C. Palecological Implications

From the former pages we learned that coralline algae can occur in a wide range of marine environments. Although several species may show very restricted distribution patterns with respect to factors such as depth and temperature, they can be hardly applied to fossil material. This is caused by the problematic identification of coralline algae in fossil material.

This page aims to summarize the potential use of encrusting coralline algae for palecological reconstructions. In fact, the predictions are scarce and most probably you will find more questions than answers, but modern paleontological studies on this topic are scarce.

RHODOLITHS

Monospecific rhodoliths indicate stable palecological conditions, while taxonomic successions within the rhodolith may point to environmental changes. This may be also true for changes in growth forms, but note that different species can show different growth forms.

Taxonimic changes with increasing rhodolith size may, however, just indicate that the larger rhodolith was more stable due to its increased weight, but not necessarily indicate changes of environmental parameters. Some species may prefer a higher degree of turning (i. e., abrasion of the thallus), others may prefer a stable substrate.

See also the notes on hydrodynamic energy below.

SALINITY

Due to the restrictive occurrence of most coralline algal species, a high specific diversity of coralline algae indicates normal marine conditions.

However, the opposite interpretation is not allowed, because the dominance of one species could be also caused by other palecological parameters.

LIGHT / DEPTH

In tropical environments, the typical lower limit for coralline algae is about 80 m., in colder waters about 20 - 40 m. In combination with sedimentary analyses (e. g., microfacies analyses), some careful rough estimations can be made, at least for the low limit of coralline algae dominated sediments.

The depth distribution depends, however, on the light permeability of the water. Therefore, the determination of absolute paleo-depths is not possible using coralline algae (which is mostly impossible in paleontology).

However, there are some approaches which allow the interpretation of general depth trends on a higher taxonomic level (follow this link to read our paper). Most probably, there are several distinct trends visible on the species and genus level, but studies on this topic are scarce and older results cannot be used due to the problematic recognition of fossil taxa.

Algal ridges, algal cup reefs, and the trottoir are restricted to the intertidal to shallowest subtidal. The coralligene de plateau is restricted to the subtidal, down to 160 m. The fossil record of these buildups is, however, scarce.

CLIMATE / TEMPERATURE

As mentioned on the former page, there are some indications that Sporolithon may be more typical for tropical waters and Phymatolithon for non-tropical environments. At the current state of research, serious interpretations are impossible.

Algal ridges and algal cup reefs are restricted to the tropics. The trottoir and the coralligene de plateau are restricted to temperate waters.

HYDRODYNAMIC ENERGY AND SUBSTRATE

High energy:

  • algal reefs on hard substrate

  • regular rhodoliths with dense, intercalary branching and lateral fusion of branches; mostly massive rhodoliths

  • maerl with high fragmentation of unbranched unattached branches and with the above described rhodoliths

Low energy:

  • coralligene de plateau growing on soft substrate, such as rhodolith accumulations

  • irregular rhodoliths with open and dichotomous branching; mostly fragile

  • maerl with above described rhodoliths and branched unattached branches

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