Marine Pollution Bulletin xxx (2014) xxx–xxx
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia Serge Andréfouët a,⇑, Yoann Thomas a, Cedrik Lo b a b
IRD, UR 227 CoRéUs, LABEX CORAIL, BP A5, 98848 Nouméa cedex, New Caledonia Direction des Ressources Marines et Minières, Papeete, BP 20 Papeete 98713, Tahiti, French Polynesia
a r t i c l e
i n f o
Keywords: Aquaculture Marine debris Pearl farm derelict gear Atoll
a b s t r a c t Pearl oyster aquaculture is a major activity in French Polynesia atoll lagoons. After the economic decline that characterized the last decade, concerns recently rose about discarded installations and materials that supported aquaculture practices and by facilities abandoned after they had to close their activities. In May 2013, a first inventory of the type and amount of pearl farms derelict gear (PFDG) was achieved on 47 sites in Ahe lagoon. Surveys were conducted within and outside the boundaries of aquaculture concessions. Twenty types of PFDG littered the lagoon floor and the water column. The most impacted areas were near abandoned grafting houses with up to nine types of PFDG. Forty-five percent of the sites were impacted, including outside concessions. While management authorities are fully aware of the problem, this first assessment is a wake-up call to stimulate the cleaning of lagoons, enhance awareness among farmers, and identify potential ecological consequences on lagoon ecosystems. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Recently, Andréfouët et al. (2012a) reviewed the most recent advances in black pearl oyster aquaculture research accomplished in Ahe atoll lagoon, in the French Polynesian Tuamotu archipelago. In the short review of this activity critical for French Polynesia’s economic income, they pointed out that the aquaculture of black pearl in French Polynesia has modified the livelihoods of thousands of islanders in the past 30 years. It has also reshaped the atollscape, with numerous farms, buildings, pontoons and boats appearing and disappearing along shores and coral pinnacles. The official 10,000 hectares of concessions authorized in French Polynesia have hosted tens of thousands of hanging lines, visible thanks to surface buoys that dot the lagoons. Millions of oysters have been artificially hanged in the water column instead of living on deep atoll floors. Naturally separated oyster populations have been mixed, and numerous epibionts were introduced in lagoons. Massive local and widespread mortalities which occurred remain poorly explained due to insufficient in situ monitoring of environmental conditions, given the remoteness of atolls and associated monitoring costs. Andréfouët et al. (2012a) concluded that ‘‘The exact ecological impact of the pearl industry remains unknown to date and will likely be a future direction of investigation’’. There is a
⇑ Corresponding author. Tel.: +687 26 08 00; fax: +687 26 43 26.
growing concern in French Polynesia regarding the amount of discarded materials, installations and trash generated by farms, some still active, but having ceased activities by now. By law, farmers have to clean their concessions and remove any type of materials, otherwise they risk a stiff fine in case of control. However, there are evidences that many lagoons and shorelines are now littered by black pearl farm derelict gears (or PFDG afterwards). A functioning farm would typically have wood and concrete pontoons and jetties with houses for epibiont-cleaning and grafting oysters. Next to these houses will be found aluminum or wood structures (cages) where baskets of oysters are temporally tied before their processing. Then, rearing stations with baskets of hanging oysters as well as spat collecting stations are spread in the concession. These are attached with submerged thick ropes and surface/sub-surface plastic buoys that are adjusted so that oysters and collectors can hang at a given depth depending on the conditions (Fig. 1). These buoys are made of acrylonitrile butadiene styrene (ABS). ABS is used due to its toughness, and impact and heat resistance. Baskets and collectors are usually made of plastic (loops of black flat polypropylene, knitted onto a 30 cm monofilament polyethylene line). An important fact is that no concessions are required for collecting, thus collecting lines can be freely deployed anywhere in the lagoon at the discretion of the farmers. The only limitations are their length (200 m), number of lines per concession (i.e., 10 lines for a concession of 5 ha and one more for each additional hectare) and submersion duration (i.e., 2 years).
E-mail address: [email protected] (S. Andréfouët). http://dx.doi.org/10.1016/j.marpolbul.2014.03.048 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
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S. Andréfouët et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
habitat qualities, with tangled ropes on the seafloor damaging the natural habitats. In the other hand, these PFDG can be the foundation of new opportunistic habitats for a number of marine creatures, resulting in habitat and behavior shifts. These concerns promt new questions that have not yet been tackled, or considered by recent reviews on anthropogenic impacts on Pacific islands (e.g., Morrison et al., 2013). For this, a first assessment of the extent of PFDG found in lagoons was needed. An inventory would be the first step for the managing authorities in order to take action and start mitigating the impacts. In May 2013, a new series of hydrodynamic and biological experiments were conducted in Ahe atoll lagoon during a five week expedition on board the R/V Alis. We took this opportunity to (1) make an inventory of all discarded materials in 47 dive sites, (2) create a typology of discarded aquaculture materials that can be found in all lagoons, (3) assess the extent of the problem for one of the busiest atoll in the recent past and infer practical recommendation for the local authorities.
