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A systematic review of floating and beach landing records of Sargassum beyond the Sargasso Sea

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Sargassum algal blooms on ocean surfaces and landings of huge Sargassum mats on beaches is an emerging global environmental challenge with wide socio-economic and environmental implications. Literature on Sargassum growth cycles, travel patterns, species and morphotypes, and quantified impacts have tended to focus on a geographic region, or a specific event. Few, if any, publications document long term continuous monitoring of Sargassum blooms in large areas such as the Pacific, or the tropical Atlantic. To address this gap, this paper systematically reviews the global evidence of Sargassum bloom monitoring beyond the Sargasso Sea, and identifies gaps in the evidence base of floating and landing influxes. This systematic review uses combinations of two key terms relating to Sargassum and monitoring, and utilises the resources in ISI Web of Knowledge, Scopus and Google Scholar. The analysis moves us past a classic literature review, and produces an unbiased assessment of empirical research on Sargassum monitoring from 1960 to 2019. We find a significant research focus on open-ocean blooms and floating mats whereas research on beach landings and their associated impacts is comparatively limited. Research is focused within specific countries or water bodies (notably, the Gulf of Mexico, the Caribbean and North Atlantic Ocean) and tends not to comprehensively assess neighbouring or regional shorelines, for example, West Africa and Central America. There was a lack of consistency in the application of methods for quantifying Sargassum biomass volume (including dry/wet weight, unit of measurement, and spatial extent of calculations). Further, in many publications Sargassum species identification was omitted. Given current attempts to understand the drivers and impacts of the exponential growth in Sargassum in some parts of the world, a consistent and replicable research approach to monitoring Sargassum could support creation of a Sargassum evidence database. To move this agenda forwards, we propose a definition for a Sargassum 'event': a continuous bloom of any Sargassum in open oceans, or, an aggregation of landed Sargassum, with the potential to disrupt social, economic or ecosystem functioning, or to impact human health. This review highlights the importance of standardising Sargassum monitoring methods to facilitate improved documentation of temporal and spatial patterns of Sargassum blooms and beach landings.
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A systematic review of floating and beach landing records of
beyond the Sargasso Sea
To cite this article: Y A Fidai et al 2020 Environ. Res. Commun. 2 122001
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Environ. Res. Commun. 2(2020)122001
A systematic review of oating and beach landing records of
Sargassum beyond the Sargasso Sea
Y A Fidai
, J Dash
, E L Tompkins
and T Tonon
Geography and Environmental Science, University of Southampton, Higheld Campus, Southampton, SO17 1BJ, United Kingdom
Department of Biology, Centre for Novel Agricultural Products, University of York, Heslington, York YO10 5DD, United Kingdom
Keywords: detection, monitoring, Sargassum, remote sensing, S. uitans,S. natans, prediction
Supplementary material for this article is available online
Sargassum algal blooms on ocean surfaces and landings of huge Sargassum mats on beaches is an
emerging global environmental challenge with wide socio-economic and environmental implications.
Literature on Sargassum growth cycles, travel patterns, species and morphotypes, and quantied
impacts have tended to focus on a geographic region, or a specic event. Few, if any, publications
document long term continuous monitoring of Sargassum blooms in large areas such as the Pacic, or
the tropical Atlantic. To address this gap, this paper systematically reviews the global evidence of
Sargassum bloom monitoring beyond the Sargasso Sea, and identies gaps in the evidence base of
oating and landing inuxes. This systematic review uses combinations of two key terms relating to
Sargassum and monitoring, and utilises the resources in ISI Web of Knowledge, Scopus and Google
Scholar. The analysis moves us past a classic literature review, and produces an unbiased assessment of
empirical research on Sargassum monitoring from 1960 to 2019. We nd a signicant research focus
on open-ocean blooms and oating mats whereas research on beach landings and their associated
impacts is comparatively limited. Research is focused within specic countries or water bodies
(notably, the Gulf of Mexico, the Caribbean and North Atlantic Ocean)and tends not to
comprehensively assess neighbouring or regional shorelines, for example, West Africa and Central
America. There was a lack of consistency in the application of methods for quantifying Sargassum
biomass volume (including dry/wet weight, unit of measurement, and spatial extent of calculations).
Further, in many publications Sargassum species identication was omitted. Given current attempts
to understand the drivers and impacts of the exponential growth in Sargassum in some parts of the
world, a consistent and replicable research approach to monitoring Sargassum could support creation
of a Sargassum evidence database. To move this agenda forwards, we propose a denition for a
Sargassum event: a continuous bloom of any Sargassum in open oceans, or, an aggregation of landed
Sargassum, with the potential to disrupt social, economic or ecosystem functioning, or to impact
human health. This review highlights the importance of standardising Sargassum monitoring methods
to facilitate improved documentation of temporal and spatial patterns of Sargassum blooms and beach
1. Introduction
Pelagic Sargassum seaweed was rst reported in the Sargasso Sea in the 15th Century and has since been
documented in this area (Fine 1970, Lapointe 1986, Wang et al 2019). In recent years, research has described
signicant pelagic Sargassum seaweed blooms (free-oating brown seaweeds)across water bodies and beach
landings globally, presenting a new environmental challenge (Langin 2018).Sargassum blooming events in the
Atlantic are thought to be initiated and inuenced by a combination of factors including: nutrient discharge
from the Amazon River, changes in ocean upwelling, higher sea surface temperatures and Ocean pattern
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changes, such as an unusually strong North Atlantic Oscillation patterns, Atlantic Multidecadal Oscillation and
El Niño-Southern Oscillation events (Sissini et al 2017, Sanchez-Rubio et al 2018, Oviatt et al 2019, Wang et al
2019, Johns et al 2020). In East Asia, blooms are thought to be caused when Sargassum is detached from beds due
to strong waves and currents (Komatsu et al 2014). Some publications have assessed annual or seasonal cycles
and transport patterns of Sargassum in the Atlantic Ocean and indicated potential origin sources of the blooms
(examples include Gower and King 2011, Wang and Hu 2016, Brooks et al 2018, Putman et al 2018, Sanchez-
Rubio et al 2018). However, there is no comprehensive study assessing the spatial distribution of Sargassum
bloom events.
Since 2011, Sargassum blooms appear to have increased in frequency and magnitude, notably in the tropical
Atlantic and the Caribbean region (Wang and Hu 2017). In 2018, Wang et al (2019)estimated there was over 20
million metric tons of Sargassum across the Tropical Atlantic in the summer months.
The socio-economic impacts of Sargassum blooms and beach landings are notable on the aquaculture and
tourist industries; for example, Sargassum clogs shing gear and limits shing ground, resulting in a reduction in
revenue and income and an increase in maintenance costs (Solarin et al 2014, Ramlogan et al 2017). Xing et al
(2017)estimated that, in China, seaweed damage cost the aquaculture industry 73 million USD. Additionally,
tourism has decreased due to the visual impact and odour of Sargassum (Chávez et al 2020a). There are claims
that decomposition of Sargassum releases toxic gases and can cause potentially fatal health problems in humans
(ANSES 2017, Resiere et al 2018). Environmental impacts of Sargassum blooms have also been observed; for
example, turtles looking to nest and neonate hatchlings accessing the sea can be hindered by Sargassum beach
landings (Maurer et al 2015). Additionally, surface blooms restrict light penetration through the water column
which affects benthic communities (McGlathery 2001). Despite the negative impacts on communities,
Sargassum inuxes also present opportunities for economic benet as it has a variety of potential uses including
for biofuel energy, soil fertiliser and animal feed, construction blocks, bioplastics and pharmaceutical products
(Milledge et al 2016, Chávez et al 2020b, Thompson et al 2020).
