A B S T R A C T
Climate change and marine litter are inextricably linked, and their interaction manifests differently depending on
the specific environmental and biological characteristics, and other human activities taking place. The negative
impacts resulting from those synergistic interactions are threatening coastal and marine ecosystems and the
many goods and services they provide. This is particularly pervasive in the coastal zone of the   subcon-
tinent. India is already experiencing severe climate change impacts, which are projected to worsen in the future.
At the same time, the country is gripped by a litter crisis that is overwhelming authorities and communities and
hindering the country's sustainable development goals. The coastal environment and communities of the
southern states of Kerala and Tamil Nadu are particularly vulnerable to the impacts of climate change. While
these state governments and authorities are stepping up efforts to improve the management of their coastal
zones, the scale and severity of these issues are mounting. Here we review the combined effects of climate change
and marine litter pollution in Southern India, focusing on the Gulf of Mannar Reserve in Tamil Nadu and the Malabar Coast in Kerala. Finally, we discuss effective management options that could help improve resilience and
sustainability.

Science of the Total Environment 902 (2023) 166061
8the beach compared to the intertidal area (average 0.20 ± 0.13 items/
m2) (Kaviarasan et al., 2022). High abundances of microplastics were
also found between June and September at the Krishna River, followed
by the Penna River and off Chilika Lake, indicating the influence of
runoff during the southwest monsoon (Sambandam et al., 2022).
Offshore, microplastic pollution appears to be more severe and wide-
spread across the coral islands within the Gulf of Mannar, and this has
been traced back to highly populated areas on the mainland where waste
management is inadequate (Patterson et al., 2022). At Nallathanni Is-
land, a small, inhabited island in the Gulf of Mannar, beach debris
comprises fishing lines, floats, and nets; textiles; plastic bags; water
bottles; wrapping and packaging materials; cosmetic materials; and
resin pellets, deposited along the high tide mark by high-energy waves
and landward winds, although some lighter items were dispersed further
into the island, presumably carried by wind (Krishnakumar et al., 2018).
Proximity to the mainland determines the distribution of microplastics
on these coral islands, and abundance is consistently higher in sediment
samples compared to water samples, suggesting that the sediments act as
a sink for microplastics (Patterson et al., 2022). In the wider Bay of
Bengal, microplastic pollution has been reported as 5.3 × 104 particles
per km2 in coastal waters, and 209 ± 99 particles per kg of dry weight in
shelf sediments (Sambandam et al., 2022). Polyethylene and poly-
propylene appear as the most common polymer types, associated with
packaging and single-use plastics, and are more abundant in surface
water than in sediments. Microplastics can adsorb chemical pollutants
such as metals or pharmaceuticals, and transfer them along the food
chain, which represents an additional threat to marine life and requires
consideration when assessing the risk of microplastic pollution (Patter-
son et al., 2022; Godoy et al., 2019).
The Gulf of Mannar is one of India's four major coral reef areas,
where coral occurs mainly around a chain of twenty-one uninhabited
islands between Thoothukudi and Rameswaram (Raj et al., 2020). These
reefs are highly stressed and disturbed by climate change impacts and
local anthropogenic pressures (Painter et al., 2023; Edward et al., 2018),
with a significantly faster decline in the last decade, linked to thermal
stress (Krishnan et al., 2018), and compounded by hypoxia die-offs (Raj
et al., 2020), and outbreaks of disease and invasive species (Raj et al.,
2019; Edward et al., 2018; Raj et al., 2016). Between 2005 and 2017,
severe bleaching events resulted in coral mortality, particularly amongst
fast growing corals such as Acropora spp. and Pocillopora spp., and also
macroalgae proliferation under the influence of terrestrial runoff, which
hinders the settlement of new coral polyps and undermines reef recovery
(Raj et al., 2021; Raj et al., 2020; Edward et al., 2018; Purvaja et al.,
2018). Coral communities in the Gulf of Mannar are shifting as a result
and assemblages of sensitive species (typically structurally complex
corals) are replaced by more thermally-tolerant species (typically
simpler, massive corals) (Raj et al., 2021). In the future under an RCP8.5
high emissions scenario, the risk of annual severe coral bleaching in the
Gulf of Mannar is expected to increase, with an earlier onset for the
easternmost reefs (20 years sooner) compared to westernmost islands
(Raj et al., 2021). On the other hand, although records of coral mortality
due to hypoxia are rare worldwide (Raj et al., 2020; Gopakumar et al.,
2009), over the past few decades there have been an increasing number
of reports of mass coral mortality following non-toxic green tides of
Noctiluca scintillans in the Indian Ocean and specifically in the Gulf of
Mannar (Gomes et al., 2018; Gomes et al., 2014; D'Silva et al., 2012). In
2019, a massive N. scintillans green tide caused oxygen levels to drop
below 2 mg/l following bloom decay, and the temporary hypoxia
resulted in >70 % coral mortality amongst Acropora spp., Montipora
spp., and Pocillopora spp. corals, as well as die-offs of fish and benthic
crustaceans, molluscs, and echinoderms (Raj et al., 2020). Hypoxia af-
fects coral respiration and productivity (Nelson and Altieri, 2019), and
fast-growing species such as Acropora and Pocillopora are more suscep-
tible, due to their higher metabolic requirements (Blakeway, 2018;
Montoya-Maya, 2015; Haas et al., 2014). Hypoxia is also a risk multi-
plier for corals as it increases susceptibility to bleaching, disease, and
algal proliferation (Alderdice et al., 2020; Raj et al., 2020; Nelson and
Altieri, 2019), and therefore it is an issue of concern. Recurrent, massive
algal blooms have been linked to climate change (Griffith and Gobler,
2020), but red and green tides of Noctiluca can also be a manifestation of
water pollution and eutrophication (Harrison et al., 2011). Pollution,
and specifically marine litter, is another concern for the structurally
complex Acropora spp. corals that form the Gulf of Mannar reefs, which
are more prone to entangle debris (Ballesteros et al., 2018; Edward et al.,
2018). The reefs on the islands near Tuticorin are particularly at risk due
to high levels of litter from fishing, shipping, and waste disposal, all of
which is causing direct fragmentation of coral structures and aggra-
vating the risk of disease and susceptibility to bleaching and invasive
species (Lamb et al., 2018; Edward et al., 2018; Glas et al., 2012). In
addition, all reefs in southern India corals are at risk from cyclone
damage, as demonstrated by cyclone Ockhi, one of the strongest cy-
clones recorded in the region that hit the Lakshadweep Islands off the
Malabar Coast in 2017, causing extensive mortality and lithification
including dislodgment of massive structures in the deeper reef sections
(Painter et al., 2023; Riyas et al., 2020).
