Abstract
The United Nations (UN)’s call for a decade of “ecosystem restoration” was prompted by the need to address the extensive impact of anthropogenic activities on natural ecosystems. Marine ecosystem restoration is increasingly necessary due to increasing habitat loss in deep waters (> 200 m depth). At these depths, which are far beyond those accessible by divers, only established and emerging robotic platforms such as remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), landers, and crawlers can operate through manipulators and their multiparametric sensor technologies (e.g., optoacoustic imaging, omics, and environmental probes). The use of advanced technologies for deep-sea ecosystem restoration can provide: ① high-resolution three-dimensional (3D) imaging and acoustic mapping of substrates and key taxa; ② physical manipulation of substrates and key taxa; ③ real-time supervision of remote operations and long-term ecological monitoring; and ④ the potential to work autonomously. Here, we describe how robotic platforms with in situ manipulation capabilities and payloads of innovative sensors could autonomously conduct active restoration and monitoring across large spatial scales. We expect that these devices will be particularly useful in deep-sea habitats, such as ① reef-building cold-water corals, ② soft-bottom bamboo corals, and ③ soft-bottom fishery resources that have already been damaged by offshore industries (i.e., fishing and oil/gas).
Keywords
Ecosystem restorationRobotic manipulationAcoustic trackingFishery resourcesArtificial reefs
1. Introduction
Anthropogenic activities are impacting marine ecosystems on a global scale, leading to losses in biodiversity [1], [2]. These effects are so widespread that even the most remote deep-sea ecosystems are now affected by industrial exploitation via fishing, oil/gas exploration and extraction, bioprospecting, and pollution, among others [3], [4]. This has led to the progressive loss of key and vulnerable ecosystems along continental margins, such as cold-water coral reefs, coral gardens, sponge grounds, and soft-bottom grounds [5], [6]. In fact, soft-bottom deep-sea habitats are arguably the most extensively impacted habitats worldwide [7], [8]. Additional future threats to deep-sea habitats include climate change [9], [10] and mineral extractions (e.g., the mining of polymetallic nodules or massive sulfide deposits from hydrothermal vent areas) down to abyssal depths [11], [12].
These anthropogenic stressors also cause severe consequences to ecosystem functioning [13], [14]. As the deep sea is the largest ecosystem on this planet [15], degradation of the deep sea could have extensive ecological impacts—including effects on carbon dioxide (CO2) storage [16]—that will reverberate on a global scale. Since the efficient functioning of deep-sea ecosystems depends on both high levels of biodiversity [17] and the presence of habitat-forming, bioengineering species [18], the continuing loss of such ecosystems is leading to an unprecedented erosion of the deep-sea natural capital and related ecosystem services [19]. Healthy ecosystems provide food and food security, clean water, carbon sinks, and protection against the natural hazards caused by climate change. Indeed, they are essential for our long-term survival, well-being, prosperity, and security and are the basis of economic and societal resilience [20].
1.1. The need for ecological restoration in the deep sea
Biodiversity loss and the degradation of ecosystems continue at an alarming rate and are transforming European seas, resulting in harm to people’s welfare, the economy, and the climate [21]. This has been widely documented, notably in reports by the Intergovernmental Panel on Climate Change (IPCC), the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), the Biodiversity Aichi Targets progress report, and The Economics of Biodiversity: The Dasgupta Review.
Strong conservation and management actions were lacking until recently, largely due to several failures of governance and implementation [22]. Many environmental policies have been designed to address the emerging issues, but coordinated cross-sectoral planning remains poor—primarily because of the complexity of more holistic approaches (given our limited baseline knowledge) and the diversity of policy approaches, society contexts, and stakeholders [23], [24]. However, there are upcoming efforts to address these issues moving forward (i.e., the UN High-Seas BBNJ Treaty 2023 “on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction”).
