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Fish assemblages of different types of artificial reefs can differ greatly in abundance, biomass and composition, with some reef types harboring over five times more herbivores than others. It is assumed that higher herbivorous fish abundance results in a higher grazing intensity, affecting the benthic community by means of enhanced coral recruitment, survival and growth. Territorial fish species might affect this process by chasing away other fish, especially herbivores. In this study we compared the fish assemblage, territorial behavior and grazing intensity by fish on two artificial reef types: reef balls and layered cakes, differing greatly in their fish assemblage during early colonization. In addition, the effect of artificial reef type on benthic development and coral recruitment, survival and growth, was investigated. Although layered cakes initially harbored higher herbivorous fish biomass, this effect was lost during consecutive monitoring events. This seems to be the result of the higher territorial fish abundance around the layered cakes where almost four times more chasing behavior was recorded compared to the reef balls. This resulted in a more than five times lower fish grazing intensity compared to the reef-ball plots. Although macroalgae were effectively controlled at both reefs, the grazing intensity did not differ enough to cause large enough structural changes in benthic cover for higher coral recruitment, survival or growth. The high turf algae cover, combined with increasing crustose coralline algae and sponge cover likely explained reduced coral development. We recommend further research on how to achieve higher grazing rates for improved coral development on artificial reefs, for example by facilitating invertebrate herbivores.

De kunstmatige riffen die bijna een jaar geleden in de Waddenzee zijn geplaatst, blijken vol met leven te zitten. Dat meldt het waterschap Noorderzijlvest.

Onderzoekers van Hogeschool Van Hall Larenstein, Wageningen University en Wageningen Marine Research hebben een nieuwe techniek ontwikkeld voor het natuurlijk herstel van Diadema zee-egels. Samen met de Saba Conservation Foundation, vonden zij een nieuw aanvullend substraat voor vestiging op het koraal en toonden aan dat een geschikte vestigingsondergrond heel belangrijk is voor het herstelproces.

Het zijn de schapen van het koraal. Zee-egels, die de riffen met hun gegraas schoonhouden van algen. En dat is belangrijk, want het koraal wordt wereldwijd enorm bedreigd. Maar in het Caribisch gebied gaat het ook niet goed met de zee-egels. Een ziekte dreigt verschillende populaties uit te roeien. Marien ecoloog Alwin Hylkema van de Universiteit Wageningen en tevens werkzaam als onderzoeker aan hogeschool Van Hall Larenstein doet onderzoek naar zee-egels en koraal-herstel. Hij is deze week gepromoveerd.

Het zijn de schapen van het koraal. Zee-egels, die de riffen met hun gegraas schoonhouden van algen. En dat is belangrijk, want het koraal wordt wereldwijd enorm bedreigd. Maar in het Caribisch gebied gaat het ook niet goed met de zee-egels. Een ziekte dreigt verschillende populaties uit te roeien. Marien ecoloog Alwin Hylkema van de Universiteit Wageningen en tevens werkzaam als onderzoeker aan hogeschool Van Hall Larenstein doet onderzoek naar zee-egels en koraal-herstel. Hij is deze week gepromoveerd.

At Van Hall Larenstein University of Applied Sciences (HVHL) in Leeuwarden, the sea urchin Diadema antillarum has been cultivated to help restore the coral reefs around Saba and St. Eustatius (Caribbean Netherlands). The first young urchins bred in Leeuwarden were released on March 24th to the Rotterdam Zoo (Diergaarde Blijdorp). The ultimate goal is to also breed this species on Saba in order to give the sea urchin populations there a helping hand. These sea urchins keep algae growth under control, giving corals more room to grow. During this project, researchers worked closely with students from the Coastal and Marine Management program.

At Van Hall Larenstein University of Applied Sciences (HVHL) in Leeuwarden, the sea urchin Diadema antillarum has been cultivated to help restore the coral reefs around Saba and St. Eustatius (Caribbean Netherlands). The first young urchins bred in Leeuwarden were released on March 24th to the Rotterdam Zoo (Diergaarde Blijdorp). The ultimate goal is to also breed this species on Saba in order to give the sea urchin populations there a helping hand. These sea urchins keep algae growth under control, giving corals more room to grow. During this project, researchers worked closely with students from the Coastal and Marine Management program.

Diadema sea-urchins play a vital role in maintaining a balanced coral reef ecosystem and their restoration is essential to assist recovery of the degraded coral reefs around Saba and St. Eustatius. A collaborative effort between University of Applied Sciences Van Hall Larenstein, WUR, STENAPA, CNSI and NIOZ studied settlement rates of sea-urchin larvae. The new findings provide insight into why the Diadema population has not been restored since the massive die-off in the mid 1980’s and are important for developing and implementing effective sea urchin restoration projects.