Healthy coastal mangrove stands are an effective natural barrier
against cyclone impact (Das and Vincent, 2009; IPCC, 2012). The dense
system of above-ground roots of mangroves that helps the trees survive
in waterlogged and tidal conditions also creates habitat for many species
and contributes to stabilising sediments and mitigating erosion by
buffering against waves, wind, and excess water during surges, flooding,
or storms, thus protecting coastal communities and infrastructure (IPCC,
2012). But this architectural complexity also facilitates the entangle-
ment and accumulation of debris (Sivadas et al., 2021). Mangrove for-
ests along the Indian coast are a documented plastic sink (Sivadas et al.,
2021), which is another risk factor to their survival. While mangroves
are relatively resilient to partial burial by waste, but excessive accu-
mulation of plastic material can create anoxic conditions, and the
affected trees may suffer suffocation and leaf loss (van Bijsterveldt et al.,
2021). In addition, in Tamil Nadu, the extent of coastal mangroves is
rapidly shrinking due to urban expansion and deforestation; it is esti-
mated that almost 4 km2 of mangrove cover were lost between the
forestry assessments of 2017 and 2019 (ISFR, 2019).
The North Indian Ocean is one of the busiest maritime traffic routes
in the world. The risk of maritime incidents and hazardous spills is
particularly high for sensitive marine areas such as Palk Bay and the Gulf
of Mannar Reserve. The sinking of the X-Press Pearl container ship in
May 2021, northwest of Colombo port, Sri Lanka, was the worst mari-
time disaster in the history of the Indian Ocean (UNEP and OCHA,
2021). It was estimated that 1600 t of plastic pellets were spilled, and
other environmental concerns included an oil slick leaking from the
ship, the potential spill of dangerous goods, the loss of cargo and debris
from the vessel, and a large smoke plume (UNEP and OCHA, 2021). The
disaster coincided with the southwest monsoon during heavy rain,
intense winds, and a rough swelled sea, making rescue and clean-up
operations difficult (UNEP and OCHA, 2021). The reversing
monsoonal winds and currents determine the dispersion of any spills in
this region. Following the X-Press Pearl disaster, models predicted that
the prevailing strong monsoonal wind-driven currents would transport
large quantities of the plastic nurdles towards the south of the Sri Lankan
coast, away from India (Karthik et al., 2022). Along the Tamil Nadu
coastline, southwest monsoon currents can reach velocities of 0.5–1.2
m/s and are largely directed eastward along Sri Lanka, until currents
weaken, turn around the south-eastern Sri Lankan coast, and change
direction towards the north (Karthik et al., 2022). However, as the post-
monsoon wind and currents reverse, any pellets still afloat would drift
towards India and the coastline of Tamil Nadu (Karthik et al., 2022). In
2017, the collision of two cargo ships near Chennai resulted in the spill
of about 196 t of residual fuel oil, which led to morphological changes
and declines of benthic foraminifera (Balachandar et al., 2023) and the
proliferation of hydrocarbon-degrading bacteria (Neethu et al., 2019).
S. Lincoln et al.
Science of the Total Environment 902 (2023) 166061
93.2.3. Interaction of climate change and marine pollution in the Malabar
Coast, Southwest India
Riverine influx plays an important role in the biogeochemistry and
high productivity of the Malabar Coast waters, along with the perma-
nent upwelling (Anandavelu et al., 2020; Jyothibabu et al., 2018) and
the seasonal inshore mudbanks (Samiksha et al., 2017). Of the 44 rivers
that traverse Kerala, 3 flow eastward, and the rest flow westward into
the Arabian Sea. The large volume of runoff from the Valapattanam,
Chaliyar, Periyar, Kayamkulam, Kallada, and Perumathura Rivers dur-
ing the summer monsoon rains enriches the inshore waters and flushes
out rich plankton communities from the estuaries, which largely control
the biological production along the entire west coast (Jyothibabu et al.,
2010). At Kerala and since the 1960s, average air and sea surface tem-
perature have both risen by over 0.5 ◦C (Valappil et al., 2022; Maz-
diyasni et al., 2017). Sea surface warming, as well as changes in rainfall
levels and in the timing and intensity of the upwelling, are likely
affecting fish populations, as evidenced by declining catches of some
pelagic fish like Indian oil sardines (Sardinella longiceps) and Indian
mackerel (Rastrelliger kanagurta), along with an increasing trend in
cephalopod landings (CMFRI, 2020). It has been suggested that the
distribution and abundance of sardines in Indian waters are shifting,
particularly along the Malabar Coast, while mackerel, typically associ-
ated with surface and subsurface waters, is moving deeper in search of
cooler water (Vivekanandan et al., 2008). Increasing temperatures,
changes in wind and wave circulation, extreme events, sea-level rise,
and declining levels of oxygen in seawater can all severely impact on
fisheries severely, and in multiple ways (Lehodey et al., 2006). However,
it is likely that these shifts in fisheries species is not a simple response to
climate change but are also the effect of other local pressures such as
overfishing, habitat destruction, eutrophication, and pollution, and even
the spread of non-native species (DoECC, 2022). A raise in the frequency
and intensity of massive phytoplankton blooms and red tides along
Kerala and inshore waters of India's west coast has been attributed to
increasing eutrophication and pollution from changes in land use
(Karthik et al., 2020; Robin et al., 2013a), but climate change is also a
contributing factor through rising temperatures as well as heavy rain
runoff (Ulloa et al., 2017). These mass blooms often result in red tides
that cause fish kills through oxygen depletion or toxicity (Robin et al.,
2013a; Madhu et al., 2011), and are reported to affect commercial fish
species such as oil sardines (Shaju et al., 2018). These colliding effects
affect not just the sustainability of the fisheries but also the lives of the
people who most directly depend on them. On the Malabar Coast in
particular, marine fisheries are the mainstay of many economically
disadvantaged communities (DoECC, 2022). Pollution issues and un-
hygienic conditions are prevalent around fishing harbours, landing
centres, and fish markets, and are compounded by the coastline's
exposure to climate change impacts (DoECC, 2022). Mudbanks are
another important seasonal feature along the Malabar Coast, known
locally as chakara (Samiksha et al., 2017). These mudbanks form during
the southwest monsoon (June–July) in the shallow coastal areas adja-
cent to estuaries (Samiksha et al., 2017) and dissipate during the
northeast monsoon. The banks are usually semi-circular in shape and
made of fine muddy sediments that create an important seasonal feeding
ground for demersal and pelagic fisheries (Jyothibabu et al., 2018;
Shyam et al., 2015). Near Kochi, the inshore mudbanks that accrete
every year from the discharge of about 20 billion m3 of backwater and
suspended sediments are crucial for the local fisheries (Madhupratap
et al., 2001; Rao et al., 2016). But these mudbanks also act as sinks for
marine litter (Mugilarasan et al., 2023), resulting in trophic transfer and
bioaccumulation of microplastics in benthic feeders and, crucially, in
many commercial fish (James et al., 2022). The appearance and dura-
tion of the mudbanks are determined by wave conditions during the
southwest monsoons, and intra-annual fluctuations have been observed
over the past forty years (Saprykina et al., 2021). The threshold aver-
aged monthly significant wave height for their formation is 2 m, but
wave height on the Malabar Coast is determined by wave climate
variability in the Arabian Sea, which in turns correlates with fluctuation
of large-scale oceanic and atmospheric systems such as the Indian Ocean
Dipole and ENSO (Saprykina et al., 2021). These interactions between
climate change and pollution pose a considerable risk to these com-
munities and by extention to Kerala, given the reliance of the state's
economy on local coastal fisheries.