2. Material and methods 2.1. Study site Ahe atoll is located in the northwestern part of the Tuamotu Archipelago (14.48S – 146.30 W), about 500 km northeast from Tahiti (Fig. 2). It is now one of the most studied atolls worldwide, with most research directly related to the black pearl industry and the aquaculture of the black lip oyster Pinctada margaritifera (Andréfouët et al., 2012a and references within). The lagoon is a 142 km2 deep water body with an average depth of 41 m, reaching up to 70 m depth and contains numerous pinnacles rising to the surface. The deeper areas are made of honeycomb-like cellular structures. The volume of the inner water body is 5.9 109 m3. The hydrodynamics of the lagoon has been well characterized (Dumas et al., 2012), and it is a poorly flushed atoll due to its closure and low exposure to swell (Andréfouët et al., 2012b).
2.2. Inventory of pearl farming derelict gear
Fig. 1. Functional pearl farms installations, from top to bottom: grafting and cleaning houses; baskets of grafted oysters; surface buoys indicating the presence of lines underneath; collecting lines.
When a farm is running, these installations are usually well maintained and visited daily. However, storms, human errors, boat propellers, and tired material may result in loss of materials that may drift ashore or sink. When farms stop their activities, it is only a short time before all structures start to fall apart due to weather conditions. Local authorities can be rightly worried about the not-so-glamorous image this situation triggers of the black pearl industry, which rather displays the image of a luxury product derived from pristine tropical blue lagoons fringed by coconut trees. The reality has in fact become quite different in some places. Concerns rose also in terms of ecological impacts. These could be related to changes in movement and behavior of mega-fauna (such as manta rays) due to hanging ropes. The impact on lagoon processes of discarded supports loaded with epibionts is unknown, as well as the impact on trophic carrying capacity of oysters left hanging on lines or on the seafloor. There are concerns about the evolution of
The 2013 survey aimed to assess the wild stock of oysters and the type and amount of derelict gear found on each dive site. Because of these two objectives, the work did not focus only on concession locations where we suspected that most of the PFDG should be found (Fig. 2) but on the entire lagoon, where oysters could be found. However, 12 dive sites among a total of 47 were located on concessions, as registered in 2012. Among the 35 other stations, some could have been in the limits of past concessions running before 2012, but this was not investigated. A 60-meter maximum depth-limit was followed for safety reasons during the SCUBA surveys, and most of the dives started at 45 m. On each dive site, 5-min search operations were conducted by default at each of the following depths 45–40, 30, 20, 15, 10, 5 and 0 m, if these depth limits were found, depending on the depth and geomorphology of the site. Each visible man-made object was photographed. Then, after the dive, the types of objects were listed as well as the number of occurrences. We did not try to measure the length of discarded ropes at that stage, or estimate precisely the weight and volume of each object. In addition, a 6 km-walk along the eastern shorelines allowed identification of materials washed ashore. The eastern lagoon shoreline was selected because this is the most exposed side of the lagoon and it receives floating debris and materials that are pushed by the tradewinds.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
S. Andréfouët et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
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Fig. 2. Locations of stations (see also Table 1) and concessions (shown as polygons). Red dots indicate the location of the diving boat, but the dive occurred around that point, or in the concession if the dot is at the edge of a concession. Land is in green and pinnacles in purple. Different shades of blue indicate different depth (lighter blue = deeper). Yellow area in the south-west is a shallow enclosed basin. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
3.1. Type, location and frequency of discarded and lost materials Studies on marine waste have looked at the types and distribution of anthropogenic debris washed ashore (Pruter, 1987), drifting in the open ocean (Mace, 2012) or sunken in the sea floor at various depth ranges (Moore and Allen, 2000). We found PFDG on the shoreline, the lagoon floor and floating in the water column. The later were still attached to the seafloor. Twenty different types of material were inventoried (Table 1 and Fig. 3). Overall, discarded and lost materials were very common. They were found on 45% of the sites, which is a high number considering that 75% of the dive sites were outside current concessions. The eastern shores were littered by an accumulation of small plastic debris intrically mixed with vegetation debris, making a new thick soil in some areas (Fig. 4). However, all the most eastern
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3. Results and discussion
Concession 0 0 0 0 0 0 0 0 1 1 Number of PFDG 0 0 0 0 5 0 0 3 4 3 Sunken buoys Bags of concrete Sunken ropes Drums Moorings Shell accumulation Cage with mesh Hanging ropes Sunken, stranded collecting lines Hanging collecting lines Cage structure (no mesh) Plastic furniture Plastic filament (carpet) Corrugated iron Wood/metal frame Metal bars Concrete pipe Hanging baskets Farm submerged piles Ghost farm (above water)
1 2 3 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 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
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Station
Table 1 Inventory (presence (x)/absence) of pearl farm derelict gear (PFDG) per station (Fig. 1). ‘‘Concession’’ indicates if the station was in a concession (1) or outside (0).
