Leontine E. Becking

Abstract

Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality.

Understanding the population composition and dynamics of migratory megafauna at key developmental habitats is critical for conservation and management. The present study investigated whether diferential recovery of Caribbean green turtle (Chelonia mydas) rookeries infuenced population composition at a major juvenile feeding ground in the southern Caribbean (Lac Bay, Bonaire, Caribbean Netherlands) using genetic and demographic analyses. Genetic divergence indicated a strong temporal shift in population composition between 2006–2007 and 2015–2016 (φST=0.101, P<0.001). Juvenile recruitment (<75.0cm straight carapace length; SCL) from the north-western Caribbean increased from 12% to 38% while recruitment from the eastern Caribbean region decreased from 46% to 20% between 2006–2007 and 2015–2016. Furthermore, the product of the population growth rate and adult female abundance was a signifcant predictor for population composition in 2015–2016. Our results may refect early warning signals of declining reproductive output at eastern Caribbean rookeries, potential displacement efects of smaller rookeries by larger rookeries, and advocate for genetic monitoring as a useful method for monitoring trends in juvenile megafauna. Furthermore, these fndings underline the need for adequate conservation of juvenile developmental habitats and a deeper understanding of the interactions between megafaunal population dynamics in diferent habitats.

Referenced in BioNews 31 article "Genetic Testing to Measure Sea Turtle Conservation Success"

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

In this review the following three reef restoration techniques are discussed: 1. Coral gardening, 2. Larval seeding, and 3. Reef balls. These techniques are commonly used in the Caribbean and have widely different approaches. Coral gardening utilize the natural process of asexual reproduction through fragmentation to provide new coral clones for population growth. Healthy wild colonies are once clipped/fragmented and further grown (and cloned multiple times) in an underwater nursery and ultimately transplanted to the reef.
In contrast, larval seeding is based on the sexual reproduction of corals, where large amounts of coral eggs and sperm are collected in the field with subsequent fertilization in the lab. The coral recruits are then made to settle and grown in aquaria until a certain size, after which they are transplanted to the reef. Reef balls are artificial concrete structures designed to provide shoreline protection and sometimes shelter for fish, while at the same time providing substrate for natural recruitment and attachment of benthic organisms such as corals.
A general introduction to coral reproduction is provided to show how life history characteristics are used in restoration efforts and how these can affect the genetic variation within coral populations. The three approaches are compared based on:
1. Survival of fragments and larvae before transplantation to the reef.
2. Survival of transplants at the restoration site.
3. Introduction of exogenous material.
4. Indirect effects of coral restoration on the reef.
5. Genetic diversity.
6. Feasibility and effectiveness.
The main advantages of the production of colonies from fragments are that it bypasses the early larval stages where mortality is high and that new colonies can be grown completely in the field. Generally, the asexual reproduction technique demands less advanced expertise and the public outreach of this method is high because volunteers can easily be incorporated into the program. Furthermore, results become apparent relatively soon since the used species are relatively fast growing. However, there is the risk of creating populations with little genetic variability and the method is only applicable to branching coral species. Presently the method is mainly used for one single species, namely staghorn coral (Acropora cervicornis).
Larval seeding (sexual reproduction) is arguably the best method since it ensures natural genetic diversity and can be used with many species. The disadvantage with this method is that it demands a reasonably high level of expertise and takes more time than the asexual production of new colonies by fragmentation. Also a high percentage of new colonies is lost during the early stages. It is still mostly in the development phase.
Reef balls may increase fish biomass and protect shorelines, but their potential for coral reef restoration is judged to be limited due to the generally low levels of natural recruitment to these structures.
The restoration techniques suffer presently from a lack of independent scientific publications with good data to validate survival, regeneration, and growth rates of colonies in the different phases of the restoration program.
Different populations of the branching Acropora species can differ fundamentally in reproductive characteristics and may respond differently to environmental change. Their difference in strategy may also be a result of adaptation to local environmental factors. All studies and protocols thus stress the necessity to adapt methods to specific locations and environments.
Consideration of genetic factors is essential because the long-term success of restoration efforts (depending on resilience of the populations) may be influenced by genetic diversity of restored coral populations. The use of molecular tools may aid managers in the selection of appropriate propagule sources, guide spatial arrangement of transplants, and help in assessing the success of coral restoration projects by tracking the performance of transplants, thereby generating important data for future coral reef conservation and restoration projects.
It is proposed to study genetic variation in the natural populations around the islands of the Dutch Caribbean and within the various restoration projects in progress. Additionally, it is recommended to assess survival, growth and regeneration of fragments ánd mother colonies in the field. We recommend to combine characteristics of the two main coral restoration techniques (fragmentation and larval rearing) to create a new hybrid approach to increase survival of sexually derived colonies and genetic diversity. In addition, the cost-effectiveness of the larval seeding method should be ascertained and compared with the fragmentation method.
We conclude by pointing out that reef restoration can only be successful if environmental conditions are adequate for survival and growth of coral colonies. This will mean that presently the selection of restoration sites with good environmental conditions is crucial. Thus, active management of anthropogenic stressors is a prerequisite for reef restoration — if a reef is not effectively managed and chronic stressors persist or develop, restoration will ultimately fail. Reef restoration must only be considered as complementary to management tools that address the wider causes of reef degradation.