Large Sargassum inuxes are generating high levels of concern among policy makers due to their impacts on
economies, health, and society. Internationally, the United Nations Environmental Programme (UNEP)has
created a Working Group on Sargassum within the Joint Group of Experts on the Scientic Aspects of Marine
Environmental Protection (GESAMP)to identify key Sargassum challenges and responses. Regionally,
conventions have been developed to acknowledge the issue and highlight the need for solutions; in the Tropical
Atlantic this can be seen within the UNs Abidjan and Cartagena Conventions (UNEP 2018). However, critical
information that could help policy makers and communities cope better with Sargassum is missing. For
example, there is a lack of data on: the drivers of Sargassumspecically input sources for specic regions; the
temporal and spatial spread of signicant Sargassum bloom events; the quantity of Sargassum in oceans and
landing on beaches; and the distribution of species and morphotypes of Sargassum within bloom events (which
can inuence re-use opportunities).
This paper aims to contribute to our understanding of the spatial and temporal distribution of Sargassum by
exploring the spectrum and prevalence of use of methods employed to monitor blooms and beach landings.
Methods to document Sargassum are categorised herein as either remote sensing-based or in situ. Remote
sensing methods include applying algorithms to identify Sargassum blooms in airborne and spaceborne imagery,
largely focusing on surface blooms in open ocean areas. In-situ methods encompass site visits, often by boat, to
survey or take samples of Sargassum blooms or deposits. Understanding which methods are being used, how
effective they are, where and how they are considered, can help support the development of higher quality
monitoring globally.
The paper is structured as follows: section 2introduces the systematic review methoda methodology
designed to reduce the potential for bias in a traditional literature review. Results are presented in section 3,
focussed around the key questions asked in the systematic review, notably: Is the research related to oating or
landing events, and if so where did it occur (beach, near-shore or open-ocean)?; What is the spatial extent of
Sargassum research? Does the literature indicate a source of Sargassum?; What was the temporal scale of
analysis?; Which species of Sargassum were identied?; What data has been used to document the occurrence of
Sargassum blooms and beach landings? What was the volume of Sargassum (if calculated)? The key ndings are
discussed in section 4, around the main themes found in the systematic review. Section 5concludes the paper,
drawing out remaining research gaps.
2. Method
Systematic literature reviews are an important method for synthesising medical evidence (Bastian et al 2010)but
are increasingly used in relation to analysis of environmental change (Berrang-Ford et al 2015). The systematic
review method utilises search engines to identify all academic literature relating to a specic topic (Moher et al
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
2016). The systematic review method offers a robust methodology to identify and analyse empirical published
evidence, however, it has limitations. Some publications will be omitted due to: the way in which the search
engines index their results (see (Beel and Gipp 2010)); because the journals appear only in print form and not
online; or because some search engines, e.g. ISI WOK, quality controls their collections and only includes long-
established journals. Nonetheless, it remains a highly used and robust research tool (Moher et al 2016).
For this paper, the systematic review method was used to identify all empirical research on Sargassum
monitoring from 1960 to 2019. Multiple systematic review researchers recommend using trusted high-quality
academic data bases, such as Scopus, or ISI Web of Knowledge (ISI WOK), see (Webb et al 2015). For example,
Berrang-Ford et al (2011)justify the use of ISI WOK as it is powerful and comprehensive; Falagas et al (2008)use
Scopus as it offers a wider journal range. Our search was supplemented with Google Scholar. The search was
undertaken using all combinations of synonyms for Sargassumand monitoring(see supplementary materials
for details (available online at A total of 106 571 results were
returned from all three search engines and a reference manager was used to organise the results. A two-step
ltering framework was applied to publications. The rst step was to read the abstracts and titles of all
publications to determine if they satised the inclusion criteria (i.e. empirical study, within our research focal
area, pelagic sargassum, see supplementary material for details), as well as to remove duplicate results. A total of
283 publications were then taken forward to the second ltering step, which involved reading the papers in full
to determine whether they still satised the inclusion criteria. Reasons for exclusion were: non-English language,
not accessible, non-empirical research; a focus only on the Sargasso Sea; or, a focus on benthic species of
Sargassum (see supplementary material for details). Once all the papers had been identied, the metadata of the
literature was collated, and the ndings within the publications were analysed to answer seven research queries
covering aspects related to Sargassum identication, location, distribution, quantity and sources:
1. Is the research related to oating or landing events, and if so where did it occur (beach, near-shore or open-
2. What is the spatial extent of Sargassum research?
3. Does the literature indicate a source of Sargassum?
4. What was the temporal scale of analysis?
5. Which species of Sargassum were identied?
6. What data has been used to document the occurrence of Sargassum blooms and beach landings?
7. What was the volume of Sargassum (if calculated)?
Figure 1. Publications by decade and the type of Sargassum documented. Publications on oating and landing were identied by the
location of evidence of Sargassum indicated. Floating includes studies which collected Sargassum data from the open ocean and near-
shore environments. Landing includes studies which collected Sargassum evidence from beaches only.
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
Finally, a paper quality review was undertaken by subjectively rating each publication on a scale of 15
(1=low; 5=high)based on clarity of methods (justication and replicability), comprehensivity of
presentation of results and relevance of themes to the research queries (based on criteria adapted from (Porter
et al 2014)). The aim of the quality review was to understand any quality patterns within publications
documenting Sargassum oating or landing events. The nal dataset contains 76 publications spanning 60 years,
which were mostly judged to have a quality rating of 3 or 4; for ease of reading, the empirical publications are
numbered in square brackets [1][76]and are provided in the annex.
3. Results
The number of publications documenting Sargassum has grown in recent years; of the 65 publications in the past
decade, 29 (45%)were published in 2018 and 2019 (gure 1). Despite the boom in publications in recent years,
there remain several identiable knowledge gaps where research is limited.
3.1. Floating and landing publications
Sargassum is reported to have a more signicant impact on the coast and near-shore and on the communities
whose livelihoods depend on access to the coast (Louime et al 2017). Yet only 5% of publications focussed only
on landing Sargassum; a signicant proportion focussed on oating Sargassum (83%), and more recently a
combined analysis of both. Only four publications undertook work on landed Sargassum and these were based in
Brazil (Atalaia beach, north-eastern Amazonian coast), Germany (island of Heligoland), San Andres Island
Figure 2. Global distribution of publications documenting evidence of oating (F)and landing (L)Sargassum. Seventy-six
publications collected evidence in 110 locations. The number in brackets refers to the number of publications which identied
Sargassum in that location. Caribbean (7)includes publications which referred to the Caribbeanas their study area, as well as
Caribbean Islands (including US territories)and the San Andres Island Archipegalo. The Sargasso Sea is included as a location as
publications which included this region as well as other areas were included in the literature analysis.
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
(Caribbean Sea)and beaches of the Mombasa Marine National Park and Reserve, Kenya. Publications that
encompassed both oating and landing Sargassum (12%)include data from Nigeria [2], Ghana [1], Atlantic
Ocean or specic countries in the Western Atlantic [23, 24, 66, 14, 4, 3]and the East China Sea [35]. Surprising
gaps in Sargassum landing research are noted in Caribbean Sea and Islands, the Western Pacic, the coasts of
West Africa and Gulf of Mexico (gure 2).
3.2. Spatial extent of oating and landing Sargassum research
Research has been undertaken in Africa, the Americas, Asia, and Europe; in the Atlantic, Pacic and Indian
Oceans, with three publications undertaking a global survey of Sargassum [18, 21, 59](gure 2). We hypothesise
that coastlines adjacent to water bodies experiencing signicant impacts of Sargassum would be the focus of
more research than those experiencing fewer and less severe inuxes; however, there are gaps, for example there
is no research with a focus on Belize, Colombia and Japan. West Africa has two pockets of research in Nigeria and
Ghana, which considers their own and neighbouring coastlines [2]. In the Caribbean region, there is a focus on
oating Sargassum on monitoring the general area, only four publications examined individual islands within
the CaribbeanVirgin Islands, San Andres Island, Puerto Rico and Barbados [7, 16, 48, 66].
