Sea balls are a group of aquatic phenomena. Real sea balls are spherical algae growth; non-real sea balls form through the movement of debris by water. The most well-known example of non-real sea balls, found on coasts of the Mediterranean Sea, are formed from decayed leaf fibres of the seagrass species Posidonia oceanica, though other variants worldwide are made of different organic materials; Mediterranean sea balls are typically referred to as Neptune balls. Neptune balls have been used for millennia, such as for making shoes, ancient medicine, or to caulk ships, though their formation process has only become clear in recent years. Potential modern applications make use of the properties of Neptune balls which are rare in nature; for example, Neptune balls have been shown to be a good soundproofing material. Neptune balls would also be a more environmentally-friendly substitute for some synthetic materials. In recent years, plastic waste, especially microplastics, has been interfering in the process of Neptune ball formation; studies and people have found plastic in many Neptune balls in the Mediterranean. Consequently, Neptune balls have been suggested as an indicator of plastic pollution in the sea, with concludingly positive first results.
Description
Names and definitions Sea balls formed in the Mediterranean Sea have a variety of names. The name aegagropilae comes from the Greek αίγαγροσ (wild goat) and πῖλος (fur). They are also known as aegagropiles, Neptune balls, egagropiles, egagropili, Posidonia oceanica spheroids, pilae stagnales, pilae marinae, pili marinae, sphaerae marinae, globuli marinae, and sphaerae thalassiae. Historically, they have been known as okr elbahr and annabdti. Neptune balls are known as pelotes marines or pelotes-de-mer in French, Zeeballen in Dutch, motolini in Italian, and Seebälle in German. Historically, the term sea balls has been used synonymously with Neptune balls and its alternative names. More recently, sea balls has been used to describe Neptune balls, other marine material spheroids, and even fossils of sea balls. According to German phycologist and botanist Bruno Schröder, there are two types of sea balls: non-real, which means sea balls formed by wave action made of discarded plant matter and encompasses Neptune balls, and real, which means sea balls that form through spherical plant growth. Schröder wrote that the genus of algae Aegagropila is an example of plants that form real sea balls. Canadian botanist W. F. Ganong also separated algal sea balls from sea balls formed by waves.
Formation
Posidonia oceanica is a seagrass species endemic to the Mediterranean Sea, whose remains form the Neptune balls found there. In autumn, Posidonia oceanica loses its leaves. The leaf sheaths remain attached to the rhizome when leaves shed, and are slowly buried by sedimentation in the "matte", an accumulation of dead rhizomes and roots. During the burial process, leaf sheaths, which are rich in lignin, are eroded, releasing constituent fibres. The sea rolls the fibres into a spherical shape, creating Neptune balls. Then, ocean currents can dislodge Neptune balls from the sea floor; some drift into deeper waters and some are washed ashore. Though details on where they travel during their relocation are not known, Neptune balls wash up on beaches especially frequently during storms.
Appearance, properties, and applications Dry Neptune balls are light brown. Neptune balls usually have a radius less than 8cm long; a study found that the mean radius is between 1.14cm and 2.68cm. The study also found that the average mass of Neptune balls is 0.212g. Another study described Neptune balls as having "diameter values from millimeters to centimeters up to 20 cm". Neptune balls can be spherical, ellipsoidal, or in-between. Their fibres are "relatively smooth", except for places in which salt crystals form following sea water evaporation. Fibres on the outside of Neptune balls are often "broken into a disordered bundle of smaller fibers" because of the transport to the shore; however, this is unlikely to impact the formation process. Leaf sheath cells in Posidonia oceanica have thin and lignified walls, so fibres provide the needed stiffness to form Neptune balls; they are composed of 32% lignin, whereas Posidonia oceanica has 19% lignin. The stiffness also comes from the density of Neptune balls. Neptune balls have been suggested as a soundproofing material, as they have similar absorption to that of mineral wool and polyester fibre. Extracted lignin from Neptune balls has been suggested as a material for reinforcement. The poor flammability and good thermal insulation of Neptune balls make them excellent for building insulation; consequently, they have been sold as a building insulation material. Neptune balls would have less of an environmental impact because Posidonia oceanica absorbs carbon dioxide, and they would replace plastic fibres, which are unsustainable as they require oil extraction. This would also reduce energy use and organic waste. Procuring Neptune balls for insulation uses up to thirty times less energy than procuring mineral wool, rock wool, or petroleum-based foams. However, Anna Sanchez-Vidal of the University of Barcelona argues against removing Neptune balls from beaches as they are part of beach ecosystems. They bring humidity to beaches, protect beaches against erosion, provide nutrients for dune plants, and feed beach arthropod communities.
Distribution
In the Mediterranean Sea Neptune balls formed from Posidonia oceanica can only be found on coasts of the Mediterranean Sea as Posidonia oceanica is endemic to there. Posidonia oceanica Neptune balls have been found on the coasts of Spain, Algeria, Tunisia, and Turkey. It is estimated that between 13 and 50% of initial Posidonia oceanica may have been lost since 1960, reducing Neptune ball numbers. WWF estimated that 34% of Posidonia oceanica meadows have been lost in the past 50 years. One cause is that seagrasses like Posidonia oceanica are at risk from heatwaves and industrial pollution.
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