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Fig. 3. Examples of pearl farm derelict gear (PFDG): (A) sunken buoys, ropes and floating ropes; (B) concrete pipes in place, used to support wooden decks, with hanging plastic lines used to attach baskets of oysters before cleaning or grafting; (C) lost collecting lines left hanging in the water column; (D) mats of entangled ropes on a coral patch; (E) baskets and sunken ropes; (F) lost hanging ropes, with presence of Porites corals growing on them; (G) accumulation of dead oyster shells with cyanobacteria growth; (H) metal cages; (I) carpet of plastic filament in sediment; (J) metal cages without mesh; (K) domestic plastic debris; (L) large sheets of corrugated iron; (M) large plastic drum attached to sunken ropes; (N) concrete pipes on reef flat; (O) collecting lines stranded; (P) abandoned wooden grafting houses on coral pinnacles; (Q) buoys with collecting lines attached, floating in the water column; and (R) sunken ropes.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
S. Andréfouët et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
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Fig. 4. Examples of pearl farm derelict gear (PFDG) washed ashore: largest debris include plastic buoys and lost collecting lines. The shoreline accumulates all sorts of small plastic debris and ropes that mix with vegetation debris to create thick layers in some places.
underwater stations (20, 22, 23, 27, 28, 35, 36, 40, 42, 45 in Fig. 2) were free of any PFGD, showing that tradewind-induced drift impact shorelines, but not really the lagoon itself. Broken buoys were also abundant. When broken, these buoys cannot be re-used as they would sink. The number of types of PFDG was on average 3 times more important in concessions than outside concessions (Fig. 5). The most common type of trash was made of sunken ropes, found on 16 sites, including outside concessions. In this case, these were probably collecting lines. Forgotten collecting lines were also found in 12 sites, hanging in the waters, sunk on the floor or stranded in the shallows. Surprisingly, entire valuable set of lines fully rigged with hundreds of collectors were found, having drifted till they got stranded along the shoreline, sitting at 2–3 m depth.
The most littered areas where found next to discarded or currently active grafting houses, with up to 9 types of material, including the houses themselves. Some installations were several years old as shown by several 50 cm wide coral Porites colonies that have grown around ropes and aluminum structures (Fig. 3). Table 1 summarizes the type of PFDG found on each diving sites. We included in our typology accumulation of dead oyster shells, obviously the results of human action, by throwing away discarded shells repeatedly from the same pontoon or house. In several cases, these accumulations were the locations of cyanobacteria development (Fig. 3). Surprisingly, in contrast with widespread aquaculture-derived gear, very few household domestic garbage were found (plastic bottles, aluminum cans, etc.). No car or truck batteries were found.
Fig. 5. Average and standard deviation of number of pearl farm derelict gear (PFDG) outside (n = 35) and inside (n = 12) concessions.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
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However, we did not investigate the immediate proximity of the main village which comprises only about 250 inhabitants. This is in contrast to the widespread pollution found in Majuro atoll in the Marshall Islands, generated by the large local population (25,000 inhabitants, Richards and Beger, 2011) or washed ashore in Midway coming from outer sea-borne sources (Ribic et al., 2012). Most frequent type of debris documented in coral reefs are derelict fishing gears (DFG). These can be of oceanic origin like trawl nets that have drifted to reach coral forereefs (Donohue et al., 2001), or fishing gear used directly on the reefs such as lobster traps (Martens and Huntington, 2012). This study seems to be the first documented case of dominant aquaculture-borne debris in a tropical lagoon, although aquaculture was responsible of significant littering in Chile (Hinojosa and Thiel, 2009). 3.2. Potential impacts The main impacts that PFDG may have on lagoons are creation of new navigation hazards and sources of ecological disturbances. There is no doubt that forgotten materials are navigation hazards. Large vessels with drafts superior to 2 m (as the R/V Alis used for this survey) cannot navigate freely anymore in Ahe beyond the charted navigation channels, even when avoiding concessions. Ecological impacts of marine debris in general and in coral reefs in particular have been discussed and reviewed at several occasions (e.g., Katsanevakis, 2008; Richards and Beger, 2011). They include creating physical barriers preventing the movement of large animals (e.g., manta rays) that can be entangled in ropes, nets, cages and hanging collecting lines. If they remain attached to the animals, the drag can be lethal on the long term. Lots of the small litter items can be ingested by grazing animals including turtles and birds, with lethal consequences. Degradation of coral habitats is likely to occur by friction and shadowing when nets, baskets, ropes get around coral heads (Richards and Beger, 2011). Large debris on the floor, especially pieces of roofs (corrugated iron) and walls from