3.2. Target marine species
There are target species that better than others can highlight alterations and problems in marine ecosystem through the study of abundance, distribution and health of their populations. For example, the Mediterranean Sea has been described as one of the most affected areas by marine litter in the world. In addition to the physical harm associated with marine litter, there is increased concern regarding the chemical harm related to marine litter ingestion. Debris that enters marine environments, spreads and accumulates in habitats and compartments, and interacting with marine organisms including the occurrence inside biota following ingestion. Plastic litter could be direct vector for plastic additives and an indirect vector of chemicals due to sorption and transport of persistent bioaccumulative and toxic substances. If these chemicals become bioavailable, they can penetrate cells and chemically interact with biologically important molecules causing adverse effects from molecular to tissue level, including alterations of gene expression, genotoxic effect, endocrine disruption, liver toxicity and histological alterations.
In general, most invertebrates can be considered as local scale indicators of the presence and impact of microlitter in specific areas of Mediterranean coastal shores. By virtue of its broad geographical distribution, abundance, low position in the food web, easy accessibility, the possibility to carry out in-cage studies as well as its well understood biology, the mussel (Mytilus galloprovincialis) is proposed as a bioindicator of microplastics in Mediterranean coastal shores. These intertidal filter-feeding invertebrates are known to accumulate high levels of contaminants (e.g. heavy metals and POPs) as well as microplastics, providing a time-integrated indication of environmental contamination.
Demersal fish live in close connection with sediments on the sea bed and depend on benthic prey for feeding. They can be used as small-scale indicators of the presence and impact of microplastic in the Mediterranean benthic environment (sea bottom). Red mullet (Mullus barbatus) and Solea spp. are fish species living on muddy and sandy bottoms, feeding mainly on benthic species. A high percentage of plastics has been already found in the stomach contents of Boops boops and Trachinotus ovatus and these species can be proposed as good sentinel species at small scale level in coastal waters. The two species do not carry out large movements and they are exploited by artisanal fisheries. Due to their trophic level and habitat mesopelagic fish can represent indicators of the presence and impact of microplastics in the Mediterranean pelagic environment at small-scales. They play an important role in the energy transfer from surface to deeper waters and from low trophic levels of the food web to top predators. At medium scale, large pelagic predators Thunnus alalunga and Coryphaena hippurus can represent a more suitable sentinel species for monitoring microplastic in the trophic web, because of the wide range of their migration within the Mediterranean basin. These important fish resources are widely distributed in Mediterranean subregions and have already been identified as species impacted by plastic ingestion.
Large filter feeding marine organisms, such as baleen whales and sharks, which can ingest microplastic during their filtrating feeding activity, are proposed as wide-scale indicators of the presence ad impact of microplastic in the whole Mediterranean pelagic environment. The fin whale (Balaenoptera physalus), one of the largest filter feeders in the world feed primarily on planktonic euphausiid species. The basking shark (Cetorhinus maximus) is a large and filter-feeding pelagic species, having migratory behavior and being widely distributed in Mediterranean waters. Basking sharks feed on zooplankton by forward swimming with an open mouth, causing a passive water flow across the gill-raker apparatus. Both species are at from the ingestion and degradation of microplastics.
The loggerhead sea turtle (Caretta caretta), which ingests macro litter during feeding, can be considered as a wide-scale indicator of the presence and impact of macro-plastics (large plastic fragments) in the whole Mediterranean pelagic environment. Depending on its age and on food availability, this species feeds in different ecological marine compartments from the surface to the bottom. Being carnivorous to omnivorous, loggerhead sea turtle can ingest a high amount of debris that may be mistaken for gelatinous prey or encrusted by food, causing the death of the animal by occlusion of the gastrointestinal tract. Stranded/dead or hospitalized loggerhead turtles (in rescue centres) can be used to monitor plastic ingestion, by analyzing: i) gastrointestinal tract contents of dead animals or the faeces excreted by live animals in tanks, ii) accumulation of contaminants in the tissue, iii) responses of a set of biomarkers.
As well as loggerhead sea turtles, the sperm whale (Physeter macrocephalus) is one of the most affected species among cetaceans. High occurrence of marine litter ingestion has been reported in stranded organisms along the Mediterranean coasts. Some other marine mammals, such as bottlenose dolphin (Tursiops truncatus), striped dolphin (Stenella coeruleoalba) and Risso’s dolphin (Grampus griseus) were found to be affected by litter ingestion too. In the Mediterranean area, detected levels of phthalates and organochlorines in blubber samples of these species and fin whale (Balaenoptera physalus) suggesting a possible exposure to plastics of these species which mostly live in pelagic areas.
