Dendronephthya Hemprichi

Dendronephthya hemprichi is a commonly found soft coral that can be found in the 🌊 Red Sea through to the Western Pacific. Typically, this coral is pink or orange in color and has a transparent trunk. It has the ability to grow up to 70 cm in size.

This particular species of Dendronephthya reproduces both sexually and asexually. Sexual reproduction occurs through broadcast spawning, where the coral releases its eggs or sperm into the water to facilitate fertilization. Asexually, it reproduces through clonal propagation.

Litophyton arboreum, another species of soft coral, is gonochoric, meaning it has distinct male and female colonies. These colonies release either eggs or sperm. It participates in mass spawning events, where its gametes are released into the water for fertilization. Unlike many other soft corals at high latitudes, Litophyton arboreum follows a diurnal spawning pattern, releasing gametes daily.

The expansion of polyps in Litophyton arboreum facilitates the release of gametes, responding to water currents. The polyps expand and contract depending on the flow rate of the water. This species has adapted to expand and release gametes when the water flow rate is between 3-25 cm/s. The eggs are anchored to the polyp's mouth with mucus, allowing the released sperm to fertilize them.

Besides sexual reproduction, Dendronephthya is also capable of asexual reproduction through clonal propagation. This method allows for rapid biomass aggregation, enabling Litophyton arboreum to dominate its environment even though it lacks zooxanthellae.

The process of fragmentation is involved in asexual reproduction, where small pieces of the coral break off from the parent colony. These fragments, which typically measure 2-5 mm in length, have root-like processes that facilitate attachment to various surfaces. Despite more fragments attaching to horizontal surfaces, coral populations on vertical surfaces, such as artificial substrata of oil jetties, have a higher survival rate due to the strong water currents that transport phytoplankton, providing necessary nutrition for this azooxanthellate soft coral.

Litophyton arboreum relies on passive suspension filter feeding to ingest phytoplankton, its main energy source. Each polyp has eight tentacles with pinnules, increasing the surface area for efficient filtration. Studies involving fluorescence microscopy, phaeopigment level measurements, and observations of phytoplankton accumulation in the coral's gut have confirmed its reliance on phytoplankton as an energy source.

Litophyton arboreum is typically found on steep slopes between 1-32 meters of the benthic zone in the 🌊 Red Sea. This depth is prone to strong water currents caused by surface wind. The presence of another Dendronephthya species, Dendronephthya sinaiensis, in the same depth range adds to niche partitioning, as Dendronephthya sinaiensis has longer and denser pinnules, limiting its consumption to smaller phytoplankton. Additionally, differences in pinnule and sclerite sizes support this theory.

Due to the significant number of divers visiting the coral reefs in Eilat and the presence of oil jetties, the natural habitat is disrupted by human activities. Diving pressure and contact with fins often result in coral breakages and damages, particularly in the benthic zone and branching corals. Artificial reefs have been constructed with Litophyton arboreum, sea urchins, and Stylophora pistillata, another coral species, to reduce diving pressure on natural reefs and provide support for local fauna. In these artificial reefs, Litophyton arboreum has attached to the bottom surface of horizontal plates to avoid algal growth and sedimentation. This niche identification allows for future coral transplantation to artificial reefs as a measure to mitigate human impact.