Lace coral

Lace coral are any of the species of coral that belong to the taxonomic family Stylasteridae. Lace corals grow in a planular fashion with pink, purple, orange, light tan, or simply white branches that may be delicate and fragile or broad, flat planes. Unlike many other corals the living tissue does not contain all of the color, but instead the stony skeleton, or coenosteum, contains the vibrant colors of coral even when the living tissuesdie. Lace corals were relatively undocumented until about a century and a half ago due to the great depth at which most of the species lie. However, many species have been studied and documented in the past century due to developing technology that allows researchers to enter into their watery world.

These beautiful colonies have three main zooids, or polyps, that perform the functions of the coral such as nutrition (gastrozooids), reproduction (gonophores), and defense (dactylozooids). They do not have the zooxanthellate algae that other stony corals do, and therefore do not require sunlight to provide the algae with the means for photosynthesis. This allows lace corals to reside in relatively deep waters with a strong current, and only about ten percent live in the top fifty meters of oceans. They grow with the flat side of their usually uniplanular branches towards a current, so as to pick up as many passing food particles and microplankton as possible. They reproduce in a brooding fashion, and therefore do not spread at the pace of broadcasting corals, which make up the majority of coral species.

Body Design
Lace corals are known for their spectacularly colored skeletons. They can be purple, pink, or orange, but can also come in the dull colors of light tan and white. Unlike many other corals, these hydrozoan corals embed the vibrant colors into their stone-like skeletons whereas other corals are colored in the living tissue. Because of this, when the living tissues of the coral die, the color remains. Their delicate branches are usually formed along a single plane and most do not grow very large due to their fragility, many only reaching lengths of tens of centimeters. They can either have fragile, detailed branches or can grow in broad plates. This beautiful, colorful skeleton is called the coenosteum and it houses several types of polyps that perform the life processes of the coral. The three types of polyps in the colony work together to aid the colony as a whole. Generally the gonophores work in reproduction, dactylozooids speciallize in defense, and the gastrozooids are the main food gatherers.

Many tubes and pores allow these polyps to catch food, reproduce, and defend the colony. The zooids (the living hydrozoans that perform the coral's functions; also called polyps) are supported by calcareous spines in most species. Thick strands of tissue throughout the skeleton connect these polyps. The pores that house the zooids are called cyclosystems. Their arrangement varies between species and is used to classify species. The skeleton also acts as defense, in some species more than others. In some species the skeleton includes lids to cover the polyps the reside inside the coenosteum. A gastrozoid (polyp whose main function is feeding) with non-stinging tentacles resides in each cyclosystem and is protected by dactylozoids armed with stingers. Spines are attatched to the coenosteum near the dactylopore (the pore used by dactylozooids). It is U or horseshoe shaped and many can be clustered together to aid further in defense. Ampullae are the skeletal coverings of the gonophore, the polyp that contains reproductive structures like the sperm or egg. They appear as a kind of blister or as a chamber beneath the surface coenosteum. Female ampullae have efferent pores or tubes through which they release their gametes, while males release gametes through smaller pores. Internal ampullae have efferent ducts through which they release gametes and by which they communicate to the skeleton surface.

Life Cycle
Lace corals, unlike many other branching corals, mature slowly, have long lives, and are brooding corals. Therefore they may be out-competed by other species as they grow and spread slowly. They are generally either male or female, with prominent dimorphisms of the ampullae used to distinguish between the sexes. Ampullae are the skeletal coverings of the gonophore, the polyp that contains reproductive structures like the sperm or egg. One species, Sylaster roseus, is known to be hermaphroditic, having both genders in the same coral colony. Hermaphroditic corals have both male and female polyps in the same colony, or the polyps themselves are hermaphroditic. After an egg is fertilized it undergoes growth into a planular stage before being released and crawling a short distance from the parent coral. Because they do not travel far from the parent organisms, spread of the corals is limited. In fact, one species in the Hawaiian islands was only found in a ten square milometer area.