Fossi, M.C., et al., Bioindicators for monitoring marine litter ingestion and its impacts on Mediterranean biodiversity, Environmental Pollution (2017)
3.2.1 Find out the definition of target species in the function of bioindicators!
Bioindicators can tell us about the cumulative effects of different pollutants in the ecosystem and about how long a problem may have been present.In order to find and study these changes better,target-species of bioindicators are used.These target-species are increasingly used as bioindicators of contaminant accumulation in pollution studies.More often examples of target species are frogs and toads as they can absorb toxic chemicals through their skin and larval gill membranes and are sensitive to alterations in their environment.They have a poor ability to detoxify pesticides that are absorbed, inhaled, or ingested by eating contaminated food.This allows residues, especially of organochlorine pesticides, to accumulate in their systems.They also have permeable skin that can easily absorb toxic chemicals, making them a model organism for assessing the effects of environmental factors that may cause the declines of the amphibian population.These factors allow them to be used as bioindicator organisms to follow changes in their habitats and in ecotoxicological studies due to humans increasing demands on the environment.Another example of a target-specie are plants becauase they are used as very sensitive tools for prediction and recognition of environmental stresses.In recent time, due to industrialization and urbanization the problem of contamination of water and water pollution has intensified. Marine plants provide valuable information to predict the status of oceanic environment,as they are immobile and rapidly obtain equilibrium with their natural surrounding.In addition,microorganisms are often used as health indicators of aquatic and terrestrial ecosystems due to their abundance as they are easy to test and readily.In conclusion a target-species are helpful,straightforward and objective bioindicators and they can be utilized at various scales,from the cell to the environmental level,for assessing the changes taking place in a specific biological community. 😉
3.2.2 What are possible alterations in marine ecosystem caused by marine litter?
Marine litter can cause many alterations in marine ecosystem. Firstly, oil spill is dangerous to marine life in several ways. The oil spilled in the ocean could get on to the gills and feathers of marine animals, whici makes it difficult for them to move or fly properly or feed their children. The long term effect on marine life can include cancer, failure in the reproductive system, behavioral changes, and even death. Secondly, the oil spill floats on the surface of water and prevents sunlight from reaching to marine plants and affects in the process of photosynthesis. Skin irritation, eye irritation, lung and liver problems can impact marine life over long period of time. Furthermore, most of the debris in the ocean do not compose and remain in the ocean for years. They use oxygen as they degrade.As a result of this, oxygen levels go down. When oxygen levels go down, the chances of survival animals like whales, turtles, sharks, dolphins, penguins for long time also goes down. Additionally, marine litter can have an effect on food chain. This happens because chemicals used in idustries get washed into the rivers and from there are carried into the oceans. These chemicals do not get dissolved and sink at the bottom of the ocean. Small animals ingest these chemicals and are later eaten by large animals, which then affects the whole food chain. Finally, animals from impacted food chain are then eaten by humans which affects their health as toxins from these contaminated animals get deposited in the tissues of people and can lead to cancer, birth defects or long term health problems. To sum up, each one of us seperately has to stop throwing trush into the ocean. In this way more marine species will be saved every day.
3.2.3 Invertebrates as bioindicators of microlitter in coastal shores
It is widely known that the continuous industrial development worldwide has led to a dramatic increase in the global production of plastics. However, despite the unquestionable economic benefits entailed by it, the extensive use of plastic, in conjunction with the careless human behaviour, present/propose a serious threat to the aquatic environment. This threat comes in the form of marine debris. Specifically, recent studies reveal that microplastics, account for the vast majority of marine litter and can be found in a great range of species in the affected habitats. On top of that, there is also luck of knowledge on the impact of microlitter injection on the marine ecosystem and its living organisms.
Thus, it is essential that we use a monitoring tool that would provide the information necessary to investigate in depth the effects of marine debris and take actions to encounter the problem. Hence, we need to define a selection of criteria for choosing organisms suitable to use as bioindicator species for environmental monitoring. The main features consist of a wide distribution range in the ecosystem, a well-known biology, immobility and the ability to provide early alert.
The result of reliable research in the area suggest that invertebrates, present in coastal shores, should be used as target species for biomonitoring as they meet almost all the key functions. Moreover, there is evidence that microplastic abundance in them is closely related to human activity and laboratory studies demonstrate that they may be good model organisms in revealing microplastic uptake, accumulation and toxicity. Consequently, invertebrates offer a uniform, efficient and economical approach that is suitable for a future large-scale biomonitoring program.
3.2.4 Demersal fish species as bioindicators of microplastic in bentic environment
The term benthic characterized all the living organisms that live and grow on the bottom of the oceans and seas or lakes and even last determination of the point observed tide until now deep trenches.The situation of Bentic community and the presence of particularly sensitive species.Τhe predominance of slow growth, non-plastic Cystoseira species is a typical feature of the multi-oligotrophic and high-grade undisturbed rocky shores in the Mediterranean.BENTIX is one biotic index, which is based on the concept of groups of indicators and uses the relative contribution of tolerant and sensitive taxa genios and weighing their reconciliation with the proportion of their appearance on bentic fauna default.Due to human activities that take place in this sea, and especially the increasing frequency, results recorded a number of significant impacts on bentic ecosystems and the scientific community has already highlighted the risks that these habitats and inventory of their natural and biological resources.Microplastic polymers are ubiquitous within aquatic environments. Due to their small size there is a risk that they may infiltrate and transfer within aquatic food webs. Fish captures for human consumption have be found to contain microplastics, as any species of fish from the Pacific, Atlantic, Indian ocean, and the Mediterranean Sea had individuals with microplastics in their digestive tracts. In addition, fish from the Nordic marine environment have also been found to contain macro and microplastic.Microplastics have only been identified in the gastrointestinal tract of fish Most fish are gutted before consumption, removing the microplastics that renders the exposure of humans to microplastics through ingesting fish negligible.However, small pelagic fish, such as sardines and anchovies are consumed whole, without the removal of the digestive system. Microplastics have been observed in few species of small marine pelagic species(ex.the Pacific anchovy).