Prolonged hot and dry weather is having a detrimental effect on
coastal mangroves, undermining their resilience to flooding and erosion
while increasing pressure on the other ecosystems supported by these
habitats (van Hespen et al., 2023; Soares et al., 2021). For example,
mangroves are important for maintaining the health of nearshore coral
reefs (Biju Kumar et al., 2017). Kerala receives about 70 % of its annual
rainfall during the southwest monsoon (Nair et al., 2021). Analyses of
historic rainfall over Kerala indicate cyclic trends in annual rainfall, but
also a long-term trend of decreasing monsoon rainfall against increasing
post-monsoon rainfall during the period 1871–2005 (Nair et al., 2014).
The frequency of dry years has also increased since 1976 (Thomas and
Prasannakumar, 2016). These changes in rainfall patterns, already
under pressure from pollution and changes in land use, are accelerating
the decline of coastal mangroves, resulting in instability in the sediments
and the capacity of soils to hold onto water and organic matter, releasing
further CO2 into the atmosphere (Santos-Andrade et al., 2021). Indeed,
mangroves play an important role in climate change mitigation through
their ability to store carbon (Biju Kumar et al., 2017). Droughts and heat
waves can also affect coastal water quality through the desiccation of
vegetated coastal habitats (Lovelock and Reef, 2020; Choudhury et al.,
2021). Heavy precipitation over deforested and desiccated wetlands that
have lost their water-holding capacity can lead to widespread uncon-
trolled flooding and excess surface water runoff, carrying excess debris
directly onto coastal regions. According to the IPCC (2022), sea-level
rise in this region is anticipated to reach 0.3–0.5 m or higher by 2100,
further increasing the risk of inundation for much of Kerala's low-lying
coastline and the backwater plains beyond (DoECC, 2022). Sea-level
rise and changes in rainfall resulting in varying inputs of freshwater
and sediment loading from rivers and lakes are also of concern to coastal
mangrove forests (Sreelekshmi et al., 2021). To keep pace with rising sea
levels, mangrove forests need to either accrete enough fresh sediment
loading from land runoff sources or be allowed to retreat landwards
(Biju Kumar et al., 2017; Kintisch, 2013). Climate change will likely
exacerbate the decline of mangroves, already under pressure from
coastal squeeze, pollution, and deforestation (Sreelekshmi et al., 2021).
In Kerala, there are concerns that rapid population growth is driving
unregulated sand mining, land reclamation, and the construction of hard
coastal defences, and resulting in the accelerating loss of mangroves and
other coastal wetlands (Biju Kumar et al., 2017). The loss of coastal
mangroves will further increase the risk of coastal erosion and inunda-
tion, increasing the risk to infrastructure assets and to vulnerable fishing
communities (Biju Kumar et al., 2017). Degradation and loss of coastal
mangroves will also have direct adverse cascading effects on fisheries
stocks, as many invertebrates and fish species depend on mangrove
habitats for their early life stages (Friess et al., 2016).
Droughts and heat waves can also have negative consequences for
aquaculture production (Froehlich et al., 2022; Soares et al., 2021), and
pose an inherent human health risk as those conditions encourage the
prevalence of pathogens and foodborne diseases (Jennings et al., 2016;
Morley and Lewis, 2014). Disease outbreaks are not confined to seafood
production but also pose a serious risk to bathers using contaminated
waters (Baker-Austin et al., 2017; Young et al., 2015). Extreme droughts
and heat waves can also amplify the negative impact of extreme rainfall
when it arrives, due to the sudden flushing of accumulated pollutants,
solid litter, sediments, and pathogens, into watercourses (Mishra et al.,
2021; Corbari et al., 2016; De Carlo et al., 2007; Bay et al., 2003). During
the 2018 and 2019 floods in Kerala, particularly at Thottappally in the
Alapuzha district, heavy rain accumulated in waterways clogged with
litter, which resulted in extensive flooding into neighbouring areas
(Robin et al., 2020). Incidentally, as heat waves become more pervasive,
S. Lincoln et al.
Science of the Total Environment 902 (2023) 166061
10they may encourage higher demand for bottled water, potentially
resulting in additional littering (Zapata, 2021).
