Antifouling coatings can reduce algal growth while preserving coral settlement

Abstract

In the early stages after larval settlement, coral spat can be rapidly overgrown and outcompeted by algae, reducing overall survival for coral reef replenishment and supply for restoration programs. Here we investigated three antifouling (AF) coatings for their ability to inhibit algal fouling on coral settlement plugs, a commonly-used restoration substrate. Plugs were either fully or partially coated with the AF coatings and incubated in mesocosm systems with partial recirculation for 37 days to track fouling succession. In addition, settlement of Acropora tenuis larvae was measured to determine whether AF coatings were a settlement deterrent. Uncoated control plugs became heavily fouled, yielding only 4–8% bare substrate on upper surfaces after 37 days. During this period, an encapsulated dichlorooctylisothiazolinone (DCOIT)-coating was most effective in reducing fouling, yielding 61–63% bare substrate. Antiadhesive and cerium dioxide (CeO2−x) nanoparticle (NP) coatings were less effective, yielding 11–17% and 2% bare substrate, respectively. Average settlement of A. tenuis larvae on the three types of AF-coated plugs did not statistically differ from settlement on uncoated controls. However, settlement on the NP-coating was generally the highest and was significantly higher than settlement found on the antiadhesive- and DCOIT-coating. Furthermore, on plugs only partially-covered with AF coatings, larval settlement on coated NP- areas was significantly higher than settlement on coated antiadhesive- and DCOIT-areas. These results demonstrate that AF coatings can reduce fouling intensity on biologically-relevant timescales while preserving robust levels of coral settlement. This represents an important step towards reducing fine-scale competition with benthic fouling organisms in coral breeding and propagation.

Applying behavioral studies to the ecotoxicology of corals: A case study on Acropora millepora

“…'spat') was found to reduce mortality (Tebben et al, 2014), which could increase the likelihood of coral survival to sizeescape thresholds and consequently improve the success of sexual coral-propagation techniques (Randall et al, 2020). A recent study also demonstrated the effectiveness of two non-toxic AF coatings (same coatings as in this study) to reduce algal growth on coral settlement surfaces, a first step towards controlling fine-scale competition with benthic organisms in coral aquaculture (Roepke et al, 2022). While these AF coatings did not affect coral larval settlement, further work is required to assess their potential influence on other aspects of larval behavior such as mobility which might represent a sensitive response relevant to the application of AF coatings for shipping and in aquaculture.…”

“…In addition to our identification of two efficient antifouling coatings with robust levels of coral settlement in Roepke et al (2022), we propose future studies on settlement, survival and growth on these antifouling coatings, as well as behavioral studies and measures of biochemical markers in response to these coatings. Approaches to settle larvae directly onto restoration deployment substrates adjacent to, or surrounded by these coatings, may offer protection against overgrowth by algae.…”

“…The results suggest three alternative interpretations of the coatings' effect on larval motility: the physical surface topographies of the coatings could have caused the larvae to move more slowly, the antifouling treatments interacted biochemically with the larvae, or the coatings had a potentially toxic effect on the larvae, or some combination of the effects. Before these coatings are applied in coral aquaculture or restoration, further information on their antifouling efficacy and effects on settlement (Roepke et al, 2022), survival and growth are necessary. Moreover, it is suggested to test the chemical stability and AF activity duration of the coatings on different materials over different time scales, under ex situ and in situ conditions, and on different coral species and developmental stages (gametes, early and late larvae, spat, recruits, adults).…”

Adults of Sun Coral Tubastraea coccinea (Lesson 1829) Are Resistant to New Antifouling Biocides

“…This lack of severe effects might be explained by the rapid degradation of DCOIT under normal conditions [ 3 , 6 , 14 , 15 ], becoming low or non-toxic. However, DCOIT can be toxic to marine organisms before degradation occurs [ 4 , 35 , 38 , 39 ]. In addition, the nanostructured forms (i.e., SiNC-DCOIT and SiNC-DCOIT-Ag) were expected to be less toxic than the free DCOIT, as previously shown for other marine organisms from temperate regions [ 17 , 18 ].…”

Fish-based herbivory and the natural maintenance of algal fouling on coral nurseries used across the Great Barrier Reef

“…90 -200% greater algae after 30 months; Hughes et al 2007) but also in other regions globally (e.g., in Japan > 40% greater after 25−50 days; Akita et al 2022). The challenge posed by algal competition has become a significant concern for restoration projects, leading to substantial investments in anti-fouling approaches, particularly through the application of coatings (Shafir et al 2009;Guest et al 2014;Roepke et al 2022). Despite these efforts, most coral nursery projects continue to rely on manual de-fouling performed by human labour (Johnson et al 2011;Hyde et al 2013;Maurer et al 2022).…”