Deep reef

Dutch below

A collaborative study, led by the University of Texas at Austin, deployed 102 specialized fish monitoring structures across six locations, including the deep reefs of Curacao.  The goal of this study was to identify a standardized simple and effective way to survey small, bottom-dwelling fish populations.

From shallow tide pools to the deep sea, unique evolutionary traits allow fish to occupy every corner of the ocean. Historically, fish populations have been tracked using visual surveys, which can often overlook small or bottom-associated (cryptobenthic) species. A collaborative study, led by the University of Texas at Austin, explored a new technique to quantify these difficult to find species by utilizing a Fish-specific Autonomous Reef Monitoring Structures (FARMS).

FARMS

These FARMS are specifically created using easily accessible and affordable materials. Through a combination of stacked PVC pipes and mesh baskets, FARMS can be deployed in a wide variety of locations to investigate these cryptobenthic populations.  Although FARMS may not fully replicate the surrounding environment, especially in habitats with no solid structures, this study did find these structures to be an efficient technique for sampling local diversity, capturing a higher number of species per unit area compared to other methods.

Curacao

During this study, FARMS were deployed across six locations (Hawaii, Texas, Panama, Saudi Arabia, Brazil and Curacao). The FARMS deployed off Curacao were used to explore deeper areas of reef, placed at 60m, 146m and 223m depth. Due to the limitations for SCUBA-based research, deep reefs are some of the least explored ecosystems and the vast majority of deep reef research has relied on visual counts. Accordingly, one of the FARMS captured a species of goby (Psilotris laurae) which has never before been documented on Curacao. This highlights the ability of these systems to provide a new, improved way of sampling populations, particularly in deep or hard to reach locations.

Fish species found using FARMS. Photo credit: Simon Brandl

Impacts

Overall, FARMS are considered a simple, standardized, and cost-effective technique for studying cryptobenthic fish communities in habitats where other sampling methods are considered impractical or restricted. The study highlighted the potential of FARMS for exploring under sampled habitats, such as deep reefs, where they could contribute to the discovery of new species and enhance our understanding of cryptobenthic fish diversity and distribution patterns.

DCNA

The Dutch Caribbean Nature Alliance (DCNA) supports science communication and outreach in the Dutch Caribbean region by making nature-related scientific information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the (in) direct impacts resulting from publishing this article.

Een collaboratieve studie, geleid door de University of Texas in Austin, heeft 102 gespecialiseerde structuren voor het monitoren van vissen ingezet op zes locaties, waaronder de diepe riffen van Curaçao. Het doel van deze studie was om een gestandaardiseerde, eenvoudige en effectieve manier te vinden om kleine, op de bodem levende vispopulaties te onderzoeken.

Van ondiepe getijdenpoelen tot de diepzee, dankzij unieke evolutionaire eigenschappen kunnen vissen elke hoek van de oceaan bezetten. Historisch gezien zijn vispopulaties gevolgd met behulp van visuele onderzoeken, die vaak kleine of met de bodem geassocieerde (cryptobenthische) soorten over het hoofd kunnen zien. Een gezamenlijke studie, geleid door de University of Texas in Austin, onderzocht een nieuwe techniek om deze moeilijk te vinden soorten te kwantificeren door gebruik te maken van een visspecifieke autonome rif monitor structuur (FARMS).

FARMS

Deze FARMS zijn speciaal gemaakt met behulp van gemakkelijk toegankelijke en betaalbare materialen. Door een combinatie van gestapelde PVC-buizen en gaasmanden kan FARMS op een groot aantal verschillende locaties worden ingezet om deze cryptobenthische populaties te onderzoeken. Hoewel FARMS de omgeving mogelijk niet volledig nabootsen, vooral in habitats zonder vaste structuren, vond deze studie deze structuren een efficiënte techniek voor het bemonsteren van lokale diversiteit, waarbij een groter aantal soorten per oppervlakte-eenheid werd gevangen in vergelijking met andere methoden.

Curaçao

Tijdens dit onderzoek werden FARMS ingezet op zes locaties (Hawaii, Texas, Panama, Saoedi-Arabië, Brazilië en Curaçao). De FARMS die buiten Curaçao werden ingezet, werden gebruikt om diepere delen van het rif te verkennen, geplaatst op 60 meter, 146 meter en 223 meter diepte. Vanwege de beperkingen van SCUBA-gebaseerd onderzoek, zijn diepe riffen een van de minst onderzochte ecosystemen en de overgrote meerderheid van diep rifonderzoek is gebaseerd op visuele tellingen. Niet geheel onverwachts ving een van de FARMS dan ook een soort grondel (Psilotris laurae) die nog nooit eerder op Curaçao was gedocumenteerd. Dit benadrukt de capaciteit van deze systemen om een nieuwe, verbeterde manier te bieden om populaties te bemonsteren, met name op diepe of moeilijk bereikbare locaties.

Vissoorten gevonden met FARMS. Foto: Simon Brandl

Effecten

Over het algemeen worden FARMS beschouwd als een eenvoudige, gestandaardiseerde en kosteneffectieve techniek voor het bestuderen van cryptobenthische visgemeenschappen in habitats waar andere bemonsteringsmethoden als onpraktisch of beperkt worden beschouwd. De studie benadrukte het potentieel van FARMS voor het verkennen van onder bemonsterde habitats, zoals diepe riffen, waar ze kunnen bijdragen aan de ontdekking van nieuwe soorten en ons begrip van de diversiteit en verspreidingspatronen van cryptobenthische vissen kunnen vergroten.

