Neospongodes atlantica, a potential case of an early biological introduction in the Southwestern Atlantic

Abstract

Soft corals (Anthozoa: Octocorallia) are discreet components in the Southwestern Atlantic reef communities. In Brazil, the native octocoral shallow-reef fauna is mostly represented by gorgonians. Consequently, except for the nephtheid Neospongodes atlantica, most of the known soft corals from this region are considered non-indigenous. Hitherto, the monotypic genus Neospongodes, which was proposed in the early 1900s, has been considered to be endemic to the Northeastern Brazilian coast. Herein, based on in situ records, we show that N. atlantica is a substrate generalist that has been probably expanding its distribution by dominating extensive shallow and mesophotic sandy and reef bottoms, generally outcompeting other reef benthic organisms, including Brazilian endemic species. Based on previously unidentified museum specimens, new records, and a broad literature review, we provide the most comprehensive modelling of the potential distribution of this species in the Southwestern Atlantic. Based on molecular inference supported by in-depth morphological analysis, the probable non-indigenous and, therefore, ancient introduction of N. atlantica in Brazilian waters is discussed. Finally, these results support that Neospongodes and the Indo-Pacific Stereonephthya are synonyms, which led us to propose the latter as taxonomically invalid.

Keywords: Brazil; Continental shelf; Habitat Modelling; Invasion; Octocorallia; Soft-bottom.

Figure 1. Study area, including the model calibration area (M) and the model projection area (G).

Figure 2. Substrate dominance and allelopathic competition of Neospongodes atlantica to Brazilian native corals at Timbebas reef (17°28′37.2″S, 39°01′37.2″W, 10–15 m deep).

(A) Aggregation of N. atlantica on sandy bottom in the Abrolhos region, Bahia. (B) N. atlantica colonies dominating a reef edge on Abrolhos reefs. (C) Bleaching and partial necrosis caused by N. atlantica on the scleractinian coral Montastraea cavernosa (arrow). (D) N. atlantica covering a black-coral colony (Stichopathes sp.). All photos by RB Francini-Filho.

Figure 3. Main distinctive morphological characters in Neospongodes atlantica (MOUFPE 431).

(A) Entire colony. (B) View of the stalk with a central channel, in which sclerites occur in a higher density. (C) View of anthocodia on a branch tip showing projecting supporting bundles. (D) Colony with its stalk transversally sectioned, showing longitudinal channels. (E) Colony channels in detail. Abbreviations: ch - channel; p - projecting tip of a spindle; sb - supporting bundle of sclerites; and ch* - pseudo-axis.

Figure 4. Sclerites of Neospongodes atlantica Kukenthal, 1903 (MOUFPE 439).

(A) Spindles of the supporting bundle; (B) spindles of the anthocodial points; (C) flattened rods of the crown region; (D) spindles of the interior of the stalk; (E) flattened rods of the adaxial portion of the polyp; (F) sclerites of the surface of the stalk.

Figure 5. Maximum Likelihood and Bayesian inference phylogenetic reconstructions of the family Nephtheidae based on the extended Octocorallia barcoding genes (mtMutS + COI + 28S) concatenated data.

The Brazilian specimen of Neospongodes atlantica sampled from Recife is highlighted in red. Green circles on nodes indicate supports over 80% for ML and posterior probability of 100 (BI). Dashed branch indicate the Gersemia clade leading branch retrieve in BI. Genbank sequences of Nephthea (40972, 40973, CO34070, CO34112) correspond to Litophyton, recently synonymized.

Figure 6. Occurrence records and current potential habitat.

(A) Modeling records of Neospongodes atlantica (new) and evaluation records (previously existing records). (B) Potential habitat area for N. atlantica in the Brazilian coast, from intertidal zone to shelf-break.

Figure 7. Potential habitat for Neospongodes atlantica at five different depths within the Brazilian coast from the intertidal zone to the end of the continental shelf.

Figure 8. Potential habitat end mobility-oriented parity analysis (MOP).

Assessment of the risk of extrapolation of M in G.