Abstract

Tropical deep reefs (~40–300 m) are diverse ecosystems that serve as habitats for diverse communities of reef-associated fishes. Deep-reef fish communities are taxonomically and ecologically distinct from those on shallow reefs, but like those on shallow reefs, they are home to a species-rich assemblage of small, cryptobenthic reef fishes, including many species from the family Gobiidae (gobies). Here we describe two new species of deep-reef gobies, Varicus prometheus sp. nov. and V. roatanensis sp. nov., that were collected using the submersible Idabel from rariphotic reefs off the island of Roatan (Honduras) in the Caribbean. The new species are the 11th and 12th species of the genus Varicus, and their placement in the genus is supported by morphological data and molecular phylogenetic analyses. Additionally, we also collected new specimens of the closely-related genus and species Pinnichthys aimoriensis during submersible collections off the islands of Bonaire and St. Eustatius (Netherland Antilles) and included them in this study to expand the current description of that species and document its range extension from Brazil into the Caribbean. Collectively, the two new species of Varicus and new records of P. aimoriensis add to our growing knowledge of cryptobenthic fish diversity on deep reefs of the Caribbean.

In 2015 an Expert group assessed the ten Dutch World Heritage candidate sites and advised the Ministry of Education, Culture and Science with regards to the potential nomination of Bonaire National Marine Park. The conclusion was that further research is needed to demonstrate its Outstanding Universal Value (OUV). According to the Expert group, the current size and boundaries of BNMP do not contain features which qualify the property as unique, hence extension of the BNMP boundaries was recommended. Possibilities for extension are the island Curaçao, the islands off the coast of Venezuela and the 12 miles zone.

In collaboration with the Ministry of Economic Affairs it was decided to start by studying the nature values of the 12 miles zone of Bonaire, because this is the most feasible boundary extension. The 12 miles zone of Bonaire has a total area of almost 360,000 ha, which is a 74-fold enlargement compared to the 4,860 ha of the current boundaries of BNMP.

The objective was to determine the existence of potential nature values per zone based on the following criteria: rare, threatened or characteristic species; rare, untouched or undisturbed geomorphological features; important physical oceanographic features; potential ecosystem services. An inventory of previous studies by IMARES and available data from two deep sea expeditions in 2000 and 2013 were incorporated in this study.

Our review updates the current state of knowledge on the deep sea of the Caribbean Sea, focussing on the 12 miles zone of Bonaire. It provides a general framework for the decision making process on the boundary extension of the potential World Heritage Site and how to strengthen the potential OUV.

The available information shows that the 12 miles zone contains some attributes that will strengthen the OUV to some extent, such as the discovery of 16 species new to science at the deeper reef of Bonaire and the presence of some species endemic to the Southern Caribbean Ecoregion. Convincing documentation is still lacking, however evidence from past deep sea expeditions indicates that further studies of deep water biodiversity will likely easily yield a wealth of new species. Also potential offshore sea mounts within the 12 miles zone of Bonaire may be worthwhile investigating, by mapping the seafloor through a bathymetric survey. These potential habitats, structures and new species in the 12 miles zone of Bonaire could greatly add to the OUV of the BNMP.

Abstract

Background: Scleractinian corals and their algal endosymbionts (genus Symbiodinium) exhibit distinct bathymetric distributions on coral reefs. Yet, few studies have assessed the evolutionary context of these ecological distributions by exploring the genetic diversity of closely related coral species and their associated Symbiodinium over large depth ranges. Here we assess the distribution and genetic diversity of five agariciid coral species (Agaricia humilis, A. agaricites, A. lamarcki, A. grahamae, and Helioseris cucullata) and their algal endosymbionts (Symbiodinium) across a large depth gradient (2-60 m) covering shallow to mesophotic depths on a Caribbean reef.

Results: The five agariciid species exhibited distinct depth distributions, and dominant Symbiodinium associations were found to be species-specific, with each of the agariciid species harbouring a distinct ITS2-DGGE profile (except for a shared profile between A. lamarcki and A. grahamae). Only A. lamarcki harboured different Symbiodinium types across its depth distribution (i.e. exhibited symbiont zonation). Phylogenetic analysis (atp6) of the coral hosts demonstrated a division of the Agaricia genus into two major lineages that correspond to their bathymetric distribution (“shallow”: A. humilis / A. agaricites and “deep”: A. lamarcki / A. grahamae), highlighting the role of depth-related factors in the diversification of these congeneric agariciid species. The divergence between “shallow” and “deep” host species was reflected in the relatedness of the associated Symbiodinium (with A. lamarcki and A. grahamae sharing an identical Symbiodinium profile, and A. humilis and A. agaricites harbouring a related ITS2 sequence in their Symbiodinium profiles), corroborating the notion that brooding corals and their Symbiodinium are engaged in coevolutionary processes.

Conclusions: Our findings support the hypothesis that the depth-related environmental gradient on reefs has played an important role in the diversification of the genus Agaricia and their associated Symbiodinium, resulting in a genetic segregation between coral host-symbiont communities at shallow and mesophotic depths.