DCNA

De Dutch Caribbean Nature Alliance (DCNA) ondersteunt wetenschapscommunicatie en outreach in de Nederlandse Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en de pers. Dit artikel bevat de resultaten van verschillende wetenschappelijke onderzoeken, maar de onderzoeken zelf zijn geen DCNA-onderzoeken. Aan de inhoud kunnen geen rechten worden ontleend. DCNA is niet aansprakelijk voor de inhoud en de (in)directe gevolgen die voortvloeien uit het publiceren van dit artikel.

Published in BioNews 67

Curaçao, Dutch Caribbean, is home to three species of gall crabs belonging to Cryptochiridae, a family obligatorily associated with a wide range of scleractinian host species. Gall crabs are reliant on their host coral; females are sedentary and never leave their dwelling (van der Meij 2014a). One of the three Atlantic gall crab species is Opecarcinus hypostegus (Shaw and Hopkins, 1977), which inhabits corals of the genus Agaricia. Corals of this genus are abundant in the photic zone (<30 m), but also in the mesophotic zone (30–150 m), where they predominantly belong to Agaricia grahamae Wells, 1973 and Agaricia lamarcki Milne- Edwards and Haime, 1851. The latter was found to be most abundant at depths of 25–60 m (Bongaerts et al. 2013). 

During a survey on 31 March, 2014, with the manned CuraSub submersible launched from Substation Curaçao (12°05 ́04.14 ̋N, 68°53 ́53.16 ̋W), a colony of A. lamarcki was observed at approximately 60 m depth (Panel B) exhibiting the characteristic tunnel formed by O. hypostegus. The shape of this tunnel is virtually identical to those found with O. hypostegus crabs in A. lamarcki at shallower depths (Panel A: Slangenbaai, Curaçao). Hence, we contend that this is strong evidence of O. hypostegus at mesophotic depth. 

The present finding is relevant in the light of the “deep reef refugia” hypothesis, which states that mesophotic reefs may act as a refuge in the face of global reef decline (Bongaerts et al. 2010), as it furthers our knowledge on the communities that presently thrive on these deep reefs. 

Four submersible dives off the coast of Bonaire (Caribbean Netherlands) and Klein Curaçao (Curaçao) to depths of 99.5–242 m, covering lower mesophotic and upper dysphotic zones, yielded 52 sponge specimens belonging to 31 species. Among these we identified 13 species as new to science. These are Plakinastrella stinapa n. sp., Pachastrella pacoi n. sp., Characella pachastrelloides n. sp., Geodia curacaoensis n. sp., Caminus carmabi n. sp., Discodermia adhaerens n. sp., Clathria (Microciona) acarnoides n. sp., Antho (Acarnia) pellita n. sp., Parahigginsia strongylifera n. sp., Calyx magnoculata n. sp., Neopetrosia dutchi n. sp., Neopetrosia ovata n. sp. and Neopetrosia eurystomata n. sp. We also report an euretid hexactinellid, which belongs to the rare genus Verrucocoeloidea, recently described (2014) as V. liberatorii Reiswig & Dohrmann. The remaining 18 already known species are all illustrated by photos of the habit, either in situ or ‘on deck’, but only briefly characterized in an annotated table to confirm their occurrence in the Southern Caribbean. The habitat investigated - steep limestone rocks, likely representing Pleistocene fossil reefs - is similar to deep-water fossil reefs at Barbados of which the sponges were sampled and studied by Van Soest and Stentoft (1988). A comparison is made between the two localities, showing a high degree of similarity in sponge composition: 53% of the present Bonaire-Klein Curaçao species were also retrieved at Barbados. At the level of higher taxa (genera, families) Bonaire-Klein Curaçao shared approximately 80% of its lower mesophotic and upper dysphotic sponge fauna with Barbados, despite a distance between them of 1000 km, indicating high faunal homogeneity. We also preliminarily compared the shallow-water (euphotic) sponge fauna of Curaçao with the combined data available for the Barbados, Bonaire and Klein Curaçao mesophotic and upper dysphotic sponges, which resulted in the conclusion that the two faunas show only little overlap

The deep reef of Bonaire, Caribbean Netherlands, was explored with the aid of the “Curasub” submarine of Substation Curaçao. The shallow reefs of the Caribbean are considered a biodiversity hotspot, an area with exceptional diversity of plants, animals and ecosystems, yet surprisingly little is known about the flora and fauna of the deeper reefs.

Dives were made to depths of 140-250m.at three locations on the Southern coast of Bonaire: Kralendijk,Cargill, and Statoil. Distinct depth zonations in substrate features were visible. Coral reef was observed until approximately 45m, then followed a zone of sand mixed with varying amounts of stones. At each site a wide layer of cyanobacteria mats covering sand were found spanning the depths of 45m.to 90m.

The depth from 90-100m was typically dominated by sand with occasional small rocks on which fan corals and sponges resided. From 100-

150m depth fossil barrier reef and rodolith beds were observed, either in long stretches or in patches within a barren sandscape. By providing hard substrate, these fossil reefs displayed heightened biodiversity in a desert landscape of sand. Below 150m the substrate was generally dominated by fine sand. The cause of the cyanobacterial mats remains unclear. These mats are generally believed to indicate nutrient enriched (disturbed) environmental conditions, and should therefore be further studied to elucidate the cause. Trash was observed at all depths. High biodiversity was observed on the sporadic hard substrate below 100m, presumably fossil reef. In total 72 species were recorded, of which at least 15 species are new to science (shrimp, sponges, fish). The major focus was on sponges due to their importance in the deep reef in terms of diversity, filtering activities, biomass, and source of pharmaceutical compounds. A species list and picture gallery are provided in this report. This is just of subset of the true biodiversity of Bonaire’s deep reef. With the description of new species also comes a better understanding of ecosystems.

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.