Benthic survey of natural and artificial reefs off Mar del Plata, Argentina, southwestern Atlantic

Abstract

ABSTRACT. This study describes the macrofaunal assemblages of subtidal rocky reefs off Mar del Plata in order to compare the macro invertebrate assemblages settled on shipwrecks with those of nearby reef sand to characterize the fish fauna associated with natural (NR) and artificial (AR) reefs. Topographic characterizations and surveys of invertebrates and fishes were performed in November and December 2005, using SCUBA diving. A non-parametric multivariate analysis was used to analyze the environmental and biological data. The reefs were mainly distinguished by their depth and the position of the substrate. The red calcareous algae, Corallina officinalis, dominated the shallowest NR, whereas conspicuous mytilid assemblages of Mytilus platensis were present at depths over 3 m, sea anemones, Anthothoe chilensis, were more abundant between 6 and 10 m, and the soft coral, Tripalea clavaria, was found at nearly 20 m depth. No differences were found between horizontal ARs and the adjacent NRs. The greatest differences were found between the communities of vertical and horizontal substrates, both in NRs and ARs. Fifteen fish species were recorded in the analyzed area. Species having strong site fidelity, e.g., Acanthistius brasilianus and Pseudopercis semifasciata, were clearly more abundant and/or frequent in ARs (shipwrecks) than in NRs. This pioneer study in the surveyed area showed that reef sallow the settlement of diverse benthic assemblages. ARs also provide refuge for fishes. As sport fishing and diving are activities being carried out in Mar del Plata, where tourism is one of the main economic resources, the protection of such areas should be considered in conservation plans.

Macrobenthic colonization on the derelict Fisheries Vessel Khronometer, Cristo Rey Submarine Park, Argentina

“…The sublittoral area of Mar del Plata is characterized by sandy sea floors and isolated hard bottoms. The latter are composed of loess (consolidated sedimentary rocks, Pleistocene) and quartzite rocky outcrops, which originated from the Tandilia mountainous system (SE of Buenos Aires Province) 550 mya (Genzano, Zamponi, Excoffon, & Acuña, ; ).…”

“…Water temperature is variable through the year. The maximum values in summer reach 18–19°C and 7–8°C is the minimum in winter (Genzano et al, ; ).…”

“…Censuses were performed by free swimming along the diving site for 15 min per survey and recording all species that could be positively identified (Lessios, ). As local species do not form dense fish schools, the species were assigned into one of four relative abundance categories: (i) occasional, a single individual, (ii) scarce, two to five individuals, (iii) abundant, six to 10 individuals, and (iv) very abundant, more than 10 individuals observed during the survey (viz., Genzano et al, ).…”

“…In the temperate waters of the Southwestern Atlantic Ocean, SCUBA diving in derelict vessels is particularly popular along the clear waters of the Patagonian coast (e.g., at Las Grutas, 40°48′S, 65°05′W, Don Felix vessel; and at Puerto Madryn, 42°46′S, 65°02′W, Follias , Albatros and Miralles vessels). Northward, at the Buenos Aires coast (38°07′S, 57°33′W), there are two vessel‐reefs of interest for divers: the shipwrecks of the freighter James Clunies (149 m length), accidently sunk in 1949 at 10‐m depth on rocky floors; and the wood vessel Cristo Rey (45 m length), intentionally sunk on soft bottoms in 1981, at 22 m depth, to create the Cristo Rey Submarine Park (see Genzano, Giberto, & Bremec, ).…”

“…Despite the recreational and touristic interest in ARs being a consequence of the marine life associated with them, the biological knowledge of this biota is still scarce. The only study of ARs in the region is of Genzano et al (), who described the macrofaunal assemblages settled on shipwrecks at 38°S, comparing them with the macroinvertebrate assemblages of the neighboring rocky outcrops. After a long‐term period of submersion (50 and 36 years for the James Clunies and the Cristo Rey , respectively), the ARs showed a similar community structure to surrounding natural rocky reefs, in concordance with the hypothesis that the ecological processes of ARs are functionally equivalent to those of natural benthic systems in an area (Perkol‐Finkel, Miloh, Zilman, Benayahu, & Benayahu, ; Seaman, ).…”