In India, beach uses involving tourism and traditional activities can
be sources of marine litter (Kaladharan et al., 2017). Most beaches in
Kerala serve as landing and fishing centres, with varying degrees of
activity depending on the season and the dominant vessel operation,
from traditional, non-motorised single-day vessels to larger, multi-day
powered fishing vessels, which then dictates the craft and gear (Daniel
et al., 2020b). Generally, fishing-related debris is almost 4 times higher
at the height of the pre-monsoon fishing season, compared to the low
fishing season (Daniel et al., 2020b), while larger and heavier debris
items are deposited as wrack on the shoreline by the higher-energy
waves typical of the post-monsoon (Jayasiri et al., 2013; Daniel et al.,
2020b). The accumulation of plastics on beaches can alter sediments
properties, raising the internal temperature by 2.45 ◦C by day and
retaining more heat at night, as plastics act as an insulating agent (La-
vers et al., 2021). This can induce changes in the abundance and di-
versity of meiofauna such as crabs, and it has also been highlighted as a
concern at turtle rookeries, as it can increase the risk of breeding failure
and hatchling feminisation (Lavers et al., 2021). Other potential indirect
effects include increased exposure to chemicals, microbes, and invasive
species (Audr´ezet et al., 2021; Lavers et al., 2021).
The extent of microplastic pollution in the marine environment has
not yet been fully quantified (Robin et al., 2020). Data from the North-
East Atlantic supports that plastic items in the marine environment are
identified as either oceanic transboundary litter, effluent waste, indus-
trial waste, or vessel waste, and that microplastics near coasts and es-
tuaries likely originate locally from the disintegration, abrasion, or
weathering of larger items (Maes et al., 2017). In Southern India, the
high abundance of microplastics is attributed to flood plumes trans-
ported by the dominant longshore southward current during the
monsoon months (Robin et al., 2020; Faure et al., 2015; Nair et al.,
2015b). A study of microplastics in Kerala indicated average values of
1.3 particles per m3 in coastal waters and 41 particles per m2 in beach
sediments, with the abundance of microplastic in sediments increasing
towards the south (Mugilarasan et al., 2023, 2021; Robin et al., 2020;
Kaladharan et al., 2017). The values of microplastics in coastal water
samples are similar to those reported from the Baltic Sea (Gewert et al.,
2017), but higher than records from the Bohai Sea, China (Zhang et al.,
2017). Similar values of 47 particles/m2 have been reported for Tamil
Nadu beaches (Karthik et al., 2018), which are in the same range as
other values reported for the Gulf of Mexico (Wessel et al., 2016), but
higher than Malta, the Central Mediterranean (Turner and Holmes,
2015), and the coast of Portugal (Martins and Sobral, 2011). Along the
Malabar Coast, the abundance of microplastics correlated spatially with
river runoff levels and proximity to urban areas (Robin et al., 2020).
State figures estimate that over 3500 t of solid waste are produced daily,
of which <1000 t per day are collected (CPCB, 2021). As most industry is
located near the coastline and on riverbanks, backwaters and rivers act
as conduits for industrial waste and sewage treatment effluents. Even-
tually, most of the waste reaches the coast, in addition to an estimated
300 million litres per day of untreated rural and municipal wastewater
(Robin et al., 2020; Kaithery and Karunakaran, 2019). Out of the frag-
ments of solid litter, fibres and lines are mostly derived from vessels and
fishing (Andrady, 2011), although they also indicate possible sewage
sources (Browne et al., 2011), particularly near shore (Cozar et al.,
2014), while foam and film originate from packaging materials (Robin
et al., 2020). Microplastics in beach sediments and coastal waters are
likely washed ashore by surface residual currents and winds, because of
their lower particle density (Robin et al., 2020; Isobe et al., 2014).
Fish interact with and ingest microplastics due to their close
resemblance to natural prey (Jovanovic, 2017). Over 21 % of the fish
sampled from major landing centres in Kerala were shown to contain
microplastics in their digestive tracts, with the highest occurrence of
microplastic found on bottom-dwelling species that feed primarily on
benthic organisms, which is attributed to the continuous supply of land-
based plastic materials from rivers and backwaters to coastal waters,
predominantly linked to fishing-derived debris (Robin et al., 2020).
These values of microplastics in fish guts are higher than other reports
from Southeast India (Karthik et al., 2018) and northeast Brazil (Pos-
satto et al., 2011), although lower than values from the English Channel
(Lusher et al., 2013). Kerala is India's second-largest marine fish-
producing state, and the beaches both generate and receive high
amounts of fishing-derived debris (Robin et al., 2020). The coastal areas
surrounding the industrial belt at Kochi also receive heavy metals from
untreated effluent discharges, and the presence of Cd, Cr, Hg, Fe, Sb, Ti,
Zn, and Pb has been confirmed associated with polymer particles,
highlighting the additional risk of chemical contamination and trophic
transfer associated to microplastics (Robin et al., 2020). Analyses of
samples of Indian white shrimp, Fenneropenaeus indicus, from Kochi have
demonstrated content of microplastic fibres (83 %) that increased dur-
ing and following the monsoon (Daniel et al., 2020a). Kochi is a densely
populated city, an important touristic destination, and includes one of
the five major fishing harbours in India as well as a major port, and an
international container terminal on the bank of the estuary (Daniel et al.,
2020a). The coastal area is highly susceptible to pollution from the large
river plumes following heavy monsoon rains, compounded with inap-
propriate waste disposal systems and intense fishing (Naidu et al., 2018;
Daniel et al., 2020a). The Kochi estuary discharges a large quantity of
debris during the summer monsoon, including plastic particles (Seena
et al., 2019). The high input of microplastics into the coastal waters
makes them bioavailable to benthic organisms, including shrimp (Daniel
et al., 2020a). F. indicus is a major commercial fishery associated with
inshore muddy substrates (Daniel et al., 2020a). Seasonal differences in
the microplastic concentration found in shrimp have been linked to
physiological life-cycle changes such as spawning (Baechler et al., 2020;
Devriese et al., 2015). Exposure to weathered polyethylene particles on
another species commonly farmed in India, the whiteleg shrimp, Penaeus
vannamei, has been shown to inhibit growth (Hariharan et al., 2022).
Ingestion of polyethylene particles affected the oxidative and antioxi-
dant systems, although no effects on survival have yet been confirmed
(Hariharan et al., 2022). A similar study on edible green mussels, Perna
viridis, showed significant accumulation in intestine tissue, suggesting
that chronic exposure to weathered polyethylene particles can have
damaging effects through oxidative injury and reduced filtering activity,
ultimately leading to starvation (Hariharan et al., 2021). Ultimately, the
exposure of commercial marine fish and invertebrates to microplastic
pollution represents a human health risk (Daniel et al., 2020a).
