Exploring Marine Urban EnvironmentsLatest update October 8, 2020 Started on January 1, 2019
Marine urban areas exist around many cities. Contrary to terrestrial urban ecosystems the marine ones are vastly unexplored and not well understood. It is time to change that and dive into these new environments and reveal their secrets.
Pollution in Marine Urban Ecosystems
The term 'pollution', contrary to the popular conception that is often focused on macro pollution (plastics and trash), describes a vast array of factors that can have perturbating consequences on living organisms. Basically, anything that is too abundant compared to what is considered normal/optimal is pollution. In Marine Urban Ecosystems (MUE), pollution can be of multiple sources and nature. Macropollutants like plastics and other waste are the most visible for the untrained eye and can be more or less abundant near cities and especially beaches (please don't litter). Urban areas can, however, exert other stresses that can have impacts that are orders of magnitude more important than plastic etc.
Most notably Chemical Pollutants like heavy metals have been shown to exert high toxicity towards the ecosystem. Cadmium, Lead, Copper, Quicksilver are produced in minuscule amounts by diverse human activities but accumulate in the environment. Persistent organic pollutants are produced in a similar manner. Wastewater conveys these chemical pollutants towards the sea where they most often accumulate in the food chain and the sediments. This accumulation concentrates the pollutants in living beings where they can harm the organism.
Biological pollution is considered equally harmful and occurs when a species spreads and reproduces without control, harming the ecosystem. Most often Non-Indigenious Species are considered as biological pollution, but local species can also contribute if they are considered harmful. The disturbed nature or MUEs favours species that use quick growth rates and high reproduction rates with a short lifecycle, which highly advantages species that are likely to become biological pollutants.
More recently, other pollutions gained the attention of the scientific community. Marine Noise and Artificial Light at Night (ALAN) are a recent focus of research and seem to influence the local fauna and flora. Here the effects are more subtle than previously mentioned pollutions but are more difficult to quantify since they mostly influence the behaviour of marine organisms.
The effects of pollution in a certain area are difficult to predict. Many organisms have adapted to cope with a high amount of any kind of pollution in MUEs. The resulting ecosystems constitute environments that are vastly different from natural ecosystems and harbour their own species with new behaviour and interactions. It is making me a little bit sad seeing a fish housing in a plastic pot on the bottom of a harbour (Picture) but I can't help but wonder how the fish sees its strange home.
I'm happy to announce that my expedition has been selected for the Science Exploration Education initiative, granting me a Sofar Trident.
Using a ROV for exploring Marine Urban Ecosystems (MUEs) has multiple advantages, which can go from security to simply higher mobility (the Trident is quite quick). Many MUEs have dangerous debris and other hazards, which does not allow for exploration without proper safety staff at the surface. Having a Trident allows me to explore new environments without the need for organizing a mission with multiple people. Remote exploration also allows me to scout locations for interesting spots before going into the water myself, since dive time is fairly limited. The Trident also allows for the exploration of sites that simply too dangerous for divers. The last will be certainly the one yielding the most interesting recordings with of the underwater drone.
But I will start slow, testing and training the use of the Trident before I get to these sites. Maybe my mother was wrong and having played all these videogames finally comes in handy!
Spotlight – Bryozoa
Bryozoa (moss animals) are a phylum of invertebrate animals (related to annelids and molluscs) living in aquatic habitats. Similar to corals, these animals are colonial where numerous, more or less specialised individuals (zooid) form a larger colony. These zooids are comprised of a lophophore with ciliated tentacles which can be retracted into a cystid (a box) containing all the organs like the digestive and reproductive system. The cystid is the part that gives structure to the colony and organises the individuals in space. It can be chitinous, membranous or mineralized, with various features like spines, opercula, avicularia, pores etc. The tentacles are used to filter particles and to ingest them. The three order of bryozoans, Cyclostomatida, Ctenostomata, Cheilostomata can take various forms, be encrusting or erect, but can be distinguished by these features. Bryozoa, like most marine animals, have planktonic larvae. These settle after a period of maturation and transform (metamorphosis) into the first individual of a colony, reproducing by budding clones. All individuals of a colony come thus from one individual.
