Occurrence of Giant Borings of Osprioneides kampto in the Lower Silurian (Sheinwoodian) Stromatoporoids of Saaremaa,Estonia

The distribution of Osprioneides is more environmentally limited than that of Trypanites in the Silurian of Baltica. Osprioneides probably occurred only in large hard substrates of relatively deepwater muddy bottom open shelf environments. Osprioneides were relatively rare, occurring in 4.7% of all stromatoporoid specimens in that environment, in contrast to small Trypanites-Palaeosabella borings, which occur in 88.4% of stromatoporoids and 88.9% of heliolitid corals. Osprioneides is reported only from the lower Sheinwoodian stromatoporoids of the exposed Silurian of Saaremaa (Wenlock to Pridoli). Osprioneides borings probably played a minor role in the general bioerosion in the Silurian of Baltica.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.     

Calcium carbonate budgets for two coral reefs affected by different terrestrial runoff regimes, Rio Bueno, Jamaica

A process-based carbonate budget was used to compare carbonate framework production at two reef sites subject to varying degrees of fluvial influence in Rio Bueno, Jamaica. The turbid, central embayment was subjected to high rates of fluvial sediment input, framework accretion was restricted to ≤30 m, and net carbonate production was 1,887 g CaCO₃ m⁻² year⁻¹. Gross carbonate production (GCP) was dominated by scleractinians (97%), particularly by sediment-resistant species, e.g. Diploria strigosa on the reef flat (<2 m). Calcareous encrusters contributed very little carbonate. Total bioerosion removed 265 g CaCO₃ m⁻² year⁻¹ and was dominated by microborers. At the clear-water site, net carbonate production was 1,236 g CaCO₃ m⁻² year⁻¹; the most productive zone was on the fore-reef (10 m). Corals accounted for 82% of GCP, and encrusting organisms 16%. Bioerosion removed 126 g CaCO₃ m⁻² year⁻¹ and was dominated by macroborers. Total fish and urchin grazing was limited throughout (≤20 g CaCO₃ m⁻² year⁻¹). The study demonstrates that: (1) carbonate production and net reef accretion can occur where environmental conditions approach or exceed perceived threshold levels for coral survival; and (2) although live coral cover (and carbonate production rates) were reduced on reef-front sites along the North Jamaican coast, low population densities of grazing fish and echinoids to some extent offset this, thus maintaining positive carbonate budgets.     

Bioerosional structures and pseudoborings from Late Jurassic and Late Cretaceous-Paleocene shallow-water carbonates (Northern Calcareous Alps, Austria and SE France) with special reference to cryptobiotic foraminifera

Examples of bioerosional processes (boring patterns) are described from shallow-water limestones of the Late Jurassic Plassen Carbonate Platform (PCP) and the Late Cretaceous to Paleocene Gosau Group of the Northern Calcareous Alps, Austria. Some micro-/macro-borings can be related to distinct ichnotaxa, others are classified in open nomenclature. In the Alpine Late Jurassic, bioerosional structures recorded from clasts in mass-flows allow palaeogeographical conclusions concerning the source areas. In particular, these are borings of the Trypanites-ichnofacies detected from clasts (Barmstein limestones) of the PCP or special type of bored ooids of unknown source areas or restricted autochthonous occurrences. In the Lower Gosau Subgroup, Gastrochaenolites macroborings occur in mobile carbonate clast substrates of shore zone deposits (“Untersberg Marmor”). Different types of borings are recorded from rudist shells and coral skeleton, some of which are referable to the ichnotaxon Entobia produced by endolithic sponges. In the present study, special attention is paid to the occurrences of the cryptobiotic foraminifera Troglotella incrustans Wernli and Fookes in the Late Jurassic and Tauchella endolithica Cherchi and Schroeder in the Late Cretaceous. The latter is so far only known to be from the Early Cenomanian of France and is reported here for the first time from the Late Turonian-Early Coniacian stratigraphic interval where it was found in turbulent carbonate deposits within borings penetrating bivalve shells or coralline algae. The records of cryptobiotic foraminifera from the Northern Calcareous Alps are supplemented by a single finding from the Middle Cenomanian of SE France. A palaeoenvironmental interpretation of the occurrences of the cryptobiotic foraminifera is provided.     

