Impacts of Marine Litter on Mediterranean Reef Systems: From Shallow to Deep Waters

Abstract

Biogenic reefs are known worldwide to play a key role in benthic ecosystems, enhancing biodiversity and ecosystem functioning at every level, from shallow to deeper waters. Unfortunately, several stressors threaten these vulnerable systems. The widespread presence of marine litter represents one of these. The harmful effects of marine litter on several organisms are known so far. However, only in the last decade, there was increasingly scientific and public attention on the impacts on reef organisms and habitats caused by litter accumulating on the seafloor. This review aims to synthesize literature and discuss the state of current knowledge on the interactions between marine litter and reef organisms in a strongly polluted basin, the Mediterranean Sea. The multiple impacts (e.g., entanglement, ghost-fishing, coverage, etc.) of litter on reef systems, the list of species impacted, and the main litter categories were identified, and a map of the knowledge available so far on this topic was provided. Seventy-eight taxa resulted impacted by marine litter on Mediterranean reefs, and the majority belonged to the phylum Cnidaria (41%), including endangered species like the red coral (Corallium rubrum) and the madrepora coral (Madrepora oculata). Entanglement, caused mainly by abandoned, lost, or otherwise discarded fishing gear (ALDFG), was the most frequent impact, playing a detrimental effect mainly on coralligenous arborescent species and cold-water corals (CWCs). The information was spatially heterogeneous, with some areas almost uncovered by scientific studies (e.g., the Aegean-Levantine Sea and the Southern Mediterranean Sea). Although many legal and policy frameworks have been established to tackle this issue [e.g., marine strategy framework directive (MSFD) and the Barcelona Convention], several gaps still exist concerning the assessment of the impact of marine litter on marine organisms, and in particular on reefs. There is a need for harmonized and standardized monitoring protocols for the collection of quantitative data to assess the impact of litter on reefs and animal forests. At the same time, urgent management measures limiting, for instance, the impact of ALDFG and other marine litter are needed to preserve these valuable and vulnerable marine ecosystems.

Highest risk abandoned, lost and discarded fishing gear

“…However, given the broad geographical distribution of documented HABs, we assume that all areas have equal risk of exposure to the dozen or so species of dinoflagellates responsible for regional spreading of HABs. •Does derelict gear initially float or sink 25 , 84 – 86 Habitat alteration and degradation •The habitat types where the derelict gear occurs •The risk that the derelict gear will damage habitat, such as through scouring, abrading, smothering or altering the habitat’s structure •Risk of damaging sensitive habitats 26 , 41 , 74 Obstruction of in-use fishing gear and navigation, creation of safety risks at sea •The risk that derelict gear will encounter marine vessels and in-use fishing gear, and cause fouling, is explained in part by: Whether the derelict gear floats or sinks, as floating debris has a higher risk of obstructing marine vessels •Whether the derelict gear occurs in areas with marine vessel traffic •Whether there is aerial and vertical overlap between the derelict gear and in-use fishing gear •Whether the derelict gear materials risk fouling vessels and in-use fishing gear •The relative visibility of surface and subsurface derelict gear •Does derelict gear initially float •Derelict gear spatial and vertical overlap with in-use fishing gear •Derelict gear materials’ risk of fouling vessels and in-use fishing gear •Derelict gear visibility 4 , 24 , 64 , 87 Reduced socioeconomic, aesthetic and use values of coastal and nearshore areas •Risk that the derelict gear will ground on coastlines and nearshore habitats used for human activities such as recreation, tourism, education and research, and residential and commercial purposes, which is explained in part by whether the fishing grounds are located in nearshore areas, and whether the derelict gear initially floats and thus has the potential to be transported to nearshore and coastal habitats. •The proportion of the derelict gear that might occur on coastlines and nearshore areas that is not made of natural and biodegradable materials.…”

“…Other adverse consequences include transporting and transferring toxins and microplastics into marine food webs; transporting invasive alien species; distributing microalgae that may cause harmful algal blooms; altering and damaging habitat; obstructing in-use fishing gear and navigation; creating safety risks at sea; and reducing the socioeconomic value of coastal and nearshore habitats (Table 1). ALDFG can also have positive ecological consequences, such as providing artificial habitat and a meeting point to re-form fish schools; and socioeconomic benefits such as repurposing for various applications [25][26][27] .…”

A Manipulative Field Experiment to Evaluate the Impact of Discarded Plastic Bags on Shallow Vegetated Benthic Communities

“…Due to their wide distribution and long-term persistence within the environment, macroplastic affects biota in several ways. The most common threats come in the form of ingestion, entanglement, the formation of artificial substrates, the release of toxic substances, and the promoted transmission of alien species (de Carvalho-Souza et al, 2018;Angiolillo and Fortibuoni, 2020). Awareness of the problem is greatest in regard to the suffering of seabirds, fish, turtles, and marine mammals by entanglement or ingestion of litter.…”

“…The majority of studies with the effect of marine litter have focused on coral reef habitats (de Carvalho-Souza et al, 2018;Angiolillo and Fortibuoni, 2020) as well as deep-sea areas (Consoli et al, 2018(Consoli et al, , 2020Canals et al, 2021). Marine litter can cause direct damage to the fragile branches of many corals (Mulochau et al, 2020), as well as increase the risk of disease (Lamb et al, 2018).…”

“…To date, information about the effect of macrolitter that has on shallow coastal region benthic communities and habitats remains poorly understood and probably underestimated (Green et al, 2015;Angiolillo and Fortibuoni, 2020). The few mesocosm experiments that have utilized seagrasses have shown the increase of the intraspecific and interspecific competition (Balestri et al, 2017), reduction of the cover of vegetation, as well as the vulnerability of seagrasses to sedimentation where plastic bags are buried in the sediment (Menicagli et al, 2021).…”