Zoanthus spp.

Common Names: Button corals, button polyps, sea mat

Phylum: Cnidaria

Class: Anthozoa

Order: Hexacorallia

Family: Zoanthidae

Range: Various species are widespread in the western and Indo-Pacific, and also the western Atlantic Ocean

Natural Environment: Generally found in shallow reef environments receiving intense light and swift water movement. Nevertheless, there are some species that prefer slower-moving waters and lower light intensities.

Water Requirements: Calcium 380 to 430 mg/l, alkalinity 2.5 to 3.0 meq/l, pH 8.1 to 8.2, specific gravity 1.024 to 1.026, phosphate < 0.015 ppm, nitrate < 15 mg/l, and a temperature range of 74° to 83°F.

Captive Care

Exact species identification based on physical appearance is extremely difficult, as most species look alike except for coloration and polyp size, which is dependent upon the collection site.Therefore, most specimens are given common names that refer to their coloration, such as blue or green Zoanthus/button polyps.

Lighting

Almost all species in this genus seem to fare better in aquariums when kept under intense lighting and in areas with swift water movement. The currents help to keep the polyps clear of detritus and sand particles that would otherwise block light from reaching them. Those placed near bright light fare better and spread faster than those in low- to moderate-lighted areas.

Feeding

Direct feeding does not have to be performed often, but additives, especially those containing highly unsaturated fatty acids (HUFAs) that contain omega-3 fatty oils, have seemed to have a positive affect on the various specimens I’ve maintained over the years, as have iodine additives.Species will exhibit a feeding response only to specific foods. For example, sea urchin eggs placed directly on the polyps of some specimens will be eagerly consumed, yet other animal matter is not accepted, such as brine shrimp and other zooplankton-type foods (Borneman, 2001).

Watch Out for Heliacus areola and Angelfishes

There is a pest snail Heliacus areola that feeds upon Zoanthus colonies, usually during the daytime when the polyps are open, making it difficult to see. Therefore, during unlit evening hours, use a flashlight with a red beam of light (simply cover the lens with a clear red plastic material to avoid disturbing the other animals, as they cannot see red light) and check out the Zoanthus colonies for this snail and remove it if present.

As a word of caution, when I have kept large angelfishes with Zoanthus species, the angels seemed to take pleasure in tearing up the corals. It was as if they were searching for something tasty to eat, even though they never ate the polyps themselves.