Diadema sea-urchins play a vital role in maintaining a balanced coral reef ecosystem and their restoration is essential to assist recovery of the degraded coral reefs around Saba and St. Eustatius. A collaborative effort between University of Applied Sciences Van Hall Larenstein, WUR, STENAPA, CNSI and NIOZ studied settlement rates of sea-urchin larvae. The new findings provide insight into why the Diadema population has not been restored since the massive die-off in the mid 1980’s and are important for developing and implementing effective sea urchin restoration projects.

The massive die-off of the sea urchin Diadema antillarum in 1983–1984 is one the main reasons for low coral recruitment and little coral recovery in the Caribbean. As the natural recovery of D. antillarum is slow to non-existent, multiple restoration studies have been attempted. There are currently three different approaches to obtain individuals for restocking: the translocation of wild-collected juveniles or adults, lab-reared juveniles cultured from wild-collected settlers, or lab-reared juveniles cultured from gametes. All three methods are costly and can only be applied on a relatively small scale. We here propose a fourth, new, approach, which we term assisted natural recovery (ANR) of D. antillarum populations. ANR, a concept already applied in terrestrial restoration to restore forests and grasslands, can accelerate succession by removing barriers to natural recovery. In this study, performed on the Dutch Caribbean island of Saba, suitable settlement substrate was provided in the form of bio ball streamers that were attached to the reef shortly before the settlement season. At the end of the experiment, reefs with streamers had significantly higher D. antillarum recruit densities than control reefs without additional settlement substrate, indicating that the lack of settlement substrate is an important factor constraining natural recovery. However, D. antillarum recruit abundance was low compared to the measured settlement rates, possibly due to low post-settlement survival. The size distribution of recruits showed that recruits almost never became larger than 20 mm, which is likely due to predation. We conclude that, next to low settlement availability, low post-settlement survival and high predation on recruits also constrain the natural recovery of D. antillarum populations on Saba. To improve the survival of settlers till adults, we propose to 1) reduce predation on settlers by using bio balls or other substrates that can provide shelter to larger individuals and 2) optimize the reef habitat by removing macroalgae, either manually or by facilitating other herbivores. To improve the survival of recruits, we suggest to 1) choose sites with a known lower predation density or 2) protect recruits with a corral around the reef underneath the streamers. The combination of these measures could improve prospects for ANR, and we expect this new approach can contribute to the recovery of D. antillarum populations in the future.

Het zou zomaar kunnen dat zich de komende jaren iets van een koraalrif ontwikkelt langs de Lauwersmeerdijk oostelijk van Lauwersoog. Om dat te bereiken is daar deze week met het plaatsen van rifelementen van beton een groot onderzoek gestart om de onderwaternatuur langs de zeedijk te stimuleren en zo het ecosysteem en dus waterkwaliteit in de Waddenzee te verbeteren.

Het zou zomaar kunnen dat zich de komende jaren iets van een koraalrif ontwikkelt langs de Lauwersmeerdijk oostelijk van Lauwersoog. Om dat te bereiken is daar deze week met het plaatsen van rifelementen van beton een groot onderzoek gestart om de onderwaternatuur langs de zeedijk te stimuleren en zo het ecosysteem en dus waterkwaliteit in de Waddenzee te verbeteren.

Langs de Lauwersmeerdijk in Groningen worden de komende tijd kunstmatige riffen in de Waddenzee geplaatst. Die moeten het onderwaterleven verbeteren en de biodiversiteit vergroten.

Langs de Lauwersmeerdijk in Groningen worden de komende tijd kunstmatige riffen in de Waddenzee geplaatst. Die moeten het onderwaterleven verbeteren en de biodiversiteit vergroten.

Langs de Lauwersmeerdijk worden de komende tijd een tiental speciaal ontworpen rifelementen in de Waddenzee geplaatst. Het doel: het onderwaterleven aangenamer maken en de biodiversiteit vergroten.

Langs de Lauwersmeerdijk worden de komende tijd een tiental speciaal ontworpen rifelementen in de Waddenzee geplaatst. Het doel: het onderwaterleven aangenamer maken en de biodiversiteit vergroten.

University of Applied Sciences Van Hall Larenstein and Wageningen University and Research recently conducted a comparative study of artificial reefs within the Caribbean. This study provides new insights into the impacts of these structures on local marine life and neighboring ecosystems and highlight the need for comprehensive monitoring and integration into marine management plans.

University of Applied Sciences Van Hall Larenstein and Wageningen University and Research recently conducted a comparative study of artificial reefs within the Caribbean. This study provides new insights into the impacts of these structures on local marine life and neighboring ecosystems and highlight the need for comprehensive monitoring and integration into marine management plans.

