Coral Reef Science:  Development Highlights

Eric Borneman

This month, I cover an article on taxonomic reappraisal of Montipora digitata...

Stobart, Ben. 2000. A taxonomic reappraisal of Montipora digitata based on genetic and morphometric evidence. Zoological Studies 3: 179-190.

Abstract:

A taxonomic reappraisal of Montipora digitata based on genetic and morphometric
evidence. Recent molecular and reproductive studies have demonstrated that two morphs of Montipora digitata are different species. In this study, skeletal morphology was examined to determine whether the species can be identified using traditional taxonomic methods, and to establish suitable names for the species. Univariate and multivariate analyses based on five skeletal characters revealed that the two species do differ in morphology. However, overlap of these characters renders them unsuitable for species identification. A further character, septal shape, was found to be species specific. Examination of museum specimens using septal shape to distinguish the species revealed that the two species correspond to the holotypes for M. digitata (Dana 1846) and M. tortuosa (Dana 1846). This study highlights the usefulness of a multiple-technique approach to coral taxonomy, with each alternative technique acting as a test for the other, which reduces the chance of an erroneous conclusion.

Comments:

In light of the recent availability, both wild and cultured, of what is commonly called "elkhorn digitata," I found this article to be of some interest. The particular morph of Montipora in the hobby that has flattened ends and tends to turn rather bluish-grey under strong light seemed to me to be clearly different from the normal morphological variations of M. digitata. Looking at the skeleton from a sample in my own tank, it appears that the description in the article above fits this coral well and that this coral should probably be described as M. tortuosa. No other species fits the consistent growth form of the genus, and although this paper describes samples taken from the Great Barrier Reef off northern Queensland, Australia, the range of the species overlaps areas where corals for the trade are collected.

This paper also presents an easy-to-read description of how multiple methods must be used to determine species in corals, and describes the skeletal feature analysis well for aquarists inclined to more carefully identify stony corals.

Ronald L. Shimek, Ph. D.

This month, I will discuss an interesting article on zooxanthellae...

Andrew C. Baker, 2003. Flexibility and specificity in coral-algal symbiosis: diversity, eco1ogy, and biogeography of Symbiodinium. Annual Review of Ecology, Evolution and Systematics. 2003. 34:661-89.

Abstract:

Reef corals (and other marine invertebrates and protists) are hosts to a group of exceptionally diverse dinoflagellate symbionts in the genus Symbiodinium. These symbionts are critical components of coral reef ecosystems whose loss during stress-related "bleaching" events can lead to mass mortality of coral hosts and associated collapse of reef ecosystems. Molecular studies have shown these partnerships to be more flexible than previously thought with different hosts and symbionts showing varying degrees of specificity in their associations. Further studies are beginning to reveal the systematic, ecological, and biogeographic underpinnings of this flexibility. Unusual symbionts normally found only in larval stages, marginal environments, uncommon host taxa, or at latitudinal extremes may prove critical in understanding the long-term resilience of coral reef ecosystems to environmental perturbation. The persistence of bleaching-resistant symbiont types in affected ecosystems, and the possibility of recombination among different partners following bleaching, may lead to significant shifts in symbiont community structure and elevations of future bleaching thresholds. Monitoring symbiont communities worldwide is essential to understanding the long-term response of reefs to global climate change because it will help resolve current controversy over the timescales over which symbiont change might occur. Symbiont diversity should be explicitly incorporated into the design of coral reef Marine Protected Areas (MPAs) where resistance or resilience to bleaching is a consideration.

Comments:

The author discusses the relationships between the many species of zooxanthellae and their respective hosts. Zooxanthellae were long thought to be all one species of alga. Evidence to the contrary began to accumulate about twenty years ago, although the implications of this still have not begun to be appreciated in the aquarium hobby. Baker discusses the present state of affairs, with about 11 described "species" of Symbiodinium in seven major groups. However, he indicates that there are indications that there may well be over 200 species of zooxanthellae, and the relationships between hosts and symbionts are by no means as simple as have been thought. This review article would be a good place to begin for any technically-oriented reef aquarist who is wondering what these zooxanthellae are and what they may be doing in the corals.