Abstract
Abstract. Biological erosion is a key process for the recycling of carbonate and the formation of calcareous sediments in the oceans. Experimental studies showed that bioerosion is subject to distinct temporal variability, but previous long-term studies were restricted to tropical waters. Here, we present results from a 14-year bioerosion experiment that was carried out along the rocky limestone coast of the island of Rhodes, Greece, in the Eastern Mediterranean Sea, in order to monitor the pace at which bioerosion affects carbonate substrate and the sequence of colonisation by bioeroding organisms. Internal macrobioerosion was visualised and quantified by micro-computed tomography and computer-algorithm-based segmentation procedures. Analysis of internal macrobioerosion traces revealed a dominance of bioeroding sponges producing eight types of characteristic Entobia cavity networks, which were matched to five different clionaid sponges by spicule identification in extracted tissue. The morphology of the entobians strongly varied depending on the species of the producing sponge, its ontogenetic stage, available space, and competition by other bioeroders. An early community developed during the first 5 years of exposure with initially very low macrobioerosion rates and was followed by an intermediate stage when sponges formed large and more diverse entobians and bioerosion rates increased. After 14 years, 30 % of the block volumes were occupied by boring sponges, yielding maximum bioerosion rates of 900 g m−2 yr−1. A high spatial variability in macrobioerosion prohibited clear conclusions about the onset of macrobioerosion equilibrium conditions. This highlights the necessity of even longer experimental exposures and higher replication at various factor levels in order to better understand and quantify temporal patterns of macrobioerosion in marine carbonate environments.
Highlights
Bioerosion, the erosion of hard substrate by living organisms (Neumann, 1966), generally comprises (i) internal microbioerosion by boring cyanobacteria, algae, and fungi; (ii) internal macrobioerosion by boring sponges, worms, and bivalves; and (iii) external bioerosion by grazing gastropods, echinoids, and fish (e.g. Glynn, 1997; Tribollet et al, 2011)
After 14 years, 30 % of the block volumes were occupied by boring sponges, yielding maximum bioerosion rates of 900 g m−2 yr−1
The trace was characterised by cylindrical chambers that were arranged in long, sublinear chains that coalesced in cross, T, or L-shape, which is characteristic for Entobia cateniformis Bromley and D’Alessandro, 1984 in the late ontogenetic growth phase C
Summary
Bioerosion, the erosion of hard substrate by living organisms (Neumann, 1966), generally comprises (i) internal microbioerosion by boring cyanobacteria, algae, and fungi; (ii) internal macrobioerosion by boring sponges, worms, and bivalves; and (iii) external bioerosion by grazing gastropods, echinoids, and fish (e.g. Glynn, 1997; Tribollet et al, 2011). Experimental studies on the succession of macrobioeroders were previously limited to tropical coral reef systems and commonly lasted about 4– 8 years (Carreiro-Silva and McClanahan, 2012; Kiene and Hutchings, 1992, 1994; Pari et al, 2002). No experimental data on longterm bioerosion from non-tropical settings are available, but they would constitute important information for evaluating global patterns of bioerosion and for modelling future impacts of bioerosion. This is relevant since bioerosion is considered to increase with ongoing ocean acidification (Tribollet et al, 2009), a trend that is especially true for bioeroding sponges This is relevant since bioerosion is considered to increase with ongoing ocean acidification (Tribollet et al, 2009), a trend that is especially true for bioeroding sponges (e.g. Fang et al, 2013; Wisshak et al, 2012, 2013, 2014), with potentially detrimental effects on carbonate-dominated ecosystems (Kennedy et al, 2013)
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