grafting houses can modify gas exchanges between the sediment and the water column, leading to suffocation of the benthos (Goldberg, 1994). The many different forms of plastic we found, including from shredded ropes and collectors, will likely stay in the lagoon sediments or along the shore for an extremely long time (Teuten et al., 2009). Their slow weathering degradation will likely produce plastic microparticles invisible to the naked eye (microplastic), of unknown concentration and toxicity in the water column. This toxicity is due to their capacity of concentrating persistent organic pollutants. Concentrations will need to be measured in the different lagoons in order to state if they are a threat to marine life and humans, by ingestion and transfer at different trophic levels (Andrady, 2011; Wright et al., 2013). In particular the impact on pearl oysters, which are very efficient filtering organisms with the highest pumping rate reported for bivalves (Pouvreau et al., 1999; Fournier et al., 2012), is unknown in Tuamotu atolls. The lagoon residence time is a factor that will control the concentrations of these passive microplastics, and residence time varies widely dependent on atoll morphology and weather forcing (Andréfouët et al., 2001; Dumas et al., 2012). However, even if PFDG are conspicuous in Ahe and offer an unpleasant sight, their presence remains low compared to other sites and other types of pollution such as found in Majuro by Richards and Beger (2011) and assessing the actual levels of risks requires first the establishment of a proper management strategy. 3.3. Management The French Polynesia local authorities in charge of environmental protection and resource exploitation are fully aware that
declining aquaculture has resulted in a growing amount of discarded materials, with lagoon and shores littering. This is now a widespread issue on all farming atolls and islands. Personal observations (by SA) in Fakarava, Hao and Toau atolls in 2013 also confirm the presence of PFDG. To assess and mitigate the problem for any given lagoon, the different steps needed are: First, conduct an inventory of the type of materials and their amount, within and outside concessions. The present study pioneers this type of assessment using a simple methodology, although more quantitative observations would be needed to estimate the weight of all the sunken materials if recovery and cleaning is planned. Also, investigations of the deeper areas (>40 m) may be needed. Second, it is necessary to investigate through a literature review and expertise the potential ecological impacts given the amounts measured in different lagoons. While many impacts would be difficult to assess directly in atolls (such as plastic-induced chemical pollution), others could be more easily assessed by comparing coral reef community status inside and outside concessions, with different degrees of littering. This includes corals, but also invertebrates or fish population. Third, above a given threshold of abundance, the cost of cleaning will need to be precisely assessed. Searching, mapping, recovering and properly recycling the tons of discarded material is likely to be a huge task, requesting significant logistics in some cases, with barges, cranes, diving operations, lifting devices and so forth. In itself this activity could bring significant economical activities in atolls, and could be a significant source of income for local inhabitants. The activity should not be itself a new source of perturbations and pollution, and should remain as green as possible. The exact economical implications of such new activity needs to be properly assessed. Finally, financial penalties could be applied to owners of concessions where litters are present, for both active concessions and past concessions. This could fund, in part or totally, the cleaning. However, in the case of old concessions not active anymore, many small farms have closed due to financial difficulties and it is thus unlikely that the French Polynesia government will be able to obtain compensation for degradation of the public domain. This study aimed to bring attention to a significant environmental issue impacting remote atoll lagoons where two decades of pearl farming have taken place before collapsing. The Ahe atoll assessment presented here is a first step towards a long term management program that should include the estimation of the volume of trash, the cleaning of lagoons, raising awareness among farmers, and identification of potential ecological consequences for lagoon ecosystems if the materials are left in the lagoons. Acknowledgements This study was funded by the Agence Nationale de la Recherche (ANR), as part of the POLYPERL project (www.polyperl.org). We acknowledge the kind help of the crew of the R/V Alis during this survey, as well as the scientific divers from the Direction des Ressources Marines de Polynésie française, Ifremer and Ministry of Marine Resources of Cook Islands who were involved in the 2013 stock assessment survey. Our research in Ahe atoll has also been supported since several years by the Direction des Ressources Marines et Minières de Polynésie française. References Andrady, A.L., 2011. Microplastics in the marine environment. Mar. Pollut. Bull. 62, 1596–1605. Andréfouët, S., Pages, J., Tartinville, B., 2001. Water renewal time for classification of atoll lagoons in the Tuamotu Archipelago (French Polynesia). Coral Reefs 20, 399–408.
