La Paz bays). The largest bed, surface canopy area, and standing crop were recorded in Concepción Bay. Coverage area, location, and seasonal changes in surface canopy, standing crop, and biomass of Sargassum beds along the southeastern coast of the Baja California Peninsula were compared with the different phenological stages of Sargassum thalli, variations in the available rocky sea floor, and oceanographic characteristics. These aspects must be considered to maintain sustainable exploitation of this potential resource.

Positive Feedbacks Enhance Macroalgal Resilience on Degraded Coral Reefs.

Many reefs have shifted from coral and fish dominated habitats to less productive macroalgal dominated habitats, and current research is investigating means of reversing this phase shift. In the tropical Pacific, overfished reefs with inadequate herbivory can become dominated by the brown alga Sargassum polycystum. This alga suppresses recruitment and survival of corals and fishes, thus limiting the potential for reef recovery. Here we investigate the mechanisms that reinforce S. polycystum dominance and show that in addition to negatively affecting other species, this species acts in a self-reinforcing manner, positively promoting survival and growth of conspecifics. We found that survival and growth of both recruit-sized and mature S. polycystum fronds were higher within Sargassum beds than outside the beds and these results were found in both protected and fished reefs. Much of this benefit resulted from reduced herbivory within the Sargassum beds, but adult fronds also grew ~50% more within the beds even when herbivory did not appear to be occurring, suggesting some physiological advantage despite the intraspecific crowding. Thus via positive feedbacks, S. polycystum enhances its own growth and resistance to herbivores, facilitating its dominance (perhaps also expansion) and thus its resilience on degraded reefs. This may be a key feedback mechanism suppressing the recovery of coral communities in reefs dominated by macroalgal beds.

Remote-Sensed Mapping of Sargassum spp. Distribution around Rottnest Island, Western Australia, Using High-Spatial Resolution WorldView-2 Satellite Data

ABSTRACT Hoang, T.C.; O'Leary, M.J., and Fotedar, R.K., 2016. Remote-sensed mapping of Sargassum spp. distribution around Rottnest Island, Western Australia, using high-spatial resolution WorldView-2 satellite data. Satellite remote sensing is one of the most efficient techniques for marine habitat studies in shallow coastal waters, especially in clear waters where field observations can be easily carried out. However, such in situ observations have certain limitations: they are time consuming, have a limited ability to capture spatial variability, and require an interdisciplinary approach between marine biologists and remote-sensing specialists. The main objective of this study was to survey and map Sargassum beds around Rottnest Island, Western Australia, through a combination of high spatial resolution WorldView-2 imagery, using a validated depth invariant index model for water-column correction, and in-field observations. The combination of field survey data and four classification methods resulted in...

Numerical modeling of propagule dispersal for Sargassum bed restoration in Gamak Bay, Korea

The Sargassum beds in Gamak Bay, Korea, have deteriorated over recent decades. We conducted numerical experiments to assess the applicability of artificial reefs and longlines for seaweed forest restoration in terms of propagule dispersal. We applied hydrodynamic (Environment Fluid Dynamics Code (EFDC)), wave (Simulating Waves Nearshore (SWAN)), and particle tracking models for tidal currents, wave-induced currents, and the dispersal of the propagules, respectively. The major factors for propagule dispersal such as forcing, settling velocity w s , and release height were included, and the results of the models were analyzed using dispersal kernel, analysis of variance (ANOVA) tests, and survival rate based on bed elevation. The dispersal distance kernel was fitted to Gaussian and polynomial functions and showed higher wave impacts, whereby the mean dispersal distance was simulated 6.3 m under pure tide and increased by 14 times under the combined tide and wave condition. Propagules were found to hit the bottom intensively during a low-to-flood phase, while wave forcing enhanced vertical dispersal and hindered the intensive sinking. A two-dimensional dispersal location kernel showed that dispersal distance increased with high release heights and its direction faced the shoreline due to shallow water depth and strong wave-induced currents. ANOVA tests regarding the mean distance indicated that w s , forcing, release heights, and the combined effect of forcing and w s contributed 49.5, 20.5, 5.4, and 22.9 %, respectively, yielding a total of 72 % from w s . Adjusting the release height to extend dispersal distances led to A, C, and B locational effects, in order from lowest to highest, while survival rates were 67, 70, and 83 % for A, B, and C, respectively. From the results, we concluded that C is the most suitable locational type for restoration.