The United Nations launched a call for “ecosystem restoration” for the decade 2021–2030 [25] to reverse the declining trends for all ecosystems. The restoration of deep-sea habitats is a pressing need from an ecological, societal, and operational point of view [26], particularly in cases where a habitat is either rare or provides a specific service, and it is demonstrated that restoration accelerates or qualitatively betters natural recovery in a long-term, financially sustainable way. Such restoration requires policies and tools for remediating environmental degradation, along with societal actions to improve ecosystem resilience, as well as innovative management strategies and the use of technology-facilitated interventions to restore keystone and vulnerable species to pre-impact levels.
1.2. The EU legal framework for marine restoration
The European Union (EU) Biodiversity Strategy for 2030 sets out targets to further protect nature in the EU. Nevertheless, it also states that reversing biodiversity loss will require greater efforts in protected areas and beyond, at all depths of the continental margin, including the deep sea. Therefore, the European Commission has proposed legally binding targets to restore degraded EU ecosystems, with particular emphasis on the ecosystems of the deep sea, that have the most potential to remove and store carbon and to prevent and reduce the impact of natural hazards. In addition, the Mission Board on Healthy Oceans, Seas, and Coastal and Inland Waters has proposed Mission Starfish 2030: Restore our Ocean and Waters by 2030, which has five overarching objectives: ① filling the knowledge gap between humanity and the ocean, ② regenerating marine and freshwater ecosystems, ③ zero pollution, ④ decarbonizing our ocean by CO2 removal, and ⑤ revamping governance. Mission Starfish 2030 emphasizes that weak international governance has currently led to inconsistencies, overlaps, and gaps between jurisdictions. As such, the “need to consider governance issues in the mission of restoring degraded marine habitats” is evident.
The European Green Deal acknowledges that a healthy ocean plays a key role in the fight against global warming and ecological collapse, stating: “lasting solutions to climate change require greater attention to nature-based solutions, including healthy and resilient seas and oceans.” Among the concrete actions/targets proposed, the Green Deal includes: ① fisheries (i.e., the Common Fisheries Policy) to reduce the adverse impacts that fishing can have on ecosystems; ② marine biodiversity, by designating additional properly managed Marine Protected Areas according to the Biodiversity Strategy; ③ Blue Economy, by planning to boost aquaculture and offshore renewable energy; ④ shipping, by extending European emissions trading to the maritime sector; and ⑤ a circular economy against microplastics. Since the year 2008, the Marine Strategy Framework Directive [27] and the Maritime Spatial Planning Directive [28] have been promoted to assess and improve the environmental status of European marine ecosystems and to plan the sustainable use of marine resources. The Directives also foresee that ecosystems that have not yet reached a good environmental status (GES), will require recovery/restoration actions with assessments of their operative reliability, environmental sustainability, economical effectiveness, and social acceptance.
1.3. Technological requirements for marine restoration
To have a meaningful impact worldwide, current protocols and technologies for marine ecosystem restoration must be effective over larger spatial scales [29]. Typically, restoration practices adopt a slow, “passive” approach based on the removal of stressors and allowing the system to recover naturally (e.g., in Marine Protected Areas). Therefore, many studies have mentioned the necessity for more “active” approaches involving the reintroduction of key species (e.g., ecosystem engineers such as seagrasses, corals, and sponges) or substrates for colonization [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31].