3.3. Input sources for the Sargassum
Of the 76 publications, only 13 (17%)speculated or indicated a theory on the origin of the Sargassum in their
respective study areas (table 1). However, it is important to note that most publications speculate the origins of
the Sargassum and conclude that the source is uncertain, with two concluding that it was unknown [23, 61].
There is a signicant number of publications focusing research on bloom origins around the Atlantic
(n=10/13). From a deeper analysis of Atlantic based publications, it can be seen there is an emphasis on the
tropical West Atlantic and Caribbean area. The Gulf of Guinea and West Africa are not always studied as a
separate region but are often encompassed in publications focusing on the Tropical or Equatorial Atlantic. Three
of the publications present research on the Pacic region around East Asia. There are no publications focussing
on other regions of the world which explore the origin of Sargassum blooms.
3.4. Temporal distribution of Sargassum research
As expected, most of the research to date (78% of all papers)document the experience of individual locations,
such as an area of sea, or an island, rather than a specic event, e.g. the 2018 bloom event. Location-based
research provides either recurrent or one-off data for a specic area based on an expectation of potential
Sargassum presence. Regular location monitoring (such as [3, 11, 47, 50])is useful for a variety of reasons such as
assessing presence, extent and frequency. Event-based monitoring (in response to the occurrence of a blooming
or landing event)was present in 16% of the publications. The notion of a Sargassum eventis rarely and
Figure 3. Sargassum species (oating and beach landings)distributed by Ocean Region and determined by publication study area.
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
inconsistently dened. Whether a publication collected evidence by location or in response to an eventwas
often inferred for this analysis, but not stated explicitly in the research. Research which appeared to focus on
specic events generally collected evidence of Sargassum immediately after or in response to the emergence of a
bloom over water bodies or the appearance of Sargassum mats in coastal or beach areas. For example, in response
to a bloom off the coast of Florida, Marmorino et al (2011)[39]used airborne imagery to collect evidence of the
Sargassum raft. Similarly, Oyesiku and Egunyomi (2014)[46]responded to reports of Sargassum in Nigeria by
visiting the site and collecting samples. Some publications collected data by both monitoring locations and
responding to Sargassum events; for example, Hu et al (2015)[28]utilised remote sensing to regularly monitor
the Gulf of Mexico and Atlantic area and the AVIRIS sensor for event response.
3.5. Prevalence of Sargassum species in research outputs
To effectively valorise Sargassum biomass, a critical piece of information is the biochemical composition of the
landing seaweed. There are more than 300 Sargassum species globally, and several morphotypes within some
species, each of which potentially has a different chemical signature (Hardouin et al 2014). Composition analysis
of many Sargassum species has not been investigated yet and, in relation to this, key questions remain: what is the
abundance of the different Sargassum species and/or morphotypes in the seaweed mats? Are some Sargassum
species more typically found in some locations than in others? Interestingly 32% (n=24)of publications did
not distinguish between different species of Sargassum in their research (gure 3).
Publications such as [9, 31, 34, 35]show that S. horneri can be found as oating in the East China and Yellow
Sea. However, Liu et al (2018)showed that these were detached Sargassum (i.e. the force of waves and currents
cause the seaweed to disconnect from the bottom and they are buoyant due to having gas vesicles)rather than
pelagic. It is possible that otherspecies of Sargassum are also detached and not pelagic, although more research
is needed to conrm this. It is apparent that the dominant holopelagic species are S. uitans and S. natans and
their respective morphotypes, particularly in and around the Atlantic region. Only three publications, identify
morphotypes of these Sargassum species [3, 17, 58]. This further heightens the uncertainty around Sargassum
nomenclature and identication. Schell et al (2015)[58]identied that the dominant species in 2014/2015 was
the morphotype S. natans VIII in the Caribbean. However, by the end of 2019, no other publications have
compared morphotype dominance in any study area or time periods. If Sargassum monitoring publications,
investigated the species and morphotypes of Sargassum, this could improve understanding of past trends, as well
as improving prediction of future events.
Table 1. Theorised sources for areas affected by Sargassum.
Sargassum location Theorised source Publications
Caribbean, Caribbean Sea, Sargasso Sea and
Gulf of Guinea
- Guiana Current/North Brazilian
current system
[8, 14, 23, 24, 29,
50, 67]
No agreement
- North of the mouth of the Amazon
- Tropical Atlantic North of Brazil
- Equatorial Atlantic between South
America and Africa
- North equatorial recirculation
- Gulf of Mexico
- Tropical Atlantic
Gulf of Mexico - Northwest Gulf of Mexico [8, 21]Agreement
- Gulf of Mexico
Pacic Region. Yellow Sea and East China Sea
(including South Korea, Japan and China
coastal areas)
- Zhejiang Coast [34, 35, 52]Agreement
- Zhejiang province
- inner part of Yellow Sea
South Atlantic - Sargasso Sea [61]No agreement
- West Africa
- Mexican Coast
San Andres Island - North of the Estuary of the Amazon
River, off the coast of Brazil
[16]No agreement
Agreement occurs when >60% of publications suggest the same source. No agreement is given when there are less than two publications for
the location.
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
3.6. Types of methods and data used to document the occurrence of Sargassum blooms and beach landings
The methods used to detect and monitor Sargassum were varied, with 46% employing a remote sensing based
approach, 28% in situ (i.e. direct surveys and sampling of Sargassum) and 26% employed a combination of both
remote sensing and in situ methods (table 2).
Table 2shows that for the Atlantic region most publications utilise remote sensing based methods, whereas
for the Pacic region, in situ approaches have been more commonly used. For global evidence collection,
understandably only remote sensing based methods are used due to the scale of the study area. Remote sensing
publications are most commonly based on satellite data sources including Moderate Resolution Imaging
Spectroradiometer (MODIS), Medium Resolution Imaging Spectrometer (MERIS)and Landsat, which were
often accompanied by ground truth data or higher spatial resolution dataset for a small subset of the study area,
examples include [4, 28, 30, 47]. A minority of publications used unmanned aerial vehicles (e.g. drones)or other
alternatives for aerial photography [39, 64]. Open-ocean Sargassum detection methods were most commonly
based on the red-edge concept, such as oating algal index (FAI)[27]. In contrast, there was less clarity about the
sampling methods used within in situ research. Often sampling methods were not clearly stated (and hence were
considered to be lower quality research, see supplementary materials). Those publications that documented
their methods most commonly used boats to access Sargassum rafts, examples include [35, 42, 55].
3.7. Estimation of Sargassum biomass
To be able to manage Sargassum inux, affected communities need to anticipate expected quantities and
volumes that are likely to land on the shore. Only twelve publications (16%)attempted to estimate the volume of
Sargassum, and the calculation methods employed differed across the literature. Various approaches for landed
and oating Sargassum were adopted for volume calculation, including: (i)determination of biomass weight
based on wet [19]or dry Sargassum weights [40, 44];(ii)calculation of the size of the measured area, by
assessment of individual rafts [42], or quantication of pixels in an aerial image [19, 23, 52, 69]. This range of
methods generated an array of results. Estimates of biomass volume include: an average of 1400 tons of wet
weight per square degree grid per MERIS count in the Tropical Atlantic (based on 11 different areas and dates)
[19], to 15 million tons in July 2017 and 32 million tons in July 2018 [23], and 2.05 tons per square nautical mile
in the Gulf Stream (estimated through sampling)[26]. A further complication is the lack of a clear distinction
within many papers between an imperial tonne or metric ton. These inconsistent practices in calculation and
display methods contribute to an inability to compare changes in Sargassum volume both temporally and
spatially; it also prevents long term analysis of Sargassum prevalence.
