Interception of nutrient rich submarine groundwater discharge seepage on European temperate beaches by the acoel flatworm, Symsagittifera roscoffensis

Geographical Distribution and Genetic Diversity of Praesagittifera naikaiensis (Acoelomorpha) in the Seto Inland Sea, Japan

Acoel flatworms are simple bilaterians that lack digestive lumens and coelomic cavities. Although they are a significant taxon for evaluating the evolution of metazoans, suitable species for biological experiments are not available in Japan. We recently focused on Praesagittifera naikaiensis, which inhabits the sandy shores of intertidal zones in the Seto Inland Sea in Japan, as a candidate for a representative acoel species to be used in experiments. However, reports on its distribution range remain limited. Here, we surveyed the habitats of P. naikaiensis on 108 beaches along the Seto Inland Sea. Praesagittifera naikaiensis is reported here from 37 sites (six previously known and 31 newly discovered sites) spread over a wide area of the Seto Inland Sea, from Awaji Island in Hyogo Prefecture to Fukuoka Prefecture (364 km direct distance). Based on the mitochondrial cytochrome oxidase subunit I (COI) gene haplotypes, we evaluated the genetic diversity of 145 individuals collected from 33 sites. Out of 42 COI haplotypes, 13 haplotypes were shared by multiple individuals. The most frequent haplotype was observed in 67 individuals collected from 31 sites. Eight other haplotypes were detected at geographically distant locations (maximum of 299 km direct distance). Multiple haplotypes were found at 32 sites. These results demonstrate that sufficient genetic flow exists among P. naikaiensis populations throughout the Seto Inland Sea. Molecular phylogenetic analysis of the COI haplotypes of P. naikaiensis revealed that all specimens were grouped into one clade. The genetic homogeneity of the animals in this area favors their use as an experimental animal.

Synthesizing the Effects of Submarine Groundwater Discharge on Marine Biota

Submarine groundwater discharge (SGD) is a global and well-studied geological process by which groundwater of varying salinities enters coastal waters. SGD is known to transport bioactive solutes, including but not limited to nutrients (nitrogen, phosphorous, silica), gases (methane, carbon dioxide), and trace metals (iron, nickel, zinc). In addition, physical changes to the water column, such as changes in temperature and mixing can be caused by SGD. Therefore SGD influences both autotrophic and heterotrophic marine biota across all kingdoms of life. This paper synthesizes the current literature in which the impacts of SGD on marine biota were measured and observed by field, modeling, or laboratory studies. The review is grouped by organismal complexity: bacteria and phytoplankton, macrophytes (macroalgae and marine plants), animals, and ecosystem studies. Directions for future research about the impacts of SGD on marine life, including increasing the number of ecosystem assessment studies and including biological parameters in SGD flux studies, are also discussed.

An Emerging System to Study Photosymbiosis, Brain Regeneration, Chronobiology, and Behavior: The Marine Acoel Symsagittifera roscoffensis

The acoel worm Symsagittifera roscoffensis, an early offshoot of the Bilateria and the only well-studied marine acoel that lives in a photosymbiotic relationship, exhibits a centralized nervous system, brain regeneration, and a wide repertoire of complex behaviors such as circatidal rhythmicity, photo/geotaxis, and social interactions. While this animal can be collected by the thousands and is studied historically, significant progress is made over the last decade to develop it as an emerging marine model. The authors here present the feasibility of culturing it in the laboratory and describe the progress made on different areas, including genomic and tissue architectures, highlighting the associated challenges. In light of these developments, and on the ability to access abundant synchronized embryos, the authors put forward S. roscoffensis as a marine system to revisit questions in the areas of photosymbiosis, regeneration, chronobiology, and the study of complex behaviors from a molecular and evolutionary perspective.

The chimerical and multifaceted marine acoel Symsagittifera roscoffensis: from photosymbiosis to brain regeneration

A remarkable example of biological engineering is the capability of some marine animals to take advantage of photosynthesis by hosting symbiotic algae. This capacity, referred to as photosymbiosis, is based on structural and functional complexes that involve two distantly unrelated organisms. These stable photosymbiotic associations between metazoans and photosynthetic protists play fundamental roles in marine ecology as exemplified by reef communities and their vulnerability to global changes threats. Here we introduce a photosymbiotic tidal acoel flatworm, Symsagittifera roscoffensis, and its obligatory green algal photosymbiont, Tetraselmis convolutae (Lack of the algal partner invariably results in acoel lethality emphasizing the mandatory nature of the photosymbiotic algae for the animal's survival). Together they form a composite photosymbiotic unit, which can be reared in controlled conditions that provide easy access to key life-cycle events ranging from early embryogenesis through the induction of photosymbiosis in aposymbiotic juveniles to the emergence of a functional "solar-powered" mature stage. Since it is possible to grow both algae and host under precisely controlled culture conditions, it is now possible to design a range of new experimental protocols that address the mechanisms and evolution of photosymbiosis. S. roscoffensis thus represents an emerging model system with experimental advantages that complement those of other photosymbiotic species, in particular corals. The basal taxonomic position of S. roscoffensis (and acoels in general) also makes it a relevant model for evolutionary studies of development, stem cell biology and regeneration. Finally, it's autotrophic lifestyle and lack of calcification make S. roscoffensis a favorable system to study the role of symbiosis in the response of marine organisms to climate change (e.g., ocean warming and acidification). In this article we summarize the state of knowledge of the biology of S. roscoffensis and its algal partner from studies dating back over a century, and provide an overview of ongoing research efforts that take advantage of this unique system.

Chemical inputs from a karstic submarine groundwater discharge (SGD) into an oligotrophic Mediterranean coastal area

The impacts of nutrient and other chemical inputs released by a submarine groundwater discharge (SGD) on the marine environment of an oligotrophic Mediterranean coastal area (Messiniakos Gulf, SE Ionian Sea) are investigated through a multidisciplinary approach. Nutrients and organic pollutants associated with the SGD are presented to study the chemical characteristics of the SGD and to investigate its effect on the marine ecosystem in comparison to freshwater discharges of the water bodies of Messinia Prefecture. Nutrient and organic pollutant fluxes were calculated from (214)Bi-based SGD estimates. An average of 22×10(3) mol of silicate per month and 8×10(3) mol of nitrate per month were released via the SGD. Nutrient concentrations at the mouth of the SGD were three times higher than in Messiniakos Gulf, and NO3(-) was the primary Dissolved Inorganic Nitrogen form discharged by SGD. Organic pollutant concentrations associated with agricultural activities were low at the SGD. The implementation of a Eutrophication Index (E.I.) showed that the water column at the SGD site corresponds to Moderate/Bad ecological quality, whereas the status switches rapidly to Good at a small distance from the SGD. Coastal areas influenced by river or sewage discharge correspond to a Moderate/Good ecological status. The BENTIX index used for the classification of the ecological quality status of the benthic macroinvertebrate communities showed that the SGD has a minor influence compared to the other freshwater discharges in Messiniakos Gulf. Though the SGD has a considerable outflow, morphology and hydrodynamics of the area favor the rapid dispersion of the upwelling water and degrades the SGD's effect even on a regional scale.