Production of carbonate particles by phytobenthic communities on the Mallorca-Menorca shelf, northwestern Mediterranean Sea

In this paper the carbonate content and production, both at the species level and at the community level, is quantified in four areas of the Mallorca-Menorca shelf, northwestern Mediterranean Sea. Eight benthic communities are identified, each living at specific depth ranges and preferentially colonising either rocky or sedimented soft bottoms: (1) Photophilic algae, (2) Hemisciaphilic algae, (3) Coralligenous algal-dominated, (4) Coralligenous animal-dominated, (5) Caulerpa-Cymodocea meadows, (6) Posidonia oceanica meadows, (7) maërl and free-Peyssonelia beds, and (8) sandy bottom communities. Encrusting and maërl species of Corallinales and of the red algal genus Peyssonnelia and, to a lesser extent, the green alga Halimeda tuna, are the main carbonate producers. Most of the modern algal carbonate production in the Mallorca-Menorca shelf occurs at depths of less than 85–90 m, which is the lower limit of the coralligenous and maërl communities. carbonate production in rocky areas is usually higher than that of soft bottoms, with the exception of the maërl beds in moderately deep waters (40–85 m). The highest algal carbonate production is found in coralligenous algal-dominated rocky bottoms (464.6 g m−2 year−1), photophilic algal communities (289.4 g m−2 year−1) and maërl beds (210 g m−2 year−1), while the lowest is displayed by seagrass meadows (60 to 70 g m−2 year−1) and sandy bottoms (0.5 g m−2 year−1). Nevertheless, the contribution of seagrass beds to benthic carbonate production in the Mallorca-Menorca shelf is outstanding due to the extent of the area occupied by these beds. an algal carbonate production rate over the upper 100 m water depth in the studied localities ranges from 90.60 to 123.89 g m−2 year−1, which correspond to the mostly sedimented Campos area and to the very rocky South Cabrera area, respectively. Overall mean carbonate production of the Mallorca-Menorca shelf is around 100 g CO3Ca m−2 year−1. These results may be viewed as a minimum estimate for total carbonate production on the Mallorca-Menorca shelf since they take into account only the phytobenthos.