Table 2. Main methods used in analysis of Sargassum by world region or sea.
Region Main methods used Publications
Atlantic Ocean Region
(70%, n=53)
Remote sensing 47% [1, 3, 5, 12, 17, 26, 32, 46, 54, 56, 57, 58, 66, 2, 4, 7, 10, 13, 28, 29, 45, 47, 48, 55,
61, 64, 71, 72, 8, 11, 14, 15, 16, 19, 20, 21, 23, 24, 25, 27, 30, 33, 38, 39, 50, 51,
60, 63, 65, 67, 68, 69, 70]
In-situ 25%
In-situ and remote sen-
sing 28%
Pacic Ocean Region
(24% n=18)
Remote sensing 33% [9, 31, 35, 37, 42, 43, 62, 36, 4, 41, 74, 75, 6, 34, 52, 53, 73, 76]
In-situ 39%
In-situ and remote sen-
sing 28%
Indian Ocean Region
(3% n=2)
Remote sensing 50% [44, 49]
In-situ 50%
In-situ and remote sen-
sing 0%
Global (4%, n=3)Remote sensing 100% [18, 22, 59]
In-situ 0%
In-situ and remote sen-
sing 0%
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
4. Discussion
The systematic documentation of locations affected by oating and landings of Sargassum presented in this work
is the rst analysis of its kind and identies some unexpected results relating to the distribution and quality of
Sargassum research outputs. Despite the global distribution of pelagic Sargassum research, there are surprising
gaps. For example, Belize shares the same Caribbean coastline as Mexico, and could be equally prone to
Sargassum inuxes, yet there is currently an absence of literature documenting Sargassum in Belize. Unless all
areas in a possible Sargassum impact area are monitored for Sargassum landings, it will not be possible to fully
appreciate the extent of Sargassum in the Caribbean. Similarly, there is no published research on Sargassum in
West African countries such as Cameroon and Gabon, yet based on their geographic location, it would make
sense to assume that Sargassum is likely to be landing there. Figure 2illustrates other areas where few
publications have been undertaken and where research could be intensied, such as South America, East Africa,
and North and West Africa. To fully understand and prepare for the impacts of Sargassum on stretches of
coastline, spatial gaps in research need to be lled.
It is worth noting that only 17 publications undertake empirical research on monitoring Sargassum in the
wider Atlantic Ocean (excluding Gulf of Mexico, Sargasso Sea and the Caribbean), which speaks to the scarcity of
research on pelagic Sargassum over the course of 60 years. It further appears that the proportion of Sargassum
research in a country may correlate with its relative wealth. For example, countries with a higher gross national
income per capita (GNI)using (The World Bank 2018)such as the USA (which has n=6 publications),
undertook substantially more research than those with a lower GNI, such as Togo (n=1), Liberia (n=1),
Guyana (n=1)and others in West Africa (n=2), Central America (n=0)and South America(n=3). The
relative levels of economic development of countries could be reected in their investment in research into
pelagic Sargassum and offer an explanation for spatial research gaps globally. Development of local empirical
evidence bases on Sargassum is very important as the potential solutions to manage the inux of Sargassum in the
future would require location specic information, and local strategies.
It was surprising to nd that one fth of the publications did not specify the species of Sargassum, and only
three publications reported on the morphotypes of the specimen. This exemplies the challenges in correctly
identifying some of the Sargassum species, and some issues with their nomenclature. As an example, S.
aquifolium appears to have a variety of synonyms according to Algae Base (Guiry 2020), which could contribute
to hesitation in identifying Sargassum species in research publications. However, for the three morphotypes that
affect the Caribbean and Western Africa clear morphological criteria and molecular markers have been
established to identify them (Amaral-Zettler et al 2017). Another important aspect to consider is that Sargassum
species may possess such similar qualities, such as their biochemical composition, that there is little need to
distinguish between them. A limited number of publications have investigated aspects of the biochemical
composition of holopelagic Sargassum biomass (Oyesiku and Egunyomi 2014, Addico and deGraft-
Johnson 2016, Baker et al 2018), and more recently of the three individual morphotypes (Davis et al 2020,
Milledge et al 2020). However, wider and more comprehensive research into composition of holopelagic
Sargassum species and of their morphotypes would offer transparency of differences and could unite species that
are currently thought to be distinguished. Further research on this topic for specic species and morphotypes
would enable this issue to be addressed, and it may also offer clarity on taxonomy. Additionally, detailed
knowledge of Sargassum composition would facilitate understanding of Sargassum uses, impacts and
management options.
The limited number of publications estimating quantities of Sargassum and their methodological
inconsistencies prevent construction of a long-term record of Sargassum inuxes and spatial-temporal analysis.
Although, more recent publications are starting to do this (García-Sánchez et al 2020); there are management
implications of this as it generates uncertainty. For example, Sargassum landing on beaches has occurred
regularly in the past; however, in years (or seasons)with signicantly high Sargassum inux, such as 2015 (which
had 20 times the historical amount (Wang and Hu 2016)), management strategies are imperative to prevent
socio-economic and environmental losses. Inconsistencies in estimating volumes of Sargassum prevent effective
management as authorities cannot accurately anticipate and prepare for Sargassum inuxes. It can be speculated
that this is especially true for developing countries which have less to invest in monitoring and management.
Therefore, to facilitate effective management, estimations of volume should be provided in a standardised
manner, ideally alongside landing forecasts.
There are many Sargassum management questions that remain outstanding, including how long do beaching
events last?,where does Sargassum occur most regularly?,what are the local socio-economic impacts and how can they
be mitigated?,what are the environmental impacts on specic areas/habitats?. None of these can be assessed or
quantied when there is little research on beach landings of Sargassum. Focussing research on oating and open-
ocean Sargassum and overlooking analysis of the magnitude and severity of beach impacts leaves management
queries unanswered. A further under-researched area which hinders management capacity is a lack of research
Environ. Res. Commun. 2(2020)122001 Y A Fidai et al
on event response. With the majority of publications focussing on regular monitoring of open-ocean areas,
event response research is limited. These research gaps hamper detailed analysis on how Sargassum interacts
with communities and its impacts on livelihoods and economies. In Mexico, management plans have been put
into place, as reported by print media, such as installing trial and errorhard engineering solutions including
barriers (Mexico News Daily 2019). Although attempts at management are possible in the absence of detailed
impact data, it can be argued that with more robust research on beach landings of Sargassum and on Sargassum
events, more reliable solutions can be introduced with a higher potential for success.
5. Conclusions
The outstanding Sargassum research gaps relate to input sources, locations and species identication, as well as
the quantity in the oceans and the amount landing on beaches. The rapid growth in publications on Sargassum
over recent years is a welcome step towards understanding Sargassum blooms and its geographic spread.
However, there is a need to improve the robustness and extent of research to ensure in-depth understanding of
the complex issue and support a comprehensive management plan for all affected communities.
First, the spatial coverage of research should be expanded to represent many missing countries and
coastlines, notably in Central America and West Africa. This will better support Sargassum management within
integrated coastline management across geopolitical boundaries. The spatial gaps in research likely contribute to
the lack of agreement on where the blooms emerge and the potential cycles and triggers.
Second, our analysis shows that most Sargassum publications have focused on longer-term regular
monitoring of specic locations and not addressed eventresponse effectively. To aid the production of
comparable research on Sargassum events, the notion of a Sargassum event needs to be more clearly dened.
