Gorgonians of the South of Portugal: biology, ecology and conservation

The ecological role of gorgonians (Octocorallia: Alcyonacea) in marine rocky bottoms is worldwide recognized, but the knowledge on the ecology and biology of NE Atlantic temperate species is insufficient, considering current global, regional and local threats. In the rocky bottoms of the Algarve several gorgonians were abundant and frequent down to 30 m, namely Eunicella labiata, Eunicella gazella, Eunicella verrucosa, Leptogorgia lusitanica and Leptogorgia sarmentosa. There is a high association of several gorgonian species that co-dominate assemblages, indicating low levels of competition among species. Nevertheless, gorgonian assemblages differed in structure, depending on local conditions. All species evidenced a similar depth pattern, i.e. abundance significantly increased with depth below 15 m. At shallower waters (up to 15 m), the distribution of gorgonians may be constrained by abiotic factors and competition with algae. Indeed, the spatial patterns of gorgonian populations along the southern coast of Portugal were driven by the interaction of both natural and anthropogenic pressures (namely fishing). Although larger colonies were not restricted to the sites with lower fishing pressure, gorgonian populations sampled in more intensively fished areas generally presented skewed distributions towards small sizes. The effects of natural disturbance events on the structure of gorgonian populations were evidenced by distinct demographic patterns in nearby areas under similar anthropogenic pressure. The present studies also showed that the effect of disturbance on size-frequency distribution of gorgonian populations is species-dependent: Eunicella labiata does not seem to be affected; Leptogorgia sarmentosa is likely affected mainly by anthropogenic pressures; Eunicella gazella and Leptogorgia lusitanica seem to be affected by both kinds of stress. The effects on sizefrequency distributions patterns, namely the trend to skewed distribution towards small sizes under disturbance may have consequences for biodiversity of rocky sublittoral areas of the Algarve coast. Indeed, the present study supports the general paradigm that corals are habitats of enhanced abundance and biodiversity. In one of the few studies examining the relationship between gorgonians and their associated non-colonial epifaunal assemblages, gorgonians (Eunicella gazella and Leptogorgia lusitanica) were found to support rich (11 phyla, 181 taxa) and abundant (7284 individuals) assemblages. The present study supports the general paradigm that corals are habitats of enhanced abundance and biodiversity. In one of the few studies examining the relationship between gorgonians and their associated non-colonial epifaunal assemblages, gorgonians (Eunicella gazella and Leptogorgia lusitanica) were found to support rich (11 phyla, 181 taxa) and abundant (7284 individuals) assemblages. These epifaunal assemblages were dominated by amphipods, but polychaetes had a relevant contribute to diversity. Colony size was found to have a relevant role on biodiversity patterns, with small size colonies contributing the least for overall biodiversity. Although both gorgonians shared most of the species collected, 11 and 18 taxa were exclusively associated with Eunicella gazella and Leptogorgia lusitanica, respectively (without considering singletons). Nevertheless, most of these exclusive taxa were either rare or uncommon. The exception was the presence of white flatworms Turbellaria in Eunicella gazella colonies probably taking advantage of crypsis with the white Eunicella gazella branches. Indeed, complementarity in the epifaunal assemblages associated with the two gorgonian hosts decreased when data was analysed after presence/absence transformation, suggesting that patterns of biodiversity are more affected by changes in the relative abundance of dominant species rather than in faunal composition. Gorgonian epifaunal assemblages not only showed high values of α-diversity but intricate patterns of variability in their composition and structure leading to high β-diversity. Although the total pool of species available in gorgonian colonies appears to be the same in both sites analysed, each colony yields a rather small set of this species pool. All together, the colonies may act as a metacommunity, but the structure of the assemblage in each colony (e.g. total number of species, dominance) apparently depends upon host attributes, namely the surface available for colonization (colony height, width and area), complexity and heterogeneity (fractal dimension and lacunarity respectively) and “colonial” epibiont cover (e.g. colonial fauna and macroscopic algae; CEC). In a first attempt to explicitly quantify the link between gorgonians and the abundance and species richness of associated non-colonial epifaunal invertebrates, the nature and intensity of these relationships were found to be not only host-dependent but varied from one taxonomic group to another. In all faunal groups associated with the two gorgonian hosts analysed, the species richness and abundance were strongly correlated with CEC. In fact, CEC possibly due to a trophic effect (direct or indirect enhancement of food availability) combined with the surface available for colonization (species-area effect) were the strongest predictors of species richness and abundance. On the other hand, although structural complexity is usually indicated as the main driver for the rich and abundant coral-associated assemblages, fractal dimension and lacunarity were only relevant for the assemblages associated with Leptogorgia lusitanica. The validity of the paradigm that structural complexity enhances biodiversity may be scaledependent. In the case of gorgonians, the effect of complexity at the “garden” level may be much more relevant than at the individual colony level reinforcing the need for the conservation of gorgonian aggregation areas as a whole in order to preserve host diversity and size structure. On the other hand, although structural complexity is usually indicated as the main driver for the rich and abundant coral-associated assemblages, fractal dimension and lacunarity were only relevant for the assemblages associated with Leptogorgia lusitanica. The validity of the paradigm that structural complexity enhances biodiversity may be scale-dependent. In the case of gorgonians, the effect of complexity at the “garden” level may be much more relevant than at the individual colony level reinforcing the need for the conservation of gorgonian aggregation areas as a whole in order to preserve host diversity and size structure. Anthropogenic activities like fishing may also have a negative impact on reproduction. Likewise the lack of information on distribution patterns of gorgonian assemblages and their role on local biodiversity patterns, no information was available for the Algarve coast concerning reproductive patterns of main gorgonian species. The annual development of reproductive structures in Eunicella gazella populations (16 m depth) was highly synchronized between sexes. The sex ratio of the population was 1.09 (F:M) being close to parity. The spermatogenic cycle extended for six to eight months, but the oogenic cycle was much longer, taking more than one year for mature oocytes to develop. Prior to spawning, high fecundity was observed in females (27.30±13.24 oocytes polyp−1) and males (49.30±31.14 sperm sacs polyp−1). These values are amongst the highest values reported to date in temperate gorgonians. Broadcast spawning of the gametes (no evidence of surface or internal brooding) occurred in September/October after a period of high sea surface temperatures during summer. Females release large sized mature oocytes but retain immature oocytes that develop only in the next season. Although the effect of fishing on gorgonian assemblages in the Algarve coast is apparent, at current rates, scuba diving does not seem to seriously affect gorgonians. However, this is a growing industry and the preference of scuba divers for natural rocky areas with diverse fauna is well known, which put these habitats under threat. The monitoring of scuba divers in the Algarve showed that most of them (88.6 %) have behaviours that can impact the habitat, presenting a mean contact rate of 0.340±0.028 contacts min−1 (±SE). This rate was higher in scuba divers with moderate experience, and in the initial part of the dive (0–10 min). Contacts with fins and hands were common, mainly resulting in sediment re-suspension, but generally presenting low impact. However, fauna was also affected by physical damage and interactions, and under a scenario of significant expansion of this activity, the impacts on local fauna may increase with consequences for the sublittoral rocky ecosystems of the Algarve coast. Overall, the information gathered in this thesis, most of it completely new for the region, is expected to have a major contribution for the management of the Algarve coast.