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Martens, J., Huntington, B.E., 2012. Creating a GIS-based model of marine debris ‘‘hot spots’’ to improve efficiency of a lobster trap debris removal program. Mar. Pollut. Bull. 64, 949–955. Moore, S.L., Allen, M.J., 2000. Distribution of anthropogenic and natural debris on the mainland shelf of the Southern California Bight. Mar. Pollut. Bull. 40, 83–88. Morrison, R.J., Denton, G.R.W., Bale-Tamata, U. Grignon, J., 2013. Anthropogenic biogeochemical impacts on coral reefs in the Pacific Islands—An overview Deep Sea Research Part II: http://dx.doi.org/10.1016/j.dsr2.2013.02.014. Pouvreau, S., Jonquieres, G., Buestel, D., 1999. Filtration by the pearl oyster, Pinctada margaritifera, under conditions of low seston load and small particle size in a tropical lagoon habitat. Aquaculture 176, 295–314. Pruter, A.T., 1987. Sources, quantities and distribution of persistent plastics in the marine environment. Mar. Pollut. Bull. 18, 305–310. Ribic, C.A., Sheavly, S.B., Klavitter, J., 2012. Baseline for beached marine debris on Sand Island, Midway Atoll. Mar. Pollut. Bull. 64, 1726–1729. Richards, Z.T., Beger, M., 2011. A quantification of the standing stock of macrodebris in Majuro lagoon and its effect on hard coral communities. Mar. Pollut. Bull. 62, 1693–1701. Teuten, E.L., Saquing, J.M., Knappe, D.R.U., Barlaz, M.A., Jonsson, S., Bjorn, A., Rowland, S.J., Thompson, R.C., Galloway, T.S., Yamashita, R., Ochi, D., Watanuki, Y., Moore, C., Pham, H.V., Tana, T.S., Prudente, M., Boonyatumanond, R., Zakaria, M.P., Akkhavong, K., Ogata, Y., Hirai, H., Iwasa, S., Mizukawa, K., Hagino, Y., Imamura, A., Saha, M., Takada, H., 2009. Transport and release of chemicals from plastics to the environment and to wildlife. Philos. Trans. R. Soc. Lond. B Biol. Sci. 364, 2027–2045. Wright, S., Thompson, R.C., Galloway, T.S., 2013. The physical impacts of microplastics on marine organisms: a review. Environ. Pollut. 178, 483–492.
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Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia Serge Andréfouët a,⇑, Yoann Thomas a, Cedrik Lo b a b
IRD, UR 227 CoRéUs, LABEX CORAIL, BP A5, 98848 Nouméa cedex, New Caledonia Direction des Ressources Marines et Minières, Papeete, BP 20 Papeete 98713, Tahiti, French Polynesia
a r t i c l e
i n f o
Keywords: Aquaculture Marine debris Pearl farm derelict gear Atoll
a b s t r a c t Pearl oyster aquaculture is a major activity in French Polynesia atoll lagoons. After the economic decline that characterized the last decade, concerns recently rose about discarded installations and materials that supported aquaculture practices and by facilities abandoned after they had to close their activities. In May 2013, a first inventory of the type and amount of pearl farms derelict gear (PFDG) was achieved on 47 sites in Ahe lagoon. Surveys were conducted within and outside the boundaries of aquaculture concessions. Twenty types of PFDG littered the lagoon floor and the water column. The most impacted areas were near abandoned grafting houses with up to nine types of PFDG. Forty-five percent of the sites were impacted, including outside concessions. While management authorities are fully aware of the problem, this first assessment is a wake-up call to stimulate the cleaning of lagoons, enhance awareness among farmers, and identify potential ecological consequences on lagoon ecosystems. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Recently, Andréfouët et al. (2012a) reviewed the most recent advances in black pearl oyster aquaculture research accomplished in Ahe atoll lagoon, in the French Polynesian Tuamotu archipelago. In the short review of this activity critical for French Polynesia’s economic income, they pointed out that the aquaculture of black pearl in French Polynesia has modified the livelihoods of thousands of islanders in the past 30 years. It has also reshaped the atollscape, with numerous farms, buildings, pontoons and boats appearing and disappearing along shores and coral pinnacles. The official 10,000 hectares of concessions authorized in French Polynesia have hosted tens of thousands of hanging lines, visible thanks to surface buoys that dot the lagoons. Millions of oysters have been artificially hanged in the water column instead of living on deep atoll floors. Naturally separated oyster populations have been mixed, and numerous epibionts were introduced in lagoons. Massive local and widespread mortalities which occurred remain poorly explained due to insufficient in situ monitoring of environmental conditions, given the remoteness of atolls and associated monitoring costs. Andréfouët et al. (2012a) concluded that ‘‘The exact ecological impact of the pearl industry remains unknown to date and will likely be a future direction of investigation’’. There is a
⇑ Corresponding author. Tel.: +687 26 08 00; fax: +687 26 43 26.
growing concern in French Polynesia regarding the amount of discarded materials, installations and trash generated by farms, some still active, but having ceased activities by now. By law, farmers have to clean their concessions and remove any type of materials, otherwise they risk a stiff fine in case of control. However, there are evidences that many lagoons and shorelines are now littered by black pearl farm derelict gears (or PFDG afterwards). A functioning farm would typically have wood and concrete pontoons and jetties with houses for epibiont-cleaning and grafting oysters. Next to these houses will be found aluminum or wood structures (cages) where baskets of oysters are temporally tied before their processing. Then, rearing stations with baskets of hanging oysters as well as spat collecting stations are spread in the concession. These are attached with submerged thick ropes and surface/sub-surface plastic buoys that are adjusted so that oysters and collectors can hang at a given depth depending on the conditions (Fig. 1). These buoys are made of acrylonitrile butadiene styrene (ABS). ABS is used due to its toughness, and impact and heat resistance. Baskets and collectors are usually made of plastic (loops of black flat polypropylene, knitted onto a 30 cm monofilament polyethylene line). An important fact is that no concessions are required for collecting, thus collecting lines can be freely deployed anywhere in the lagoon at the discretion of the farmers. The only limitations are their length (200 m), number of lines per concession (i.e., 10 lines for a concession of 5 ha and one more for each additional hectare) and submersion duration (i.e., 2 years).