Longer term records of Sargassum are needed to monitor temporal changes in frequency of events and quantities
landedboth of which are required to better understand how to reuse or manage the events. Research focussing
on inux and blooming events should generate a longer and more detailed temporal record. To address the lack
of a denition of a Sargassum event, we propose the following: A Sargassum eventis a continuous bloom of any
Sargassum in open oceans, or, an aggregation of landed Sargassum with the potential to disrupt local social,
economic or ecosystem functioning, or to impact human health. An event can affect one country, or several
contiguous countries.
Third, at present Sargassum species identication and reporting is not standardised, creating
incomparability issues in the Sargassum evidence base. Standard species identication should clarify which
species are dominant in different regions and enable determination of the variation of dominant species
seasonally and annually. Important questions need to be answered, such as do the mats in the tropical Atlantic
have the same species mix throughout the season or does it differ?Are different species dominant in different regions of
the Atlantic Ocean?Are mats of one type of species invading other coastal areas or restricted to one location? These
cannot be addressed if the species and morphotypes of Sargassum are not always recorded in publications.
Similarly, a robust and standardised method for estimating volume needs to be developed and implemented to
enable research gaps to be addressed and effective management strategies to be implemented.
Finally, there is a key research gap in understanding the nature and extent of the impact of Sargassum landing
on the socio-economic activities of the affected communities. Further research on short- and longer-term
impacts of Sargassum landing on coastal communities would be crucial to developing any Sargassum risk
mitigation strategy.
This publication is supported by Economic and Social Research Council GCRF (Grant number: ES/T002964/1),
a scholarship from Southampton Marine and Maritime Institure, University of Southampton, andthe School of
Geographyand Environmental Sciences, University of Southampton.
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... Since 2011, many Atlantic coasts have suffered recurrent, massive strandings of pelagic Sargassum species, with no apparent solution soon (Fidai et al. 2020). Huge amounts of biomass have been washed ashore, with a negative socioeconomic impact on tourism, fishing, and health (Smetacek and Zingone 2013). ...
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Sargassum C. Agardh is a highly diverse genus within the brown algae, with 615 currently recognized species, varieties and forms worldwide. This high level of species diversity led early taxonomists, using morphological-anatomical criteria only, to divide the genus into up to five sub-genera and several lower-ranking taxonomic units (e.g., sections, tribes). With the advent of molecular data, subsequent authors revised this complex and archaic classification, with the genus now comprising only two sub-genera: Sargassum and Bactrophycus. Whilst most Sargassum species are benthic, only two are known to be holopelagic and responsible for strandings along tropical Atlantic coasts. The rest of the genus is cosmopolitan, occurring from tropical to temperate regions. Sargassum has not yet been reported in polar regions. Where Sargassum is present, macroalgal populations can grow in large quantities, and the resulting biomass can be valuable to the local communities for a variety of uses. Here we review the genus Sargassum from a taxonomic, ecological and physiological perspectives, and explore the different ways of taking advantage of this extraordinary biomass, which while becoming an invasive pest in some countries, could represent opportunities for coastal populations worldwide.
... The marine macroalgal genus Sargassum is one of the most speciesrich genera among the brown macroalgae, encompassing over 350 recognized species (Guiry and Guiry, 2022). Most of the species are benthic and are attached via a holdfast; although some species, like S. horneri may form drifting masses that last for several months (Fidai et al., 2020). Only two truly holopelagic Sargassum species are described: S. natans and S. fluitans. ...
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The holopelagic brown macroalgae Sargassum natans and Sargassum fluitans form essential habitats for attached and mobile fauna which contributes to a unique biodiversity in the Atlantic Ocean. However, holopelagic Sargassum natans (genotype I & VIII) and Sargassum fluitans (genotype III) have begun forming large accumulations with subsequent strandings on the western coast of Africa, the Caribbean and northern Brazil, threatening local biodiversity of coastal ecosystems and triggering economic losses. Moreover, stranded masses of holopelagic Sargassum may introduce or facilitate growth of bacteria that are not normally abundant in coastal regions where Sargassum is washing ashore. Hitherto, it is not clear how the holopelagic Sargassum microbiome varies across its growing biogeographic range and what factors drive the microbial composition. We determined the microbiome associated with holopelagic Sargassum from the Great Atlantic Sargassum Belt to coastal stranding sites in Mexico and Florida. We characterized the Sargassum microbiome via amplicon sequencing of the 16S V4 region hypervariable region of the rRNA gene. The microbial community of holopelagic Sargassum was mainly composed of photo(hetero)trophs, organic matter degraders and potentially pathogenic bacteria from the Pseudomonadaceae, Rhodobacteraceae and Vibrionaceae. Sargassum genotypes S. natans I, S. natans VIII and S. fluitans III contained similar microbial families, but relative abundances and diversity varied. LEfSE analyses further indicated biomarker genera that were indicative of Sargassum S. natans I/VIII and S. fluitans III. The holopelagic Sargassum microbiome showed biogeographic patterning with high relative abundances of Vibrio spp., but additional work is required to determine whether that represents health risks in coastal environments. Our study informs coastal management policy, where the adverse sanitary effects of stranded Sargassum might impact the health of coastal ecosystems.
... In the south of Singapore, coral reef flats and crests along the Singapore Strait can be covered by up to 30 % in macroalgae, contributed mainly by the brown macroalga Sargassum (Low et al., 2019;Low & Chou, 2013). Sargassum is the largest canopy-forming alga in the tropics and subtropics, typically growing on rocky substrata or as floating aggregations (Fidai et al., 2020). Globally, Sargassum forests can have a high average biomass of 840.5 Mg ha − 1 (Gouvêa et al., 2020). ...
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The ability of vegetated coastal ecosystems to sequester high rates of “blue” carbon over millennial time scales has attracted the interest of national and international policy makers as a tool for climate change mitigation. Whereas focus on blue carbon conservation has been mostly on threatened rural seascapes, there is scope to consider blue carbon dynamics along highly fragmented and developed urban coastlines. The tropical city state of Singapore is used as a case study of urban blue carbon knowledge generation, how blue carbon changes over time with urban development, and how such knowledge can be integrated into urban planning alongside municipal and national climate change obligations. A systematic review of blue carbon studies in Singapore was used to support a qualitative review of Singapore’s blue carbon ecosystems, carbon budget, changes through time and urban planning and policy. Habitat loss across all blue carbon ecosystems is coarsely estimated to have resulted in the release of ∼12.6 million tonnes of carbon dioxide since the beginning of the 20th century. However, Singapore’s remaining blue carbon ecosystems still store an estimated 568,971 – 577,227 tonnes of carbon (equivalent to 2.1 million tonnes of carbon dioxide) nationally, with a small proportion of initial loss offset by habitat restoration. Carbon is now a key topic on the urban development and planning agenda, as well as nationally through Singapore’s contributions to the Paris Agreement. The experiences of Singapore show that coastal ecosystems and their blue carbon stocks can be successfully managed along an urban coastline, and can help inform blue carbon science and management along other rapidly urbanizing coastlines throughout the tropics.
... They can be cultivated in offshore marine farms, using no power, fresh water, chemicals, fertilizers or land resources. They can also occur as natural blooms in different parts of the world [13]. The global commercial seaweed market size is projected to reach in excess of USD $29 billion by 2 028 [14]. ...
