Becker, T.

Expansion of invasive seagrass inhibited by nutrient and grazing stress; a case study in Aruba

Student Report

Seagrass ecosystems are rapidly declining around the world as human pressures are increasing. To build the resilience of seagrass ecosystems, a holistic understanding is needed of the bottom-up and top-down influences on a seagrass community. This is ever more relevant in the Caribbean, where the recent invasion by Halophila stipulacea is believed to be enhanced by the preferential grazing of green sea turtles on the native Thalassia testudinum. In this study, we tested the response of the native and invasive seagrass in Aruba to grazing and nutrient pressures. Grazed plots were mimicked by clipping treatments, while enriched plots were mimicked with fertilizer treatments. Then the two responses, recovery and competition, were tested in each plot by applying gaps in the seagrass cover and transplanting either native or non-native seagrass. The experiments showed that in stark contrast to the native T. testudinum, the invasive H. stipulacea was easily able to recover and occupy new territory. It expanded into native habitats with an average distance of 16.6 cm after 76 days. Nonetheless, the combined stress of intensive grazing and nutrients significantly reduced the expansion of the invasive in its damaged habitat. This was contrary to the notion that the invasive is facilitated by eutrophication and grazing. On the other hand this experiment was not able to (dis)prove the competitive facilitation of the invasive seagrass under nutrient and grazing stress. The finding of this study suggests that the invasion by H. stipulacea will not easily be halted. Despite this threat, it is suggested that resource managers should put great efforts in preventing physical disturbances and mitigating eutrophication in Caribbean seagrass systems. 

Keywords 

seagrass invasive grazing seaturtle eutrophication resilience recovery competition Caribbean

Date
2018
Data type
Other resources
Theme
Research and monitoring
Geographic location
Aruba
Author

Linking spatial gradients and habitat to reef fish assemblages: Insights from a remote coral reef system

Student Report 

Drastic loss of Caribbean coral reef habitat in the past decades has recently begun to negatively affect reef fish assemblage structures in the region. Additionally, significant reef fish declines have been caused by local anthropogenic pressures, including even small-scale fisheries. It is commonly suggested that healthy stocks of herbivore fish are needed on reefs to inhibit algal dominance and support coral reef resilience. Despite that the threats and ecological interactions are complex, we can improve our understanding of the impacts on reef fish and their associated benthos by studying their variability along a spatial gradient from land. To that end, data on twelve Underwater Visual Census (UVC) sites of the remote reef system known as the Saba Bank (neighbored by Saba and St. Eustatius) were explored for the relationship between the fish community and the influences of remoteness and benthic cover. As expected, fish density and biomass was generally higher (i.e. at least two-fold increase) at more remote sites and species composition was significantly different between the near- and far sided (i.e. E-NE vs. S-SE, respectively) reefs. In spite of the small-scale operations, the higher fishing pressure in the near-sided reefs mainly suggests that current fish communities at Saba Bank are (partly) shaped by local anthropogenic influences. While this relationship was also expected to be reflected in the trophic community, seemingly contradicting results were found between the univariate and multivariate analyses; top predator proportions were four-fold higher in remote sites, however insignificant trophic composition was found with relation to far-sided reefs. Hence, these particular findings do not allow concluding remarks regarding their potential influences. Besides remoteness, variability in fish assemblages was also significantly linked to gorgonians, bare substrate and macro algae cover. This suggested the driving role of the benthic habitat. Furthermore, a negative relationship between herbivore fish and macro algae was found to suggest the opposing ecological pathway. Nevertheless, the relationship was insignificant and the effectiveness of herbivore fish in controlling algae blooms on the Saba Bank can be strongly debated. Continued data collection of the biotic and abiotic environment from the Saba Bank and other remote reefs, consistent UVC methodology and advancements in multivariate analysis techniques could help reduce our doubts about the local and wide-spread impacts in Caribbean reef systems. 

Keywords: coral reefs, reef fish, algae, herbivory, remote, fisheries, Caribbean

For more information, contact Tatiana Becker- tatjabecker@gmail.com

 

 

Date
2019
Data type
Research report
Theme
Research and monitoring
Geographic location
Saba bank
Author

Beach Debris on Aruba

A large-scale study of beach debris on Aruba has shown just how much marine debris pollution there is on the island’s beaches. The study also locates the different sources of this debris, emphasizing the need for both local and global action. 

 

This news article was published in BioNews 24.

BioNews is produced by the Dutch Caribbean Nature Alliance and funded by the Ministry of Economic Affairs.

Date
2016
Data type
Media