4 DEVELOPING A SCIENTIFIC FRAMEWORK IN SUPPORT OF MANAGEMENT INSTRUMENTS TOWARDS ELIMINATING OR MITIGATING THE EFFECT OF BLOOMS

4.1. Human impacts and ecosystem functioning

Man removes the fish in an industrial way, with more and more sophisticated technologies. It is worthwhile considering that, in the ocean, we are still hunters and gatherers, and we draw resources from natural populations, as we did in pre-agriculture periods also in terrestrial systems.

The natural populations of the species we hunted on, however, could not cope with our pressure when we became too efficient as hunters, and we had to shift to agriculture, due to depletion of natural resources ensuing overexploitation. Marine systems, due to their faster turnovers, can support a stronger pressure than terrestrial ones, but they too have their limits in supporting us. Overfishing means that we are fishing at a faster rate than the turnover rate of the populations we predate upon. We have seen that fish, if not stressed, can cope well with the competition of gelatinous macrozooplankton, being overwhelmed by it just episodically and being able to recover at a fast pace. But, in the last 50 years, we have overexploited most of the oceans (Jackson et al., 2001). After having depleted the populations of large fish, we are now "fishing down marine food webs" as evocated by Pauly et al. (1998) (Fig. 8). This has released gelatinous zooplankton from fish competition, and the blooms of gelatinous plankton, once episodic, are becoming the rule (Mills, 1995; 2000). Besides removing the fish, so leaving space to the jellyfish, we are introducing species into ecosystems that did not coevolve with the resident species (see Purcell et al., 2007, for a list of introduced gelatinous predators). If these aliens are voracious carnivores, they might disrupt the “normal” functioning of ecosystems, channeling towards their own populations the resources that should go to the fish. If we introduce one of these species in a system that is already stressed by overfishing, the impact will be even greater.

4.2. Multiple stressors

In experimental ecology, impacts are usually evaluated in isolation. In the real life, however, several impacts (each having almost negligible effect) can sum to each other so as to impair the impacted system. If the impact of fisheries (on adult fish) is not associated to the impact of predation and competition on early stages in fish life cycles, it might happen that a fisheries impact that is predicted as bearable by the exploited populations can become unbearable when summed to the impact of gelatinous plankton predation and competition. Under these circumstances, gelatinous plankton impacts might be the proverbial straw that broke the camel’s back. The logic of the ecosystem approach should be just this: it is not sufficient to analyze the impact of fisheries on single species, as if there were no other predators of those species out there. Humans surely are the most efficient predators of adult fish. So efficient that it is not necessary to evaluate the predation pressure of other predator species. But the case of Mnemiopsis shows that gelatinous predators of fish eggs and larvae can have a high impact on fish populations. So, the first step to apply the ecosystem approach to fisheries should be to consider fish as life cycles and evaluate potential impacts on the whole array of life stages that defines each species. If this is done, then the importance of gelatinous zooplankton becomes immediately apparent, both as a competitor and as a predator of fish.

4.3. The ecosystem approach

The highly advocated ecosystem approach requires that it is tenuous to focus on single ecosystem nodes, disregarding the rest. The appreciation of ecological links is crucial for the management of the resources. If something “goes wrong” and the resources we expect to extract from the ecosystems (e.g. the fish) are not produced anymore, we must single out the processes that led to a different functioning of the ecosystems. The reasons for such malfunction (from our point of view) are often ascribed to direct human pressure, and usually the blame falls on overfishing. But they might also be the result of different ways of ecosystem functioning that are less directly dependent on our pressures. Stability is nonsense: in nature nothing remains the same. Boero (1994) distinguished between normal fluctuations, such as the seasonal ones, leading to recurrent patterns of biodiversity expression, and variations, i.e. changes in biodiversity expression that might be labeled as regime shifts, deviations from the norm of fluctuations. Furthermore, Boero (1996) analyzed the importance of episodic events in determining the changes we observe when dealing with the history of a system. Jellyfish blooms have been “normal” episodes in the history of marine ecosystems, but now they seem to have become the rule (Mills, 2001). Boero et al. (2008) reached the conclusion that “irregularities rule the world, sometimes”, since history is governed by contingencies. History, in fact, would not exist if natural systems were governed by rules that constrain them into a restricted range of possible developments. Contingencies (such as jellyfish blooms) lead to changes in the systems, and history is just this: deviation from the norms dictated by constraints (Boero et al., 2004). As it often happens in complex systems (and ecosystems are the most complex systems of the planet) the causes for a pattern might be multiple, with a blend of different pressures. Most analyses are correlational, so we might find a correlation between one activity (e.g. fishing) and an ecosystem response (e.g. the decline of fish), but this correlation might not be the only cause of the observed pattern. Correlation does not imply causation, or might hide multiple causality. With the ecosystem approach we should disentangle the possible causes of the observed patterns, so as to enforce proper management, based on a good knowledge of the functioning of the ecosystems that we want to manage, of course considering the history of the system we want to manage. If fisheries science focuses just on fish, the results of management might not be as good as expected. The problems in resource extraction from natural fish populations might be due also to mismanagement due to lack of knowledge about the functioning of the system that sustains the resources that we are directly interested in. The ecosystem approach to fisheries, thus, must invoke the study of the whole ecosystem, because the fish are just an epiphenomenon that cannot persist in isolation from the rest of the ecosystem. Management, thus, cannot be divorced from understanding patterns and processes.