音響反射強度測定による来留見ノ瀬のホンダワラ科藻場の現存量推定と季節変化

Sargassum beds play important ecological roles in coastal ecosystems. However, it is difficult to estimate the spatial distribution of their biomass, because traditional surveys require a great deal of time and work. In this study, we tried to estimate the distribution using an acoustic method. For this purpose, we measured the acoustic intensity per unit dry weight, and field surveys were conducted in the coastal waters (12 km2) of Kuruminose, Yamaguchi, Japan, in spring 2007, autumn 2007, and spring 2008. The acoustic data were geostatistically interpolated to estimate the distribution. Acoustic data were collected using a quantitative echosounder at 200 kHz. The acoustic intensity per unit dry weight was -19.9 dB/kg. Using the intensity, the estimated biomass of the Sargassum bed in spring 2007, autumn 2007, and spring 2008 were 466 t (2.18 km2), 59 t (1.05 km2) and 287 t (2.36 km2), respectively. A spatial characteristic of the distribution was that the Sargassum beds were distributed from 0 to 11 m in depth. In particular, Sargassum beds were most often distributed at a depth of around 5 m. Because the distribution and its characteristics were able to be estimated, it was suggested that the acoustic method is adequate for estimating the spatial distribution of the biomass of Sargassum beds.

Mapping Sargassum beds off the coast of Chon Buri Province, Thailand, using ALOS AVNIR-2 satellite imagery

Abstract Sargassum species grow on rocks and dead coral, forming dense seaweed beds in their growth seasons. Sargassum beds play a range of ecological roles in coastal waters, but their sustainability is threatened by pollution and reclamation within ASEAN countries with rapid economic growth. Before conservation initiatives can be implemented, it is necessary to establish their present distribution. These beds can be mapped using the noncommercial satellite, ALOS, which can provide multiband images using high spatial resolution optical sensors (sensitive to 10 m-2 plots), AVNIR-2. These images are of sufficient quality for examining coastal ecosystems and, in this study, for mapping the Sargassum beds in the waters off the coast of Sattahip, Chon Buri Province, Thailand. This coastal zone is a natural marine park reserve and protected from human activities such as fishery and reclamation. Biomass data were obtained in January, February, March, and December 2009 from quadrat sampling. The biomass of Sargassum aquifolium (Turner) C.Agardh at a bottom depth of 1 m and 1.5–2 m was determined to be 7.73 and 92.75 g dw m-2, while that of Sargassum oligocystum Montagne was found to be 44.05 and 87.97 g dw m-2, respectively. Ground truth data were obtained in February and October 2012 from serial images taken by manta tow. Supervised classification is a procedure for identifying spectrally similar areas on an image by identifying “training” sites of known targets and then extrapolating those spectral signatures to other areas of unknown targets. By applying this methodology, the Sargassum beds off Sattahip can be detected with an accuracy of about 70%. It is estimated that the error is caused by mixel effects of the bottom substrates in individual pixels, each of which covers an area of 10×10 m. Our results indicate that the images captured by ALOS AVNIR-2 are informative and useful for mapping the Sargassum beds in Southeast Asia.

The role of epiphytic algae and different species of Sargassum in the distribution and feeding of herbivorous amphipods

The presence of particular algal species can directly influence the distribution and abundance of mesoherbivores. The aim of this study was to answer the following questions: Do Sargassum beds of different localities show variation in the load of epiphytic algae? Do Sargassum beds of different localities show variation in the density of herbivore amphipods? Does the density of these amphipods in the same algal bed vary with epiphyte load? Are species of Sargassum and their epiphytes equally consumed by amphipods? The collections were carried out in three infralitoral algal beds in southeastern Brazil. Fronds of Sargassum were collected at each algal bed and the associated ampithoid and hyalid amphipods were separated, identified and counted. Sargassum fronds and epiphytes were identified, dryed and weighted. Experiments were carried out to determine the consumption of Sargassum species and epiphytes by amphipods. The weight of the epiphytes Hypnea musciformis and Dyctiopteris delicatula and the density of amphipods were different among sampling sites. There was a relationship between amphipod density and epiphyte weight at two sampling sites. The four amphipod species tested consumed algae, but showed different patterns of consumption. Despite consuming the epiphytes, the ampithoids preferentially feed on the three species of Sargassum , while Hyale nigra had a preference for Hypnea musciformis .