3.3. Summary of key issues
The main findings regarding the interactions between climate
change and marine pollution in the Gulf of Mannar are summarised in
Table 1.
The main interactions between climate change and marine pollution
on the Malabar Coast are summarised in Table 2.
4. Discussion
The synergistic impacts of climate change and marine litter are an
increasing threat to the marine environment and the many goods and
services on which societies and economies depend (Ford et al., 2022;
Lincoln et al., 2022). These two global emergencies are ubiquitous, but
their combined effects depend on characteristics of the physical envi-
ronment, types of habitats and biological communities, and pressures
from other human activities (Lincoln et al., 2022). Despite their signif-
icance and their pervasive effects, the linkages between climate change
and marine litter remain understudied, and it is crucial that we improve
our understanding in order to manage their combined impacts. The
urgency of this issue is not unique to extensive and populated countries
such as India, but it would also be vitally important to other regions,
such as small oceanic islands for instance, where managing the
S. Lincoln et al.
Science of the Total Environment 902 (2023) 166061
11combined risk of climate change and transboundary oceanic litter would
be key to enabling long-lasting protection of highly sensitive and rare
species and habitats (Kiruba-Sankar et al., 2023; Lincoln et al., 2022).
The coastal zone of the Indian subcontinent is experiencing severe
impacts of climate change, which are projected to worsen and accelerate
into the future, and at the same time, the country is gripped by a litter
crisis that is overwhelming authorities and communities and hindering
the country's sustainable development. We aimed to assess such linkages
in Southern India by reviewing the evidence of the combined impacts of
climate change and marine pollution in the Gulf of Mannar Reserve and
the Malabar Coast.
Our findings highlight how climate change and marine pollution act
as threat multipliers, for example through the interaction of litter and
extreme weather, where land-based litter accumulates in waterways and
is mobilised by heavy rain and flushed out into coastal areas together
with other pollutants and runoff. In India, poor drainage systems often
become blocked during heavy rainfall events due to the accumulation of
litter and debris (IPCC, 2012; Ranger et al., 2011), and this can result in
debris flows and worsen flood-associated damage (Honingh et al., 2020;
Kundzewicz et al., 2014). Plastic materials gathered by debris flows lead
to larger blockages in watersheds, further raising backwater flood levels
and exacerbating the environmental and public health risks (Honingh
et al., 2020; Kundzewicz et al., 2014). In Kerala and Tamil Nadu, coastal
locations attract millions of visitors every year, and this mass tourism
contributes to large-scale littering, as well as forest fires and soil erosion
(Gandhi et al., 2021; Robin et al., 2020). Studies of extreme weather
such as cyclones and cyclone-induced flash floods in these states suggest
that most of the recognisable coastal debris is from local inputs or is
mobilised through waterways from further inland, as opposed to long-
distance transboundary litter (Gandhi et al., 2021; Veerasingam et al.,
2016). Even cyclonic overwash deposits on beaches have been traced
back to nearby rivers and urban areas and to local activities (Gandhi
et al., 2021; Lo et al., 2020), which confirms that the majority of the
coastal litter is of local origin and also offers an opportunity for imple-
menting or improving control measures.
Once adrift in the ocean, litter becomes nearly impossible to elimi-
nate or control. Plastics can persist at sea for hundreds of years (Bra-
tovcic, 2021) and, depending on buoyancy, their transport is regulated
by tides, currents, waves, and wind (UNEP, 2021). In coastal areas, tides
also interact with shoreline topography to move litter onshore and
offshore, as debris floats, sinks, or breaks up depending on density, size,
and shape, as well as chemical composition (UNEP, 2021). Abrasion and
fragmentation into smaller particles mostly occurs once debris is
deposited onshore, and the smaller the particle size, the more likely the
transfer across trophic levels unless they become trapped within marine
sediments long-term (UNEP, 2021). Either pathway represents a range
of potential negative impacts on marine organisms, ecosystems, and
ecosystem services (Ajith et al., 2020), and even poses a risk to human
health (Bhattacharya and Khare, 2022; Campanale et al., 2020; Robin
et al., 2020).
Table 1
Summary of fundamental climate change and marine litter issues in the Gulf of Mannar, Tamil Nadu.
Key issues Description
Extreme sea levels, coastal erosion, and
inundation
Ongoing coastal erosion is increasing the risk of coastal inundation from future sea-level rise. Coastal habitats are also subject to degradation
from mining, deforestation, and the disposal of waste and untreated effluents.
Marine litter and extreme weather Plastic pollution is severe and widespread across the coral islands in the Gulf of Mannar. Several hundred tonnes of waste generated daily are
either uncollected or inappropriately disposed of. Rainfall and flooding flush large amounts of litter and other contaminants onto coastal
areas, particularly following cyclones, although at tourist beaches most of the litter is local, deposited by visitors and other users.
Coral reefs Coral reefs are significantly disturbed by climate change impacts and other local anthropogenic pressures, manifested as severe bleaching,
coral disease, predation, and macroalgae growth. Depending on the emissions scenario, severe coral bleaching events will likely recur every
year, changing reef composition and structure. The reefs are also exposed to mortality from hypoxia caused by algal blooms, cyclone damage,
and high quantities of litter from fishing, waste disposal, and shipping, particularly around the islands.
Coastal mangroves The mangroves in Tamil Nadu are in decline, exposing the coastline to extreme weather impacts. Mangroves accumulate debris, which in
large quantities can cause suffocation and leaf loss.
Maritime spill risk Shipping activity in the North Indian Ocean represents a risk of hazardous spills. Weather and sea conditions can make rescue and clean-up
operations difficult during the monsoon season. The seasonal wind and current patterns would disperse the spill either towards the coast or
away, towards Sri Lanka and into the Bay of Bengal.
Table 2
Summary of fundamental climate change and marine litter issues on the Malabar Coast, Kerala.
Key issues Description
Fishing Observed shifts in fish distribution are linked to changes in sea temperature, upwelling, and rainfall. Catches of some traditional commercial species
are declining, although these changes are also likely linked to overfishing, habitat destruction, pollution, and the spread of invasive species. These
issues put the sustainability of fisheries at risk, which are the mainstay for millions of people, particularly in exposed and disadvantaged coastal areas
where poor conditions are prevalent. Fishing beaches are also a significant source of debris, depending on the fishing season and the predominant
vessel type, craft, and gear.
