Restoring Damaged Coral Reefs Using Mass Coral Larval Reseeding

Project and Seminar Material for Fishery and Aquaculture

Restoring Damaged Coral Reefs Using Mass Coral Larval Reseeding


Abstract


The aim of this study is to quantify the effectiveness of mass larval reseeding to restore damaged coral communities on reefs in Nigeria, and to use this assessment as a case study for future global reef restoration management strategies. A total of 134 respondents were selected from the population figure out of which the sample size was determined. The primary source of data collected was mainly the use of a structured questionnaire which was designed to elicit information on the restoration of damaged coral reefs using mass coral larval transplantation. Data collected will be analyzed using frequency table, percentage and mean score analysis while the nonparametric statistical test (Chi-square) was used to test the formulated hypothesis using SPSS (statistical package for social sciences). The findings from this study will reveal that mass coral spawning significantly increases coral recruitment rates, coral cover and genetic diversity that may improve coral adaptive and evolutionary potential and increase resilience in depleted coral populations, damaging reef ecosystems’ health and resilience and reducing species abundance. However, whether corals are derived from asexual or sexual propagation, the transplantation of corals remains costly, labor-intensive, time consuming and in many cases has failed to restore self-sustaining coral populations and associated ecological functions at the restoration site.


Chapter One


Introduction

1.1 Background to the Study

Reef corals are critically important because they build the primary reef framework, supply essential habitats for thousands of fish and other species, and provide direct energy and other nutrient inputs to the ecosystem (Gardner et al, 2003). But the loss of substantial live coral cover on reefs – fundamentally through overfishing, eutrophication and other disturbances arising from human activity – has seriously disrupted their ecology. Continued human pressures on damaged reefs leads to further reef decline and ecosystem collapse. But this situation may be alleviated through mass reseeding with coral larvae. The aim of this study is to quantify the effectiveness of mass larval reseeding to restore damaged coral communities on reefs in Nigeria, and to use this assessment as a case study for future global reef restoration management strategies.

The continuous degradation of coral reef ecosystems on a global level, the disheartening expectations of a gloomy future for reefs’ statuses, the failure of traditional conservation acts to revive most of the degrading reefs and the understanding that it is unlikely that future reefs will return to historic conditions, all call for novel management approaches. Among the most effective approaches is the “mass coral larval reseeding” concept of active reef restoration, centered, as in silviculture, on a two-step restoration process (nursery and transplantation). In the almost two decades that passed from its first presentation, the “mass coral larval reseeding” tenet was tested in a number of coral reefs worldwide, revealing that it may reshape coral reef communities (and associated biota) in such a way that novel reef ecosystems with novel functionalities that did not exist before are developed (Chen et al, 2011). Factors such as such as elevation of seawater temperature, extreme weather events, ocean acidification and intensifying tropical storms that cause, for example, enhanced frequency and intensity of mass coral bleaching has directly or indirectly influence coral survival, coral growth rates, reproduction efforts, larval development and settlement, and post-settlement survivorship/development of corals, damaging reef ecosystems’ health and resilience and reducing species abundance.

Graham et al (2014) further attests to the decimation of key reef-building coral populations, to a dramatic shrinkage in global reef structural complexity and that many reefs experience phase shift phenomena in addition to reefs that are continuously changing in unprecedented ways towards new ecosystem configurations and novel reef compositions that did not exist before. As the major emerging sources of global reef degradation, such as coral bleaching, seawater acidification impacts and coral diseases, interact synergistically and also in concert with local/regional anthropogenic specific stressors, among them pollution, eutrophication, sedimentation, coastal development and overfishing, augmentation of existing climate change impacts is anticipated. Large-scale rearing of coral larvae during mass spawning events and subsequent direct introduction of competent larvae onto denuded reefs (larval seeding) has been proposed as a low-tech and affordable way of enhancing coral settlement and hence recovery of degraded reefs.

While some studies have shown positive short-term effects on settlement, to date, none have examined the long-term effects of larval seeding for a broadcast-spawning coral. However, this study will test whether mass larval reseeding significantly increases coral recruitment rates both in the short and longer term towards restoring damaged coral reefs. Mass coral larval reseeding plays a critical role in the persistence and resilience of reef coral populations (Richmond 1997) but its relative importance in coral population and community dynamics can vary according to species, habitat and reef location (Connell et al. 1997). Recent data indicate quite different patterns of reseeding and post-reseeding mortality occurring in reef crest coral communities along the length of the reef (Hughes et al. 1999). Characterizing the site-specific nature of processes and mechanisms influencing the arrival and survival of corals onto reefs is necessary for sound reef management.


