Macrobioerosion and Microbioerosion in Marine Molluscan Shells from Holocene and Modern Beaches (39°-40°S, South of Buenos Aires Province, Argentina)

The marine sediments of the area of Verde Peninsula - Jabali Island （39°28＇S/62°19%V-40°28＇ S/62°11＇W） Holocene in age （3-2 ky）, and modern beaches contain a significant amount of bioeroded mollusc shells. Fifteen sites were analyzed, in which 20.11% of the mollusc shells （2168 valves） presented bioerosion traces, in 54 species （30 bivalves and 24 gastropods）. Fourteen ichnogenera were reported： Entobia, Maeandropolydora, Iramena, Caulostrepsis, Pennatichnus, Pinaceocladichnus, Trypanites, and Gastrochaenolites （Domichnia）, Gnathichnus and Radulichnus （Pascichnia）, Finichnus and Centrichnus （Fixichnia）, Oichnus （Praedicnia） （macrobioerosion）, y Semidendrina （microbioerosion）, the latter is first reported in mollusc shells in Argentina. Eleven ichnospecies were identified Finichnus peristroma, Maeandropolydora sulcans, Gnathichnus pentax, Pinaceocladichnus onubensis, Caulostrepsis taeniola, Centrichnus eccentricus, Radulichnus inopinatus, Oichnus simplex, Oichnus paraboloides, Oichnus gradatus, and Gastrochaenolites torpedo （lithic remains）. The dominant ichnogenera in the Holocene deposits are Iramena, Entobia and Oichnus. The same ichnogenera are constant with different abundance in the modern beaches, and increasing representation of Pinaceocladichnus and Pennatichnus. The dominant ichnofacies in the Holocene deposits is Trypanites, revealing a benthonic marine community composed of cheilostome bryzoans, clionaid sponges, predator gastropods, regular echinoids, polychaete annelids, bivalves, thallophytas and fungi. Generally, the area was described as a sublittoral, low-energy, stable environment with high rate of oxygenation, and sandy bottoms, with rocky bottoms at Villalonga locality.

Bioerosion on Late Pleistocene Marine Mollusks:A Paleoclimatological and Paleoecological Comparison of MIS 7 and MIS 5e with Modern Beaches(Río Negro,Argentina)

The Late Pleistocene littoral ridges of southern South America,especially those of the north of Argentinean Patagonia,contain remains of mollusk shells with bioerosion traces.Eleven sites from marine isotope stages(2 from MIS 7,4 from MIS 5 e)and five sites from modern beaches from northern Río Negro Province,with 40 taxa(17 bivalves and 23 gastropods)were analyzed,in the area between west of Baliza San Matías and Las Grutas(41°S).Three ichnogenera were identified in deposits of MIS 7:Entobia,Gastrochaenolites(Domichnia)and Oichnus(Praedichnia)with one ichnospecies(G.torpedo).Six ichnogenera were identified in deposits of MIS 5 e:Entobia,Meandropolydora,Pinaceocladichnus,Iramena,Caulostrepsis and Oichnus with one ichnospecies(O.simplex).Seven ichnogenera were identified from modern beaches:Entobia,Meandropolydora,Iramena,Caulostrepsis,Pinaceocladichnus,Gastrochaenolites(Domichnia)and Oichnus(Praedicnia),with two ichnospecies(O.simplex and O.paraboloides).On this basis,it is inferred that Pleistocene benthic communities were constituted from cheilostome bryzoans and polychaete annelids,together with drilling bivalves,predatory gastropods and overall warm-water species of mollusks.Of these,Chama iudicai was found on Plicatula gibbosa from MIS 7 and MIS 5 e.The record of warm temperature species suggests a higher sea surface temperature(SST)than the present one and/or the influence of the warm southward Brazilian Current affecting the waters of Golfo San Matías.On the modern beaches surveyed,there is an increase in polychaete annelids,cheilostome bryzoans,temperate-cold species and drilling bivalves,as well as sandy substrate species,which together with an increase of Gastrochaenolites and Caulostrepsis,suggest a colder climate due to the greater influence of the Malvinas Current during the Holocene.

