The “Benthic Plankton”: An Oxymoron or a Smart Tool in Marine Ecology?

C.N.R. Institute for Coastal Marine Environment, Talassografico “A. Cerruti” Taranto, Italy

*Corresponding Author:

Dr. Fernando Rubino
Laboratory of Plankton Ecology
C.N.R. Institute for Coastal Marine Environment
Talassografico “A. Cerruti”, Taranto, Italy
Tel: +39-099-4542-225
Fax: +39-099-4542-215
E-mail: rubino@iamc.cnr.it

Received date: April 24, 2012; Accepted date: April 25, 2012; Published date: April 27, 2012

Citation: Rubino F, Belmonte M (2012) The “Benthic Plankton”: An Oxymoron or a Smart Tool in Marine Ecology? J Marine Sci Res Dev 2:e112. doi:10.4172/2155-9910.1000e112

Copyright: © 2012 Rubino F, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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One of the major problems to be faced in the study of plankton dynamics is the patchy distribution of plankton in space and time [1]. A deep knowledge about the structure of the planktonic communities of a marine basin requires very high cost in terms of work and money spent for sampling and observation [2].

Approximately 30 years ago, innovative ideas about the ecology of planktonicdino flagellates came out from the work of a marine geologist Dale [3]. Dale’s fortuitous observation of a fossil’s “resurrection” under the microscope opened a new way to the study of plankton dynamics, at least in marine coastal environments. That fossil, actually, was a dormant stage produced by a planktonicdino flagellate that had the capability to rest, even for long time, in sedimentary strata. Now we know that the production of such resting stages is a common strategy, adopted by planktonic species to persist in the environment by enhancing the irresilience [4]. So, the “benthic plankton” is the planktonic population transferred to the sea bottom in form of resting stages. They are non-motiled ormant zygotes or embryos, usually called cysts that have a peculiar morphology, very different from that of the corresponding active stage, with a robust, sculptured wall bearing spines or different types of processes [5]. Once produced, they lose the capacity of remaining in suspension in the water and fall to the bottom where they rest, like the seeds of terrestrial plants in the ground, waiting for the next favourable season. Such a strategy allows an escape to the future for the species, to over ride harsh conditions deriving from the natural seasonal fluctuations or the less regular variations linked to biotic factors such as competition and/or predation. Now, after 30 years since that casual observation, a lot of work has been done aimed to the discovering of these dormant forms and, in particular during the last 10-15 years, about their ecological role. The correspondence between active and resting stage has been demonstrated in the lifecycle of hundreds of planktonic species and new concepts, or major revisions to old views in marine ecology, have been developed [6].

The so-called holoplankton, i.e. the organisms that spend their entire life-cycle in the water column, probably is a fake, or, atleast, a non leading actorin the more articulated plankton movie that includes a tight integration between the pelagic and benthic domains run by the life-cycle of the species. Belmonte et al. [7] introduced a new category to identify the organisms whose adults are in the plankton and the products of their sexual reproduction in the benthos and called it “merobenthos” to emphasize its specular correspondence with meroplankton. The merobenthos/benthic planktonis is a key to unlock the rigid compartimentation existing between pelagos and benthos in marine scientific research and opens new ways of investigation for plankton’s researchers [8].

The rain of cysts to the bottom over the time forms a seed-bank, i.e. millions of cysts per square meter of sediments with hundreds of different species that constitutes a reservoir of biodiversity for the plankton, stored in the benthos. The germination of little amounts of these cysts is sufficient to re-start the planktonic cycle, producing also blooms and all the well-known phenomena in the water [9,10].

Confined basins, where the low hydro dynamism and high productivity create favourable conditions for cyst accumulation, are considered as hot-spots of “potential” biodiversity for the plankton, as modelled in the supply-vertical ecology by Marcus & Boero [11] that, besides the supply-side ecology [12], tries to explain the patterns of recruitment in the marine environment.

So, the idea is to merge the information coming from pelagos and benthos to acquire more knowledge with a more fruitful sampling effort. During the last years only few studies have been conceived using this integrated approach, even if, all of them revealed a till then unexplored fraction of plankton diversity with the discovering in the sediments of planktonic species never recorded before in the study area [13].

Moreover, often in these surveys the list of species obtained by the study of the water column was very different from that acquired through sediments’ analysis. Most of the plankters are not in the plankton for most of their life. If we observe the temporal trends of abundance of active stages in the water vs. resting cysts in the sediments, they are closely complementary. So, the plankton’s biodiversity in a given area is the sum of the “potential” biodiversity resting for most of the time in the sediments as cysts and the “realized” biodiversity in the water column. The former is an investment for the future, millions of cysts x square meter of bottom ready to germinate and re-fuel the plankton; the latter is the result of that investment, a pulse that, depending on the life-cycle length of the species can finish in few days or weeks. Moscatello et al. [14] demonstrated that an integrated pelagos/benthos approach enhances of more than 35% the knowledge of plankton biodiversity. The transfer of biomass to and from the sediments is an important block of the pelagic-benthic coupling in marine coastal areas, but often marine biologists are still divided between planktonologists and benthologists; in some cases different life-cycle stages of the same species are studied by different specialists because they live in different compartments. We have to pass from biology to ecology and apply our knowledge to the whole plankton, and this term must refer not only to organisms inhabiting the water column, otherwise the benthic plankton will remain an oxymoron.

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