The Effect of Filamentous Turf Algal Removal on the Development of Gametes of the Coral Orbicella annularis

Abstract

Macroalgae and filamentous turf algae (FTA) are abundant on degraded coral reefs, and the reproductive responses of corals may indicate sub-lethal stress under these conditions. The percentage of gametogenic stages (PGS) and the maximum diameter of eggs (MDE; or egg size) of Orbicella annularis were used to evaluate the effect of long- (7–10 months) and short-term (2.5 months) FTA removal (treatments T1 and T2, respectively) at both the beginning (May) and the end (August) of gametogenesis. Ramets (individual lobes of a colony) surrounded by FTA (T3) or crustose coralline algae (CCA; T4) were used as controls. The removal of FTA enhanced the development of gametes (i.e., a larger and higher percentage of mature gametes (PMG)) of O. annularis for T1 vs. T3 ramets in May and T1 and T2 vs. T3 ramets in August. Similar values of PGS and MDE between gametes from T3 and T4 in both May and August were unexpected because a previous study had shown that the same ramets of T4 (with higher tissue thickness, chlorophyll a cm-2 and zooxanthellae density and lower mitotic index values) were less stressed than ramets of T3. Evaluating coral stress through reproduction can reveal more sensitive responses than other biological parameters; within reproductive metrics, PGS can be a better stress indicator than egg size. The presence of turf algae strongly impacted the development of gametes and egg size (e.g., PMG in ramets with FTA removal increased almost twofold in comparison with ramets surrounded by FTA in August), most likely exerting negative chronic effects in the long run due to the ubiquity and permanence of turf algae in the Caribbean. These algae can be considered a stressor that affects coral sexual reproduction. Although the effects of turf algae on O. annularis are apparently less severe than those of other stressors, the future of this species is uncertain because of the combined impacts of these effects, the decline of O. annularis populations and the almost complete lack of recruitment.

Rehabilitation of coral reefs through removal of macroalgae: state of knowledge and considerations for management and implementation

“…While macroalgae are a natural and important component of coral reef ecosystems, when present in high abundance, they are usually seen as an indicator or symptom of a decline in coral community condition caused by human impacts and/or natural disturbances (Nugues et al ; Birrell et al ; Hughes et al ). This view is based on numerous studies that have documented negative effects of macroalgae, including reduced production of coral gametes (Cetz‐Navarro et al ), inhibited larval recruitment (Webster et al ) and larval metamorphosis (Baird & Morse ), reduced juvenile coral growth and survival (Hughes et al ), and impacts on coral colony fitness and health (Tanner ; van Woesik et al ; Fig. ).…”

Macroalgal assemblages on dead surfaces of scleractinian corals (Anthozoa: Scleractinia) in the Oro Verde reef, Veracruz, Mexico

“…Los corales masivos del arrecife Oro Verde presentan asentamientos de macroalgas representados principalmente por algas foliosas, corticadas y filamentosas, estos grupos morfo-funcionales establecen competencia contra los corales mediante mecanismos diversos, como abrasión, sobre crecimiento, sombreado y alelopatía (McCook et al, 2001;Jompa & McCook, 2003;Márquez & Díaz, 2005;Box & Mumby, 2007). Así, actúan como agentes estresores de los corales (Cetz-Navarro et al, 2015), dado que llegan a recubrir rápidamente las colonias coralinas adyacentes (McCook et al, 2001), pueden transmitir patógenos (Barott et al, 2012), y favorecer la acumulación de sedimentos (Birell et al, 2005); además, prosperan en condiciones de alta sedimentación (Nugues & Roberts, 2003b) y permanecen durante más de un año cuando la herbivoría es baja (Díaz-Pulido & McCook, 2002;Nugues & Roberts, 2003b).…”

“…Estudios experimentales han demostrado que las algas afectan la estabilidad de los corales masivos del Atlántico Occidental; específicamente se ha comprobado en O. annularis y O. faveolata que las algas césped pueden causar estrés crónico, por ejemplo, pérdida del tejido coralino, disminución en la densidad de zooxantelas y de la concentración de clorofila (Quan-Young & Espinoza-Avalos, 2006;Cetz-Navarro et al, 2013); también afectan la reproducción sexual (Cetz-Navarro et al, 2015). Incluso los sedimentos retenidos por los céspedes de algas pueden transmitir patógenos y afectar las colonias coralinas adyacentes (Barott et al, 2012).…”

Markov chain analysis of sessile community dynamics in a degraded Philippine reef to support restoration of coral populations

“…Crustose coralline algae with cropped turf formed a single state (hereafter referred to as C or crustose algae) that is often considered available for coral recruitment and growth (Spencer & Tanner, ; Tanner et al, ). MA and dense turf algal assemblages were combined due to their similar detrimental effects on corals (Cetz‐Navarro, Carpizo‐Ituarte, Espinoza‐Avalos, & Chee‐Barragán, ). Heavily calcified algae with higher contribution to reef building (Steneck & Dethier, ) formed the articulated calcareous algae (ACA) state.…”