1.2 Statement of the Problem

Globally, coral reef ecosystems throughout the tropics have been progressively damaged in the last century by a wide range of direct anthropogenic pressures, including over-exploitation, physical destruction, pollution, eutrophication, sediment loads from agricultural and urbanized terrestrial catchments and coastal development. On top of that, the last few decades have seen exacerbated sways of climate-change associated impacts, such as elevation of seawater temperature, extreme weather events, ocean acidification and intensifying tropical storms that cause a number of damage to coral reefs. However, this study seeks to examine how these damaged reefs can be restored using mass coral larval reseeding.


1.3 Objectives of the Study

The following are the objectives of this study:

  1. To identify the factors causing damages to coral reefs.
  2. To examine the process of restoration of damaged coral reefs using mass coral larval reseeding.
  3. To examine other ways by which damaged coral reefs can be restored.

1.4 Research Questions

  1. What are the factors causing damages to coral reefs?
  2. What are the processes involved in the restoration of damaged coral reefs using mass coral larval reseeding?
  3. What are the other ways by which damaged coral reefs can be restored?

1.5 Hypothesis

  • HO: Damaged coral reefs cannot be restored using mass coral larval reseeding.
  • HA: Damaged coral reefs can be restored using mass coral larval reseeding.

1.6 Significance of the Study

Based on the importance of coral reefs to the production and development in fisheries industry, findings from this study will reveal how mass larval reseeding can be used to restore damaged coral reefs. This research will be a contribution to the body of literature in the area of the effect of personality trait on student’s academic performance, thereby constituting the empirical literature for future research in the subject area.


1.7 Scope / Limitations of the Study

This study will cover the larval reseeding ponds specifically designed to enhance the survival of coral larval.


1.8 Limitation of Study

Financial constraint

Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).

Time constraint

The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.


Chapter Five


Conclusion and Recommendation

5.1 Conclusion

In the initial stages of coral restoration research, direct coral transplantation gained popularity as one approach to rapidly increase coral cover by re-attaching coral fragments or whole colonies to degraded reefs. As an alternative, an intermediate step of rearing coral nubbins in different types of nurseries increased the number of transplant materials from a few source colonies. While this grow-out nursery phase increases the size and robustness of coral transplants, which may lead to higher post-transplantation survival rates. it also increases production costs from hatchery and nursery facility construction, grow-out costs, and outplanting costs .

More recently, sexual larval propagation has become more widely used in restoration studies. This approach aims to increase recruitment rates, coral cover and genetic diversity that may improve coral adaptive and evolutionary potential, and increase resilience in depleted coral populations . Using this approach, millions of sexually derived coral larvae can be sourced from sexually mature coral colonies from ex situ spawning in a controlled hatchery facility, or in situ by using spawn collectors placed on top of individual corals, or from natural coral spawn slicks. Typically, competent larvae are then settled on artificial substrata and kept in land- or ocean-based nurseries before they are outplanted on the reef.


5.2 Recommendation

To reduce these labor-intensive and costly grow-out and outplanting phases, coral larvae can be immediately outplanted shortly after the completion of metamorphosis and onset of skeleton formation . For example, Acropora palmata settlers outplanted to the reef at the age of two weeks were 7 times more likely to survive and were 25 fold less costly to produce than conspecifics kept within a land-based nursery for 2.5 years.

In addition, new tetrapod-shaped substrates have been developed that can be “seeded’ onto the reef in much less time and 5–18 fold lower costs compared with traditional outplanting techniques because their geometry allows them to be wedged within reef crevices, thus avoiding the need for adhesives and nails for attachment.

Nonetheless, whether corals are derived from asexual or sexual propagation, the transplantation of corals remains costly, labor-intensive, time consuming and in many cases, has failed to restore self-sustaining coral populations and associated ecological functions at the restoration site.

A less commonly used approach that avoids the need for manual transplantation of corals settled onto artificial substrates is the introduction of large numbers of competent larvae directly onto reef areas.


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