Assessing the potential for recovery of a Sargassum siliquastrum community in Hong Kong

Tung Ping Chau Marine Park in Hong Kong was designated in 2001 with aims to protect its highly-diverse marine habitats from destructive human activities. Sargassum spp. (mainly Sargassum siliquastrum) formed a dense canopy in Lung Lok Shiu (LLS) in southwestern side of the Marine Park. This Sargassum bed, however, disappeared and a barren ground developed 7 years after the marine park designation. The increase in density of the short-spined sea urchin Anthocidaris crassispina, and thus the grazing pressure, as a result of restriction on its commercial fishery within the Marine Park was hypothesized as the immediate cause of the barren ground formation. In this study, we tested this hypothesis and manipulated the density of A. crassispina in exclusion cages underwater in LLS, where S. siliquastrum canopy originally existed. Transplantation of S. siliquastrum thalli and ceramic tiles with their recruits was carried out in these cages in February–May 2012 and May 2013. The results showed that the transplanted Sargassum thalli could not survive outside exclusion cages, whereas the induced recruits were almost wiped out in all tiles even inside exclusion cages. This provides evidence that the sea urchin A. crassispina could have overgrazed S. siliquastrum thalli and decimated the Sargassum canopy in LLS. It also suggested that other than A. crassispina, other grazers also contributed to the removal of S. siliquastrum recruits. Therefore, natural recovery of Sargassum bed seems unlikely if the grazing pressure remains high in this site. Proactive management strategies may need to be adapted to restore this Sargassum bed.

Sargassum bed restoration by transplantation of germlings grown under protective mesh cage

Studies on the construction of artificial seaweed beds were carried out for the restoration of barren grounds that extend along the coast of Jeju Island in Korea. Fertilized eggs of Sargassum fulvellum and Sargassum horneri were induced from receptacles of mature plants and adhered to concrete block substrata. When the germlings that settled on the artificial substrata had grown to 3–5 mm in indoor cultures, they were moved to the ocean for intermediate cultivation, where they were cultivated under seed-cultivating nets to prevent damage from grazing animals. After the germlings had grown to 25–50 cm, the artificial substrata with settled germlings were taken out from the protective cage and transplanted on the barren grounds along the coast of Jeju Island. In the early stage of transplanting, the Sargassum thalli were partially eaten by grazing animals. Two months post-transplantation, the plants grew quickly, and their stems were harder and free from grazing damage. Most of the Sargassum had grown to over 300 cm by 6 months after transplantation on the barren grounds, and they were forming a marine forest community at the transplant sites.

The Role of Thin Sediment Cover in the Persistence and Extension of Artificial Sargassum Beds off Sakinoyama, Kasasa, Kagoshima

The Role of Thin Sediment Cover in the Persistence and Extension of Artificial Sargassum Beds off Sakinoyama, Kasasa, Kagoshima

&lt;p&gt;&lt;strong&gt;Growth and gonad development of the sea urchin &lt;em&gt;Hemicentrotus pulcherrimus &lt;/em&gt;in an &lt;em&gt;Eisenia &lt;/em&gt;kelp bed in the Oshika Peninsula, northern Japan*&lt;/strong&gt;&lt;/p&gt;

To elucidate growth and gonad development of Hemicentrotus pulcherrimus in the bed of Eisenia bicyclis, we examined gonad indices, gonad histology, gut content indices and ages of the sea urchins collected approximately monthly from March 2008 to September 2009 in Kitsunezaki in the Oshika Peninsula, northern Japan. We also monitored the densities of the kelp in six 1 m2 quadrates. The kelp at 1- to 3-years of age decreased in density from January to July due to strong wave action. The urchin test diameters at 1-, 2- and 3-years of age were 12.7 mm, 23.7 mm and 30.5 mm, respectively and these growth rates were equal to that measured in Sargassum beds in previous studies. The gonad recovering stage was classified into the two sub-class stages; the recovering I stage with relict spermatozoa or ova surrounded by renewed nutritive phagocytes, and the recovering II stage with nutritive phagocytes filling the lumen. The recovering I stages was prolonged from February to April when the gonad indices were around 10 % of total body weight, then rose sharply through the recovering II stage during May to August and the growing stage until October. The gonad indices rose sharply from November and reached a maximum of 18.8 in December when the gonad shifted from the premature to mature stages, then fell in January at the partly spawned and spent stages. Gut content indices were high at the recovering I stage, suggesting high availability of the drift thalli and lateral blades dislodged from the kelps and accumulation of nutrients in nutritive phagocytes.

