Bioerosion and fungal colonization of the invasive foraminiferan <i>Amphistegina lobifera</i> in a Mediterranean seagrass meadow

Abstract

Abstract. Foraminiferans are diverse micro- to macroscopic protists abundant especially in (sub)tropical seas, often forming characteristic benthic communities known as “living sands”. Numerous species have migrated through the Suez Canal to the Mediterranean and one of them, i.e., Amphistegina lobifera, turned invasive, gradually outcompeting the indigenous species. At some places, A. lobifera creates thick seabed sediments, thus becoming an important environmental engineer. However, little is known about the turnover of its shells in the invaded ecosystems. Using vital staining, stereomicroscopy, scanning electron microscopy, and cultivation and DNA fingerprinting, I investigated the vital status, destruction/decomposition and mycobiota of A. lobifera in the rhizosphere of the dominant Mediterranean seagrass Posidonia oceanica in an underwater Maltese meadow (average 284 shells g−1, representing 28.5 % of dry substrate weight), in comparison with epiphytic specimens and P. oceanica roots. While 78 % of the epiphytes were alive, nearly all substrate specimens were dead. On average, 80 % of the epiphytes were intact compared to 21 % of the substrate specimens. Abiotic dissolution and mechanical damage played only a minor role, but some bioerosion was detected in 18 % and >70 % of the epiphytic and substrate specimens, respectively. Few bioerosion traces could be attributed to fungi, and the majority probably belonged to photoautotrophs. The seagrass roots displayed fungal colonization typical for this species and yielded 81 identified isolates, while the surface-sterilized substrate specimens surprisingly yielded no cultivable fungi compared to 16 other identified isolates obtained from the epiphytes. While the epiphytes' mycobiota was dominated by ascomycetous generalists also known from terrestrial ecosystems (alongside with, for example, a relative of the “rock-eating” extremophiles), the roots were dominated by the seagrass-specific dark septate endophyte Posidoniomyces atricolor and additionally contained a previously unreported lulworthioid mycobiont. In conclusion, at the investigated locality, dead A. lobifera shells seem to be regularly bioeroded by endolithic non-fungal organisms, which may counterbalance their accumulation in the seabed substrate.

Are lulworthioid fungi dark septate endophytes of the dominant Mediterranean seagrass Posidonia oceanica?

“…Nevertheless, as far as the ITS rDNA sequences can tell, probably only one lulworthioid species had been isolated by Torta et al (2015) and the same species was detected at all localities investigated here. In addition, probable members of seven other genera were isolated here, suggesting that the seagrass root mycobiota at the Sicilian localities is not only richer than what reported by Torta et al (2015), but the richest ever reported in studies employing mycobiont cultivation from surface sterilized P. oceanica root segments (Vohník et al 2016(Vohník et al , 2017Vohník 2021).…”

“…(2015), but the richest ever reported in studies employing mycobiont cultivation from surface sterilized P. oceanica root segments (Vohník et al . 2016, 2017; Vohník 2021).…”

“…atricolor forms the DSE colonization detailed above (Vohník et al . 2019; Vohník 2021). At the same time, although ubiquitous in P. oceanica roots, this fungus has not been reported from any other host or environment.…”

Lower Paleocene foraminiferal assemblages from the Tibeisale Formation in the Arctic region of Western Siberia

“…In the Russian-language literature, rare references to such structures can be found, but without detailed descriptions, systematization, or photographs (Maslakova, 1974). However, traces of lifetime damage on foraminiferal tests have been widely published on, for both benthic (Reyment, 1966;Collen, 1973;Hickman and Lipps, 1983;Nielsen, 2002;Malumian et al, 2007;Sengupta and Nielsen, 2009;Vohnik, 2021) and planktonic taxa Nielsen, 1999;Nielsen et al, 2003;Frozza et al, 2020). A classification of structures and their terminology has been developed, and possible means of formation of these structures have been proposed .…”

Novel epiphytic root-fungus symbiosis in the Indo-Pacific seagrass Thalassodendron ciliatum

“…Comparison of the seagrasses Thalassodendron ciliatum and Posidonia oceanica with focus on their interactions with fungi It has been repeatedly shown that Pos. atricolor mycelium develops from the intracellular microsclerotia occurring in the hypodermis of P. oceanica(Vohník et al, 2016Vohník, 2021Vohník, , 2022 and Pos. atricolor has been detected in the terminal roots of P. oceanica adults at every sampled locality in the whole N Mediterranean (M. Vohník, unpublished data).…”