About Habitat complexity & Community Ecology

Habitat complexity, through structural and functional assessments, is important for provision of biodiversity. Through anthropogenic pressures and climate change, habitats are experiencing ‘habitat simplification’ by loss of structure and functional components e.g. through trawling impacts or loss of structural species such as gorgonians. For understanding of community level effects, habitat complexity assessments need to be taken into account.

List of Dissertations

The following are the abstracts from past dissertations at the University of Gibraltar.

Form follows function?: The influence of algal architecture on epifaunal assemblages in the invasive algae Rugulopteryx okamurae in Gibraltar

Lilli Marie Blume

 Over the last decades the number of marine invasive species around the world has increased as a consequence of high anthropogenic mobility, i.e., in particular shipping traffic, the destruction and degradation of habitat resilience, caused by e.g., exploitation or pollution, and the progressing change to a globally warmer climate. The arrival of invasive species to a recipient ecosystem can have drastic effects on the local communities. One of the more recent invaders in the Mediterranean and the Strait of Gibraltar is the brown seaweed Rugulopteryx okamurae. Algae provide and form habitat for many species of epifaunal invertebrates, a change in algal species composition and resulting changes in the habitat structural complexity can influence these communities. To test the effect that R. okamurae and especially its structural complexity has on the native invertebrate fauna of Gibraltar, algae was collected from four locations during summer. The interstitial space index was calculated as an approximate representation of the algal complexity and the epifauna was counted and identified. The study aimed to test two hypothesis: Firstly, the complexity of R. okamurae is different at the chosen locations corresponding to different levels of relative exposure to drag and secondly, the epifaunal assemblages will differ from each other. A total of 11 taxonomic groups were identified. Most abundant groups were amphipods, followed by isopods, and gastropods. The study found several significant differences for both, algal complexity and epifaunal diversity using both univariate and multivariate analysis. However, no universal patterns were found for differences between locations, neither for the algal complexity nor the epifaunal diversity. The diversity and complexity differed between the two sheltered locations. Highest complexity coincided with highest diversity and vice versa, lowest complexity of R. okamurae coincided with lowest diversity in the epifaunal assemblage. The results suggest that relative exposure to drag force influences the morphology of Rugulopteryx okamurae, displaying a finely fronded morphotype that is reduced in height, in locations less exposed to water flow. Further, data indicates that morphological complexity of R. okamurae and the epifaunal diversity are positively correlated, where higher complexity promotes diversity. This study gives a first insight into the ecological role R. okamurae assumes in the coastal communities of Gibraltarian waters and highlights, the need for research on the connection between environmental factors and algal complexity, and further the resulting impacts on the associated communities.
Read more about Lilli’s research here.
Keywords: Habitat complexity, Epifauna, Rugulopteryx okamurae, Gibraltar
Primary supervisor:                  Dr Awantha Dissanayake
Secondary supervisor:             Dr Darren Fa

Community structure and its role within ecosystem artificial reef The Ark

Lucinda Rosheuvel

This research report gives insight into the community structure of artificial reef (AR) in Gibraltar, named ‘the Ark’ and the conditions that are relevant influencing factors of success in performance. The usage of ARs is worldwide established. Purposes of usage vary from tourism; scuba diving or snorkelling, fishing; commercial or recreational, nature conservation; protection of shorelines, fish stock rehabilitation, biodiversity enhancement, habitat restoration or rehabilitation and science. In the end, various purposes all aim for the enhancement of marine life but there is a distinction to make between economic, socioeconomic or environmental purposes. ‘The Ark’ can be considered as an ecosystem in itself. Quantitative and qualitative collected field data yields a total of 74 different taxa habiting this particular AR in 2021, indicating a biodiverse reef in terms of species that might be interesting from a socio-economic
perspective and a variety of habitat-building organisms that also host other marine life. The field data were collected in the month of June by using 0,25 m x 0,25 m quadrats to quantify the microbenthic community. Underwater Visual Census (UVC) is used to conduct a quantitative fish survey. The AR was divided into 7 different sectors in order to test if different factors such as spatial orientation and substrate could be of influence on the community structure. Additional qualitative data is collected to get a complete as possible overview of species presence. The identification of taxa is done in the software
program BIIGLE. To assess if time has changed the community structure, imagery from 2004, 2008 and 2012 have been analysed and compared to the present qualitative dataset. Multivariate data analysis has been done in PRIMER 7. An extensive literature review is carried out to help to answer the question of what factors can be of influence in the performance of ARs and as preparation for the field study. Reviewing the literature and comparing these to the field data result, structural complexity and spatial
orientation are suggested factors of influence most relevant to these results. Sector 4 counted the highest biodiversity, richness and abundance. Sector 1-6 showed a similar community structure, but amongst individual samples, ANOSIM analysis showed several significant differences, driven by the factors spatial orientation and substrates. The community structure in sector 7 is distinct from other sectors. This sector was mostly covered by algae, causing a potential bias in the lower abundance, species richness and
diversity count. Interestingly two Bryozoa taxa Myriapora truncata and Pentapora were found present in sector 7, sector 4 and sector 1, indicating that these species were well recruited throughout the entire AR. Concluding it is possible to say that each sector with different features contributed to biodiversity in its way. The studied literature points out that non-adequate management in terms of lack of ownership and responsibility, insufficient monitoring and the choice of unfavourable materials, location or other
environmental factors can be causes of failure in ARs’ performance. Ecological engineering has the perspective to look at the environment by choosing more natural materials, for example, ECOncrete© or BIOROCK, and attempts to mimic the structural complexity of habitat in the design. Future AR planning should consider using new ecological engineering solutions to maintain or restore a natural balance in
marine habitats. Another management suggestion is to designate individual ARs as small-scale MPAs. Various protected species in Gibraltar are found on the studied AR, including Diplodus annularis, D. puntzzo, D. cervinus, D. vulgaris, D. sargus, Spondyliosoma cantharus, Sarpa salpa, Serranus cabrilla, Conger conger, Epinephelus spp., Octopus vulgaris, Mullididae, Scorpaenidae, Labrus viridis. Potentially, a small, protected area can enforce a higher level of protection and better regulation of anthropogenic activities. Small-scale protection can also enable adequate management in terms of creating clearer boundaries with a demarcated object that also makes monitoring and protection of marine life more feasible. There are still gaps in knowledge on ecosystem functioning of individual species and structural
complexity is not quantified as a potential factor of influence. Lastly, the effect of this AR on the surrounding natural habitat including associated behavioural patterns can be the next step in research to further investigate.
Read more about Lucinda’s research here.
Primary Supervisor:               Dr Awantha Dissanayake
Secondary Supervisors:         Dr Darren Fa
Dr Jaime Davis, University of Plymouth

Thematic Leader

Dr Awantha Dissanayake
Head of School (Marine Science)