symbiotic relationship

Seagrasses represent the unique re-colonization of the marine ecosystem by angiosperms. As their terrestrial relatives, seagrasses are important habitat providers but in contrast, their microbiomes are still poorly known. The microbial community associated with terrestrial plants is intensively studied and plays an important role in plant fitness. The close relation of seagrasses to terrestrial plants suggests a resemblance in survival strategies, including the creation of a microbiome distinct of the surrounding environment. To obtain more knowledge regarding seagrass microbiomes and their intra- and interspecies differentiation, samples of three tropical seagrass species occurring around the island of Curaçao, the invasive Halophila stipulacea and the natives Halodule wrightii and Thalassia testudinum, were collected. Root and leaf-associated microbes were separately analyzed using high throughput Illumina sequencing of the region V5-V7 of the 16S rRNA gene. Sequences were aligned and clustered into Operational Taxonomic Units (OTUs). Results displayed the occurrence of a seagrass-specific microbiome, distinct from that of the surrounding seawater and sediment. The existence of a species and tissue (root/leaf) specific bacterial community and structure was detected, along with a bacterial community that was shared among the seagrasses. OTUs belonging to the shared seagrass community were mostly of the orders rhizobiales. Desulfobacterales was the most abundant order associated with the roots and Rhodobacterales with the leaves of the three seagrass species. Species-specific bacteria are represented mostly by OTUs of the same orders as the common OTUs, along with a few species-specific orders. The high abundant and widespread bacterial OTUs were identified to be mostly associated with sulfur and nitrogen cycling, which point towards the importance of these processes in seagrass fitness.

Various symbiotic relationships build and maintain coral reefs. Mutualistic relationships provide the organisms involved with an increased chance of survival and reproduction which prove important for the health and function of reef communities. The increasing presence of macroalgae is an indication of declining reef health. In order to maintain the growth of certain species of macroalgae, Threespot damselfish, Stegastes planifrons, cultivate and maintain algae gardens. If there is an abundance of algae in the gardens of S. planifrons, there is a limited opportunity for coral recruitment and growth; this makes them an important species in the ecosystem. Damselfish are very territorial and will defend their gardens by chasing and biting intruders. This study tested whether there is a particular sized territory surrounding the garden that correlates to the size of the garden itself. Attacks by S. planifrons in the gardens toward a laser pointer allowed the determination of garden and territory area. The area of the garden, the point where the attacks ended and the total surrounding territory of the damselfish were measured using a measuring tape. A positive trend between area of garden and area of territory was found indicating that both increased correspondingly. The algae gardens and territorial behavior of S. planifrons can be indicative of the current phase shift from a coral reef to a coral depauperate ecosystem. More algal cover is indicative of decreased coral cover and coral recruitment success. By understanding ecological dynamics, protection of coral reefs from a degrading phase shift can be implemented.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 96-102 from CIEE Bonaire.