Fish response to expanding tropical Sargassum beds on the temperate coasts of Japan

Fish response to expanding tropical Sargassum beds on the temperate coasts of Japan

Estimation of the spatial distribution of a Sargassum bed in Kuruminose, Yamaguchi, Japan, using an acoustic method

山口県来留見ノ瀬のガラモ場は，周辺の沿岸生態系において重要であり分布の把握が求められている。本研究は，音響手法により同海域（12 km2）のガラモ場の分布推定を試みた。推定されたガラモ場は，来留見ノ瀬から北西および南南東の方向に分布し，総面積は 1.94 km2（高さ 0.50～2.24 m）であった。特に南南東の領域の内側は繁茂しており，沿岸生態系における重要性が高いと考えられた。本手法は分布推定の有効な手段であり，現存量の広域評価なども今後に期待できると考えられた。

가막만 모자반 군락지 어류군집의 종조성 및 계절변동

Species composition and seasonal variation of fish assemblages in Sargassum beds in Gamak Bay was determined using fish samples collected monthly by a surrounding net from October 2008 to September 2009. A total of 21 species, 582 individuals and 5,345.1 g of fishes were collected during the study period and Perciformes accounted for 47.6 % of the total number of species. Takifugu niphobles, Engraulis japonicus and Lateolabrax japonicus predominated in number, accounting for 55 % of the total number of individuals. Higher number of species and individuals occurred in June and in September-October. Species were grouped into three by cluster analysis: A) dominant species such as Leiognathus nuchalis and Takifugu niphobles, B) fish collected mainly in spring such as Sebastes inermis, Chaenogobius heptacanthus, Pterogobius zonoleucus, Pholis nebulosa, and Trachyrhamphus serratus, and C) fish collected mainly in autumn such as Engraulis japonicus, Lateolabrax japonicus, and Hyporhamphus sajori.

Re-Assessment of Sargassum Beds at Hon Chong Area, Nha Trang Bay, Vietnam

Sargassum beds play an important role in terms of ecology and economic likelihood (ecosystem services) for coastal communities along the Hon Chong area, in the bay of Nha Trang, Vietnam. It is a matter of concern that the Sargassum beds at Hon Chong, in particular, and Vietnam, in general, have strongly decreased due to anthropogenic perturbations including land reclamation. Our research focused on a reassessment of Sargassum beds including coverage, occupied area, species composition, branch length frequencies and output (production) over the last 30 years. Remotely-obtained (satellite) information and field data processed through GIS software were used during this study. Results show that the area covered by the Sargassum beds was reduced by 49%. In 1980 the coverage of Sargassum was 75% for all the area (30 ha), but now we observed that 75% of the coverage occurred in area of only 2.2 ha. The average length of Sargassum mcclurei and S. serratum branches recorded in 2009 were reduced by 58% and 65%, respectively, compared with data recorded in 1980. Moreover, in 1980 Sargassum crassifolium was very common in this area, however, during this study it was not found.

Restoration of Sargassum Bed on an Urchin Barren Along the Northwestern Coast of Izu Peninsula, Shizuoka

Restoration of Sargassum Bed on an Urchin Barren Along the Northwestern Coast of Izu Peninsula, Shizuoka

Trial to Restore Sargassum Beds together with Fisheries Senior High School

Trial to Restore Sargassum Beds together with Fisheries Senior High School

BANCOS DE Sargassum cymosum (PHAEOPHYCEAE) NA ENSEADA DE ARMAÇÃO DO ITAPOCOROY, PENHA, SC: BIOMASSA E RENDIMENTO EM ALGINATO

The seaweed Sargassum occurs in large beds along Brazilian Coast, mainly in Southern and Southeastern areas. This seaweed is very important to local fauna and flora. It is also economically important mainly due alginate to production. Several kinds of approaches are needed to planning its sustainable management. This work aims to evaluate the size of subtidal Sargassum cymosum beds in Armação do Itapocoroy Bay (Penha, SC), quantifying its spatial variations on biomass and associated seaweed community, and also evaluate alginate yield separately for vegetative and reproductive branches, for each bed. The Sargassum beds area in Armação do Itapocoroy Bay reached 14,137 m2. Total estimated biomass in the bay was 17.90 ± 9.07 ton wet mass. Mean biomass ranged from 142,64 (± 34,25) to 214,76 (±131,68) g dry mass m-2 between the beds. The alginate yield ranged from 18.63 to 25.00%, and reproductive branches yield was higher than vegetative branches yield. Reproductive structures alone yield about 30%. Despite many additional works are needed, these results indicate potential for Sargassum exploitation in Santa Catarina Coast.