Anthropogenic effects on reproductive effort and allocation of energy reserves in the Mediterranean octocoral Paramuricea clavata

Abstract

In order to better understand the sources, patterns and consequences of anthro pogenic effects on populations of the Mediterranean gorgonian Paramuricea clavata, we examined the proportion of injured colonies among populations exposed to a combination of anthropogenic disturbances (recreational cast fishing, commercial lobster pots, gill nets and SCUBA diving), as well as the physiological response of injured corals. Between 10 and 33% of the colonies in unprotected populations were partially colonized by epibionts, most likely following tissue injury, whereas only 4 to 10% of the populations in a marine protected area were affected. Populations that were simultaneously exposed to fishing as well as intensive SCUBA diving showed the highest proportion of colonization. Colonies with approximately 30 to 35% of epibiont coverage showed significantly lower numbers of gonads per polyp. Similarly, concentrations of lipids were lower in females with epibionts, thus indicating allocation of resources into recovery of injured tissue instead of reproduction. Furthermore, whereas unaffected colonies showed a uniform distribution of carbohydrates and proteins through apical branches to more central ones, colonies with epibionts had significantly lower protein concentrations in branches that are positioned 3 branching order levels closer to the stem. The results thus indicate a preference of apical growth in recovering colonies, via a different distribution of food within the colony. Reproductive success in surface-brooding corals growing on walls and overhangs might also be reduced by SCUBA bubbles from divers passing below, as bubbles efficiently remove eggs brooded on colony branches.

Demographic responses to warming: reproductive maturity and sex influence vulnerability in an octocoral

“…These specific compromises have been documented in many anthozoan species following human-induced disturbances (e.g., Montastrea annularis: van Veghel and Bak 1994; Paramuricea clavata: Tsounis et al 2012; see Henry and Hart 2005 for a review) and thermal anomalies (e.g., M. annularis: Szmant and Gassman 1990). Moreover, several studies have assessed the effects of thermal stress on the early-life stages and reproductive output of these organisms at an immediate timescale (Negri et al 2007;Randall and Szmant 2009;Kipson et al 2012;Airi et al 2014).…”

Sexual reproductive cycle of the epibiotic soft coral Alcyonium coralloides (Octocorallia, Alcyonacea)

“…The sampling site is a large tunnel connecting 2 sides of one of the islets, and harbours a population of P. clavata. The abundance of A. coralloides is higher in this tunnel than usually found in other populations of P. clavata, due to the impact of SCUBA diving tourists that injure the corals, which thus favours colonization by A. coralloides (Tsounis et al 2012). The tunnel is among the major SCUBA attractions along the Costa Brava and receives about 70 000 visitors per yr (Lloret 2003, Coma et al 2004.…”

“…Simnia and Coralliophilia species; Crocetta & Spanu 2008) or environmental causes (mortality events and diseases linked to climate warming; see Cerrano et al 2000, Linares et al 2008, Garrabou et al 2009) or due to physical damage (e.g. excessive SCUBA diving activities in particular areas, fishing nets and lines; see Harmelin & Marinopoulos 1994, Tsounis et al 2012, as occurred at our study site. …”

“…These organisms are highly vulnerable to environmental perturbations because their slow growth rates, low recruitment, sessile life form and exposed structural colonial forms imply slow recovery rates (Coma et al 2004). Disturbances of anthropogenic origin include injuries due to contact with fishing lines, anchors or SCUBA divers that may result in decreased fecundity and increase opportunities for colonization by epibionts (Bavestrello et al 1997, Tsounis et al 2012. Furthermore, partial mortalities due to persistent heat waves may be an advantage for new settlers in the denuded skeletons (Cerrano et al 2000).…”

Overview of the conservation status of Mediterranean anthozoa

“…Anchor lines, ropes connecting lobster pots, gill nets placed across gorgonian populations and lost monofilament lines may cause tissue abrasion or detachment of the whole coral colonies (Bavestrello et al 1997;Tsounis et al 2012). Ghost fishing litter has been showed to directly impact benthic organisms, primarily gorgonians (P. clavata, E. cavolini, C. verticillata, C. rubrum, etc.…”