Abstract
Reef ecosystem growth and maintenance is closely related to sea urchin feeding activities. Hence, quantifying the bioerosive capacity of the sea urchin Diadema mexicanum is necessary to evaluate its impact on coral communities and reefs that develop off the Pacific coast of southern Mexico. Sea urchin density, size, bioerosion rate, and type of carbonate removed were estimated, and the carbonate budget of 15 coral communities and reefs found off Guerrero and Oaxaca was calculated. Sea urchin density (H = 13.4, P = 0.001) and size (H = 139.5, P = 0.000) varied over space and were significantly (density, r2 = 0.79, P = 0.00; size, r2 = 0.28, P = 0.03) related to substrate characteristics. In general, size (test diameter) and density were directly related to rock coverage but inversely related to live coral cover. Carbonate removal was directly related to sea urchin size (<3.4 cm = 0.052 g/ind/d, 3.4–6.1 cm = 0.202 g/ind/d, >6.1 cm = 0.325 g/ind/d). Of the total carbonate removed, 22% corresponded to aragonite and 78% to magnesium calcite, indicating that sea urchin impact on coral reef skeletons is small. When reef carbonate budget was calculated, only 3.1% of the total carbonate deposited by reef corals was removed. The above data indicate that sea urchin feeding activity alone does not compromise reef ecosystem growth and maintenance in southwestern Mexico. Nonetheless, in the near future, the current policy of use and development in and around reef systems may boost the bioerosive impact of D. mexicanum in the area.
Highlights
The growth and maintenance of coral reef communities depend on a dynamic process that involves the accumulation and removal of carbonates over time (Goldber 2013)
The feeding activity of sea urchins has been shown to be relevant in reef systems because of their capacity to control algal communities (Carpenter 1986, Hughes et al 1987) and facilitate coral recruitment (Sammarco 1980)
In the Tropical Eastern Pacific, studies have been conducted on the bioerosion rate of the sea urchins Toxopneustes roseus, Eucidaris thouarsii, and Diadema mexicanum (Glynn 1988, Reaka-Kudla et al 1996, Reyes-Bonilla and CalderónAguilera 1999, Herrera-Escalante et al 2005) and on their role in coral reefs of Mexico (Gulf of California, Oaxaca), Costa Rica, Panama, and the Galapagos Islands
Summary
The growth and maintenance of coral reef communities depend on a dynamic process that involves the accumulation and removal of carbonates over time (Goldber 2013). Sea urchins are known to play a role in carbon removal (Glynn 1988, Reaka-Kudla et al 1996) and, in the growth and maintenance of reef ecosystems (Bellwood et al 2004). In the Tropical Eastern Pacific, studies have been conducted on the bioerosion rate of the sea urchins Toxopneustes roseus, Eucidaris thouarsii, and Diadema mexicanum (Glynn 1988, Reaka-Kudla et al 1996, Reyes-Bonilla and CalderónAguilera 1999, Herrera-Escalante et al 2005) and on their role in coral reefs of Mexico (Gulf of California, Oaxaca), Costa Rica, Panama, and the Galapagos Islands. Because of its ability to remove cabonates (Glynn 1988, Reaka-Kudla et al 1996), its high abundance (Glynn and Leyte-Morales 1997, Herrera-Escalante et al 2005, Alvarado et al 2012), and gregarious behavior (Levitan 1988), D. mexicanum is considered the most relevant echinoderm in reef ecosystems of the eastern Pacific (Alvarado et al 2015)
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