River plumes and mudbanks The productivity of the Malabar Coast depends on nutrient enrichment through monsoon runoff and upwelling. Mudbanks are also a major seasonal
biologically productive feature that forms during the southwest monsoon in shallow areas, which are crucial for maintaining local fisheries, but also
act as sinks for microplastics. Mudbank fluctuations have been linked to wave variability in the Arabian Sea.
Rainfall, droughts, and heat
waves
The timing and rainfall levels of monsoons are changing with earlier onset and declining precipitation, while post-monsoon rainfall is increasing.
Overall, dry years are becoming more common. Droughts and heat waves can accelerate deforestation and desiccation of wetlands and aggravate
coastal water quality. They also increase the risk of pathogens and disease. Extreme droughts can also amplify the damaging impacts of heavy rainfall
events when they arrive, leading to debris flows and flash floods. Incidentally, they also increase the consumption of bottled water and contribute to
additional plastic littering.
Coastal mangroves Sea-level rise, and varying rainfall and sediment loading driven by climate change are accelerating the decline of mangroves, already at risk from
destruction and coastal squeeze, resulting in increased coastal erosion and inundation. In addition, the loss of mangroves results in additional negative
effects on fisheries, and it leads to carbon dioxide emissions due to disturbance of the sediment layer and the loss of blue carbon storage capacity, an
important climate change mitigation service.
Microplastic pollution Microplastic pollution correlates spatially with major urban areas and with runoff levels from rivers. Sources of plastic pollution include untreated
effluents, food packaging, tourism, shipping, and fishing activities. Microplastics have been found in fish and shrimp gut contents at landing centres in
Kerala, along with traces of heavy metals associated with the plastic fragments. Plastic accumulation in sediments has a variety of negative effects on
marine fauna and provides incidental habitat for invasive species.
S. Lincoln et al.
Science of the Total Environment 902 (2023) 166061
124.1. Integrated Coastal Zone Management
It is widely recognised across the world's countries that climate
change and marine pollution are serious threats to environment and
people, and India is no exception. Relevant policies and plans are
already in place, at the national and sub-national levels. At a national
level, a Coastal Regulation Zone notification was issued in 1991 by the
Ministry of Environment and Forests of the Government of India, to
protect the livelihood of coastal communities, and conserve the coastal
areas from hazards, including sea-level rise, and to restrict the expansion
of industrial areas and the disposal of hazardous waste in the coastal
zone (Parthasarathy and Natesan, 2015). But this notification is not fully
operational, and coastal areas across India remain under severe stress
from illegal mining, waste disposal, and the discharge of untreated ef-
fluents (Parthasarathy and Natesan, 2015). In Kerala, a State Action Plan
on Climate Change (SAPCC) is built into policy to integrate programs at
both state and national levels, such as the National Action Plan on
Climate Change of India. Amongst other key adaptation and mitigation
actions directly related to energy use, disaster response, etc., the SAPCC
targets other compounding pressures, for example, through better waste
management, pollution abatement, and enhancement and restoration of
vegetated environments. Litter management practices include reduction
at the source, mitigation, beach management, and behavioural change
through education (Mugilarasan et al., 2021). In Tamil Nadu, a Coastal
Zone Management Plan was developed in consultation with relevant
authorities, stakeholders, local communities, and non-government or-
ganizations and entrusted to the National Centre for Sustainable Coastal
Management (NCSCM) in Chennai in 2011 (DoE, 2023b). In 2014, the
Tamil Nadu Climate Change Cell was also established, to focus on
climate change-related initiatives and activities, build capacity, create
awareness, and to collate and disseminate climate change information to
enable effective governance and services. A National Adaptation Fund
for Climate Change also manages and rehabilitates coastal habitats and
biodiversity (DoE, 2023a). However, there is still a need to improve the
enforcement of urban development regulations, waste management,
forestry management, and extracting industries such as sand mining
(DoECC, 2022), particularly where activities occur across the coastal
boundary and involve connected catchment areas. For example, along
the Malabar Coast, mangrove deforestation is exposing coastal villages
to a higher risk of impact from extreme weather and is contributing to
the depletion of Kerala's fisheries, which compounds with unsustainable
inshore fishing practices that continue unchecked due to a lack of
enforcement (DoE, 2009), while mass reclamation of land for agriculture
and urbanization is also resulting in a widespread loss of backwaters and
floodplains in the state (Robin et al., 2013b; DoE, 2009; Balachandran
et al., 2008), worsening the effects of soil erosion and flooding.
When fully implemented, Integrated Coastal Zone Management
(ICZM) approaches provide a decision-making framework that can be
tailored to the unique characteristics and needs of a particular coastal
environment. An ICZM pulls together all the complex functions and
dynamic interactions that characterise the coastal environment, as well
as the services and resources provided, and involves the participation of
key stakeholders. Some of the geospatial tools that can be used to sup-
port decision-making, management, and planning of coastal zones
include risk maps, built using data layers based on, for example, sensi-
tive habitats and marine protected areas; climate change projections;
litter source points (e.g., coastal landfill sites and open waste dumps);
high flood-and erosion-risk areas; touristic spots; beaches; ports and
harbours; and, fishing grounds. There are litter pollution control options
that can be adapted for coastal communities, which typically include a
suite of measures such as: bans of single-use plastic items and promotion
of sustainable alternatives; circular economy approaches; improvements
to waste management practices, including recycling drop-off locations,
deposit-refund schemes, and processing of recyclable materials; active
recovery of plastic materials from waterways; reviews of policies and
regulations; and public awareness and engagement. These measures can
effectively reduce marine litter inputs at the source, improve marine
ecosystems' health, and create economic opportunities for coastal
communities. For example, the Tamil Nadu government has installed
debris barrier devices (also known as debris “booms”) in urban rivers
such as the Cooum and Adyar. Surf rakes and similar beach cleaning
devices are also used to collect litter from Marina Beach. Similarly, the
Kerala government initiated “Suchithwa Sagaram”, a pilot effort to
eliminate marine litter that encourages fishermen to return fishing litter,
which can be upcycled and transformed into higher-value, usable items.