However, most active restoration efforts in marine habitats are currently limited to depths < 60 m, which are accessible by self-contained underwater breathing apparatus (SCUBA) divers [32]. As 99% of marine habitats exceed these depths, and as active restoration in the deep sea is economically and operationally challenging, technological solutions are urgently required, especially for the deep sea (i.e., at depths > 200 m), based on geomorphology, physical oceanography, and the light penetration supporting photosynthesis [33], [34]. First, deep-sea restoration’s reliance on vessels increases its costs compared with those of shallow habitats [35], [36]. The operational costs of an 85-m-long research vessel (RV), such as the Spanish fleet’s “Sarmiento de Gamboa,” working round the clock with a crew of 25 and equipped with one ROV (model: LIROPUS-2000), CTD (referring to a set of instruments measuring conductivity, temperature, and depth), and multibeam mapping devices currently costs 35 000 EUR (approx. 39 000 USD, 275 000 CNY) per day. For an ordinary 12-day data-collection cruise in deep-sea continental margin areas, this translates to 420 000 EUR (approx. 465 000 USD, CNY 3 297 000). Second, deep-sea areas will require the use of novel technologies that can enable interventions over broad enough spatial scales similar to coastal zones [37], [38] and can measure success through long-term, post-intervention, ecological monitoring (as well as dynamically adapt efforts to unpredicted environmental events; see below).
We propose that a strategic increase in deep-sea active restoration capacity should be based on three interdependent and consecutive steps:
(2) Active restoration. The next step involves reintroducing bioengineering sessile and motile umbrella species to accelerate the demographic recovery of other targeted taxa (e.g., stocks biomass enhancement) and overall biodiversity (e.g., favoring the reconstruction of ecosystem functions based on predator-prey relationships). This will be achieved by deploying bioengineering species in the sites identified in Step 1, prioritizing a surface delimited by an in situ network of fixed and mobile sensor platforms.
(3) Feedback monitoring. The third step involves measuring the progress of interventions and post-intervention ecological results and planning eventual adjustments. This will require long-term multiparametric data collection to quantify ecosystem recovery, with the possibility of adaptive interventions in response to stochastic environmental events (e.g., landslides, cascading, and turbidites).
Achieving these three steps would require the development of new (or the adaptation of already available) technologies (i.e., marine robotics) [39] equipped with manipulators [40] and various sensors [41]. Furthermore, these technologies must be able to function in an at least partially autonomous manner [42], [43], which will lower the costs associated with operating vessels—a major constraint on the duration and frequency of cruises [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [26].
1.4. Marine restoration in relation to precision agriculture developments
Marine restoration could benefit from recent innovation in robotics, as the latter field is moving from the structured environments of factories to natural and unstructured environments [44]. In this manner, active marine restoration will likely follow a similar path to agricultural robotics. Below, we describe the parallels of technological development in robotics within precision agriculture and marine restoration. We focus on the coordination capability of platforms that perform cooperative missions in which sessile organisms’ manipulation for transference is similar to agricultural monoculture approaches. Nevertheless, we are aware that the restoration of ecosystem function requires the reintroduction of a wider pool of bioengineering sessile species to better promote the recovery of overall biodiversity, which would make it more similar to silviculture than to monoculture. In this framework, for example, the specifications of robotic manipulators may differ in suitability among species, elevating the complexity of the envisaged technological development (see Section 3).
Examples of technology-assisted plant seeding on land support the idea that the large-scale robotic restoration of marine habitats could be feasible on the seafloor, achieving similar accuracies to the more than 90% precision planting expected on land [45], [46]. Internet-operated vehicles (IOVs) such as crawlers [47] are the best current equivalents for agricultural robots, and their high-precision positioning and manipulation capabilities (see Section 3) could be used to undertake marine restoration operations similarly to how they are used in land restoration [48]. Such operations would include simulating functionalities similar to those of agricultural robots (AgBots) at various stages of the crop cycle, from planting and weeding [49] to harvesting [50] and sorting [51]. Crawlers may alter the substrate, depending on geomorphological conditions, and its composition (e.g., eroding and resuspending silts and clays in deep-sea muddy seafloors) [52]. A strategy to mitigate operational impact could consist of using crawlers as a pre-seeding ploughing exercise in certain terrains based on transferring items to be implanted from trays on the back of the vehicle with robotic arms. Next, it would be preferable to have the crawlers move along constant transect lines at a very slow speed (i.e., a stepping-stone progression mode, in which large pauses serve to reduce sediment resuspension) for post-intervention monitoring. In any case, the design of the crawlers’ caterpillar wheels should reflect the need to minimize their footprint.
