Seasonal patterns of megafauna on rocky shore communities of the upper infralittoral : a conservation approach

Abstract

Some of the most significant temporal fluctuations in the upper infralittoral (between 3 and 6m) are related to seasons. The term ‘seasons’ refers to periods of the year driven by periodic climatic conditions, and marked by particular weather and light patterns. Factors tend to change more rapidly in shallow coastal waters than in deeper habitats. Studies of sea surface temperature in the Mediterranean tend to focus on long-term variability with few studies describing intra-seasonal variability. Underwater visual censuses, through strip transects of a total area of 90m2 at ~3 metres depth, were performed at 10 sites around Malta to assess seasonal patterns in species diversity and density of megafauna (body sizes ranging between >1cm and ~25cm). Between October 2020 and October 2021, research surveys recorded 48,066 individual megafaunal organisms and area coverage ranging 3440cm2 of colonial organisms from 179 different species in the upper infralittoral. Most phyla species diversity analysis revealed relatively similar ranges of Shannon-Weaver’s Diversity compared to other similar studies in the Mediterranean. Chordates, molluscs and colonial sponges, along with 15 individually analysed species, showed significant seasonal differences in their abundances. Spatial and temporal patterns were also illustrated in dominant species and species which were only found in one site. Various observations related to feeding, mating and spawning were also made. During the study 13 alien species were recorded which were observed to vary seasonally. During the study 13 legally protected species were recorded, amounting to 7% of the total species density. Studying seasonal patterns in species diversity, abundance and activities in coastal shallow waters is essential for conservation, especially in striving toward local and EU targets to restore ecosystems and safeguard biodiversity.