4.2. Other management approaches
In addition to ICZM, there are other recommended approaches to
tackle the cumulative impacts of climate change and marine litter (or
other local pressures) in large-scale coastal and marine areas.
Marine strategy directives are one example. A marine strategy
directive, typically adopted by countries or administrations that share
the same marine region, such as the European Union Marine Strategy
Framework Directive, operates by mandate, by requiring the signatory
member states to achieve a set environmental status in a cooperative
manner and by using sets of agreed descriptors and indicators (MSFD,
2008). A marine strategy aims to tackle the intertwining pressures and
impacts on the marine environment derived from human activities
taking place at sea and on land, including those from climate change.
Underpinning a marine strategy, climate resilience frameworks can be
used to tackle specific climate change impacts on society, the economy,
and the environment at a national level, by developing and imple-
menting targeted measures to minimize the adverse effects of climate
change “on the ground”, as well as taking advantage of opportunities for
adaptation and mitigation.
The IPCC defines risk as the potential for future negative impacts
induced by the interaction of social and ecological systems, and the
vulnerability to physical hazards and exposure variables (Cardona et al.,
2012). Measures to mitigate or avoid any of the factors of risk – hazard,
exposure, and vulnerability – may help to control these risks and build
ecosystem resilience (Cardona et al., 2012). The control and mitigation
of other synergistic stressors, such as pollution, are key components of a
climate resilience framework (Fig. 4). Thus, climate resilience frame-
works can be used to support communities and governments to better
adapt and respond to the impacts of climate change and other co-
stressors, while reducing vulnerability, and building resilience. Coor-
dination and cooperation between the departments, sectors, and states
that share a marine space are vital to ensuring sustainable management
of resources and effective management of risks and impacts. In the case
of Kerala and Tamil Nadu states, and indeed India, this could be ach-
ieved through an overarching marine strategy that facilitates the inte-
gration of policies at a high level and defines appropriate descriptors and
indicators that can then be applied to, for example, assessments, moni-
toring, and interventions as part of a climate resilience framework.
A climate resilience framework typically includes the following
elements:
- Risk and vulnerability assessments: This involves identifying climate
change risks, as well as risks from other co-stressors such as pollu-
tion, and scoring and prioritising them by quantifying the magnitude
and the urgency of their potential impacts on sectors, systems, and
populations. It can also involve quantifying the overall confidence in
those assessments depending on available evidence and expert
agreement.
- Adaptation and mitigation strategies: This involves developing strate-
gies and measures to minimize the impacts of climate change and
other synergistic pressures, taking advantage of opportunities for
adaptation and mitigation. Examples of adaptation strategies can
include: improving building codes; sustainable management of ma-
rine fisheries; catchment area management; and enhancement of
natural coastal buffer and protection habitats. Examples of
S. Lincoln et al.
Science of the Total Environment 902 (2023) 166061
13mitigation strategies include de-carbonisation of sectors and activ-
ities, and protection of natural blue carbon habitats such as coastal
mangrove forests.
- Policy and institutional frameworks: These involve policies and insti-
tutional schemes that support climate-smart regulations, incentives,
and financial mechanisms. It may also involve building partnerships
and collaborations between governments, non-governmental orga-
nizations, and other stakeholders.
- Adaptive frameworks: To be effective and resource-efficient, it is
advisable that frameworks have built-in monitoring, self-evaluation,
self-learnt, and evidence gathering processes.
Climate resilience frameworks require a collaborative and interdis-
ciplinary approach with the active participation of governments and
local authorities, industry and the private sector, communities, re-
searchers, and individuals. Following prioritisation, actions and in-
terventions can then be implemented for climate adaptation and
mitigation, and to effectively regulate human activities, and to reduce
stress on the environment such as marine pollution (Maynard et al.,
2017). Examples of actions and interventions range from improvements
of waste management processes and facilities, tax incentives, and
habitat restoration, to outreach and education encouraging positive
behavioural and lifestyle changes (Mugilarasan et al., 2023). In a related
issue, during the COVID-19 pandemic in India, as in many other coun-
tries, there was a sharp increase in biomedical waste and personal
protective equipment items made of polymeric material (Robin et al.,
2021; Schnurr et al., 2018; Fadare and Okoffo, 2020). In Tamil Nadu's
state capital, Chennai, the pandemic is estimated to have generated 47 t
of biomedical waste daily (The Hindu, 2020). The surge in plastic waste
was amongst the worst environmental consequences of the pandemic,
and it has been recommended that India should develop plastic pollution
management strategies that consider both climate change and pan-
demics (Sivadas et al., 2022). In addition, restrictions imposed on ac-
tivities such as fishing and tourism in Tamil Nadu were perceived to
have a “positive” environmental effect and emphasize the importance of
applying ecosystem-based approaches to enhance and safeguard the
sustainability of ecosystem services and the wellbeing of communities
against risks such as pollution and natural disasters (Robin et al., 2021).
Further research and monitoring can continue to address knowledge
gaps, which can progress in parallel, while effective actions and in-
terventions are implemented.
Despite the high profile of the environmental emergency of marine
litter, including microplastics, a sharper focus in global frameworks such
as the Sustainable Development Goals (SDGs) (Walker, 2021) is still
required. The UN proposed 17 SDGs and 169 targets to be achieved by
2030, and amongst those, the issue of marine (micro)plastics has been
recognised under Goal 14, which is to: Conserve and sustainably use the
oceans, seas and marine resources for sustainable development (Walker,
2021). Specifically, target 14.1 says: By 2025, prevent and significantly
reduce marine pollution of all kinds, in particular from land-based activities,
including marine debris and nutrient pollution, which is to be measured by
indicator 14.1.1: Index of coastal eutrophication and floating plastic debris
density (Walker, 2021). Governments and corporations have widely
adopted the SDGs to improve their sustainability, and the international
community understands that reducing floating plastic debris is central to
the sustainable use of the oceans (Walker, 2021). However, currently
there is no internationally accepted index of floating plastics debris
density, which presents challenges for governments and organizations,
exacerbated by the pervasive nature of (micro)plastic pollution as long
as it is not properly monitored (Walker, 2021).
Fig. 4. Schematic representation of the key components of a climate resilience framework.