4.4. Recommendations for management

The management of natural events is based on several steps:
1. Identification of the phenomenon ensuing from perceived symptoms (in this case: jellyfish blooms are increasing).
2. Identification of the causes (in this case the causes are multiple and are not the same for all species, at all places).
3. Alleviation of the symptoms (but this does not solve the problem).
4. Removal of the causes.
5. If the causes are difficult to remove, adaptation to the new situation is the only solution.
The drivers of jellyfish blooms, as described in Section 3 of this report, are many and concur to determine a situation that, contrary to the past, seems persistent and of global scale. It is obvious that “local” management can only alleviate the symptoms but will not remove the causes.
In the past, jellyfish blooms have been studied episodically, since their occurrence was episodic, and most of the times the studies started after the onset of the blooms, and came to an end when the phenomena became less evident. Obviously, this research strategy is not conducive to a good understanding of these phenomena. So, the first strategy to manage jellyfish blooms is to incorporate jellyfish research into fisheries research, and treat the jellyfish just as the fish are treated, with monitoring of their diversity, life cycles, fluctuations etc. Early warning of the onset of blooms might lead to better understanding of the triggering conditions that, eventually, might be artificially modified, if possible, so as to impair the population boom.
Richardson et al. (2009) proposed a series of management measures to cope with jellyfish blooms. They listed in a table the management responses, the research needs, the benefits and the risks and issues. Their contributions are as follows:
•Develop jellyfish products for food and medicine
In other words: If you cannot fight them... eat them. Some jellyfish species are a food source in some countries (e.g. China) and the development of conservation and packaging practices to sell them where they are appreciated might be a wise strategy, adapting the fishing fleets and the commercial network behind them to take advantage of sudden abundances of this product-to-be. Jellyfish are widely diverse and some species might contain chemicals that are conducive to the development of new drugs and other biotechnological products based on active molecules. Jellyfish are the oldest among the living animals and contain the premises of the evolutionary “innovations” that characterize the whole metazoan evolution (Boero and Piraino, 2010), their basic features might hide important potentials, as suggested by the discovery of the so-called “immortal jellyfish” (Piraino et al., 1996), a species with promising features in the field of aging prevention.
•Use cutting nets to destroy the jellyfish
This practice is used to physically destroy jellyfish that, transported by the currents, are pushed against these nets and are destroyed then. This might be a solution to defend power plants, since the fragments transported into the cooling systems might not clog them (but this is far from being certain). The pieces of jellyfish might lead to regeneration of new jellyfish through asexual reproduction (Boero et al., 2002). Furthermore, jellyfish fragments retain their stinging properties and can become even more lethal for, for instance, fish kept in aquaculture cages.
•Destroy the polyps
Many species do have polyp stages (Fig. 1) that are the real “seeds” where blooms come from. Also polyps, however, do have very high potentials for asexual reproduction from fragments, and attempts at destroying them might even exacerbate the phenomena. The use of chemicals and other practices can be problematic (Sandifer et al., 1974) and, furthermore, antifouling paints contain chemicals that cause serious problems to biodiversity in general and cannot be used on a wide scale. The great abundance of the stinging cubozoan Carybdea marsupialis
along the Adriatic coast of Italy (Boero, unpublished observation) is probably linked to the hundreds of kilometres of coastal defenses that have been established to prevent beach erosion. The availability of hard bottom habitats in a region previously dominated by soft bottoms might have favored the establishment of the species that, in fact, was unknown from the Adriatic sea before 1986 (Boero and Minelli, 1986). To clean 500 km of coastal defenses is surely unfeasible. Di Camillo et al. (2010) however, reported that ship wrecks in the Adriatic are the ideal substrate for the polyps of Aurelia aurita and estimated that the extensive blooms of this species in their study area might well be sustained by just one wreck. They did not find the polyps growing on any other substrate. In this case, of course, the removal of the wreck(s) might remove the cause for the blooms of this species. The disappearance of species with polyps, however, might pave the way for species that do not have a polyp stage, such as the mauve stinger Pelagia noctiluca. The study of jellyfish presence in Italian waters in 2009-2011 (Boero, unpublished), for instance, showed that Pelagia was almost absent from the Adriatic Sea, whereas it was very abundant in the western coasts of the Italian peninsula. Instead of Pelagia, Aurelia was most abundant in the Adriatic, together with Carybdea. Both species are polyp formers, whereas Pelagia is not. Their presence might have outcompeted Pelagia which, when these species are absent or less abundant, might find less restrictions to the numerical increase of its populations.
•Biocontrol agents
