Mark J.A. Vermeij

ABSTRACT  

A coral community was examined on a semi-submersible platform that was moored at the leeward side of Curaçao, in the southern Caribbean, from August 2016 until August 2017. This community included several non- native or cryptogenic species. Among them were two scleractinian corals (Tubastraea coccinea and T. tagusensis) and two octocorals (Chromonephthea sp. and an unidentified Nephtheidae sp.). This is the first reported presence of T. tagusensis in the southern Caribbean, and the genus Chromonephthea in the Caribbean region. An ascidian, Perophora cf. regina, is also reported from the southern Caribbean for the first time, as well as a coral-associated vermetid gastropod, Petaloconchus sp., first recorded in the Caribbean in 2014. Lack of biofouling management could potentially harm indigenous marine fauna through the introduction of non-native species. Therefore monitoring communities associated with semi-submersible platforms is essential to track the presence and dispersal of non-native, potentially invasive species.   

Corals have built reefs on the benthos for millennia, becoming an essential element in marine ecosystems. Climate change and human impact, however, are favoring the invasion of non-calcifying benthic algae and reducing coral coverage. Corals rely on energy derived from photosynthesis and heterotrophic feeding, which depends on their surface area, to defend their outer perimeter. But the relation between geometric properties of corals and the outcome of competitive coral-algal interactions is not well known. To address this, 50 coral colonies interacting with algae were sampled in the Caribbean island of Curaçao. 3D and 2D digital models of corals were reconstructed to measure their surface area, perimeter, and polyp sizes. A box counting algorithm was applied to calculate their fractal dimension. The perimeter and surface dimensions were statistically non-fractal, but differences in the mean surface fractal dimension captured relevant features in the structure of corals. The mean fractal dimension and surface area were negatively correlated with the percentage of losing perimeter and positively correlated with the percentage of winning perimeter. The combination of coral perimeter, mean surface fractal dimension, and coral species explained 19% of the variability of losing regions, while the surface area, perimeter, and perimeter-to-surface area ratio explained 27% of the variability of winning regions. Corals with surface fractal dimensions smaller than two and small perimeters displayed the highest percentage of losing perimeter, while corals with large surface areas and low perimeter-to-surface ratios displayed the largest percentage of winning perimeter. This study confirms the importance of fractal surface dimension, surface area, and perimeter of corals in coral-algal interactions. In combination with non-geometrical measurements such as microbial composition, this approach could facilitate environmental conservation and restoration efforts on coral reefs.

Coral reef restoration requires efficient, effective and scalable techniques and methodologies to counteract the continued decline of coral reefs. Here we tested an in situ method to collect and settle fully developed planulae shed by the brooding coral species (Stylophora pistillata). Three devices called Coral Settlement Boxes (CSB; L × W × H: 50 × 40 × 6 cm; V: 4.5 L) were built from transparent Plexiglas and designed to be easily assembled and disassembled. Each CSB contained two integrated biofilm-covered nets (0.5 × 0.5 cm mesh size), which functioned as settlement substrate. The trap container of a traditional planulae trap was replaced by the CSB, and this new construction was used to collected planulae over 4 consecutive days. The CSBs were then transported to a mid-water coral nursery at 12 m depth. One CSB was disassembled immediately, the two settlement substrates were removed and each was placed in a protective cage (mesh size 4 cm²). The other two CSBs were opened after a 4-month period, leaving the four settlement substrates attached to the Plexiglas plates and covered by protective cages. None of the settlement substrates were cleaned of fouling organisms in the nursery. After 5 months in the mid-water nursery, a total of 120 healthy juvenile coral colonies had resulted from the estimated 2045 planulae initially trapped. This inexpensive and simple approach to producing sexually propagated stocks of colonies entirely in situ may enhance the efficiency, effectiveness and scalability of restoration activities that include brooding coral species.

Abstract

Reef-building corals are ecosystem engineers that compete with other benthic organisms for space and resources. Corals harvest energy through their surface by photosynthesis and heterotrophic feeding, and they divert part of this energy to defend their outer colony perimeter against competitors. Here, we hypothesized that corals with a larger space-filling surface and smaller perimeters increase energy gain while reducing the exposure to competitors. This predicted an association between these two geometric properties of corals and the competitive outcome against other benthic organisms. To test the prediction, fifty coral colonies from the Caribbean island of Curaçao were rendered using digital 3D and 2D reconstructions. The surface areas, perimeters, box-counting dimensions (as a proxy of surface and perimeter space-filling), and other geometric properties were extracted and analyzed with respect to the percentage of the perimeter losing or winning against competitors based on the coral tissue apparent growth or damage. The increase in surface space-filling dimension was the only significant single indicator of coral winning outcomes, but the combination of surface space-filling dimension with perimeter length increased the statistical prediction of coral competition outcomes. Corals with larger surface space-filling dimensions (Ds > 2) and smaller perimeters displayed more winning outcomes, confirming the initial hypothesis. We propose that the space-filling property of coral surfaces complemented with other proxies of coral competitiveness, such as life history traits, will provide a more accurate quantitative characterization of coral competition outcomes on coral reefs. This framework also applies to other organisms or ecological systems that rely on complex surfaces to obtain energy for competition.

Abstract. In contrast with a general decline of Caribbean reef corals, a previously rare sun coral is
increasing in abundance within shallow coral communities on Curacao. This azooxanthellate scleractinian
was identified as Cladopsammia manuelensis, which has an amphi-Atlantic distribution. Over the last decade,
C. manuelensis has increased abundance along the leeward coast of Curacao (southern Caribbean)
between depths of 4 and 30 m. This species was initially not noticed because it resembles the invasive coral
Tubastraea coccinea, which was introduced to Curacao from the Indo-Pacific around 1940. However, in contrast
to T. coccinea, C. manuelensis was previously only present on deeper reef sections (>70 m) of Caribbean
reefs. Our observations illustrate how the sudden increase in abundance of a previously unnoticed, apparently
cryptogenic species could result from natural dynamics on present-day reefs, but also could easily be
mistaken for an invasive species. The finding that deep reef sections can harbor species capable of colonizing
shallower reef zones highlights the importance of thorough inventories of reef communities across
large depth ranges, which can help us to discriminate between range increases of native species and the
arrival of invasives.

Key words: bathymetric distribution; Cladopsammia; coral reefs; cryptogenic; deep water; Dendrophylliidae; invasive;
native; Rhizopsammia; Tubastraea;.