Caribbean coral reefs are in decline and the deployment of artificial reefs, structures on the sea bottom that mimic one or more characteristics of a natural reef, is increasingly often considered to sustain ecosystem services. Independent of their specific purposes, it is essential that artificial reefs do not negatively affect the already stressed surrounding habitat. To evaluate the ecological effects of artificial reefs in the Caribbean, an analysis was performed on 212 artificial reefs that were deployed in the Greater Caribbean between 1960 and 2018, based on cases documented in grey (n = 158) and scientific (n = 54) literature. Depending on the availability of data, reef type and purpose were linked to ecological effects and fisheries management practices around the artificial reefs. The three most common purposes to deploy artificial reefs were to create new dive sites (41%), to perform research (22%) and to support ecosystem restoration (18%), mainly by stimulating diversity. Ship wrecks (44%), reef balls© (13%) and piles of concrete construction blocks (11%) were the most-often deployed artificial reef structures and metal and concrete were the most-used materials. The ecological development on artificial reefs in the Caribbean appeared to be severely understudied. Research and monitoring has mostly been done on small experimental reefs that had been specifically designed for science, whereas the most commonly deployed artificial reef types have hardly been evaluated. Studies that systematically compare the ecological functioning of different artificial reef types are virtually non-existent in the Caribbean and should be a research priority, including the efficacy of new designs and materials. Comparisons with natural reef ecosystems are scarce. Artificial reefs can harbor high fish densities and species richness, but both fish and benthos assemblages often remain distinct from natural ecosystems. Studies from other parts of the world show that artificial reefs can influence the surrounding ecosystem by introducing non-indigenous species and by leaking iron. As artificial reefs attract part of their marine organisms from surrounding habitats, intensive exploitation by fishers, without clear management, can adversely affect the fish stocks in the surrounding area and thus counteract any potential ecosystem benefits. This study shows that over 80% of artificial reefs in the Caribbean remain accessible to fishers and are a risk to the surrounding habitat. To ensure artificial reefs and their fisheries do not negatively affect the surrounding ecosystem, it is imperative to include artificial reefs, their fisheries and the surrounding ecosystem in monitoring programs and management plans and to create no-take zones around artificial reefs that are not monitored.

In this study, we compared the early fish colonization of three types of artificial reefs deployed in the coastal waters of Saba and St Eustatius in the Caribbean: reef balls®, layered cakes and piles of locally obtained basaltic rock. As an indicator of performance, three fish assemblage parameters (abundance, biomass, species richness) were measured using underwater visual censuses at 11 months post-deployment and 4 months after restoration from hurricane damage. All artificial reef plots showed higher values for fish abundance, biomass and species richness than control plots covered by bare sand, which shows that artificial reefs can locally enhance the fish assemblage. However, the effect differed among artificial reef plots. Fish abundance was 3.8 times higher on the layered cake plots compared to the reef ball plots, while fish biomass was 4.6 times higher. Rock pile plots had intermediate values. Species richness did not differ significantly among different artificial reef plots. Three-dimensional modelling revealed that layered cakes had a smaller gross volume, shelter volume and total surface area than reef balls. The availability of multiple small shelters in the layered cake design appeared to be more relevant than other physical parameters, as the layered cake plots had higher fish abundance than the reef balls plots. We concluded that on Saba and St. Eustatius, layered cake plots performed better than reef ball plots after one year of colonization. Rock pile plots, made of local volcanic rock, showed an intermediate performance, and were 4–10 times cheaper to construct. If observed differences are consistent with other locations and persist during further colonization, current efforts to deploy reef balls could better be allocated to deploy artificial reef structures with a higher shelter density.

Als vissen niet meer terecht kunnen in koraalriffen, wat is dan het beste kunstmatige onderkomen dat wij mensen ze kunnen bieden? Alwin Hylkema, onderzoeker aan Hogeschool van Hall Larenstein in Leeuwarden, onderzoekt of, en zo ja welke, kunstmatige riffen een tijdelijke schuilplaats kunnen bieden voor vissen.

Hogeschool Van Hall Larenstein en Wageningen University en Research hebben onlangs een vergelijkend onderzoek gedaan naar kunstmatige riffen in het Caribisch gebied. Deze studie biedt nieuwe inzichten in de effecten van deze structuren op het lokale zeeleven en aangrenzende ecosystemen en benadrukt de noodzaak van uitgebreide monitoring en integratie in mariene beheerplannen.

Hogeschool Van Hall Larenstein en Wageningen University en Research hebben onlangs een vergelijkend onderzoek gedaan naar kunstmatige riffen in het Caribisch gebied. Deze studie biedt nieuwe inzichten in de effecten van deze structuren op het lokale zeeleven en aangrenzende ecosystemen en benadrukt de noodzaak van uitgebreide monitoring en integratie in mariene beheerplannen.