The use of chemicals to kill jellyfish or polyps is not advisable, since active substances (which are anyway still not developed) will almost surely induce resistance in the target species, while impacting even more on their potential predators. The control of noxious species such as Mnemiopsis leidyi by focused predators such as the ctenophore Beroe ovata
might lead to consider the introduction of predators into systems heavily invaded by some gelatinous plankter. These practices have been used on land, but with very debatable success. In several cases, in fact, the supposed controller became a pest itself once it destroyed the target species! It seems, as shown in a previous section of this document, that medusiphagous species (fishes and turtles) are increasing, due to greater food availability. The natural systems, thus, are answering to the fish-jellyfish regime shift and might provide a buffer to it without any need of intervention from our side. Of course, medusiphagous species should be somehow protected, so that they can continue to play their role. Many of them, however, are already protected (marine turtles) or do have little commercial value (the sun fish).
•Prevent any activity that might promote the spread of gelatinous plankters Many species became a nuisance when they were introduced into basins with communities that had not coevolved with their ecological traits. The case of Mnemiopsis is the most famous one. CIESM (2002) reviewed the ways non-indigenous species can be spread by ships, both as fouling on their hulls, or as resting stages. Policies have been designed to prevent the spread of NIS through ships, and they must be extended also to leisure boats. Jellyfish can be transported as polyps growing on animals that are shipped around the world, such as oysters (Edwards, 1976), or they can be spread through aquarium trades (Bolton et al., 2006). Obviously these activities must be carefully controlled to prevent the spread of potentially noxious species.
Other ways to prevent jellyfish risks, especially for fisheries activities might be:
•Design nets that are not clogged by gelatinous plankton
The efficacy of such nets is probably very debatable, since it is very difficult to sort jellyfish from fish.
•Employ selective fishing gear
The use of hooks is probably the most effective way to avoid jellyfish interference with fisheries activities. If jellyfish are around, it is advisable to shift from nets to hooks.
•Set early warning systems
The identification of swarms, and the prediction of their movements based on knowledge of oceanographic patterns, can lead to adaptive measures to cope with the presence of gelatinous plankton. This is extremely important for cage aquaculture, with the employment of protective barriers against jellyfish. Also fisheries activities might be regulated when particularly intense events do occur.
The management measures described above are aimed at mitigating local effects of gelatinous plankton blooms, and might be useful to cope with them but, surely, not to avoid their occurrence, especially for indigenous species, whereas the control of artificial transport is itself a definitive measure. The prevention of these phenomena must act directly on their causes that, we have seen, are manifold. Richardson et al. (2009) suggest to reduce:
? Eutrophication
? Overfishing
? Global warming
These obvious measures would undoubtedly improve environmental quality at large and might, thus, also reduce the present prevalence of jellyfish. The mitigation of these impacts cannot be obtained by single-country initiatives and its enforcement is far from being universally agreed upon, as many world summits showed, since the Rio Convention in 1992. Aquaculture, furthermore, is widely proposed as a valid alternative to fisheries to satisfy the demand of fish by the food market. In fact, it is suggested that the development of aquaculture will release natural populations from the pressures of overfishing. As remarked by various authors (see Boero, 2009), however, aquaculture species are invariably carnivores (especially in the Mediterranean area) and they are fed with pellets that derive from smaller fish taken from natural populations. After having taken the larger fish, thus, we are fishing down marine food webs (Pauly et al., 1998) to feed the fish that we rear. Cage aquaculture, furthermore, enhances eutrophication (Pusceddu et al., 2007), so exacerbating both nutrient enrichment and overfishing.

4.5. Conclusion

The possibility of enjoying the goods and services offered by natural biodiversity depends on the rate we utilize them. The natural resources are renewable but the rate we consume them cannot be higher than the rate they renew themselves. One of the paradigms of current economy is growth. Production, income, and consumption must grow, in order to have a healthy economy. The expectation, thus, is infinite growth. Obviously this is not possible, since our planet is finite, and the biomass ecosystems can produce is limited. The growth of human populations is exerting an unbearable pressure on natural systems that, obviously, are on the edge of collapse. The scientific community is warning about this problem since the times of Malthus and Darwin, but it is apparently unheard by decision-makers, economists having much greater influence than ecologists. However, if the principles we invented to regulate our activities (economy, with its infinite growth) are in conflict with natural principles (ecology, with the finiteness of natural systems), we can only expect that we will be defeated.
Jellyfish are just a symptom of this situation, another warning that Nature is giving us!