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There is an urgent need to replace petroleum-based plastic with bio-based and biodegradable alternatives. Polyhydroxyalkanoates (PHAs) are attractive prospective replacements that exhibit desirable mechanical properties and are recyclable and biodegradable in terrestrial and marine environments. However, the production costs today still limit the economic sustainability of the PHA industry. Seaweed cultivation represents an opportunity for carbon capture, while also supplying a sustainable photosynthetic feedstock for PHA production. We mined existing gene and protein databases to identify bacteria able to grow and produce PHAs using seaweed-derived carbohydrates as substrates. There were no significant relationships between the genes involved in the deconstruction of algae polysaccharides and PHA production, with poor to negative correlations and diffused clustering suggesting evolutionary compartmentalism. We identified 2 987 bacterial candidates spanning 40 taxonomic families predominantly within Alphaproteobacteria, Gammaproteobacteria and Burkholderiales with enriched seaweed-degrading capacity that also harbour PHA synthesis potential. These included highly promising candidates with specialist and generalist specificities, including Alteromonas , Aquisphaera , Azotobacter , Bacillus , Caulobacter , Cellvibrionaceae , Duganella , Janthinobacterium , Massilia , Oxalobacteraceae , Parvularcula , Pirellulaceae , Pseudomonas , Rhizobacter , Rhodanobacter , Simiduia , Sphingobium , Sphingomonadaceae , Sphingomonas , Stieleria , Vibrio and Xanthomonas . In this enriched subset, the family-level densities of genes targeting green macroalgae polysaccharides were considerably higher ( n =231.6±68.5) than enzymes targeting brown ( n =65.34±13.12) and red ( n =30.5±10.72) polysaccharides. Within these organisms, an abundance of FabG genes was observed, suggesting that the fatty acid de novo synthesis pathway supplies (R)−3-hydroxyacyl-CoA or 3-hydroxybutyryl-CoA from core metabolic processes and is the predominant mechanism of PHA production in these organisms. Our results facilitate extending seaweed biomass valorization in the context of consolidated biorefining for the production of bioplastics.
... En las últimas décadas, las floraciones de macroalgas han aumentado en todo el mundo (Lapointe, 1997), lo que representa una gran amenaza para la salud pública, la salud de los ecosistemas, la pesca y el desarrollo económico (Anderson, 2007). Sin embargo, a nivel regional, la biomasa promedio llegada en los últimos años al Caribe ha sido 200 veces mayor a la documentada históricamente (Gower et al., 2013;Fidai et al., 2020). Durante la última década, grandes volúmenes han inundado las costas del Caribe, África occidental y N de Brasil. ...
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Article La retirada de restos vegetales de Sargassum spp. depositados sobre la playa emergida constituyen una parte de la limpieza de playas en el Caribe. Estas gestiones realizadas a lo largo de las últimas décadas han dado lugar a la pérdida de superficies y volúmenes de playa y dunas. El estudio analiza los volúmenes de sedimento retirados mediante la limpieza de Sargassum spp. en 12 playas de México y República Dominicana, cuantificando el volumen total en 18.987,3 m 3 , con un 61,23 % de sedimento intercalado, equivalente a 9.872,36 T de arena. Este tipo de ges-tión supone un impacto geomorfológico continuo con una importante pérdida de sedimento anual que afecta a la estabilidad del balance sedimentario del sistema playa. Palabras clave: Caribe, Sargassum spp., limpieza de playas, erosión. Loss of sediment associated with the removal of deposits of Sargassum spp. on the beaches of the Caribbean Part of the cleaning of beaches in the Caribbean islands involves the removal of Sargassum spp. that remains deposited on the emerged beach and dunes. The study analyses the volumes of sediment removed with the Sar-gassum spp. at 12 beaches in México and the Dominican Republic, quantifying the volume of material removed at 18,987.3 m 3 , of which an estimated 61.23 % (or 9,872.36 T) was sand. This kind of management involves a continuous geomorphological impact with an important loss of sediment that affects the stability of the sedimentary balance of the beach system. El turismo de sol y playa es la modalidad que mayores flujos genera a escala internacional y supone una importante aportación al producto interior bruto (PIB) en países denominados turísticos. En el Caribe, México y República Dominicana son unos de los principales destinos turísticos de este tipo con una aportación al PIB de 8,7 y 8,4 % respectivamente, y modelos turísticos basados en el producto turístico litoral. Para mantener una playa a largo plazo, el balance debe ser positivo, o al menos equilibrado, ya que los balances negativos en última instancia causan su erosión (Komar, 1999). La presión derivada de la industria turística ha hecho que muchos ambientes sedimentarios litorales se hayan visto gravemente afectados a lo largo de la costa. Los ambientes litorales de México y República Dominicana (Fig. 1) están some-tidos desde hace décadas a una problemática geoam-biental asociada a su uso y explotación (Peynador & Méndez-Sánchez, 2010; Roig-Munar et al., 2018; Guima-rais et al., 2021), pero en la última década presentan la llegada y varado masivo de sargazo, la gestión de su retirada generando impactos geoambientales con pérdida de superficie y volumen de playa. Una de las preocupaciones fundamentales nace inicialmente desde el sector turístico en la región del Caribe por la afectación que implican las grandes masas de sargazo Pérdida de sedimento asociada a la retirada de depósitos de Sargassum spp. en las playas del Caribe
... There are opportunities related to the implementation of sargassum anaerobic digestion on a large scale. In addition to their low BMP, sargassum blooms are seasonal and only arrive in the spring and summer months [84]. Consequently, the raw material source is limited or non-existent for the rest of the year. ...
Technical Report
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Resumen de aplicaciones y usos potenciales del sargazo en México.
... Sargassum, a genus of brown algae in the Sargassaceae family, is a seaweed commonly found in tropical and subtropical coastal areas, with more than 400 species distributed in almost all marine basins [1,2]. In particular, massive Sargassum biomass found from the Atlantic Ocean to the Caribbean Sea is called the Great Atlantic Sargassum Belt and is responsible for stranding numerous algae in coastal areas, causing severe environmental, ecological, and economic problems [3,4]. ...
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Seaweeds are receiving much attention as a rich source of bioactive compounds with cosmeceutical potential. Recent studies have revealed that Sargassum spp., a genus of brown algae in the family Sargassaceae, has multiple functions in preventing and improving skin aging. Sargassum spp. contains many bioactive compounds, such as fucoidan, fucoxanthin, terpenoids, flavonoids, and meroterpenoids. These Sargassum spp. extracts and derivative compounds have excellent potential for skincare, as they exhibit skin health-promoting properties, including antioxidants, anti-inflammation, whitening, skin barrier repair, and moisturizing. Therefore, searching for bioactive compounds in marine resources such as Sargassum spp. could be an attractive approach to preventing and improving skin aging. The current review focused on the various biological abilities of Sargassum extracts or derived compounds for anti-skin aging.
Seaweeds are important components of marine ecosystems and can form a large biomass in a few months. The decomposition of seaweed litter provides energy and material for primary producers and consumers and is an important link between material circulation and energy flow in the ecosystem. However, during the growth process, part of the seaweed is deposited on the sediment surface in the form of litter. Under the joint action of the environment and organisms, elements enriched in seaweed can be released back into the environment in a short time, causing pollution problems. The cultivation yield of seaweed worldwide reached 34.7 million tons in 2019, but the litter produced during the growth and harvest process has become a vital bottleneck that restricts the further improvement of production and sustainable development of the seaweed cultivation industry. Seaweed outbreaks worldwide occur frequently, producing a mass of litter and resulting in environmental pollution on coasts and economic losses, which have negative effects on coastal ecosystems. The objective of this review is to discuss the decomposition process and ecological environmental effects of seaweed litter from the aspects of the research progress on seaweed litter; the impact of seaweed litter on the environment; and its interaction with organisms. Understanding the decomposition process and environmental impact of seaweed litter can provide theoretical support for coastal environmental protection, seaweed resource conservation and sustainable development of the seaweed cultivation industry worldwide. This review suggests that in the process of large-scale seaweed cultivation and seaweed outbreaks, ageing or falling litter should be cleared in a timely manner, mature seaweed should be harvested in stages, and dried seaweed produced after harvest and washed up on shore should be handled properly to ensure the benefits of environmental protection provided by seaweed growth and sustainable seaweed resource development.
