Diel Variability and Influence of Artificial Light on Fish and Macroinvertebrate Communities in Gulf of Mexico Seagrass Beds

Abstract

Seagrasses are productive habitats that support diverse communities of economically and ecologically important fishes and macroinvertebrates. However, most seagrass faunal assessments are conducted only during daylight hours. Here, we documented diel patterns in seagrass-associated fish and macroinvertebrate community structure in seagrass near Seahorse Key, Florida (USA). Artificial light is prevalent in many coastal areas and may influence day/night assemblages; therefore, we added lights to the natural environment to get a better understanding of its effect on community composition. Seagrass inhabitants were quantified using 25-m seine transects during different diel periods (day or night) and in areas where light was manipulated to mimic light pollution (artificial + natural light or natural light). Results suggest that the magnitude of diel effects exceeded that of light addition. While total abundance was similar between day and night, communities did change, with Lagodon rhomboides (Pinfish) dominating day samples and Farfantepenaeus duorarum (pink shrimp) most abundant at night. Other fishes such as Orthopristis chrysoptera (Pigfish) and Strongylura notata (Needlefish) had higher catches during the day, while invertebrates such as Callinectes sapidus (blue crab) and Palaeomonetes spp. (grass shrimp) were more prominent at night. In addition to the differences in abundance and community structure, we also identified diel differences in sizes for some species. No clear patterns were observed with the short-term addition of artificial light. This research highlights the role of diel variability in seagrass communities and suggests that diel movement of organisms may represent an important conduit for the transfer of energy to adjacent habitats.