Excavating sponges are among the most important macro-eroders of carbonate substrates in marine systems. Their capacity to remove substantial amounts of limestone makes these animals significant players that can unbalance the reef carbonate budget of tropical coral reefs. Nevertheless, excavating sponges are currently rarely incorporated in standardized surveys and experimental work is often restricted to a few species. Here were provide chemical and mechanical bioerosion rates for the six excavating sponge species most commonly found on the shallow reef of Curaçao (southern Caribbean): Cliona caribbaea, C. aprica, C. delitrix, C. amplicavata, Siphonodictyon brevitubulatum and Suberea flavolivescens. Chemical, mechanical and total bioerosion rates were estimated based on various experimental approaches applied to sponge infested limestone cores. Conventional standing incubation techniques were shown to strongly influence the chemical dissolution signal. Final rates, based on the change in alkalinity of the incubation water, declined significantly as a function of incubation time. This effect was mitigated by the use of a flow-through incubation system. Additionally, we found that mechanically removed carbonate fragments collected in the flow-through chamber (1 h) as well as a long-term collection method (1 wk) generally yielded comparable estimates for the capacity of these sponges to mechanically remove substratum. Observed interspecific variation could evidently be linked to the adopted boring strategy (i.e. gallery-forming, cavity-forming or network-working) and presence or absence of symbiotic zooxanthellae. Notably, a clear diurnal pattern was found only in species that harbour a dense photosymbiotic community. In these species chemical erosion was substantially higher during the day. Overall, the sum of individually acquired chemical and mechanical erosion using flow-through incubations was comparable to rates obtained gravimetrically. Such consistency is a first in this field of research. These findings support the much needed confirmation that, depending on the scientific demand, the different approaches presented here can be implemented concurrently as standardized methods.
The coasts of Curacao as well as the other leeward islands of the Netherlands Antilles, consists predominately of limestone cliffs, cut into Pleistocene reef rocks. Several erosional cliff types are distinguised as examples from a continuous range of variations, depending largely upon the degree of exposure (water turbulence). The most sheltered end member of this range shows only marine undercutting of the cliff, basically representing the difference between marine and terrestial erosion rates. The most exposed end member is characterized by a zone fo karren, a well developed surf platform, and a subtitdal notch. Intermediate cliffs show combinations of notches and benches. One of the intermediate profiles consists of a surf bench and two separate notches, both of which are contemporaneous. The surf benches result from the protective effect of organic accretions, build predominately by vermetid gastropods and coralline algae, are are shown to be genetically similar to world=wide features described as platforms, cornices, trottoirs,e tc. The term notch is redefined as an indention in a cliff, genertically related to sea level. Notches occur below and above, rather than within tidal intervals, and condequently the term tidal nip is not maintained. Eroison fo the cliffs results primarily from biodegradation of limestone, and the morphological units of the prifles correspond to the zonate occurance of those orgnaizms which are crucial in eroding the cliff, or reversely, protectin gthe cliff anaginst erosion with accretions..
The coast of Curacao as well as the other leeward islands of the Netherlands Antilles consist predominantly of cliffs cut into Pleistocene limestone. Several erosional cliff types are distinguished as a function of the degree of exposure to wind and surf. The most sheltered cliff type shows only marine undercutting, basically representing the difference between marine (relatively fast) and non-marine (relatively slow in this dry climate) erosion rates. The most exposed cliff type is characterized by a zone of karren, a well-developed surf platform, and a subtidal notch. Intermediate cliff types can be found everywhere. One type consists of a surf bench and two notches, above and below the bench. The benches result from the protective effect of vermetid/coralline algal accretions, with fabrics similar to those of boiler reefs in Bermuda, including internal sediment and marine cements (aragonite and magnesian calcite). The entire cliff profile is erosional, the accretions only delay erosion. Ultimately the bench collapsed when the notch below it reaches a certain depth. All erosion is caused by marine organisms, there is no sign of mechanical erosion. The morphological components of the cliff profile correspond to the zonate occurrence of boring and accretionary organisms.
Abstract: Bioerosion caused by boring mussels (Mytilidae: Lithophaginae) can negatively impact coral reef health. During biodiversity surveys of coral-associated fauna in Curaçao (southern Caribbean), morphological variation in mussel boreholes was studied. Borings were found in 22 coral species, 12 of which represented new host records. Dead corals usually showed twin siphon openings, for each mussel shaped like a figure of eight, which were lined with a calcareous sheath and protruded as tubes from the substrate surface. Most openings surrounded by live coral tissue were deeper and funnel-shaped, with outlines resembling dumbbells, keyholes, ovals or irregular ink blotches. The boreholes appeared to contain black siphon and mantle tissue of the mussel. Because of the black color and the hidden borehole opening in live host corals, the mantle tissue appeared to mimic dark, empty holes, while they were actually cloaking live coral tissue around the hole, which is a new discovery. By illustrating the morphological range of borehole orifices, we aim to facilitate the easy detection of boring mussels for future research.