Many reviews referred to as ‘systematic reviews’ in ecology are not consistent with best practice in that they generally lack appropriate critical appraisal of included studies. This limitation is particularly important in applied ecology, where there have been increasing calls for more systematic reviews to guide decision making. To identify the available critical appraisal tools and hierarchies of evidence available for ecology studies, we systematically searched for: studies that described the development and/or examination of tools to assess the potential methodological bias in studies of ecology; and the tools used to assess potential methodological bias of included studies in ecological systematic reviews. We identified 680 reviews labelled as ‘systematic reviews’ in ecology, however only 4.0% performed critical appraisal of the included studies. Three hierarchies of evidence and 23 critical appraisal tools were identified, and assessed as lacking independent development, validity and reliability testing, and/or completeness. The authors of the reviews that included critical appraisal have appropriately identified the need to move reviews in ecology in the direction of this higher level of evidence, and have taken applied ecology further in the direction of evidence‐based practice. However, we identified shortcomings in these approaches when compared to best practice, and conclude that new tools are needed that reflect a range of questions posed in ecology. Through increasing the availability of such tools, the strength of evidence provided by systematic reviews in ecology would improve. This article is protected by copyright. All rights reserved.
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Atlantic Bonefish (Albula vulpes) are economically important due to their popularity with recreational anglers. In the State of Florida, USA, bonefish population numbers declined by approximately 60% between the 1990s and 2015. Habitat loss, water quality impairment, chemical inputs, and other anthropogenic factors have been implicated as causes, but the role of pathogens has been largely overlooked, especially with respect to viruses. We used a metagenomic approach to identify and quantify viruses in the blood of 103 A. vulpes sampled throughout their Western Atlantic range, including populations in Florida that have experienced population declines and populations in Belize, Mexico, Puerto Rico, and The Bahamas that have remained apparently stable. We identified four viruses, all of which are members of families known to infect marine fishes (Flaviviridae, Iflaviridae, Narnaviridae, and Nodaviridae), but all of which were previously undescribed. Bonefish from Florida and Mexico had higher viral richness (numbers of distinct viruses per individual fish) than fish sampled from other areas, and bonefish from the Upper Florida Keys had the highest prevalence of viral infection (proportion of positive fish) than fish sampled from any other location. Bonefish from Florida also had markedly higher viral loads than fish sampled from any other area, both for a novel narnavirus and for all viruses combined. Bonefish viruses may be indicators of environmentally driven physiological and immunological compromise, causes of ill health, or both. Supplementary information: The online version contains supplementary material available at 10.1007/s10641-022-01306-9.
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Massive strandings of the pelagic brown algae Sargassum have occurred in the Caribbean, and to a lesser extent, in western Africa, almost every year since 2011. These events have major environmental, health, and economic impacts in the affected countries. Once on the shore, Sargassum is mechanically harvested and disposed of in landfills. Existing commercial applications of other brown algae indicate that the pelagic Sargassum could constitute a valuable feedstock for potential valorisation. However, limited data on the composition of this Sargassum biomass was available to inform on possible application through pyrolysis or enzymatic fractionation of this feedstock. To fill this gap, we conducted a detailed comparative biochemical and elemental analysis of three pelagic Sargassum morphotypes identified so far as forming Atlantic blooms: Sargassum natans I (SnI), S. fluitans III (Sf), and S. natans VIII (SnVIII). Our results showed that SnVIII accumulated a lower quantity of metals and metalloids compared to SnI and Sf, but it contained higher amounts of phenolics and non-cellulosic polysaccharides. SnVIII also had more of the carbon storage compound mannitol. No differences in the content and composition of the cell wall polysaccharide alginate were identified among the three morphotypes. In addition, enzymatic saccharification of SnI produced more sugars compared to SnVIII and Sf. Due to high content of arsenic, the use of pelagic Sargassum is not recommended for nutritional purposes. In addition, low yields of alginate extracted from this biomass, compared with brown algae used for industrial production, limit its use as viable source of commercial alginates. Further work is needed to establish routes for future valorisation of pelagic Sargassum biomass.
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Since late 2014, the Mexican Caribbean coast has periodically received massive, atypical influxes of pelagic Sargassum spp. (sargasso). Negative impacts associated with these influxes include mortality of nearshore benthic flora and fauna, beach erosion, pollution, decreasing tourism and high management costs. To understand the dynamics of the sargasso influx, we used Landsat 8 imagery (from 2016 to mid-2020) to record the coverage of sargasso in the sea off the Mexican Caribbean coastline, with a maximum reported in September 2018. Satellite image analysis also showed local differences in the quantity of beached sargasso along the coastline. Over the years, good practice for collection on the beach and for offshore collection of sargasso have been established through trial and error, and the Mexican Government and hotel industry have spent millions of dollars on removal and offshore detention of sargasso. Notwithstanding, sargasso also has various properties that could be harnessed in local industries. The stimulation of local industrial growth would offer alternatives to the dependence on tourism, as a circular economy, based on sargasso, is developed.
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The Caribbean has been experiencing beach inundations of pelagic Sargassum, causing environmental, health and financial issues. This study showed variations in the composition and methane potential (MP) between the species of Sargassum. The MPs for S. natans VIII, S. natans I and S. fluitans (145, 66 and 113 mL CH4 g −1 Volatile Solids) were considerably below theoretical potentials, possibly due to the high levels of indigestible fibre and inhibitors. The mixed mats Sargassum composition was substantially different from the individual species, being higher in ash, calcium, iron, arsenic and phenolics. The mixed mats produced no methane, perhaps due to the high levels of phenolics. There was a strong correlation between MP and phenolic content. Heavy metals and metalloids were at levels that should not cause concern, except for arsenic (21-124 mg kg −1 dry weight). Further work on the speciation of arsenic in Sargassum is required to fully determine the risk to health and agriculture. Both protein and lipid levels were low. The 'indispensable amino acid' profile compares favourably with that recommended by the World Health Organisation. Lipids had a high proportion of Polyunsaturated Fatty Acids. The use of Sargassum for biogas production could be challenging, and further work is required.