3.2.5 Pelagic fish species as sentinel species for monitoring microplastic in pelagic environment
Studies a little offshore of Scotland report plastic ingestion in various fish.There are reports that show that a small percentage of them had ingested it, mainly the pelagic kind.These fish can be used to monitor the plastic littering of seas and oceans by analyzing the percentage of plastic litter ingested in them.
Plastic is the most problematic litter.A study A 2004 assessment of marine water samples found six times more plastic than plankton, while a more recent study estimated that as many as 5.25 trillion plastic particles, weighing some 269 000 tonnes, are floating on the sea’s surface.Not only do they poison fish with chemicals they release but the also transfer them into humans when they are eaten.
Only the idea of getting poisoned by our own product and element , let alone poisoning other living creatures is awful.
So the idea here is to use the fish , particularly the pelagic kind , to monitor the littering of plastic in oceans and seas.The concept is basic.To study how much plastic have the fish been ingested.After that we can convert the answer to a percentage and compare them with previous numbers. With this idea we can keep track of the littering.
This idea can also lead to finding ways to counteract the pollution that has already been done. From there , the idea of dealing with litter can be a lot more apprehensive and could be countered once and for all.
This although is only a study and therefore nothing is certain. But only the idea of pollution free seas and oceans is worth the effort ,money and time spend studying and trying to keep the our waters clean.
3.2.6 Large filter feeding marine organismsas wide-scale indicators of microplastic in pelagic environment
Microplastics are considered to be plastic fragments smaller than 5mm. The main sources of microplastics in the pelagic environment are adjacent to land areas, rivers discharging garbage and boats. The negative effect of microplastics in marine organisms has been proven. Although, microplastic is a hot research topic, its impact on large marine organisms is largely unexploited.
Large filter feeding marine species such as the baleen whales, sharks (basking shark etc.) and devil rays are long-lived organisms found in a decisive position in the food chain. They filter big volumes of water and consume the suspended particles in it, which may include planktonic organisms, and other substances, including toxic and persistent constituents of microplastics (phthalates, endocrine disruptors, DDT, PCBs). Due to this, they are exposed to a wider magnitude of toxic substances microplastics may leach. The presence of such substances in large filter feeding marine species has been recently proven. Based on the above, and due to the wide home-range and mobility of these animals, the bioaccumulation of these substances in the creatures they ingest/filter, the persistence of the substances and their longer life spam in the water column, along with their key position in the food chain, can be considered effective indicators of the presence of microplastics in the pelagic environment.
Plastics and their micro-particles (microplastics) are a completely man-made creation. Therefore, nature does not have an “antidote” able to completely diminish them. Microscopic constituents will always be around, posing a threat and/or causing harm to marine organisms. In spite of the fact that large marine filter feeding organisms can be considered as wide scale indicators of microplastic existence in the pelagic environment, there is still great need for further research in the theme, and even further need for actions leading towards the reduction of the production and use of plastics in general.
3.2.7 Loggerhead sea turtle (Caretta caretta)as a wide-scale indicator of the presence and impact of macro-plastics in pelagic environment
The plastic amount of world’s oceans has been and is continuing to be a major problem, since the number is estimated to 4-12 million tons of plastic annually entering the world’s wide waters, therefore resulting to be recognised as a global environmental threat and the principal component of marine debris which severely affects the marine ecosystems in the pelagic environment and not only. Although all seven species of sea turtles are reported to be affected, the European Union’s Marine Strategy Flamework Directive (MSFD) proposed the loggerhead sea turtles also known by their scientific name Caretta Caretta which are the most abundant chelonians founded in the Mediterranean Sea and also founded in the North Atlantic Ocean, to be the bio-indicator species of the environmental conditions. The threats caused by the plastic pollution differ between species, populations and life stages and by them the sea turtles may suffer lethal or sub-lethal effects if the plastics such as plastic bags are mistaken for food or when debris is mixed with natural prey. Studies have shown that out of 24 turtles 20 (83%) of them were founded to have debris in their gastrointestinal tract, white and transparent plastics being the dominant items founded in loggerheads sampled. Also had established that the ingestion of debris rarely can be the direct cause of death resulting that in most of the cases they have sub-lethal effects. Due to their wide digestive tract, loggerheads have the ability to defecate most of the ingested debris, but this stage takes time due to the debris which can remain in the gut for at least 41 days before being defecated. The MSFD study who has been considered further in 2014 ‘’trends in the amount and composition of litter ingested by marine animals’’, the results have shown that monitoring plastic ingestions by oceanic-stage loggerheads inhabiting in Azores could be used to assess temporal and spatial trends in plastic pollution within the scope of the MSFD.