Life in the surf: faunal assemblage diversity and distribution in temperate sandy beaches of the South American Atlantic

FIORI SADRA; ANDREA LOPEZ CAZORLA; MARTINEZ ANA; CARCEDO CECILIA; BLASINA, G.E.; JUAN MANUEL MOLINA; GARZON CARDONA JOHN; MOYANO JESSICA; MENENDEZ CLARA

CONTINENTAL SHELF RESEARCH

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2022

0278-4343

This study explores the changes of diversity and distribution of faunal surf-zone assemblages along a coastal fringe adjacent to the Bahía Blanca Estuary (BBE, Argentina). Three mesotidal sandy beaches located at 18 (S1: Punta Tejada), 28 (S2: Pehuén Co) and 52 (S3: Monte Hermoso) km away from the BBE (38ºS) were seasonally sampled during a year. Zooplankton, zoobenthos and fish samples were taken in the surf-zone by hand-towing sampling gear for 200 m parallel to the shoreline, and a set of potential explanatory environmental variables were measured and quantified. Beaches varied from tide-dominated flat (S1) to tide-modified reflective to intermediate (S2, S3). The width of the surf-zone increased toward S3 where waves reached maximum heights and periods. Mean turbidity and photopigments concentrations also showed an increasing gradient toward S3, while dissolved inorganic nitrogen and organic matter (DOM) concentrations showed higher values in S1 and S2. The analysis of DOM suggests an enrichment of BBE salt marshes to the humic-DOM mainly into beaches closest to the estuary. Also aquatic and microbial sources are an important component of DOM. The energy of waves and the connection with the BBE drove the main structural changes of the surf-zone assemblage. The zoobenthos represented 70.69%, the zooplankton 22.61% and the fishes 6.70% of total abundance. The assemblage included 108 taxa, of which few were numerical dominant, and many of them can also be found in BBE. Richness of each biological group was similar along the shore and higher values of alfa-diversity were associated with minimum values of total abundance. Beta-diversity was mainly a consequence of turnover, mostly due to changes in zoobenthic and zooplankton taxa. Benthic species peaked at maximum abundance in beaches with calm conditions (S1 and S2) which could be advantageous for those taxa that escape from predators burying or for species that actively swim near the sea floor. Conversely, the zooplankton species were most abundant in S3, where the higher wave energy promoted primary productivity. Trophic relationship determined the abundance of fishes, zooplanthophages species were maximum in S3 while benthophages taxa reached maximum near the estuary.