E-mail address: [email protected] (S. Andréfouët). http://dx.doi.org/10.1016/j.marpolbul.2014.03.048 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
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habitat qualities, with tangled ropes on the seafloor damaging the natural habitats. In the other hand, these PFDG can be the foundation of new opportunistic habitats for a number of marine creatures, resulting in habitat and behavior shifts. These concerns promt new questions that have not yet been tackled, or considered by recent reviews on anthropogenic impacts on Pacific islands (e.g., Morrison et al., 2013). For this, a first assessment of the extent of PFDG found in lagoons was needed. An inventory would be the first step for the managing authorities in order to take action and start mitigating the impacts. In May 2013, a new series of hydrodynamic and biological experiments were conducted in Ahe atoll lagoon during a five week expedition on board the R/V Alis. We took this opportunity to (1) make an inventory of all discarded materials in 47 dive sites, (2) create a typology of discarded aquaculture materials that can be found in all lagoons, (3) assess the extent of the problem for one of the busiest atoll in the recent past and infer practical recommendation for the local authorities.
2. Material and methods 2.1. Study site Ahe atoll is located in the northwestern part of the Tuamotu Archipelago (14.48S – 146.30 W), about 500 km northeast from Tahiti (Fig. 2). It is now one of the most studied atolls worldwide, with most research directly related to the black pearl industry and the aquaculture of the black lip oyster Pinctada margaritifera (Andréfouët et al., 2012a and references within). The lagoon is a 142 km2 deep water body with an average depth of 41 m, reaching up to 70 m depth and contains numerous pinnacles rising to the surface. The deeper areas are made of honeycomb-like cellular structures. The volume of the inner water body is 5.9 109 m3. The hydrodynamics of the lagoon has been well characterized (Dumas et al., 2012), and it is a poorly flushed atoll due to its closure and low exposure to swell (Andréfouët et al., 2012b).
2.2. Inventory of pearl farming derelict gear
Fig. 1. Functional pearl farms installations, from top to bottom: grafting and cleaning houses; baskets of grafted oysters; surface buoys indicating the presence of lines underneath; collecting lines.
When a farm is running, these installations are usually well maintained and visited daily. However, storms, human errors, boat propellers, and tired material may result in loss of materials that may drift ashore or sink. When farms stop their activities, it is only a short time before all structures start to fall apart due to weather conditions. Local authorities can be rightly worried about the not-so-glamorous image this situation triggers of the black pearl industry, which rather displays the image of a luxury product derived from pristine tropical blue lagoons fringed by coconut trees. The reality has in fact become quite different in some places. Concerns rose also in terms of ecological impacts. These could be related to changes in movement and behavior of mega-fauna (such as manta rays) due to hanging ropes. The impact on lagoon processes of discarded supports loaded with epibionts is unknown, as well as the impact on trophic carrying capacity of oysters left hanging on lines or on the seafloor. There are concerns about the evolution of
The 2013 survey aimed to assess the wild stock of oysters and the type and amount of derelict gear found on each dive site. Because of these two objectives, the work did not focus only on concession locations where we suspected that most of the PFDG should be found (Fig. 2) but on the entire lagoon, where oysters could be found. However, 12 dive sites among a total of 47 were located on concessions, as registered in 2012. Among the 35 other stations, some could have been in the limits of past concessions running before 2012, but this was not investigated. A 60-meter maximum depth-limit was followed for safety reasons during the SCUBA surveys, and most of the dives started at 45 m. On each dive site, 5-min search operations were conducted by default at each of the following depths 45–40, 30, 20, 15, 10, 5 and 0 m, if these depth limits were found, depending on the depth and geomorphology of the site. Each visible man-made object was photographed. Then, after the dive, the types of objects were listed as well as the number of occurrences. We did not try to measure the length of discarded ropes at that stage, or estimate precisely the weight and volume of each object. In addition, a 6 km-walk along the eastern shorelines allowed identification of materials washed ashore. The eastern lagoon shoreline was selected because this is the most exposed side of the lagoon and it receives floating debris and materials that are pushed by the tradewinds.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
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Fig. 2. Locations of stations (see also Table 1) and concessions (shown as polygons). Red dots indicate the location of the diving boat, but the dive occurred around that point, or in the concession if the dot is at the edge of a concession. Land is in green and pinnacles in purple. Different shades of blue indicate different depth (lighter blue = deeper). Yellow area in the south-west is a shallow enclosed basin. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
3.1. Type, location and frequency of discarded and lost materials Studies on marine waste have looked at the types and distribution of anthropogenic debris washed ashore (Pruter, 1987), drifting in the open ocean (Mace, 2012) or sunken in the sea floor at various depth ranges (Moore and Allen, 2000). We found PFDG on the shoreline, the lagoon floor and floating in the water column. The later were still attached to the seafloor. Twenty different types of material were inventoried (Table 1 and Fig. 3). Overall, discarded and lost materials were very common. They were found on 45% of the sites, which is a high number considering that 75% of the dive sites were outside current concessions. The eastern shores were littered by an accumulation of small plastic debris intrically mixed with vegetation debris, making a new thick soil in some areas (Fig. 4). However, all the most eastern
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3. Results and discussion
Concession 0 0 0 0 0 0 0 0 1 1 Number of PFDG 0 0 0 0 5 0 0 3 4 3 Sunken buoys Bags of concrete Sunken ropes Drums Moorings Shell accumulation Cage with mesh Hanging ropes Sunken, stranded collecting lines Hanging collecting lines Cage structure (no mesh) Plastic furniture Plastic filament (carpet) Corrugated iron Wood/metal frame Metal bars Concrete pipe Hanging baskets Farm submerged piles Ghost farm (above water)
1 2 3 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 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
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Station
Table 1 Inventory (presence (x)/absence) of pearl farm derelict gear (PFDG) per station (Fig. 1). ‘‘Concession’’ indicates if the station was in a concession (1) or outside (0).
