Forams are single-celled organisms ranging from less than 1mm up to 20mm in diameter, that secrete a calcium carbonate shell. The shell is perforated and the cell protoplasm extends in and around the shell, and is used to gather food and for mobility.
Sponges are the simplest form of multi-cellular animal life. Often overlooked, they are an important component of reef systems and other marine habitats.
Sponges are the filters of the sea, filtering the water as they pump it through a complex system of canals in their bodies, to collect small bacteria and particles of organic debris for food. Water circulation inside the sponge is achieved by the beating action of millions of tiny whip-like flagella on cells that line the canals.
Reef-building corals extract calcium, carbon and oxygen from their marine environment, and combine these elements into a rigid, hard skeleton of calcium carbonate.
Soft corals are related to hard corals and often compete strongly with hard corals for space on reefs.
A coral colony grows by asexual budding to produce identical polyps, and the precise manner in which this takes place determines the coral’s final shape, which can be encrusting, massive or branching.
Anemones are similar to corals but lack a hard skeleton, and can also reproduce asexually by budding into two individuals.
Hard coral – Goniastrea australensis
A red tide – coral spawn blown onto shore
Anemone – Entacmaea quadricolor
There are four main groups of molluscs: Chitons, Snails and slugs, Bivalves and Squid, Cuttlefish and Octopus.
Chitons have a small, oval-shaped, flattened, bilaterally symmetrical body covered with eight overlapping calcareous shell plates.
They can flex their body and fasten onto an uneven rock substratum using the strong muscular foot on the undersurface. Chitons feed on encrusting algae, sponges and bryozoans by scraping the surface with a long tongue-like radula.
Snails and slugs are the most diverse group of molluscs and generally have a hard, spirally coiled calcium carbonate shell for protection (snails), although in opisthobranch sea slugs the shell is usually reduced or absent. Most are mobile grazers, feeding on a variety of algae and animals, but some groups are specialised carnivores or feed on detritus. Most groups have separate sexes although some are hermaphrodites. Some gastropods release eggs for external fertilisation, while other groups have internal fertilisation and attach numerous tiny eggs to the substratum in a jelly-like material. Some of the soft-bodied nudibranchs and other opisthobranchs are brightly coloured and patterned, serving as a warning to predators that they are toxic to eat.
Bivalves are a very diverse group of molluscs characterised by having two shells that enclose their laterally flattened body. The shells are joined at the margin by a ligament, and have hinged teeth. Two adductor muscles attached to the shells can close them tightly for protection, or to prevent desiccation. Most bivalves are filter feeders, pumping water across the highly modified gills to filter out food particles. Bivalves are well adapted for living in soft substrata such as sand and mud, although some bivalves attach to hard substrata or bore into rock, coral or wood. Most species have separate sexes and shed eggs and sperm into the water for external fertilisation.
Squid, Cuttlefish and Octopus are the most highly evolved molluscs and are probably the most intelligent invertebrates. The head is partially or fully fused with the foot, which is usually modified into 8 or 10 arms and tentacles around the mouth, each having suckers or hooks. These suction discs are used to catch fish and invertebrates, and the parrot-like beak and radula are used to eat the flesh. The shell is greatly reduced or absent, except in the tropical Nautilus, which is also unusual in possessing tentacles that lack suckers. Cephalopods have a well-developed brain and nervous system and complex sensory organs that allow them to respond rapidly to their environment. The eyes of most species are particularly well developed and allow colour vision.
Crabs, Prawns, Shrimps and Lobsters are the most familiar group of crustaceans, and are termed decapods because they have ten legs. The first pair of legs is usually modified for feeding and/or defence, and has a claw. The other four pairs of legs are modified for walking, while in swimmer crabs the last pair is modified as paddles.
Crustaceans possess a hard, jointed, external, skeleton for protection, consisting of chitin strengthened by calcium salts. While the skeleton protects the creature inside, it must be periodically discarded to allow the animal to grow. Once the old skeleton is shed, the animal grows rapidly before the soft skin again calcifies and hardens. Hermit crabs have a soft abdomen and utilise a discarded snail shell for protection. Most crustaceans have separate sexes and after internal fertilisation, the female carries the eggs under the abdomen, and the larvae swim away after hatching. In contrast, female prawns release their eggs directly into seawater.
Echinoderms are a diverse group of marine invertebrates, which on close inspection share similar characteristics such as a five-fold body plan, an internal skeleton of reticulate calcite plates, and a water vascular system that operates tube feet by hydraulic pressure.
Many echinoderms have the ability to regrow limbs and a gut if injured by predators. Sexual reproduction is generally external, with many thousands of eggs and sperm released into the sea where fertilisation takes place, resulting in a planktonic larval stage. A few species brood their larvae.
Seastar – Ophidiaster confertus
Red-tipped urchin – Heliocidaris tuberculata
Green feather star
Lincka laevigata
Sea cucumber
7-armed starfish – Astrostole insularism
Various classes of echinoderms include the Seastars, Sea Cucumbers, Brittle Stars, Sea Urchins and Feather stars.
The fish fauna of Lord Howe Island has been well documented, with more than 490 species recorded. Approximately 60% of the fish species are tropical, 15 species are endemic to the region, and the remainder are sub-tropical and temperate fish species. Most of the fishes are widely distributed in the Indian and Pacific Ocean areas, as well as in the adjacent waters in eastern Australia. It is generally concluded that there are still unrecorded species, and that the total count could easily exceed 500 species. As a result of ongoing larval dispersal from the Great Barrier Reef, the Lord Howe Island fish fauna will always be changing, and may never be completely known.
Sea turtles visit Lord Howe Island, but do not breed here. The most common sea turtles you may see are Green Turtles Chelonia mydas, which are mainly herbivores that feed on algae and seagrasses. Other Sea Turtles are mainly carnivores that eat a variety of food including cnidarians, molluscs, crustaceans, ascidians and fish. Sea snakes are highly venomous and feed on a variety of small reef fish such as gobies, or on fish eggs. Sea snakes can survive out of the water for some time and should not be handled, even if they appear to be dead.
Dolphins live in the waters around Lord Howe Island, and the most commonly encountered species is the Bottlenose Dolphin Tursiops truncatus. Noted for their playfulness, Bottlenose Dolphins are most often seen from boats outside the lagoon, where they sometimes swim alongside the bow of the boat, occasionally leaping gracefully from the water. Sometimes these dolphins enter the lagoon and are seen from the shore. Other dolphin species including the Common Dolphin Delphinus delphis, are occasionally spotted at sea.
Whales are another group of marine mammals recorded around Lord Howe Island.
Anecdotal evidence points to more regular sightings of whales near the Island in past decades when whale populations were greater before commercial whaling decimated their populations.
Following the moratorium on killing Humpback Whales and the gradual increase in their populations, sightings of Humpback Whales Megaptera novaeangliae, are becoming more frequent at Lord Howe Island, particularly in June and again in October and November as they pass on migratory tracks between Antarctic waters and northern breeding grounds in the Coral Sea. Sperm Whales Physeter macrocephalus, Pilot Whales Globicephala sp., and Blainville’s beaked-whales Mesoplodon densirostris have also been recorded around Lord Howe Island.