Lace corals are brooding corals. While broadcasting corals release all of their gametes and eggs at once, brooding corals release only male gametes into the water. Once a male gamete encounters a female polyp, fertilization will occur inside the polyp and a planula is produced. Once it reaches a certain stage of maturity, it is released out of the mouth of the female polyp and will settle a short way from the parent coral. In lace coral, gonophores release sperm or planulae (free-swimming larva ) via efferent ducts which appear as small pores. In studies on Stylantheca petrograpta and S. californicus revealed that eggs appeared in the gastrodermal canals and traveled to the ampullae where they were fertilized and developed. S. californicus had eggs fertilized in May, June, and July that left the parent coral in November through the pore of the ampullae or through the gastropore. In similar studies, it was found that, unlike broadcasting corals, the gametes’ stages of maturity were somewhat unsynchronized, as females contained eggs and planulae in the same colony.

Ecology
Lace corals exists in many areas of the world. In fact, the only major area they do not inhabit is the cold waters of the northern and southern polar regions. The Gulf of Alaska and the Sea of Okhotsk house the northern most documented species. The western Pacific hosts the most number of species, but upon further documentation it is speculated that the New Caledonia region will surpass even this flourishing area. The vast majority, 90 percent in fact, live in at a depth of fifty meters or deeper, with 200 to 400 meters being the most common range. The deepest recorded species, Crypthelia affinis, was documented at an astonishing 2789 meters! Hydrocorals are generally found in shady areas such as ledges beneath overhangs or underwater caves. They tend to grow with the most flat part of their structure towards a current so that more surface area can be exposed to the nutrient carrying water.

Lace coral colonies do not rely on photosynthesis for food because they do not have the algae that other corals do (zooxanthellate algae) that require sunlight to make food. Therefore, they obtain nutrition by capturing microplankton and by nutrient absorbtion. Nutrient absorption is when the polyps of the coral absorb passing nutrients through their body walls. These nutrients are dissolved in the water that flows around them, and if the water is stagnant it will not be refreshed by new water carrying nutrients. This is why it is important for lace corals to grow with as much surface area in the current as possible, as more microplankton and nutrients will flow by them.

Lace corals also have relationships with other organisms in their environment. Some fish may hide in them to temporarily escape predators, and their bright color can sabotage some hunters that rely on camouflage. One particular species in the genus Stylaster, Stylaster brochi (one of the most common lace corals in the Aleutian Islands), shares a parasitic relationship with a worm from the genus Polydora. This worm burrows into the coral’s skeleton forming longitudinal tubes that, in a cross section, look like figure eights. There may be numerous worms in just one colony of S. brochi that obtain protection in the coral. They may also compete with the coral for food, which can limit the growth of the colony. This species also forms a habitat for other invertebrates like sponges, barnacles, bivalves, and hydroids. This type of relationship may occur in other species as well.



Documentation
Due to most of the members of Stylasteridae residing in relatively deep waters, most of their documentation has had to wait for technology that would allow researchers to traverse the depths of the sea to develop. There was little interest in these creatures before the nineteen hundreds, as only thirteen valid species descriptions resulted from the late seventeen and mid-eighteen hundreds. Most of the documentation of stylasterid species was performed in the last century and a half. Pourtalès and Moseley used collection from deep water for their research. Pourtalès documented seventeen species and two genera and Moseley documented nine species and two genera in an eighteen year period from 1876 to 1884. Many of Pourtalès’s works can be found at the Museum of Comparative Zoology at Harvard (Cambridge) while Moseley’s writings can be found at The Natural History Museum in London. Another researcher from London, Hickson (along with his team), described sixteen species from collections primarily taken in the southwestern Indian Ocean between 1905 and 1909.

Another increase in species knowledge was provided by Fisher and Broch in the span of 1932 and 1947. Fisher was able to describe two genera and fifteen species that are found primarily in the deep waters of the Aleutian Islands. Broch wrote the “Investigations on Stylasteridae, parts 1 and 2” that described twenty-four species and three new general. Most of these new species were from a Pacific and South African excursions. Between 1960 and 1968 Boschma found ten new species and two genera from all over the world. He also wrote sixty-five papers on the family. Also during this time, Eguchi wrote three papers that elaborated on six species from Japan and Sagami Bay. In 1978 to 1992 the researcher Cairns was early in his career. However he was able to document an astonishing one-hundred new species and seven genera! He made some revisions based on other deep-sea expeditions like the revision of species from the eastern and western Atlantic and New Zealand.

In 2012, 247 species and 26 genera had been documented and described. This is even excluding twenty-one fossil species and one fossil genus.