Welcome to Tornadoropa : Here you find a description about Ecology , Symbiosis and Predation of Echinoids ( Sea Urchins ), presented by Christian Neumann .

Ecology

Sea urchins, also known as echinoids, play the role of keystone organisms for many marine ecosystems. This is especially true for the herbivorous "regular" echinoids or Euechinoida. For instance, they control the growth of kelp forests by their grazing activity. In coral reefs, echinoids grasp off algae from coral rubble, thus providing barren surfaces necessary for the settlement of coral larvae and those of other sessile organisms. The role of deposit-feeding sea urchins in nutrient-deficient soft-bottom communities is not well understood but is probably of great importance for the energy flow in the deep sea.

Commercial sea urchin fishery as well as fishery on predatory fishes preying on sea urchins poses a serious threat on marine benthic communities and may lead to trophic cascades. On this page, which will be updated regularly, you will find various topics dealing with sea urchin ecology such as predation and symbiosis.

Visualizing the invisible: Symbionts dwelling inside Fossil echinoderm skeletons

The intimate relationship of different organisms living close together is called symbiosis. The degree of dependence is often so high that none of both partners can exist alone. Obviously, symbiont-host systems are highly specialized. Since evidence of symbiosis is rarely preserved in the fossil record, the timing of the evolution and speciation of symbiont-host-systems often remains a puzzle.

Fortunately, symbiont traces sometimes get fossilized. Especially echinoderms may act as a study model because their skeleton favours the preservation of symbiotic interactions: As an endoskeleton, it represents a living tissue which is able to react directly to symbiont-induced disturbances. When fossilized, these tissue responses can be studied by the palaeontologist.

In a current project, I study symbionts of various taxonomical groups dwelling inside crinoid and echinoid skeletons and the response of the host's skeletal tissues to symbiont/parasite infestation. Echinoderms are often colonized by other organisms which settle on their body surface. By doing so, the intruder provokes tissue reactions of the host. These reactions may include callus formation ( neoplasia ) and embedment of the parasite by the host tissue ( bioclaustration ). As a defense reaction, the host tries to overgrow the intruders with its own skeleton. Some organisms took advantage of this behavior and subsequently switched to an endoskeletal mode of life. They benefited from protection from predators and some also exploited the host's nutrients. Application of non-destructive computer tomography (neutron- micro- and synchrotron-CT) allows undisturbed insights into the hidden live of parasites and commensals dwelling deep in the skeleton of their hosts.

Non-predatory borings in echinoid skeletons

Borings penetrating the test of echinoids are often used to evaluate the impact of boring predation on echinoids. In fact, predatory gastropods of the family Cassidae ( helmet conchs ) are specialized to feed on sea urchins and produce characteristic boreholes in the echinoid test. These holes are the result of a mixed etching and rasping process. In contrast to the holes produce by other predatory gastropods (e.g., naticid ), cassid boreholes are by far not perfect circular holes. Moreover, they are rather irregular in outline. For all of those working on drilling predation, it is essential to distinguish between predatory and non predatory borings. Many other organisms, i.e. parasites and commensals bore in echinoid tests without killing their host. Many of these borings may be confused with predatory borings. The aim of this paper is to show the diversity of non predatory borings produced by echinoid associates. This will help to recognize and distinguish holes produced by predators from those produced by symbionts.

Some borers, e.g., many gastropods of the eulimid family live permanently attached on the surface of their host but penetrate the test to feed inside with a prolonged proboscus. Some polychaetes of the family Amphynomidae live in the coelomic cavity or the host intestine but produce holes to enter the test. Commensal polychaetes of the Polydora group ( Spionidae ) bore in the test of echinoids without penetrating it. The bizarre ascothoracid Ulophysema enters its echinoid host through the ambulacral or genital pores but bores holes from inside to release its offspring. Finally, some parasites, while invading the host through pre-existing openings of the test, (i.e. the opening of the periproct or ambulacral pores), alter or enlarge these holes. These pseudoborings may also be confused with predatory borings.