Epi- and endobiont faunal communities on an Egyptian Mediterranean rocky shore: species composition and their competition for space

The exposed calcareous rocky area of the Abu Qir Headland,east of Alexandria,Egypt which range from coarse grains,through pebbles,cobbles,and boulders to rocky platforms,was signifi cantly colonized by sclerobionts(epibionts and endobionts).The epibiont species diversity was comparatively higher than that of endobionts.Epibiont communities included bryozoans(the anascan-grade cheilostome Bifl ustra savartii),serpulid(Hydroides elegans,Spirobranchus cf.tetraceros,Vermiliopsis striaticeps and Protula or Apomatus)and spirorbid(Spirorbis)wormtubes,and balanoid barnacles(Amphibalanus amphitrite,Balanus trigonus,and Perforatus perforatus).The cheilostome bryozoan colonies,which developed extensive sheets,proliferated on the study rocky shore either encrusting the bioeroded basement directly,or encrusting other epilithic taxa,particularly balanoid barnacles and serpulid worms.Encrusters displayed a remarkable marginal competitive interaction(overgrowth and stand-off)for space on the study rocky shore.On the other hand,endobionts were not well represented on the studied rocky shore exposure.It was possible to identify three ichnotaxa:Gastrochaenolites,Maeandropolydora,and Finichnus.The fi ndings documented represent a signifi cant contribution to our knowledge of sclerobionts composition,sequence of their colonization and/or bioerosion,and their mutual relationships on the intertidal rocky shore of the Abu Qir Headland.

The role of aerial algae in the formation of the landscape of the Yunnan Stone Forest,Yunnan Province, China

Aerial algae on the surface of carbonate rocks at the Stone Forest, Shilin County, Yunnan Province, China, and their bioerosion were investigated in the field and studied in the laboratory in detail. Through the observation, identification and statistics of more than one hun- dred algal samples and rock samples with the optical microscopes (stereomicroscope, biological microscope) and the scanning electronic microscope (SEM), the relationships between erosional forms on the surface of the Stone Forest and algae and/or algal communities and the genetic mechanism for the formation of erosional forms were analyzed. It is suggested that aerial algae play an active role in bioerosive processes that may affect the formation of karst erosional forms. These effects include both direct and indirect ones. The direct effect is the initiative control (algal shape-controlling role) of algae on the formation of karst forms of various scales, mostly mi- cro-scale (<10-3m) and minor-scale (10-3-10-1m) erosional forms. The algal shape-controlling roles can be divided into the algal individual shape-controlling role and the algal community shape-controlling role. The former mostly controls the formation of micro-scale erosional forms, while the latter mostly controls the formation of micro-scale and smaller minor-scale erosional forms. The indirect effect refers to the promoting role of algae in the formation of karst forms, which may affect the formation of karst forms of all types and scales. The bioerosion of algae accelerates the weathering process of the whole Stone Forest karst landforms.

From rock-boring organisms to tunnel boring machines:A new rock breaking technology by bioinspiration

The purpose of this study is to achieve better understanding of associated mechanisms and to recommend and identify new strategies to develop new rock breaking technology for Tunnel Boring Machines(TBMs).Tunnel Boring Machine tunnelling mainly depends upon the rock breakage caused by cutters moving on a rock surface in a rolling and sliding motion while under the action of thrust force.The rock breaking behaviour is controlled by the mechanical interaction between the cutters and the rock.Due to the high hardness and high abrasiveness of rock,the cutters have to work under very high thrust force and suffer heavy-load-impact and abrasive wear,causing serious wear and low rock breaking efficiency.Rock-boring organisms exist in nature,which achieve drilling and/or tunnelling in rocks through a tribochemical interaction.This phenomenon is called bioerosion and the organisms are natural‘TBMs’to some degree.In this study,the interaction between TBM cutters and rock is presented,and current measures to improve cutter wear and rock breaking efficiency and their limitations are reported.Then,the connotation,mechanism and typical cases of bioerosion are presented.Finally,inspired by bioerosion,a new chemically assisted rock breaking technology is proposed for TBMs.