An ethological framework for animal bioerosion trace fossils upon mineral substrates with proposal of a new class, fixichnia

Animal bioerosion trace fossils upon mineral substrates are analyzed from the point of view of the Seilacherian ethological classification. Several of the currently accepted ethological classes: cubichnia, fugichnia, repichnia, fodinichnia, agrichnia, calichnia and aedificichnia are not represented in these substrates. This fact points out a lower behavioral diversity of hard substrate trace fossils when compared with soft sediment trace fossils. Bioerosion traces can be classified in just five classes: domichnia, pascichnia, equilibrichnia, praedichnia and fixichnia. Fixichnia is here erected to gather superficial etching scars resulting from the anchoring of fixation of sessile epiliths by means of a soft or skeletal body part. Praedichnia and fixichnia are exclusive of the bioerosion realm.     

Bioerosion caused by foraging of the tropical chiton Acanthopleura gemmata at One Tree Reef, southern Great Barrier Reef

The bioerosive potential of the intertidal chiton Acanthopleura gemmata on One Tree Reef was determined by quantification of CaCO₃ in daily faecal pellet production of individuals transplanted into mesocosms after nocturnal-feeding forays. Mean bioerosive potential was estimated at 0.16 kg CaCO₃ chiton⁻¹ yr⁻¹. Bioerosion rates were estimated for populations on two distinct chiton habitats, reef margin (0.013 kg CaCO₃ m⁻² yr⁻¹) and beachrock platform (0.25 kg CaCO₃ m⁻² yr⁻¹). Chiton density on the platform was orders of magnitude greater than on the reef margin. The surface-lowering rate (0.16 mm m⁻² yr) due to bioerosion by the beachrock population is a substantial contribution to the total surface-lowering rate of 2 mm m⁻² yr⁻¹ previously reported for One Tree Reef across all erosive agents. At high densities, the contribution of A. gemmata to coral reef bioerosion budgets may be comparable to other important bioeroders such as echinoids and fish.     

Parrotfish bioerosion on Egyptian Red Sea reefs

Parrotfishes (family Scaridae) are important agents in marine bioerosion. Here, the feeding ecology of seven species of parrotfishes was studied on Egyptian Red Sea reefs. The most abundant species on both the reef flat and slope was Chlorurus sordidus. In contrast, C. gibbus had the lowest abundance on the reef flat, and Cetoscarus bicolor was the least abundant species on the reef slope. Scarus niger exhibited the highest feeding rate (98.9 bites 5 min^− 1), followed by C. sordidus (76.5 bites 5 min^− 1), whereas the rates for C. bicolor and C. gibbus were low (29.4 and 31.9 bites 5 min^− 1, respectively). The daily feeding patterns of all seven species showed agreement in that activity was relatively constant over the day, with highest values in the early afternoon (1400 h) and a steady decrease until 1800 h. C. sordidus was more similar to S. niger and S. ghobban in showing somewhat higher activities in the morning (0800 h) followed by a slight decrease until noon. The average bite volumes of C. gibbus and C. bicolor were high (0.114 and 0.110 cm³, respectively), whereas S. niger had the lowest average value (0.002 cm³). Based on their feeding intensity, C. gibbus, S. ghobban and C. bicolor have high bioerosion rates on the Egyptian Red Sea reefs. Overall, S. ghobban is the most important bioeroder because it is more abundant than the other two species. All parrotfish species fed on dead coral and hard substrates which are rich in algae, but C. gibbus, C. bicolor and S. ghobban also fed on live coral on both reef zones; C. sordidus avoided live coral. The fresh scars on live coral were bigger than on dead coral because the three large parrotfish (C. gibbus, C. bicolor and S. ghobban) fed mainly on live corals.     

