Overgrowth of Caribbean octocorals by milleporid hydrocorals

Abstract

On Caribbean reefs, colonies of the hydrocoral Millepora alcicornis are capable of pursuing and overgrowing arborescent octocorals (Wahle ). Nearly four decades since these interactions were described, we quantified arborescent octocorals encrusted by Millepora spp. (Linnaeus 1758) on shallow reefs in St. John, U.S. Virgin Islands, and evaluated encrusted colonies for evidence of an origin through pursuit. In 2014, 8% of octocorals (n=1684 colonies) were encrusted by Millepora spp., and in 2015, 12% were encrusted (n=847 colonies). Millepora spp. encrusted colonies of 10 octocoral genera, and in 2014, the most frequently encrusted were Eunicea spp. (40% of encrusted octocorals); in 2015, the most frequently encrusted were Gorgonia spp. (46% of encrusted colonies). In both years, ≥67% of encrusted octocorals were >21 cm from other colonies of Millepora spp.; 7% of octocorals were >1.3 m from colonies of Millepora spp. in 2014; and 16% of octocorals were >2.0 m from colonies of Millepora spp. in 2015. Relative to the ~5% of octocorals encrusted by Millepora spp. in Jamaica in the late 1970s, a high percentage (~9%) of octocorals were encrusted by Millepora spp. in St. John in 2014 and 2015. The large distances from most encrusted octocorals to the nearest colonies of Millepora spp. in St. John are inconsistent with a hypothesized origin through pursuit, contact, and overgrowth (sensu Wahle ).

Ecology, Biology and Genetics ofMilleporaHydrocorals on Coral Reefs

“…Recently, Dubé and colleagues [58] demonstrated phenotypic plasticity among clonal colonies distributed in habitats with different hydrodynamic characteristics (see Section 4). To further complicate the matter, fire corals have been shown to overgrow stony corals, hydrocorals and gorgonians, which gives them additional peculiar growth forms ( Figure 3) [59,60]. Consequently, about 100 nominal species were described [61].…”

“…( Figure 3) [59,60]. This ability to inhabit different substrates and its rapid colonization rates [79] provide a competitive advantage for potential habitat expansions.…”

Acquisition of Adaptive Traits via Interspecific Association: Ecological Consequences and Applications

“…(B) The ring-tailed lemur (Lemur catta L.) engages in "territoriality" by using its scent-producing glands to broadcast olfactory signals [29]. (C) The hydrocoral Millepora alcicornis L. engages in "overgrowth" when it encrusts arborescent octocorals of the genus Gorgonia [30]. (D) Garlic mustard engages in "allelopathy" when it inhibits germination of competing plants by releasing toxic root exudates into the soil [31].…”