Soft corals are captivating marine invertebrates that add vibrant colors and dynamic forms to underwater landscapes. These organisms are often observed swaying gently with ocean currents, presenting a stark contrast to their rigid counterparts. Understanding soft corals reveals their unique biology and significant roles within oceanic ecosystems.
Defining Soft Corals
Soft corals, scientifically classified under the subclass Octocorallia, are colonial animals composed of numerous individual polyps. Unlike hard corals, they do not produce a rigid, external calcium carbonate skeleton for support. Instead, their flexible, often leathery texture comes from a jelly-like matrix called mesoglea, embedded with microscopic calcareous structures known as sclerites. These sclerites provide internal support and some protection from predators, while allowing the coral to remain pliable.
Each soft coral polyp features eight tentacles, distinguishing them from other coral types. These tentacles are often feathery or branched, aiding in their feeding processes. Soft corals form colonies that can take on various shapes, resembling trees, bushes, fans, or whips.
Soft Corals Versus Hard Corals
The primary distinction between soft and hard corals lies in their skeletal structures and polyp morphology. Hard corals, also known as Scleractinia, secrete a rigid, calcium carbonate (aragonite) exoskeleton that forms the structural foundation of coral reefs. This hard skeleton persists after the coral dies, contributing to reef accretion. In contrast, soft corals lack this massive external skeleton, relying instead on internal sclerites for shape and support.
Their polyps also differ. Soft corals, belonging to the Octocorallia, have polyps with eight tentacles. Hard corals, classified as Hexacorallia, typically have polyps with tentacles in multiples of six, and these tentacles are generally smoother and unbranched. While hard corals are the primary reef-builders, soft corals contribute to the reef ecosystem without forming the same rigid structures. Soft corals also exhibit greater flexibility, allowing them to sway with currents.
Habitat and Lifestyle
Soft corals inhabit diverse marine environments across the globe, thriving in tropical and subtropical waters, and extending into deeper, colder regions. They are often found attached to the seabed, living on coral reefs or providing vertical relief in soft-bottom areas. Their flexible structure enables them to flourish in areas with strong water currents, as they can bend and sway without breaking.
Many soft corals obtain nutrients through filter feeding, using their eight tentacles to capture plankton. This feeding mechanism allows some species to survive in deeper waters where sunlight is scarce. While some soft corals do not contain symbiotic algae, many species, like hard corals, host microscopic single-celled algae called zooxanthellae within their tissues. These algae perform photosynthesis, providing the coral with energy and nutrients, and in return, the coral offers the algae a protected environment.
Ecological Importance
Soft corals play a significant role in marine ecosystems, contributing to biodiversity and habitat. They provide shelter, breeding grounds, and feeding areas for a variety of marine organisms, including fish, invertebrates, and pygmy seahorses. The intricate structures formed by soft coral colonies offer refuge from predators and strong currents.
Beyond providing habitat, soft corals contribute to nutrient cycling. Their presence helps maintain water quality by filtering out sediments and excess nutrients. Although they do not build massive, rigid reef structures like hard corals, the accumulation and cementing of their sclerites can contribute to shoreline protection by dissipating wave energy. This highlights their contributions to marine ecosystem health and resilience.