Autonomous operations in marine restoration would require the precise definition of the reciprocal positioning of mobile platforms in real time. In marine networks, this can be achieved through acoustic communication (Section 2). In precision agriculture, reciprocal positioning is measured via real-time kinematic (RTK) positioning using a high-precision global navigation satellite system (GNSS), radio beacons (into closed environments), and visual simultaneous localization and mapping (vSLAM) [53], [54]. Of these technologies, only vSLAM is relevant in a marine context, as it uses cameras and computer vision algorithms to create a map of an area in order to determine the position of platforms in real time [53].
In marine operations, area reckoning relies on seabed mapping (by means of acoustics and photogrammetry; see Section 4) via hoovering platforms such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) (Fig. 1). These platforms require underwater positioning, based on long base line (LBL) or ultra-short base line (USBL) acoustics, as the most used approaches for the geo-localization of the robots in relation to the vessels operating in the surveyed areas [42].
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Fig. 1. LBL and USBL communication procedures for the spatiotemporal coordination of benthic and pelagic platforms operating in restoration and monitoring networks. (a) The LBL system uses three or more spread baseline transponders (a1) in the area, which allow for underwater devices such as (a2) static, or (a3) AUVs or (a4) moving seabed stations equipped with other transponders, to be geo-localized, taking the baseline transponders’ position as a reference. Also, boats can include a Global Navigation Satellite System (GNSS) receiver to calibrate the underwater baseline transponders (where the GNSS signal is not available; a5). The transceiver will accurately determine the position of the baseline transponders in real-world coordinates. (b) The USBL system uses (b1) a USBL transceiver, which integrates the baseline transponders within a very small volume (cm3). Underwater devices (b2: landers; b3: seabed crawlers; b4: AUVs) are geo-localized using the USBL position as a reference. In addition, transponders and transceivers permit underwater communications between the devices and the vessel, for the exchange of position information.
Another relevant aspect of precision agriculture that could be adapted for marine restoration is proximal sensing for monitoring. Field-based sensors in contact with (or within a few meters of) soil, plants, crops, and so forth are deployed for temporally intensive and long-lasting environmental measurements [55]. When deployed into networks, sensors can facilitate the collection of vast amounts of multiparametric data with a consequent spatiotemporal scaling of proximal sensing [56]. A similar approach should be pursued in the ecological monitoring of marine restoration (Section 4), based on long-lasting deployments of biological and environmental sensors into intervention areas.
Here, we describe how a combination of established and innovative marine robotic platforms with different levels of vessel autonomy and adaptable sensor arrays can perform in situ autonomous or semi-autonomous restoration interventions, spatial upscaling, and monitoring in deep-sea habitats. Accordingly, we detail three potential case studies for such a combination of platforms, where different in situ manipulative actions are envisaged for sessile and motile fauna in iconic deep-sea environments.
2. Technological requirements for maintaining and upscaling marine restoration
A variety of fixed and mobile platforms are already in use for restoration interventions and/or monitoring in specific and focused areas of interest (Table 1 [31,58−86]). These include both autonomous robots with (remotely) controlled missions and vessel-assisted and tele-operated platforms. Alternatively, larger sites can be monitored using passively drifting buoys or mobile marine megafauna equipped with bio-logging devices that may move transiently through areas of interest [59]. With the capacity to collect data over what are often larger spatial scales than autonomous or remotely controlled robots, passively drifting or animal-borne technologies could represent interesting solutions for understanding the ecological results of restoration via a geographical upscaling of monitoring (even though a detailed spatial coverage is difficult).
Table 1. Fixed and mobile robotic platforms (see Fig. 1 for schematic features), autonomous and partially autonomous (i.e., vessel-assisted, tele-operated), with potential for use in restoration interventions and monitoring, including a summary of their operational spatiotemporal ranges and degrees of mission autonomy.