2.4 Morphology

Macromorpholoy

Macromorphology is here defined as the shape of the entire colony which can express inter- or intraspecific (polymorphic) variation.

Colony Shapes

Micromorphology

Anatomy of a Calice

• corallite - the entire structure of the coral skeleton

• calice - cup in coral skeleton

• Septa - wall-like structures that radiate from the sides of each corallite

• Columella - extends upward from the floor of the calice

• Basal plate - partition that provides new elevated bottom in the corallite when coral polyps grow by withdrawing itself upward and secreting a new basal plate

Variation with depth

Macromorphology

• massive → tabular (Graus)

• Spherical/massive → tabular/platelike (Gleason 1992)

• More → less branching (Muko 2000, Oliver 1983)

• Higher rugosity → lower (Todd 2002/2004)

• hemispherical → flat branching morphology (Jauber 1977)

• massive → flat OANN (Dustan 1975)

• vertical → horizontal plates in Turbinaria (Anthony et al. 2005)

• growth in any direction → vertical growth only

• slower growth -> faster (Bosscher & Meesters 1992)

• Massive -> platelike (Bosscher & Meesters 1992)

• low -> high skeleton density (Bosscher & Meesters 1992)

• high -> low calcification rate (Goreau 1959)

• fast -> slow growth of branch tips (Goreau 1959)

• large -> small branch diameter (Einbinder 2009)

• hemispherical -> platelike branching structure (Einbinder 2009)

• 3D -> 2D architecture (Dustan 1975; Falkowski and Dubinsky 1981;

  Fricke and Schuhmacher 1983; Vermeij and Bak 2002;

  Anthony and Hoegh-Guldberg 2003)

• low -> high branch spacing and long -> short branches (Kaniewska et al. 2008)

• high -> low intra-colony shading (Dustan 1975; Falkowski and Dubinsky 1981;

  Fricke and Schuhmacher 1983; Vermeij and Bak 2002;

  Anthony and Hoegh-Guldberg 2003)

• thicker -> thinner branches (Bak and Meesters 1998; Muko et al. 2000; Mass et al. 2007, Nir et al. 2011)

• hemispherical -> horizontal/flattened/encrusting (Bak and Meesters 1998; Muko et al. 2000; Mass et al. 2007)

Micromorphology

• small -> large calice size in MCAV (Studivan et al. 2019)*

• small → large polyps (Nir et al. 2011)*

• corallite expansion/ larger → smaller corallites (Todd 2004b, 2004c)

• larger → smaller corallites in MCAV (Wijsman-Best, 1974; Beltran-Torres & Carricart-Gavinet, 1993),

• Deeper → shallower calice relief in OANN may be shading strategy (Klaus et al. 2007)

• large -> small calices (Einbinder 2009)

• A whole bunch of changes (Soto et al. 2018)

*cryptic lineage or morphotype?

Summary from Todd 2008

• Summary: in shallow, more complex colony morphology, corallite extension, branch or tuberculae formation, higher surface area to capture more sun or provide self shading, reduce drag resistance and increase sedimentation shedding ability

• Summary: in deep, simple flat morphology and decrease in corallite size will maximize light collection and minimize the amount of tissue needing support

Light Interactions

• Skeletal structure is critical to light scattering to either maximize or minimize the number of photons that get to the symbionts for photosynthesis.

• Micro-structure appears to be more important than colony structure for light scattering, and scattering happens most within the recently deposited, surface CaCO3 (Swain et al. 2018)

References

Bosscher & Meesters 1992

Shallow corals grow more slowly. Colonies go from massive - platylike along a depth gradient. Denser skeleton at depth.

Brakel 1977

No change in calice morphology along a light gradient in Porites sp.

Goreau 1959

Calcification rate was significantly higher in light environments. Top/end of branches & colonies grow faster. Detailed description of calcium carbonate reactions

Studivan, Milstein & Voss 2019

This study assessed morphological calice variation MCAV across a depth gradient. Mean corallite diameters were smaller and spacing was greater in deeper areas. The authors also identified two morphotypes (shallow depth specialist w/ large calices + generalist), which were associated with genetic structure in some sites. The generalist species was associated with higher chl and symbiont concentrations.

Einbinder 2009

Calices got smaller with depth. Branch diameter got smaller with depth. macromorphology changed from branching structure being hemispherical to more platelike.

Todd 2008

This is a review of morphological plasticity in corals. Many of the findings they synthesized are listed above. Todd summarizes best practices for measuring plasticity in coral (must be on genotype clones).

Nir et al. 2011

The authors quantified morphology, chl, PAM and ITS2 along a depth gradient. They did not find expected decreasing patterns in chl but offered other explanations for this trend. They found thinner branches and larger polyps at depth. They also suggest that this species has multiple ecomorphotypes (so maybe a cryptic lineage situation).