Feeding ecology of the black coral, Antipathes Fiordensis, from Doubtful Sound, Fiordland, and description of a new species, Thamnomolgus, N.SP. (Poecilostomatoida: Thamnomolgidae), a Copepod associated with A. Fiordensis.

László Kiss
July 2000

Abstract

This study was undertaken to investigate aspects of the feeding ecology of the black coral, Antipathes fiordensis, from Doubtful Sound, New Zealand. The focus was on feeding behavior during prey capture and ingestion, the role spirocysts play in prey capture, and changes that occur on a cellular basis during feeding action. In addition, the diet of A. fiordensis was investigated.

Several laboratory experiments on black coral feeding were conducted in 1998/1999, recording feeding posture, prey capture and handling. Most prey of Antipathes fiordensis was larger than the tentacle spacing (400 µm), and could, therefore, be retained by direct interception which is likely to be the primary mode of particle encounter. The feeding response of black coral polyps was elicited by a combination of chemical and mechanical stimuli. Polyps responded to water movement without chemical stimuli (e.g., when stirred with a syringe) with increasing tentacle motion and increasing body size. The same response was observed when adding live zooplankton to the water.

The expanded tentacles readily captured zooplankton and investigation of the tentacular ultrastructure using transmission electron microscopy showed that spirocysts play an important role in prey capture. An increasing mucus layer on the polyps' tentacles functioned in trapping the prey items that were ingested within a short time. In average, ingestion time was 14.8 minutes (9.1 SD), and digestion time was 18 minutes (9.1 SD). The digestion time for various types of prey in A. fiordensis was observed examining fresh collected samples at two occasions, in September 22, 1998, and March 16, 1999. While gelatinous prey was digested fastest (1.5 to 2.5 hours), bivalves remained longest in the guts (>6.5 hours). Average digestion time was 6.2 hours (±1.05 SE).

It has been demonstrated that nutrients (labelled with 14C) were transported through the gastrovascular system of A. fiordensis, which has not been shown for any antipatharian to this stage.

Dynamic changes in the tentacular ultrastructure during feeding action were observed in A. fiordensis. Mucus cells transport vesicles to the tentacle surface, and the deterioration of cnidae and mucus cells result in a significant structural change in the epidermal cytoplasm. The experiment showed furthermore, that columnar cells containing prominent Golgi complexes with accompanying secretion products developed in the epidermis during feeding action, providing the insight that these cells are an induced and not persistent morphology.

The discovery of this type cell in the tentacular epidermis of A. fiordensis suggests that there is, in addition to planktonic prey, another nutritive source available for the black coral, which is dissolved or colloidal organic material.

The diet of A. firodensis consisted mostly of epipelagic copepods of the species Oithona, Oncaea, Paracalanus, and Clausocalanus. The prey items were mostly larval stages with an average size of 500 µm, but larger copepods of the species Calanus australis and Metridia were also occasionally found. Bivalves, appendicularia, hydrozoa, and invertebrate eggs were also present in the coelenterons.

When examining gut contents of the black coral, a new species of a symbiotic copepod was found and described in chapter 4. This chapter has been reviewed and accepted for publication by the New Zealand Journal of Marine and Freshwater Research.