Resource Partitioning by Sand Dollars in Carbonate and Siliceous Sediments: Evidence From Podial and Particle Dimensions

Abstract

The sand dollars, Leodia sexiesperforata (Leske) and Encope michelini L. Agassiz, have overlapping geographical ranges and may co-occur in mixed flocks. Leodia is restricted entirely to biogenic carbonate sediments. Mellita quinquiesperforata (Leske), which has a similar geographical range to Leodia, occurs only on siliceous terrigenous substrates and the two species never co-exist. Encope michelini L. Agassiz occurs on both types of substrate. All three species are podial particle pickers, and use barreltipped podia, especially the long type surrounding the geniculate spine fields of the oral surface, for food collection. A typical mellitid of 100 mm diameter can have up to one million barrel-tipped podia. These podia have the same mean diameters in Leodia (71.6 5.62 ^m) and Mellita (71.8 3.59 urn). The diversity of sizes is significantly greater in Leodia. The barrel-tipped podia of E. michelini are very much larger (104.4 11.1 ^m). The substrates inhabited by the three species have approximately 90% of their particles in the 100-400 urn range. Whereas Mellita is nonselective in collecting food particles, Leodia clearly selects small particles (50-200 fj.m) and shuns those above 200 nm. Encope michelini includes 26% of particles over 200 ^m in its food grooves, but does not take those below 100 nm. Differences in feeding behavior thus provide a basis for resource partitioning between these sympatric species. They are discussed in relation to podial dimensions and spination, and compared with feeding behavior in Mellita quinquiesperforata.

Evaluation of sand grain crushing in the sand dollar Mellita tenuis (Echinoidea: Echinodermata)

“…In both August and December samples, less than 1% of the natural sediment was comprised of grains <100 µm and only 2.5% of the sand grains removed from sand dollar guts were <100 µm. This pattern is similar to the observations of Ellers & Telford (1984), who studied grain size selection in the sand dollar Echinarachnius parma in siliceous sediments in the North Atlantic, and Telford & Mooi (1986), who studied Encope michelini in both siliceous and carbonate sediments in the Gulf of Mexico. Both Echinarachnius parma and Encope michelini did not select grain sizes <100 µm, but did select against larger grains.…”

“…Both Echinarachnius parma and Encope michelini did not select grain sizes <100 µm, but did select against larger grains. In Leodia sexiesperforata, which occurs solely on carbonate sediments, selection occurred for grains in the 50 to 200 µm size class (Telford & Mooi 1986). In addition, Hilber & Lawrence (in press) recently found that Mellita tenuis and Encope michelini both selected smaller particles that those found in the surrounding sediments off the central Florida gulf coast.…”

“…Sand dollars consume large amounts of sediment during feeding activities, and species that inhabit carbonate-rich substrates are known to pulverize the carbonate sands they ingest (Telford & Mooi 1986, Telford et al 1987. It is also suggested that at least one species that occupies quartz-rich (siliciclastic) sediments, Mellita isometra, alters the size of quartz grains during feeding by crushing grains with the teeth associated with a modified Aristotle's lantern (Telford et al 1985).…”

Echinodermata da Baía de Todos os Santos e da Baía de Aratu (Bahia, Brasil)

“…Observações: Leodia sexiesperforata foi coletada entre 12 e 24 m de profundidade, em sedimentos formados por areia média, areia muito grossa. Esta espécie é restrita a sedimentos biogênicos e carbonáticos e se alimenta de pequenas partículas de detritos que são selecionados por seus pódios (Telford & Mooi, 1986). (Leske, 1778) (Figura 5d,e,f) Material examinado: Um espécime coletado na estação M3.…”

Phylogeography of the sand dollar genus Mellita: Cryptic speciation along the coasts of the Americas

“…As Mellita specialise in living in terrigenous (siliceous) sands (Telford and Mooi, 1986), this flexibility in timing of settlement is vital for successful recruitment and is likely to be mediated by a chemosensitive response to either suitable terrigenous sands or adult conspecifics.…”