Image credited to ©NCSCM.
S. Lincoln et al.
Science of the Total Environment 902 (2023) 166061
14The critical issues of climate change and marine litter highlighted by
this review could be explored in more detail, for instance, using a
regional participatory approach that involves risk scoring and ranking,
such as that used for the United Kingdom Climate Change Risk Assess-
ment and subsequent applications (CCRA, 2012; Garrett et al., 2015;
Maltby et al., 2022). Such an approach accounts for receptors of climate
change risk that may also be threatened by other anthropogenic pres-
sures, including marine litter, and helps to identify areas of low confi-
dence due to a lack of evidence or expert agreement, so that critical
knowledge gaps can then be addressed through targeted monitoring and
research (Maltby et al., 2022).
Globally, the principles and approaches for the conservation and
sustainable use of marine biodiversity can be used to help improve our
understanding as well as our ability to manage the cumulative impacts
of marine litter and climate change, and to improve the resilience of
marine ecosystems and services (Lincoln et al., 2022; Devlin et al., 2021;
Yadav and Gjerde, 2020). However, it is up to countries to ultimately
develop and implement plans and actions for climate change mitigation
and adaptation and marine litter reduction, that can effectively tackle
these two emergencies. But even at the national and sub-national levels,
this requires integration between sectors and across regions to address
infrastructural roadblocks, and other factors hindering action such as
lack of awareness and low community participation (Lincoln et al.,
2022; Lyons et al., 2020). The designation of marine protected areas,
and the protection of vulnerable habitats and species, are effective
measures that help build resilience against climate change and other
anthropogenic pressures, as demonstrated by remote oceanic coral atolls
in a relatively “pristine” condition, but a lack of data often hinders the
assessment of that resilience (Lincoln et al., 2022; de Oliveira Soares,
2018; Aswani et al., 2015; Standish et al., 2014). One option is to
combine monitoring, research, and marine planning activities as part of
marine protection practices (Lincoln et al., 2022; de Oliveira Soares,
2018), which is precisely the latest advice from UNEP on the issue of
marine litter: to apply ecosystem-based and holistic ocean governance
approaches, measurable targets, and blue economy principles (UNEP,
2021). To be effective, ocean and coastal management measures must
consider observed and future stressors from climate change and other
human activities and apply marine spatial prioritisation approaches that
acknowledge the ecological connectivity of terrestrial, coastal, and
marine systems (Ford et al., 2022; Lincoln et al., 2022; de Oliveira
Soares, 2018).
5. Conclusions
The interaction between climate change and plastics calls for stron-
ger attention and action given the pervasive interaction of these two
global emergencies, which has an uneven effect worldwide by causing a
much greater impact on disadvantaged coastal communities. In the case
of India, while the efforts made by coastal states are important and
commendable, the combined climate change and marine litter crisis is
overwhelming authorities and communities and hindering their poten-
tial for sustainable development. To our knowledge, 18 Indian states
have banned single-use plastic, but enforcement remains a problem.
This study adds clear evidence to the importance and urgency of the
issue, specifically in Southern coastal states. The combined negative
effects of litter and climate change on the marine environment and the
communities and economies that depend on it can potentially obstruct
efforts to achieve the SDGs. To tackle the problem, it is important to
consider the regional and national context to guide targeted monitoring,
and research, and practical policy and management actions. The Mala-
bar Coast and the Gulf of Mannar are globally important marine areas;
however, they are increasingly at risk from climate change, litter
pollution, and other pressures derived from the rapid economic devel-
opment that the country is experiencing. The scale of these issues
requires coordinated and innovative approaches guided by evidence-
based, measurable indicators and achievable outcomes.
Coastal management should prioritise protecting and restoring
coastal habitats and promoting sustainable fishing and responsible
tourism practices. These practices can be developed in collaboration
with local communities and stakeholders to ensure they are culturally
appropriate, socially acceptable, and economically viable, while
balancing the needs, health, and wellbeing of the people and the envi-
ronment. Local communities often hold valuable knowledge and expe-
rience regarding their local area and should be best placed to become
custodians and researchers of their coasts and seas, with the appropriate
training and resources, to detect and document evidence of changes in
the ecosystem. In addition, when devising coastal management frame-
works and plans, it is desirable to include representation of environ-
mental groups, authorities, industries, and communities.
Finally, specifically for Kerala and Tamil Nadu but also generally for
other Indian coastal states, we would recommend the undertaking of a
critical review of current policies, frameworks, plans, and actions
related to the coastal zone management, to understand and highlight
existing gaps and barriers that prevent their effectiveness, as well as
enablers and opportunities for improvement, at the district, state, or
national levels as appropriate. Such a review would help identify areas
where policies could benefit from a more robust evidence base, where
whole-ecosystem approaches are feasible, where there are opportunities
for enhancing integration and coordination across relevant departments
and sectors, and where a stronger community and stakeholder
involvement is required. The expected outcome of these interventions
would be effective, long-term climate change adaptation and resilience
while tackling marine litter with a higher probability of success.
CRediT authorship contribution statement
Susana Lincoln: Conceptualization, Methodology, Writing – orig-
inal draft, Writing – review & editing. Piyali Chowdhury: Writing –
original draft, Writing – review & editing. Paulette E. Posen: Writing –
review & editing. R.S. Robin: Methodology, Writing – original draft,
Writing – review & editing. Purvaja Ramachandran: Writing – original
draft, Writing – review & editing. Nithin Ajith: Writing – review &
editing. Olivia Harrod: Writing – review & editing. Danja Hoehn:
Writing – review & editing. Richard Harrod: Visualization. Bryony L.
Townhill: Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
No data was used for the research described in the article.
Acknowledgements
This work received funding from the Ocean Country Partnership
Programme (OCPP), a UK Government-led programme part of the Blue
Planet Fund. We are very grateful to Dr. Michelle Devlin, and to two
anonymous reviewers, for their constructive suggestions and comments
on previous versions of this article. We are also very grateful to Mr.
Nirmal Raj G., science communicator at the National Centre for Sus-
tainable Coastal Management (NCSCM), for producing the graphic ab-
stract and the climate resilience framework conceptual diagram, and to
other NCSCM colleagues for sharing their valuable thoughts in support
of this study
make a presentation by taking reference from the above text in 10-15 pages