"Neptune Balls" Polysaccharides: Disentangling the Wiry Seagrass Detritus.

Lukas Pfeifer

doi:10.3390/polym13244285

Abstract

Each year, high amounts of dead seagrass material are washed ashore at beaches world-wide. In the Mediterranean region, the seagrass Posidonia oceanica is responsible for huge agglomerates of ball-like seagrass litter. As these are often removed due to touristic reasons, a reuse method would be a step towards a more ecologically oriented society. In this study, the main polysaccharide components were analyzed, in order to propose possible usage options. To do this, different aqueous fractions were extracted, analyzed by classical carbohydrate analysis methods (GC-FID/MS, colorimetric assay and elemental analysis), and purified by ion-exchange chromatography, as well as selective precipitation with a detecting agent for highly glycosylated glycoproteins. The obtained purified fractions were analyzed in detail and a linkage-type analysis of the most promising extract was conducted via permethylation. Only low amounts of glycoproteins, as well as medium amounts of the characteristic apiogalacturonan were likely to be present, while xylan seemed to be the most abundant polysaccharide in most fractions. A partial structural proposal showed general accordance with land plant xylans, presenting reuse options in the field of biofuel and bioplastic generation.

Highlights

Visitors of Mediterranean coasts may have seen brown, fibrous balls—so-called Ægagropili or Neptune balls
A fractionated cell wall extraction with different aqueous solvents was conducted in order to get an overview of the main groups of polysaccharides present in the remaining seagrass balls
This is a strong hint for the presence of xylans as the main polysaccharide in the seagrass balls

Summary

Introduction

Visitors of Mediterranean coasts may have seen brown, fibrous balls—so-called Ægagropili or Neptune balls. They show structural similarity [1] to the green algae Aegagropila linnaei Cladophora aegagropila), they are, in contrast to that, dead plant parts of the angiosperm plant Posidonia oceanica (L.) Delile. This endemic seagrass species is a member of the sole genus in the family of Posidoniaceae and forms wide and dense meadows [2] across the Mediterranean Sea. While most members of this seagrass family are only found in Australia, the species P. oceanica occurs uniquely in the Mediterranean Sea [3]. Being once the dominant seagrass species in that area, it is heavily endangered— by invading algae (especially Caulerpa species, see [6]), decreasing water and sediment quality [7] and human coast use projects [8]

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Conclusion