Bioerosion rates of the sponge Cliona orientalis Thiele, 1900: spatial variation over short distances

We studied bioerosion rates and tissue growth of the sponge Cliona orientalis Thiele, 1900. Experimental blocks grafted with sponge tissue were deployed at three sites in Moreton Bay, QLD, Australia, which have different environmental conditions. Bioerosion rates varied between 4, 5, and 10 kg m⁻² year⁻¹ when related to final tissue area and between 4, 7, and 16 kg m⁻² year⁻¹ when related to initial tissue area of the graft, which supports findings of earlier studies. Comparing results between the sites, eutrophication appeared to have the most stimulating effect and is most likely to have caused the measured differences. However, slight differences between shading and current speeds may also have played a role. Variation may have masked spatial differences of sponge growth, which were insignificant between study sites. Growth and bioerosion nevertheless followed the same trend and were weakly correlated. Habitat quality itself had no influence. Overall, the twofold difference in sponge bioerosion over a distance as short as 10 km suggests that when estimating bioerosion rates, subsamples should be tested at different locations.     

Molluskan Grazing Traces (Ichnogenus Radulichnus Voigt, 1977) on a Pleistocene Bivalve from Southern Brazil,With the Proposal of a New Ichnospecies

The ichnogenus Radulichnus Voigt, 1977 Voigt, E. 1977. On grazing traces produced by the radula of fossil and recent gastropods and chitons. In Trace fossils 2, eds. T. P. Crimes, and J. C. Harper, 335–346. Geological Journal, Special Issue 9. [Google Scholar] is recorded for the first time from a bivalve, Anomalocardia brasiliana (Gmelin, 1791 Gmelin, J. F. 1791. Caroli a Linné, Systema Naturae. Tom. I, Pars VI. Leipzig: G.E. Beer, pp. 3021–3910. [Google Scholar]), in a late Pleistocene molluskan assemblage from the southern Brazilian coastal plain. Grazing traces comprise short (<1?mm), parallel furrows, arranged in rows on the inner (concave) shell surface and mostly concentrated in its central area. Radulichnus accommodates scratches on hard substrates produced by the radula of grazing gastropod or polyplacophorans. Our literature survey on fossil and extant traces, as well as studies on the grazing mechanism in living mollusks, document at least two distinct morphotypes that are related to differences in the feeding modes of the producers. We propose to distinguish a second ichnospecies of Radulichnus, in addition to the type, R. inopinatus Voigt, 1977 Voigt, E. 1977. On grazing traces produced by the radula of fossil and recent gastropods and chitons. In Trace fossils 2, eds. T. P. Crimes, and J. C. Harper, 335–346. Geological Journal, Special Issue 9. [Google Scholar] (produced by gastropods), which is named R. transversus isp. nov., and attributed to polyplacophorans. Grazing traces on the shell of A. brasiliana match the morphotype produced by polyplacophorans mollusks, and are indicative of its complex taphonomic history in comparison with other shells in this assemblage.     

Biological degradation of coral framework in a turbid lagoon environment,Discovery Bay,north Jamaica

The potentially negative effects of increased sedimentation on corals are well documented, whereas, the impacts upon early diagenetic processes, such as bioerosion, remain poorly understood. This study examined macroboring through image analysis of coral slabs from two high sedimentation and turbid reefs, Columbus Park and Red Buoy, within Discovery Bay, north Jamaica. Infestation of coral framework by macroborers was significant at both Columbus Park and Red Buoy for all depth zones sampled: 0–8 m (6.5 versus 8.3%), 8–16 m (11.4 versus 10.7%), and 16–25 m (6.2 versus 18.5%), with only the deepest zone significantly different (P<0.001). Bioeroding communities exhibit a shift from mainly sponge-dominated (>90%) assemblages in clear-water settings towards a greater relative importance of worms (up to 17.2%) and bivalves (up to 40.5%) with increasing sedimentation. The high infestation levels of the bivalve Lithophaga spp. offset the reduced sponge bioerosion. As a result, macroboring infestation levels are comparable to those reported from adjacent clear-water reef sites. This study indicates that macroboring of coral framework continues under environmental conditions previously inferred to be detrimental to coral growth and survival.