Bramanti, L. | Search bioRxiv

bioRxiv2025

Caribbean octocoral communities: finding the forest for the trees?

Octocorals have increased in abundance on many Caribbean coral reefs, and at some sites "octocoral forest" may be a better community descriptor than "coral reef." Implicit to the concept of a forest is that structural elements, trees, colonies, etc., alter the environment in ways that affect the structural elements themselves and the organisms that inhabit the forest. At what density do the structural elements create the emergent properties of a "forest?" Communities traditionally characterized as hardgrounds and coral reefs around Puerto Rico and St John, US Virgin Islands, varied in density of octocoral colonies from a few to >100 colonies m-2in surveys conducted in 2021 and 2022. Canopy cover was correlated with the density of colonies. Among the quadrats with the highest octocoral density there was no significant correlation between numbers of colonies and canopy cover. Frontal area, a measure related to the communitys effect on water flow, as well as the volume occupied by colonies followed patterns similar to canopy cover. Vertical profiles of flow velocity were measured from the substratum to 3 m above the bottom on a reef on St John where octocoral population density ranged from 0 to 16 colonies m-2. Profiles of orbital velocity exhibited perturbations which were more pronounced in locations with > 12 colonies m-2. Using the effect on flow as a criterion, 4 of the 8 surveyed sites would function as forests. Understanding the density at which emergent properties appear is critical to understanding the bio-physical interactions affecting the community.

ecology↗

bioRxiv2017

Spearfishing promotes a timidity syndrome and increases the safe operating distances in fish

In a landscape of fear, humans are altering key behaviors expressed by wild-living animals, including those related to foraging, reproduction and survival. When exposed to potentially lethal human actions, such as hunting or fishing, fish and wildlife is expected to behaviorally respond by becoming more timid, but proving such responses underwater in the wild has been challenging. Using a rich dataset collected in situ, we provide evidence of spearfishing-induced behavioral effects in five coastal fish species using the flight initiation distance (FID) as a proxy of predator avoidance and boldness. We document that spearfishing promotes a timidity syndrome (i.e., an increase of the average timidity of harvested populations) and that the wariness of preys wariness is influenced by individual size, level of protection offered through marine protected areas and the ability to recognize the risk posed by underwater human predators. In particular, we show that changes in the appearance of the observer (spearfisher vs. snorkeler) modulate the risk perception among the exploited species, and these differences are more evident outside marine protected areas where spearfishing is allowed. We also detected a positive correlation between FID and fish size, with larger specimens (that are more likely targets of spearfishers) revealing larger FID. The behavioral effects were most clearly expressed in the most heavily exploited species and declined towards the less desired and less targeted ones, which may be a result of learning mechanisms and plasticity and/or fisheries-induced evolution of timidity. Our study reveals a trade-off where intensive spearfishing negatively affects future spearfishing success through behavior-based alteration of catchability. Either rotating harvest or implementation of mosaics of protected and exploited areas might be needed to manage spearfishing-induced timidity in exploited stocks.

ecology↗