Jellyfish blooms, why?!? [untranslated science!]

[a "translated" version will follow that defines the words that are less common in day-to-day language]

by S. Abboud 

A bloom is a consequence of seasonal life cycles when there is localized increases in asexual reproduction and growth typical of all metagenic organisms that result in normal or abnormal seasonal biomass (we are currently verifying permissions regarding Figure 1, an alternate photo of a bloom has been inserted). Blooms can be influenced by localized anthropogenic effects attributed to oceanic sea surface temperature, nutrient inputs (Purcell et al. 2007, Brodeur et al. 2008), disturbances (Brodeur et al. 2002) including over-harvesting fisheries and translocations (Purcell 2005, Howarth et al. 2002). Apparent sudden jellyfish population increases (i.e. blooms, Figure 2) are possible due to increased recruitment from local asexual reproduction (Madin & Deibel 1998), high fecundity (i.e. enhanced fertilization success), aggregation of mature medusae (Strathmann 1990, Purcell and Madin 1991, and Hamner et al. 1994), and previously mentioned ecophysiological and reproductive versatility (Hadfield & Strathmann 1996, Lucas 2001, Deibel & Lowen 2011).

Term	Description (Lucas & Dawson 2013)
bloom	A true bloom is a consequence of seasonal life cycles when there is localized increased asexual reproduction and growth typical of all metagenic organisms, resulting in normal or abnormal seasonal biomass. A true bloom is categorized as an endemic bloom staying in the same location over time). Though apparent blooms are either transient blooms (blooms that move spatially over time) or an accumulation within enclosed habitats, not reflecting true blooms
accumulation	A long-term summation of fluctuations in relative number compared on temporal and spatial scales without causation
mass occurrence	Similar to an accumulation but larger in magnitude and/or biomass
aggregation	Accumulation of individuals likely emigrated from natural or apparent blooms due to passive drifting, active behavior, or a combination of the two
swarm	A very dense aggregation of individuals coming together primarily through individual motion than currents alone
outbreak	Extraordinary increases in biomass over a short time period within a reproductive season that is typically associated with anthropogenic ecosystem changes

 

           
            Due to the pelagic mobility of jellyfish, it is often difficult to properly describe a mass of jellyfish as a bloom or any of the other previously described related events. These events similar to jellyfish blooms differ by location of reproduction, mode of how they came together and other factors that influence jellyfish distributions (Mills 2001; Graham et al. 2001; Hamner & Dawson 2009; and Richardson et al. 2009; also see Lucas & Dawson submitted 2012). It is imperative to consistently use the following relative terms to facilitate interpretation of scientific literature and best present cause and consequences (Lucas & Dawson 2013): bloom, accumulation, mass occurrence, aggregation, swarm, and outbreak (Table 1).Due to the pela et al. 2001; Hamner & Dawson 2009; and Richardson et al. 2009; also see Lucas & Dawson submitted 2012). It is imperative to consistently use the following relative terms to facilitate interpretation of scientific literature and best present cause and consequences  (Lucas & Dawson 2013): bloom, accumulation, mass occurrence, aggregation, swarm, and outbreak (Table 1).

            The key to understanding the distributions of jellyfishes is in identifying the original source of jellyfish blooms. Bloom biology focus is on the meditative medusae form, which, in large numbers, can have negative economic impacts on commercial fisheries from fish larvae consumption (Sandlifer et al. 1974), on aquaculture by destroying equipment and stock (Purcell et al. 1999; Delano 2006), and on power station operations by impairing equipment (as seen in Brodeur et al. 2008; Clark 2008).

            Due to the complexity of jellyfish life histories and the consequences of their blooms, Parsons (1993) and Mills (1995) implored jellyfish scientists to study the functional role of jellyfish in maintaining the ecology of the oceans. This call resulted in much of the current information that we know and highlighted what remains to be known about jellyfish blooms.