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Fig. 3. Examples of pearl farm derelict gear (PFDG): (A) sunken buoys, ropes and floating ropes; (B) concrete pipes in place, used to support wooden decks, with hanging plastic lines used to attach baskets of oysters before cleaning or grafting; (C) lost collecting lines left hanging in the water column; (D) mats of entangled ropes on a coral patch; (E) baskets and sunken ropes; (F) lost hanging ropes, with presence of Porites corals growing on them; (G) accumulation of dead oyster shells with cyanobacteria growth; (H) metal cages; (I) carpet of plastic filament in sediment; (J) metal cages without mesh; (K) domestic plastic debris; (L) large sheets of corrugated iron; (M) large plastic drum attached to sunken ropes; (N) concrete pipes on reef flat; (O) collecting lines stranded; (P) abandoned wooden grafting houses on coral pinnacles; (Q) buoys with collecting lines attached, floating in the water column; and (R) sunken ropes.
Please cite this article in press as: Andréfouët, S., et al. Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon, French Polynesia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.03.048
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Fig. 4. Examples of pearl farm derelict gear (PFDG) washed ashore: largest debris include plastic buoys and lost collecting lines. The shoreline accumulates all sorts of small plastic debris and ropes that mix with vegetation debris to create thick layers in some places.
underwater stations (20, 22, 23, 27, 28, 35, 36, 40, 42, 45 in Fig. 2) were free of any PFGD, showing that tradewind-induced drift impact shorelines, but not really the lagoon itself. Broken buoys were also abundant. When broken, these buoys cannot be re-used as they would sink. The number of types of PFDG was on average 3 times more important in concessions than outside concessions (Fig. 5). The most common type of trash was made of sunken ropes, found on 16 sites, including outside concessions. In this case, these were probably collecting lines. Forgotten collecting lines were also found in 12 sites, hanging in the waters, sunk on the floor or stranded in the shallows. Surprisingly, entire valuable set of lines fully rigged with hundreds of collectors were found, having drifted till they got stranded along the shoreline, sitting at 2–3 m depth.
The most littered areas where found next to discarded or currently active grafting houses, with up to 9 types of material, including the houses themselves. Some installations were several years old as shown by several 50 cm wide coral Porites colonies that have grown around ropes and aluminum structures (Fig. 3). Table 1 summarizes the type of PFDG found on each diving sites. We included in our typology accumulation of dead oyster shells, obviously the results of human action, by throwing away discarded shells repeatedly from the same pontoon or house. In several cases, these accumulations were the locations of cyanobacteria development (Fig. 3). Surprisingly, in contrast with widespread aquaculture-derived gear, very few household domestic garbage were found (plastic bottles, aluminum cans, etc.). No car or truck batteries were found.
Fig. 5. Average and standard deviation of number of pearl farm derelict gear (PFDG) outside (n = 35) and inside (n = 12) concessions.
