This article is a part of WIOMSAs video series “Voices of MARG Grantees”.
Marine Research Grant I (MARG I) is a capacity building programme of WIOMSA that targets young and upcoming scientists with the aim of providing them with opportunities to undertake independent studies. Some of this research has led to publications in international peer reviewed journals and also produced innovative solutions to address issues at the local level. “Voices of MARG Grantees” is a series of videos that showcases some outstanding MARG I case studies that WIOMSA has funded over the years. We will feature 4 case studies in the video series. First out is Juliet Karisa.
New knowledge about Kenyan corals
The results of a comprehensive assessment of coral reef benthic communities across the 536 km long Kenyan coast offer a glimmer of hope for the survival of corals in the face of increased bleaching, and other threats such as sedimentation and pollution.
The study “Spatial heterogeneity of coral reef benthic communities in Kenya” was published in the open access journal Plos One in 2020. It was authored by Juliet Karisa, David Obura and Chaolun Chen and identified two distinct patterns of benthic community structure. First, there was a clear difference in coral community composition between the north and south of the country – three different geographic zones were identified. Then, habitat factors and management activities were found to influence the pattern of benthic communities within each of the zones.
“I found geographic patterns in the abundance of the benthic community,” explains Juliet Karisa, a research scientist with the Kenya Marine and Fisheries Research Institute and lead author of the study. “Whereas the southern zone featured a high diversity of corals and is believed to be a receiving area for coral larvae transported into Kenyan waters by northward flowing currents, the northern zone is an area of low coral diversity. However, the northern zone features a greater abundance of large coral colonies which suggests a high survival of adult corals.”
This finding is important in the context of climate change because the northern zone may provide some protection to coral communities from bleaching.
Climate change poses one of the biggest threats to coral reefs. As temperatures rise, coral bleaching events and infectious disease outbreaks are becoming more frequent. Coral reefs are also impacted by sea level rise, changes in the frequency and intensity of tropical storms, ocean acidification (changes in the chemistry of seawater) and altered circulation patterns. Climate scenarios suggest that 99% of global coral reefs could disappear in this century.
A second key finding of the study of Kenyan coral reefs was the identification of localized patterns of benthic community composition within the three geographic zones. Four habitats were identified: deep-exposed patch reef in reserve areas; deep-exposed fringing reefs in unprotected areas; shallow fringing and lagoon reefs in protected and reserve areas; and shallow patch and channel reefs.
Again, the northern zone exhibited a wide range of habitat types.
“The northern zone is a very heterogenous area,” explains Karisa, “there are several islands in that area so this creates a mosaic of different habitats. That’s really good because it ensures a wide range of functional traits of the coral community, making them resilient to bleaching.”
The presence of very large colonies of Porites corals in the north compared to the south could imply that bleaching mortality is lower in the north because of the presence of habitats that protect corals against bleaching.
In the south, the low abundance of large colonies within fringing reefs is a concern considering this zone is an area of high coral diversity. This is likely due to bleaching mortality which has been recurrent over the past two decades.
The dominance of macroalgae and turf algae on shallow fringing and lagoon reefs in the north and central zones is also of concern. Macroalgae and turf algae take over when hard corals die and their high abundance within these habitats indicates a worrying level of coral reef degradation. Most of these habitats are close to land and are highly influenced by land use activities such as effluents from rivers, and fishing.
Karisa believes her study has important implications for Kenya:
“At the national level the implication is pretty clear because we are living in an era where climate change is destroying coral reefs,” she says. “We have to find ways to protect these ecosystems until we find a solution to climate change. This means proper planning and conservation initiatives. My study helps to understand the spatial pattern of corals which is very useful information for marine spatial planning and could support the process of designing effective marine protected areas.”
For Karisa, who has studied corals in Kenya for the past 10 years, the discovery of reefs that are proving resilient to bleaching is very encouraging.
“I have seen some transition, some sites that are being destroyed, most often because of bleaching which we have no control over,” she says, “but as I did this study I realised there are many reefs that can cope with climate change but they are barely known. There are hidden reefs in unprotected areas – often in channels with murky water or in deep water – and these could be our hope.”
Karisa is grateful for a research grant funded by the Western Indian Ocean Marine Science Association which enabled her to undertake the fieldwork for her study. She surveyed 38 study sites, using SCUBA gear and snorkel gear. She used photographs to document the composition of benthic communities and belt transects to determine the demographic structure of coral populations.
“This study enabled me to publish my first peer-reviewed journal article as a first author, which was like breaking a barrier, and I also managed to meet the requirements to graduate with my PhD,” she says, adding that she has produced two more papers that are in press.
“The funding from WIOMSA provided a very good foundation for me to advance in my field of study and I’m very grateful,” says Karisa who graduated with a PhD from the National Taiwan Normal University in December 2020.