.ecomorphology

Management of reef fish populations requires insight in their resilience to anthropogenic stressors. Studies on temporal variations in reef fish populations and their abundance responses to environmental changes are crucial to the development of ecosystem-based management.

Seventeen years of voluntary fish survey data of reef fish at the west coast of Bonaire Marine Park (Caribbean) were analysed to investigate the effect of environmental changes on local reef fish populations. Various anthropogenic stressors that influence the coral reefs of Bonaire were studied in recent years, this study focusses on population responses to loss of coral cover, the establishment of a fishery protected area, and reef fishery pressure. In addition, reef fish responses to specific events were analysed at species or family level.

In general fluctuations in sighting frequencies were species-specific and difficult to interpret. Three large parrotfish decreased by approximately 50% over time and there were indications of a negative trend in mid-sized parrotfish as well. In fishery targets, the most intensive fished group (large to mid-sized grouper species), decreased strongly. After their abundance decreased to near zero, two species belonging to other fish families showed signs of sequential overfishing. It is unclear if larval import will compensate for the loss in reproductive capacity of the species in decline, recent literature on recruitment distances suggest that the level of self recruitment is high in Bonaire. An exception to short recruitment distances was noted earlier in the balloon fish Diodon holocanthus. The data suggest that the balloon fish population till 2010 originated from the mass recruitment in 1994, from the start of the studied period in 2000 to 2010 their abundance steadily declined to near zero. Another event with direct effect on population dynamics is the mass mortality events in moray eels in 2008. With a lag time of a year, especially two Enchelycore species strongly declined afterwards, which could elucidate the highly variable population densities of these species over the period. A following moray eel mass mortality event in 2022, also occurred at the onset of a period of sea water warming, paralleling various reef fish species in the Red Sea. Increase in warming events carries the risk of more frequent mass mortalities.

https://www.sciencedirect.com/science/article/abs/pii/S1055790323000325

Abstract

Symbioses play important roles in forming the structural and distributional patterns of marine diversity. Understanding how interspecies interactions through symbioses contribute to biodiversity is an essential topic. Host switching has been considered as one of the main drivers of diversification in symbiotic systems. However, its process and patterns remain poorly investigated in the marine realm. Hexacoral species of the order Zoantharia (=zoantharians) are often epizoic on other marine invertebrates and generally use specific taxa as hosts. The present study investigates the patterns of host switching and the diversification history of zoantharians based on the most comprehensive molecular phylogenetic analyses to date, using sequences from three mitochondrial and three nuclear markers from representatives of 27 of 29 genera. Our results indicate that symbiotic zoantharians, in particular those within suborder Macrocnemina, diversified through repeated host switching. In addition, colonization of new host taxa appears to have driven morphological and ecological specialization in zoantharians. These findings have important implications for understanding the role of symbioses in the morphological and ecological evolution of marine invertebrates.

Many environmental variables may influence fish assemblage structures in terms of abundance, biomass and mean size. The aim of this study is to provide a baseline survey on reef fish assemblages and shark presence covering the whole Saba bank (Dutch Caribbean). Hereby determining the influence of habitat, depth and fishing pressure on the structure of reef fish assemblages and shark presence. Baited Remote Underwater Video (BRUV) survey was used to describe reef fish assemblage structures on the Saba bank. Between 2012-2014, a total of 165 60 min BRUV deployments were conducted on locations varying in habitat complexity (0-4, Polunin and Roberts, 1993), depth (15-40m) and fisheries. The eleven most abundant fish species observed on the Saba bank represented eight families and accounted for nearly 50% of the total number of individual fish observed. Labridae was the most abundant fish family observed with a relative abundance of 22%. Most abundant fish species by number of individuals were Thalassoma bifasciatum (N=849 (9.8%)) Stegastus partitus (N=725 (8.4%)) and Acanthurus bahianus (N=430 (5.0%)).

Habitat complexity was positively correlated with species richness (Nsp), fish abundance (MaxN), and mean biomass, and negatively correlated with mean fish length. Strongly developed vertical relief habitats were found to support high numbers of fish species (N=19.1±0.6SE) of relatively low mean lengths (22.4cm±0.3SE), whereas less complex habitats were characterized by low numbers of species (N=8.3±0.8SE) with relatively high mean lengths (24.6cm ±0.81SE). Depth was negatively correlated with Nsp, MaxN and mean biomass and positively correlated with mean fish length. These relationships were all according to expectations based on earlier studies.

A minor part of the variability in the structure of reef fish assemblages was explained by differences in fisheries activity, indicating that no clear fisheries effect was observed in fish assemblages in this study. Furthermore, no significant differences in average size of target species were observed between areas with different fishing pressure. However, the general absence of piscivores such as large snappers and groupers was an indication of the indelible effects of past fisheries on the Saba bank.

A total of 85 shark observations were made with Ginglymostoma cirratum as most abundant species (N=41), followed by Carcharhinus perezii (N=36), Galeocerdo cuvier (N=5) and Carcharhinus limbatus (N=3). Relatively high shark abundances (0.20 sharks hour-1) were observed on the Saba bank compared with other Caribbean regions (The Bahamas: 0.14 sharks hour-1, Belize, 0.17 sharks hour-1). Shark abundance (CPUE) was positively correlated with habitat complexity, whereas depth exerted a negative influence on shark abundances. High shark numbers are a good sign for the health of the Saba Bank ecosystem, since sharks are apex predators, making them a prime indicator for ecosystem health.

Besides ‘traditional’ measures, ecomorphology was presented as an alternative measure in explaining variation in reef fish assemblages. For ecomorphological analysis insight in trophic morphology was obtained by using a Fish Food Model (FFM). The FFM in this study quantitatively related properties of 14 marine food types to morphological characterics of 15 common fish species on the Saba bank and predicted the capacity of utilizing these food types for each species. Strong differences in morphology and little overlap was observed for all different fish species in the FFM-analysis, which was mainly explained by two sets of variables involving predatory and herbivorous lifestyle. By multiplying each species’ capacity of using food types with its abundance an ecomorphological profile of each fish assemblage was calculated. On a functional level reef fish assemblages showed less variability than on species composition level, this possibly is an indication for high levels of robustness in niche differentiation in reef fish communities on the Saba bank.