Abstract
Cyanobacteria have multifaceted ecological roles on coral reefs. Moorena bouillonii, a chemically rich filamentous cyanobacterium, has been characterized as a pathogenic organism with an unusual ability to overgrow gorgonian corals, but little has been done to study its general growth habits or its unique association with the snapping shrimp Alpheus frontalis. Quantitative benthic surveys, and field and photographic observations were utilized to develop a better understanding of the ecology of these species, while growth experiments and nutrient analysis were performed to examine how this cyanobacterium may be benefiting from its shrimp symbiont. Colonies of M. bouillonii and A. frontalis displayed considerable habitat specificity in terms of occupied substrate. Although found to vary in abundance and density across survey sites and transects, M. bouillonii was consistently found to be thriving with A. frontalis within interstitial spaces on the reef. Removal of A. frontalis from cyanobacterial colonies in a laboratory experiment altered M. bouillonii pigmentation, whereas cyanobacteria-shrimp colonies in the field exhibited elevated nutrient levels compared to the surrounding seawater.
Highlights
Cyanobacteria, known as blue-green algae, represent a wide array of organisms that operate in a diversity of roles in marine ecosystems
Transects at Piti Bomb Holes were less consistent, with 76% of the colonies along the first transect growing with P. rus, while 97% of colonies along transect two and 93% along transect three were growing with P. cylindrica
Study of M. bouillonii—A. frontalis colonies across the surveyed reefs in Laulau Bay and Apra Harbor allowed for the identification of three common habits of M. bouillonii growth (Fig. 7)
Summary
Cyanobacteria, known as blue-green algae, represent a wide array of organisms that operate in a diversity of roles in marine ecosystems. Cyanobacteria, often empowered by anthropogenic perturbations, can disrupt aquatic ecosystems by forming sustained and deleterious blooms (CyanoHABs) that produce toxins and can cause localized hypoxia (Paerl and Paul 2012). In addition to CyanoHABs occurring in and around coral reefs, cyanobacteria have been implicated in coral diseases, such as black band disease and grey-patch disease (Frias-Lopez et al 2003; Sweet et al 2019). Cyanobacteria contribute positively to coral reef ecosystems, serving as habitat and sources of food (Cruz-Rivera and Paul 2002, 2006), and engaging in specialized symbioses, including with sponges (Schorn et al 2019) and shrimp (Banner and Banner 1982)
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