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However, we did not investigate the immediate proximity of the main village which comprises only about 250 inhabitants. This is in contrast to the widespread pollution found in Majuro atoll in the Marshall Islands, generated by the large local population (25,000 inhabitants, Richards and Beger, 2011) or washed ashore in Midway coming from outer sea-borne sources (Ribic et al., 2012). Most frequent type of debris documented in coral reefs are derelict fishing gears (DFG). These can be of oceanic origin like trawl nets that have drifted to reach coral forereefs (Donohue et al., 2001), or fishing gear used directly on the reefs such as lobster traps (Martens and Huntington, 2012). This study seems to be the first documented case of dominant aquaculture-borne debris in a tropical lagoon, although aquaculture was responsible of significant littering in Chile (Hinojosa and Thiel, 2009). 3.2. Potential impacts The main impacts that PFDG may have on lagoons are creation of new navigation hazards and sources of ecological disturbances. There is no doubt that forgotten materials are navigation hazards. Large vessels with drafts superior to 2 m (as the R/V Alis used for this survey) cannot navigate freely anymore in Ahe beyond the charted navigation channels, even when avoiding concessions. Ecological impacts of marine debris in general and in coral reefs in particular have been discussed and reviewed at several occasions (e.g., Katsanevakis, 2008; Richards and Beger, 2011). They include creating physical barriers preventing the movement of large animals (e.g., manta rays) that can be entangled in ropes, nets, cages and hanging collecting lines. If they remain attached to the animals, the drag can be lethal on the long term. Lots of the small litter items can be ingested by grazing animals including turtles and birds, with lethal consequences. Degradation of coral habitats is likely to occur by friction and shadowing when nets, baskets, ropes get around coral heads (Richards and Beger, 2011). Large debris on the floor, especially pieces of roofs (corrugated iron) and walls from grafting houses can modify gas exchanges between the sediment and the water column, leading to suffocation of the benthos (Goldberg, 1994). The many different forms of plastic we found, including from shredded ropes and collectors, will likely stay in the lagoon sediments or along the shore for an extremely long time (Teuten et al., 2009). Their slow weathering degradation will likely produce plastic microparticles invisible to the naked eye (microplastic), of unknown concentration and toxicity in the water column. This toxicity is due to their capacity of concentrating persistent organic pollutants. Concentrations will need to be measured in the different lagoons in order to state if they are a threat to marine life and humans, by ingestion and transfer at different trophic levels (Andrady, 2011; Wright et al., 2013). In particular the impact on pearl oysters, which are very efficient filtering organisms with the highest pumping rate reported for bivalves (Pouvreau et al., 1999; Fournier et al., 2012), is unknown in Tuamotu atolls. The lagoon residence time is a factor that will control the concentrations of these passive microplastics, and residence time varies widely dependent on atoll morphology and weather forcing (Andréfouët et al., 2001; Dumas et al., 2012). However, even if PFDG are conspicuous in Ahe and offer an unpleasant sight, their presence remains low compared to other sites and other types of pollution such as found in Majuro by Richards and Beger (2011) and assessing the actual levels of risks requires first the establishment of a proper management strategy. 3.3. Management The French Polynesia local authorities in charge of environmental protection and resource exploitation are fully aware that
declining aquaculture has resulted in a growing amount of discarded materials, with lagoon and shores littering. This is now a widespread issue on all farming atolls and islands. Personal observations (by SA) in Fakarava, Hao and Toau atolls in 2013 also confirm the presence of PFDG. To assess and mitigate the problem for any given lagoon, the different steps needed are: First, conduct an inventory of the type of materials and their amount, within and outside concessions. The present study pioneers this type of assessment using a simple methodology, although more quantitative observations would be needed to estimate the weight of all the sunken materials if recovery and cleaning is planned. Also, investigations of the deeper areas (>40 m) may be needed. Second, it is necessary to investigate through a literature review and expertise the potential ecological impacts given the amounts measured in different lagoons. While many impacts would be difficult to assess directly in atolls (such as plastic-induced chemical pollution), others could be more easily assessed by comparing coral reef community status inside and outside concessions, with different degrees of littering. This includes corals, but also invertebrates or fish population. Third, above a given threshold of abundance, the cost of cleaning will need to be precisely assessed. Searching, mapping, recovering and properly recycling the tons of discarded material is likely to be a huge task, requesting significant logistics in some cases, with barges, cranes, diving operations, lifting devices and so forth. In itself this activity could bring significant economical activities in atolls, and could be a significant source of income for local inhabitants. The activity should not be itself a new source of perturbations and pollution, and should remain as green as possible. The exact economical implications of such new activity needs to be properly assessed. Finally, financial penalties could be applied to owners of concessions where litters are present, for both active concessions and past concessions. This could fund, in part or totally, the cleaning. However, in the case of old concessions not active anymore, many small farms have closed due to financial difficulties and it is thus unlikely that the French Polynesia government will be able to obtain compensation for degradation of the public domain. This study aimed to bring attention to a significant environmental issue impacting remote atoll lagoons where two decades of pearl farming have taken place before collapsing. The Ahe atoll assessment presented here is a first step towards a long term management program that should include the estimation of the volume of trash, the cleaning of lagoons, raising awareness among farmers, and identification of potential ecological consequences for lagoon ecosystems if the materials are left in the lagoons. Acknowledgements This study was funded by the Agence Nationale de la Recherche (ANR), as part of the POLYPERL project (www.polyperl.org). We acknowledge the kind help of the crew of the R/V Alis during this survey, as well as the scientific divers from the Direction des Ressources Marines de Polynésie française, Ifremer and Ministry of Marine Resources of Cook Islands who were involved in the 2013 stock assessment survey. Our research in Ahe atoll has also been supported since several years by the Direction des Ressources Marines et Minières de Polynésie française. References Andrady, A.L., 2011. Microplastics in the marine environment. Mar. Pollut. Bull. 62, 1596–1605. Andréfouët, S., Pages, J., Tartinville, B., 2001. Water renewal time for classification of atoll lagoons in the Tuamotu Archipelago (French Polynesia). Coral Reefs 20, 399–408.
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