Bryozoa are one of the most abundant groups in Marine Urban Ecosystems (MUEs), due to high abundance of material to filter out of the water. Merely a fraction of the Bryozoa species living in the wild are able to survive in MUEs; Those who can, however, thrive and develop quickly, covering large surfaces of the substrate, thus contributing to biofouling. In harbour environments like in the Port du Chateau in Brest, bryozoans take the number 2, and 4 spot of the most abundant animals on experimentally deployed surfaces. Their high abundance in MUEs and specifically harbour environments is partly due to the fact that many of them are non-indigenous species (NIS), species coming from distant locations by boat traffic. Their larvae are transported by ships and settle (if they survive) in their new environment, and may become invasive like Bugula neritina, the brown bryozoan (Picture 2 and 4 top). This species now has a worldwide distribution and occurs in almost every MUE. For yet not completely understood reasons, Bugula neritina almost never occurs in natural habitats. Watersipora (also a NIS) is a genus of intensely red encrusting bryozoans and is able to settle in the harshest, most polluted zones of harbours (Picture 3 and 4). In contrary to these two species, many Bryozoa are impossible to identify with the naked eye and must be observed with Binocular magnifiers (Future update).
Invasive or not, these species are major contributors to the communities in Marine Urban Ecosystems and even if we should try everything possible to avoid them spreading into regions where they are not supposed to be, we must try to understand their place and their importance in these ecosystems. They surely contribute aesthetically to the diversity of MUEs.
What is fouling?
Fouling is the process of living communities settling on (artificial) surfaces. These communities are mostly comprised of filtering organisms like bryozoans, ascidians, sponges, etc. (Individual spotlights coming soon), but at surface level algae can also contribute.
Most marine organisms release their eggs into the water where larvae hatch and mature through different processes. This larvae phase is the only moment when sessile (fixed) organisms can disperse. The larvae seek for suitable fixation spots which can be on artificial structures like pontoons, boats or ladders (photos).
Generally, boats have special paints on their hull which contain toxic substances called anti-fouling, this is why many ships don't have visible colonization. If this painting wears off, it releases substances into the water, which can influence living organisms, but it allows fouling communities to settle on the hull. This perfectly illustrates the dynamics one can observe in Marine Urban Ecosystems. There is always a balance between harsh conditions (pollution, fresh water, warming, disturbances) and fouling pressure by incoming larvae.
Can you dive in marine urban ecosystems?
The answers to this question can be as diverse as the spots you can consider. Certain marine urban ecosystems are easier to access and can be seen by everyone, like dykes or breakwater around beaches, others are strictly forbidden to access without special authorisation. Most of the artificial structures have not been designed with explorers and divers in mind and can, therefore, pose serious risks of injury. Diving in harbours and marinas, as we mostly do in our scientific diving team requires special training and authorisations and poses health risks due to poor water conditions (pollution) and due to numerous stinging animals. The risk of injury is also high due to obstacles and unidentified objects that sunk to the bottom.
Recent developments of technology make underwater drones or ROV affordable for an increasing number of laboratories and citizens. ROVs like the Sofar Trident are excellent companions to explore unknown sites before diving to assess the danger potential and to identify the hotspots of interest. They also allow accessing sites in conditions that wouldn't allow diver intervention like when high current is present or if authorisations for divers could not be gathered.
Like for most situations, a combination of methods yields the best results for studies on these ecosystems. By combining wide ROV observations with photos taken by Divers and sampling, community dynamics of artificial structures can be understood on different spatial scales, which allows integrating the variability of the present fauna and flora.
Understanding what non-indigenous species are and what their impacts/contribution to marine urban environments are is primordial to understand harbour and other man-made environments.
Non-indigenious species (or NIS) are species that have been introduced (accidentally or voluntarily) to a new geographical area, with a distinct separation between their native and introduced distribution range. Originally this happened mostly by cargo ships and their ballast waters, but these species are equally spread by recreational boating due to hull fouling (species living on the boat hull). In their introduced range they are often characterised by low genetic diversity compared to their native counterparts. This results from the bottleneck of only a few members of the native population founding being introduced in a new area to spread. Despite this, NIS can often become invasive and spread widely.
In marine urban ecosystems and especially in harbours, NIS are one of the largest contributors to the living community. They make up a significant part of the living beings and multiply and compete together with native species. It is difficult to describe their impact since it is variable on a species basis, but altogether they seem to claim space and replace local species. Other findings show that they simply profit from the absence of competitors in difficult conditions like in contaminated water.
Understanding marine urban ecosystems means understanding non-indigenous species. This is why they are a fundamental part of all scientific work on harbour and other marine urban ecosystems. They are an inherent part of these environments and will probably remain one, especially when climate change alters native living communities further.
In October 2018 I started my PhD at the Station Biologique de Roscoff in Brittany, France. My work focuses on the diversity and functioning of harbour ecosystems. I'm basing my research on previous work, showing very high variability and diversity of ecosystems within very small scales. I want to share my explorations and new insights into a brought audience because even in the nasty harbour water, beautiful ecosystems thrive.
Contribute to this expedition
Thank You for Your Contribution!