Phylogenetics and population genetics have proven to be useful for understanding jellyfish biology (Hamner & Dawson 2008; 2009), their geographic distribution (e.g., Dawson 2005), and genetic variation between populations. Jellyfish that aggregate, bloom, or swarm are clustered taxonomically and phylogenetically, though taxa that bloom and swarm are typically more diverse than non-accumulating sister taxa (Hamner & Dawson 2008).

Hamner and Dawson (2009) presents an inventory for species that occur en masse, encompassing jellyfish biodiversity, jellyfish molecular phylogenetics, species richness, and phenotypic diversity on a global scale. Conclusions include that taxa are not randomly distributed within medusoid Cnidaria, and there are synergistic effects of environmental attributes and organismal traits promoting en masse occurrences. Phylogenetics can be used to differentiate between aggregations, blooms, and swarms (Hamner & Dawson 2009), and population genetics can differentiate between evolutionary significant units at the population level (Waples 1994). The integration of these molecular analyses with ecology can distinguish endemic versus transient blooms and identify putative environmental and genetic influences. This integration allows for the previously mentioned knowledge gaps to be addressed, since jellyfish blooms are characterized by increased biomass ascribed to local conditions. Therefore, it is necessary to know the condition exposure overtime, not just a snap-shot of present conditions, to fully understand the spatial distribution of jellyfish. Combining population dynamics and population genetics is essential for tracking jellyfish blooms throughout the season. Categorizing a bloom as endemic or transient will provide necessary information to identify putative causes.

Similar to the development of molecular ecology, using more a evolutionary approach incorporating molecular techniques and focusing on the mechanisms of evolution to understand ecology is how best to understand jellyfish blooms. Many questions in ecology are not framed to include evolution as part of the question asked or as part of the solution in finding its answer. Though, an evolutionary context is necessary to find a resolved and robust answer (Dobzhansky 1964, 1973) through providing a framework allowing for correct assumptions to be made.  Current jellyfish molecular studies emphasize the macroevolution ('deep' timeline between taxa, e.g. Gingerich 1987, Benton 2015), but few consider jellyfish microevolution ('shallow' timeline evident through population genetics, eg. Dobzhansky 1937, Kothe et al. 2016). Microevolutionary studies typically exist in the space between ecological and evolutionary processes since their population dynamics both are influenced by overlapping processes (Lucas & Dawson 2012). After all, there cannot be ecology without the mechanisms of evolution: mutation, genetic drift, gene flow, and selection.  Therefore it is necessary to integrate ecology and population genetics in a novel framework (Lucas & Dawson 2012) to identify types and causes of blooms (Figure 3). This integration can distinguish endemic versus transient blooms and tease out environmental or genetic influences on blooms. Beyond using population genetics as a tool to find (1) what causes jellyfish blooms, and providing the foundation for (2) how jellyfish affect ecosystems/communities: there are some other necessary techniques that should be utilized in concert. Some of these techniques rely on specific methodology. More rigorous sampling is necessary within a jellyfish season (intra-annual) and also between jellyfish seasons (inter-annual) to understand if the bloom has normal or abnormal biomass and whether it is endemic or transient. Additionally, understanding dispersal (a mode of gene flow) through mathematical and oceanographic modeling will result in more accurate identification of possible environmental variables that cause blooms, which would then be empirically tested with laboratory manipulations.  The combination of these techniques must be applied through integrating population genetics and ecology to answer (a) how frequent is genetic structure between species (phylogenetics) and populations (within species)? & (b) on what geographic scale does genetic structure exist (macroevolution or microevolution)? With these answers we can finally have more substantiated conclusions about the causes of jellyfish blooms and what actions we can take to minimize them as the oceans continue to change.

Figure. 2. Hypothetical preliminary quantitative evolutionary-ecological framework (adapted Lucas & Dawson 2013) to define jellyfish en masse events. The abscissa shows a single jellyfish season (May-September) and the ordinate axis shows distance along a northern flowing current. Jellyfish abundance & biomass increase with diameter. The theoretical blooming event dictated by the arrows for two separate possible patterns for these blooms due to reproduction and then subsequent decrease due to mortality or emigration. (A) shows an endemic bloom that remains at the same location throughout the season. (B) shows a transient bloom that moves throughout the season.

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