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Starting in 2011, coastal areas of the Caribbean Sea and tropical Atlantic Ocean began to experience extraordinary yearly accumulations of pelagic Sargassum brown alga. Historical reports place large quantities of Sargassum only in the North Atlantic (mostly in the Gulf of Mexico and the Sargasso Sea). Accumulations of Sargassum in the tropical Atlantic have continued. We used a numerical particle-tracking system, wind and current reanalysis data, drifting buoy trajectories, and satellite imagery to determine the origin of the Sargassum that is now found persistently in the tropical Atlantic. Our analyses suggest that during the extreme negative phase of the winter 2009-2010 North Atlantic Oscillation (NAO), unusually strong and southward-shifted westerly winds explain the transport of Sargassum from the Sargasso Sea (∼20-40oN, 80-20oW) into the far eastern North Atlantic. Our hindcast Sargassum distributions agree with surface current simulations with the inclusion of “windage”. Windage is the additional, wind-induced drift of material floating at the free surface resulting from direct wind forcing on the sea surface, as well as on floating or partially-submerged objects. In our simulations, windage is included as an added vector (speed and direction) to the model-computed surface ocean currents equivalent to 1% of surface wind velocities. Lagrangian analysis of the regional circulation suggests that (1) part of the Sargassum subsequently drifted to the southwest in the North Equatorial Current (NEC) and entered the central tropical Atlantic, arriving in the Caribbean by the spring of 2011, with (2) another portion continuing southward along the coast of Africa in the Canary Current, eventually joining the seasonally-varying system of tropical Atlantic currents and thereby delivering a large Sargassum population to the tropical Atlantic. Since then, Sargassum patches aggregate from March to September in massive windrows along the Inter-Tropical Convergence Zone (ITCZ) under the action of converging winds. The windrows follow the ITCZ in its seasonal northward migration in the central tropical Atlantic. They are stretched across the central tropical Atlantic as the ITCZ crosses the latitude of the seasonal formation of the North Equatorial Counter Current (NECC). These patches and windrows are exposed to high sunlight and open-ocean upward flux of nutrients due to eddy and wind-driven mixing in the central tropical Atlantic. During the northern spring and summer, as the Sargassum drifts farther north with the ITCZ, large portions of the population are advected into the eastern Caribbean Sea. Some of these patches remain dispersed as the ITCZ migrates southward, and re-aggregate into new windrows as the ITCZ intensifies the following March-April. If wind mixing is strong and the mixed layer is deeper than about 50-60 m in the southern tropical Atlantic at this time, the Sargassum will bloom and form a massive windrow. Otherwise, the bloom will be inhibited. The extreme 2009-2010 NAO wind anomaly could be considered as triggering a biosphere “tipping point” that caused important ocean-scale ecosystem changes in the tropical Atlantic, with significant recurrent social and economic consequences. Understanding whether this new expanded geographic range of massive Sargassum blooms is temporary or whether it will revert to its pre-2009 distribution requires sustained monitoring and research.
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Since 2011, beach inundation of massive amounts of pelagic Sargassum algae has occurred around the Caribbean nations and islands. Previous studies have applied satellite ocean color to determine the origins of this phenomenon. These techniques, combined with complementary approaches, suggest that, rather than blooms originating in the Caribbean, they arrive from the Equatorial Atlantic. However, oceanographic context for these occurrences remains limited. Here, we present results from synthetic particle tracking experiments that characterize the interannual and seasonal dynamics of ocean currents and winds likely to influence the transport of Sargassum from the Equatorial Atlantic into the Caribbean Sea. Our findings suggest that Sargassum present in the western Equatorial Atlantic (west of longitude 50 W) has a high probability of entering the Caribbean Sea within a year's time. Transport routes include the Guiana Current, North Brazil Current Rings, and the North Equatorial Current north of the North Brazil Current Retroflection. The amount of Sargassum following each route varies seasonally. This has important implications for the amount of time it takes Sargassum to reach the Caribbean Sea. By weighting particle transport predictions with Sargassum concentrations at release sites in the western Equatorial Atlantic, our simulations explain close to 90% of the annual variation in observed Sargassum abundance entering the Caribbean Sea. Additionally, results from our numerical experiments are in good agreement with observations of variability in the timing of Sargassum movement from the Equatorial Atlantic to the Caribbean, and observations of the spatial extent of Sargassum occurrence throughout the Caribbean. However, this work also highlights some areas of uncertainty that should be examined, in particular the effect of "windage" and other surface transport processes on the movement of Sargassum. Our results provide a useful launching point to predict Sargassum beaching events along the Caribbean islands well in advance of their occurrence and, more generally, to understand the movement ecology of a floating ecosystem that is essential habitat to numerous marine species.
Since 2011, unusually large quantities of pelagic Sargassum fluitans and S. natans (sargasso) have been washing ashore along the coasts of some African countries and the Greater Caribbean, impacting ecosystems and economies. We estimated biomass and composition of sargasso arriving to a Mexican Caribbean coast from September 2016 until May 2020. In 2016, the beached masses comprised S. natans VIII and S. fluitans III. S. fluitans III was the predominant form throughout the study period, comprising on average > 60 % of total wet biomass. The relative abundance of S. natans VIII decreased in time from 2016 to 2019 (41 to 3 %), although it became prevalent again in the first months of 2020. The third morphological form, S. natans I, was not registered until February 2018, and its relative abundance increased from 23 % in 2018 to 31 % in 2019. The initial composition of Sargassum species and morphotypes of the beached sargasso in Mexico differed from that com- monly reported in the Sargasso Sea. The total biomass of beached sargasso varied considerably among years and seasons, with peaks during the summer months of 2018 and 2019. Seasonal variations in biomass were explained by 1) presence of sargasso in the Yucatan Current and 2) prevailing trade winds. This study is the first report on biomass and species composition of beached sargasso in the Western Caribbean and may help to understand patterns of the massive influxes; which will aid in the management of this new phenomenon.
In recent years pelagic Sargassum has invaded the coastlines of the Caribbean region, Gulf of Mexico, Florida and West Africa, triggering human health concerns and negatively impacting environmental and economic productivity. Sargassaceae are nutrient-dense and currently utilized as fertiliser and food, while extracts of their phytochemicals exhibit unique biosorption and medicinal properties. This macroalgae also shows biofuel potential but hitherto, methane recovery is low due to a carbon to nitrogen ratio below 20:1, the restricted bioavailability of structurally complex carbohydrates for degradation and high insoluble fibre, salt, polyphenol and sulfur content. To optimise the microbial bioconversion of this biomass, pre-treatment and co-fermentation with other substrates have been explored. This paper reviews the challenges associated with, and potential solutions for, Sargassum inundation, and provides a critical evaluation of its bioconversion to biogas and fertiliser using anaerobic digestion technology. As the Caribbean region is primarily impacted by drifting Sargassum blooms, the paper concludes with a case study on Barbados and investigates the feasibility of repurposing this brown macroalgae from landfill disposal to a feedstock for electricity and fertiliser production. The results of this study indicate that Sargassum mono-digestion is unsustainable for energy extraction given its low bioconversion efficiency and unpredictable influx volume. Alternatively, the co-digestion of these seaweeds with organic municipal solid waste is economically and energetically advantageous, potentially enhancing energy recovery by 5-fold. Notably, the hydrogen sulfide fraction of the biogas generated must be controlled given its corrosive properties and potential to effect co-generation engine damage and failure. Additional income can also be derived through the agricultural application of the digestate generated both locally and externally, following ammonia treatment and heavy metal stripping. Further research and pilot-scale studies are therefore necessary to support the utilisation of this marine biomass in commercial energy and fertiliser production.
Since 2011, tropical beaches from Africa to Brazil, Central America, and the Caribbean have been inundated by tons of sargassum seaweed from a new equatorial source of pelagic sargassum in the Atlantic. In recent years the extraordinary accumulations of sargassum make this a nuisance algal bloom for tropical coasts. In 2018 satellite data indicated floating mats of sargassum that extended throughout the Caribbean to the northeast coast of Brazil with the highest percent coverage over the water yet recorded. A literature review suggests that Atlantic equatorial recirculation of seaweed mats combined with nutrients from several possible sources may be stimulating the growth and accumulations of sargassum. In the western equatorial recirculation area, new nutrient sources may include Amazon River floods and hurricanes; in the eastern equatorial recirculation area, nutrient sources that could sustain the sargassum blooms include coastal upwelling and Congo River freshwater and nutrients.
The biggest bloom Floating mats of Sargassum seaweed in the center of the North Atlantic were first reported by Christopher Columbus in the 15th century. These mats, although abundant, have until recently been limited and discontinuous. However, Wang et al. report that, since 2011, the mats have increased in density and aerial extent to generate a 8850-kilometer-long belt that extends from West Africa to the Caribbean Sea and Gulf of Mexico (see the Perspective by Gower and King). This represents the world's largest macroalgal bloom. Such recurrent blooms may become the new normal. Science , this issue p. 83 ; see also p. 27