Competitive effects of macroalgae on the fecundity of the reef-building coral Montastraea annularis

Abstract

In recent decades, a rise in coral mortality, attributed to increased frequency of massbleaching events, increased prevalence of disease, and more frequent and severe hurricanes, has contributed to a rapid proliferation of macroalgae across many Caribbean reefs. As a consequence, the frequency of coral-algal interactions has risen. Here, we document the effects of 2 dominant Caribbean macroalgae, Dictyota spp. and Lobophora variegata, and a mixed algal community on the fecundity of a massive coral. Montastraea annularis is a dominant Caribbean reef-building coral characterised by a low recruitment rate. To investigate the effects of macroalgae on coral fecundity, algal contact was experimentally manipulated around the perimeter of M. annularis patches. Fecundity was measured as the diameter of eggs (ES), the number of eggs per gonad (E#) and the number of gonads per polyp (G#). Algal contact was shown to significantly reduce the diameter of eggs at both the coral-algal boundary and at the centre of coral patches. The presence of Dictyota spp. or a mixed algal community was shown to have more detrimental effects on ES than the presence of L. variegata. Removal of algal contact immediately prior to gametogenesis increased the reproductive output of polyps directly adjacent to the cleared areas, with an increase in ES, E# and G#. Our results imply that algal competitors can reduce the fecundity of M. annularis through mechanical and/or allelochemical damage of polyps directly adjacent to the algae and by causing the reallocation of energy within the coral patch from reproduction to defence and repair. KEY WORDS: Fecundity · Competition · Coral · Macroalgae · Energy allocation Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 367: [143][144][145][146][147][148][149][150][151][152] 2008 macroalgal blooms are mostly a consequence of coral mortality, rather than the prime cause (McCook et al. 2001, Diaz-Pulido & McCook 2002. Algal recruits are hypothesised to rapidly pre-empt coral settlement space and may settle directly onto stressed or dead coral tissue, rather than overgrowing healthy coral tissue (McCook et al. 2001, Diaz-Pulido & McCook 2002, 2004, although direct overgrowth of healthy coral tissue has been observed (Hughes et al. 2007). Macroalgae have been shown to inhibit coral recruitment (Kuffner et al. 2006), and coral-algal interactions can result in reduced coral growth rates and increased tissue mortality (Lirman 2001, River & Edmunds 2001, Jompa & McCook 2002, Nugues & Bak 2006, Box & Mumby 2007. Furthermore, the presence of algae around coral colonies has also been documented to reduce the fecundity of the entire coral colony (Tanner 1995, Hughes et al. 2007). While mortality of coral tissue is likely due to the mechanical and/or allelochemical effects of direct contact with the algal fronds (River & Edmunds 2001, Jompa & McCook 2003, a reduction in growth rate or colony fecundity suggests a possible diversion of energy away from reproduction o...

Macroalgal terpenes function as allelopathic agents against reef corals

“…Such interactions also may contribute to the algal suppression of coral fecundity and recruitment documented in previous investigations (12,19,44) and may become increasingly damaging to corals as oceans acidify (20). If so, chemically mediated algal-coral competition may play a critical and increasing role in both the degradation of coral reefs and the formation of negative feedbacks limiting reef recovery (12,13).…”

Microbial to reef scale interactions between the reef-building coral Montastraea annularis and benthic algae

“…While this phenomenon has been well documented, the mechanisms by which algae overtake corals are not well understood. Competition between corals and benthic algae is common on coral reefs worldwide [17][18][19][20], and these interactions are frequently harmful to the coral, causing tissue damage and necrosis [3,[20][21][22][23], reduced zooxanthellar function [23][24][25][26] and reduced coral fecundity [3,20,27]. On the other hand, some algae have little effect on corals [28,29], such as certain species of CCA that promote coral settlement [30,31] and inhibit recruitment of macroalgae that would otherwise compete with corals [32,33].…”

Long-term reduced spawning in Orbicella coral species due to temperature stress

“…If bleaching events occur at a frequency of 2 to 3 events per decade, our data suggest that at least these coral species would constantly be in a condition of reproductive recovery and diminished reproductive output and success. In addition to bleaching stress, the presence of macroalgae on reefs can interact with Orbicella and reduce both egg size and number (Foster et al 2008). Thus both the increased thermal stress, and reduced herbivory, are likely to reduce the reproductive potential of these corals.…”